Fas-induced caspase denitrosylation

Differential gene expression in primary and recurrent carotid stenosis

Apoptosis of the cellular components of complex atherosclerotic plaque may lead to plaque instability and rupture. In this study, five primary plaques and one recurrent fibrointimal lesion obtained from patients undergoing carotid endarterectomy for symptomatic carotid stenosis > or = 70% were analyzed by immunohistochemistry and cDNA microarray to identify gene expression patterns that may determine plaque susceptibility or resistance to apoptosis. Immunohistochemistry showed expression of active caspase 3, an effector of apoptosis, in macrophages and lymphocytes surrounding the lipid core, in smooth muscle cells in the fibrous cap, and media of primary plaques as well as in occasional smooth muscle cells in the recurrent lesion. Among the genes demonstrating increased expression in primary plaques were IGFR2, DR4, DAPK1, Bak, and ERK 1 and 2 and those showing decreased expression included the TNF receptors 1 and 2, akt1, and IGFBP3. When comparing the recurrent lesion to the normal tissue, the expression of 13 genes was decreased by 3-fold, including IGFBP2 and IGFBP3, and none were increased by more than 1.5-fold. The analysis of gene expression patterns in primary and recurrent stenotic lesions provides a powerful approach to identify the signaling pathways that alter cellular apoptotic patterns in such lesions.

Proteomic analysis of S-nitrosylated proteins in mesangial cells

NO participates in numerous biological events in a variety of cell types including activated glomerular mesangial cells. Many of these events appear to be independent of the known effects of NO on soluble guanylyl cyclase. NO derived from all major isoforms of NO synthase can S-nitrosylate cysteine residues in target proteins, potentially altering their functional activities. Recent evidence suggests that S-nitrosylation is specific, is regulated, and may play an important regulatory role akin to phosphorylation. In the present study, the "biotin-switch" method of isolating S-nitrosylated proteins was coupled with two-dimensional PAGE protein separation followed by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and peptide mass fingerprinting to identify target proteins for S-nitrosylation in murine mesangial cells treated with NO donors or appropriate controls. This approach resolved 790 protein spots. We analyzed the most abundant spots and identified 34 known proteins. Of these, 31 are unique S-nitrosylated proteins not previously identified, including signaling proteins, receptors and membrane proteins, cytoskeletal or cell matrix proteins, and cytoplasmic proteins. Prominent among these were peroxisome proliferator activated receptor gamma, uroguanylin, GTP-binding protein alpha, protein 14-3-3, NADPH-cytochrome P450 oxidoreductase, transcription factor IIA, melusin, mitosin, phospholipase A2-activating protein, and protein-tyrosine phosphatase. The in vivo induction of S-nitrosylation was assayed by treating mesangial cells with interleukin-1beta followed by the biotin-switch and Western blot of selected targets. These results broaden our knowledge of potential signal transduction pathways and other cell functions mediated by NO S-nitrosylation.

TP53 and liver carcinogenesis

Primary hepatocellular carcinoma (HCC) is one of the most common malignancies and has the fourth highest mortality rate worldwide. The major risk factors, including chronic infections with the hepatitis B or C virus, are exposure to dietary aflatoxin B1(AFB1), vinyl chloride, or alcohol consumption. Southern China and sub-Saharan Africa have the highest dietary AFB1 exposure, making it and hepatitis B virus (HBV) the major causes of cancer mortality in these geographic areas. Recent studies have discovered genetic and epigenetic changes involved in the molecular pathogenesis of HCC, including somatic mutations in the p53 tumor suppressor gene (TP53). AFB1 induces typical G:C to T:A transversions at the third base in codon 249 of p53. Chronic active hepatitis B and C (HCV) infection, and further inflammatory and oxyradical disorders including Wilson disease (WD) or hemochromatosis, generate reactive oxygen/nitrogen species that can damage DNA and mutate the p53 gene. The X gene of HBV (HBx) is the most common open reading frame integrated into the host genome in HCC. The integrated HBx is frequently mutated and has a diminished ability to function as a transcriptional cotransactivator and to activate the NF-kappa B pathway. However, the mutant HBx proteins still retain their ability to bind to and abrogate p53-mediated apoptosis. In summary, both viruses and chemicals are implicated in the etiology and molecular pathogenesis of HCC. The resultant molecular changes in the ras and Wnt signal-transduction pathways, and the p53 and Rb tumor suppressor pathways significantly contribute to liver carcinogenesis

Necrosis: a specific form of programmed cell death?

For a long time necrosis was considered as an alternative to programmed cell death, apoptosis. Indeed, necrosis has distinct morphological features and it is accompanied by rapid permeabilization of plasma membrane. However, recent data indicate that, in contrast to necrosis caused by very extreme conditions, there are many examples when this form of cell death may be a normal physiological and regulated (programmed) event. Various stimuli (e.g., cytokines, ischemia, heat, irradiation, pathogens) can cause both apoptosis and necrosis in the same cell population. Furthermore, signaling pathways, such as death receptors, kinase cascades, and mitochondria, participate in both processes, and by modulating these pathways, it is possible to switch between apoptosis and necrosis. Moreover, antiapoptotic mechanisms (e.g., Bcl-2/Bcl-x proteins, heat shock proteins) are equally effective in protection against apoptosis and necrosis. Therefore, necrosis, along with apoptosis, appears to be a specific form of execution phase of programmed cell death, and there are several examples of necrosis during embryogenesis, a normal tissue renewal, and immune response. However, the consequences of necrotic and apoptotic cell death for a whole organism are quite different. In the case of necrosis, cytosolic constituents that spill into extracellular space through damaged plasma membrane may provoke inflammatory response; during apoptosis these products are safely isolated by membranes and then are consumed by macrophages. The inflammatory response caused by necrosis, however, may have obvious adaptive significance (i.e., emergence of a strong immune response) under some pathological conditions (such as cancer and infection). On the other hand, disturbance of a fine balance between necrosis and apoptosis may be a key element in development of some diseases.

IL-4 and interferon gamma regulate expression of inducible nitric oxide synthase in chronic lymphocytic leukemia cells

Chronic lymphocytic leukemia (B-CLL) is characterized by the accumulation of long-lived non-dividing CD5(+) B cells. Nitric oxide (NO) is an important regulator of apoptosis, and the viability of cultured B-CLL cells may be dependent on the autocrine production of nitric oxide by inducible nitric oxide synthase (NOS2). We performed this study to determine whether cytokine factors that prevent spontaneous in vitroapoptosis of B-CLL cells induce B-CLL cell NOS2 enzyme activity. B-CLL cells expressed NOS enzyme activity and NOS2 protein and mRNA. IL-4 and IFN-gamma increased B-CLL cell NOS2 enzyme activity and protein expression during in vitro culture. IFN-gamma, but not IL-4, increased NOS2 mRNA expression in cultured B-CLL cells suggesting that IL-4-mediated changes of NOS2 protein expression occurred at the post-transcriptional level. We were unable to detect increased concentrations of nitrite or nitrate (NO(x)) as surrogate markers of NO production in B-CLL cell cultures treated with IL-4 or IFN-gamma. IL-4 and IFN-gamma diminished NOS inhibitor-induced B-CLL cell death. In summary, we found that B-CLL cells expressed NOS2 and that IL-4 and IFN-gamma increased B-CLL NOS2 expression. Cytokine-mediated expression of NOS2 by B-CLL cells may promote their survival, and therapeutic strategies that target NOS2 or quench NO may be beneficial in patients with B-CLL.

Cyclic GMP-dependent protein kinase regulates the expression of thioredoxin and thioredoxin peroxidase-1 during hormesis in response to oxidative stress-induced apoptosis

Human neuroblastoma cells, SH-SY5Y, contain relatively low levels of thioredoxin (Trx); thus, they serve favorably as a model for studying oxidative stress-induced apoptosis (Andoh, T., Chock, P. B., and Chiueh, C. C. (2001) J. Biol. Chem. 277, 9655-9660). When these neurotrophic cells were subjected to nonlethal 2-h serum deprivation, their neuronal nitric oxide synthase and Trx were up-regulated, and the cells became more tolerant of oxidative stress, indicating that NO may protect cells from serum deprivation-induced apoptosis. Here, the mechanism by which NO exerts its protective effects was investigated. Our results reveal that in SH-SY5Y cells, NO inhibits apoptosis through its ability to activate guanylate cyclase, which in turn activates the cGMP-dependent protein kinase (PKG). The activated PKG is required to protect cells from lipid peroxidation and apoptosis, to inhibit caspase-9 and caspase-3 activation, and to elevate the levels of Trx peroxidase-1 and Trx, which subsequently induces the expression of Bcl-2. Furthermore, active PKG promotes the elevation of c-Jun, phosphorylated MAPK/ERK1/2, and c-Myc, consistent with the notion that PKG enhances the expression of Trx through its c-Myc-, AP-1-, and PEA3-binding motifs. Elevation of Trx and Trx peroxidase-1 and Mn(II)-superoxide dismutase would reduce H(2)O(2) and O(2)(), respectively. Thus, the cytoprotective effect of NO in SH-SY5Y cells appears to proceed via the PKG-mediated pathway, and S-nitrosylation of caspases plays a minimal role.

Nitric oxide-induced cellular stress and p53 activation in chronic inflammation

Free radical-induced cellular stress contributes to cancer during chronic inflammation. Here, we investigated mechanisms of p53 activation by the free radical, NO. NO from donor drugs induced both ataxia-telangiectasia mutated (ATM)- and ataxia-telangiectasia mutated and Rad3-related-dependent p53 posttranslational modifications, leading to an increase in p53 transcriptional targets and a G(2)M cell cycle checkpoint. Such modifications were also identified in cells cocultured with NO-releasing macrophages. In noncancerous colon tissues from patients with ulcerative colitis (a cancer-prone chronic inflammatory disease), inducible NO synthase protein levels were positively correlated with p53 serine 15 phosphorylation levels. Immunostaining of HDM-2 and p21(WAF1) was consistent with transcriptionally active p53. Our study highlights a pivotal role of NO in the induction of cellular stress and the activation of a p53 response pathway during chronic inflammation.

Nitric oxide in liver transplantation: pathobiology and clinical implications

The gaseous molecule nitric oxide is involved in a variety of liver transplant-relevant processes, including ischemia-reperfusion injury, acute cellular rejection, and circulatory changes characteristic of advanced liver disease. This review article focuses on new advances relating to the role of nitric oxide in these syndromes with an emphasis on pathobiology and potential clinical implications.

Redox Regulation of Apoptosis before and after Cytochrome C Release

Programmed cell death, or apoptosis, is one of the most studied areas of modern biology. Apoptosis is a genetically regulated process, which plays an essential role in the development and homeostasis of higher organisms. Mitochondria, known to play a central role in regulating cellular metabolism, was found to be critical for regulating apoptosis induced under both physiological and pathological conditions. Mitochondria are a major source of reactive oxygen species (ROS) but they can also serve as its target during the apoptosis process. Release of apoptogenic factors from mitochondria, the best known of which is cytochrome c, leads to assembly of a large apoptosis-inducing complex called the apoptosome. Cysteine proteases (called caspases) are recruited to this complex and, following their activation by proteolytic cleavage, activate other caspases, which in turn target for specific cleavage a large number of cellular proteins. The redox regulation of apoptosis during and after cytochrome c release is an area of intense investigation. This review summarizes what is known about the biological role of ROS and its targets in apoptosis with an emphasis on its intricate connections to mitochondria and the basic components of cell death.

Increased S-nitrosothiols and S-nitrosoalbumin in cerebrospinal fluid after severe traumatic brain injury in infants and children: indirect association with intracranial pressure

Nitric oxide (NO) is implicated in both secondary damage and recovery after traumatic brain injury (TBI). Transfer of NO groups to cysteine sulfhydryls on proteins produces S-nitrosothiols (RSNO). S-nitrosothiols may be neuroprotective after TBI by nitrosylation of N-methyl-D-aspartate receptor and caspases. S-nitrosothiols release NO on decomposition for which endogenous reductants (i.e., ascorbate) are essential, and ascorbate is depleted in cerebrospinal fluid (CSF) after pediatric TBI. This study examined the presence and decomposition of RSNO in CSF and the association between CSF RSNO level and physiologic parameters after severe TBI. Cerebrospinal fluid samples (n = 72) were obtained from 18 infants and children on days 1 to 3 after severe TBI (Glasgow Coma Scale score < 8) and 18 controls. Cerebrospinal fluid RSNO levels assessed by fluorometric assay peaked on day 3 versus control (1.42 +/- 0.11 micromol/L vs. 0.86 +/- 0.04, P< 0.05). S-nitrosoalbumin levels were also higher after TBI (n = 8, 0.99 +/- 0.09 micromol/L on day 3 vs. n = 6, 0.42 +/- 0.02 in controls, P< 0.05). S-nitrosoalbumin decomposition was decreased after TBI. Multivariate analysis showed an inverse relation between CSF RSNO and intracranial pressure and a direct relation with barbiturate treatment. Using a novel assay, the presence of RSNO and S-nitrosoalbumin in human CSF, an approximately 1.7-fold increase after TBI, and an association with low intracranial pressure are reported, supporting a possible neuroprotective role for RSNO. The increase in RSNO may result from increased NO production and/or decreased RSNO decomposition.

Liver protection from apoptosis requires both blockage of initiator caspase activities and inhibition of ASK1/JNK pathway via glutathione S-transferase regulation

Hepatoprotection mediated by free radical scavenging molecules such as dimethyl sulfoxide (Me(2)SO) arose the question as to whether this effect involved one or several anti-apoptotic signals. Here, using primary cultures of rat hepatocytes and in vivo thioacetamide-induced liver failure, we showed that Me(2)SO failed to prevent any cleavage of initiator caspase-8 and -9 but constantly inhibited procaspase-3 maturation and apoptosis execution, pointing to an efficient inhibition of cleaved initiator caspase activities. Evidence was recently provided that apoptosis might require both caspase and ASK1/JNK-p38 activities. We demonstrated that this kinase pathway was strongly inhibited in the presence of Me(2)SO whereas overexpression of ASK1 was able to restore caspase-3 activity and apoptosis. Interestingly, we also found that GST M1/2 and GST Alpha1/2 dropped under apoptotic conditions; furthermore transfection of GST M1, A1, or P1 to cells overexpressing ASK1, abolished caspase-3 activity and restored viability. This role of GSTs was further assessed by showing that their high expression level was tightly associated with inhibition of ASK1 activity in Me(2)SO-protected hepatocytes. Together, these results demonstrate that Me(2)SO-mediated hepatoprotection involves a dual inhibition of cleaved initiator caspase and ASK1/JNK-p38 activities. Furthermore, in highlighting the control of apoptosis by GSTs, these data provide new insights for analyzing the complex mechanisms of hepatoprotection.

Spatial redox regulation of a critical cysteine residue of NF-kappa B in vivo

Reduction-oxidation (redox) regulation has been implicated in the activation of the transcription factor NF-kappaB. However, the significance and mechanism of the redox regulation remain elusive, mainly due to the technical limitations caused by rapid proton transfer in redox reactions and by the presence of many redox molecules within cells. Here we establish versatile methods for measuring redox states of proteins and their individual cysteine residues in vitro and in vivo, involving thiol-modifying reagents and LC-MS analysis. Using these methods, we demonstrate that the redox state of NF-kappaB is spatially regulated by its subcellular localization. While the p65 subunit and most cysteine residues of the p50 subunit are reduced similarly in the cytoplasm and in the nucleus, Cys-62 of p50 is highly oxidized in the cytoplasm and strongly reduced in the nucleus. The reduced form of Cys-62 is essential for the DNA binding activity of NF-kappaB. Several lines of evidence suggest that the redox factor Ref-1 is involved in Cys-62 reduction in the nucleus. We propose that the Ref-1-dependent reduction of p50 in the nucleus is a necessary step for NF-kappaB activation. This study also provides the first example of a drug that inhibits the redox reaction between two specific proteins.

S-nitrosylation of dimethylarginine dimethylaminohydrolase regulates enzyme activity: further interactions between nitric oxide synthase and dimethylarginine dimethylaminohydrolase

The enzyme dimethylarginine dimethylaminohydrolase (DDAH) hydrolyses asymmetrically methylated arginine residues that are endogenously produced inhibitors of nitric oxide synthases (NOS). We and others have proposed that DDAH activity is a key determinant of intracellular methylarginine concentrations and that factors that regulate the activity of DDAH may modulate nitric oxide (NO) production in vivo. We recently solved the crystal structure of a bacterial DDAH and identified a Cys-His-Glu catalytic triad [Murray-Rust, J., Leiper, J. M., McAlister, M., Phelan, J., Tilley, S., Santa Maria, J., Vallance, P. & McDonald, N. (2001) Nat. Struct. Biol. 8, 679-683]. The presence of a reactive cysteine residue (Cys-249) in the active site of DDAH raised the possibility that DDAH activity might be directly regulated by S-nitrosylation of this residue by NO. In the present study, we demonstrate that recombinant DDAH is reversibly inhibited after incubation with NO donors in vitro. Similarly mammalian DDAH in cytosolic extracts is also reversibly inhibited by NO donors. In cultured endothelial cells, heterologously expressed human DDAH II was S-nitrosylated after cytokine induced expression of the inducible NOS isoforms. The implication of these findings is that under certain conditions when NO generation increases, S-nitrosylation diminishes DDAH activity and this would be expected to lead to accumulation of asymmetric dimethylarginine and inhibition of NOS. This observation may help explain why expression of iNOS often leads to inhibition of activity of constitutively expressed NOS isozymes. We also identify Cys-His-Glu as a nitrosylation motif that is conserved in a family of arginine handling enzymes.

S-nitrosothiols inhibit cytokine-mediated induction of matrix metalloproteinase-9 in airway epithelial cells

Inflammatory lung diseases are associated with increased production of matrix metalloproteinase-9 (MMP-9) from infiltrating granulocytes or from the respiratory epithelium, and inappropriate expression and activation of MMP-9 may be associated with tissue injury and airway remodeling. Inflammatory conditions also result in increased expression of inducible nitric oxide synthase (iNOS), and nitric oxide (NO(.)) has been reported to have variable effects on MMP-9 gene expression and activation in various cell types. We investigated the involvement of NO(.) or its metabolites on MMP-9 expression in human bronchial and alveolar epithelial cells by studying effects of NOS inhibition or exogenous NO(.) donors on cytokine-induced MMP-9 expression. Although inhibition of NOS, transfection with iNOS, or addition of NO(.) donors did not affect MMP-9 induction by inflammatory cytokines, addition of S-nitrosothiols dramatically inhibited MMP-9 expression, which was potentiated by depletion of cellular GSH. Cytokine-induced MMP-9 expression involves the activation of the transcription factor NF-kappaB, and S-nitrosothiols, in contrast to NO(.), were found to inhibit cytokine-induced nuclear translocation and DNA binding of NF-kappaB. The inhibitory effects of S-nitrosothiols on cytokine-induced lung epithelial MMP-9 expression illustrate an additional mechanism by which nitrosative stress may affect epithelial injury and repair processes during conditions of airway inflammation.

Immunity to cancer: attack and escape in T lymphocyte-tumor cell interaction

Tumor cells may express antigens which are recognized in a form of HLA/peptide complexes by T cells. The frequency at which different antigens are seen by T cells of melanoma patients and healthy donors was evaluated by human leukocyte antigen (HLA)/peptide tetramer technology which stains T cells bearing the specific receptor for a given epitope. By this technique, it was found that the majority of metastatic melanoma patients can recognize differentiation antigens (particularly Melan-A/MART-1), whereas such a recognition is scanty in the early phase of the disease and in healthy subjects. Despite the presence of melanoma-specific T cells infiltrating tumor lesions, tumor rejection rarely occurs. Among the different mechanisms of such inefficient antitumor response, this review discusses the possible anti-T-cell counterattack mediated by FasL-positive tumor cells, and shows that FasL is located in the cytoplasm of melanoma cells and is transported in the tumor microenvironment through the release of melanosomes. Additionally, mechanisms of suboptimal T cell activation through tumor cell expression of peptide analogs with antagonist activity are described, together with the possibility of overcoming such anergy induction by the usage of optimized tumor epitopes. Down-modulation of HLA expression by target tumor cells and its multiple mechanisms is also considered. Finally, we discuss the role of inducible nitric oxide synthases in determining the inhibition of apoptosis in melanoma cells, which can make such tumor cells resistant to the T-cell attack.

Peptides in apoptosis research

Apoptosis is a complex process that plays a central role in physiological and pathological cell death. This fast evolving research area has experienced incredible development in the past few years. Progress in the knowledge of the structure of many of the main molecular actors of the apoptotic signal transduction pathways has driven the design of synthetic peptides that in some cases can function as simplified versions of their parent proteins. These molecules are contributing to a better understanding of the activity and regulation of apoptotic proteins and also are setting the basis for the discovery of effective drugs to combat important diseases related to apoptosis. Most applications of peptides in apoptosis research are so far related to caspases, caspase regulatory proteins, such as LAPs and Smac, and proteins of the Bcl-2 family. Additionally, important perspectives are open to other systems, such as the macromolecular assemblies that are responsible for the activation of initiator caspases.

NCX-4016, a nitric oxide-releasing aspirin, protects endothelial cells against apoptosis by modulating mitochondrial function

We investigated the effect of a nitric oxide (NO)-releasing derivative of aspirin (NCX-4016) on a mitochondria-dependent model of apoptosis in human umbilical endothelial cells (HUVEC). Exposure of HUVEC to staurosporine caused a progressive fall in mitochondrial membrane potential (DeltaPsi(m)) and apoptosis. Exposure to an NO donor, (z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO), caused an early (1-3h) hyperpolarization of DeltaPsi(m) and reduction of apoptosis that was followed (at 4-8 h) by an accelerated collapse of DeltaPsi(m) and cell death. In contrast, treatment with NCX-4016, but not with aspirin or a non-NO-releasing analogue of NCX-4016, protected HUVEC against the apoptotic actions of staurosporine for up to 8 h. Confocal microscopy demonstrated that although NCX-4016 released NO in subcellular compartments, DETA-NO caused a generalized increase in cytosolic fluorescence. Exposure to DETA-NO resulted in a rapid and profound inhibition of cell respiration (78.3 +/- 6.4%), whereas NCX-4016 caused a less pronounced reduction in oxygen consumption (43.5 +/- 5.3%). Staurosporine caused a time-dependent activation of proapoptotic caspases. NCX-4016 prevented this activation, whereas DETA-NO failed to inhibit caspase activity. In contrast to DETA-NO, NCX-4016 did not increase mitochondrial oxidative stress. These data demonstrated that NCX-4016 conveys NO directly inside endothelial cells and modulates mitochondrial function.

Cholangiocarcinoma: recent progress. Part 2: molecular pathology and treatment

Part 2 of this review discusses DNA damage in biliary epithelial cells in the development of cholangiocarcinoma, alterations in cell kinetics of biliary epithelial cells, biliary epithelial mitoinhibition, and apoptosis that includes the role of Bcl-2, transforming growth factor-beta, telomerase activities and deregulation of Ras and p53, cancer-associated antigens in cholangiocarcinoma, precancerous lesions, stroma formation and angiogenesis, cancer invasion, cell-cell and cell-matrix interactions, and the mechanism of evasion from immune surveillance. These discussions are followed briefly by treatments such as photodynamic therapy, and surgical approaches comparing resection and liver transplantation.

Redox regulatory and anti-apoptotic functions of thioredoxin depend on S-nitrosylation at cysteine 69

Thioredoxin 1 (Trx) is a known redox regulator that is implicated in the redox control of cell growth and apoptosis inhibition. Here we show that Trx is essential for maintaining the content of S-nitrosylated molecules in endothelial cells. Trx itself is S-nitrosylated at cysteine 69 under basal conditions, and this S-nitrosylation is required for scavenging reactive oxygen species and for preserving the redox regulatory activity of Trx. S-nitrosylation of Trx also contributes to the anti-apoptotic function of Trx. Thus, Trx can exert its complete redox regulatory and anti-apoptotic functions in endothelial cells only when cysteine 69 is S-nitrosylated.

Nitrosative stress-induced apoptosis through inhibition of NF-kappa B

Nitrosative stress produced by cytokines predisposes to apoptotic cell death. However, the molecular mechanism by which this occurs is not well understood. We have shown previously that nitric oxide (NO) regulates the activity of the anti-apoptotic transcription factor NF-kappaB. Here we demonstrate that the inhibition of NF-kappaB by NO sensitizes A549 and Jurkat T cells to tumor necrosis factor-alpha (TNFalpha)-induced apoptosis. The molecular basis of NF-kappaB inhibition is different in the two cell types. In A549 cells, NO functions at the nuclear level to inhibit NF-kappaB by S-nitrosylation. In Jurkat cells, NO inhibits the NF-kappaB activating pathway in the cytoplasm at a step proximal to the degradation of IkappaBalpha. The inhibition of NF-kappaB is reflected in the level of intracellular S-nitrosothiols, which are constitutively metabolized. These data suggest that NO can influence cell death by modulating NF-kappaB activity with the sites of inhibition being cell type-specific. The data also show that NO bioactivity regulates tumor necrosis factor-alpha signaling.

Inactivation of annexin II tetramer by S-nitrosoglutathione

We investigated the effect of nitric oxide (NO) donors on the activities of annexin II tetramer (AIIt), a member of the Ca2+- dependent phospholipid-binding protein family. Incubation of purified AIIt with S-nitrosoglutathione (GSNO) led to the inhibition of AIIt-mediated liposome aggregation. This effect was dose-dependent with an IC50 of approximately 100 micro m. Sodium nitroprusside, another NO donor also inhibited AIIt-mediated liposome aggregation, whereas reduced glutathione, nitrate, or nitrite had no effects. GSNO also inhibited AIIt-mediated membrane fusion, but not the binding of AIIt to the membrane. GSNO only has a modest effect on liposome aggregation mediated by annexins I, III or IV. The binding of AIIt to the membrane protected the reactive sites of GSNO on AIIt. GSNO did not inhibit AIIt-mediated liposome aggregation in the presence of dithiothreitol. Taken together, our results suggest that GSNO inactivates AIIt possibly via S-nitrosylation and/or the formation of disulfide bonds.

Regulation of heme oxygenase-1 by redox signals involving nitric oxide

Heme oxygenase-1 (HO-1) is an inducible stress protein the expression of which can be markedly augmented in eukaryotes by a wide range of substances that cause a transient change in the cellular redox state. The importance of this protein in physiology and disease is underlined by the versatility of HO-1 inducers and the functional role attributed to HO-1 products (carbon monoxide and bilirubin) in conditions that are associated with moderate or severe cellular stress. An intriguing aspect is the recent evidence showing that nitric oxide, a ubiquitous signaling molecule, finely modulates the activation of HO-1 expression. As the effects of oxidative stress on the regulation of the HO-1 gene have been well established and characterized, this review will focus on the biological relevance of redox signals involving nitric oxide and reactive nitrogen species that lead to up-regulation of the HO-1 pathway, with particular emphasis on vascular tissues and the cardiovascular system.

Regulation of mammalian liver methionine adenosyltransferase

S-adenosylmethionine (SAM) is an essential metabolite in all cells. SAM is the most important biological methyl group donor and is a precursor in the synthesis of polyamines. Methionine adenosyltransferase (MAT; EC 2.5.1.6) catalyzes the only known SAM biosynthetic reaction from methionine and ATP. In mammalian tissues, three different forms of MAT (MAT I, MAT III and MAT II) have been identified that are the product of two different genes (MAT1A and MAT2A). Although MAT2A is expressed in all mammalian tissues, the expression of MAT1A is primarily restricted to adult liver. In mammals, up to 85% of all methylation reactions and as much as 48% of methionine metabolism occurs in the liver, which indicates the important role of this organ in the regulation of blood methionine. Recent evidence indicates that not only is SAM the main biological methyl group donor and an intermediate metabolite in methionine catabolism, but it is also an intracellular control switch that regulates essential hepatic functions such as liver regeneration and differentiation as well as the sensitivity of this organ to injury. Therefore, knowledge of factors that regulate the activity of MAT I/III, the specific liver enzyme, is essential to understand how cellular SAM levels are controlled.

Regulation and measurement of oxidative stress in apoptosis

Cells are constantly generating reactive oxygen species (ROS) during aerobic metabolism. As a consequence, each cell is equipped with an extensive antioxidant defence system to combat excessive production of ROS. Oxidative stress occurs in cells when the generation of ROS overwhelms the cell's natural antioxidant defences. There is a growing consensus that oxidative stress and the redox state of a cell plays a pivotal role in regulating apoptosis, a tightly controlled form of cell death in which a cell partakes in its own demise. More recently, a role for reactive nitrogen species (RNI) as both positive and negative regulators of cell death has been established. This review describes the major sources of ROS and RNI in a cell, the control of cell death by these species and the role of antioxidants as regulators of oxidative stress and apoptosis. Finally, the various methods that can be employed in establishing a role for both ROS and RNI in apoptosis will be discussed with particular emphasis on their intracellular detection.

Heterogeneous susceptibility to spontaneous and induced apoptosis characterizes two related transplantable melanomas with different biological properties

A family of phenotypically and biologically different transplantable hamster melanomas was derived from a single tumor more than 40 yr ago. In this work, we were seeking the differences between the abilities of the cells from two biologically heterogeneous (melanotic and amelanotic) members of this family to undergo spontaneous or camptothecin-induced apoptosis. We studied these differences by looking at three important features of the apoptotic process, i.e. binding of annexin V, DNA fragmentation and caspase-3 activity. Of these, annexin binding and DNA fragmentation were more pronounced in the parental, melanotic line while the activity of caspase-3 was stronger in the amelanotic tumor cells. We concluded that a spontaneous alteration of the original, melanotic melanoma line into an amelanotic one, associated with more aggressive tumor progression, was accompanied by significant decrease in ability to undergo spontaneous and camptothecin-induced apoptosis, and that apoptosis of these two cell types may not depend on the activity of caspase-3.

Thioredoxin-related regulation of NO/NOS activities

The role of regulation of nitric oxide synthase (NOS) activity in mitigating oxidative stress in neonatal lungs and contributing to pulmonary vasodilation at birth is still unclear. Furthermore, it is known that, depending on interactions between the individual components of the mitogen-activated protein kinase (MAPK) signaling cascades, many biological consequences, including apoptosis, are initiated. Although the importance of nitric oxide (NO) in apoptosis is controversial and likely depends on NO concentrations and cell types, this highly reactive free radical can activate the p38 MAPK signal cascade. Recent studies have suggested that thioredoxin may play an important role as an effector for some of these functions. Thioredoxin is a major redox protein for many enzymes/transcription factors and is involved in cellular functions, such as viability, activation, and proliferation. In addition to its redox regulation, thioredoxin binds directly to the apoptosis signal-regulating kinase 1 (ASK1), thus inhibiting the activation of stress-induced MAPK signaling cascades that lead to apoptosis. Furthermore, NO produced from newly induced neuronal NOS was reported to induce expression of thioredoxin and several other genes for preconditioning-induced neuroprotection. Moreover, although exposure of endothelial cells to NO decreases NOS activity, this inhibition was shown to be reversed by thioredoxin. Finally, the correlation of expression of thioredoxin with endothelial NOS activity seems to suggest an important role played by this protein in perinatal changes of pulmonary artery functions. Therefore, thioredoxin may participate in the regulation of NOS activity and be involved in NO functions via multiple mechanisms.

Regulation of caspases by nitric oxide

Nitric oxide can prevent or induce apoptosis depending on its concentration, cell type, and the oxidative milieu. Nitric oxide inhibits apoptosis and inflammation by S-nitrosylation of the active site cysteine of caspases, the central effector molecules of cell death as well as maturation of IL-1beta and IL-18. The ability of nitric oxide to S-nitrosylate caspases depends on multiple factors including the presence of free iron and intracellular redox potential. There are no known direct effects of nitric oxide on promoting caspase activation or activity. However, nitric oxide has been shown to promote apoptotic pathways in numerous cell types through the indirect activation of caspases. In this article we review the relationship of nitric oxide and caspase activity, modulation of this effect by iron, and clinical implications for the use of nitric oxide in regulating inflammation and apoptosis.

NO sensitizes rat hepatocytes to proliferation by modifying S-adenosylmethionine levels

BACKGROUND & AIMS

Liver regeneration is a fundamental response of this organ to injury. Hepatocyte proliferation is triggered by growth factors, such as hepatocyte growth factor. However, hepatocytes need to be primed to react to mitogenic signals. It is known that nitrous oxide (NO), generated after partial hepatectomy, plays an important role in hepatocyte growth. Nevertheless, the molecular mechanisms behind this priming event are not completely known. S-adenosylmethionine (AdoMet) synthesis by methionine adenosyltransferase is the first step in methionine metabolism, and NO regulates hepatocyte S-adenosylmethionine levels through specific inhibition of this enzyme. We have studied the modulation of hepatocyte growth factor-induced proliferation by NO through the regulation of S-adenosylmethionine levels.

METHODS

Studies were conducted in cultured rat hepatocytes isolated by collagenase perfusion, which triggers NO synthesis.

RESULTS

The mitogenic response to hepatocyte growth factor was blunted when inducible NO synthase was inhibited; this process was overcome by the addition of an NO donor. This effect was dependent on methionine concentration in culture medium and intracellular S-adenosylmethionine levels. Accordingly, we found that S-adenosylmethionine inhibits hepatocyte growth factor-induced cyclin D1 and D2 expression, activator protein 1 induction, and hepatocyte proliferation.

CONCLUSIONS

Together our findings indicate that NO may switch hepatocytes into a hepatocyte growth factor-responsive state through the down-regulation of S-adenosylmethionine levels.

Selective delivery of nitric oxide to a cellular target: a pseudosubstrate-coupled dinitrosyl-iron complex inhibits the enteroviral protease 2A

Nitric oxide (NO) regulates multiple biological processes. To use NO as a potential therapeutic substance, a more selective modulation of individual NO targets is desirable. Here, we tested whether peptide conjugation of the dinitrosyl-iron complex (DNIC), a potent NO donor, confers targeted NO delivery. As target, we used the protease 2A of Coxsackie-B-viruses (2A(pro)), which can cause dilated cardiomyopathy. Through S-nitrosylation, NO inhibits this protease, which is essential for viral replication. The tetrapeptide Leu-Ser-Thr-Cys (LSTC) (based on the 2A(pro) substrate recognition motif) and DNIC generated LSTC-DNIC in vitro by S-nitrosylation as evidenced by reverse-phase chromatography. In vitro, LSTC-DNIC (IC(50) 510 nM) dose-dependently inhibited purified 2A(pro) 4.7-fold more effectively than DNIC (IC(50) 2.4 microM), whereas LSTC alone had no effect. In intact cells, expression of Coxsackievirus protease 2A by transient transfection led to eIF4G-I-cleavage. LSTC-DNIC (IC(50) 23 microM) dose-dependently inhibited eIF4G cleavage in 2A(pro)-transfected cells 3.8-fold more effectively than DNIC (IC(50) 88 microM). To test the specificity of the DNIC-conjugated LSTC peptide part, we investigated its influence on Caspase-3, a known target for S-nitrosylation. LSTC-DNIC and DNIC inhibited purified Caspase-3 in vitro (IC(50) 3.7 microM) and in intact cells similarly. LSTC conjugation of DNIC enhances its fidelity for inhibition of 2A(pro) in vitro and intracellularly. Peptide-DNIC may be useful to selectively modulate cellular processes by NO, i.e., to enhance its antiviral properties.

Inhibition of inducible NO synthase by TH2 cytokines and TGF beta in rheumatoid arthritic synoviocytes: effects on nitrosothiol production

The aim of this study was to compare the effects on NO production of IL-4, IL-10, and IL-13 with those of TGF-beta. RA synovial cells were stimulated for 24 h with IL-1 beta (1 ng/ml), TNF-alpha (500 pg/ml), IFN-gamma (10(-4)IU/ml) alone or in combination. Nitrite was determined by the Griess reaction, S-nitrosothiols by fluorescence, and inducible NO synthase (iNOS) by immunofluorescence and fluorescence activated cell sorter analysis (FACS). In other experiments, IL-4, IL-10, IL-13, and TGF beta were used at various concentrations and were added in combination with proinflammatory cytokines. The addition of IL-1 beta, TNF-alpha, and IFN-gamma together increased nitrite production: 257.5 +/- 35.8 % and S-nitrosothiol production : 413 +/- 29%, P < 0.001. None of these cytokines added alone had any significant effect. iNOS synthesis increased with NO production. IL-4, IL-10, IL-13, and TGF beta strongly decreased the NO production caused by the combination of IL-1 beta, TNF-alpha, and IFN-gamma. These results demonstrate that stimulated RA synoviocytes produce S-nitrosothiols, bioactive NO* compounds, in similar quantities to nitrite. IL-4, IL-10, IL-13, and TGF-beta decrease NO production by RA synovial cells. The anti-inflammatory properties of these cytokines may thus be due at least in part to their effect on NO metabolism.

Interaction with substrate sensitises caspase-3 to inactivation by hydrogen peroxide

Caspases have an active site cysteine whose oxidation blocks catalytic activity. Caspase activity, measured in lysates of apoptotic cells, was inhibited by H2O2 with an IC50 of 7 microM. Recombinant caspase-3 was directly inhibited by H2O2, with an estimated second-order rate constant of 750 M-1 s-1. These values were determined when H2O2 was added while the caspases were cleaving a peptide substrate. There was a 40-fold decrease in sensitivity to inactivation if the substrate was absent at the time of H2O2 addition. These results rationalise conflicting reports of the sensitivity of caspase-3 to H2O2, and identify a novel mechanism for sensitising a thiol enzyme to oxidative inactivation.

P53-responsive genes and the potential for cancer diagnostics and therapeutics development

P53 protein regulates cell responses to DNA damage to keep genomic stability by transactivation and trans-repression of its downstream target genes. P53 protein also has activators, inactivators, or co-factors via interaction with other proteins. Both the p53-regulated genes and interacted proteins form a huge network. As tumors usually escape from proliferating controls by means of accumulation of genetic alterations, p53 is one of the most important tumor suppressor genes that can be targeted for diagnosis, prognosis, and therapeutic intervention. Reviewing the p53-network is of great importance. In this review, we are focusing on cancer-related p53 downstream-regulated genes. Various methods dealing with the discovery of p53-regulated genes by the detection of gene expression have been applied. Recently high throughput functional genomics methods, such as DNA microarray, serial analysis of gene expression (SAGE), differential display, and protein two-dimensional gel electrophoresis, have provided a wealth of information on the dynamics of cell context responses. Hundreds of genes have been discovered whose transcriptions are regulated by p53 protein. They were grouped, based on their functions, into sub-classes including cell-cycle regulation, DNA repair, angiogenesis, metastasis, and multidrug resistance. P53 plays a pivotal role in keeping genomic stability and tumor suppression. The deeper we investigate the cell responses as mediated by p53, the more complex p53-network becomes. However, understanding p53-network, offers great opportunities to develop more sensitive and accurate diagnostic/prognostic tools, as well as more efficient therapies for cancer.

The biochemistry and physiology of S-nitrosothiols

S-nitrosothiols are biological metabolites of nitric oxide. It has often been suggested that they represent a more stable metabolite of nitric oxide that can either be stored, or transported, although the evidence for this is sparse. There are many unanswered questions concerning how S-nitrosothiols are formed, how they are metabolized and how they elicit biological responses. These questions are highlighted by the fact that the known chemistry of nitric oxide, thiols, and S-nitrosothiols cannot serve to explain their proposed biological activities. This review attempts to highlight the gulf between our chemical understanding of S-nitrosothiols and the proposed biological activities of these compounds with respect to guanylyl cyclase-independent nitric oxide bioactivity and also the control of vascular tone.

Basal and stimulated protein S-nitrosylation in multiple cell types and tissues

There is substantial evidence that protein S-nitrosylation provides a significant route through which nitric oxide (NO)-derived bioactivity is conveyed. However, most examples of S-nitrosylation have been characterized on the basis of analysis in vitro, and relatively little progress has been made in assessing the participant forms of nitric-oxide synthase (NOS) or the dynamics of protein S-nitrosylation in situ. Here we utilize antibodies specific for the nitrosothiol (SNO) moiety to provide an immunohistochemical demonstration that protein S-nitrosylation is coupled to the activity of each of the major forms of NOS. In cultured endothelial cells, SNO-protein immunoreactivity increases in response to Ca(2+)-stimulated endothelial NOS (eNOS) activity, and in aortic rings, endothelium-derived and eNOS-mediated relaxation (EDRF) is coupled to increased protein S-nitrosylation in both endothelial and associated smooth muscle cells. In cultured macrophages, SNO-protein levels increase upon cytokine induction of induced NOS (iNOS), and in PC12 cells, increased protein S-nitrosylation is linked to nerve growth factor induction of neuronal NOS (nNOS). In addition, we describe developmental and pathophysiological increases in SNO-protein immunoreactivity within human lung. These results, which demonstrate Ca(2+), neurohumoral, growth factor, cytokine, and developmental regulation of protein S-nitrosylation that is coupled to NOS expression and activity, provide unique evidence for the proposition that this ubiquitous NO-derived post-translational protein modification serves as a major effector of NO-related bioactivity.

Nitric oxide and cell signaling pathways in mitochondrial-dependent apoptosis

Nitric oxide, generated by endogenous nitric oxide synthases or nitric oxide donors, can promote or prevent apoptosis induced by diverse pro-apoptotic stimuli in cell culture models. Both mitochondrial-dependent and -independent apoptotic signaling pathways mediate this dichotomous cellular response to nitric oxide. The molecular mechanisms behind these effects are complex and involve a number of nitrogen oxide-related species that are more reactive than nitric oxide itself. The local cellular environment plays a dynamic role in determining the nature and concentration of these species. Important components of the microenvironment include: the cellular redox state, glutathione, transition metals and the presence of other oxygen- and nitrogen-centered radicals. In particular, redox-sensitive nitrosating species are favorably generated under physiological conditions and capable of modifying multiple cell signaling pathways through reversible S-nitrosation reactions. Cytochrome c release from mitochondria is an important mechanism for the activation of caspase-3 and the initiation of cell death in response to 'intrinsic' pro-apoptotic stimuli, including oxidative and nitrosative stress. In turn, caspases and mitogen associated protein kinases may modulate cytochrome c release through their effects on the Bcl-2 family of proteins. This review will focus on (i) the importance of the cellular environment in determining the fate of nitric oxide and (ii) the ability of S-nitrosation to regulate mitochondrial-dependent apoptosis at the level of mitochondrial bioenergetics, cytochrome c release, caspases, mitogen associated protein kinases, and the Bcl-2 family of proteins.

Nitric oxide modulates branching morphogenesis in fetal rat lung explants

Cells of the developing lung express the constitutive nitric oxide synthases (NOSs) I and III. The developmental importance of these enzymes is largely unknown, although a role for nitric oxide (NO) in the regulation of pulmonary blood flow at birth is established. Known effects of NO on transcription factors, apoptosis, and cellular proliferation, plus the time and spatial limits of pulmonary NOS expression, suggest that NO might influence lung development. We tested the potential of NO to modulate lung branching morphogenesis by exposing lung explants from gestational day 13 rat fetuses to varying doses of several NO donors (NONO-ate). We counted the number of airway branches that were added between the first and 72nd h of culture. NO released only from a NONO-ate with a long half-life [(Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]-diazen-1-ium-1,2-diolate-NO], increased branching in ambient O(2) by twofold. The NO effect was not mimicked with a cyclic guanine monophosphate analog; nonspecific NOS inhibitors in millimolar concentrations inhibited branching. We conclude that endogenous and exogenous NO can modulate branching morphogenesis in the rat lung.

Calpain activation after mitochondrial permeability transition in microcystin-induced cell death in rat hepatocytes

Previous studies have shown that microcystin-LR (MLR), a specific hepatotoxin, induces onset of mitochondrial permeability transition (MPT) and apoptosis in cultured rat hepatocytes. Here we attempted to investigate the downstream events after the onset of MPT in MLR-treated hepatocytes. Various mitochondrial electron transport chain (ETC) inhibitors effectively prevented the onset of MPT, suggesting that the mitochondrial ETC plays an important role in MLR-induced MPT. MLR also induced mitochondrial cytochrome c release, which can be prevented by a specific MPT inhibitor (cyclosporin A, CsA), and by various ETC inhibitors. Interestingly, the release of cytochrome c did not activate caspase-9 and -3, the main caspases involved in apoptosis. Instead, MLR activated calpain in rat hepatocytes, probably through the increase of intracellular Ca(2+) released from mitochondria. Both ALLN and ALLM, two calpain inhibitors, significantly blocked MLR-induced calpain activation and subsequent cell death. CsA also prevented MLR-induced calpain activation and cell death, suggesting that the activation of calpain may be a post-mitochondrial event. These data demonstrate for the first time that calpain rather than caspases plays an important role in MLR-induced apoptosis.

Characterization of fortilin, a novel antiapoptotic protein

Apoptosis is meticulously controlled in living organisms. Its dysregulation has been shown to play a key role in a number of human diseases, including neoplastic, cardiovascular, and degenerative disorders. Bcl-2 family member proteins and inhibitors of apoptosis proteins are two major negative regulators of apoptosis. We report here the characterization of novel antiapoptotic protein, fortilin, which we identified through yeast two-hybrid library screening. Sequence analysis of fortilin revealed it to be a 172-amino acid polypeptide highly conserved from mammals to plants. Fortilin is structurally unrelated to either Bcl-2 family member proteins or inhibitors of apoptosis proteins. Northern blot analysis showed the fortilin message to be ubiquitous in normal tissue but especially abundant in the liver, kidney, and small intestine. Western blot analysis using anti-fortilin antibody showed more extensive expression in cancerous cell lines (H1299, MCF-7, and A549) than in cell lines derived from normal tissue (HEK293). Immunocytochemistry using HeLa cells transiently expressing FLAG-tagged fortilin and immunohistochemistry using human breast ductal carcinoma tissue and anti-fortilin antibody both showed that fortilin is predominantly localized in the nucleus. Functionally, the transient overexpression of fortilin in HeLa cells prevented them, in a dose-dependent fashion, from undergoing etoposide-induced apoptosis. Consistently, U2OS cells stably expressing fortilin protected the cells from cell death induced by etoposide over various concentrations and durations of exposure. In addition, fortilin overexpression inhibited caspase-3-like activity as assessed by the cleavage of fluorogenic substrate benzyloxycarbonyl-DEVD-7-amido-4-(trifluoromethyl)coumarin. Furthermore, the antisense depletion of fortilin from breast cancer cell line MCF-7 was associated with massive cell death. These data suggest that fortilin represents a novel antiapoptotic protein involved in cell survival and apoptosis regulation.