S-nitrosylation: physiological regulation of NF-kappaB

Sepiapterin ameliorates chemically induced murine colitis and azoxymethane-induced colon cancer

The effects of modulating tetrahydrobiopterin (BH4) levels with a metabolic precursor, sepiapterin (SP), on dextran sodium sulfate (DSS)-induced colitis and azoxymethane (AOM)-induced colorectal cancer were studied. SP in the drinking water blocks DSS-induced colitis measured as decreased disease activity index (DAI), morphologic criteria, and recovery of Ca(2+)-induced contractility responses lost as a consequence of DSS treatment. SP reduces inflammatory responses measured as the decreased number of infiltrating inflammatory macrophages and neutrophils and decreased expression of proinflammatory cytokines interleukin 1β (IL-1β), IL-6, and IL-17A. High-performance liquid chromatography analyses of colonic BH4 and its oxidized derivative 7,8-dihydrobiopterin (BH2) are inconclusive although there was a trend for lower BH4:BH2 with DSS treatment that was reversed with SP. Reduction of colonic cGMP levels by DSS was reversed with SP by a mechanism sensitive to 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ), a specific inhibitor of the NO-sensitive soluble guanylate cyclase (sGC). ODQ abrogates the protective effects of SP on colitis. This plus the finding that SP reduces DSS-enhanced protein Tyr nitration are consistent with DSS-induced uncoupling of NOS. The results agree with previous studies that demonstrated inactivation of sGC in DSS-treated animals as being important in recruitment of inflammatory cells and in altered cholinergic signaling and colon motility. SP also reduces the number of colon tumors in AOM/DSS-treated mice from 7 to 1 per unit colon length. Thus, pharmacologic modulation of BH4 with currently available drugs may provide a mechanism for alleviating some forms of colitis and potentially minimizing the potential for colorectal cancer in patients with colitis.

Enteric glia cells attenuate cytomix-induced intestinal epithelial barrier breakdown

BACKGROUND

Intestinal barrier failure may lead to systemic inflammation and distant organ injury in patients following severe injury. Enteric glia cells (EGCs) have been shown to play an important role in maintaining gut barrier integrity through secretion of S-Nitrosoglutathione (GSNO). We have recently shown than Vagal Nerve Stimulation (VNS) increases EGC activation, which was associated with improved gut barrier integrity. Thus, we sought to further study the mechanism by which EGCs prevent intestinal barrier breakdown utilizing an in vitro model. We postulated that EGCs, through the secretion of GSNO, would improve intestinal barrier function through improved expression and localization of intestinal tight junction proteins.

METHODS

Epithelial cells were co-cultured with EGCs or incubated with GSNO and exposed to Cytomix (TNF-α, INF-γ, IL-1β) for 24 hours. Barrier function was assessed by permeability to 4kDa FITC-Dextran. Changes in tight junction proteins ZO-1, occludin, and phospho-MLC (P-MLC) were assessed by immunohistochemistry and immunoblot.

KEY RESULTS

Co-culture of Cytomix-stimulated epithelial monolayers with EGCs prevented increases in permeability and improved expression and localization of occludin, ZO-1, and P-MLC. Further, treatment of epithelial monolayers with GSNO also prevented Cytomix-induced increases in permeability and exhibited a similar improvement in expression and localization of occludin, ZO-1, and P-MLC.

CONCLUSIONS & INFERENCES

The addition of EGCs, or their secreted mediator GSNO, prevents epithelial barrier failure after injury and improved expression of tight junction proteins. Thus, therapies that increase EGC activation, such as VNS, may be a novel strategy to limit barrier failure in patients following severe injury.

Contribution of either YY1 or BclXL-induced inhibition by the NO-donor DETANONOate in the reversal of drug resistance, both in vitro and in vivo. YY1 and BclXL are overexpressed in prostate cancer

Nitric oxide (NO) donors have been shown to activate or inhibit constitutively-activated survival/anti-apoptotic pathways, such as NF-κB, in cancer cells. We report here that treatment of drug-resistant human prostate carcinoma cell lines with high levels (500-1000 μM) of the NO-donor DETANONOate sensitized the resistant tumor cells to apoptosis by CDDP and the combination was synergistic. We hypothesized that DETANONOate inhibits previously identified NF-κB-regulated resistant factors such as Yin Yang 1 (YY1) and Bcl-2/BclXL. Lysates from tumor cells treated with DETANONOate showed inhibition of YY1 and BclXL expressions. Transfection with either YY1 or BclXL siRNA resulted in the inhibition of both YY1 and BclXL expressions and sensitized the cells to CDDP apoptosis. Mice bearing PC-3 tumor xenografts and treated with the combination of DETANONOate and CDDP resulted in significant inhibition of tumor growth; treatment with single agent alone did not have any effect on tumor growth. Analysis of patients TMA tissues with prostatic cancer revealed higher expression of both YY1 and BclXL as a function of tumor grades and their levels were directly correlated. Thus, both YY1 and BclXL are potential prognostic biomarkers. Overall, the above findings suggest that one mechanism of DETANONOate-induced sensitization of resistant tumor cells to CDDP correlated with the inhibition of NF-κB and its targets YY1 and BclXL. The examination of the combination of NO donors and cytotoxic therapy in the treatment of resistant prostate cancer may be warranted.

Chemical methods for the direct detection and labeling of S-nitrosothiols

SIGNIFICANCE

Posttranslational modification of proteins through phosphorylation, glycosylation, and oxidation adds complexity to the proteome by reversibly altering the structure and function of target proteins in a highly controlled fashion.

RECENT ADVANCES

The study of reversible cysteine oxidation highlights a role for this oxidative modification in complex signal transduction pathways. Nitric oxide (NO), and its respective metabolites (including reactive nitrogen species), participates in a variety of these cellular redox processes, including the reversible oxidation of cysteine to S-nitrosothiols (RSNOs). RSNOs act as endogenous transporters of NO, but also possess beneficial effects independent of NO-related signaling, which suggests a complex and versatile biological role. In this review, we highlight the importance of RSNOs as a required posttranslational modification and summarize the current methods available for detecting S-nitrosation.

CRITICAL ISSUES

Given the limitations of these indirect detection methods, the review covers recent developments toward the direct detection of RSNOs by phosphine-based chemical probes. The intrinsic properties that dictate this phosphine/RSNO reactivity are summarized. In general, RSNOs (both small molecule and protein) react with phosphines to yield reactive S-substituted aza-ylides that undergo further reactions leading to stable RSNO-based adducts.

FUTURE DIRECTIONS

This newly explored chemical reactivity forms the basis of a number of exciting potential chemical methods for protein RSNO detection in biological systems.

Regulation of cell cycle and stress responses under nitrosative stress in Schizosaccharomyces pombe

Nitric oxide (NO) acts as a signaling molecule in numerous physiological processes but excess production generates nitrosative stress in cells. The exact protective mechanism used by cells to combat nitrosative stress is unclear. In this study, the fission yeast Schizosaccharomyces pombe has been used as a model system to explore cell cycle regulation and stress responses under nitrosative stress. Exposure to an NO donor results in mitotic delay in cells through G2/M checkpoint activation and initiates rereplication. Western blot analysis of phosphorylated Cdc2 revealed that the G2/M block in the cell cycle was due to retention of its inactive phosphorylated form. Interestingly, nitrosative stress results in inactivation of Cdc25 through S-nitrosylation that actually leads to cell cycle delay. From differential display analysis, we identified plo1, spn4, and rga5, three cell cycle-related genes found to be differentially expressed under nitrosative stress. Exposure to nitrosative stress also results in abnormal septation and cytokinesis in S. pombe. In summary we propose a novel molecular mechanism of cell cycle control under nitrosative stress based on our experimental results and bioinformatics analysis.

Protein glutathionylation in the regulation of peroxiredoxins: a family of thiol-specific peroxidases that function as antioxidants, molecular chaperones, and signal modulators

SIGNIFICANCE

Reversible protein glutathionylation plays an important role in cellular regulation, signaling transduction, and antioxidant defense. This redox-sensitive mechanism is involved in regulating the functions of peroxiredoxins (Prxs), a family of ubiquitously expressed thiol-specific peroxidase enzymes. Glutathionylation of certain Prxs at their active-site cysteines not only provides reducing equivalents to support their peroxidase activity but also protects Prxs from irreversible hyperoxidation. Typical 2-Cys Prx also functions as a molecular chaperone when it exists as a decamer and/or higher molecular weight complexes. The hyperoxidized sulfinic derivative of 2-Cys Prx is reactivated by sulfiredoxin (Srx). In this review, the roles of glutathionylation in the regulation of Prxs are discussed with respect to their molecular structure and functions as antioxidants, molecular chaperones, and signal modulators.

RECENT ADVANCES

Recent findings reveal that glutathionylation regulates the quaternary structure of Prx. Glutathionylation of Prx I at Cys(83) converts the decameric Prx to its dimers with the loss of chaperone activity. The findings that dimer/oligomer structure specific Prx I binding proteins, e.g., phosphatase and tensin homolog (PTEN) and mammalian Ste20-like kinase-1 (MST1), regulate cell cycle and apoptosis, respectively, suggest a possible link between glutathionylation and those signaling pathways.

CRITICAL ISSUES

Knowing how glutathionylation affects the interaction between Prx I and its nearly 20 known interacting proteins, e.g., PTEN and MST1 kinase, would reveal new insights on the physiological functions of Prx.

FUTURE DIRECTIONS

In vitro studies reveal that Prx oligomerization is linked to its functional changes. However, in vivo dynamics, including the effect by glutathionylation, and its physiological significance remain to be investigated.

Exogenous, but not Endogenous Nitric Oxide Inhibits Adhesion Molecule Expression in Human Endothelial Cells

Nitric oxide (NO) has many beneficial actions on the vascular wall including suppression of inflammation. The mechanism(s) by which NO antagonizes cytokine signaling are poorly understood, but are thought to involve inhibition of the pro-inflammatory transcription factor, NF-κB. NO represses nuclear translocation of NF-κB via the S-nitrosylation of its subunits which decreases the expression of target genes including adhesion molecules. In previous studies, we have shown that the intracellular location of endothelial nitric oxide synthase (eNOS) can influence the amount of NO produced and that NO levels are paramount in regulating the S-nitrosylation of target proteins. The purpose of the current study was to investigate the significance of subcellular eNOS to NF-κB signaling induced by pro-inflammatory cytokines in human aortic endothelial cells (HAECs). We found that in HAECs stimulated with TNFα, L-NAME did not influence the expression of intercellular adhesion molecule 1 (ICAM-1) or vascular cell adhesion molecular 1 (VCAM-1). In eNOS "knock down" HAECs reconstituted with either plasma membrane or Golgi restricted forms of eNOS, there was no significant effect on the activation of the NF-κB pathway over different times and concentrations of TNFα. Similarly, the endogenous production of NO did not influence the phosphorylation of IκBα. In contrast, higher concentrations of NO derived from the use of the exogenous NO donor, DETA NONOate, effectively suppressed the expression of ICAM-1/VCAM-1 in response to TNFα and induced greater S-nitrosylation of IKKβ and p65. Collectively these results suggest that neither endogenous eNOS nor eNOS location is an important influence on inflammatory signaling via the NF-κB pathway and that higher NO concentrations are required to suppress NF-κB in HAECs.

Nitric oxide modulates sodium vitamin C transporter 2 (SVCT-2) protein expression via protein kinase G (PKG) and nuclear factor-κB (NF-κB)

Ascorbate is an important antioxidant, which also displays important functions in neuronal tissues, including the retina. The retina is responsible for the initial steps of visual processing, which is further refined in cerebral high-order centers. The retina is also a prototypical model for studying physiologic aspects of cells that comprise the nervous system. Of major importance also is the cellular messenger nitric oxide (NO). Previous studies have demonstrated the significance of NO for both survival and proliferation of cultured embryonic retinal cells. Cultured retinal cells express a high-affinity ascorbate transporter, and the release of ascorbate is delicately regulated by ionotropic glutamate receptors. Therefore, we proposed whether there is interplay between the ascorbate transport system and NO signaling pathway in retinal cells. Here we show compelling evidence that ascorbate uptake is tightly controlled by NO and its downstream signaling pathway in culture. NO also modulates the expression of SVCT-2, an effect mediated by cGMP and PKG. Kinetic studies suggest that NO increases the transport capacity for ascorbate, but not the affinity of SVCT-2 for its substrate. Interestingly, NO utilizes the NF-κB pathway, in a PKG-dependent manner, to modulate both SVCT-2 expression and ascorbate uptake. These results demonstrate that NO exerts a fine-tuned control of the availability of ascorbate to cultured retinal cells and strongly reinforces ascorbate as an important bioactive molecule in neuronal tissues.

The role of melanoma tumor-derived nitric oxide in the tumor inflammatory microenvironment: its impact on the chemokine expression profile, including suppression of CXCL10

Melanoma appears to be heterogeneous in terms of its molecular biology, etiology and epidemiology. We previously reported that the expression of inducible nitric-oxide synthase (iNOS) in melanoma tumor cells is strongly correlated with poor patient survival. Therefore, we hypothesized that nitric oxide (NO) produced by iNOS promotes the melanoma inflammatory tumor microenvironment associated with poor outcome. To understand the role of NO and iNOS in the melanoma inflammatory tumor microenvironment, polymerase chain reaction arrays of inflammatory and autoimmunity genes were performed on a series of stage III melanoma lymph node metastasis samples to compare the gene expression profiles of iNOS-expressing and nonexpressing tumor samples. The results indicate that expression of CXC chemokine ligand 10 (CXCL10) was inversely correlated with iNOS expression, and the high CXCL10-expressing cases had more favorable prognoses than the low CXCL10-expressing cases. Functional studies revealed that treating iNOS-negative/CXCL10-positive melanoma cell lines with a NO donor suppressed the expression of CXCL10. Furthermore, scavenging NO from iNOS-expressing cell lines significantly affected the chemokine expression profile. Culture supernatants from NO scavenger-treated melanoma cells promoted the migration of plasmacytoid dendritic cells, which was diminished when the cells were treated with a CXCL10-neutralizing antibody. CXCL10 has been reported to be an antitumorigenic chemokine. Our study suggests that the production of NO by iNOS inhibits the expression of CXCL10 in melanoma cells and leads to a protumorigenic tumor microenvironment. Inhibiting NO induces an antitumorigenic environment, and thus, iNOS should be considered to be an important therapeutic target in melanoma.

Hippocampal neuronal nitric oxide synthase mediates the stress-related depressive behaviors of glucocorticoids by downregulating glucocorticoid receptor

The molecular mechanisms underlying the behavioral effects of glucocorticoids are poorly understood. We report here that hippocampal neuronal nitric oxide synthase (nNOS) is a crucial mediator. Chronic mild stress and glucocorticoids exposures caused hippocampal nNOS overexpression via activating mineralocorticoid receptor. In turn, hippocampal nNOS-derived nitric oxide (NO) significantly downregulated local glucocorticoid receptor expression through both soluble guanylate cyclase (sGC)/cGMP and peroxynitrite (ONOO(-))/extracellular signal-regulated kinase signal pathways, and therefore elevated hypothalamic corticotrophin-releasing factor, a peptide that governs the hypothalamic-pituitary-adrenal axis. More importantly, nNOS deletion or intrahippocampal nNOS inhibition and NO-cGMP signaling blockade (using NO scavenger or sGC inhibitor) prevented the corticosterone-induced behavioral modifications, suggesting that hippocampal nNOS is necessary for the role of glucocorticoids in mediating depressive behaviors. In addition, directly delivering ONOO(-) donor into hippocampus caused depressive-like behaviors. Our findings reveal a role of hippocampal nNOS in regulating the behavioral effects of glucocorticoids.

Nitric oxide potentiates TNF-α-induced neurotoxicity through suppression of NF-κB

Modulation of enzyme activity through nitrosylation has recently been identified as a new physiological activity of nitric oxide (NO). We hypothesized that NO enhances the TNF-α-induced death of retinal neurons through a suppression of nuclear factor-κB (NF-κB) by nitrosylation. In this study, cells from the RGC-5 line were exposed to different concentrations (2.0, 10, and 50 ng/ml) of TNF-α, and the degree of TNF-α-induced cell death was determined by the WST-8 assay and by flow cytometric measurements of the externalization of phosphatidylserine. The effects of etanercept, a soluble TNFR-Fc fusion protein, and S-nitroso-N-penicillamine (SNAP), an NO donor, on the toxicity were determined. Experiments were also performed to determine whether nitric oxide synthase (NOS) was associated with the toxicity of TNF-α. The activation of NF-κB was determined by the detection of the p65 subunit in the nuclear extracts. Our results showed that exposure of RGC-5 cells to different concentrations of TNF-α significantly decreased the number of living cells in a dose-dependent way. The death was partially due to apoptosis with an externalization of phosphatidylserine, and the death was suppressed by etanercept. Exposure to TNF-α increased the activation of NF-κB and the expression of iNOS. Although NF-κB inhibitors suppressed the increase of iNOS, they also potentiated the TNF-α-induced death. Both L-NAME and aminoguanidine, both NOS inhibitors, rescued the cells from death. In contrast, addition of SNAP caused nitrosylation of the inhibitory κB kinase, and suppressed the NF-κB activation and potentiated the TNF-α-induced neurotoxicity. These results indicate that NO potentiates the neurotoxicity of TNF-α by suppressing NF-κB.

S-Nitrosylation signaling regulates cellular protein interactions

BACKGROUND

S-Nitrosothiols are made by nitric oxide synthases and other metalloproteins. Unlike nitric oxide, S-nitrosothiols are involved in localized, covalent signaling reactions in specific cellular compartments. These reactions are enzymatically regulated.

SCOPE

S-Nitrosylation affects interactions involved in virtually every aspect of normal cell biology. This article is part of a Special Issue entitled Regulation of Cellular Processes by S-nitrosylation.

MAJOR CONCLUSIONS AND SIGNIFICANCE

S-Nitrosylation is a regulated signaling reaction.

SNO-ing at the nociceptive synapse?

Nitric oxide is generally considered a pronociceptive retrograde transmitter that, by activation of soluble guanylyl cyclase-mediated cGMP production and activation of cGMP-dependent protein kinase, drives nociceptive hypersensitivity. The duality of its functions, however, is increasingly recognized. This review summarizes nitric-oxide-mediated direct S-nitrosylation of target proteins that may modify nociceptive signaling, including glutamate receptors and G-protein-coupled receptors, transient receptor potential channels, voltage-gated channels, proinflammatory enzymes, transcription factors, and redoxins. S-Nitrosylation events require close proximity of nitric oxide production and target proteins and a permissive redox state in the vicinity. Despite the diversity of potential targets and effects, three major schemes arise that may affect nociceptive signaling: 1) S-Nitrosylation-mediated changes of ion channel gating properties, 2) modulation of membrane fusion and fission, and thereby receptor and channel membrane insertion, and 3) modulation of ubiquitination, and thereby protein degradation or transcriptional activity. In addition, S-Nitrosylation may alter the production of nitric oxide itself.

Nitric oxide affects IL-6 expression in human peripheral blood mononuclear cells involving cGMP-dependent modulation of NF-κB activity

Interleukin 6 (IL-6) and nitric oxide (NO) are important mediators of the inflammatory response. We report that in human peripheral blood mononuclear cells (PBMCs), NO exerts a biphasic effect on the expression of IL-6. Using sodium nitroprusside (SNP) and S-nitrosoglutathione (GSNO) as NO-donating compounds, we observed that both mRNA and protein levels of IL-6 increased at lower (≤10μM) and decreased at higher (>100μM) concentrations of NO donors. Changes in the expression of IL-6 correlated with changes in the activity of NF-κB, which increased at lower and decreased at higher concentrations of both NO donors as shown by the electrophoretic mobility shift assay (EMSA). The effects of NO on NF-κB activity were cGMP-dependent because they were reversed in the presence of ODQ, the inhibitor of soluble guanylyl cyclase (sGC), and KT5823, the inhibitor of cGMP-dependent protein kinase (PKG). Moreover, the membrane permeable analog of cGMP (8-Br-cGMP) mimicked the effect of the NO donors. These observations show that NO, depending on its concentration, may act in human PBMCs as a stimulator of IL-6 expression involving the sGC/cGMP/PKG pathway.

Nitric oxide and redox mechanisms in the immune response

The role of redox molecules, such as NO and ROS, as key mediators of immunity has recently garnered renewed interest and appreciation. To regulate immune responses, these species trigger the eradication of pathogens on the one hand and modulate immunosuppression during tissue-restoration and wound-healing processes on the other. In the acidic environment of the phagosome, a variety of RNS and ROS is produced, thereby providing a cauldron of redox chemistry, which is the first line in fighting infection. Interestingly, fluctuations in the levels of these same reactive intermediates orchestrate other phases of the immune response. NO activates specific signal transduction pathways in tumor cells, endothelial cells, and monocytes in a concentration-dependent manner. As ROS can react directly with NO-forming RNS, NO bioavailability and therefore, NO response(s) are changed. The NO/ROS balance is also important during Th1 to Th2 transition. In this review, we discuss the chemistry of NO and ROS in the context of antipathogen activity and immune regulation and also discuss similarities and differences between murine and human production of these intermediates.

Divergent roles of superoxide and nitric oxide in liver ischemia and reperfusion injury

Liver ischemia and reperfusion-induced injury is a major clinical complication associated with hemorrhagic or endotoxin shock and thermal injury as well as liver transplantation and resectional surgery. Data obtained from several different studies suggest that an important initiating event in the pathophysiology of ischemia and reperfusion-induced tissue injury is enhanced production of superoxide concomitant with a decrease in the bioavailability of endothelial cell-derived nitric oxide. This review will summarize the evidence supporting the hypothesis that the redox imbalance induced by alterations in superoxide and nitric oxide generation creates a more oxidative environment within the different cells of the liver that enhances the nuclear transcription factor-κB-dependent expression of a variety of different cytokines and mediators that may promote as well as limit ischemia and reperfusion-induced hepatocellular injury. In addition, the evidence implicating endothelial cell nitric oxide synthase-dependent and -independent generation of nitric oxide as important regulatory pathways that act to limit ischemia and reperfusion-induced liver injury and inflammation is also presented.

Role of nitric oxide in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) occurs upon restoration of hepatic blood flow after a period of ischemia. Decreased endogenous nitric oxide (NO) production resulting in capillary luminal narrowing is central in the pathogenesis of IRI. Exogenous NO has emerged as a potential therapy for IRI based on its role in decreasing oxidative stress, cytokine release, leukocyte endothelial-adhesion and hepatic apoptosis. This review will highlight the influence of endogenous NO on hepatic IRI, role of inhaled NO in ameliorating IRI, modes of delivery, donor drugs and potential side effects of exogenous NO.

The protective effect of overexpression of extracellular superoxide dismutase on nitric oxide bioavailability in the lung after exposure to hyperoxia stress

The objective of this study was to determine whether overexpression of human extracellular superoxide dismutase (hEC-SOD) can preserve nitric oxide (NO) bioavailability. In vitro studies examined the transient expression of hEC-SOD in mouse epithelial (C10) cells and its effect on extracellular accumulation of NO, intracellular cyclic guanosine monophosphate (cGMP), and nuclear factor kappa B (NF-κB) activation under normal and oxidative stress conditions. In vivo, newborn rabbits were treated with a plasmid containing hEC-SOD cDNA or vehicle plasmid alone, followed by exposure to hyperoxia (Fio₂ = 95% for 7 days). A third group was raised under normoxic conditions. cGMP and NF-κB activation were studied. There was significantly higher NO accumulation in cells expressing hEC-SOD exposed to oxidative stress compared with nontransfected cells. Accumulation of cGMP was significantly higher in cells expressing hEC-SOD. Oxidative stress induced NF-κB activation, which was abrogated by hEC-SOD expression. In vivo, there was significantly higher cGMP accumulation in transfected neonatal rabbit lung tissue at 3 and 7 days of hyperoxic exposure. Immunostaining for NF-κB, showed a marked increase in NF-κB concentration in nontreated neonatal rabbit lung tissue compared to transfected neonatal lung with hEC-SOD and the control air group. These results show that transient EC-SOD overexpression maintains NO bioavailability, which directly leads to maintenance of cGMP activity and reduction of NF-κB activation under oxidative stress.

S-alkylating labeling strategy for site-specific identification of the s-nitrosoproteome

S-nitrosylation, a post-translational modification of cysteine residues induced by nitric oxide, mediates many physiological functions. Due to the labile nature of S-nitrosylation, detection by mass spectrometry (MS) is challenging. Here, we developed an S-alkylating labeling strategy using the irreversible biotinylation on S-nitrosocysteines for site-specific identification of the S-nitrosoproteome by LC-MS/MS. Using COS-7 cells without endogenous nitric oxide synthase, we demonstrated that the S-alkylating labeling strategy substantially improved the blocking efficiency of free cysteines, minimized the false-positive identification caused by disulfide interchange, and increased the digestion efficiency for improved peptide identification using MS analyses. Using this strategy, we identified total 586 unique S-nitrosylation sites corresponding to 384 proteins in S-nitroso-N-acetylpenicillamine (SNAP)/l-cysteine-treated mouse MS-1 endothelial cells, including 234 previously unreported S-nitrosylated proteins. When the topologies of 84 identified transmembrane proteins were further analyzed, their S-nitrosylation sites were found to mostly face the cytoplasmic side, implying that S-nitrosylation occurs in the cytoplasm. In addition to the previously known acid/basic motifs, the ten deduced consensus motifs suggested that combination of local hydrophobicity and acid/base motifs in the tertiary structure contribute to the specificity of S-nitrosylation. Moreover, the S-nitrosylated cysteines showed preference on beta-strand, having lower relative surface accessibility at the S-nitrosocysteines.

Protein modifications involved in neurotransmitter and gasotransmitter signaling

Covalent modifications of intracellular proteins, such as phosphorylation, are generally thought to occur as secondary or tertiary responses to neurotransmitters, following the intermediation of membrane receptors and second messengers such as cyclic AMP. By contrast, the gasotransmitter nitric oxide directly S-nitrosylates cysteine residues in diverse intracellular proteins. Recently, hydrogen sulfide has been acknowledged as a gasotransmitter, which analogously sulfhydrates cysteine residues in proteins. Cysteine residues are also modified by palmitoylation in response to neurotransmitter signaling, possibly in reciprocity with S-nitrosylation. Neurotransmission also elicits sumoylation and acetylation of lysine residues within diverse proteins. This review addresses how these recently appreciated protein modifications impact our thinking about ways in which neurotransmission regulates intracellular protein disposition.

Protein tyrosine nitration in cellular signal transduction pathways

How specificity and reversibility in tyrosine nitration are defined biologically in cellular systems is poorly understood. As more investigations identify proteins involved in cell regulatory pathways in which only a small fraction of that protein pool is modified by nitration to affect cell function, the mechanisms of biological specificity and reversal should come into focus. In this review experimental evidence has been summarized to suggest that tyrosine nitration is a highly selective modification and under certain physiological conditions fulfills the criteria of a physiologically relevant signal. It can be specific, reversible, occurs on a physiological time scale, and, depending on a target, can result in either activation or inhibition.

Modulation of NF-κB and hypoxia-inducible factor--1 by S-nitrosoglutathione does not alter allergic airway inflammation in mice

Induction of nitric oxide synthase (NOS)-2 and production of nitric oxide (NO) are common features of allergic airway disease. Conditions of severe asthma are associated with deficiency of airway S-nitrosothiols, a biological product of NO that can suppress inflammation by S-nitrosylation of the proinflammatory transcription factor, NF-κB. Therefore, restoration of airway S-nitrosothiols might have therapeutic benefit, and this was tested in a mouse model of ovalbumin (OVA)-induced allergic inflammation. Naive or OVA-sensitized animals were administered S-nitrosoglutathione (GSNO; 50 μl, 10 mM) intratracheally before OVA challenge and analyzed 48 hours later. GSNO administration enhanced lung tissue S-nitrosothiol levels and reduced NF-κB activity in OVA-challenged animals compared with control animals, but did not lead to significant changes in total bronchoalveolar lavage cell counts, differentials, or mucus metaplasia markers. Administration of GSNO also altered the activation of hypoxia-inducible factor (HIF)-1, leading to HIF-1 activation in naive mice, but suppressed HIF-1 activation in OVA-challenged mice. We assessed the contribution of endogenous NOS2 in regulating NF-κB and/or HIF-1 activation and allergic airway inflammation using NOS2(-/-) mice. Although OVA-induced NF-κB activation was slightly increased in NOS2(-/-) mice, associated with small increases in bronchoalveolar lavage neutrophils, other markers of allergic inflammation and HIF-1 activation were similar in NOS2(-/-) and wild-type mice. Collectively, our studies indicate that instillation of GSNO can suppress NF-κB activation during allergic airway inflammation, but does not significantly affect overall markers of inflammation or mucus metaplasia, thus potentially limiting its therapeutic potential due to effects on additional signaling pathways, such as HIF-1.

Role of oxidative stress in stem, cancer, and cancer stem cells

The term ‘‘oxidative stress” refers to a cell’s state characterized by excessive production of reactive oxygen species (ROS) and oxidative stress is one of the most important regulatory mechanisms for stem, cancer, and cancer stem cells. The concept of cancer stem cells arose from observations of similarities between the self-renewal mechanism of stem cells and that of cancer stem cells, but compared to normal stem cells, they are believed to have no control over the cell number. ROS have been implicated in diverse processes in various cancers, and generally the increase of ROS in cancer cells is known to play an important role in the initiation and progression of cancer. Additionally, ROS have been considered as the most significant mutagens in stem cells; when elevated, blocking self-renewal and at the same time, serving as a signal stimulating stem cell differentiation. Several signaling pathways enhanced by oxidative stress are suggested to have important roles in tumorigenesis of cancer or cancer stem cells and the self-renewal ability of stem or cancer stem cells. It is now well established that mitochondria play a prominent role in apoptosis and increasing evidence supports that apoptosis and autophagy are physiological phenomena closely linked with oxidative stress. This review elucidates the effect and the mechanism of the oxidative stress on the regulation of stem, cancer, and cancer stem cells and focuses on the cell signaling cascades stimulated by oxidative stress and their mechanism in cancer stem cell formation, as very little is known about the redox status in cancer stem cells. Moreover, we explain the link between ROS and both of apoptosis and autophagy and the impact on cancer development and treatment. Better understanding of this intricate link may shed light on mechanisms that lead to better modes of cancer treatment.

Formaldehyde dehydrogenase: beyond phase I metabolism

Formaldehyde dehydrogenase, formally Class III alcohol dehydrogenase (ADH3), has recently been discovered to partially regulate nitrosothiol homeostasis by catalyzing the reduction of the endogenous nitrosylating agent S-nitrosoglutathione (GSNO). Several studies have implicated this enzyme, and in particular GSNO reduction, as playing an important role in conditions such as asthma, cardiovascular disease, and immune function. While ADH3 has received considerable attention in the biomedical literature where it is often referred to as GSNO reductase (GSNOR), ADH3-mediated GSNO reduction has received comparatively less attention in the environmental toxicology community. Herein, evidences for a role of ADH3 in cell signaling through thiol homeostasis is highlighted, underscoring that the enzyme functions more broadly than to metabolize formaldehyde.

Commentary: mechanistic considerations for associations between formaldehyde exposure and nasopharyngeal carcinoma

Occupational exposure to formaldehyde has been linked to nasopharyngeal carcinoma. To date, mechanistic explanations for this association have primarily focused on formaldehyde-induced cytotoxicity, regenerative hyperplasia and DNA damage. However, recent studies broaden the potential mechanisms as it is now well established that formaldehyde dehydrogenase, identical to S-nitrosoglutathione reductase, is an important mediator of cGMP-independent nitric oxide signaling pathways. We have previously described mechanisms by which formaldehyde can influence nitrosothiol homeostasis thereby leading to changes in pulmonary physiology. Considering evidences that nitrosothiols govern the Epstein-Barr virus infection cycle, and that the virus is strongly implicated in the etiology of nasopharyngeal carcinoma, studies are needed to examine the potential for formaldehyde to reactivate the Epstein-Barr virus as well as additively or synergistically interact with the virus to potentiate epithelial cell transformation.

Epigallocatechin-3-gallate inhibits osteoclastogenesis by down-regulating c-Fos expression and suppressing the nuclear factor-kappaB signal

Epigallocatechin-3-gallate (EGCG), the major anti-inflammatory compound in green tea, has been shown to suppress osteoclast differentiation. However, the precise molecular mechanisms underlying the inhibitory action of EGCG in osteoclastogenesis and the effect of EGCG on inflammation-mediated bone destruction remain unclear. In this study, we found that EGCG inhibited osteoclast formation induced by osteoclastogenic factors in bone marrow cell-osteoblast cocultures but did not affect the ratio of receptor activator of nuclear factor kappaB (NF-kappaB) ligand (RANKL) to osteoprotegerin induced by osteoclastogenic factors in osteoblasts. We also found that EGCG inhibited osteoclast formation from bone marrow macrophages (BMMs) induced by macrophage colony-stimulating factor plus RANKL in a dose-dependent manner without cytotoxicity. Pretreatment with EGCG significantly inhibited RANKL-induced the gene expression of c-Fos and nuclear factor of activated T-cells (NFATc1), essential transcription factors for osteoclast development. EGCG suppressed RANKL-induced activation of c-Jun N-terminal protein kinase (JNK) pathway, among the three well known mitogen-activated protein kinases and also inhibited RANKL-induced phosphorylation of the NF-kappaB p65 subunit at Ser276 and NF-kappaB transcriptional activity without affecting the degradation of IkappaBalpha and NF-kappaB DNA-binding in BMMs. The inhibitory effect of EGCG on osteoclast formation was somewhat reversed by retroviral c-Fos overexpression, suggesting that c-Fos is a downstream target for antiosteoclastogenic action of EGCG. In addition, EGCG treatment reduced interleukin-1-induced osteoclast formation and bone destruction in mouse calvarial bone in vivo. Taken together, our data suggest that EGCG has an antiosteoclastogenic effect by inhibiting RANKL-induced the activation of JNK/c-Jun and NF-kappaB pathways, thereby suppressing the gene expression of c-Fos and NFATc1 in osteoclast precursors.

Kinetic and cellular characterization of novel inhibitors of S-nitrosoglutathione reductase

S-Nitrosoglutathione reductase (GSNOR) is an alcohol dehydrogenase involved in the regulation of S-nitrosothiols (SNOs) in vivo. Knock-out studies in mice have shown that GSNOR regulates the smooth muscle tone in airways and the function of beta-adrenergic receptors in lungs and heart. GSNOR has emerged as a target for the development of therapeutic approaches for treating lung and cardiovascular diseases. We report three compounds that exclude GSNOR substrate, S-nitrosoglutathione (GSNO) from its binding site in GSNOR and cause an accumulation of SNOs inside the cells. The new inhibitors selectively inhibit GSNOR among the alcohol dehydrogenases. Using the inhibitors, we demonstrate that GSNOR limits nitric oxide-mediated suppression of NF-kappaB and activation of soluble guanylyl cyclase. Our findings reveal GSNOR inhibitors to be novel tools for regulating nitric oxide bioactivity and assessing the role of SNOs in vivo.

The ontogeny, distribution, and regulation of alcohol dehydrogenase 3: implications for pulmonary physiology

Class III alcohol dehydrogenase (ADH3), also termed formaldehyde dehydrogenase or S-nitrosoglutathione reductase, plays a critical role in the enzymatic oxidation of formaldehyde and reduction of nitrosothiols that regulate bronchial tone. Considering reported associations between formaldehyde vapor exposure and childhood asthma risk, and thus potential involvement of ADH3, we reviewed the ontogeny, distribution, and regulation of mammalian ADH3. Recent studies indicate that multiple biological and chemical stimuli influence expression and activity of ADH3, including the feedback regulation of nitrosothiol metabolism. The levels of ADH3 correlate with, and potentially influence, bronchial tone; however, data gaps remain with respect to the expression of ADH3 during postnatal and early childhood development. Consideration of ADH3 function relative to the respiratory effects of formaldehyde, as well as to other chemical and biological exposures that might act in an additive or synergistic manner with formaldehyde, might be critical to gain better insight into the association between formaldehyde exposure and childhood asthma.

Peroxynitrite induces gene expression in intervertebral disc cells

STUDY DESIGN

In vitro stimulation of human intervertebral disc (IVD) cells.

OBJECTIVE

To investigate the oxidative/nitrosative effects of peroxynitrite on human nucleus pulposus (NP) cells.

SUMMARY OF BACKGROUND DATA

Peroxynitrite is an important tissue-damaging species generated at sites of inflammation and degeneration. The aim of this study was to examine the effects of oxidative/nitrosative stress caused by peroxynitrite and the peroxynitrite donor SIN-1 in human NP cells.

METHODS

Degenerated human IVD tissue was analyzed for nitrosylation by immunofluorescence. In addition, human NP cells were isolated from IVDs, expanded and stimulated either with peroxynitrite itself or a stable peroxynitrite donor (SIN-1). Nitrosylation, accumulation of intracellular reactive oxygen species, NF-kappaB nuclear translocation, and cell viability were analyzed by fluorescence. Gene expression of TNF-alpha, IL-1beta, IL-6, IL-8, and IL-10 was quantified by real-time (RT)-PCR.

RESULTS

Degenerated IVD tissue showed strong nitrosylation, especially in the NP. Isolated human NP cells showed a strong signal for nitrosylation and intracellular reactive oxygen species on stimulation with peroxynitrite or SIN-1. NF-kappaB/p65 sustained nuclear translocation of NF-kappaB/p65 and stimulation of IL-1beta, IL-6, and IL-8 expression was noted on treatment of cells with SIN-1.

CONCLUSION

This study provides evidence that peroxynitrite may play a role in disc degeneration and discogenic back pain development by an increased synthesis of proinflammatory cytokines. Nuclear translocation of NF-kappaB was identified as the potential underlying pathway. Therefore, neutralizing peroxynitrite and its derivatives (e.g., via the use of antioxidants) may be a novel treatment option for discogenic back pain.

Hepatocellular protection by nitric oxide or nitrite in ischemia and reperfusion injury

Ischemia and reperfusion (I/R)-induced liver injury occurs in several pathophysiological disorders including hemorrhagic shock and burn as well as resectional and transplantation surgery. One of the earliest events associated with reperfusion of ischemic liver is endothelial dysfunction characterized by the decreased production of endothelial cell-derived nitric oxide (NO). This rapid post-ischemic decrease in NO bioavailability appears to be due to decreased synthesis of NO, enhanced inactivation of NO by the overproduction of superoxide or both. This review presents the most current evidence supporting the concept that decreased bioavailability of NO concomitant with enhanced production of reactive oxygen species initiates hepatocellular injury and that endogenous NO or exogenous NO produced from nitrite play important roles in limiting post-ischemic tissue injury.

Cell Defence and Survival

Central to immune defence mechanisms is the role of transcription factor nuclear factor kappa B (NF-kB). This is a complex biochemical topic with ever more controls revealed. NF-kB determines the production of proinflammatory cytokines and chemokines. Pharmacologists step in with possible means of control. Other systems involved in defence include the cyclooxygenase 2 (Cox-2) enzyme and perioxisome proliferator-activated receptors. Insulin receptor activation needs to be seen in context. The mTOR system directs uptake of nutrients by cells. mTOR is suppressed by rapamycin, whose usage is now quite considerable in the control of transplant rejection.

Nitric oxide inhibits human rhinovirus-induced transcriptional activation of CXCL10 in airway epithelial cells

BACKGROUND

Human rhinovirus (HRV) infections trigger exacerbations of asthma and chronic obstructive pulmonary disease. Nitric oxide (NO) inhibits HRV replication in human airway epithelial cells and suppresses HRV-induced epithelial production of several cytokines and chemokines.

OBJECTIVE

We sought to delineate the mechanisms by which NO inhibits HRV-induced epithelial production of CXCL10, a chemoattractant for type 1 T cells and natural killer cells.

METHODS

Primary human bronchial epithelial cells or cells of the BEAS-2B human bronchial epithelial cell line were exposed to HRV-16 in the presence or absence of the NO donor 3-(2-hydroxy-2-nitroso-1-propylhydrazino)-1-propanamine (PAPA NONOate). A cGMP analogue and an inhibitor of soluble guanylyl cyclase were used to examine the role of the cyclic guanosine monophosphate (cGMP) pathway in the actions of NO. BEAS-2B cells were transfected with CXCL10 promoter-luciferase constructs and the effects of PAPA NONOate were examined to study mechanisms of transcriptional regulation. Electrophoretic mobility shift assays were also used.

RESULTS

PAPA NONOate inhibited HRV-16-induced increases in CXCL10 mRNA and protein. Inhibition of CXCL10 production occurred through a cGMP-independent pathway. PAPA NONOate inhibited HRV-16-induced CXCL10 transcription by blocking nuclear translocation, binding, or both of both nuclear factor kappaB and IFN response factors (IRFs) to their respective recognition elements in the CXCL10 promoter.

CONCLUSIONS

NO inhibits HRV-16-induced production of CXCL10 by inhibiting viral activation of nuclear factor kappaB and of IRFs, including IRF-1, through a cGMP-independent pathway. The broad-ranging inhibition of HRV-induced epithelial cytokine and chemokine production by NO suggests a potential therapeutic utility of NO donors in viral exacerbations of asthma and chronic obstructive pulmonary disease.

S-Nitrosylation of histone deacetylase 2 induces chromatin remodelling in neurons

Brain-derived neurotrophic factor (BDNF) and other neurotrophins have a vital role in the development of the rat and mouse nervous system by influencing the expression of many specific genes that promote differentiation, cell survival, synapse formation and, later, synaptic plasticity. Although nitric oxide (NO) is known to be an important mediator of BDNF signalling in neurons, the mechanisms by which neurotrophins influence gene expression during development and plasticity remain largely unknown. Here we show that BDNF triggers NO synthesis and S-nitrosylation of histone deacetylase 2 (HDAC2) in neurons, resulting in changes to histone modifications and gene activation. S-nitrosylation of HDAC2 occurs at Cys 262 and Cys 274 and does not affect deacetylase activity. In contrast, nitrosylation of HDAC2 induces its release from chromatin, which increases acetylation of histones surrounding neurotrophin-dependent gene promoters and promotes transcription. Notably, nitrosylation of HDAC2 in embryonic cortical neurons regulates dendritic growth and branching, possibly by the activation of CREB (cyclic-AMP-responsive-element-binding protein)-dependent genes. Thus, by stimulating NO production and S-nitrosylation of HDAC2, neurotrophic factors promote chromatin remodelling and the activation of genes that are associated with neuronal development.

Nitric oxide activated by p38 and NF-kappaB facilitates apoptosis and cell cycle arrest under oxidative stress in evodiamine-treated human melanoma A375-S2 cells

Nitric oxide (NO) has been identified as a fundamental molecule that interplays with reactive oxygen species (ROS) in determining cell fate. As a previous study indicated that ROS was stimulated in evodiamine-induced human melanoma A375-S2 cell apoptosis, the goal of this study was to investigate the role of NO in the cells. In this study, it was found that evodiamine has a strong inductive effect on NO production synthesized by inducible NOS (iNOS) enzyme in a positive-feedback manner. The generated NO was further showed to induce apoptosis and cell cycle arrest and linked to the activation of p53 and p21. After interruption of p38 and nuclear factor-kappaB (NF-kappaB) by pre-treatment with SB203580 and PDTC, iNOS expression, NO synthesis and cell damage were all significantly blocked. It was concluded that p38 and NF-kappaB were critical to the NO producing system, which contributed greatly to the apoptosis and cell cycle arrest in evodiamine-incubated cells.

On-gel fluorescent visualization and the site identification of S-nitrosylated proteins

Mounting evidence indicates that S-nitrosylation of critical cysteine residues in a protein represents a common feature of protein function regulation and cell signaling. However, the progress in studying the exact role of S-nitrosylation has been hampered by a lack of rapid and accurate methods for the detection of these S-nitrosylated proteins and the exact modification sites. In this article, we report a fluorescence-based method in which the S-nitrosylated cysteines are converted into 7-amino-4-methylcoumarin-3-acetic acid (AMCA) fluorophore-labeled cysteines-termed the AMCA switch method. The labeled proteins are then analyzed by nonreducing SDS-PAGE, and the S-nitrosylated proteins can be readily detected as brilliant blue bands after the activation of ultraviolet light. Furthermore, the sites of modification can be determined by liquid chromatography-tandem mass spectrometry (LC-MS/MS) after in-gel tryptic digestion of the fluorescent band, and the recognizable AMCA tag in the MS spectra ensures the accurate site identification of the nitrosocysteines. Therefore, our method offers some apparent advantages by direct visualization of on-gel image of S-nitrosylated proteins, shorter experiment time by skipping the anti-biotin immunoblotting step, and elimination of the potential interference of endogenous biotinylated proteins. Based on this method, we detected the S-nitrosylation and the modified site in bovine serum albumin and gankyrin after in vitro S-nitrosylation. Overall, our results indicate that the AMCA switch method is a fast and accurate method to identify the S-nitrosylated protein and the modification sites.

Inflammation and lung cancer: roles of reactive oxygen/nitrogen species

The lung is a highly specialized organ that facilitates uptake of oxygen and release of carbon dioxide. Due to its unique structure providing enormous surface area to outside ambient air, it is vulnerable to numerous pathogens, pollutants, oxidants, gases, and toxicants that are inhaled continuously from air, which makes the lung susceptible to varying degrees of oxidative injury. To combat these unrelenting physical, chemical, and biological insults, the respiratory epithelium is covered with a thin layer of lining fluid containing several antioxidants and surfactants. Inhaled toxic agents stimulate the generation of reactive oxygen/nitrogen species (ROS/RNS), which in turn provoke inflammatory responses resulting in the release of proinflammatory cytokines and chemokines. These subsequently stimulate the influx of polymorphonuclear leukocytes (PMNs) and monocytes into the lung so as to combat the invading pathogens or toxic agents. In addition to the beneficial effects, persistent inhalation of the invading pathogens or toxic agents may result in overwhelming production of ROS/RNS, producing chronic inflammation and lung injury. During inflammation, enhanced ROS/RNS production may induce recurring DNA damage, inhibition of apoptosis, and activation of proto-oncogenes by initiating signal transduction pathways. Therefore, it is conceivable that chronic inflammation-induced production of ROS/RNS in the lung may predispose individuals to lung cancer. This review describes the complex relationship between lung inflammation and carcinogenesis, and highlights the role of ROS/RNS in cancer development.

Regulation of MyD88-dependent signaling events by S nitrosylation retards toll-like receptor signal transduction and initiation of acute-phase immune responses

Nitric oxide (NO) has been thought to regulate the immune system through S nitrosylation of the transcriptional factor NF-kappaB. However, regulatory effects of NO on innate immune responses are unclear. Here, we report that NO has a capability to control Toll-like receptor-mediated signaling through S nitrosylation. We found that the adaptor protein MyD88 was primarily S nitrosylated, depending on the presence of endothelial NO synthase (eNOS). S nitrosylation at a particular cysteine residue within the TIR domain of MyD88 resulted in slight reduction of the NF-kappaB-activating property. This modification could be restored by the antioxidant glutathione. Through S nitrosylation, NO could negatively regulate the multiple steps of MyD88 functioning, including translocation to the cell membrane after LPS stimulation, interaction with TIRAP, binding to TRAF6, and induction of IkappaBalpha phosphorylation. Interestingly, glutathione could reversely neutralize such NO-derived effects. We also found that an acute febrile response to LPS was precipitated in eNOS-deficient mice, indicating that eNOS-derived NO exerts an initial suppressive effect on inflammatory processes. Thus, NO has a potential to retard induction of MyD88-dependent signaling events through the reversible and oxidative modification by NO, by which precipitous signaling reactions are relieved. Such an effect may reflect appropriate regulation of the acute-phase inflammatory responses in living organisms.

S-nitrosylation of peroxiredoxin 2 promotes oxidative stress-induced neuronal cell death in Parkinson's disease

Peroxiredoxins (Prx), a family of peroxidases that reduce intracellular peroxides with the thioredoxin system as the electron donor, are highly expressed in various cellular compartments. Among the antioxidant Prx enzymes, Prx2 is the most abundant in mammalian neurons, making it a prime candidate to defend against oxidative stress. Here we report that Prx2 is S-nitrosylated (forming SNO-Prx2) by reaction with nitric oxide at two critical cysteine residues (C51 and C172), preventing its reaction with peroxides. We observed increased SNO-Prx2 in human Parkinson's disease (PD) brains, and S-nitrosylation of Prx2 inhibited both its enzymatic activity and protective function from oxidative stress. Dopaminergic neurons, which are lost in PD, become particularly vulnerable. Thus, our data provide a direct link between nitrosative/oxidative stress and neurodegenerative disorders such as PD.

Tumour necrosis factor induces phosphorylation primarily of the nitric-oxide-responsive form of glyoxalase I

We have previously shown that TNF (tumour necrosis factor) induces phosphorylation of GLO1 (glyoxalase I), which is required for cell death in L929 cells. In the present paper, we show that the TNF-induced phosphorylation of GLO1 occurs primarily on the NO (nitric oxide)-responsive form of GLO1. In addition, analysis of several cysteine mutants of GLO1 indicated that Cys-138, in combination with either Cys-18 or Cys-19, is a crucial target residue for the NO-mediated modification of GLO1. Furthermore, the NO-donor GSNO (S-nitrosogluthathione) induces NO-mediated modification of GLO1 and enhances the TNF-induced phosphorylation of this NO-responsive form. GSNO also strongly promotes TNF-induced cell death. By the use of pharmacological inhibition of iNOS (inducible NO synthase) and overexpression of mutants of GLO1 that are deficient for the NO-mediated modification, we have shown that the NO-mediated modification of GLO1 is not a requirement for TNF-induced phosphorylation or TNF-induced cell death respectively. In summary, these data suggest that the TNF-induced phosphorylation of GLO1 is the dominant factor for cell death.

Impact of post-translational modifications of proteins on the inflammatory process

PTM (post-translational modification) is the chemical modification of a protein after its translation. The well-studied PTM is phosphorylation, but, recently, PTMs have been re-focused by extensive studies on histone modifications and the discovery of the ubiquitin system. Histone acetylation is the well-established epigenetic regulator for gene expression. Recent studies show that different patterns of PTMs and cross-talk of individual modifications (acetylation, methylation, phosphorylation) are keys of gene regulation (known as the 'histone code'). As well as histone, non-histone proteins are also targets of acetylation. For instance, NF-kappaB (nuclear factor kappaB), a transcriptional factor, is regulated dynamically by acetylation/deacetylation. Acetylation of NF-kappaB [RelA (p65)] at Lys(310) enhances its transcriptional activity, which is inhibited by SIRT1 deacetylase, type III HDAC (histone deacetylase). We also found that acetylated NF-kappaB preferentially bound to the IL-8 (interleukin 8) gene promoter, but not to GM-CSF (granulocyte/macrophage colony-stimulating factor), suggesting NF-kappaB acetylation is involved in selective gene induction as well as an increased level of transcription. A receptor of glucocorticoid, a potent anti-inflammatory agent, is also a target of acetylation. The glucocorticoid receptor is highly acetylated after ligand binding but its deacetylation is necessary for gene repression through binding to NF-kappaB. As well as acetylation, other PTMs, such as nitration, carbonylation and ubiquitination on transcriptional/nuclear factors, are taking part in the inflammatory process. Cross-talk of individual modifications on proteins deserves further evaluation in the future (as 'protein code').