[Show abstract][Hide abstract] ABSTRACT: The induction of hypoxia-inducible factors (HIFs) is essential for the adaptation of tumor cells to a low-oxygen environment.
We found that the expression of the apoptosis inhibitor ARC (apoptosis repressor with a CARD domain) was induced by hypoxia
in a variety of cancer cell types, and its induction is primarily HIF1 dependent. Chromatin immunoprecipitation (ChIP) and
reporter assays also indicate that the ARC gene is regulated by direct binding of HIF1 to a hypoxia response element (HRE) located at bp −190 upstream of the transcription
start site. HIFs play an essential role in the pathogenesis of renal cell carcinoma (RCC) under normoxic conditions, through
the loss of the Von Hippel-Lindau gene (VHL). Accordingly, our results show that ARC is not expressed in normal renal tissue but is highly expressed in 65% of RCC tumors,
which also express high levels of carbonic anhydrase IX (CAIX), a HIF1-dependent protein. Compared to controls, ARC-deficient
RCCs exhibited decreased colony formation and increased apoptosis in vitro. In addition, loss of ARC resulted in a dramatic reduction of RCC tumor growth in SCID mice in vivo. Thus, HIF-mediated increased expression of ARC in RCC can explain how loss of VHL can promote survival early in tumor formation.
[Show abstract][Hide abstract] ABSTRACT: Decreased mitochondrial oxidative metabolism is a hallmark bioenergetic characteristic of malignancy that may have an adaptive role in carcinogenesis. By stimulating proton leak, mitochondrial uncoupling proteins (UCP1-3) increase mitochondrial respiration and may thereby oppose cancer development. To test this idea, we generated a mouse model that expresses an epidermal-targeted keratin-5-UCP3 (K5-UCP3) transgene and exhibits significantly increased cutaneous mitochondrial respiration compared with wild type (FVB/N). Remarkably, we observed that mitochondrial uncoupling drove keratinocyte/epidermal differentiation both in vitro and in vivo. This increase in epidermal differentiation corresponded to the loss of markers of the quiescent bulge stem cell population, and an increase in epidermal turnover measured using a bromodeoxyuridine (BrdU)-based transit assay. Interestingly, these changes in K5-UCP3 skin were associated with a nearly complete resistance to chemically-mediated multistage skin carcinogenesis. These data suggest that targeting mitochondrial respiration is a promising novel avenue for cancer prevention and treatment.Oncogene advance online publication, 23 January 2012; doi:10.1038/onc.2011.630.
[Show abstract][Hide abstract] ABSTRACT: A common genetic mutation found in clear cell renal cell carcinoma (CC-RCC) is the loss of the von Hippel-Lindau (VHL) gene, which results in stabilization of hypoxia-inducible factors (HIFs), and contributes to cancer progression and metastasis. CUB-domain-containing protein 1 (CDCP1) was shown to promote metastasis in scirrhous and lung adenocarcinomas as well as in prostate cancer. In this study, we established a molecular mechanism linking VHL loss to induction of the CDCP1 gene through the HIF-1/2 pathway in renal cancer. Also, we report that Fyn, which forms a complex with CDCP1 and mediates its signaling to PKCδ, is a HIF-1 target gene. Mechanistically, we found that CDCP1 specifically regulates phosphorylation of PKCδ, but not of focal adhesion kinase or Crk-associated substrate. Signal transduction from CDCP1 to PKCδ leads to its activation, increasing migration of CC-RCC. Furthermore, patient survival can be stratified by CDCP1 expression at the cell surface of the tumor. Taken together, our data indicates that CDCP1 protein might serve as a therapeutic target for CC-RCC.
Proceedings of the National Academy of Sciences 02/2011; 108(5):1931-6. DOI:10.1073/pnas.1011777108 · 9.67 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species contribute to the pathogenesis of a number of disparate disorders including tissue inflammation, heart failure, hypertension, and atherosclerosis. In response to oxidative stress, cells activate expression of a number of genes, including those required for the detoxification of reactive molecules as well as for the repair and maintenance of cellular homeostasis. In many cases, these induced genes are regulated by transcription factors whose structure, subcellular localization, or affinity for DNA is directly or indirectly regulated by the level of oxidative stress. This review summarizes the recent progress on how cellular redox status can regulate transcription-factor activity and the implications of this regulation for cardiovascular disease.
Circulation Research 12/2005; 97(10):967-74. DOI:10.1161/01.RES.0000188210.72062.10 · 11.02 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Aging has often been viewed as a random process arising from the accumulation of both genetic and epigenetic changes. Increasingly, the notion that aging is a stochastic process is being supplanted by the concept that maximum lifespan of an organism is tightly regulated. This knowledge has led to a growing overlap between classical signal transduction paradigms and the biology of aging. We review certain specific examples where these seemingly disparate disciplines intersect. In particular, we review the concept that intracellular reactive oxygen species function as signalling molecules and that oxidants play a central role as mediators of cellular senescence.
International Union of Biochemistry and Molecular Biology Life 05/2005; 57(4-5):277-81. DOI:10.1080/15216540500091890 · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Ethanol consumption represents a major risk factor for cancer development, and a significant fraction of hepatocarcinomas arises in alcoholic liver cirrhosis. Increasing evidence indicates that ethanol acts as a tumor promoter on genetically initiated cells, by increasing the intracellular concentration of reactive oxygen species and promoting tissue necrosis/regeneration and cell proliferation. The tumor suppressor p53 restrains the expansion of carcinogen-initiated cells by inducing cell cycle arrest and apoptosis; accordingly, p53-deficient mice develop spontaneous and chemically induced neoplasms at a much higher frequency than normal mice. In normal mice exposed to a subacute (3 weeks) ethanol intoxication, a significant increase in the number of apoptotic hepatocytes was observed in concomitance with the up-regulation of the mitochondrial superoxide scavenger MnSOD, a reliable indicator of oxidative stress. Cell death occurred in the absence of liver inflammation and necrosis. Ethanol-induced hepatocyte apoptosis was completely abrogated in the p53 null background, suggesting that the tumor suppressor is necessary for hepatocyte death by ethanol. Accordingly, p53 -/- MEF were, unlike wild type cells, completely insensitive up to 0.5M ethanol in the culture medium. Strikingly, marked and widespread signs of dysplasia, with nuclear pleomorphisms and initial loss of normal architecture, heralding malignant transformation, were scored in all the mutant mice exposed to ethanol, but not in the control-fed littermates nor in ethanol-fed normal mice. These observations suggest that p53-dependent apoptosis restrains the tumorigenic effect of ethanol on liver cells, in agreement with the frequent loss of p53 function in HCC, and reveal an unexpected carcinogenic potential of alcohol which appears to be independent from the induction of cirrhosis and hepatocyte regeneration.
Biochemical and Biophysical Research Communications 01/2005; 325(1):97-100. DOI:10.1016/j.bbrc.2004.09.213 · 2.30 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Compelling experimental and epidemiological evidence involves oxygen radicals in carcinogenesis, acting reactive oxygen species both as endogenous genotoxins during cell initiation and as messenger molecules in mitogenesis and in tumor promotion. Moreover, oxidants stimulate neoangiogenesis, which is a prerequisite for tumor growth. However, while several natural as well as synthetic antioxidant compounds appear to be chemopreventive in mutagenicity assays, antioxidant-based treatments for the prevention or cure of cancer have led to non-conclusive if not disappointing results. This is likely due to the fact that oxygen radicals have also a major role in the natural defences against the propagation of cancer cells, i.e. tumor cell apoptosis and immune surveillance, and mediate the beneficial cytotoxic effect of both the chemo-and radio-therapy. In recent years, the mitochondrial antioxidant enzyme, Manganous Superoxide Dismutase (MnSOD), has received a growing attention as a negative modulator of cellular apoptosis and as a survival factor for cancer cells. In fact, while overexpression of this enzyme in cancer cells decreases proliferation and tumor incidence in transgenic models, it is clear that even small amounts of this enzyme are crucial for cell resistance to inflammatory stimuli and anticancer drugs, and prevent oncogene-induced apoptosis triggered by the tumor suppressor protein p53. A previously unexpected oncogenic potential of MnSOD is also suggested by the elevated levels of this enzyme in several classes of human neoplasms, in a fashion which often correlates with the degree of their malignancy. This review focuses on the debated issue of the pro- and/or anti-tumoral effect of MnSOD, with special emphasis on recent observations suggesting that pharmacological inhibition of MnSOD may represent an effective strategy to selectively kill cancer cells and to circumvent their resistance to the commonly used anticancer treatments.
Current Medicinal Chemistry 06/2004; 11(10):1299-308. DOI:10.2174/0929867043365297 · 3.85 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Although in the past several mechanisms and factors have been proposed to be responsible for alcoholic liver disease (ALD), at present the involvement of oxygen free radicals and consequently of oxidative stress has acquired remarkable credit. In numerous experimental studies it has been shown the occurrence of alcohol-induced generation of oxygen- and ethanol-derived free radicals through different pathways and from different sources. Mitochondria appear to be both an important source of reactive oxygen species (ROS) and also a primary target of ethanol-induced damage. The consistent induction of the mitochondrial antioxidant enzyme manganese superoxide dismutase (Mn-SOD) observed in experimental animals after acute and chronic ethanol administration has all the characteristics of a "stress response" to an oxidative insult.
Molecular Aspects of Medicine 02/2004; 25(1-2):191-8. DOI:10.1016/j.mam.2004.02.019 · 10.24 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Signal transduction by reactive oxygen species (ROS; "redox signaling") has recently come into focus in cellular biology studies. The signaling properties of ROS are largely due to the reversible oxidation of redox-sensitive target proteins, and especially of protein tyrosine phosphatases, whose activity is dependent on the redox state of a low pKa active site cysteine. A variety of mitogenic signals, including those released by receptor tyrosine kinase (RTKs) ligands and oncogenic H-Ras, involve as a critical downstream event the intracellular generation of ROS. Signaling by integrins is also essential for the growth of most cell types and is constantly integrated with growth factor signaling. We provide here evidence that intracellular ROS are generated after integrin engagement and that these oxidant intermediates are necessary for integrin signaling during fibroblast adhesion and spreading. Moreover, we propose a synergistic action of integrins and RTKs for redox signaling. Integrin-induced ROS are required to oxidize/inhibit the low molecular weight phosphotyrosine phosphatase, thereby preventing the enzyme from dephosphorylating and inactivating FAK. Accordingly, FAK phosphorylation and other downstream events, including MAPK phosphorylation, Src phosphorylation, focal adhesion formation, and cell spreading, are all significantly attenuated by inhibition of redox signaling. Hence, we have outlined a redox circuitry whereby, upon cell adhesion, oxidative inhibition of a protein tyrosine phosphatase promotes the phosphorylation/activation and the downstream signaling of FAK and, as a final event, cell adhesion and spreading onto fibronectin.
The Journal of Cell Biology 07/2003; 161(5):933-44. DOI:10.1083/jcb.200211118 · 9.83 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species (ROS) act as both signaling molecules and mediators of cell damage in the nervous system and are implicated in the pathogenesis of neurodegenerative diseases. Neurotrophic factors such as the nerve-derived growth factor (NGF) support neuronal survival during development and promote regeneration after neuronal injury through the activation of intracellular signals whose molecular effectors and downstream targets are still largely unknown. Here we present evidence that early oxidative signals initiated by NGF in PC12 cells, an NGF-responsive cell line, play a critical role in preventing apoptosis induced by serum deprivation. This redox-signaling cascade involves phosphatidylinositol 3-kinase, the small GTPase Rac-1, and the transcription factor cAMP-responsive element-binding protein (CREB), a molecule essential to promote NGF-dependent survival. We found that ROS are necessary for NGF-dependent phosphorylation of CREB, an event directly correlated with CREB activity, whereas hydrogen peroxide induces a robust CREB phosphorylation. Cells exposed to NGF show a late decrease in the intracellular content of ROS when compared with untreated cells and increased expression of the mitochondrial antioxidant enzyme manganese superoxide dismutase, a general inhibitor of cell death. Accordingly, serum deprivation-induced apoptosis was selectively inhibited by low concentrations of the mitochondrially targeted antioxidant Mito Q (mitoquinol/mitoquinone). Taken together, these data demonstrate that the oxidant-dependent activation of CREB is a component of NGF survival signaling in PC12 cells and outline an intriguing circuitry by which a cytosolic redox cascade promotes cell survival at least in part by increasing mitochondrial resistance to oxidative stress.
[Show abstract][Hide abstract] ABSTRACT: Recent evidence shows the involvement of reactive oxygen species (ROS) in the mitogenic cascade initiated by the tyrosine kinase receptors of several growth factor peptides. We have asked whether also the vascular endothelial growth factor (VEGF) utilizes ROS as messenger intermediates downstream of the VEGF receptor-2 (VEGFR-2)/KDR receptor given that the proliferation of endothelial cells during neoangiogenesis is physiologically regulated by oxygen and likely by its derivative species. In porcine aortic endothelial cells stably expressing human KDR, receptor activation by VEGF is followed by a rapid increase in the intracellular generation of hydrogen peroxide as revealed by the peroxide-sensitive probe dichlorofluorescein diacetate. Genetic and pharmacological studies suggest that such oxidant burst requires as upstream events the activation of phosphatidylinositol 3-kinase and the small GTPase Rac-1 and is likely initiated by lipoxygenases. Interestingly, ROS generation in response to VEGF is not blocked but rather potentiated by endothelial nitric-oxide synthase inhibitors diphenyleneiodonium and N(G)methyl-l-arginine, ruling out the possibility of nitric oxide being the oxidant species here detected in VEGF-stimulated cells. Inhibition of KDR-dependent generation of ROS attenuates early signaling events including receptor autophosphorylation and binding to a phospholipase C-gamma-glutathione S-transferase fusion protein. Moreover, catalase, the lipoxygenase inhibitor nordihydroguaiaretic acid, the synthetic ROS scavenger EUK-134, and phosphatidylinositol 3-kinase inhibitor wortmannin all reduce ERK phosphorylation in response to VEGF, and antioxidants prevent VEGF-dependent mitogenesis. Finally, cell culture and stimulation in a nearly anoxic environment mimic the effect of ROS scavenger on receptor and ERK phosphorylation, reinforcing the idea that ROS are necessary components of the mitogenic signaling cascade initiated by KDR. These data identify ROS as a new class of intracellular angiogenic mediators and may represent a potential premise for new antioxidant-based antiangiogenic therapies.
[Show abstract][Hide abstract] ABSTRACT: From a growing body of evidence on the role of Reactive Oxygen Species as intracellular signaling molecules, the concept starts to emerge that cell responses to redox changes are function of the intracellular site where oxidants are produced and/or meet their molecular targets. In particular, a major distinction between oxidative events in the cytosolic versus the mitochondrial compartment appears to exist in terms of physiological stimuli, signaling mechanisms and functional consequences. Experimental data supporting this view are reviewed here, and the potential implications of this new perspective in redox signaling are discussed.
International Union of Biochemistry and Molecular Biology Life 08/2001; 52(1-2):7-16. DOI:10.1080/15216540252774702 · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Reactive oxygen species (ROS) have recently drawn significant attention as putative mitogenic mediators downstream of activated growth factor receptors and oncogenic Ras; however, the possibility that a redox-related mechanism also operates in the negative control of cell proliferation by inhibitory signals has not been investigated thus far. Here we show that the arrest of growth induced by cell confluence ("contact inhibition") is due, at least in part, to a decrease in the steady-state levels of intracellular ROS and the consequent impairment of mitogenic redox signaling. In confluent fibroblast cultures, the decrease in the concentration of oxygen species was associated with diminished activity of the small GTPase Rac-1, a signal transducer directly involved in the ligand-dependent generation of oxygen-derived molecules, and was effectively mimicked by exposure of sparse cultures to dithiothreitol (DTT) and inhibitors of enzymes (phospholipase A2 and lipoxygenase) acting in the arachidonic acid cascade downstream of growth factor receptors and Rac-1. Sparse fibroblasts treated with nontoxic amounts of DTT underwent growth arrest, whereas a low concentration of hydrogen peroxide significantly increased thymidine incorporation in confluent cultures, demonstrating a causal link between redox changes and growth control by cell density. Removal of oxygen species from sparse cultures was accompanied by a drastic decrease of protein tyrosine phosphorylation after epidermal growth factor stimulation, which, at a biochemical level, reproduced the signaling hallmarks of contact inhibition. Moreover, the cytosolic tyrosine phosphatase SHP-2 was identified as a putative target for redox signaling by cell density because the enzyme itself and the associated substrates appear markedly dephosphorylated in both confluent and reductant-treated cells after exposure to epidermal growth factor, and SHP-2 enzymatic activity is strongly activated by DTT in vitro. Taken together, these data support a model in which impaired generation of ROS and increased protein tyrosine phosphatase activity impede mitogenic signaling in contact-inhibited cells.
[Show abstract][Hide abstract] ABSTRACT: Loss of function of the tumor suppressor protein p53 represents a very frequent event in human carcinogenesis, but the molecular mechanisms linking impaired p53 activity to increased cell malignancy are still incompletely understood. p53 is normally involved in both cell cycle control and the induction of cell death and is involved in the latter mainly through the transcriptional regulation of pro- and antiapoptotic proteins. Reactive oxygen species are known to be powerful inducers of p53 activity; moreover, they play a role in the execution of p53-dependent apoptosis. Here we show that transformed mouse fibroblasts lacking p53 are significantly more resistant than wild-type (wt) controls to the cytotoxic effect of a number of pro-oxidant treatments. Interestingly, these cells also exhibit deregulated expression of the antioxidant enzyme manganese superoxide dismutase (MnSOD), a protein known to protect cancer cells from the oxidative injury inflicted by antitumoral cytokines and anticancer drugs. MnSOD activity was also increased in liver tissue from p53-deficient mice in comparison with wt tissue. Transient transfection of wt p53 in HeLa cells led to a significant reduction in steady-state MnSOD mRNA levels and enzymatic activity, confirming that the expression of this antioxidant enzyme is negatively regulated by p53. Forced expression of MnSOD rendered HeLa cells resistant to p53-dependent cytotoxic treatments and, in cotransfection experiments, counteracted the growth-inhibitory effect of p53. Taken together, these data identify MnSOD as a potential target for tumor suppressor protein p53 and underscore the relevance of MnSOD modulation in the context of normal p53 functions because it is consistent with many reports of abnormally increased MnSOD expression in human cancers.
Cancer Research 09/2000; 60(16):4654-60. · 9.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Compelling evidence exists that reactive oxygen species can deliver intracellular signals in mammalian cells, and elicit a broad array of physiological responses according to the cell type, the oxidative burden and the cellular compartment where radicals are generated. When applied to immune cells, these concepts gain a particular relevance, in relation to the plasticity of immune functions and the biological complexity of lymphocyte response to antigens. Here we review some recent and somehow conflicting observations on the involvement of oxygen radicals and redox balance in lymphocyte activation, and propose models for how radical species could contribute to normal and pathological immunity.
International Union of Biochemistry and Molecular Biology Life 06/2000; 49(5):381-9. DOI:10.1080/152165400410227 · 3.14 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Molecular events mediating the T-lymphocyte response to lectins are still incompletely understood, although much evidence suggests that both the mitogenic and the death-promoting effects of these agents involve the biochemical cascade initiated by the CD3/T-cell antigen receptor (TCR) complex. Reactive oxygen species (ROS) and in particular H(2)O(2) have been shown to have a role in cell response to cytokines and growth factors. Here we report that the proliferation of mouse thymocytes in response to the mitogenic lectin concanavalin A (ConA) is strongly and selectively inhibited by the intracellular ROS scavenger N-acetylcysteine (NAC) and by diphenyleneiodonium (DPI), a potent inhibitor of NADPH-dependent membrane oxidases activated by surface receptors. A rapid 'burst' of intracellular oxygen radicals was observed in mouse thymocytes stimulated by ConA, with kinetics that paralleled the appearance of tyrosine-phosphorylated proteins. This burst was abrogated by the pretreatment of cells with NAC or DPI. Only a modest increase in intracellular oxygen species was found in thymocytes stimulated by strong cross-linking of TCR together with CD4 or CD28. Pharmacological interference with ROS production in ConA-stimulated thymocytes resulted in a decreased tyrosine phosphorylation of multiple protein species, including a 38 kDa band able to recruit the adapter protein Grb2 and corresponding to the recently identified transducer LAT (linker for activation of T-cells), a molecule involved in linking activated TCR to the production of interleukin 2 and the proliferation of T-cells. Furthermore, ROS inhibition markedly attenuated the activation of stress-activated protein kinase/JNK-1 (c-Jun N-terminal kinase 1) in response to lectins. Taken together, these results identify ROS as important modulators of the signalling cascade initiated by mitogenic lectins in thymocytes and, by extension, as a novel class of mediators downstream of antigen receptors.
[Show abstract][Hide abstract] ABSTRACT: Molecular events mediating the T-lymphocyte response to lectins are still incompletely understood, although much evidence suggests that both the mitogenic and the death-promoting effects of these agents involve the biochemical cascade initiated by the CD3/T-cell antigen receptor (TCR) complex. Reactive oxygen species (ROS) and in particular H2O2 have been shown to have a role in cell response to cytokines and growth factors. Here we report that the proliferation of mouse thymocytes in response to the mitogenic lectin concanavalin A (ConA) is strongly and selectively inhibited by the intracellular ROS scavenger N-acetylcysteine (NAC) and by diphenyleneiodonium (DPI), a potent inhibitor of NADPH-dependent membrane oxidases activated by surface receptors. A rapid 'burst' of intracellular oxygen radicals was observed in mouse thymocytes stimulated by ConA, with kinetics that paralleled the appearance of tyrosine-phosphorylated proteins. This burst was abrogated by the pretreatment of cells with NAC or DPI. Only a modest increase in intracellular oxygen species was found in thymocytes stimulated by strong cross-linking of TCR together with CD4 or CD28. Pharmacological interference with ROS production in ConA-stimulated thymocytes resulted in a decreased tyrosine phosphorylation of multiple protein species, including a 38 kDa band able to recruit the adapter protein Grb2 and corresponding to the recently identified transducer LAT (linker for activation of T-cells), a molecule involved in linking activated TCR to the production of interleukin 2 and the proliferation of T-cells. Furthermore, ROS inhibition markedly attenuated the activation of stress-activated protein kinase/JNK-1 (c-Jun N-terminal kinase 1)in response to lectins. Taken together, these results identify ROS as important modulators of the signalling cascade initiated by mitogenic lectins in thymocytes and, by extension, as a novel class of mediators downstream of antigen receptors.