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Human NK Cells Express Endothelial Nitric Oxide Synthase, and Nitric Oxide Protects Them from Activation-Induced Cell Death by Regulating Expression of TNF-α
Abstract
Although NO appears important in rodent immune responses, its involvement in the human immune system is unclear. We report that human NK cells express constitutive endothelial NO synthase mRNA and protein, but not detectable levels of inducible NO synthase. They produce NO following activation by coculture with target cells or cross-linking with anti-CD16 mAb, and production is increased in the presence of IL-2. N-monomethyl-L-arginine (L-NMA), a NOS inhibitor, partially inhibited NK cell lysis of four different target cells (<40% inhibition at 500 microM L-NMA), but not granule release following coculture with target cells, or Fas ligand induction following cross-linking with anti-CD16 mAb. However, L-NMA augmented apoptosis of NK cells induced by activation through CD16 ligation or coculture with K562. An NO donor, S-nitroso-N-acetylpenicillamine (SNAP), suppressed apoptosis of NK cells induced by CD16 cross-linking or coculture with target cells, suggesting that endogenous NO production is involved in protection of NK cells from activation-induced apoptosis, thereby maintaining NK activity. SNAP also suppressed, and L-NMA enhanced, expression of TNF-alpha, reported to be involved in activation-induced NK cell death, in response to CD16 cross-linking. Suppression of anti-CD16-induced apoptosis by SNAP was reversed by the addition of rTNF-alpha. DNA-binding activity of the transcription factor, NF-AT, which is involved in TNF-alpha induction upon ligation of CD16, was inhibited by SNAP and enhanced by L-NMA. Our results suggest that down-regulation of TNF-alpha expression, possibly due to suppression of NF-AT activation, is a mechanism by which endogenous NO protects NK cells from activation-induced apoptosis, and maintains lytic capacity.
... For both type of NK cells studied, L-Arg deficiency inhibited cytotoxicity without totally abolishing it. Similarly, L-Arg limitation alters the cytotoxicity of human NK cells isolated from healthy subjects [29], and impaired NK cell cytotoxicity has been also reported in human NK cell lines cultured in L-Arg-free medium [36]. In contrast, Oberlies et al. [28] show that human NK cytotoxicity was independent of the extracellular L-Arg concentration. ...
... These differences might be due to the high proliferative activity and NO production of the NK-92 cells compared to human isolated NK. Indeed, unlike human isolated NK cells that express only eNOS mRNA [36], we shown for the first time that NK-92 cell line expresses both eNOS and iNOS mRNA. It has been demonstrated that endogenous NO production protects human isolated NK cells from apoptosis and maintains lytic capacity [36]. ...
... Indeed, unlike human isolated NK cells that express only eNOS mRNA [36], we shown for the first time that NK-92 cell line expresses both eNOS and iNOS mRNA. It has been demonstrated that endogenous NO production protects human isolated NK cells from apoptosis and maintains lytic capacity [36]. Although NO is involved in different signaling pathways [40] its potential role in the modulation of the f chain by L-Arg is unknown. ...
... In addition to an inhibitory or proapoptotic role, NO has also been shown to enhance cellular survival [6][7][8][9]. We have previously reported that NO protects human natural killer (NK) cells from activation-induced cell death [10] and that, under certain oxidation-reduction (redox) conditions, protects porcine endothelial cells (PAEC) from being lysed by interleukin (IL)-2 stimulated human NK cells [11]. In the cardiovascular system, production of NO is crucial to maintaining homeostasis [12] and vascular tone, through its role in vasodilation, antiatherogenesis, inhibition of leukocyte-endothelial cell interactions, smooth muscle proliferation, and platelet aggregation [13]. ...
... eNOS is constitutively expressed in endothelial cells and is activated under conditions of Ca 2+ influx [15,16]. eNOS, but not iNOS or nNOS, was associated with NO production in the two systems (NK cells [10] and PAEC [11]) in which we observed a cytoprotective effect of NO, suggesting a role for eNOS in these protective processes. eNOS activation is induced by a number of stimulants, such as shear stress, estrogen, or cytokines, resulting in phosphorylation of human eNOS on Ser 1177 [17,18] (corresponding to Ser in the 1179 position in the highly homologous porcine eNOS [19,20]) through a pathway involving phosphatidylinositol 3-kinase (PI3-K), and the Ser/Thr kinase, Akt. ...
... It is known that the PI3-K/Akt signaling pathway transmits survival or antiapoptotic signaling and is activated by stimulation through several cytokine receptors [28]. Because eNOS activation is downstream of Akt phosphorylation, eNOS-mediated production of NO may provide a survival signal and is consistent with other reports that NO can be antiapoptotic [6][7][8]10,11]. Therefore, stimulation of NO with low levels of oxidative stress may also be involved in signaling cell survival. ...
Oxidative stress mediates positive and negative effects on physiological processes. Recent reports show that H(2)O(2) induces phosphorylation and activation of endothelial nitric oxide synthase (eNOS) through an Akt-phosphorylation-dependent pathway. In this study, we assessed activation of eNOS and Akt by determining their phosphorylation status. Whereas moderate levels of H(2)O(2) (100 microM) activated the Akt/eNOS pathway, higher levels (500 microM) did not, suggesting differential effects by differing levels of oxidative stress. We then found that two pro-oxidants with activity on sulfhydryl groups, 1-chloro-2,4-dinitrobenzene (CDNB) and diethyl maleate (DEM), blocked the phosphorylation events induced by 100 microM H(2)O(2). GSH was not a target thiol in this system because buthionine sulfoximine did not inhibit this phosphorylation. However, down-regulation of cell membrane surface and intracellular free thiols was associated with the inhibition of phosphorylation, suggesting that oxidation of non-GSH thiols inhibits the H(2)O(2)-induced phosphorylation of eNOS and Akt. DTT reversed the inhibitory effects of CDNB and DEM on Akt phosphorylation and concomitantly restored cell surface thiol levels more efficiently than it restored intracellular thiols, suggesting a more prominent role for the former. Similarly, DEM and CDNB inhibited TNF-alpha-induced Akt and eNOS phosphorylation, suggesting that thiol modification is involved in eNOS inductive pathways. Our findings suggest that eNOS activation is exquisitely sensitive to regulation by redox and that cell surface thiols, other than glutathione, regulate signal transduction leading to phosphorylation of Akt and eNOS.
... constitutive NOS (NOS1 + NOS3) inhibitor L-NAME was added during drug pretreatment step ( Figure 3E; p < 0.01). This inding maybe explained by the fact that endogenous NO from NOS3 prevents NK cells from activation-induced self-apoptosis via suppression of TNF-α [24]. Alternatively, hemodynamic depletion of the marginating NK cells in the cPTIO/TPA-exposed skin from nitric oxide depletion and CD45+ leukocyte crowding is also possible since NO is needed in NK cell activation (For a review, see ref. [25]). ...
... While the present indings and those by others implicate stimulation of NO generation from constitutive synthases (mainly NOS3) as the main driver of antihyperplastic and antiinlammatory effects against the TPA-induced tumor-promoting tissue changes ( Figure 1) [26], stimulated generation of NO from NOS3 or exogenous sources have been also reported with three other modes of direct and indirect anticancer mechanisms. Firstly, endogenous NO from NOS3 maintains lytic capacity of NK cells while it also protects NK cells from their activation-induced self-apoptosis via suppression of TNF-α [24]. This is consistent with our own inding that the addition of L-NAME abolished the attenuating effect of heptaminol against the depletion of tissue-marginating NK cell in the TPA-exposed mouse ear skin ( Figure 3E). ...
Recently a mouse skin carcinogenesis study reported that a β-blocker carvedilol displayed antitumor-properties via antihyperplastic effects. However, the antihyperplastic mechanism is unclear as the β-blocker is characterized with multiple pleiotropic effects including stimulation of endothelial NO release and verapamil-like calcium channel blocking activity. To investigate the nature and the origin of the antihyperplastic effects, we tested topical pretreatment with pindolol, heptaminol, ATRA or verapamil against Balb/c mouse ear skin hyperplasia that was induced by TPA. We found that pindolol, heptaminol or ATRA, but not verapamil, inhibited the TPA-induced immunoinflammatory skin changes in an NO-dependent manner, which included epidermal hyperplasia, skin edema and fibrosis. Furthermore, we also observed NO-dependent alleviation of the TPA-induced NK cell depletion in the ear tissues by heptaminol pretreatment. Together our results suggest that stimulation of NO generation from constitutive synthases may be primarily responsible for the reported antihyperplastic and NK cell-preserving effects of the β-blockers, and that similar effects may be observed in other immunity normalizing compounds that also promote endothelial NO synthesis.
... A series of previous studies revealed that NO can be involved in various aspects of NK cell biology, depending on the species and tissue origin (mouse, rat, or human NK cells; lymph node, splenic, and blood NK cells), the prior activation status of the NK cells [resting NK cells vs. IL-2-expanded NK cells (lymphokine-activated killer cells, LAK)], and the source of NO. The NO was either generated by iNOS-positive myeloid cells or derived from iNOS [122][123][124] or eNOS expressed within the NK cell itself [125]. Although the picture is far from uniform, three major categories of actions of NO on NK cells have emerged: ...
... In mouse uterine NK cells, which accumulate in the placenta during pregnancies, iNOS was necessary for the expression of perforin [127]. In human peripheral blood NK cells, which were positive for eNOS and released NO in response to target cells or anti-CD16 stimulation in the presence of IL-2, NO impeded apoptosis and TNF expression and contributed to target cell lysis [125]. ...
Shortly after the identification of nitric oxide (NO) as a product of macrophages, it was discovered that NO generated by inducible NO synthase (iNOS) inhibits the proliferation of T lymphocytes. Since then, it has become clear that iNOS activity also regulates the development, differentiation, and/or function of various types of T cells and B cells and also affects NK cells. The three key mechanisms underlying the iNOS-dependent immunoregulation are (a) the modulation of signaling processes by NO, (b) the depletion of arginine, and (c) the alteration of accessory cell functions. This chapter highlights important principles of iNOS-dependent immunoregulation of lymphocytes and also reviews more recent evidence for an effect of endothelial or neuronal NO synthase in lymphocytes.
... A series of previous studies revealed that NO can be involved in various aspects of NK cell biology, depending on the species and tissue origin (mouse, rat, or human NK cells; lymph node, splenic, and blood NK cells), the prior activation status of the NK cells [resting NK cells vs. IL-2-expanded NK cells (lymphokine-activated killer cells, LAK)], and the source of NO. The NO was either generated by iNOS-positive myeloid cells or derived from iNOS [122][123][124] or eNOS expressed within the NK cell itself [125]. Although the picture is far from uniform, three major categories of actions of NO on NK cells have emerged: ...
... In mouse uterine NK cells, which accumulate in the placenta during pregnancies, iNOS was necessary for the expression of perforin [127]. In human peripheral blood NK cells, which were positive for eNOS and released NO in response to target cells or anti-CD16 stimulation in the presence of IL-2, NO impeded apoptosis and TNF expression and contributed to target cell lysis [125]. ...
Macrophages are not only host cells for many pathogens, but also fulfill several key functions in the innate and adaptive immune response, including the release of pro- and anti-inflammatory cytokines, the generation of organic and inorganic autacoids, the phagocytosis and killing of intracellular microorganisms or tumor cells, and the degradation and presentation of antigens. Several of these functions are shared by other immune cells, including dendritic cells, granulocytes, NK cells, and/or T lymphocytes. Thus, the analysis of macrophage functions in vitro using primary mouse cell populations requires standardized methods for the generation and culture of macrophages that guarantee high cell purity as well as the absence of stimulatory microbial contaminants. This chapter presents methodology to achieve these aims.
... Adherence of leukocytes to endothelium is inhibited by NO (40,41), and De Caterina et al. (42) reported that NO decreased activation of EC induced by cytokines, whereas others have reported that endogenous NO protected EC from cytokine-mediated and oxidant-mediated cytotoxicity (38,39). We have reported that endogenous NO protected human NK cells from activation-induced apoptosis (36). ...
... The amount of nitrite and nitrate accumulation has been used to estimate NO production in culture supernatants. The products of NO, nitrite, and nitrate were measured using a procedure based on the Griess reaction, as described previously (36). PAECs were cultured in CYS(Ϫ) medium for 24 h, SNAP was added for an additional 1 h, and TNF-␣ for an additional 4 h. ...
Evidence suggests that NK cells contribute to the pathogenesis of delayed rejection of vascularized xenografts, and NK cells have been suggested to participate in hyperacute xenograft rejection. Endothelial cells have been shown to be the primary target of the recipient's immune responses that mediate both hyperacute and delayed xenograft rejection. Under conditions of oxidative stress induced by thiol deprivation, but not under normal conditions, pretreatment of porcine aortic endothelial cells (PAECs) with the NO donor, S-nitroso-N-acetyl-penicillamine, dramatically inhibited killing of PAEC target cells by IL-2-activated human NK cells. This same combined treatment reduced both surface expression and mRNA levels of E-selectin. Moreover, anti-E-selectin mAb, but not Ab to VCAM-1, protected PAEC from lysis by human IL-2-activated NK cells in a dose-dependent manner. These findings suggest that expression of porcine E-selectin is important for the cytotoxicity of PAEC mediated by activated human NK cells and may be involved in the redox-mediated modulation of that cytotoxicity. It is known that NF-kappa B activation is required for transcription of E-selectin, and the current data show that the suppression of E-selectin expression by S-nitroso-N-acetyl-penicillamine pretreatment and thiol deprivation was associated with reduced NF-kappa B DNA-binding activity in PAEC. These data suggest that the regulation of porcine E-selectin may be important for modulating delayed xenograft rejection and that manipulation of cellular redox systems may provide a means to protect xenogeneic endothelial cells from NK cell-mediated cytotoxicity.
... The primitive vascular plexus evolves via arteriovenous EC specifications that are determined by the VEGFA concentration in the microenvironment (Sriram, Tan, Islam, Rufaihah, & Cao, 2015): that is, a high concentration of VEGFA favors an EC arterial specification characterized by the expression of neuropilin 1, DLL4, EPHB2 and CXCR4 mediated via the NOTCH pathway, whereas a low VEGFA concentration supports venous EC commitment. In different animal species, Hedgehog signaling in the mesoderm (Fish & Wythe, 2015) promotes the expression of VEGFA, which activates VEGFR2 in angioblast determining the arterial program through NOTCH ( Remodeling phase of angiogenesis Inflammatory response (Armesilla et al., 1999;Furuke et al., 1999;Graef, Chen, Chen, Kuo, & Crabtree, 2001;Zeini et al., 2009) Nuclear factor KB (NF-kB) Inflammatory response; Vascular Tone (Lan et al., 1994;Nagel et al., 1999;Pober & Sessa, 2007;Read et al., 1994) Myocyte enhancer factor-2 (MEF2) ...
Endothelial cells (ECs) that line vascular and lymphatic vessels are being increasingly recognized as important to organ function in health and disease. ECs participate not only in the trafficking of gases, metabolites, and cells between the bloodstream and tissues but also in the angiocrine-based induction of heterogeneous parenchymal cells, which are unique to their specific tissue functions. The molecular mechanisms regulating EC heterogeneity between and within different tissues are modeled during embryogenesis and become fully established in adults. Any changes in adult tissue homeostasis induced by aging, stress conditions, and various noxae may reshape EC heterogeneity and induce specific transcriptional features that condition a functional phenotype. Heterogeneity is sustained via specific genetic programs organized through the combinatory effects of a discrete number of transcription factors (TFs) that, at the single tissue-level, constitute dynamic networks that are post-transcriptionally and epigenetically regulated. This review is focused on outlining the TF-based networks involved in EC specialization and physiological and pathological stressors thought to modify their architecture.
... Several reports have shown that the NOS pathway is active in NK cells. Unlike other immune cells, NK cells constitutively express the endothelial NOS or NOS3 [262]. The synthesis of NO by NK cells supports their cytotoxic functions in different in vitro settings. ...
A growing body of evidence indicates that, over the course of evolution of the immune system, arginine has been selected as a node for the regulation of immune responses. An appropriate supply of arginine has long been associated with the improvement of immune responses. In addition to being a building block for protein synthesis, arginine serves as a substrate for distinct metabolic pathways that profoundly affect immune cell biology; especially macrophage, dendritic cell and T cell immunobiology. Arginine availability, synthesis, and catabolism are highly interrelated aspects of immune responses and their fine-tuning can dictate divergent pro-inflammatory or anti-inflammatory immune outcomes. Here, we review the organismal pathways of arginine metabolism in humans and rodents, as essential modulators of the availability of this semi-essential amino acid for immune cells. We subsequently review well-established and novel findings on the functional impact of arginine biosynthetic and catabolic pathways on the main immune cell lineages. Finally, as arginine has emerged as a molecule impacting on a plethora of immune functions, we integrate key notions on how the disruption or perversion of arginine metabolism is implicated in pathologies ranging from infectious diseases to autoimmunity and cancer.
... NK cells require L-ARG for proliferation, expression of activating receptors, and IFNg production in vitro (154). Human NK cells constitutively express endothelial NOS, inhibition of which impairs cytotoxicity (155,156). Like T cells, NK cells are inhibited by myeloid-derived Arg1 (157)(158)(159). In hepatitis C virus infection, Arg1-producing myeloid-derived suppressor cells decreased NK cell IFNg production through mTOR inhibition, which was reversed upon in vitro L-ARG supplementation (158). ...
Mycobacterium tuberculosis ( Mtb ), the causative agent of tuberculosis (TB), is a leading cause of death worldwide. Despite decades of research, there is still much to be uncovered regarding the immune response to Mtb infection. Here, we summarize the current knowledge on anti- Mtb immunity, with a spotlight on immune cell amino acid metabolism. Specifically, we discuss L-arginine and L-tryptophan, focusing on their requirements, regulatory roles, and potential use as adjunctive therapy in TB patients. By continuing to uncover the immune cell contribution during Mtb infection and how amino acid utilization regulates their functions, it is anticipated that novel host-directed therapies may be developed and/or refined, helping to eradicate TB.
... NO production has been largely demonstrated as a key mechanism in MDSC-mediated immunosuppression (90,92) (Figure 1). Some studies showed that autocrine production of NO by NK cells results in positive effect on NK cell function, and that human NK cells can express endothelial nitric oxide synthase (eNOS) but not inducible nitric oxide synthase (iNOS) (93,94). In contrast, Stiff et al. recently demonstrated that NO production by MDSCs limits NK cell cytotoxicity by impairing Fc receptor-mediated NK cell function, resulting in altered ADCC (92). ...
Myeloid-derived suppressor cells (MDSCs) contribute to the induction of an immune suppressive/anergic, tumor permissive environment. MDSCs act as immunosuppression orchestrators also by interacting with several components of both innate and adaptive immunity. Natural killer (NK) cells are innate lymphoid cells functioning as primary effector of immunity, against tumors and virus-infected cells. Apart from the previously described anergy and hypo-functionality of NK cells in different tumors, NK cells in cancer patients show pro-angiogenic phenotype and functions, similar to decidual NK cells. We termed the pro-angiogenic NK cells in the tumor microenvironment “tumor infiltrating NK” (TINKs), and peripheral blood NK cells in cancer patients “tumor associated NK” (TANKs). The contribution of MDSCs in regulating NK cell functions in tumor-bearing host, still represent a poorly explored topic, and even less is known on NK cell regulation of MDSCs. Here, we review whether the crosstalk between MDSCs and NK cells can impact on tumor onset, angiogenesis and progression, focusing on key cellular and molecular interactions. We also propose that the similarity of the properties of tumor associated/tumor infiltrating NK and MDSC with those of decidual NK and decidual MDSCs during pregnancy could hint to a possible onco-fetal origin of these pro-angiogenic leukocytes.
... Titers of uNKs are lower in mice with genetic deletion of eNOS, HO-1, or CBS. Decreased decidual uNKs in eNOS knockouts [4] is consistent with eNOS-dependent human NK resistance to apoptosis [210] and indicates NO autocrine or paracrine facilitation of uNK proliferation. Remarkably, early pregnancy CO inhalation (50 ppm) rescued uNK levels in pregnant HO-1 heterozygous mice and normalized the growth of HO-1 knockout conceptuses [6,211]. ...
Background
Gaso-transmitters are endogenous small gaseous messengers exemplified by nitric oxide (NO), carbon monoxide (CO), and hydrogen sulfide (H2S or sulfide). Gasotransmitters are implicated in myriad physiologic functions including many aspects of reproduction.
Objective
Comprehensively review basic mechanisms and functions of gasotransmitters during pregnancy from conception to uterine involution and highlight future research opportunities.
Methods
We searched PubMed and Web of Science databases using combinations of keywords nitric oxide, carbon monoxide, sulfide, placenta, uterus, labor, and pregnancy. We included English language publications on human and animal studies from any date through August 2018 and retained basic and translational articles with relevant original findings.
Findings
All gasotransmitters activate cGMP signaling. NO and sulfide also covalently modify target protein cysteines. Protein kinases and ion channels transduce gasotransmitter signals, and co-expressed gasotransmitters can be synergistic or antagonistic depending on cell type. Gasotransmitters influence tubal transit, placentation, cervical remodeling, and myometrial contractility. NO, CO, and sulfide dilate resistance vessels, suppress inflammation, and relax myometrium to promote uterine quiescence and normal placentation. Cervical remodeling and rupture of fetal membranes coincide with enhanced oxidation and altered gasotransmitter metabolism. Mechanisms mediating cellular and organismal changes in pregnancy due to gasotransmitters are largely unknown.
Wider implications
Altered gasotransmitter signaling has been reported for preeclampsia, intrauterine growth restriction, premature rupture of membranes, and preterm labor. However, in most cases specific molecular changes are not yet characterized. Non-classical signaling pathways and the crosstalk among gasotransmitters are emerging investigation topics.
... Cytokines such as IL-15, IL-12 and IL-2 augment the cytolytic activity of NK cells against tumours (Wu and Lanier, 2003). Studies have previously shown that increased NO production through NOS2 contributes to IL-2mediated enhanced cytotoxicity and IFN-γ production (Hibbs Jr. et al., 1992;Diefenbach et al., 1998;Cifone et al., 1999;Furuke et al., 1999;Cifone et al., 2001). Depletion of L-arginine, the substrate of NOS and Arg, has a profound impact on NK cells functions that was reflected in lower cytotoxicity and decreased NK cell viability (Lamas et al., 2012). ...
Recent findings suggest that co‐expression of NOS2 and COX2 is a strong prognostic indicator in triple‐negative breast cancer patients. These two key inflammation‐associated enzymes are responsible for the biosynthesis of NO and PGE 2 , respectively, and can exert their effect in both an autocrine and paracrine manner. Impairment of their physiological regulation leads to critical changes in both intra‐tumoural and intercellular communication with the immune system and their adaptation to the hypoxic tumour micro‐environment. Recent studies have also established a key role of NOS2–COX2 in causing metabolic shift. This review provides an extensive overview of the role of NO and PGE 2 in shaping communication between the tumour micro‐environment composed of tumour and immune cells that in turn favours tumour progression and metastasis.
Linked Articles
This article is part of a themed section on Nitric Oxide 20 Years from the 1998 Nobel Prize. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.2/issuetoc
... Few studies have investigated the relationship between NO and NK cell function. Earlier studies revealed that autocrine production of NO by NK cells could have a positive effect on NK cell function, and that human NK cells appear to express endothelial nitric oxide synthase but not inducible nitric oxide synthase (48,49). The amount of NO produced by activated NK cells is reported to be in the nanomolar range, which is substantially lower than the 2-20 μM range of NO produced by MDSC. ...
Purpose:
Monoclonal antibodies (mAb) are used to treat solid and hematological malignancies, and work in part through Fc receptors (FcR) on natural killer cells (NK). However, FcR mediated functions of NK cells from cancer patients are significantly impaired. Identifying the mechanisms of this dysfunction and impaired response to mAb therapy could lead to combination therapies and enhance mAb therapy. Experimental Design: Co-cultures of autologous NK cells and MDSC from cancer patients were used to study the effect of MDSC on NK cell FcR mediated functions including antibody dependent cellular cytotoxicity, cytokine production, and signal transduction in vitro. Mouse breast cancer models were utilized to study the effect of MDSC on antibody therapy in vivo and test the efficacy of combination therapies including a mAb and a MDSC targeting agent. Results: Cancer patient MDSC were found to significantly inhibit NK cell FcR mediated functions including ADCC, cytokine production, and signal transduction in a contact independent manner. In addition, adoptive transfer of MDSC abolished the efficacy of mAb therapy in a mouse model of pancreatic cancer. Inhibition of iNOS restored NK cell functions and signal transduction. Finally, non-specific elimination of MDSC or inhibition of iNOS in vivo significantly improved the efficacy of mAb therapy in a mouse model of breast cancer.
Conclusions:
MDSC antagonize NK cell FcR mediated function and signal transduction leading to impaired response to mAb therapy in part through nitric oxide production. Thus, elimination of MDSC or inhibition of nitric oxide production offers a strategy to improve mAb therapy.
... Activation of the calcium pathway by ITAMcoupled receptors results in the activation of the phosphatase calcineurin and dephosphorylation and activation of the transcription factor NFAT as well as phosphorylation and activation of CREB by a Ca2 + /calmodulin-dependent protein kinase [9,17]. The NFAT family of transcription factors bind DNA weakly and associates with other DNA-binding proteins including the transcription factors NFκB and AP1 [8,18,19]. ITAM-coupled receptors have also been reported to interact with other signaling pathways including the Jak-STAT pathway [9]. In keeping with these results, we have shown that the NFAT, CREB, NFκB, AP1, and the Jak-STAT pathways are all activated when Jurkat effector cells, cotransfected with a reporter gene construct specific for an individual transcription factor and CD16a, interact with CD20 positive Raji target cells in the presence of rituximab. ...
Novel ADCC effector cells expressing the V-variant or F-variant of Fc γ RIIIa (CD16a) and firefly luciferase under the control of a chimeric promoter incorporating recognition sequences for the principal transcription factors involved in Fc γ RIIIa signal transduction, together with novel target cells overexpressing a constant high level of the specific antigen recognized by rituximab, trastuzumab, cetuximab, infliximab, adalimumab, or etanercept, confer improved sensitivity, specificity, and dynamic range in an ADCC assay relative to effector cells expressing a NFAT-regulated reporter gene and wild-type target cells. The effector cells also contain a normalization gene rendering ADCC assays independent of cell number or serum matrix effects. The novel effector and target cells in a frozen thaw-and-use format exhibit low vial-to-vial and lot-to-lot variation in their performance characteristics reflected by CVs of 10% or less. Homologous control target cells in which the specific target gene has been invalidated by genome editing providing an ideal control and a means of correcting for nonspecific effects were observed with certain samples of human serum. The novel effector cells and target cells expressing noncleavable membrane-bound TNF α have been used to quantify ADCC activity in serum from patients with Crohn’s disease treated with infliximab and to relate ADCC activity to drug levels.
... TNF-α produced by activated NK cells can also induce tumor-cell apoptosis (31); (c) Secretion of various effector molecules: Effector molecules, such as cytokines, mediate antitumor functions in various ways, including hindering tumor angiogenesis and stimulating adaptive immunity (32,33). Exposure of tumors to NK cells is also associated with nitric oxide (NO) production, which leads to tumor DNA fragmentation and cell lysis (34,35); (d) Antibody-dependent cytotoxicity: NK cells can sometimes express CD16, a marker that can interact with antibody receptors on tumor cells in order to induce antibodydependent cellular cytotoxicity (ADCC) in tumor cells (36)(37)(38)(39)(40)(41). ...
... NK cells express constitutive eNOS mRNA and protein, however the levels of iNOS are not detectable. The endogenous NO production is involved in protection of NK cells from activation of apoptosis induced by CD16 cross-linking, thereby maintaining NK activity [49]. This is the further evidence that, unlike NO produced by iNOS, cNOS-derived NO is critical for normal physiology. ...
The correlation between high exhaled nitric oxide levels and eosinophilic-mediated airway inflammation in patients with atopic asthma has been well documented. This generates prerequisites that a regulatory feedback mechanism exists between them. Therefore, the paper briefly describes evidence implementing biosynthesis, enzyme structural features, expression regulation of its isoforms and effects of nitric oxide, which have helped elucidate molecular mechanisms by which nitric oxide selectively promotes asthma exacerbation. In previous study we have demonstrated that airway infiltrate of immune cells contributes to NO synthesis in the respira-tory tract during allergic inflammation under guinea pig model of acute asthma with multiple challenges. On the basis of these findings the authors posits that nitric oxide represents an additional signal of the induction of Th2 subset response and be considerably involved in the complex network of immune regulation distinctive for atopic asthma phenotype.
... An interesting report designated NO as the driving force for the generation of a new subset of the mechanism of NO production in NK cells needs to be clarified. It was proposed that the endogenous NO generation by active eNOS isoform prevents NK cells from activationinduced apoptosis, thereby maintaining cell fitness [85] . Mast cells (MCs) are widely distributed throughout the extravascular area in the body where they play versatile roles dealing with innate immunity, IgEmediated allergy and inflammation. ...
Over the last decades, nitric oxide (NO) has been definitively recognised as one of the key players involved in immunity and inflammation. NO generation was originally described in activated macrophages, which still represent the prototype of NO-producing cells. Notwithstanding, additional cell subsets belonging to both innate and adaptive immunity have been documented to sustain NO propagation by means of the enzymatic activity of different nitric oxide synthase isoforms. Furthermore, due to its chemical characteristics, NO could rapidly react with other free radicals to generate different reactive nitrogen species (RNS), which have been intriguingly associated with many pathological conditions. Nonetheless, the plethora of NO/RNS-mediated effects still remains extremely puzzling. The aim of this manuscript is to dig into the broad literature on the topic to provide intriguing insights on NO-mediated circuits within immune system. We analysed NO and RNS immunological clues arising from their biochemical properties, immunomodulatory activities and finally dealing with their impact on different pathological scenarios with far prompting intriguing perspectives for their pharmacological targeting.
... Particularly, ATF2 has been shown to increase UVC-induced apoptosis in melanoma cells by downregulating TNF expression (64,65). In NK cells, production of endogenous NO can inhibit NFAT, and thus downregulate TNF transcription, protecting the cells from activation-induced apoptosis (66). Interestingly, engagement of TNFR1 by TNF can also modulate TNF gene expression, by a mechanism involving ATF2 and p38 MAPK (67). ...
... Given that eNOS is activated by the PI3K-Akt pathway [107], it is most likely that NO generated by the PI3K-Aktdependent eNOS activation pathway positively regulates the Ca v 1.2 LTCC activity. Interestingly, the PI3K-Akt pathway and/or eNOS have been shown to play key roles in the survival of various cell types as well as in chronic inflammation and cancer [109][110][111][112][113][114][115]. Since the absence of Ca v 1.2 LTCCs is significantly compensated for by blocking PTPC opening or inhibiting the downstream caspase cascade pathway, this type of Ca 2+ channel may prevent extensive PTPC opening, thereby playing a key role in the maintenance of mitochondrial integrity. ...
Aspirin (acetylsalicylic acid) is a well-known nonsteroidal anti-inflammatory drug (NSAID) that has long been used as an anti-pyretic and analgesic drug. Recently, much attention has been paid to the chemopreventive and apoptosis-inducing effects of NSAIDs in cancer cells. These effects have been thought to be primarily attributed to the inhibition of cyclooxygenase activity and prostaglandin synthesis. However, recent studies have demonstrated unequivocally that certain NSAIDs, including aspirin and its metabolite salicylic acid, exert their anti-inflammatory and chemopreventive effects independently of cyclooxygenase activity and prostaglandin synthesis inhibition. It is becoming increasingly evident that two potential common targets of NSAIDs are mitochondria and the Ca2+ signaling pathway. In this review, we provide an overview of the current knowledge regarding the roles of mitochondria and Ca2+ in the apoptosis-inducing effects as well as some side effects of aspirin, salicylates and other NSAIDs, and introducing the emerging role of L-type Ca2+ channels, a new Ca2+ entry pathway in non-excitable cells that is up-regulated in human cancer cells.
... NK cells also express constitutive, but not inducible, endothelial NO synthase (NOS) and secrete NO. Interestingly, NOS inhibitors can significantly inhibit functions of HNK cells [204]. Several studies have shown that the profile of NK cell-secreted cytokines depends on the milieu in which they develop and differentiate. ...
Le virus de l’immunodéficience humaine ou VIH est l’agent qui cause le SIDA. Le VIH donne lieu à une dérégulation dans la production de certaines cytokines qui ont un rôle immunologique très important chez les patients infectés. L’IL-18, autrement nommé facteur inducteur d’IFN-γ, est une cytokine pro-inflammatoire qui affecte le système immunitaire de façon importante. Son activité est régulée par l’"IL-18 Binding Protein" (IL-18BP), une autre cytokine qui se lie avec l’IL-18 et inhibe son activité biologique. Des études ultérieures ont montré des niveaux élevés d’Il-18 chez les patients infectés par le VIH par rapport aux personnes saines. Cependant, aucune étude n’a été réalisée concernant la production d’IL-18BP chez ces patients. Due à sa relevance dans la régulation de l’IL-18, nous avons étudié l’effet de l’infection par le VIH sur l’équilibre entre ces deux facteurs et l’impact de cet équilibre sur l’homéostasie des cellules NK. Nous avons mesuré les taux de l’IL-18 et de l’IL-18BP circulantes dans les sérums des patients infectés par le VIH en les comparants avec le même nombre de personnes saines et séronégatives. Nous avons aussi déterminé le nombre total des différents sous-types de cellules NK et analysé l’activité des cellules NK (Natural Killer). Finalement nous avons cherché à déterminer si l’IL-18 pouvait induire l’apoptose des cellules NK en activant l’expression de Fas ligand. Nos résultats nous démontrent que les patients infectés par le VIH ont trois fois plus d’IL-18 que les donneurs sains. Cependant les niveaux d’IL-18BP sont plus bas chez les patients infectés comparés aux donneurs sains. Alors, le ratio IL-18/IL-18BP est augmenté chez les patients infectés, ce qui entraîne une grande quantité d’IL-18 libre et biologiquement active circulante dans leur organisme. Nos études démontrent que chez ces patients, les concentrations d’IL-18 sont en corrélation négative avec l’activité cytotoxique de leurs cellules NK. Nos études in vitro démontrent que le traitement des cellules NK par l’IL-18 induit de façon fratricide leur apoptose en augmentant l’expression de Fas ligand. Finalement, cette production non coordonnée de ces deux facteurs pourrait contribuer à une immunopathologie induite par l’IL-18 en entraînant une apoptose fratricide des cellules NK qui possèdent un rôle important dans la réponse antivirale. Le dérèglement de l’homéostasie des cellules NK pourrait donc contribuer à la pathogenèse induite par le VIH. HIV-1, the causative agent of AIDS, induces a deregulated production of several immunologically important cytokines in the infected persons. One of these cytokines is IL-18: a powerful proinflammatory cytokine that can regulate both innate and adaptive immune responses. In vivo, its activity is tightly regulated by IL-18 Binding Protein (IL-18BP), another cytokine that specifically binds and neutralizes IL-18 with high affinity. Previous studies have shown that IL-18 concentrations are significantly increased in the circulation of HIV-infected AIDS patients compared to those in healthy people. However, it is not yet clear how the increased levels of this cytokine affect the development of AIDS in HIV infected persons. Furthermore, little is known concerning the production of IL-18 antagonist (IL-18BP) in these patients. These issues were addressed in the studies presented in this thesis. We measured levels of IL-18 and IL-18BP in the sera of HIV-infected patients by using commercial ELISA kits and compared them with the values obtained from a similar number of healthy HIV-seronegative persons. We also determined the absolute and total number of different NK cell subsets and NK cell activity in the peripheral blood mononuclear cells (PBMC) of these individuals. Finally we determined the effects of recombinant human IL-18 as well as of IL-18-rich sera from AIDS patients on cytolytic activity and survival of human NK cells. Our results show that sera from HIV- infected patients contain up to 3 fold higher levels of IL-18 compared to the sera from healthy people. However, levels of IL-18BP were lower in the infected individuals compared to the healthy ones. Consequently, IL-18/IL-18BP ratio is increased in the patients resulting in a further increase in the concentrations of biologically active IL-18 in the circulation of these patients. Our results show that the concentrations of IL-18 correlated inversely with NK cell numbers as well as with their cytolytic activity in the infected persons. These results suggested the involvement of IL-18 in the disappearance of NK cells that prompted us to determine the potential cytocidal effects of this cytokine on human NK cells. The results from our in vitro experiments show that recombinant human IL-18 and IL-18-rich sera from AIDS patients caused apoptosis in a human NK cell line as well as in primary human NK cells. Anti-FasL antagonist antibodies inhibited this cell death. In a series of experiments, we found that IL-18 enhances expression of FasL but does not affect the expression of Fas on human NK cells. In vitro IL-18 also stimulated transcription from human FasL promoter. Furthermore, the cytokine also enhanced susceptibility of NK cells to Fas-mediated death, as it decreased the expression of an anti-apoptotic protein Bcl-XL. Our study shows that enhanced IL-18 bioactivity in HIV-infected patients may contribute to the pathogenesis of AIDS by disrupting NK cell homoeostasis.
... Given that eNOS is activated by the PI3K-Akt pathway (Inoue et al., 2008b), it is most likely that FcRI stimulation results in PI3K-Akt-dependent eNOS phosphorylation and NO generation, which in turn stimulates Ca v 1.2 LTCC activity. Interestingly, both the PI3K-Akt pathway and eNOS have been shown to play key roles in the survival of various cell types, including NK cells and vascular endothelial cells (Martelli et al., 2006;Dimmeler and Zeiher, 1999;Choi et al., 2002;Parcellier et al., 2007;Furuke et al., 1999;Ho et al., 2006). Since the absence of Ca v 1.2 LTCCs is significantly compensated for blocking mPTP opening or inhibiting the downstream caspase cascade pathway, this kind of Ca 2+ channels may prevent extensive mPTP opening, and therefore be required for the maintenance of mitochondrial integrity. ...
Ca(2+) is a highly versatile intracellular second messenger in many cell types, and regulates many complicated cellular processes, including cell activation, proliferation and apoptosis. Influx of Ca(2+) from the extracellular fluid is required for sustained elevation of the cytosolic Ca(2+) concentration and full activation of Ca(2+)-dependent processes. It is widely accepted that Ca(2+) release-activated Ca(2+) channels are the major routes of Ca(2+) influx in electrically non-excitable cells, including hematopoietic cells, whereas voltage-gated Ca(2+) channels such as L-type Ca(2+) channels (LTCCs) serve as the principal routes of Ca(2+) entry into electrically excitable cells such as neurons and myocytes. However, recent pharmacological and molecular genetic studies have revealed the existence of functional LTCCs and/or LTCC-like channels in a variety of immune cells including mast cells. In this article, we review recent advances in our understanding of Ca(2+) signaling in immune cells with a special interest in mast cells. We highlight roles for LTCCs in antigen receptor-mediated mast cell activation and survival.
... Given that eNOS is activated by the PI3K-Akt pathway [32], it is the most likely that FcɛRI delivers a pro-survival signal by evoking PI3K-Akt-dependent eNOS phosphorylation and NO generation, which in turn stimulates Ca v 1.2 LTCC activity. Interestingly, both the PI3K-Akt pathway and eNOS have been shown to play key roles in the survival of various cells, including NK cells and vascular endothelial cells [51][52][53][54]. It is noteworthy that the absence of eNOS and Ca v 1.2 LTCCs was completely compensated by the presence of BKA and z-DEVD-fmk, a caspase-3/7-selective inhibitor, which block mPTP opening and the downstream caspase cascade pathway, respectively. ...
Recent pharmacological and molecular genetic approaches have revealed the existence of functional L-type Ca2+ channels (LTCCs) in a variety of hematopoietic cells. We previously reported that Ca(v)1.2 LTCCs are expressed on mast cell surfaces, activated by the high-affinity IgE receptor (FcvarepsilonRI) engagement and protect mast cells against activation-induced cell death (AICD). We also demonstrated that FcvarepsilonRI engagement evokes nitric oxide (NO) generation in a phosphatidylinositol-3-kinase- and NO synthase (NOS)-dependent manner, which is also required for mast cell survival. Here we demonstrate that this endogenous NO mediates Ca(v)1.2 LTCC activation. FcvarepsilonRI engagement but not thapsigargin, a potent Ca2+ release-activated Ca2+ (CRAC) channel agonist, induced Ca2+ influx via NOS-dependent NO generation. RT-PCR analyses revealed predominant expression of eNOS in mast cells. Subsequent experiments involving siRNA-mediated gene silencing of eNOS or Ca(v)1.2 LTCC revealed that eNOS was essential for NOS-dependent NO generation and Ca(v)1.2 LTCC activation but not CRAC channel activation. Similar to Ca(v)1.2 LTCCs, eNOS prevented the dissipation of the mitochondrial membrane potential and mitochondrial integrity collapse, thereby protecting mast cells against AICD. Taken together, the present findings demonstrate the key roles of the eNOS-NO-LTCC axis in mast cell survival after FcvarepsilonRI engagement.
... This ®nding is consistent with data suggesting that the involvement of NO in the protection of T cells from Fas-mediated cell death was partially [23] or completely independent of cGMP [24]. Recent results suggest that NO can also protect human NK cells from apoptosis induced by activation through CD16 [30]. Causal relations between NO-induced growth facilitation, enhanced IL-2Ra expression, and resistance to apoptosis in IL-2-treated lymphocytes are currently under investigation in our laboratory. ...
The effect of nitric oxide (NO) on growth and major histocompatibility complex(MHC)-unrestricted cytotoxicity of interleukin(IL)-2-cultivated rat spleen nonadherent mononuclear cells was examined. NO donor sodium nitroprusside (SNP) at relatively low concentrations increased magnitude, as well as duration of IL-2-induced proliferative response of nonadherent splenocytes. SNP effect depended completely on released NO, because it was prevented by NO scavenger haemoglobin, but not mimicked by expired SNP solution, unable to generate NO, or ferricyanide, a second breakdown product of SNP. Other NO donors - SIN-1, SNAP and GSNO failed to exert SNP-like growth-enhancing action, probably as a consequence of rapid NO generation, compared to sustained NO release by SNP. All NO-releasing chemicals at high concentration blocked IL-2-induced proliferation. Growth-promoting effect of SNP-derived NO was independent of guanilat cyclase activation, because dibutyryl cGMP did not affect IL-2-triggered splenocyte proliferation. Macrophage NO acted in a manner similar to SNP; at low concentrations it promoted IL-2-induced splenocyte growth, however higher amounts were suppressive. Cytotoxicity of IL-2-activated splenocytes against NK-sensitive K562 cell line was significantly increased when SNP was present during cultivation with IL-2. Proportion of NKR-P1+ and CD25+ cells, as well as per cell expression of these important activation molecules were increased upon SNP treatment, suggesting possible mechanism for the observed NO action.
... However, the generated NO appeared to downregulate stimulation of lytic potential induced by these cytokines rather than to play a role as w x cytotoxic effector molecule. Furuke et al. 100 reported that human NK cells constitutively expressed eNOS mRNA and protein, and the constitutive level of eNOS expression was maintained in the presence of IL-2 in vitro. Activation of the eNOS in freshly purified and IL-2-stimulated human NK cells was induced by IL-2 and CD16 cross-linking. ...
Natural killer (NK) cells and nitric oxide (NO) are both important components of the natural or innate immune response. NK cells are large granular lymphocytes capable of destroying cells infected by virus or bacteria and susceptible tumor cells without prior sensitization and restriction by MHC antigens. They are abundant in blood, spleen, liver and lungs and are distinct from both T and B lymphocytes in their circulation patterns, profile of surface antigens, receptor repertoire and the way in which they discriminate between self and non-self. Uniquely, NK cells express receptors that can recognize and discriminate between normal and altered MHC class I determinants. NK cell cytotoxic activity is strongly induced by cytokines such as IL-2 and IL-12, and this activation is associated with synthesis of NO. Inhibitors of NO synthesis impair NK cell-mediated target cell killing, demonstrating a role for NO in NK cell function. Furthermore, NO itself can regulate NK cell activation. In this article, evidence that NO is a mediator of NK cell-mediated target cell killing, and that NO is a regulator of NK cell activation will be reviewed. Results of NO synthase gene deletion studies will be discussed, and rodent and human NK cells will be compared.
... For instance, while lipopolysaccharide (LPS) induces TNF-␣ expression in cardiac myocytes (13,19), the mechanism has been suggested to occur by a novel CD14-independent pathway (3). In contrast to macrophage cell lines, where nitric oxide inhibits TNF-␣ production (6,8), this messenger induces TNF-␣ generation in feline cardiac myocytes (12). These studies offer a caution for making assumptions about the regulatory mechanisms of TNF-␣ expression in cardiomyocytes based upon previous studies performed upon myeloid cell types. ...
Although tumor necrosis factor (TNF)-alpha is implicated in numerous cardiac pathologies, the intracellular events leading to its production by heart cells are largely unknown. The goal of the present study was to identify the role of the transcription factor nuclear factor (NF)-kappaB in this process. Among the many inducers of TNF-alpha expression in myeloid cells, only lipopolysaccharide (LPS) led to its induction in cultured neonatal myocytes. LPS also activated the NF-kappaB pathway, as evidenced by the degradation of the inhibitory protein IkappaB and the appearance of NF-kappaB-binding complexes in nuclear extracts. Furthermore, inhibitors of NF-kappaB activation, such as lactacystin, MG132, and pyrrolidine dithiocarbamate, were found to completely block the production of TNF-alpha in response to LPS stimulation, indicating a requirement of NF-kappaB for TNF-alpha expression. However, interleukin-1beta and phorbol 12-myristate 13-acetate also activated NF-kappaB but did not evoke TNF-alpha expression, revealing that this factor is not sufficient for cytokine production. Detailed examination of the NF-kappaB cascade revealed that cardiac cells displayed a unique pattern of IkappaB degradation in response to LPS, with IkappaBbeta but not IkappaBalpha being degraded upon stimulation. Additionally, two specific p65-containing DNA-binding complexes were observed in the nuclear extracts of neonatal cardiomyocytes: an inducible complex that is necessary for TNF-alpha expression and a constitutive species. Taken together, these results reveal that NF-kappaB is not only involved in cytokine production but also may be linked to other pathways that subserve a constitutive, protective mechanism for the heart cell.
... In addition, eNOS has been shown to be antiapoptotic against TNF-a-induced apoptosis, in endothelial cells (Iadecola 1997;Agnoletti et al. 1999;Dimmeler et al. 1999), NK cells (Furuke et al. 1999) and HeLa cells (Bulotta et al. 2001). Nitric oxide (NO) from eNOS can be protective against oxidative stress and excitotoxic damage (Iadecola 1997). ...
Erythropoietin (EPO), a pleiotropic cytokine involved in erythropoiesis, is tissue-protective in ischemic, traumatic, toxic and inflammatory injuries. In this study, we investigated the effect of EPO in experimental intracerebral hemorrhage (ICH). Two hours after inducing ICH via the stereotaxic infusion of collagenase, recombinant human EPO (500 or 5000 IU/kg, ICH + EPO group) or PBS (ICH + vehicle group) was administered intraperitoneally, then once daily afterwards for 1 or 3 days. ICH + EPO showed the better functional recovery in both rotarod and modified limb placing tests. The brain water content was decreased in ICH + EPO dose-dependently, as compared with ICH + vehicle. The effect of EPO on the brain water content was inhibited by N(omega)-Nitro-L-arginine methyl ester hydrochloride (L-NAME, 10 mg/kg). Mean hemorrhage volume was also decreased in ICH + EPO. EPO reduced the numbers of TUNEL +, myeloperoxidase + or OX-42 + cells in the perihematomal area. In addition, EPO reduced the mRNA level of TNF-alpha, Fas and Fas-L, as well as the activities of caspase-8, 9 and 3. EPO treatment showed up-regulations of endothelial nitric oxide synthase (eNOS) and p-eNOS, pAkt, pSTAT3 and pERK levels. These data suggests that EPO treatment in ICH induces better functional recovery with reducing perihematomal inflammation and apoptosis, coupled with activations of eNOS, STAT3 and ERK.
The tumor microenvironment is a complex domain that not only contains tumor cells but also a plethora of other host immune cells. By nature, the tumor microenvironment is a highly immunosuppressive milieu providing growing conditions for tumor cells. A major immune cell population that contributes most in the development of this immunosuppressive microenvironment is the MDSC, a heterogenous population of immature cells. Although found in small numbers only in the bone marrow of healthy individuals, they readily migrate to the lymph nodes and tumor site during cancer pathogenesis. MDSC mediated disruption of antitumor T cell activity is a major cause of the immunosuppression at the tumor site, but recent findings have shown that MDSC mediated dysfunction of other major immune cells might also play an important role. In this article we will review how crosstalk with MDSC alters the activity of both conventional and unconventional immune cells that inhibits the antitumor immunity and promotes cancer progression.
Coronavirus disease 2019 (COVID-19) represents a major public health crisis that has caused the death of nearly six million people worldwide. Emerging data have identified a deficiency of circulating arginine in patients with COVID-19. Arginine is a semi-essential amino acid that serves as key regulator of immune and vascular cell function. Arginine is metabolized by nitric oxide (NO) synthase to NO which plays a pivotal role in host defense and vascular health, whereas the catabolism of arginine by arginase to ornithine contributes to immune suppression and vascular disease. Notably, arginase activity is upregulated in COVID-19 patients in a disease-dependent fashion, favoring the production of ornithine and its metabolites from arginine over the synthesis of NO. This rewiring of arginine metabolism in COVID-19 promotes immune and endothelial cell dysfunction, vascular smooth muscle cell proliferation and migration, inflammation, vasoconstriction, thrombosis, and arterial thickening, fibrosis, and stiffening, which can lead to vascular occlusion, muti-organ failure, and death. Strategies that restore the plasma concentration of arginine, inhibit arginase activity, and/or enhance the bioavailability and potency of NO represent promising therapeutic approaches that may preserve immune function and prevent the development of severe vascular disease in patients with COVID-19.
Assessment of nitric oxide (NO) dynamics in immune cells, commonly measured using NO surrogates such as inducible nitric oxide synthase (iNOS) rather than NO itself, has been effective in understanding pathophysiology across a wide range of diseases. Although the intracellular measurement of NO is now feasible, many technical issues remain unresolved. The principle aim of our study was to determine the effect of storage time of whole blood on nitric oxide (NO) level expression in leukocytes. This is important because immune cells remain chemically dynamic even after they are removed from the circulation, and the impact of storage time must be known to optimally quantify the effect of a disease or condition on NO dynamics in circulating leukocytes. We measured NO levels using the fluorescent probe, diaminofluorescein (DAF-2DA), and flow cytometry in monocytes, neutrophils, and natural killer cells from healthy subjects immediately after blood draw (Time 0) and 30, 60, and 120 min following the blood draw. There was no significant difference among the 4 study time points in NO (DAF-2) levels, though there was wide intra-subject variability at all time points. Using LPS stimulation, we compared iNOS (the more traditional surrogate marker of NO dynamics) with NO (by DAF-2) in either natural killer cells or monocytes. In these experiments, we found no difference in the response patterns. We did find that within a 2-hour interval from blood draw to sample processing, there was a remarkably wide intra-subject variability in expression of intracellular NO (DAF-2) in leukocytes of healthy individuals at baseline and over time. The mechanism(s) for these differences are not known but could clearly confound efforts to detect changes in NO metabolism in white blood cells. We speculate that rapid pulsatility of NO could explain the wide variability seen.
Similar to other biological systems where the effect of nitric oxide (NO) has been examined, paradoxical findings on the effects of NO on lymphocyte function have been reported. The most paradoxical effect may be that on the one hand, NO can inhibit apoptosis, a major mechanism of down-regulation of the immune response. In this capacity, NO would serve as a facilitator of the immune response, promoting survival of effector lymphocyte populations. Yet, NO also has been shown to inhibit lymphocyte proliferation and promote apoptosis and thus effectively prevent amplification of the immune response. Therefore, the challenge in the study of the effect of NO on lymphocytes is to determine under which circumstances NO acts as a facilitator versus an inhibitor of the immune response.
This study was designed to investigate the role of nitric oxide (NO) on the apoptosis of human luteinized granulosa cells and its possible pathways. Granulosa cell suspensions were incubated for 48 h after adding NO donor (S-nitroso-N-acetyl-penicillamine, SNAP) and NO synthase inhibitor (nitro-L-arginine methyl ester, L-NAME) at different concentrations. Apoptosis was examined using a terminal deoxynucleotide-transferase-mediated dUTP-biotin nick end labeling method in 70 patients, and immunocytochemical staining was performed for six apoptosis-related proteins in 50 patients. Apoptotic rates were significantly lower in cells incubated with 0.5 mM SNAP, but higher with 0.5, 1.0, and 5.0 mM L-NAME. SNAP (0.5 mM) lowered the expression of Fas and p53 in luteinized granulosa cells, but Bcl-2 expression was increased, and Fas ligand or Bax remained unchanged. Using L-NAME (0.5 and 5.0 mM), the expression of p53 and Bax was increased, but Bcl-2 was unchanged. Fas/Fas ligands were also activated especially in 5.0 mM L-NAME. In conclusion, NO may inhibit apoptosis via decreased Fas and p53, and increased Bcl-2 expression in human luteinized granulosa cells.
Natural killer (NK) cells play critical roles in host immunity against cancer. In response, cancers develop mechanisms to escape NK cell attack or induce defective NK cells. Current NK cell-based cancer immunotherapy aims to overcome NK cell paralysis using several approaches. One approach uses expanded allogeneic NK cells, which are not inhibited by self histocompatibility antigens like autologous NK cells, for adoptive cellular immunotherapy. Another adoptive transfer approach uses stable allogeneic NK cell lines, which is more practical for quality control and large-scale production. A third approach is genetic modification of fresh NK cells or NK cell lines to highly express cytokines, Fc receptors and/or chimeric tumor-antigen receptors. Therapeutic NK cells can be derived from various sources, including peripheral or cord blood cells, stem cells or even induced pluripotent stem cells (iPSCs), and a variety of stimulators can be used for large-scale production in laboratories or good manufacturing practice (GMP) facilities, including soluble growth factors, immobilized molecules or antibodies, and other cellular activators. A list of NK cell therapies to treat several types of cancer in clinical trials is reviewed here. Several different approaches to NK-based immunotherapy, such as tissue-specific NK cells, killer receptor-oriented NK cells and chemically treated NK cells, are discussed. A few new techniques or strategies to monitor NK cell therapy by non-invasive imaging, predetermine the efficiency of NK cell therapy by in vivo experiments and evaluate NK cell therapy approaches in clinical trials are also introduced.Cellular & Molecular Immunology advance online publication, 22 April 2013; doi:10.1038/cmi.2013.10.
Nitric oxide (NO), a short-lived pleiotropic messenger, is known to interact with signaling pathways operated by other messenger
molecules, including ions, cyclic nucleotides, protein kinases and phosphatases. Through these interactions NO regulates a
variety of biological functions. Recendy, NO has been shown to interact with ceramide signaling by regulating enzymes in the
metabolic pathway of sphingolipids. This leads to increases or de- creases in ceramide cell content, depending on the concentration
of NO and the time of expo- sure. Ceramide in turn may activate NO synthases to generate NO. The cross-talk between the two
messenger molecules appears of biological relevance in the regulation of the signal trans- duction pathways triggered by death
receptors and leads to modulation of the ability of these receptors to induce cell death via apoptosis.
In this study, we investigate the relationship between natural killer (NK) cell susceptibility and the surface markers of cancer cells. Through phenotypic analysis, we found evidence that more susceptible cancer cell lines (K562 and Jurkat) express more NKG2D ligands. Major histocompatibility complex (MHC) class I chain-related A/B (MIC-A/B) and UL16 binding protein (ULBP) 1-5 molecules are typical ligands of NKG2D. The high killing activity of NK cells against K562 was abolished through the addition of a NKG2D blocking antibody. Upon in vitro stimulation with quercetin, low susceptible cancer cells increased NKG2D ligand expression, leading to enhancement of NK cell cytolytic activity. These results suggested that the anti-cancer activity of NK cells is not dependent on the origin and growth style of the target cells, but is dependent on the surface markers of the target cells.
Nitric oxide (NO) is a multi-faceted molecule with dichotomous regulatory roles in many areas of biology. The complexity of its biological effects is a consequence of its numerous potential interactions with other molecules such as reactive oxygen species (ROS), metal ions, and proteins. The effects of NO are modulated by both direct and indirect interactions that can be dose-dependent and cell-type specific. For example, in some cell types NO can promote apoptosis, whereas in other cells NO inhibits apoptosis. In hepatocytes, NO can inhibit the main mediators of cell death—caspase proteases. Moreover, low physiological concentrations of NO can inhibit apoptosis, but higher concentrations of NO may be toxic. High NO concentrations lead to the formation of toxic reaction products like dinitrogen trioxide or peroxynitrite that induce cell death, if not by apoptosis, then by necrosis. Long-term exposure to nitric oxide in certain conditions like chronic inflammatory states may predispose cells to tumorigenesis through DNA damage, inhibition of DNA repair, alteration in programmed cell death, or activation of proliferative signaling pathways. Understanding the regulatory mechanisms of NO in apoptosis and carcinogenesis will provide important clues to the diagnosis and treatment of tissue damage and cancer. In this article we have reviewed recent discoveries in the regulatory role of NO in specific cell types, mechanisms of pro-apoptotic and anti-apoptotic induction by NO, and insights into the effects of NO on tumor biology.
Natural killer (NK) cells were first described as immune leukocytes that could kill tumor cells and soon after were reported to kill virus-infected cells. In the mid-1980s, 10 years after their discovery, NK cells were also demonstrated to contribute to the fight against bacterial infection, particularly because of crosstalk with other leukocytes. A wide variety of immune cells are now recognized to interact with NK cells through the production of cytokines such as interleukin (IL)-2, IL-12, IL-15 and IL-18, which boost NK cell activities. The recent demonstration that NK cells express pattern recognition receptors, namely Toll-like and nucleotide oligomerization domain (NOD)-like receptors, led to the understanding that these cells are not only under the control of accessory cells, but can be directly involved in the antibacterial response thanks to their capacity to recognize pathogen-associated molecular patterns. Interferon (IFN)-γ is the predominant cytokine produced by activated NK cells. IFN-γ is a key contributor to antibacterial immune defense. However, in synergy with other inflammatory cytokines, IFN-γ can also lead to deleterious effects similar to those observed during sepsis. Accordingly, as the main source of IFN-γ in the early phase of infection, NK cells display both beneficial and deleterious effects, depending on the circumstances.
In der vorliegenden Arbeit wurde die zelluläre Regulation des monocyten-/ macrophagenspezifischen Oberflächenproteins CD163 untersucht und klinische Aspekte der löslichen Form des CD163 (sCD163) diskutiert. sCD163 wird in vivo durch einen inflammatorischen Reiz von der Zelloberfläche abgespalten. Bislang waren jedoch noch keine Mediatoren charakterisiert worden, die immer unter Entzündungsbedingungen vorhanden sind. In den eigenen Untersuchungen des Shedding von CD163 konnten für die Generierung des sCD163 neue endogene Aktivatoren identifiziert werden. Sowohl reaktive Sauerstoffspezies, wie Wasserstoffperoxid oder Stickstoffmonoxid, als auch das Produkt von endogenen Oxidationsreaktionen mit reaktiven Sauerstoffspezies 8-iso Prostaglandin F2a erwiesen sich als potente Aktivatoren des Shedding von CD163. Neben den bekannten physiologischen Funktionen des 8-iso Prostaglandin F2a konnte erstmals eine neue Funktion bei Entzündungen definiert werden. Dieser Effekt wurde spezifisch durch 8-iso Prostaglandin F2a hervorgerufen, da das isomere Prostaglandin F2a unter gleichen Bedingungen keinen Einfluss auf das Shedding von CD163 ausübte. Das Immunsuppressivum Cyclosporin A konnte ebenfalls als Induktor des Shedding von CD163 ermittelt werden. Damit konnte zusätzlich zur bekannten immunmodulatorischen Wirkung des Cyclosporin A eine weitere antiinflammatorische Wirkung über Monocyten/Macrophagen aufgezeigt werden. Durch Untersuchungen der Inhibierung des Shedding von CD163 konnten Gemeinsamkeiten bezüglich der in die sCD163-Generierung involvierten Mediatoren dargestellt werden. Obwohl die untersuchten Verbindungen wahrscheinlich über unterschiedliche Signalwege das Shedding von CD163 induzieren, waren die Anwesenheit von reaktiven Sauerstoffspezies und intrazellulärem Calcium und die Beteiligung einer TIMP-3-sensitiven Metalloproteinase an diesem Prozess essentiell. Bei einem Vergleich zwischen dem Shedding von CD163 und Tumor necrosis factor-a (TNF-a) ergaben sich Gemeinsamkeiten durch die Induktion des Shedding beider Verbindungen durch 8-iso Prostaglandin F2a und in sehr viel geringerem Maße durch Wasserstoffperoxid. Im Gegensatz dazu waren deutliche Unterschiede in dem Ausmaß der induzierten Stimulation des Shedding durch Stickstoffmonoxid, Prostaglandin F2a und Cyclosporin A zu erkennen. Im Hinblick auf die entgegengesetzten Wirkungen von sCD163 als antiinflammatorisch wirkende Verbindung und TNF-a als proinflammatorisches Cytokin, konnte dargestellt werden, dass die Freisetzung durch unterschiedliche Aktivatoren erfolgt. Nach Bestimmung der Konzentrationen von sCD163 und 8-iso PGF2a in bronchoalveolärer Lavage-Flüssigkeit von Patienten mit Cystischer Fibrose konnten keine abschließende Aussagen über die Eignung beider Parameter als biologische Marker für chronische Entzündungen der Lunge bei diesen Patienten getroffen werden. Weiterführend zu der Kenntnis, dass sCD163 die antiinflammatorische Wirkung über eine Interaktion des Proteins mit humanen T-Lymphocyten und nachfolgender Hemmung der Proliferation dieser Zellen ausübt, wurde diese Wechselwirkung genauer untersucht. In quantitativen Bestimmungen des sCD163 in isolierten T-Lymphocyten verschiedener Spender konnte erstmals gezeigt werden, dass sCD163 zu einem Teil konstitutiv in die T-Lymphocyten aufgenommen wird und dass diese Aufnahme durch proinflammatorische Aktivierung der T-Lymphocyten stark gesteigert werden kann. Durch fluoreszenzmikroskopische Aufnahmen unstimulierter T-Lymphocyten konnte die intrazelluläre Lokalisation des sCD163 visualisiert werden. Nach Aktivierung der Zellen mit einem proinflammatorischen Reiz fand innerhalb der Zellen eine Translokalisation des sCD163 aus dem cytoplasmatischen Bereich zur Zellmembran statt. Damit konnte erstmals gezeigt werden, dass abhängig vom Aktivierungsstatus der T-Lymphocyten eine Umverteilung des sCD163 innerhalb der Zellen erfolgt. Eine quantitative Bestimmung des sCD163 und seines Bindungspartners in T-Lymphocyten nichtmuskuläres Myosin Typ IIA gelang mittels eines neu entwickeltem ELISA, der spezifisch sCD163 und Myosin ausschließlich im Komplex erfasst. Damit konnte durch die in dieser Arbeit beschriebenen Untersuchungen ein grundlegender Beitrag zur Charakterisierung der Regulation der Proteinexpression und des Shedding von CD163 in humanen Monocyten sowie der Interaktion des sCD163 mit T-Lymphocyten geleistet werden. In the present thesis, cellular regulation of the monocyte/macrophage specific membrane protein CD163 was investigated and clinical aspects of the soluble form of CD163 (sCD163) were discussed. sCD163 is shed from the cell surface in vivo upon an inflammatory stimulus. So far no mediators had been characterized that are persistently present under inflammatory conditions. In the present investigation of the shedding of CD163, new endogenous activators for the generation of sCD163 were successfully identified. Both reactive oxygen species, as hydrogen peroxide or nitric monoxide, and the product of endogenous oxidative reactions 8-iso prostaglandin F2a turned out to be potent activators of the shedding of CD163. In addition to the known physiological functions of 8-iso prostaglandin F2a a novel function of this compound in inflammation was defined. This effect was specifically generated by 8-iso prostaglandin F2a as prostaglandin F2a did not influence the shedding of CD163 under the same conditions. The immunosuppressive drug cyclosporine A was also established as an inductor of the shedding of CD163. Accordingly, another anti-inflammatory effect via monocytes/macrophages was pointed out in addition to the well known immunomodulatory effects of cyclosporine A. Investigations of the inhibition of shedding of CD163 led to the identification of key mediators involved in the generation of sCD163. Even though the tested compounds may induce shedding via different signal transduction pathways, the presence of reactive oxygen species and intracellular calcium and the involvement of a TIMP-3 sensitive metalloproteinase were essential in this process. The tested activators revealed different abilities for inducing the formation of reactive oxygen species. Comparing shedding of CD163 and tumor necrosis factor-a (TNF-a), similarities in induced shedding by 8-iso prostaglandin F2a and to a lower extend by hydrogen peroxide were seen. In contrast, significant differences were recognized in the extent of shedding induced via stimulation by nitric oxide, prostaglandin F2a, and cyclosporine A. With regard to the opposite effects of sCD163 as an anti-inflammatory compound and TNF-a as a pro-inflammatory cytokine it was demonstrated that shedding occurred via induction by different activators. The determination of concentrations of sCD163 and 8-iso prostaglandin F2a in bronchoalveolar lavage fluid of patients with cystic fibrosis allowed no conclusive statement about the suitability of both parameters as marker for chronic inflammation. In extension to earlier insights in the anti-inflammatory effects of sCD163 via interaction of the protein with human T-lymphocytes and subsequent inhibition of the proliferation of these cells these interactions were analyzed in detail. Quantifications of sCD163 in isolated T-lymphocytes from different donors revealed for the first time that sCD163 is constitutively taken up into T-lymphocytes and that this process can significantly be enhanced by pro-inflammatory activation of T-lymphocytes. The intracellular localization of sCD163 was visualized by fluorescence microscopy of T-lymphocytes. Upon activation of the cells by a pro-inflammatory stimulus a translocalization of sCD163 was observed within the cells from the cytoplasmatic region to the cell membrane. Thus, it was shown for the first time that an activation dependent translocalization of sCD163 occurs within the T-lymphocytes. The quantitative determination of sCD163 and non-muscular myosin type IIA as its intracellular binding partner in T-lymphocytes was successful using a newly developed ELISA that detects specifically sCD163 and myosin as a complex. To conclude, the investigations described in this thesis contributed substantially to the understanding of the regulation of the protein expression and shedding of CD163 in human monocytes and of the interaction of sCD163 with T-lymphocytes.
Nitrotyrosine formation is a hallmark of vascular inflammation, with polymorphonuclear neutrophil–derived (PMN-derived) and monocyte-derived myeloperoxidase (MPO) being shown to catalyze this posttranslational protein modification via oxidation of nitrite (NO2–) to nitrogen dioxide (NO2•). Herein, we show that MPO concentrates in the subendothelial matrix of vascular tissues by a transcytotic mechanism and serves as a catalyst of ECM protein tyrosine nitration. Purified MPO and MPO released by intraluminal degranulation of activated human PMNs avidly bound to aortic endothelial cell glycosaminoglycans in both cell monolayer and isolated vessel models. Cell-bound MPO rapidly transcytosed intact endothelium and colocalized abluminally with the ECM protein fibronectin. In the presence of the substrates hydrogen peroxide (H2O2) and NO2–, cell and vessel wall–associated MPO catalyzed nitration of ECM protein tyrosine residues, with fibronectin identified as a major target protein. Both heparin and the low–molecular weight heparin enoxaparin significantly inhibited MPO binding and protein nitrotyrosine (NO2Tyr) formation in both cultured endothelial cells and rat aortic tissues. MPO–/– mice treated with intraperitoneal zymosan had lower hepatic NO2Tyr/tyrosine ratios than did zymosan-treated wild-type mice. These data indicate that MPO significantly contributes to NO2Tyr formation in vivo. Moreover, transcytosis of MPO, occurring independently of leukocyte emigration, confers specificity to nitration of vascular matrix proteins.
The free radical nitric oxide (NO) has emerged in recent years as a fundamental signaling molecule for the maintenance of homeostasis, as well as a potent cytotoxic effector involved in the pathogenesis of a wide range of human diseases. Although this paradoxical fate has generated confusion, separating the biological actions of NO on the basis of its physiologic chemistry provides a conceptual framework which helps to distinguish between the beneficial and toxic consequences of NO, and to envision potential therapeutic strategies for the future. Under normal conditions, NO produced in low concentration acts as a messenger and cytoprotective (antioxidant) factor, via direct interactions with transition metals and other free radicals. Alternatively, when the circumstances allow the formation of substantial amounts of NO and modify the cellular microenvironment (formation of the superoxide radical), the chemistry of NO will turn into indirect effects consecutive to the formation of dinitrogen trioxide and peroxynitrite. These "reactive nitrogen species" will, in turn, mediate both oxidative and nitrosative stresses, which form the basis of the cytotoxicity generally attributed to NO, relevant to the pathophysiology of inflammation, circulatory shock, and ischemia-reperfusion injury.
The role of endogenous NO on cell survival was investigated in human melanoma cells and melanocytes. Inducible NO synthase (iNOS) was always expressed in a panel of melanoma cell lines from metastatic lesions and in normal adult melanocytes. iNOS was also detected by immunohistochemistry in melanoma cells from metastases. Release of NO by tumor cells and melanocytes was inhibited by a specific iNOS inhibitor, aminoguanidine (AMG). Inhibition of endogenous NO synthesis did not affect cell cycle progression of melanoma cells but led to cell death by apoptosis, as indicated by Annexin V/propidium iodide and terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling assays. By contrast, iNOS inhibition by AMG did not promote apoptosis in normal adult melanocytes. A mitochondrial pathway was involved in melanoma apop tosis, as indicated by altered mitochondrial membrane potential (delta psi(m)) and down-regulation of Bcl-2 protein level after iNOS inhibition. AMG treatment triggered release of caspase-1, enzymatic activation of caspase-3, and degradation of poly(ADP-ribose) polymerase, one of the main caspase-3 substrates. Melanoma cell apoptosis induced by iNOS inhibition was completely blocked by peptide inhibitors of caspase-1 and caspase-3 (Ac-DEVD-CHO and AC-YVAD-CHO) or by an exogenous NO donor, sodium nitroprusside, or by addition of serum. Finally, comparison of control and AMG-treated melanoma cells by pathway-specific gene array analysis indicated that inhibition of NO synthesis led, before induction of apoptosis, to up-regulation of mRNA levels of genes involved in the apoptosis pathway such as Bax, caspase-1, caspase-3, caspase-6, gadd45beta, mdm2, and TRAIL. Taken together, these results indicate that melanoma cell survival is regulated by endogenous NO resulting from iNOS activity.
We summarize here our current knowledge about inducible nitric oxide synthase (NOS) activity in human diseases and disorders. As basic research discovers more and more effects of low or high concentrations of NO toward molecular and cellular targets, successful therapies involving inhibition of NO synthesis or application of NO to treat human diseases are still lacking. This is in part due to the fact that the impact of NO on cell function or death are complex and often even appear to be contradictory. NO may be cytotoxic but may also protect cells from a toxic insult; it is apoptosis-inducing but also exhibits prominent anti-apoptotic activity. NO is an antioxidant but may also compromise the cellular redox state via oxidation of thiols like glutathione. NO may activate specific signal transduction pathways but is also reported to inhibit exactly these, and NO may activate or inhibit gene transcription. The situation may even be more complicated, because NO, depending on its concentration, may react with oxygen or the superoxide anion radical to yield reactive species with a much broader chemical reaction spectrum than NO itself. Thus, the action of NO during inflammatory reactions has to be considered in the context of timing and duration of its synthesis as well as stages and specific events in inflammation.
During the past two decades, nitric oxide (NO) has been recognized as one of the most versatile players in the immune system. It is involved in the pathogenesis and control of infectious diseases, tumors, autoimmune processes and chronic degenerative diseases. Because of its variety of reaction partners (DNA, proteins, low-molecular weight thiols, prosthetic groups, reactive oxygen intermediates), its widespread production (by three different NO synthases (NOS) and the fact that its activity is strongly influenced by its concentration, NO continues to surprise and perplex immunologists. Today, there is no simple, uniform picture of the function of NO in the immune system. Protective and toxic effects of NO are frequently seen in parallel. Its striking inter- and intracellular signaling capacity makes it extremely difficult to predict the effect of NOS inhibitors and NO donors, which still hampers therapeutic applications.
Although endothelial nitric oxide synthase (eNOS) is a constitutively expressed enzyme, its expression is regulated by a number of biophysical, biochemical, and hormonal stimuli, both under physiological conditions and in pathology. This review summarizes the recent findings in this field. Shear stress, growth factors (such as transforming growth factor-beta, fibroblast growth factor, vascular endothelial growth factor, and platelet-derived growth factor), hormones (such as estrogens, insulin, angiotensin II, and endothelin 1), and other compounds (such as lysophosphatidylcholine) upregulate eNOS expression. On the other hand, the cytokine tumor necrosis factor-alpha and bacterial lipopolysaccharide downregulate the expression of this enzyme. The growth status of cells, the actin cytoskeleton, and NO itself are also important regulators of eNOS expression. Both transcriptional and posttranscriptional mechanisms are involved in the expressional regulation of eNOS. Different signaling pathways are involved in the regulation of eNOS promoter activity and eNOS mRNA stability. Changes in eNOS expression and activity under pathophysiological conditions and the pharmacological modulation of eNOS expression are subject of a subsequent brief review (part 2) to be published in the next issue of this journal.
Natural-killer (NK) cells form a first line of defence against pathogens or host cells that are stressed and/or cancerous. NK cells express surface receptors that receive signals from the environment and determine their response to foreign or malignant cells. NK cells respond to these signals by producing effector molecules that can both directly suppress tumour growth and convey important information to the rest of the immune system. We have only recently begun to appreciate the potential for NK cells to be rationally manipulated in the treatment of human cancers.
Nitric oxide synthase (NOS) has recently been shown to be an important pathophysiological regulator in experimental implantation glioma since manipulation of NOS can significantly alter tumoural blood flow and inhibit tumour growth. In this study we investigated the role of iNOS (inducible NOS) in glioma tumourogenisis using the rodent C6 striatal implantation model. We produced genetically engineered C6 clones that do not express iNOS activity even after stimulation with a mixture of lipopolysaccaride (LPS) and tumour necrosis factor (TNF)-alpha. These iNOS knockout cells showed a similar growth rate to control cells in vivo at 5 days. We then performed an in vivo implantation glioma study using either the iNOS knockout clone or two genetically engineered control C6 clones. There was a significant reduction (p < 0.01) of tumour mass with the iNOS knockout clone 28 days after the implantation. Immunocytochemistry indicated infiltrates of CD3 positive T cells and macrophages in the controls and the iNOS knockout group. These studies indicate that iNOS expression by tumour parenchymal cells is a critical factor for tumour growth with this model. The mechanisms that cause failure of tumour growth need clarification prior to considering that specific iNOS inhibitors might be candidates for adjuvant treatment of malignant glioma.
In the preceding companion article, we showed that the neurotoxin methylpyridinium (MPP(+)) increases mitochondrial nitric oxide (NO), causes a post-transcriptional, NO-dependent increase in Bax protein and produces caspase-dependent apoptosis and caspase-independent cell death. In the present study, we show that exogenous NO replicates these findings. The long-term NO generator diethylenetriamine-NO (DETA-NO) reproduced the post-transcriptional Bax protein increase, but did not increase Bcl-2 or Bcl-X(L) proteins. Like MPP(+), DETA-NO caused an early decrease in Bcl-2 mRNA, did not increase Bax protein in rho(0) cells and caused caspase- and cycloheximide-dependent apoptosis and caspase-independent cell death. We developed cell lines with inducible overexpression of Bcl proteins, at levels relevant to those we found in cells exposed to MPP(+) or DETA-NO. Inducible overexpression ( approximately 2-fold) of Bcl-2 or Bcl-X(L) proteins reduced MPP(+) or NO-induced apoptosis but did not affect cell death. Inducible Bax overexpression ( approximately 5-fold) slightly increased cell death. Our results show that exogenous NO mimics actions of MPP(+) on SH-SY5Y neuroblastoma cells and supports the mediation of MPP(+) neurotoxicity by NO generated intracellularly in mitochondria.
Studies of the regulation of iNOS expression have provided many contradictory results. Comparing iNOS expression profile between cell types or organs of the same animal under the same experimental conditions may provide an explanation for these conflicting results. We have examined iNOS mRNA and protein expression in heart and liver of the same group of pigs. We found that there is a sharp difference in iNOS expression between heart and liver. The iNOS mRNA and protein was constitutively expressed in the heart at high level, but was not detectable in the liver of the same control animal. Lipopolysaccharide (LPS, 100 microg/kg, i.v.) caused a marked iNOS induction in the liver, but significantly down-regulated iNOS expression in the heart. This differential iNOS expression appears to be physiologically relevant, since LPS and the iNOS inhibitor, S-methylisothiourea, exerted different effects on hepatic and myocardial blood flow. Our data demonstrate a fundamental difference in iNOS regulation in the heart and liver of swine, and may explain the contradictory data on the regulation of iNOS expression.
Nitric oxide (NO) has an established role in the defense against bacterial infections and exerts multiple modulatory activities on both inflammatory and immune responses. However, the relevance of NO on dendritic cell (DC) functions has been poorly investigated. In this study, we found that addition of the NO donor S-nitrosoglutathione (GSNO) to monocyte-derived DCs matured by lipopolysaccharide (LPS) or soluble CD40 ligand led to a decreased capacity to activate naive allogeneic T cells but a more prominent Th1 polarization, with increased interferon-gamma (IFN-gamma) secretion and reduced interleukin-5 (IL-5) release. The presence of GSNO during maturation of DCs caused a reduced expression of surface CD86, whereas CD80, CD83, and MHC molecule expression was not affected. Moreover, GSNO induced a dose-dependent decrease of IL-10 and enhancement of tumor necrosis factor-alpha (TNF-alpha) release from mature DCs. In parallel, a marked reduced production of IL-12 p40 subunit but no significant perturbation of the bioactive IL-12 p70 production was observed. Finally, GSNO significantly reduced the release of IP-10/CXCL10 and RANTES/CCL5 but not IL-8/CXCL8 by mature DCs. Although GSNO can strengthen the capacity of mature DCs to induce type 1 polarization of T lymphocytes, our data suggest that it elicits distinct anti-inflammatory functions, eventually reducing T lymphocyte proliferation and recruitment.
Low NO concentrations synthesized by constitutively expressed NO synthases act on several signaling pathways activating transcription factors (TF), such as NF-kappaB or AP-1, and thereby influence gene expression. In contrast, during inflammatory reactions the inducible NO synthase produces NO for prolonged periods of time. The resulting nitrosative stress directly affects redox-sensitive TF like NF-kappaB, AP-1, Oct-1, c-Myb, or zinc finger-containing TF, but also additional mechanisms have been identified. Nitrosative stress in some cases induces expression of TF (AP-1, p53), indirectly modulates activity or stability of TF (HIF-1, p53) or their inhibitors (NF-kappaB), or modulates accessibility of promoters via increased DNA methylation or histone deacetylation. Depending on the promoter the result is induced, increased, decreased or even totally inhibited expression of various target genes. In unstimulated cells nitrosative stress increases NF-kappaB- or AP-1-dependent transcription, while in activated cells nitrosative stress rather abolishes NF-kappaB- or AP-1-dependent transcription. Sometimes the oxygen concentration also is of prime importance, since under normoxic conditions nitrosative stress activates HIF-1-dependent transcription, while under hypoxic conditions nitrosative stress leads to inhibition of HIF-1-dependent transcription. This review summarizes what is known about effects of physiological NO levels as well as of nitrosative stress on transcription.
The expression and function of CD69, a member of the natural killer cell gene complex family of signal transducing receptors, was investigated on human monocytes. CD69 was found expressed on all peripheral blood monocytes, as a 28- and 32-kD disulfide-linked dimer. Molecular cross-linking of CD69 receptors induced extracellular Ca2+ influx, as revealed by flow cytometry. CD69 cross-linking resulted also in phospholipase A2 activation, as detected by in vivo arachidonic acid release measurement from intact cells and by direct in vitro measurement of enzymatic activity using radiolabeled phosphatidylcholine vesicles. Prostaglandin E 2 alpha, 6-keto-prostaglandin F 1 alpha, and leukotriene B4 were detected by radioimmunoassay in supernatants from CD69-stimulated monocytes, suggesting the activation of both cyclooxygenase and lipoxygenase pathways after CD69 stimulation. CD69 cross-linking, moreover, was able to induce strong nitric oxide (NO) production from monocytes, as detected by accumulation of NO oxydixed derivatives, and cyclic GMP. It is important to note that NO generation was responsible for CD69-mediated increase in spontaneous cytotoxicity against L929 murine transformed fibroblast cell line and induction of redirected cytotoxicity towards P815 FcRII+ murine mastocytoma cell line. These data indicate that CD69 can act as a potent stimulatory molecule on the surface of human peripheral blood monocytes.
A new automated system for the analysis of nitrate via reduction with a high-pressure cadmium column is described. Samples of urine, saliva, deproteinized plasma, gastric juice, and milk can be analyzed for nitrate, nitrite, or both with a lower limit of detection of 1.0 nmol NO3− or NO2−/ml. The system allows quantitative reduction of nitrate and automatically eliminates interference from other compounds normally present in urine and other biological fluids. Analysis rate is 30 samples per hour, with preparation for most samples limited to simple dilution with distilled water. The application of gas chromatography/mass spectrometry for the analysis of 15NO3− in urine after derivatization to 15NO2-benzene is also described.
Fas ligand (FasL) is a type II integral membrane protein homologous with tumor necrosis factor (TNF). Recent studies indicate that TNF is processed to yield the soluble cytokine by metalloproteinases at the cell surface of activated macrophages and T cells. In the present study, we investigated whether FasL is also released by metalloproteinases. Treatment with hydroxamic acid inhibitors of matrix metalloproteinases specifically led to accumulation of membrane-type FasL (p40) on the surface of human FasL cDNA transfectants and activated human T cells, as estimated by surface immunofluorescence and immunoprecipitation with newly established anti-human FasL monoclonal antibodies. This surface accumulation of mFasL was associated with the decrease of soluble FasL (p27) in the supernatant as estimated by quantitative ELISA and immunoprecipitation with anti-human FasL monoclonal antibodies. These results indicate that human FasL is efficiently released from the cell surface by metalloproteinases like TNF.
Mononuclear phagocytes (monocytes, macrophages, and dendritic cells) play major roles in human immunodeficiency virus (HIV) persistence and disease pathogenesis. Macrophage antigen presentation and effector cell functions are impaired by HIV-1 infection. Abnormalities of macrophage effector cell function in bone marrow, lung, and brain likely result as a direct consequence of cellular activation and HIV replication. To further elucidate the extent of macrophage dysfunction in HIV-1 disease, a critical activation-specific regulatory molecule, nitric oxide (NO.), which may contribute to diverse pathology, was studied. Little, if any, NO. is produced by uninfected human monocytes. In contrast, infection with HIV-1 increases NO. production to modest, but significant levels (2-5 microM). Monocyte activation (with lipopolysaccharide, tumor necrosis factor alpha, or through interactions with astroglial cells) further enhances NO. production in HIV-infected cells, whereas its levels are diminished by interleukin 4. These results suggest a possible role for NO. in HIV-associated pathology where virus-infected macrophages are found. In support of this hypothesis, RNA encoding the inducible NO synthase (iNOS) was detected in postmortem brain tissue from one pediatric AIDS patient with advanced HIV encephalitis. Corresponding iNOS mRNA was not detected in brain tissue from five AIDS patients who died with less significant brain disease. These results demonstrate that HIV-1 can influence the expression of NOS in both cultured human monocytes and brain tissue. This newly described feature of HIV-macrophage interactions suggests previously unappreciated mechanisms of tissue pathology that result from productive viral replication.
When mast cells are activated through their immunoglobulin (Ig)E receptors, release of low molecular weight mediators like histamine is followed by secretion of multiple cytokines, including interleukin (IL)-3, IL-4, IL-5, and granulocyte/macrophage colony-stimulating factor. Here we report that stimulated mast cells also synthesize IL-13 mRNA and protein; secretion of this cytokine may be of particular importance because of its ability to stimulate IgE expression. IL-13 transcripts detected by a semiquantitative reverse transcriptase-mediated polymerase chain reaction assay were induced within 30 min after stimulation of mast cells by dinitrophenyl plus monoclonal IgE anti-dinitrophenyl, and peaked at about 1 h. Within 3 h of IgE stimulation, secreted IL-13 bioactivity, estimated by proliferation of an IL-13-dependent cell line, reached levels equivalent to 1-2 ng/ml of IL-13. When added to human B lymphocytes, the mast cell-derived IL-13 activity (like bone fide IL-13) induced Ig C epsilon transcripts, DNA recombination characteristic of the isotype switch to C epsilon, and the secretion of IgE protein. These results suggest a model of local positive feedback interactions between mast cells and B cells, which could play a role in the pathogenesis of atopy.
Nitric oxide (NO) is produced by numerous different cell types, and it is an important regulator and mediator of many processes including smooth muscle relaxation, neurotransmission, and murine macrophage-mediated cytotoxicity for microbes and tumor cells. Although murine macrophages produce NO readily after activation, human monocytes and tissue macrophages have been reported to produce only low levels of NO in vitro. The purpose of this study was to determine if stimulated human mononuclear phagocytes produce inducible nitric oxide synthase (iNOS) mRNA, protein, and enzymatic activity. By reverse transcriptase-polymerase chain reaction (RT-PCR) analysis, we show that human monocytes can be induced to express iNOS mRNA after treatment with lipopolysaccharide (LPS) and/or interferon-gamma (IFN-gamma). By immunofluorescence and immunoblot analyses, we show monocytes and peritoneal macrophages contain detectable levels of iNOS antigen after stimulations with cytokines in vitro. Control monocytes or those cultured with LPS and/or various cytokines have low levels of NOS functional activity as measured by the ability of cell extracts to convert L-arginine to L-citrulline, and they produce low levels of the NO catabolites nitrite and nitrate. Peritoneal macrophages have significantly enhanced nitrite/nitrate production and NOS activity after treatment with LPS and/or IFN-gamma, whereas monocyte nitrite/nitrate production and NOS activity are not altered by the treatments. Monocytes cultured with various live or heat-killed bacteria, fungi, or human immunodeficiency virus (HIV)-1 do not produce high levels of nitrite/nitrate. Antibodies against transforming growth factor-beta (TGF-beta), a factor known to inhibit iNOS expression and NO production in mouse macrophages, do not enhance NO production in human monocytes or macrophages. Biopterin, an obligate cofactor of iNOS enzymatic activity, is undetectable in freshly isolated or cultured human monocytes and peritoneal macrophages. However, replenishment of intracellular levels of tetrahydrobiopterin by culture with the cell-permeable, nontoxic precursor sepiapterin does not enhance the abilities of the human mononuclear phagocytes to produce NO in vitro. Mixing experiments show no evidence of a functional NOS inhibitor in human mononuclear phagocytes. Thus, we demonstrate that human mononuclear phagocytes can produce iNOS mRNA and protein, and (despite this) their abilities to generate NO are very low.
The putative factors that couple the signal transduction from surface receptors to the activation of cytokine synthesis in natural killer (NK) cells have not been elucidated. We report here that the nuclear factor of activated T cells (NFATp), a cyclosporin A (CsA)-sensitive factor that regulates the transcription of several cytokines, mediates CD16-induced activation of cytokine genes in human NK cells. CD16 (Fc gamma RIIIA)-induced expression of cytokine mRNA in NK cells occurs via a CsA-sensitive and Ca(2+)-dependent mechanism. Stimulation of NK cells with CD16 ligands induces NFAT-like DNA binding activity in the nuclear extracts from these cells, as detected in electrophoretic mobility shift assays. This occurs with fast kinetics after stimulation, via a CsA-sensitive and Ca(2+)-dependent mechanism that does not require de novo protein synthesis. NK cell NFAT is present in the cytosol of nonstimulated cells, migrates to the nucleus upon stimulation, and can associate with AP-1. Two distinct molecules, NFATp and NFATc, have been reported to mediate NFAT activity. The results of supershift assays using NFATp- and NFATc- specific antibodies indicate that NK cell activation early after CD16 ligand binding involves primarily, if not exclusively, NFATp, and Western blot analysis shows that this has the same electrophoretic mobility (approximately 120 kD) as that of T lymphocytes. NK cells do not express NFATc constitutively, but NFATc mRNA accumulation is induced in these cells within 2 h of stimulation with CD16 ligands. However, supershift assays using the available mAb recognizing the T cell NFATc revealed no detectable NFATc protein in nuclear and cytoplasmic extracts from CD16- or phorbol ester-stimulated cells at any time tested, up to 4 h. These results provide the first direct evidence that both CsA-sensitive transcription factors, NFATp and NFATc, are expressed in human NK cells, and that their activation and/or expression can be regulated in primary cells by a single stimulus, that, in the case of CD16 in NK cells, results in early activation of NFATp and subsequently induced expression of NFATc mRNA.
The expression and function of CD69, a member of the natural killer cell gene complex family of signal transducing receptors, was investigated on human monocytes. CD69 was found expressed on all peripheral blood monocytes, as a 28- and 32-kD disulfide-linked dimer. Molecular cross-linking of CD69 receptors induced extracellular Ca2+ influx, as revealed by flow cytometry. CD69 cross-linking resulted also in phospholipase A2 activation, as detected by in vivo arachidonic acid release measurement from intact cells and by direct in vitro measurement of enzymatic activity using radiolabeled phosphatidylcholine vesicles. Prostaglandin E 2 alpha, 6-keto-prostaglandin F 1 alpha, and leukotriene B4 were detected by radioimmunoassay in supernatants from CD69-stimulated monocytes, suggesting the activation of both cyclooxygenase and lipoxygenase pathways after CD69 stimulation. CD69 cross-linking, moreover, was able to induce strong nitric oxide (NO) production from monocytes, as detected by accumulation of NO oxydixed derivatives, and cyclic GMP. It is important to note that NO generation was responsible for CD69-mediated increase in spontaneous cytotoxicity against L929 murine transformed fibroblast cell line and induction of redirected cytotoxicity towards P815 FcRII+ murine mastocytoma cell line. These data indicate that CD69 can act as a potent stimulatory molecule on the surface of human peripheral blood monocytes.
The tumor necrosis factor-alpha (TNF alpha) gene is an immediate early gene in activated T cells, in that it is rapidly induced without a requirement for protein synthesis. Maximal induction of TNF alpha mRNA can be induced by treatment of T cells with calcium ionophores alone, via a calcineurin-dependent process that is blocked by cyclosporin A. We have previously identified a promoter element, kappa 3, that is required for calcium-stimulated, cyclosporin A-sensitive induction of the TNF alpha gene in activated T cells. Here, we demonstrate that the kappa 3 binding factor contains NFATp, a cyclosporin-sensitive DNA-binding protein required for interleukin-2 gene transcription. NFATp binds to two sites within the kappa 3 element, and occupancy of both sites is required for TNF alpha gene induction. Thus, although the kappa 3 element has little sequence similarity to other NFATp-binding sites, it appears to function as a cyclosporin-sensitive promoter element in T cells by virtue of its ability to bind NFATp. The involvement of NFATp in transcriptional activation of both the interleukin-2 and TNF alpha genes suggests that this factor plays an important role in the coordinate induction of multiple cytokine genes, starting at the earliest stages of T cell activation.
Activated human natural killer (NK) cells undergo rapid apoptotic cell death after ligand binding to the Fc receptor (CD16). We examined whether human NK cells die after engagement in cytolytic functions. Peripheral blood NK cells, with and without prior activation in vitro with interleukin-2 (IL-2), were tested for the occurrence of cell death after incubation with K562, the prototype NK-sensitive target cell. A proportion (15.2%) of NK cells that were stimulated for 3 days with IL-2 and then incubated for 4 hours with K562 cells showed rapid cell death, but NK cells not stimulated with IL-2 did not. This cell death was found to involve nuclear condensation and fragmentation and DNA cleavage, all of which are characteristic of apoptosis. These data indicate that a proportion of activated human NK cells undergo apoptosis as they engage in target cell lysis. Target-induced NK cell death may represent an important mechanism for regulation of inflammatory processes involving NK cells.
Although it has been recognized for sometime that target cells destroyed by natural killer (NK) cells die largely by apoptosis, the underlying mechanisms are not fully understood. The aim of the present study was to examine the role of nitric oxide (NO) in mediating murine NK-cell-induced killing of YAC-1 lymphoma cells. NK calls induced extensive release of 125I-DNA and 51Cr from YAC-1 cells. The target killing ability of NK cells was associated with an increased production of NO as measured by concentrations of nitrite in the culture medium. That YAC-1 killing resulted, in part, from the production of NO was confirmed by the significant protection of cell lysis in L-arginine-depleted medium and by approximately 30 % attenuation of cell lysis and DNA fragmentation by an inhibitor of NO synthase, NG-nitro-L-arginine methyl ester (L-NAME) in a culture medium containing 1 mmol/L L-arginine. Fluorescence microscopic examination of YAC-1 cells showed the presence of changes in nuclear morphology characteristic for apoptosis. The percentage of apoptotic cells was markedly decreased by L-NAME. Further evidence for apoptosis is provided by the specific pattern of internucleosomal DNA fragmentation both in the absence and presence of L-NAME. During target-cell killing, an increased oxidation of intracellularly trapped dichlorofluorescein was observed in cells labeled with an antimouse NK-cell monoclonal antibody, as measured by flow cytometry. These increases were effectively prevented by L-NAME, but not W-13, an inhibitor of calmodulin. The ability of NO to induce cell lysis and DNA fragmentation in YAC-1 cells was further demonstrated by exposing tumor cells to chemically generated NO. Taken together, these observations suggest a role for NO as one of the mediators of NK-cell-mediated DNA fragmentation and cell lysis.
We previously reported that natural killer (NK)-sensitive target cells, K562, kill interleukin-2-stimulated (lymphokine-activated killer [LAK]) but not unstimulated NK cells. We have now investigated the molecular basis of this phenomenon. Soluble monoclonal antibody (MoAb) to CD18 inhibited 75% of K562-induced DNA fragmentation and membrane disruption, whereas blocking MoAb to Fas partially inhibited only the DNA fragmentation. MoAbs to CD2, CD11a, CD11b, B7, or CD16 had limited or no effect on K562-induced death of LAK cells. Receptor ligation with either immobilized MoAb to CD18 or Fas induced membrane disruption and DNA degradation in LAK cells independently of K562, and MoAb to CD18, CD11a, or CD11b enhanced DNA fragmentation induced by anti-Fas. Fas-L-transfected Raji cells also killed LAK cells, but only if Fas-L expression was amplified. K562 cells rapidly triggered protein phosphorylation in LAK cells, and the tyrosine kinase inhibitor, Herbimycin A, inhibited DNA fragmentation and membrane disruption. Protease inhibitors strongly suppressed K562-mediated DNA fragmentation of LAK cells, but not membrane disruption. In conclusion, (1) K562-induced death of LAK cells involves primarily CD18, although other molecules, such as Fas, may also be involved; (2) K562-mediated apoptosis of LAK cells requires tyrosine phosphorylation and protease activity; (3) engagement of Fas by immobilized MoAb or Fas-L on target cells can also kill LAK cells; and (4) Fas-immobilized MoAb synergizes with coimmobilized MoAb to CD11a, CD11b, or CD18 for LAK cell killing. Activation-induced death of NK cells may represent a mechanism for NK cell regulation.
It has been suggested that the NF-κB transcription factor family may mediate expression of the gene encoding the cytokine-inducible
form of nitric oxide synthase (iNOS). To establish if nitric oxide (NO) could in turn affect activity of NF-κB, the ability
of NO-donor compounds to influence NF-κB DNA binding activity in vitro was investigated. NO-donor compounds sodium nitroprusside (SNP) and S-nitroso-N-acetylpenicillamine (SNAP) both inhibited
the DNA binding activity of recombinant NF-κB p50 and p65 homodimers and of p50–p65 heterodimers. Inhibition of NF-κB p50
DNA binding by NO-donor compounds involved modification of the conserved redox-sensitive C62 residue, as a C62S p50 mutant
was significantly more resistant to SNP-mediated inactivation. Non-reducing SDS-polyacrylamide gel electrophoresis demonstrated
that SNP could inhibit p50 DNA binding by mechanisms other than the formation of intersubunit disulphide bonds involving p50
residue C62. Electrospray ionization mass spectrometry of a synthetic NF-κB p50 peptide containing the C62 residue suggested
that NO gas can modify C62 by S-nitrosylation. This study indicates that NO-donors can directly inhibit the DNA binding activity
of NF-κB family proteins, suggesting that cellular NO provides another control mechanism for modulating the expression of
NF-κB-responsive genes.
Calcineurin is the only protein phosphatase known to be under the control of Ca2+ and calmodulin. It is targeted by immunosuppressive drugs and has a critical role in T-cell activation. It is specifically inhibited by immunosuppressant immunophilin complexes, which enabled its function in regulating a wide range of cellular responses to Ca2+-mobilizing signals to be identified. Calcineurin in situ is 10-20 times more active than in the purified form and is subject to a time- and Ca2+/calmodulin-dependent reversible inactivation that is facilitated by small, heat-stable molecules. Here we identify a factor that prevents the inactivation of calcineurin in vitro and in vivo as the enzyme superoxide dismutase, which indicates that inactivation may be the result of oxidative damage to the Fe-Zn active centre of calcineurin. The redox state of iron provides a mechanism to regulate calcineurin activity by desensitizing the enzyme and coupling Ca2+-dependent protein dephosphorylation to the redox state of the cell. The protection of calcineurin against inactivation by superoxide dismutase constitutes a new physiological role for this enzyme which enables the Ca2+-dependent regulation of cellular processes to be modulated by the redox potential.
Nitric oxide (NO) and tumor necrosis factor-α (TNFα) play important roles in the pathogenesis of liver disease during acute inflammation. The present study was designed to elucidate the effect of NO pre-exposure on TNFα-induced hepatotoxicity. Pretreatment of primary cultures of rat hepatocytes with the NO donor S-nitroso-N-acetylpenicillamine (SNAP) induced the expression of heat shock protein 70 (HSP70) mRNA and protein, which was associated with thermotolerance and cytoprotection from TNFα+actinomycin D-induced hepatotoxicity and apoptosis. SNAP transiently changed the intracellular redox state by inducing glutathione (GSH) oxidation associated with the formation of S-nitrosoglutathione (GSNO). HSP70 mRNA was also induced by the GSH-oxidizing agent diamide and the GSH-conjugating agent N-ethylmaleimide, suggesting that NO induces HSP70 expression through GSH oxidation.
The protective effect of SNAP pretreatment on TNFα-induced apoptosis correlated with the level of HSP70 expression. SNAP pretreatment inhibited reactive oxygen intermediate generation and lipid peroxidation effects that were reversed by blocking HSP70 expression using an antisense oligonucleotide to HSP70. Finally, endogenous NO formation, induced in hepatocytes stimulated with interferon-γ and interleukin-1β, led to the formation of GSNO and GSSG, induced HSP70, and attenuated TNFα-mediated cytotoxicity. These findings demonstrated that NO can induce resistance to TNFα-induced hepatotoxicity, possibly through the stimulation of HSP70 expression.
Interferon-gamma (IFN-gamma) is critical for an effective innate immune response against infection. A combination of interleukins (ILs) derived from activated T cells (IL-2) and monocytes (IL-12), or monocytes alone (IL-15 and IL-12), induces optimal production of IFN-gamma from natural killer (NK) cells. The mechanism by which human NK cells downregulate their production of IFN-gamma is unknown. Here we show that the same cytokines that induce human NK cell IFN-gamma production subsequently induce apoptosis of the NK cells. Fas, bcl-2, or bax do not appear to be involved in this process. The mechanism of cytokine-induced apoptosis of human NK cells appears to involve NK cell production of tumor necrosis factor-alpha (TNF-alpha). Neutralization of TNF-alpha or inhibition of TNF-alpha binding to the p80 TNF-alpha receptor partially inhibited apoptosis. Transforming growth factor-beta, which inhibits cytokine-induced NK cell production of IFN-gamma and TNF-alpha, also decreased cytokine-induced NK cell apoptosis. Costimulation of a CD3-CD56+ NK leukemia cell line with IL-2 and IL-12 or IL-15 and IL-12 induced apoptosis in vitro, which increased when combined with a chemotherapeutic agent. In summary, costimulation of human NK cells via the IL-2 receptor and the IL-12 receptor induces significant IFN-gamma production, followed by NK cell apoptosis and a decline in IFN-gamma production. Hence, cytokines that activate this innate immune response may also serve to limit it via apoptosis. This novel observation may have implications for the regulation of the innate immune response during infection, the toxicity of combination cytokine therapy, and the treatment of NK cell leukemia.
The understanding of the induction and regulation of inducible nitric-oxide synthase (iNOS) in human cells may be important in developing therapeutic interventions for inflammatory diseases. In the present study, we not only demonstrated that human fetal mixed glial cultures, as well as enriched microglial cultures, synthesize iNOS and nitric oxide (NO) in response to cytokine stimulation, but also assessed the kinetics of iNOS and NO synthesis in human fetal mixed glial cultures. The iNOS mRNA was expressed within 2 h after stimulation and decreased to base line by 2 days. Significant levels of iNOS protein appeared within 24 h after stimulation and remained elevated during the culture period. A dramatic increase in NO production and NO-mediated events, such as the induction of cyclic guanosine monophosphate (cGMP), NADPH diaphorase activity, and nitrotyrosine occurred 3 days after stimulation, a delay of 48 h from the time of the first expression of iNOS enzyme. This delay of NO production was altered by the addition of tetrahydrobiopterin, but not by the addition of L-arginine, heme, flavin adenine dinucleotide (FAD), flavin mononucleotide (FMN), or NADPH. These findings suggest that a post-translational regulatory event might be involved in iNOS-mediated NO production in human glia.
We have investigated the interleukin-12 (IL-12) and tumor necrosis factor- (TNF)-induced regulation of human natural killer (NK) cell function and their relationship with nitric oxide (NO) generation. We demonstrate that both cytokines were efficient to trigger the transcription of the inducible nitric oxide synthase (iNOS) mRNA, as detected by reverse transcriptase-polymerase chain reaction (RT-PCR). Western blot analysis and intracytoplasmic fluorescence showed that iNOS protein was also induced by both cytokines. However, our data indicate that NO does not play a significant role in the effector phase of the cytotoxic activity mediated by NK-stimulated cells, inasmuch as the lytic activity was not affected in the presence of specific NO synthase inhibitors. When aminoguanidine (AMG), an inhibitor of iNOS, was added during the afferent phase of NK stimulation with IL-12 and TNF, a subsequent increase in the lytic potential of the effector cells towards the NK-sensitive target cells (K562) and lymphokine-activated killer (LAK) target cells (Daudi) was observed. Conversely, the addition of chemical NO donors during the afferent step resulted in a dose-dependent inhibition of the NK and LAK cytotoxicity. Our data suggest that the enhancement of NK-cell cytotoxic activity resulting from iNOS inhibition may be correlated, at least in part, to an increase in interferon-γ production and granzyme B expression.
© 1998 by The American Society of Hematology.
Cells maintain an intracellular environment that is reducing in the face of a highly oxidizing extracellular environment. Regulated alterations in the intracellular redox state (redox signaling) can modulate events such as DNA synthesis, enzyme activation, selective gene expression, and regulation of the cell cycle. The primary consequence of intracellular redox signaling is a change in the oxidation state of cysteine residues of key proteins. This form of posttranslational modification of protein is difficult to follow because it lacks a convenient marker and is readily reversed when the cell contents are exposed to extracellular oxidizing conditions. For this reason, knowledge of the role that redox signaling may play in cell function has lagged behind that of protein modification produced. This chapter discusses the components of the cellular machinery used for the redox regulation of protein activity and its consequences for cell growth and death. Discussed here are the cellular redox systems—glutathione/glutathione reductase, thioredoxin reductase/thioredoxin, protein disulfide isomerase, glutaredoxin, ref-I, and metallothionein. NADPH reduces oxidized glutathione (GSSG) and thioredoxin [Trx (ox)] through glutathione reductase and thioredoxin reductase, respectively, giving reduced glutathione (GSH) and reduced thioredoxin Trx (red). GSH reduces oxidized glutaredoxin [Grx (ox)], and Trx reduces oxidized Ref-1.Trx and Grx provide reducing equivalents to ribonucleotide reductase (RR) for deoxyribonucleotide synthesis. The chapter details the redox targets—ribonucleotide reductase, receptor proteins, and the transcription factors: OxyR, NF-KB/Rel, AP-1—and protein folding and degradation. Mentioned are the cellular responses to redox changes—cell proliferation and activities of thioredoxin related to cell proliferation, oxidant signaling and apoptosis, oxidative stress, and hypoxia. Compelling evidence from in vitro studies shows that alterations in the redox state of proteins involving key cysteine residues lead to conformational changes. Recent studies have identified several redox systems in cells that appear to respond to external stimuli.
When mast cells are activated through their immunoglobulin (Ig)E receptors, release of low molecular weight mediators like histamine is followed by secretion of multiple cytokines, including interleukin (IL)-3, IL-4, IL-5, and granulocyte/macrophage colony-stimulating factor. Here we report that stimulated mast cells also synthesize IL-13 mRNA and protein; secretion of this cytokine may be of particular importance because of its ability to stimulate IgE expression. IL-13 transcripts detected by a semiquantitative reverse transcriptase-mediated polymerase chain reaction assay were induced within 30 min after stimulation of mast cells by dinitrophenyl plus monoclonal IgE anti-dinitrophenyl, and peaked at about 1 h. Within 3 h of IgE stimulation, secreted IL-13 bioactivity, estimated by proliferation of an IL-13-dependent cell line, reached levels equivalent to 1-2 ng/ml of IL-13. When added to human B lymphocytes, the mast cell-derived IL-13 activity (like bone fide IL-13) induced Ig C epsilon transcripts, DNA recombination characteristic of the isotype switch to C epsilon, and the secretion of IgE protein. These results suggest a model of local positive feedback interactions between mast cells and B cells, which could play a role in the pathogenesis of atopy.
The putative factors that couple the signal transduction from surface receptors to the activation of cytokine synthesis in natural killer (NK) cells have not been elucidated. We report here that the nuclear factor of activated T cells (NFATp), a cyclosporin A (CsA)-sensitive factor that regulates the transcription of several cytokines, mediates CD16-induced activation of cytokine genes in human NK cells. CD16 (Fc gamma RIIIA)-induced expression of cytokine mRNA in NK cells occurs via a CsA-sensitive and Ca(2+)-dependent mechanism. Stimulation of NK cells with CD16 ligands induces NFAT-like DNA binding activity in the nuclear extracts from these cells, as detected in electrophoretic mobility shift assays. This occurs with fast kinetics after stimulation, via a CsA-sensitive and Ca(2+)-dependent mechanism that does not require de novo protein synthesis. NK cell NFAT is present in the cytosol of nonstimulated cells, migrates to the nucleus upon stimulation, and can associate with AP-1. Two distinct molecules, NFATp and NFATc, have been reported to mediate NFAT activity. The results of supershift assays using NFATp- and NFATc- specific antibodies indicate that NK cell activation early after CD16 ligand binding involves primarily, if not exclusively, NFATp, and Western blot analysis shows that this has the same electrophoretic mobility (approximately 120 kD) as that of T lymphocytes. NK cells do not express NFATc constitutively, but NFATc mRNA accumulation is induced in these cells within 2 h of stimulation with CD16 ligands. However, supershift assays using the available mAb recognizing the T cell NFATc revealed no detectable NFATc protein in nuclear and cytoplasmic extracts from CD16- or phorbol ester-stimulated cells at any time tested, up to 4 h. These results provide the first direct evidence that both CsA-sensitive transcription factors, NFATp and NFATc, are expressed in human NK cells, and that their activation and/or expression can be regulated in primary cells by a single stimulus, that, in the case of CD16 in NK cells, results in early activation of NFATp and subsequently induced expression of NFATc mRNA.
Harald H. H. W. Schmidt and Ulrich Walter Medizinische Universitatsklinik Wiirzburg Klinische Biochemie und Pathobiochemie Versbacher Strasse 5 D-97078 Wiirzburg Federal Republic of Germany Nitroglycerine has been used for over a century to treat coronary heart disease, and it has long been suggested that humans synthesize oxides of nitrogen (Mitchell et al., 1916). These observations have recently been brought into focus by the demonstration that endogenous nitric oxide (NO) regulates mammalian blood vessels and other systems (Moncada and Higgs, 1991) such that virtually every mammalian cell is under the influence of NO. The three “classics” of NO-mediated functions-endothelium- dependent relaxation (Furchgott and Zawadzki, 1980) neurotransmission (Garthwaite et al., 1988; Gillespie et al., 1989) and cell-mediated immune response (Nathan and Hibbs, 1991)-have suggested principles for the mode of action of NO and for its functions. General Principles Networks In many systems, NO derives from two or more different cellular sources, forming networks of paracrine communi- cation (Figure 1). For example, we now know that vascular and bronchial NO originates not only from endothelial cells, where it iscalledendotheliumderived relaxing factor (EDRF), but also from adventitial nerves and epithelial cells (Schmidt et al., 1992a; Wilcox et al., 1992), where it mediates endothelium-independent smooth muscle relax- ation. Neurons use NO to regulate transmitter release of adjacent neurons (Meffert et al., 1994) and also to match cerebral blood flow with neuronal activity; similarly, bron- chial epithelial and endothelial cells use NO to match venti- lation and perfusion (Gaston et al., 1994). Macula densa renal tubular epithelial cells release NO to dilate the neigh- boring afferent artery and increase glomerular filtration (Wilcox et al., 1992). NO Toxicity NO is a double-edged sword (Table l), beneficial as a messenger or modulator and for immunologic self-defense, but potentially toxic. In several different scenarios (Figure 2) with factors such as oxidative stress, generation of reactive oxygen intermediates (ROls), and deficient anti- oxidant systems, NO switches from friend to foe. A pre- dominant mechanism by which this occurs is through the diffusion-limited reaction of NO with superoxide to gener- ate peroxynitrite (Beckman et al., 1990) which may modu- late signaling functions of NO (Gaston et al., 1994; Moro et al., 1994) and is directly cytotoxic (Beckman, 1991). e.g., by causing extensive protein tyrosine nitration (Beck- man et al., 1994).
To detect mRNA expression of nitric oxide synthase (NOS) isoforms in human monocytes/macrophages reverse transcription polymerase chain reaction (RT-PCR) was used. mRNA was isolated from stimulated or unstimulated monocytes/macrophages and RT-PCR was performed using oligonucleotide primers derived from mRNA sequences of either human endothelial constitutive (c) or human hepatocyte inducible (i) NOS. RT-PCR of mRNA isolated from resting monocytes and macrophages resulted in the amplification of a cNOS specific mRNA fragment. When the cells were stimulated with lipopolysaccharide (LPS)/interferon-γ (IFN-γ) prior to mRNA extraction, RT-PCR yielded an iNOS-specific amplification product. Whereas the activation of both cell types was accompanied by expression of iNOS mRNA, the cNOS signal seemed to be diminished upon immunostimulation. Not only in purified human monocytes but also in the human monocytoid cell lines MonoMac 6, THP-1, and U937 cNOS mRNA was detected. The data clearly demonstrate the presence of iNOS and cNOS mRNA in human monocytes/macrophages and provide the necessary tools to investigate the regulation of NO synthesis in these cell populations.
Calcineurin (CaN) is a calcium- and calmodulin-dependent protein serine/threonine phosphate which is critical for several important cellular processes, including T-cell activation. CaN is the target of the immunosuppressive drugs cyclosporin A and FK506, which inhibit CaN after forming complexes with cytoplasmic binding proteins (cyclophilin and FKBP12, respectively). We report here the crystal structures of full-length human CaN at 2.1 A resolution and of the complex of human CaN with FKBP12-FK506 at 3.5 A resolution. In the native CaN structure, an auto-inhibitory element binds at the Zn/Fe-containing active site. The metal-site geometry and active-site water structure suggest a catalytic mechanism involving nucleophilic attack on the substrate phosphate by a metal-activated water molecule. In the FKBP12-FK506-CaN complex, the auto-inhibitory element is displaced from the active site. The site of binding of FKBP12-FK506 appears to be shared by other non-competitive inhibitors of calcineurin, including a natural anchoring protein.
Evolution has resorted to nitric oxide (NO), a tiny, reactive radical gas, to mediate both servoregulatory and cytotoxic functions. This article reviews how different forms of nitric oxide synthase help confer specificity and diversity on the effects of this remarkable signaling molecule.
Most current methods for measuring cell death are based on plasma membrane disintegration and the consequent release of cytoplasm. The relevant cells are usually loaded with a label (usually 51Cr or 125I), the release of which is measured. I describe here a method, based on the recent evidence that dying cells often degrade their DNA into small fragments, which measures the DNA retained by living cells rather than the cellular components lost by dying cells. The assay is set up essentially like the current cell lysis assays and harvested like a cell proliferation assay. It is faster, more sensitive, easier to set up, less expensive and safer than the current standard 51Cr release assay.
Natural cell mediated cytotoxicity has been expressed as percent cytotoxicity, as the slope of the titration curve obtained by testing different effector: target cell ratios, and as lytic units. Objections can be raised to each method as used. The present report involves the study of cytotoxicity by subpopulations of lymphocytes obtained by Percoll density gradient centrifugation. The subpopulations vary greatly in cytotoxic activity, making accurate comparisons by traditional means difficult. A method was therefore developed for making objective comparisons between activities of subpopulations of lymphocytes. Cytotoxicity titration curves, which were sigmoidal on linear-linear plots, were found to best fit the sigmoidal curves described by the Von Krogh equation. A best fitting scale family of curves having the identical maximum cytotoxicity and shape parameter was fitted simultaneously to cytotoxicity measurements obtained by titrating all subpopulations of effector cells obtained from each patient. Values expressing relative cytotoxicities were obtained from the ratios of the scale parameters of the different curves or by obtaining lytic units from the fitted curves. In addition to the enriched natural cytotoxic activity found among the lighter cells obtained by Percoll density gradient centrifugation, activity was also increased among cells sedimenting at the very bottom of the gradient. This was found in subpopulations of cells obtained from 16/21 gradients in tests against K562 and in subpopulations obtained from both of 2 gradients in tests against Daudi cells. These findings are consistent with the existence of at least 2 subpopulations of lymphocytes which can mediate natural cytotoxicity, and which are separable by density.
Several lines of evidence suggest that nitric oxide (NO), generated through nitric oxide synthase (NOS) by cleavage of terminal guanidino nitrogen from L-arginine, mediates tumor cell killing by mononuclear phagocytes. Natural killer (NK) cells are cytotoxic effector cells that lyse a variety of tumor and virus-infected cells in a MHC-unrestricted manner. NK cells cultured with interleukin 2 proliferate and acquire the ability to lyse a wide range of targets, including NK-resistant tumor cells (LAK activity). The present study was designed to investigate whether a NOS pathway exists in fresh or IL-2-activated NK cells and to assess the importance of NO synthesis in their activation and cytotoxic functions. NKR-P1 triggering, which is known to induce NK cell activation and mediate reverse ADCC, was able to induce arginine metabolism with consequent increase of nitrite and citrulline levels. Moreover, stimulated NO synthesis leads to guanylate cyclase activity with consequent cGMP generation. We also report that cytotoxic activities of fresh or IL-2-activated NK cells appear to be dependent on arginine levels in medium. Tumoricidal activity of both these effector cells, assessed against YAC-1 and P815 target cells, respectively, was indeed significantly reduced when cytotoxic assays were performed in arginine-free medium or in the presence of the L-arginine analog L-N-monomethyl-arginine, which inhibits nitroxide formation from L-arginine. Normal levels of cytotoxic activities could be restored by addition of exogenous L-arginine. NO generation by NK and LAK cells, determined as nitrite, citrulline, and cGMP synthesis, correlated well with their cytotoxic activities. Moreover, NOS activity gradually increased during the LAK generation and correlated well with the increasing capability of IL-2-activated NK cells to lyse NK-resistant targets, such as P815.
Michael A. Marletta Interdepartmental Program in Medicinal Chemistry College of Pharmacy and Department of Biological Chemistry School of Medicine The University of Michigan Ann Arbor, Michigan 46109-l 065 The rapid development of our understanding of the biologi- cal actions of nitric oxide (NO) has, to a large degree, been paralleled by our understanding of the enzyme responsi- ble for the synthesis of NO, nitric oxide synthase (NOS). The relatively fast pace of advance in NOS enzymology is primarily due to the fact that structure/function questions have crossed over several well-established enzymatic problems. As will be outlined below, NOS is a complex enzyme involving several tightly bound redox cofactors that are apparently organized into discrete domains that can be associated with a particular activity. First, the en- zyme has significant homology to NADPH cytochrome P-450 reductase and has been shown to contain a cyto- chrome P-450-type heme and to carry out P-450 chemistry in the formation of NO. What then is the relationship of NOS to the large class of cytochrome P-450 isoenzymes? Second, constitutive NOS isoforms require Ca*+ and cal- modulin (CaM) while inducible NOS (INOS) shows no re- quirement, although these isoforms apparently have CaM as a tightly bound subunit. What is the nature of this im- portant difference in the recognition and binding of CaM? NOS also has a tightly associated reduced pterin that is very important for an enzyme activity whose function is still not known. Third, the product of the reaction, NO, typically is a strong heme ligand. How is it that the enzyme escapes self-inactivation during turnover? These ques- tions shall be the main the focus of this review. General Characteristics of the Reaction The reaction catalyzed by NOS is illustrated in Figure 1. As shown, the reaction requires molecular oxygen (02) and reducing equivalents in the form of NADPH (Marletta, 1993). Except for some minor structural modifications, all NOS isoforms specifically utilize L-arginine as the sub- strate. The products of the reaction are NO and citrulline (presumed to be the L-isomer). It is assumed, given the monooxygenase-like activity of NOS and the heavy iso- tope labeling studies, that H20 is the ultimate fate of the other oxygen atom. The initial NOS cDNA isolated was that of the neuronal isoform from rat cerebellum, where sequence analysis showed a significant homology of NADPH cytochrome P-450 reductase to the C-terminal sequence of this NOS isoform (Bredt et al., 1991). All clones isolated subsequently have demonstrated the same homology. Given that the normal function of this reductase is to supply reducing equivalents to cytochrome P-450, it has been assumed that this domain in NOS serves the same function. The findings that NOS also con-
Nitric oxide (NO) produced by murine macrophages is important in murine resistance to ectromelia virus, herpes simplex virus, and vaccinia virus infection. In contrast, NO production by human mononuclear cells has been difficult to demonstrate, and a role for NO in human responses to infection is uncertain. We report constitutive, low level, macrophage-type NO synthase (iNOS) expression in Epstein-Barr virus (EBV)-transformed human B lymphocytes and Burkitt's lymphoma cell lines. Immune NOS activity is involved in maintaining EBV latency through down-regulation of the expression of the immediate-early EBV transactivator Zta. NO also inhibits apoptosis in B lymphocyte cell lines. The effects of NO are largely independent of cGMP and influential on signaling pathways regulated by (sulfhydryl) redox status. These results suggest that NO plays a physiological role in human B cell biology by inhibiting programmed cell death and maintaining viral latency.
Cell-mediated cytotoxicity (CMC) has traditionally been thought to involve the release of granule components, including perforin and granzymes, from the effector cell (EC) onto the target cell (TC) membrane. Recently, a granule-independent cytolytic mechanism involving the interaction of Fas antigen (CD95) with Fas ligand has been described. We have generated antisense perforin (YT-xP1) and granzyme B (YT-xGrB) transfectants of the human NK-like cell line YT-INDY. These transfectants have greatly reduced cytolytic ability when compared to the vector-transfected control cell line (YT-neo). In this study, however, we demonstrate that the antisense transfectants retain the ability to lyse Fas+ TC. Fas-mediated lysis is Ca(2+)-independent and is inhibited by a monoclonal anti-Fas blocking Ab, M3. By RT-PCR, we detect message for FasL in unstimulated YT-xP1 and YT-xGrB transfectants, as well as in unstimulated YT-neo. By flow cytometry, we show that YT-neo, YT-xGrB, and YT-xP1 constitutively express surface FasL. These data indicate that in a human NK-like cell line, similar to the murine system, the granule and Fas pathways of cytotoxicity function independently of one another. At least with the TC tested, our data also indicate that the granule and Fas pathways together account for nearly 100% of the cytolytic ability of YT-INDY.
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Many agents which induce apoptosis are either oxidants or stimulators of cellular oxidative metabolism. Conversely, many inhibitors of apoptosis have antioxidant activities or enhance cellular antioxidant defenses. Mammalian cells exist in a state of oxidative siege in which survival requires an appropriate balance of oxidants and antioxidants. Thomas Buttke and Paul Sandstrom suggest that eukaryotic cells may benefit from this perilous existence by invoking oxidative stress as a common mediator of apoptosis.
Thiol-related compounds, such as L-cystine, 2-ME or reduced glutathione (GSH), are important in many lymphoid cell activation pathways. We investigated their role in IL-2-generated lymphokine-activated killer (LAK) activity in human NK (CD16+ and/or CD56+) cells. Depletion of GSH and L-cystine, but not L-leucine or glycine, from medium used during culture of NK cells with IL-2 inhibited LAK and proliferative activities, whereas IL-2-independent lytic function of NK cells remained intact. Addition of L-cysteine, 2-ME or GSH, but not methylated analogs of these compounds (which cannot function as proton donors) to L-cystine/GSH-depleted medium restored proliferative response of NK cells and LAK generation. In the presence of L-buthionine-(S,R)-sulfoximine, an inhibitor of GSH synthesis, IL-2-induced LAK activity and proliferation of NK cells in medium without L-cystine and GSH, could be restored, at least in part, by addition of GSH, but not 2-ME or L-cystine. Furthermore, intracellular GSH levels were depressed in cells cultured in L-cystine/GSH-depleted medium but could be restored by the addition of 2-ME. The results suggest that (1) L-cystine or thiol containing compounds such as L-cysteine, 2-ME, or GSH are necessary for effective IL-2-activation of human NK cells, (2) these compounds must be functional proton-donors, i.e., reducing agents, implying regulation of the IL-2 activation pathway by oxidation-reduction, and (3) GSH synthesis is necessary for the activation. Experiments were performed to begin to dissect the redox-sensitive step(s) in LAK development. Depletion of reducing agents had no effect on internalization of rIL-2. In contrast, intracellular granzyme A activity was significantly depressed in NK cells cultured with rIL-2 in L-cystine/GSH-depleted medium compared with those cultured in medium in which L-cystine levels had been replenished. The findings suggest that step(s) in the transduction of the IL-2 signal in NK cells, between the internalization of IL-2 and the maturation of the lytic mechanism, are subject to regulation by oxidation-reduction.
The nuclear factor of activated T cells (NF-AT)3 is an inducible DNA-binding protein that is essential for transcriptional induction of the IL-2 gene during T cell activation. NF-AT is thought to consist of two components: a ubiquitous, inducible nuclear component that we have identified as Fos and Jun proteins, and a preexisting, T cell-specific component (NF-ATp) which is the target for the immunosuppressive agents cyclosporin A (CsA) and FK506. We have previously shown that nuclear extracts from activated T cells form two inducible NF-AT complexes with an oligonucleotide corresponding to the distal NF-AT site of the murine IL-2 promoter, although hypotonic extracts of unstimulated T cells form a single complex containing NF-ATp. We show that the ability to detect NF-ATp in a gel shift assay, which is essential for purification and biochemical studies of this protein, is strikingly dependent on the precise sequence of the NF-AT oligonucleotide used as the labeled probe. Moreover we present evidence that the component that forms the faster-migrating ("lower") nuclear NF-AT complex is derived by a calcium-dependent, cyclosporin-sensitive, posttranslational modification of NF-ATp, and that Fos and Jun proteins stabilize its interaction with DNA. The results are discussed in the context of a model relating the two nuclear NF-AT complexes to NF-ATp.
Freshly isolated human blood monocytes were spontaneously cytotoxic toward K562 tumor cells. During culture of the monocytes in vitro cytotoxicity decreased during the first 48 h but tumoricidal competence was restored after 3 to 4 days in vitro. These changes were accompanied by changes in both reactive oxygen intermediate generating capacity and reactive nitrogen intermediate production. Lucigenin-dependent chemiluminescence stimulated with either FMLP or PMA declined during the first 2 days in culture and was negligible during the later days in culture. Superoxide radical production in response to either FMLP or PMA remained fairly constant for the first few days in vitro and then declined. NO2- concentration in monocyte-conditioned medium was fairly constant during the first few days in vitro but increased after 6 days. The return to tumoricidal competence after 3 to 4 days in culture was decreased by the addition of NG-monomethyl-L-arginine. These results indicate that reactive oxygen intermediates are employed by monocytes in the killing of tumor cells. However, after maturation of monocytes to macrophages, this mechanism becomes less important and reactive nitrogen intermediates are employed in mediating macrophage cytotoxicity.
Ligation of the Fc gamma R on NK cells by Ab-coated target cells initiates a mode of killing referred to as antibody-dependent cell-mediated cytotoxicity (ADCC). There is clear evidence that the release from NK cells of granules containing pore-forming proteins and serine proteases can result in the rapid (within minutes) cell death of Ab-coated targets. However, little information is available as to whether NK cells can initiate subsequent killing through granule-independent mechanisms and as to the mechanisms that down-regulate NK cell-mediated responses. We demonstrate in this study that FcR stimulation of activated human NK cells not only induces granule exocytosis, but also subsequently results in the transcriptional up-regulation of Fas ligand. These FcR-stimulated NK cells can then kill targets that bear Fas (CD95/APO-1), as this cytotoxicity can be inhibited by blocking Abs to the Fas receptor. In addition, as resting NK cells become activated, their Fas receptors become competent to deliver autocrine suicide signals. We demonstrate in this work that the interaction of Fas ligand on the FcR-stimulated NK cells with their Fas receptors can result in apoptosis of the NK cells. These results suggest that the FcR-induced expression of Fas ligand on activated NK cells can critically influence the capacity of these cells to mediate paracrine and autocrine cell death.
The transcription factor NF-kappa B has attracted widespread attention among researchers in many fields based on the following: its unusual and rapid regulation, the wide range of genes that it controls, its central role in immunological processes, the complexity of its subunits, and its apparent involvement in several diseases. A primary level of control for NF-kappa B is through interactions with an inhibitor protein called I kappa B. Recent evidence confirms the existence of multiple forms of I kappa B that appear to regulate NF-kappa B by distinct mechanisms. NF-kappa B can be activated by exposure of cells to LPS or inflammatory cytokines such as TNF or IL-1, viral infection or expression of certain viral gene products, UV irradiation, B or T cell activation, and by other physiological and nonphysiological stimuli. Activation of NF-kappa B to move into the nucleus is controlled by the targeted phosphorylation and subsequent degradation of I kappa B. Exciting new research has elaborated several important and unexpected findings that explain mechanisms involved in the activation of NF-kappa B. In the nucleus, NF-kappa B dimers bind to target DNA elements and activate transcription of genes encoding proteins involved with immune or inflammation responses and with cell growth control. Recent data provide evidence that NF-kappa B is constitutively active in several cell types, potentially playing unexpected roles in regulation of gene expression. In addition to advances in describing the mechanisms of NF-kappa B activation, excitement in NF-kappa B research has been generated by the first report of a crystal structure for one form of NF-kappa B, the first gene knockout studies for different forms of NF-kB and of I kappa B, and the implications for therapies of diseases thought to involve the inappropriate activation of NF-kappa B.
Fas (APO-1, CD95) is a type I integral membrane protein initially identified by mAbs that induce apoptotic cell death upon binding to certain tumor cells and its belongs to the TNFR family. Fas is expressed on activated lymphocytes and in various tissues including the liver, lung, intestine, and skin. Molecular cloning of Fas ligand (FasL) revealed that it is a type II integral membrane protein homologous to TNF. FasL is predominantly expressed on activated T and NK cells, and mediates Fas divided by target cell lysis by these effector cells. The Fas/FasL system has been also implicated in the pathogenesis of autoimmune diseases, fulminant hepatitis, GVHD, and AIDS. It has been recently reported that human FasL was released as a 26 kD soluble form from COS cells transfected with human FasL cDNA and activated human T cells. In this communication, metalloproteinase-mediated release of FasL and it's clinical relevance are discussed.
The addition of nitric oxide (NO)-releasing agents, S-nitroso-N-acetyl-DL-penicillamine (SNAP), 1-hydroxy-2-oxo-2,3-bis(2-aminoethyl)-1-triazene (NOC18), 30{(+/-)-(E)-ethyl-2'-[(E)-hydroxyimino]-5-nitro-3-hexenecarbam oyl} -pyridine (NOR4) significantly inhibited NK cell activity against VZV-infected cells, while antibody-dependent cell-mediated cytotoxicity (ADCC) against VZV-infected cells was unaffected. Interferon-alpha (IFN-alpha) production by non-adherent peripheral blood mononuclear cells (NPBMC) cultured with VZV-infected cells was decreased by the addition of NO-releasing agents. Lymphocyte proliferation and the expression IL-2 receptor (CD25) in response to VZV antigen were also inhibited by the addition of NO-releasing agents. These results suggest that the production of NO by an inflammatory process may lead to inhibition of NK cell- and T cell-mediated immunity to VZV infection.
The addition of nitric oxide (NO)-releasing agents, S-nitroso-N-acetyl-D,L-penicillamine (SNAP), 1-hydroxy-2-oxo-3,3-bis(2-aminoethyl)-1-triazene (NOC18), or 3-[(+/-)-(E)-ethyl-2'-[(E)-hydroxyimino]-5-nitro-3-hexenecarbam oyl]-pyridine (NOR 4), significantly inhibited natural killer (NK) cell activity against cytomegalovirus (CMV)-infected cells. Inhibition of NK cell activity was due to NO released in the culture medium because the concentration of nitrite in the culture medium correlated with the inhibition of NK cell activity and the addition of an antagonist of NO, [2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide] (carboxy-PTIO), to NK assay restored NK cell activity. The mechanism of inhibition of NK cell activity against CMV-infected cells by NO-releasing agents includes (1) inhibition of the production of interferon (IFN)-alpha by CD16 (Leu11b)-depleted cells cultured with CMV-infected cells and (2) inhibition of the activation process of NK cell by IFN-alpha. It is suggested that the production of NO by an inflammatory process may lead to the inhibition of NK cell-mediated cytotoxicity against CMV-infected cells.
Although the role of natural killer (NK) cells in defense against certain viral infections has been appreciated for a number of years, characterization of the virus-induced endogenous mechanisms regulating NK cell responses and functions has been limited to interferon (IFN)-alpha/beta-mediated activation of NK cell cytotoxicity. Studies of experimental infections have demonstrated that virus-induced NK cells undergo blastogenesis and can be activated to produce IFN-gamma. Recent work has shown that some, but not all, viral infections induce IL-12, the expression of which results in NK cell IFN-gamma production, and that NK cell IFN-gamma production contributes to an antiviral state. IL-12 expression can be regulated by IFN-alpha/beta, and endogenous IFN-alpha/beta is responsible for the lack of IL-12 during viral infections that fail to elicit detectable production of this factor. Once T cell responses are activated, additional mechanisms are in place to turn off NK cell functions. These studies demonstrate that viral infections elicit unique mechanisms for regulating NK cell responses, and suggest that the host requires tight control of NK cells under these conditions.
HLA class I downregulation is a frequent event associated with tumour invasion and development. Altered HLA class I tumour phenotypes can have profound effects on T-cell and natural killer (NK)-cell antitumour responses. Here, Federico Garrido and colleagues analyse these altered tumour phenotypes in detail, indicating their potential relevance for implementation of immunotherapeutic protocols and strategies to overcome tumour escape mechanisms.
At the interface between the innate and adaptive immune systems lies the high-output isoform of nitric oxide synthase (NOS2 or iNOS). This remarkable molecular machine requires at least 17 binding reactions to assemble a functional dimer. Sustained catalysis results from the ability of NOS2 to attach calmodulin without dependence on elevated Ca2+. Expression of NOS2 in macrophages is controlled by cytokines and microbial products, primarily by transcriptional induction. NOS2 has been documented in macrophages from human, horse, cow, goat, sheep, rat, mouse, and chicken. Human NOS2 is most readily observed in monocytes or macrophages from patients with infectious or inflammatory diseases. Sustained production of NO endows macrophages with cytostatic or cytotoxic activity against viruses, bacteria, fungi, protozoa, helminths, and tumor cells. The antimicrobial and cytotoxic actions of NO are enhanced by other macrophage products such as acid, glutathione, cysteine, hydrogen peroxide, or superoxide. Although the high-output NO pathway probably evolved to protect the host from infection, suppressive effects on lymphocyte proliferation and damage to other normal host cells confer upon NOS2 the same protective/destructive duality inherent in every other major component of the immune response.
Using thiol deprivation, we have previously shown that the response of natural killer (NK) cells to interleukin-2 (IL-2) is subject to redox regulation downstream of IL-2 binding and internalization. We have now used the IL-2-dependent cell line, NK3.3 to study redox regulation of NK cells further, and found that NK3.3 cells neither incorporated [3H]-thymidine nor completed the G1-S phase transition in medium lacking the thiol-related compounds, L-cystine, and glutathione, despite the presence of sufficient IL-2. Thiol deprivation did not alter the induction of DNA interferon-gamma activated sequence (GAS)-binding activity in response to IL-2. However, the retinoblastoma gene product (RB), a cyclin-dependent kinase (CDK) substrate, was phosphorylated within 24 hours after IL-2 stimulation in standard medium, but its expression and phosphorylation were reduced in thiol-depleted medium in both NK3.3 cells and freshly isolated NK cells. These reductions were not associated with an increased level of p27Kip1, an inhibitor of CDKs CDK6/2 in association with G1 cyclins. Reducing agents, N-acetylcysteine, reduced glutathione or 2-ME restored both RB phosphorylation and DNA synthesis in thiol-deprived NK3.3 cells. The in vitro kinase activities of CDK6 and CDK2 were prematurely increased by thiol deprivation. This enhancement was associated with CDK hyperphosphorylation and prolonged phosphorylation, and could be observed before and beyond IL-2 stimulation. The data suggest the possibility that the premature and prolonged enhancement of CDK activity in thiol-deprived NK cells is associated with, and therefore may contribute to, the reduced expression and phosphorylation of RB, and the associated cell cycle arrest.