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ABSTRACT: Voltage-dependent K (+) (Kv) channels are tightly regulated during the immune system response. Leukocytes have a limited repertoire of Kv channels, whose physiological role is under intense investigation. A functional Kv channel is an oligomeric complex composed of pore-forming and ancillary subunits. The KCNE gene family is a novel group of modulatory Kv channel elements in leukocytes. Here, we characterized the gene expression of KCNEs (1-5) in leukocytes and investigated their regulation during leukocyte proliferation and mode of activation. Murine bone-marrow-derived macrophages, human Jurkat T-lymphocytes and human Raji B-cells were analyzed. KCNEs (1-5) are expressed in all leukocytes lineages. Most KCNE mRNAs show cell cycle-dependent regulation and are differentially regulated under specific insults. Our results further suggest a new and yet undefined physiological role for KCNE subunits in the immune system. Putative associations of these ancillary proteins with Kv channels would yield a wide variety of biophysically and pharmacologically distinct channels that fine-tune the immunological response.
Channels (Austin, Tex.) 01/2013; 7(2). · 1.91 Impact Factor
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ABSTRACT: Kv1.3 plays a crucial role in the activation and proliferation of T-lymphocytes and macrophages. While Kv1.3 is responsible for the voltage-dependent potassium current in T-cells, in macrophages this K(+) current is generated by the association of Kv1.3 and Kv1.5. Patients with autoimmune diseases show a high number of effector memory T cells that are characterized by a high expression of Kv1.3 and Kv1.3 antagonists ameliorate autoimmune disorders in vivo. Diclofenac is a non-steroidal anti-inflammatory drug (NSAID) used in patients who suffer from painful autoimmune diseases such as rheumatoid arthritis. In this study, we show that diclofenac impairs immune response via a mechanism that involves Kv1.3. While diclofenac inhibited Kv1.3 expression in activated macrophages and T-lymphocytes, Kv1.5 remained unaffected. Diclofenac also decreased iNOS levels in Raw 264.7 cells, impairing their activation in response to lipopolysaccharide (LPS). LPS-induced macrophage migration and IL-2 production in stimulated Jurkat T-cells were also blocked by pharmacological doses of diclofenac. These effects were mimicked by Margatoxin, a specific Kv1.3 inhibitor, and Charybdotoxin, which blocks both Kv1.3 and Ca(2+)-activated K(+) channels (K(Ca)3.1). Because Kv1.3 is a very good target for autoimmune therapies, the effects of diclofenac on Kv1.3 are of high pharmacological relevance.
Biochemical pharmacology 09/2010; 80(6):858-66. · 4.25 Impact Factor
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ABSTRACT: For the last 20 years, knowledge of the physiological role of voltage-dependent potassium channels (Kv) in the immune system has grown exponentially. Leukocytes express a limited repertoire of Kv channels, which contribute to the membrane potential. These proteins are involved in the immune response and are therefore considered good pharmacological targets. Although there is a clear consensus about the physiological relevance of Kv1.3, the expression and the role of Kv1.5 are controversial. However, recent reports indicate that certain heteromeric Kv1.3/Kv1.5 associations may provide insight on Kv1.5. Here, we summarize what is known about this issue and highlight the role of Kv1.5 partnership interactions that could be responsible for this debate. The Kv1.3/Kv1.5 heterotetrameric composition of the channel and their possible differential associations with accessory regulatory proteins warrant further investigation.
Frontiers in physiology. 01/2010; 1:152.
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David Parra,
Joan Manils,
Bàrbara Castellana,
Arnau Viña-Vilaseca,
Eva Morán-Salvador,
Nuria Vázquez-Villoldo,
Gemma Tarancón,
Miquel Borràs,
Sara Sancho,
Carmen Benito,
Sagrario Ortega, Concepció Soler
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ABSTRACT: TREX2 is a proofreading 3'-5' exonuclease that can be involved in genome maintenance; however, its biological role remains undefined. To better understand the function and physiologic relevance of TREX2, we generated mice deficient in TREX2 by targeted disruption of its unique coding exon. The knockout mice are viable and do not show relevant differences in growth, survival, lymphocyte development, or spontaneous tumor incidence compared with their wild-type counterparts over a period of up to 2 years. Also, we did not observe chromosomal instability or defects in cell proliferation and cell cycle upon loss of TREX2. We have observed that TREX2 expression is not ubiquitous, being expressed preferentially in tissues with stratified squamous epithelia, such as the skin or esophagus, and specifically in keratinocytes. Interestingly, TREX2-null mice are more susceptible to skin carcinogenesis induced by 7,12-dimethylbenz(a)anthracene (DMBA) compared with wild-type mice. This phenotype correlates with a reduction of DMBA-induced apoptosis in both the epidermis and keratinocytes of TREX2-null mice. Altogether, our results suggest a tumor suppressor role for TREX2 in skin carcinogenesis through which it contributes to keratinocyte apoptosis under conditions of genotoxic stress.
Cancer Research 09/2009; 69(16):6676-84. · 7.86 Impact Factor
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ABSTRACT: Surface expression of voltage-dependent K(+) channels (Kv) has a pivotal role in leukocyte physiology. Although little is known about the physiological role of lipid rafts, these microdomains concentrate signaling molecules and their ion channel substrates. Kv1.3 associates with Kv1.5 to form functional channels in macrophages. Different isoform stoichiometries lead to distinct heteromeric channels which may be further modulated by targeting the complex to different membrane surface microdomains. Kv1.3 targets to lipid rafts, whereas Kv1.5 localization is under debate. With this in mind, we wanted to study whether heterotetrameric Kv1.5-containing channels target to lipid rafts. While in transfected HEK-293 cells, homo- and heterotetrameric channels targeted to rafts, Kv1.5 did not target to rafts in macrophages. Therefore, Kv1.3/Kv1.5 hybrid channels are mostly concentrated in non-raft microdomains. However, LPS-induced activation, which increases the Kv1.3/Kv1.5 ratio and caveolin, targeted Kv1.5 back to lipid rafts. Moreover, Kv1.5 did not localize to low-buoyancy fractions in L6E9 skeletal myoblasts, which also coexpress both channels, heart membranes or cardiomyocyes. Coexpression of a Cav3(DGV)-mutant confined Kv1.5 to Cav3(DGV)-vesicles of HEK cells. Contrarily, coexpression of Kvbeta2.1 impaired the Kv1.5 targeting to raft microdomains in HEK cells. Our results indicate that Kv1.5 partnership interactions are underlying mechanisms governing channel targeting to lipid rafts.
Journal of Cellular Physiology 08/2008; 217(3):667-73. · 3.87 Impact Factor
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ABSTRACT: Voltage-dependent K(+) channels (Kv) are involved in the proliferation of many types of cells, but the mechanisms by which their activity is related to cell growth remain unclear. Kv antagonists inhibit the proliferation of mammalian cells, which is of physiological relevance in skeletal muscle. Although myofibres are terminally differentiated, some resident myoblasts may re-enter the cell cycle and proliferate. Here we report that the expression of Kv1.5 is cell-cycle dependent during myoblast proliferation. In addition to Kv1.5 other Kv, such as Kv1.3, are also up-regulated. However, pharmacological evidence mainly implicates Kv1.5 in myoblast growth. Thus, the presence of S0100176, a Kv antagonist, but not margatoxin and dendrotoxin, led to cell cycle arrest during the G(1)-phase. The use of selective cell cycle blockers showed that Kv1.5 was transiently accumulated during the early G(1)-phase. Furthermore, while myoblasts treated with S0100176 expressed low levels of cyclin A and D(1), the expression of p21(cip-1) and p27(kip1), two cyclin-dependent kinase inhibitors, increased. Our results indicate that the cell cycle-dependent expression of Kv1.5 is involved in skeletal muscle cell proliferation.
Biochimica et Biophysica Acta 06/2008; 1783(5):728-36. · 4.66 Impact Factor
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ABSTRACT: Kv1.3 activity is determined by raft association. In addition to Kv1.3, leukocytes also express Kv1.5, and both channels control physiological responses. Because the oligomeric composition may modify the channel targeting to the membrane, we investigated heterotetrameric Kv1.3/Kv1.5 channel traffic and targeting in HEK cells. Kv1.3 and Kv1.5 generate multiple heterotetramers with differential surface expression according to the subunit composition. FRET analysis and pharmacology confirm the presence of functional hybrid channels. Raft association was evaluated by cholesterol depletion, caveolae colocalization, and lateral diffusion at the cell surface. Immunoprecipitation showed that both Kv1.3 and heteromeric channels associate with caveolar raft domains. However, homomeric Kv1.3 channels showed higher association with caveolin traffic. Moreover, FRAP analysis revealed higher mobility for hybrid Kv1.3/Kv1.5 than Kv1.3 homotetramers, suggesting that heteromers target to distinct surface microdomains. Studies with lipopolysaccharide-activated macrophages further supported that different physiological mechanisms govern Kv1.3 and Kv1.5 targeting to rafts. Our results implicate the traffic and localization of Kv1.3/Kv1.5 heteromers in the complex regulation of immune system cells.
Journal of Biological Chemistry 04/2008; 283(13):8756-64. · 4.77 Impact Factor
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Rubén Vicente,
Artur Escalada,
Nuria Villalonga,
Laura Texidó,
Meritxell Roura-Ferrer,
Mireia Martín-Satué,
Carmen López-Iglesias, Concepció Soler,
Carles Solsona,
Michael M Tamkun,
Antonio Felipe
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ABSTRACT: Voltage-dependent K(+) (Kv) currents in macrophages are mainly mediated by Kv1.3, but biophysical properties indicate that the channel composition could be different from that of T-lymphocytes. K(+) currents in mouse bone marrow-derived and Raw-264.7 macrophages are sensitive to Kv1.3 blockers, but unlike T-cells, macrophages express Kv1.5. Because Shaker subunits (Kv1) may form heterotetrameric complexes, we investigated whether Kv1.5 has a function in Kv currents in macrophages. Kv1.3 and Kv1.5 co-localize at the membrane, and half-activation voltages and pharmacology indicate that K(+) currents may be accounted for by various Kv complexes in macrophages. Co-expression of Kv1.3 and Kv1.5 in human embryonic kidney 293 cells showed that the presence of Kv1.5 leads to a positive shift in K(+) current half-activation voltages and that, like Kv1.3, Kv1.3/Kv1.5 heteromers are sensitive to r-margatoxin. In addition, both proteins co-immunoprecipitate and co-localize. Fluorescence resonance energy transfer studies further demonstrated that Kv1.5 and Kv1.3 form heterotetramers. Electrophysiological and pharmacological studies of different ratios of Kv1.3 and Kv1.5 co-expressed in Xenopus oocytes suggest that various hybrids might be responsible for K(+) currents in macrophages. Tumor necrosis factor-alpha-induced activation of macrophages increased Kv1.3 with no changes in Kv.1.5, which is consistent with a hyperpolarized shift in half-activation voltage and a lower IC(50) for margatoxin. Taken together, our results demonstrate that Kv1.5 co-associates with Kv1.3, generating functional heterotetramers in macrophages. Changes in the oligomeric composition of functional Kv channels would give rise to different biophysical and pharmacological properties, which could determine specific cellular responses.
Journal of Biological Chemistry 01/2007; 281(49):37675-85. · 4.77 Impact Factor
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ABSTRACT: In murine macrophages, as a result of arginine catabolism during activation, citruline is produced under the effect of IFN-gamma and LPS, and ornithine and polyamines by IL-4 and IL-10. For proliferation, arginine is required from the extracellular medium and is used for protein synthesis. During activation, most arginine (>95% in 6 h) was metabolized, while under proliferation only half was incorporated into proteins. Under basal conditions, this amino acid was preferentially transported by y(+)L activity. During activation, arginine transport increased drastically (4-5-fold) through y(+) cationic amino acid transporter (CAT) activity. By contrast, M-CSF induced only a modest increase in uptake (0.5-fold). The increase in arginine transport during activation, but not proliferation, was mediated by the SLC7A2/Cat2 gene. SLC7A1/Cat1 is constitutively expressed, and is not modified by proliferating or activating agents. M-CSF-dependent proliferation was not affected in the macrophages of SLC7A2 knockout mice; however, these cells showed a drastic reduction in the production of citruline or ornithine and polyamines during activation. The data show that a large increase in a specific transport system (CAT2) is necessary for activation-induced arginine metabolism, while arginine is in excess for the requirements of proliferation and a modest increase in transport occurs.
European Journal of Immunology 07/2006; 36(6):1516-26. · 5.10 Impact Factor
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Andrée Yeramian,
Lorena Martin,
Neus Serrat,
Luis Arpa, Concepció Soler,
Joan Bertran,
Carol McLeod,
Manuel Palacín,
Manuel Modolell,
Jorge Lloberas,
Antonio Celada
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ABSTRACT: Arginine is processed by macrophages in response to the cytokines to which these cells are exposed. Th1-type cytokines induce NO synthase 2, which metabolizes arginine into nitrites, while the Th2-type cytokines produce arginase, which converts arginine into polyamines and proline. Activation of bone marrow-derived macrophages by these two types of cytokines increases L-arginine transport only through the y(+) system. Analysis of the expression of the genes involved in this system showed that Slc7A1, encoding cationic amino acid transporters (CAT)1, is constitutively expressed and is not modified by activating agents, while Slc7A2, encoding CAT2, is induced during both classical and alternative activation. Macrophages from Slc7A2 knockout mice showed a decrease in L-arginine transport in response to the two kinds of cytokines. However, while NO synthase 2 and arginase expression were unmodified in these cells, the catabolism of arginine was impaired by both pathways, producing smaller amounts of nitrites and also of polyamines and proline. In addition, the induction of Slc7A2 expression was independent of the arginine available and of the enzymes that metabolize it. In conclusion, the increased arginine transport mediated by activators is strongly regulated by CAT2 expression, which could limit the function of macrophages.
The Journal of Immunology 06/2006; 176(10):5918-24. · 5.79 Impact Factor
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ABSTRACT: Voltage-dependent potassium channels (Kv) in leukocytes are involved in the immune response. In bone marrow-derived macrophages (BMDM), proliferation and activation induce delayed rectifier K+ currents, generated by Kv1.3, via transcriptional, translational, and posttranslational controls. Furthermore, modulatory Kv beta subunits coassociate with Kv alpha subunits, increasing channel diversity and function. In this study we have identified Kv beta subunits in mouse BMDM, studied their regulation during proliferation and activation, and analyzed K+ current parameters influenced by these proteins. BMDM express all isoforms of Kv beta1 (Kv beta1.1, Kv beta1.2, and Kv beta1.3) and Kv beta2 (Kv beta2.1), but not Kv beta4, the alternatively spliced murine Kv beta3 variant. M-CSF-dependent proliferation induced all Kv beta isoforms. However, LPS- and TNF-alpha-induced activation differentially regulated these subunits. Although LPS increased Kv beta1.3, reduced Kv beta1.2, and maintained Kv beta1.1 mRNA levels constant, TNF-alpha up-regulated Kv beta1.1, down-regulated Kv beta1.2, and left Kv beta1.3 expression unchanged. Moreover, in contrast to TNF-alpha, M-CSF- and LPS- up-regulated Kv beta2.1. K+ currents from M-CSF- and LPS-stimulated BMDM exhibited faster inactivation, whereas TNF-alpha increased tau values. Although in M-CSF-stimulated cells the half-inactivation voltage shifted to more positive potentials, the incubation with LPS and TNF-alpha resulted in a hyperpolarizing displacement similar to that in resting BMDM. Furthermore, activation time constants of K+ currents and the kinetics of the tail currents were different depending upon the mode of activation. Our results indicate that differential Kv beta expression modifies the electrical properties of Kv in BMDM, dependent upon proliferation and the mode of activation. This could determine physiologically appropriate surface channel complexes, allowing for greater flexibility in the precise regulation of the immune response.
The Journal of Immunology 05/2005; 174(8):4736-44. · 5.79 Impact Factor
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ABSTRACT: The expressions of CNT and ENT (concentrative and equilibrative nucleoside transporters) in macrophages are differentially regulated by IFN-gamma (interferon-gamma). This cytokine controls gene expression through STAT1-dependent and/or -independent pathways (where STAT1 stands for signal transduction and activator of transcription 1). In the present study, the role of STAT1 in the response of nucleoside transporters to IFN-gamma was studied using macrophages from STAT1 knockout mice. IFN-gamma triggered an inhibition of ENT1-related nucleoside transport activity through STAT1-dependent mechanisms. Such inhibition of macrophage growth and ENT1 activity by IFN-gamma is required for DNA synthesis. Interestingly, IFN-gamma led to an induction of the CNT1- and CNT2-related nucleoside transport activities independent of STAT1, thus ensuring the supply of extracellular nucleosides for the STAT1-independent RNA synthesis. IFN-gamma up-regulated CNT2 mRNA and CNT1 protein levels and down-regulated ENT1 mRNA in both wild-type and STAT1 knockout macrophages. This is consistent with a STAT1-independent, long-term-mediated, probably transcription-dependent, regulation of nucleoside transporter genes. Moreover, STAT1-dependent post-transcriptional mechanisms are implicated in the regulation of ENT1 activity. Although nitric oxide is involved in the regulation of ENT1 activity in B-cells at a post-transcriptional level, our results show that STAT1-dependent induction of nitric oxide by IFN-gamma is not implicated in the regulation of ENT1 activity in macrophages. Our results indicate that both STAT1-dependent and -independent pathways are involved in the regulation of nucleoside transporters by IFN-gamma in macrophages.
Biochemical Journal 12/2003; 375(Pt 3):777-83. · 4.90 Impact Factor
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ABSTRACT: Voltage-dependent K+ channels (VDPC) are expressed in most mammalian cells and involved in the proliferation and activation of lymphocytes. However, the role of VDPC in macrophage responses is not well established. This study was undertaken to characterize VDPC in macrophages and determine their physiological role during proliferation and activation. Macrophages proliferate until an endotoxic shock halts cell growth and they become activated. By inducing a schedule that is similar to the physiological pattern, we have identified the VDPC in non-transformed bone marrow-derived macrophages and studied their regulation. Patch clamp studies demonstrated that cells expressed outward delayed and inwardly rectifying K+ currents. Pharmacological data, mRNA, and protein analysis suggest that these currents were mainly mediated by Kv1.3 and Kir2.1 channels. Macrophage colony-stimulating factor-dependent proliferation induced both channels. Lipopolysaccharide (LPS)-induced activation differentially regulated VDPC expression. While Kv1.3 was further induced, Kir2.1 was down-regulated. TNF-alpha mimicked LPS effects, and studies with TNF-alpha receptor I/II double knockout mice demonstrated that LPS regulation mediates such expression by TNF-alpha-dependent and -independent mechanisms. This modulation was dependent on mRNA and protein synthesis. In addition, bone marrow-derived macrophages expressed Kv1.5 mRNA with no apparent regulation. VDPC activities seem to play a critical role during proliferation and activation because not only cell growth, but also inducible nitric-oxide synthase expression were inhibited by blocking their activities. Taken together, our results demonstrate that the differential regulation of VDPC is crucial in intracellular signals determining the specific macrophage response.
Journal of Biological Chemistry 12/2003; 278(47):46307-20. · 4.77 Impact Factor
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ABSTRACT: Using mouse bone marrow-derived macrophages we determined the role of interferon (IFN)-% at the different steps in expression of the I-A! chain of MHC class II molecules, from transcription to the cell surface. Levels of transcription, RNA, and protein were low in cells not stimulated with IFN-%. Treatment with IFN-% for 24 or 48 h induced an increase in mRNA levels (7- and 12-fold) that did not correlate with the increase in transcription (2.5- and 2.7-fold). The half-life of mRNA was not modified by IFN-%. These data suggest a block at the level of translation. In fact, IFN-% increased ribosome loading, which confirms regulation at the translational level. Treatment with IFN-% increased protein synthesis (6-fold after 48 h) and level of expression at the cell surface (3- and 9-fold after 24 and 48 h, respectively). Interestingly, treatment with IFN-% also increased the I-A! protein half-life from 2 to 6-7 h. This is the first attempt to determine qualitatively and quantitatively the regulation of an inducible gene at all the putative levels of control. The data indicate that IFN-% plays a critical role in MHC class II protein expression in macrophages through the regulation of different steps, from transcription to surface expression.
Immunogenetics 02/2001; 53(2):136-144. · 2.93 Impact Factor
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ABSTRACT: When cells enter the cycle from quiescence (G 0), during the G 1 interval, D-type and E-type cyclins are sequen-tially synthesized (Matsushime et al., 1991); both cyclins are rate limiting for entry in the S phase. D-type cyclins are regulated by extracellular signals, whereas the ex- Departament de Fisiologia (Biologia del macrò fag) Facultat de Biologia and Fundació August Pi i Sunyer pression of E, A, and B cyclins during the cell cycle is Campus de Bellvitge periodic. Unlike other cdks, cyclin D–dependent kinases Universitat de Barcelona have a distinct substrate preference for the retinoblas-Avenida Diagonal 645 toma protein (pRb) (Matsushime et al., 1992). pRb binds 08028 Barcelona and negatively regulates transcription factors that are Spain necessary for S phase entry (Sherr, 1994b). However, the phosphorylation of pRb by cyclin D/E-cdk complexes at or near the R point cancels its growth-suppressive function, thus releasing the transcription factors and Summary allowing them to activate genes necessary for S phase entry (Sherr and Roberts, 1995). Incubation of bone marrow macrophages with lipo-Recently, two families of mammalian G 1 cdk inhibi-polysaccharide (LPS) or interferon (IFN) blocks mac-tors, the CIP/KIP (p21, p27, and p57) and the INK-4 (p15, rophage proliferation. LPS treatment or M-CSF with-p16, p18, and p19), have been described (reviewed in drawal arrests the cell cycle at early G 1 and induces Sherr and Roberts, 1995). These inhibitors help to ex-apoptosis. Treatment of macrophages with IFN stops plain how antiproliferative signals arrest cells in G 1 and the cell cycle later, at the G 1 /S boundary, induces also the arrest induced by DNA damage, terminal differ-p21 Waf1 , and does not induce apoptosis. Moreover, pre-entiation, or cell senescence. These cdk inhibitors bind treatment of macrophages with IFN protects from to cyclin-cdk complexes, particularly to G 1 -cyclin-cdk apoptosis induced by several stimuli. Inhibition of complexes, thus inducing cell cycle arrest. p21 Waf1 with antisense oligonucleotides or using KO Apoptosis is a genetically controlled process of pro-mice shows that the induction of p21 Waf1 by IFN medi-grammed cell death. Recently, genes important for the ates this protection. Thus, IFN makes macrophages regulation of apoptosis have been identified (White, unresponsive to apoptotic stimuli by inducing p21 Waf1 1996). These include many genes first thought to be and arresting the cell cycle at the G 1 /S boundary. involved in cell growth and differentiation (Vaux and Therefore, the cells of the innate immune system could Strasser, 1996). Apoptosis sustains tissue homeostasis only survive while they were functionally active. by balancing the proliferative capabilities of different cells. Thus, cells with a higher proliferation rate are more susceptible to apoptosis. The regulatory coupling of Introduction proliferation and apoptosis is suggested by several ob-servations. For example, the expression of the protoon-Under different external stimuli, cells are able to prolifer-cogene c-myc stimulates cell proliferation and can also ate, to become activated and carry out their function, to predispose cells toward apoptosis when growth factors remain quiescent, or to die through apoptosis. Although are scarce (Evan et al., 1992). Moreover, the activation these events were initially considered as independent, of the expression of cyclin D (Freeman et al., 1994) or recent reports have shown a cross-talk between the the activation of various cdks has been linked with the proliferative capacity of the cells and their activation induction of apoptosis (Meikrantz et al., 1994; Shi et al., or susceptibility to die through apoptosis. Thus, many 1994; Wei et al., 1997; Zhang et al., 1997). More recent mechanisms that induce cells to proliferate or become work now indicates that the apoptosis regulatory pro-activated also induce them to undergo apoptosis (Evan teins themselves can also directly modulate the cell cy-et al., 1992; Meikrantz and Schlegel, 1995; Zhu and Ana-cle progression of the cells (Brady et al., 1996; Linette setti, 1995; Levkau et al., 1998). et al,. 1996; Mazel et al., 1996; O'Reilly et al., 1996). The commitment of cells to enter the S phase of the Whereas antiapoptotic genes like bcl-2 delay cell cycle cell cycle occurs at a restriction point (R) late in G 1 progression, bax and other proapoptotic genes increase phase, after which the cells do not need mitogenic the number of cycling cells. growth factors to complete division (Pardee, 1989). The To carry out their functional activities, macrophages progression from the G 1 to the S phases is controlled have to become activated. After interacting with IFN, by G 1 cyclins that bind to cdks (cyclin-dependent ki-a cytokine released by activated T lymphocytes, the nases) to form holoenzymes that phosphorylate sub-macrophages undergo biochemical and morphological strates that facilitate the progression (Sherr, 1994a). modifications that allow them to perform their functional activity (Schreiber and Celada, 1985). Although IFN is the major macrophage activator, other molecules such * To whom correspondence should be addressed (e-mail: acelada@ bio.ub.es).
Immunity 07/1999; 11(1):103-113. · 21.64 Impact Factor
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ABSTRACT: Nucleoside transport systems and their regulation in human B-lymphocytes have been characterized using the cell lines Raji
and Bare lymphoma syndrome-1 (BLS-1) as experimental models. These cells express at least three different nucleoside transport
systems as follows: a nitrobenzylthioinosine-sensitive equilibrative transport system of the es-type, which appears to be associated with hENT1 expression, and two Na+-dependent transport systems that may correspond to N1 and to the recently characterized N5-type, which is nitrobenzylthioinosine-sensitive
and guanosine-preferring. B cell activators such as phorbol 12-myristate 13-acetate and lipopolysaccharide (LPS) up-regulate
both concentrative transport systems but down-regulate the equilibrativees-type transporter, which correlates with lower hENT1 mRNA levels. These effects are dependent on protein kinase C activity.
Phorbol 12-myristate 13-acetate and LPS also induce an increase in tumor necrosis factor-α (TNF–α) mRNA levels, which suggest
that this cytokine may mediate some of the effects triggered by these agents, since addition of TNF-α alone can increase N1
and N5 transport activities by a mechanism that also depends on protein kinase C activation. Interestingly, TNF-α down-regulates
esactivity, but this effect cannot be abolished by inhibiting protein kinase C. This study reveals differential regulation of
nucleoside transport systems following activation of human B-lymphocyte cell lines by agents of physiological relevance such
as TNF-α and LPS. Moreover, it indicates that the recently characterized N5 transport system can also be regulated following
B cell activation, which may be relevant to lymphocyte physiology and to the treatment of lymphocyte malignancies.
Journal of Biological Chemistry 10/1998; 273(41):26939-26945. · 4.77 Impact Factor
