Regulation of apoptosis by protein S-nitrosylation

Post-translational modifications and their implications in cancer

Post-translational modifications (PTMs) are crucial regulatory mechanisms that alter the properties of a protein by covalently attaching a modified chemical group to some of its amino acid residues. PTMs modulate essential physiological processes such as signal transduction, metabolism, protein localization, and turnover and have clinical relevance in cancer and age-related pathologies. Majority of proteins undergo post-translational modifications, irrespective of their occurrence in or after protein biosynthesis. Post-translational modifications link to amino acid termini or side chains, causing the protein backbone to get cleaved, spliced, or cyclized, to name a few. These chemical modifications expand the diversity of the proteome and regulate protein activity, structure, locations, functions, and protein-protein interactions (PPIs). This ability to modify the physical and chemical properties and functions of proteins render PTMs vital. To date, over 200 different protein modifications have been reported, owing to advanced detection technologies. Some of these modifications include phosphorylation, glycosylation, methylation, acetylation, and ubiquitination. Here, we discuss about the existing as well as some novel post-translational protein modifications, with their implications in aberrant states, which will help us better understand the modified sites in different proteins and the effect of PTMs on protein functions in core biological processes and progression in cancer.

Amino acid metabolism in health and disease

Amino acids are the building blocks of protein synthesis. They are structural elements and energy sources of cells necessary for normal cell growth, differentiation and function. Amino acid metabolism disorders have been linked with a number of pathological conditions, including metabolic diseases, cardiovascular diseases, immune diseases, and cancer. In the case of tumors, alterations in amino acid metabolism can be used not only as clinical indicators of cancer progression but also as therapeutic strategies. Since the growth and development of tumors depend on the intake of foreign amino acids, more and more studies have targeted the metabolism of tumor-related amino acids to selectively kill tumor cells. Furthermore, immune-related studies have confirmed that amino acid metabolism regulates the function of effector T cells and regulatory T cells, affecting the function of immune cells. Therefore, studying amino acid metabolism associated with disease and identifying targets in amino acid metabolic pathways may be helpful for disease treatment. This article mainly focuses on the research of amino acid metabolism in tumor-oriented diseases, and reviews the research and clinical research progress of metabolic diseases, cardiovascular diseases and immune-related diseases related to amino acid metabolism, in order to provide theoretical basis for targeted therapy of amino acid metabolism.

Ribonucleotide reductase: Implications of thiol S-nitrosylation and tyrosine nitration for different subunits

Ribonucleotide reductase (RNR) is a multi-subunit enzyme responsible for catalyzing the rate-limiting step in the production of deoxyribonucleotides essential for DNA synthesis and repair. The active RNR complex is composed of multimeric R1 and R2 subunits. The RNR catalysis involves the formation of tyrosyl radicals in R2 subunits and thiyl radicals in R1 subunits. Despite the quaternary structure and cofactor diversity, all the three classes of RNR have a conserved cysteine residue at the active site which is converted into a thiyl radical that initiates the substrate turnover, suggesting that the catalytic mechanism is somewhat similar for all three classes of the RNR enzyme. Increased RNR activity has been associated with malignant transformation, cancer cell growth, and tumorigenesis. Efforts concerning the understanding of RNR inhibition in designing potent RNR inhibitors/drugs as well as developing novel approaches for antibacterial, antiviral treatments, and cancer therapeutics with improved radiosensitization have been made in clinical research. This review highlights the precise and potent roles of NO in RNR inhibition by targeting both the subunits. Under nitrosative stress, the thiols of the R1 subunits have been found to be modified by S-nitrosylation and the tyrosyl radicals of the R2 subunits have been modified by nitration. In view of the recent advances and progresses in the field of nitrosative modifications and its fundamental role in signaling with implications in health and diseases, the present article focuses on the regulations of RNR activity by S-nitrosylation of thiols (R1 subunits) and nitration of tyrosyl residues (R2 subunits) which will further help in designing new drugs and therapies.

Deciphering the Path of S-nitrosation of Human Thioredoxin: Evidence of an Internal NO Transfer and Implication for the Cellular Responses to NO

Nitric oxide (NO) is a free radical with a signaling capacity. Its cellular functions are achieved mainly through S-nitrosation where thioredoxin (hTrx) is pivotal in the S-transnitrosation to specific cellular targets. In this study, we use NMR spectroscopy and mass spectrometry to follow the mechanism of S-(trans)nitrosation of hTrx. We describe a site-specific path for S-nitrosation by measuring the reactivity of each of the 5 cysteines of hTrx using cysteine mutants. We showed the interdependence of the three cysteines in the nitrosative site. C73 is the most reactive and is responsible for all S-transnitrosation to other cellular targets. We observed NO internal transfers leading to C62 S-nitrosation, which serves as a storage site for NO. C69-SNO only forms under nitrosative stress, leading to hTrx nuclear translocation.

S-nitrosated proteomic analysis reveals the regulatory roles of protein S-nitrosation and S-nitrosoglutathione reductase during Al-induced PCD in peanut root tips

Nitric oxide-mediated S-nitrosation through S-nitrosoglutathione reductase (GSNOR) plays important roles in cellular processes and signaling of plants; however, the regulatory mechanism of programmed cell death (PCD) by S-nitrosation remains unclear. In this study, the S-nitrosated proteomic and functions of GSNOR during Al-induced PCD in peanut were investigated. Al stress induced an increase of S-nitrosothiol (SNO) content and GSNOR activity in Al-induced PCD. There was significant positive correlation between SNO content and hydrogen peroxide content. The S-nitrosated proteomic analysis identified 402 S-nitrosated proteins containing 551 S-nitrosated sites during Al-induced PCD in the root tips of peanut. These S-nitrosated proteins were involved in regulation of various biological processes including energy metabolism, maintenance of cell wall function and organic acid secretion. Among them, 128 S-nitrosated proteins were up-regulated and one was down-regulated after Al stress. Experiments with recombinant AhGSNOR revealed that activity of the enzyme was inhibited by its S-nitrosation, with a moderate decrease of 17.9 % after 100 μM GSNO incubation. These data provide novel insights to understanding the functional mechanism of NO-mediated S-nitrosation during plant PCD.

Dual Roles of GSNOR1 in Cell Death and Immunity in Tetraploid Nicotiana tabacum

S-nitrosoglutathione reductase 1 (GSNOR1) is the key enzyme that regulates cellular homeostasis of S-nitrosylation. Although extensively studied in Arabidopsis, the roles of GSNOR1 in tetraploid Nicotiana species have not been investigated previously. To study the function of NtGSNOR1, we knocked out two NtGSNOR1 genes simultaneously in Nicotiana tabacum using clustered regularly interspaced short palindromic repeats (CRISPR)/caspase 9 (Cas9) technology. To our surprise, spontaneous cell death occurred on the leaves of the CRISPR/Cas9 lines but not on those of the wild-type (WT) plants, suggesting that NtGSNOR1 negatively regulates cell death. The natural cell death on the CRISPR/Cas9 lines could be a result from interactions between overaccumulated nitric oxide (NO) and hydrogen peroxide (H₂O₂). This spontaneous cell death phenotype was not affected by knocking out two Enhanced disease susceptibility 1 genes (NtEDS11a/1b) and thus was independent of the salicylic acid (SA) pathway. Unexpectedly, we found that the NtGSNOR1a/1b knockout plants displayed a significantly (p < 0.001) enhanced resistance to paraquat-induced cell death compared to WT plants, suggesting that NtGSNOR1 functions as a positive regulator of the paraquat-induced cell death. The increased resistance to the paraquat-induced cell death of the NtGSNOR1a/1b knockout plants was correlated with the reduced level of H₂O₂ accumulation. Interestingly, whereas the N gene-mediated resistance to Tobacco mosaic virus (TMV) was significantly enhanced (p < 0.001), the resistance to Pseudomonas syringae pv. tomato DC3000 was significantly reduced (p < 0.01) in the NtGSNOR1a/1b knockout lines. In summary, our results indicate that NtGSNOR1 functions as both positive and negative regulator of cell death under different conditions and displays distinct effects on resistance against viral and bacterial pathogens.

Biotin Switch Processing and Mass Spectrometry Analysis of S-Nitrosated Thioredoxin and Its Transnitrosation Targets

S-Nitrosation is a key posttranslational modification in regulating proteins in both normal physiology and diverse human diseases. To identify novel therapies for human diseases linked to oxidative and nitrosative stress, understanding how cells control S-nitrosation specificity could be critical. Among the enzymes known to control S-nitrosation of proteins, thioredoxin 1 (Trx1), a conserved disulfide reductase, transnitrosates and denitrosates distinct sets of target proteins. To recognize the function of Trx1 in both normal and dysfunctional cells, S-nitrosation targets of Trx1 in different cells need to be identified. However, S-nitrosation is usually too labile to be detected directly by mass spectrometry (MS). Here we present two optimized MS techniques to identify S-nitrosated Trx1 and its transnitrosation targets, using both direct and indirect MS methods.

S-Nitrosylation inhibits the kinase activity of tomato phosphoinositide-dependent kinase 1 (PDK1)

It is well known that the reactive oxygen species NO can trigger cell death in plants and other organisms, but the underlying molecular mechanisms are not well understood. Here we provide evidence that NO may trigger cell death in tomato (Solanum lycopersicum) by inhibiting the activity of phosphoinositide-dependent kinase 1 (SlPDK1), a conserved negative regulator of cell death in yeasts, mammals, and plants, via S-nitrosylation. Biotin-switch assays indicated that SlPDK1 is a target of S-nitrosylation. Moreover, the kinase activity of SlPDK1 was inhibited by S-nitrosoglutathione in a concentration-dependent manner, indicating that SlPDK1 activity is abrogated by S-nitrosylation. The S-nitrosoglutathione-induced inhibition was reversible in the presence of a reducing agent but additively enhanced by hydrogen peroxide (H₂O₂). Our LC-MS/MS analyses further indicated that SlPDK1 is primarily S-nitrosylated on a cysteine residue at position 128 (Cys¹²⁸), and substitution of Cys¹²⁸ with serine completely abolished SlPDK1 kinase activity, suggesting that S-nitrosylation of Cys¹²⁸ is responsible for SlPDK1 inhibition. In summary, our results establish a potential link between NO-triggered cell death and inhibition of the kinase activity of tomato PDK1.

The role of hypernitrosylation in the pathogenesis and pathophysiology of neuroprogressive diseases

There is a wealth of data indicating that de novo protein S-nitrosylation in general and protein transnitrosylation in particular mediates the bulk of nitric oxide signalling. These processes enable redox sensing and facilitate homeostatic regulation of redox dependent protein signalling, function, stability and trafficking. Increased S-nitrosylation in an environment of increasing oxidative and nitrosative stress (O&NS) is initially a protective mechanism aimed at maintaining protein structure and function. When O&NS becomes severe, mechanisms governing denitrosylation and transnitrosylation break down leading to the pathological state referred to as hypernitrosylation (HN). Such a state has been implicated in the pathogenesis and pathophysiology of several neuropsychiatric and neurodegenerative diseases and we investigate its potential role in the development and maintenance of neuroprogressive disorders. In this paper, we propose a model whereby the hypernitrosylation of a range of functional proteins and enzymes lead to changes in activity which conspire to produce at least some of the core abnormalities contributing to the development and maintenance of pathology in these illnesses.

A combined NMR- and HPLC-MS/MS-based metabolomics to evaluate the metabolic perturbations and subacute toxic effects of endosulfan on mice

Endosulfan is the newly persistent organic pollutants (POPs) added to the Stockholm Convention as its widespread use, persistence, bioaccumulation, long-range transport, endocrine disruption, and toxicity related to various adverse effects. In the present study, male mice were administrated endosulfan at 0, 0.5, and 3.5 mg/kg by gavage for 2 weeks. ¹H-NMR-based urinary metabolomics, HPLC-MS/MS-based targeted serum metabolomics, clinical analysis, and histopathology techniques were employed to evaluate the metabolic perturbations of subacute endosulfan exposure. Endosulfan exposures resulted in weight loss, liver inflammation and necrosis, and alterations in serum amino acids and urine metabolomics. Based on altered metabolites, several significantly perturbed pathways were identified including glycine, serine, and threonine metabolism; TCA cycle; pyruvate metabolism; glycolysis or gluconeogenesis; glycerophospholipid metabolism; and glyoxylate and dicarboxylate metabolism. Such pathways were highly related to amino acid metabolism, energy metabolism, and lipid metabolism. In addition, metabolomic results also demonstrated that gut microbiota was remarkably altered after endosulfan exposure. These observations may provide novel insight into revealing the potential toxic mechanism and evaluating the health risk of endosulfan exposure at metabolomic level.

Enantioselective Effects of Metalaxyl Enantiomers on Breast Cancer Cells Metabolic Profiling Using HPLC-QTOF-Based Metabolomics

In this study, an integrative high-performance liquid chromatography coupled with quadrupole time-of-flight tandem mass spectrometry (HPLC-QTOF) based metabolomics approach was performed to evaluate the enantioselective metabolic perturbations in MCF-7 cells after treatment with R-metalaxyl and S-metalaxyl, respectively. Untargeted metabolomics profile, multivariate pattern recognition, metabolites identification, and pathway analysis were determined after metalaxyl enantiomer exposure. Principal component analysis (PCA) and partitial least-squares discriminant analysis (PLS-DA) directly reflected the enantioselective metabolic perturbations induced by metalaxyl enantiomers. On the basis of multivariate statistical results, a total of 49 metabolites including carbohydrates, amino acids, nucleotides, fatty acids, organic acids, phospholipids, indoles, derivatives, etc. were found to be the most significantly changed metabolites and metabolic fluctuations caused by the same concentration of R-metalaxyl and S-metalaxyl were enantioselective. Pathway analysis indicated that R-metalaxyl and S-metalaxyl mainly affected the 7 and 10 pathways in MCF-7 cells, respectively, implying the perturbed pathways induced by metalaxyl enantiomers were also enantioselective. Furthermore, the significantly perturbed metabolic pathways were highly related to energy metabolism, amino acid metabolism, lipid metabolism, and antioxidant defense. Such results provide more specific insights into the enantioselective metabolic effects of chiral pesticides in breast cancer progression, reveal the underlying mechanisms, and provide available data for the health risk assessments of chiral environmental pollutants at the molecular level.

Chronic Heat Stress Induces Immune Response, Oxidative Stress Response, and Apoptosis of Finishing Pig Liver: A Proteomic Approach

Heat stress (HS) negatively affects human health, animal welfare, and livestock production. We analyzed the hepatic proteomes of finishing pigs subjected to chronic heat stress (HS), thermal neutral (TN), and restricted feed intake conditions, identifying differences between direct and indirect (via reduced feed intake) HS. Twenty-four castrated male pigs were randomly allocated to three treatments for three weeks: (1) thermal neutral (TN) (22 °C) with ad libitum feeding; (2) chronic HS (30 °C) with ad libitum feeding; and (3) TN, pair-fed to HS intake (PF). Hepatic proteome analysis was conducted using two-dimensional gel electrophoresis and mass spectrometry. Both HS and PF significantly reduced liver weight (p < 0.05). Forty-five hepatic proteins were differentially abundant when comparing HS with TN (37), PF with TN (29), and HS with PF (16). These proteins are involved in heat shock response and immune defense, oxidative stress response, cellular apoptosis, metabolism, signal transduction, and cytoskeleton. We also observed increased abundance of proteins and enzymes associated with heat shock response and immune defense, reduced the redox state, enhanced multiple antioxidant abilities, and increased apoptosis in HS liver. Heat-load, independent of reduced feed intake, induced an innate immune response, while food restriction caused stress and cellular apoptosis. Our results provide novel insights into the effects of chronic HS on liver.

Peroxynitrite is Involved in the Apoptotic Death of Cultured Cerebellar Granule Neurons Induced by Staurosporine, but not by Potassium Deprivation

Nitric oxide (NO) regulates numerous physiological process and is the main source of reactive nitrogen species (RNS). NO promotes cell survival, but it also induces apoptotic death having been involved in the pathogenesis of several neurodegenerative diseases. NO and superoxide anion react to form peroxynitrite, which accounts for most of the deleterious effects of NO. The mechanisms by which these molecules regulate the apoptotic process are not well understood. In this study, we evaluated the role of NO and peroxynitrite in the apoptotic death of cultured cerebellar granule neurons (CGN), which are known to experience apoptosis by staurosporine (St) or potassium deprivation (K5). We found that CGN treated with the peroxynitrite catalyst, FeTTPs were completely rescued from St-induced death, but not from K5-induced death. On the other hand, the inhibition of the inducible nitric oxide synthase partially protected cell viability in CGN treated with K5, but not with St, while the inhibitor L-NAME further reduced the cell viability in St, but it did not affect K5. Finally, an inhibitor of the soluble guanylate cyclase (sGC) diminished the cell viability in K5, but not in St. Altogether, these results shows that NO promotes cell survival in K5 through sGC-cGMP and promotes cell death by other mechanisms, while in St NO promotes cell survival independently of cGMP and peroxynitrite results critical for St-induced death. Our results suggest that RNS are differentially handled by CGN during cell death depending on the death-inducing conditions.

Health risks of space exploration: targeted and nontargeted oxidative injury by high-charge and high-energy particles

SIGNIFICANCE

During deep space travel, astronauts are often exposed to high atomic number (Z) and high-energy (E) (high charge and high energy [HZE]) particles. On interaction with cells, these particles cause severe oxidative injury and result in unique biological responses. When cell populations are exposed to low fluences of HZE particles, a significant fraction of the cells are not traversed by a primary radiation track, and yet, oxidative stress induced in the targeted cells may spread to nearby bystander cells. The long-term effects are more complex because the oxidative effects persist in progeny of the targeted and affected bystander cells, which promote genomic instability and may increase the risk of age-related cancer and degenerative diseases.

RECENT ADVANCES

Greater understanding of the spatial and temporal features of reactive oxygen species bursts along the tracks of HZE particles, and the availability of facilities that can simulate exposure to space radiations have supported the characterization of oxidative stress from targeted and nontargeted effects.

CRITICAL ISSUES

The significance of secondary radiations generated from the interaction of the primary HZE particles with biological material and the mitigating effects of antioxidants on various cellular injuries are central to understanding nontargeted effects and alleviating tissue injury.

FUTURE DIRECTIONS

Elucidation of the mechanisms underlying the cellular responses to HZE particles, particularly under reduced gravity and situations of exposure to additional radiations, such as protons, should be useful in reducing the uncertainty associated with current models for predicting long-term health risks of space radiation. These studies are also relevant to hadron therapy of cancer.

IL-15 maintains T-cell survival via S-nitrosylation-mediated inhibition of caspase-3

Caspase activity is critical for both T-cell survival and death. However, little is known regarding what determines caspase activity in cycling T cells. Interleukin (IL)-2 and IL-15 confer very different susceptibilities to T-cell death. We therefore considered that IL-2 and IL-15 differentially regulate caspase activity to influence T-cell survival. We observed that IL-2-cultured primary murine effector T cells manifested elevated levels of caspase-3 activity compared with IL-15-cultured T cells. T cell receptor (TCR) restimulation further increased caspase activity and induced considerable cell death in IL-2-cultured T cells, but provoked only a minimal increase of caspase activity and cell death in IL-15-cultured T cells. IL-2 sensitization to cell death was caspase-3 mediated. Interestingly, increased active caspase-3 levels with IL-2 were independent of active initiator caspase-8 and caspase-9 that were similar with IL-2 and IL-15. Rather, caspase-3 activity was inhibited by posttranslational S-nitrosylation in IL-15-cultured T cells, but not in the presence of IL-2. This paralleled increased reactive nitrogen and oxygen species with IL-15 and reduced glycolysis. Taken together, these data suggest that the metabolic state conferred by IL-15 inhibits T-cell apoptosis in part by maintaining low levels of active caspase-3 via S-nitrosylation.

Thioredoxins, glutaredoxins, and peroxiredoxins--molecular mechanisms and health significance: from cofactors to antioxidants to redox signaling

Thioredoxins (Trxs), glutaredoxins (Grxs), and peroxiredoxins (Prxs) have been characterized as electron donors, guards of the intracellular redox state, and "antioxidants". Today, these redox catalysts are increasingly recognized for their specific role in redox signaling. The number of publications published on the functions of these proteins continues to increase exponentially. The field is experiencing an exciting transformation, from looking at a general redox homeostasis and the pathological oxidative stress model to realizing redox changes as a part of localized, rapid, specific, and reversible redox-regulated signaling events. This review summarizes the almost 50 years of research on these proteins, focusing primarily on data from vertebrates and mammals. The role of Trx fold proteins in redox signaling is discussed by looking at reaction mechanisms, reversible oxidative post-translational modifications of proteins, and characterized interaction partners. On the basis of this analysis, the specific regulatory functions are exemplified for the cellular processes of apoptosis, proliferation, and iron metabolism. The importance of Trxs, Grxs, and Prxs for human health is addressed in the second part of this review, that is, their potential impact and functions in different cell types, tissues, and various pathological conditions.

Differential S-nitrosylation of proteins in Alzheimer's disease

Numerous studies have provided evidence regarding the involvement of protein S-nitrosylation in the progression of Alzheimer's disease (AD) pathology and its implication in the formation and accumulation of misfolded protein aggregates. The identification of S-nitrosylated proteins can be a major step toward the understanding of mechanisms leading to neuronal degeneration. The present study targeted S-nitrosylated proteins in AD hippocampus, substantia nigra and cortex using the following work-flow that combines S-nitrosothiol-specific antibody detection, classical biotin switch method labeled with fluorescence dye followed by electrospray ionization quadrupole time of flight tandem MS (ESI-QTOF MS/MS) identification. Endogenous nitrosocysteines were identified in 45 proteins, mainly involved in metabolism, signaling pathways, apoptosis and redox regulation as assigned by REACTOME and KEGG pathway database analysis. Superoxide dismutase (SOD2) [Mn], fructose-bisphosphate aldolase C (ALDOC) and voltage-dependent anion-selective channel protein 2 (VDAC2) showed differential S-nitrosylation signal, not previously reported in AD regions. Extensive neuronal atrophy with increased protein S-nitrosylation in AD regions is also evident from immunofluorescence studies using S-nitrosocysteine antibody. A number of plausible cysteine modification sites were predicted via Group-based Prediction System-S-nitrosothiols (GPS-SNO) 1.0 while STRING 8.3 analysis revealed functional annotations in the modified proteins. The findings are helpful in characterization of functional abnormalities and may facilitate the understanding of molecular mechanisms and biological function of S-nitrosylation in AD pathology.

Increased expression of GAPDH protein is not indicative of nitrosative stress or apoptosis in liver of starved rainbow trout (Oncorhynchus mykiss)

Short-term starvation has been linked to in vivo protein degradation in liver of rainbow trout (Oncorhynchus mykiss). However, it is unclear whether this proposed increase in protein degradation is followed by programmed cell death (apoptosis) in liver of starved trout. A preliminary study in our laboratory revealed an isoform of glyceraldehyde-3-phosphate dehydrogenase (GAPDH) protein that increased 4.5-fold in liver of starved trout. GAPDH is a glycolytic enzyme involved in other cellular functions, including apoptosis. Increased intracellular nitric oxide (NO) promotes nuclear translocation of GAPDH that is associated with increased apoptosis in mammals. If GAPDH protein is associated with apoptosis in rainbow trout, it could potentially be used as a biomarker of cellular stress in liver of teleost fish species. The purpose of this study was to determine whether increased GAPDH protein expression in liver of starved rainbow trout is associated with NO-induced apoptosis. Targeted proteomic analysis using multiple reaction monitoring (MRM) was used to determine the level of GAPDH in nuclear and cytoplasmic fractions and inducible nitric oxide synthase (iNOS) in cell lysates. Dot blot and DNA fragmentation analyses were conducted to evaluate protein S-nitrosylation and apoptosis, respectively. Results showed that cytoplasmic GAPDH was 3.4-fold higher in liver of starved versus fed rainbow trout but could not be detected in nuclear fractions. Starvation significantly reduced hepato-somatic index but had no effect on iNOS protein expression, protein S-nitrosylation, or apoptosis. Our results indicate that starvation promoted significant reduction in liver mass that was not associated with increased apoptosis or NO-induced stress and that greater GAPDH concentration in liver of starved rainbow trout was located primarily in the cytoplasm.

Insidious role of nitric oxide in migration/invasion of colon cancer cells by upregulating MMP-2/9 via activation of cGMP-PKG-ERK signaling pathways

Nitric oxide (NO), an uncharged free radical is implicated in various physiological and pathological processes. The present study is an investigation on the effect of NO on proliferation, apoptosis and migration of colon cancer cells. Colon adenocarcinoma cells, WiDr, were used for the in vitro experiments. Tissues from colon adenocarcinoma, adjacent normal and inflammatory tissue and lymph node with metastasis were evaluated for iNOS, MMP-2/9 and Fra-1/Fra-2. NO increases the proliferation of cancer cells and simultaneously prevents apoptosis. Expression of MMP-2/9, RhoB and Rac-1 was enhanced by NO in a time dependent manner. Further, NO increased phosphorylation of ERK1/2 and induced nuclear translocation of Fra-1 and Fra-2. Electrophoretic mobility shift analysis and use of deletion mutant promoter constructs identified role of AP-1 in NO-mediated regulation of MMP-2/9. iNOS, MMP-2/9, Fra-1 and Fra-2 in normal and colon adenocarcinoma tissues were analyzed and it was found that increased expression of these proteins in cancer when compared to normal provides support to our in vitro findings. The study showed that the NO-cGMP-PKG promotes MMP-2/9 expression by activating ERK-1/2 and AP-1. This study reveals the insidious role of NO in imparting tumor aggressiveness.

Protein S-nitrosylation and cancer

Protein S-nitrosylation is a covalent post-translational modification through coupling of a nitric oxide (NO) moiety with the reactive thiol group of a protein cysteine residue to form an S-nitrosothiol (SNO). S-nitrosylation is a key mechanism in the transmission of NO-based cellular signals in the vital cellular processes, including transcription regulation, DNA repair, and apoptosis. Contemporary research has implicated dysregulation of S-nitrosylation in severe pathological events, including cancer onset, progression, and treatment resistance. The S-nitrosylation status may be directly linked to many cancer therapy outcomes as well as therapeutic-resistance, emphasizing the need to develop S-nitrosylation-related anti-cancer therapeutics. The role of S-nitrosylated proteins in the development and progression of cancer are varied, generating a critical need for a thorough review of the current dynamic research in this area.

Regulation of pancreatic β-cell survival by nitric oxide: clinical relevance

The reduction of pancreatic β-cell mass is an important factor in the development of type 1 and type 2 diabetes. Understanding the mechanisms that regulate the maintenance of pancreatic β-cell mass as well as β-cell death is necessary for the establishment of therapeutic strategies. In this context, nitric oxide (NO) is a diatomic, gaseous, highly reactive molecule with biological activity that participates in the regulation of pancreatic β-cell mass. Two types of cellular responses can be distinguished depending on the level of NO production. First, pancreatic β-cells exposed to inflammatory cytokines, lipid stress or hyperglycaemia produce high concentrations of NO, mainly due to the activation of inducible NO synthase (iNOS), thus promoting cell death. Meanwhile, under homeostatic conditions, low concentrations of NO, constitutively produced by endothelial NO synthase (eNOS), promote cell survival. Here, we will discuss the current knowledge of the NO-dependent mechanisms activated during cellular responses, emphasizing those related to the regulation of cell survival.

Nitric oxide and protein S-nitrosylation are integral to hydrogen peroxide-induced leaf cell death in rice

Nitric oxide (NO) is a key redox-active, small molecule involved in various aspects of plant growth and development. Here, we report the identification of an NO accumulation mutant, nitric oxide excess1 (noe1), in rice (Oryza sativa), the isolation of the corresponding gene, and the analysis of its role in NO-mediated leaf cell death. Map-based cloning revealed that NOE1 encoded a rice catalase, OsCATC. Furthermore, noe1 resulted in an increase of hydrogen peroxide (H(2)O(2)) in the leaves, which consequently promoted NO production via the activation of nitrate reductase. The removal of excess NO reduced cell death in both leaves and suspension cultures derived from noe1 plants, implicating NO as an important endogenous mediator of H(2)O(2)-induced leaf cell death. Reduction of intracellular S-nitrosothiol (SNO) levels, generated by overexpression of rice S-nitrosoglutathione reductase gene (GSNOR1), which regulates global levels of protein S-nitrosylation, alleviated leaf cell death in noe1 plants. Thus, S-nitrosylation was also involved in light-dependent leaf cell death in noe1. Utilizing the biotin-switch assay, nanoliquid chromatography, and tandem mass spectrometry, S-nitrosylated proteins were identified in both wild-type and noe1 plants. NO targets identified only in noe1 plants included glyceraldehyde 3-phosphate dehydrogenase and thioredoxin, which have been reported to be involved in S-nitrosylation-regulated cell death in animals. Collectively, our data suggest that both NO and SNOs are important mediators in the process of H(2)O(2)-induced leaf cell death in rice.

L-glutamine supplementation prevents myenteric neuron loss and has gliatrophic effects in the ileum of diabetic rats

BACKGROUND

Peripheral neuropathy caused chronically by diabetes mellitus is related to exacerbation of oxidative stress and a significant reduction in important endogenous antioxidants. L: -Glutamine is an amino acid involved in defense mechanisms and is a substrate for the formation of glutathione, the major endogenous cellular antioxidant.

AIM

This study investigated the effects of 2% L: -glutamine supplementation on peripheral diabetic neuropathy and enteric glia in the ileum in rats.

METHODS

Male Wistar rats were divided into four groups: normoglycemics (N), normoglycemics supplemented with L: -glutamine (NG), diabetics (D), and diabetics supplemented with L: -glutamine (DG). After 120 days, the ileums were processed for HuC/D and S100 immunohistochemistry. Quantitative and morphometric analysis was performed.

RESULTS

Diabetes significantly reduced the number of HuC/D-immunoreactive myenteric neurons per unit area and per ganglion in group D compared with normoglycemic animals (group N). L: -Glutamine (2%) prevented neuronal death induced by diabetes (group DG) compared with group D. The glial density per unit area did not change with diabetes (group D) but was significantly reduced after L: -glutamine supplementation (groups NG and DG). Ganglionic glial density was similar among the four groups. The neuronal area was not altered in groups D and DG. Glial size was reduced in group D; this was reversed by L: -glutamine supplementation (group DG).

CONCLUSIONS

We concluded that 2% L: -glutamine had neuroprotective effects directly on myenteric neurons and indirectly through glial cells, which had gliatrophic effects.

Thioredoxin 1-mediated post-translational modifications: reduction, transnitrosylation, denitrosylation, and related proteomics methodologies

Despite the significance of redox post-translational modifications (PTMs) in regulating diverse signal transduction pathways, the enzymatic systems that catalyze reversible and specific oxidative or reductive modifications have yet to be firmly established. Thioredoxin 1 (Trx1) is a conserved antioxidant protein that is well known for its disulfide reductase activity. Interestingly, Trx1 is also able to transnitrosylate or denitrosylate (defined as processes to transfer or remove a nitric oxide entity to/from substrates) specific proteins. An intricate redox regulatory mechanism has recently been uncovered that accounts for the ability of Trx1 to catalyze these different redox PTMs. In this review, we will summarize the available evidence in support of Trx1 as a specific disulfide reductase, and denitrosylation and transnitrosylation agent, as well as the biological significance of the diverse array of Trx1-regulated pathways and processes under different physiological contexts. The dramatic progress in redox proteomics techniques has enabled the identification of an increasing number of proteins, including peroxiredoxin 1, whose disulfide bond formation and nitrosylation status are regulated by Trx1. This review will also summarize the advancements of redox proteomics techniques for the identification of the protein targets of Trx1-mediated PTMs. Collectively, these studies have shed light on the mechanisms that regulate Trx1-mediated reduction, transnitrosylation, and denitrosylation of specific target proteins, solidifying the role of Trx1 as a master regulator of redox signal transduction.

Genetic deletion of NOS3 increases lethal cardiac dysfunction following mouse cardiac arrest

STUDY AIMS

Cardiac arrest mortality is significantly affected by failure to obtain return of spontaneous circulation (ROSC) despite cardiopulmonary resuscitation (CPR). Severe myocardial dysfunction and cardiovascular collapse further affects mortality within hours of initial ROSC. Recent work suggests that enhancement of nitric oxide (NO) signaling within minutes of CPR can improve myocardial function and survival. We studied the role of NO signaling on cardiovascular outcomes following cardiac arrest and resuscitation using endothelial NO synthase knockout (NOS3(-/-)) mice.

METHODS

Adult female wild-type (WT) and NOS3(-/-) mice were anesthetized, intubated, and instrumented with left-ventricular pressure-volume catheters. Cardiac arrest was induced with intravenous potassium chloride. CPR was performed after 8min of untreated arrest. ROSC rate, cardiac function, whole-blood nitrosylhemoglobin (HbNO) concentrations, heart NOS3 content and phosphorylation (p-NOS3), cyclic guanosine monophosphate (cGMP), and phospho-troponin I (p-TnI) were measured.

RESULTS

Despite equal quality CPR, NOS3(-/-) mice displayed lower rates of ROSC compared to WT (47.6% [10/21] vs. 82.4% [14/17], p<0.005). Among ROSC animals, NOS3(-/-) vs. WT mice exhibited increased left-ventricular dysfunction and 120min mortality. Prior to ROSC, myocardial effectors of NO signaling including cGMP and p-TnI were decreased in NOS3(-/-) vs. WT mice (p<0.05). Following ROSC in WT mice, significant NOS3-dependent increases in circulating HbNO were seen by 120min. Significant increases in cardiac p-NOS3 occurred between end-arrest and 15min post-ROSC, while total NOS3 content was increased by 120min post-ROSC (p<0.05).

CONCLUSIONS

Genetic deletion of NOS3 decreases ROSC rate and worsens post-ROSC left-ventricular function. Poor cardiovascular outcomes are associated with differences in NOS3-dependent myocardial cGMP signaling and circulating NO metabolites.

Redox regulatory mechanism of transnitrosylation by thioredoxin

Transnitrosylation and denitrosylation are emerging as key post-translational modification events in regulating both normal physiology and a wide spectrum of human diseases. Thioredoxin 1 (Trx1) is a conserved antioxidant that functions as a classic disulfide reductase. It also catalyzes the transnitrosylation or denitrosylation of caspase 3 (Casp3), underscoring its central role in determining Casp3 nitrosylation specificity. However, the mechanisms that regulate Trx1 transnitrosylation and denitrosylation of specific targets are unresolved. Here we used an optimized mass spectrometric method to demonstrate that Trx1 is itself nitrosylated by S-nitrosoglutathione at Cys(73) only after the formation of a Cys(32)-Cys(35) disulfide bond upon which the disulfide reductase and denitrosylase activities of Trx1 are attenuated. Following nitrosylation, Trx1 subsequently transnitrosylates Casp3. Overexpression of Trx1(C32S/C35S) (a mutant Trx1 with both Cys(32) and Cys(35) replaced by serine to mimic the disulfide reductase-inactive Trx1) in HeLa cells promoted the nitrosylation of specific target proteins. Using a global proteomics approach, we identified 47 novel Trx1 transnitrosylation target protein candidates. From further bioinformatics analysis of this set of nitrosylated peptides, we identified consensus motifs that are likely to be the determinants of Trx1-mediated transnitrosylation specificity. Among these proteins, we confirmed that Trx1 directly transnitrosylates peroxiredoxin 1 at Cys(173) and Cys(83) and protects it from H(2)O(2)-induced overoxidation. Functionally, we found that Cys(73)-mediated Trx1 transnitrosylation of target proteins is important for protecting HeLa cells from apoptosis. These data demonstrate that the ability of Trx1 to transnitrosylate target proteins is regulated by a crucial stepwise oxidative and nitrosative modification of specific cysteines, suggesting that Trx1, as a master regulator of redox signaling, can modulate target proteins via alternating modalities of reduction and nitrosylation.

Suppression by Ghrelin of Porphyromonas gingivalis-Induced Constitutive Nitric Oxide Synthase S-Nitrosylation and Apoptosis in Salivary Gland Acinar Cells

Oral mucosal inflammatory responses to periodontopathic bacterium, P. gingivalis, and its key virulence factor, LPS, are characterized by a massive rise in epithelial cell apoptosis and the disturbances in NO signaling pathways. Here, we report that the LPS-induced enhancement in rat sublingual salivary gland acinar cell apoptosis and NO generation was associated with the suppression in constitutive nitric oxide synthase (cNOS) activity and a marked increase in the activity of inducible nitric oxide synthase (iNOS). We demonstrate that the detrimental effect of the LPS on cNOS was manifested by the enzyme protein S-nitrosylation, that was susceptible to inhibition by iNOS inhibitor, 1400 W. Further, we show that a peptide hormone, ghrelin, countered the LPS-induced changes in apoptosis and cNOS activity. This effect of ghrelin was reflected in the decrease in cNOS S-nitrosylation and the increase in phosphorylation. Our findings imply that P. gingivalis-induced disturbances in the acinar cell NO signaling pathways result from upregulation in iNOS-derived NO that causes cNOS S-nitrosylation that interferes with its activation through phosphorylation. We also show that ghrelin protection against P. gingivalis-induced disturbances involves cNOS activation associated with a decrease in its S-nitrosylation and the increase in phosphorylation.

Role of constitutive nitric oxide synthase S-nitrosylation in Helicobacter pylori-induced gastric mucosal cell apoptosis: effect of ghrelin

Infection with H. pylori is a primary factor in the etiology of gastric disease, and the excessive NO generation and a massive rise in apoptosis are well recognized features that characterize the mucosal inflammatory responses to the bacterium and its lipopolysaccharide (LPS). Here, we report that H. pylori LPS-induced enhancement in gastric mucosal cell apoptosis and NO generation was associated with the suppression in constitutive nitric oxide synthase (cNOS) activity and a marked up-regulation in the activity of inducible nitric oxide synthase (iNOS). Further, we demonstrate that the detrimental effect of the LPS on cNOS was manifested in the enzyme protein S-nitrosylation, that was susceptible to suppression by iNOS inhibitor, 1400W. Moreover, we show that the countering effect of peptide hormone, ghrelin, on the LPS-induced changes in apoptosis and cNOS activity was reflected in the loss in cNOS S-nitrosylation and the increase in the enzyme phosphorylation. These findings demonstrate that the disturbances in gastric mucosal NO generation system caused by H. pylori result from the iNOS-derived NO suppression of cNOS activation through S-nitrosylation. We also report that ghrelin protection against H. pylori-induced gastric mucosal proapoptotic events involves cNOS activation manifested by the increase in enzyme protein phosphorylation and a decrease in its S-nitrosylation.

Identification and characterization of cysteinyl exposure in proteins by selective mercury labeling and nano-electrospray ionization quadrupole time-of-flight mass spectrometry

We describe a method for probing surface-exposed cysteines in proteins by selective labeling with p-hydroxymercuribenzoate (PMB) combined with nano-electrospray ionization mass spectrometric analysis (nanoESI-MS). The rapid, stoichiometric, and specific labeling by PMB of surface-exposed cysteines allows for characterization of the accessibility of the cysteines using a single MS analysis. Moreover, by taking advantage of the large mass shift of 321 Da, unique isotopic pattern, and enhanced MS signal of PMB-labeled cysteine-containing peptide fragments, the surface-exposed cysteines in proteins can be accurately identified by peptide mapping. The number and sites of reactive cysteines on the surface of human and rat hemoglobins (hHb and rHb) were identified as examples. Collision-induced dissociation tandem mass spectrometric (MS/MS) analysis of specific peptides further confirmed the selective labeling of PMB in hHb. The subtle difference between the different cysteine residues in rHb was also evaluated by multiple PMB titrations. The difference between the two cysteines in their environment may partially explain their reaction specificity. Cysteine 125 in the beta unit of rHb is exposed on the surface, explaining its reactivity with glutathione. Cysteine 13 in the alpha subunit of rHb is much less exposed, and is located in a hydrophobic pocket, a conclusion that is consistent with the previous observation of its selective binding with dimethylarsinous acid, a reactive arsenic metabolite. The method is potentially useful for probing cysteines in other biologically important proteins and for studying proteins that are associated with conformational or structural changes induced by denaturing processes, protein modifications, protein-protein interactions and protein assemblies.

Electrochemistry and nitric oxide mass transport in cancer: why ingestion of sodium nitrite could be effective in treating vascularized tumors

Nitric oxide concentrations in tumors do not reach apoptosis inducing levels when their excess NO is rapidly depleted. The out-flux of NO from a tumor to air or blood scales with the contacting area and with the concentration gradient; the gradient scales with the tumor-air or tumor-blood concentration difference and scales inversely with the thickness of the boundary layer, i.e. the fluid's flow rate. Air-contacting skin and lung cancers account for approximately 60% of all cancers in part because out-diffusion of NO from nascent tumors to air increases the likelihood of their survival. Out-diffusion of NO also explains their initially 2-D spreading at the air interface. Blood is an NO sink because its proteins are rapidly S-nitrosated; depletion of NO by the blood explains the dormancy of tumors until their vascularization and their virulence after vascularization. Erythrocytes store NO(2)- and their carbonic anhydrase converts it to NO and NO(3)(-). Thus, NaNO(2), a common additive in cured meats, may reduce NO out-diffusion by raising the blood NO concentration.

Regulatory role of nitric oxide in the reduced survival of erythrocytes in visceral leishmaniasis

BACKGROUND

Nitric oxide (NO) plays a vital role in maintaining the survivability of circulating erythrocytes. Here we have investigated whether NO depletion associated with visceral leishmaniasis (VL) is responsible for the reduced survival of erythrocytes observed during the disease.

METHODS

Infected hamsters were treated with standard anti-leishmanial sodium stibogluconate (SAG) and NO donor isosorbide dinitrate (ISD). Erythrophagocytosis by macrophages was determined by labelling the cells with FITC followed by flow cytometry. Aggregation of band3 was estimated from band3 associated EMA fluorescence. Caspase 3 activity was measured using immunosorbent assay kit. Phosphatidylserine (PS) externalization and cell shrinkage were determined using annexin V. Aminophspholipid translocase and scramblase activities were measured following NBD-PS and NBD-PC internalization, respectively.

RESULTS

Impairment of both synthesis and uptake of NO resulted in decreased bioavailability of this signaling molecule in erythrocytes in VL. NO level was replenished after simultaneous treatment with ISD and SAG. Combination treatment decreased red cell apoptosis in infected animals by deactivating caspase 3 through s-nitrosylation. Drug treatment prevented infection-mediated ATP depletion and altered calcium homeostasis in erythrocytes. Improved metabolic environment effectively amended dysregulation of aminophospholipid translocase and scramblase, which in turn reduced cell shrinkage, and exposure of phosphatidylserine on the cell surface under the diseased condition.

CONCLUSION AND GENERAL SIGNIFICANCE

In this study, we have identified NO depletion to be an important factor in promoting premature hemolysis with the progress of leishmanial infection. The study implicates NO to be a possible target for future drug development towards the promotion of erythrocyte survival in VL.

Nitric oxide-mediated bcl-2 stabilization potentiates malignant transformation of human lung epithelial cells

Hexavalent chromium (Cr(VI)) compounds are known human carcinogens associated with the incidence of lung cancer. Although a direct correlation between Cr(VI) exposure and lung cancer has been established, several studies aimed at generating animal models for Cr(VI) have yielded inconsistent data that do not affirmatively support findings from epidemiologic studies. Because the lack of a good animal model has hindered the identification of molecular mechanisms involved in Cr(VI) exposure, we developed an in vitro model that facilitates mechanistic studies of Cr(VI)-induced carcinogenesis. We report here that long-term exposure to Cr(VI) leads to the malignant transformation of nontumorigenic human lung epithelial cells. Cr(VI)-transformed cells exhibited loss of contact inhibition, colony formation, and increased rates of cell invasion, migration, and proliferation, as compared with passage-matched control cells. Cr(VI)-transformed cells evaded apoptosis by a mechanism involving S-nitrosylation and stabilization of Bcl-2 protein in a nitric oxide-dependent manner. This study establishes an important in vitro model that facilitates mechanistic studies of Cr(VI)-induced carcinogenesis, and elucidates a novel mechanism that causes apoptosis-resistant malignant transformation of nontumorigenic lung cells in response to a human carcinogen.

Ghrelin protection against lipopolysaccharide-induced gastric mucosal cell apoptosis involves constitutive nitric oxide synthase-mediated caspase-3 S-nitrosylation

Ghrelin, a peptide hormone produced mainly in the stomach, has emerged as an important modulator of the inflammatory responses that are of significance to the maintenance of gastric mucosal integrity. Here, we report on the role of ghrelin in controlling the apoptotic processes induced in gastric mucosal cells by H. pylori lipopolysaccharide (LPS). The countering effect of ghrelin on the LPS-induced mucosal cell apoptosis was associated with the increase in constitutive nitric oxide synthase (cNOS) activity, and the reduction in caspase-3 and inducible nitric oxide synthase (NOS-2). The loss in countering effect of ghrelin on the LPS-induced changes in apoptosis and caspase-3 activity was attained with Src kinase inhibitor, PP2, as well as Akt inhibitor, SH-5, and cNOS inhibitor, L-NAME. Moreover, the effect of ghrelin on the LPS-induced changes in cNOS activity was reflected in the increased cNOS phosphorylation that was sensitive to SH-5. Furthermore, the ghrelin-induced up-regulation in cNOS activity was associated with the increase in caspase-3 S-nitrosylation that was susceptible to the blockage by L-NAME. Therefore, ghrelin protection of gastric mucosal cells against H. pylori LPS-induced apoptosis involves Src/Akt-mediated up-regulation in cNOS activation that leads to the apoptotic signal inhibition through the NO-induced caspase-3 S-nitrosylation.

Protein cysteine S-guanylation and electrophilic signal transduction by endogenous nitro-nucleotides

Nitric oxide (NO), a gaseous free radical that is synthesized in organisms by nitric oxide synthases, participates in a critical fashion in the regulation of diverse physiological functions such as vascular and neuronal signal transduction, host defense, and cell death regulation. Two major pathways of NO signaling involve production of the second messenger guanosine 3',5'-cyclic monophosphate (cGMP) and posttranslational modification (PTM) of redox-sensitive cysteine thiols of proteins. We recently clarified the physiological formation of 8-nitroguanosine 3',5'-cyclic monophosphate (8-nitro-cGMP) as the first demonstration, since the discovery of cGMP more than 40 years ago, of a new second messenger derived from cGMP in mammals. 8-Nitro-cGMP is electrophilic and reacts efficiently with sulfhydryls of proteins to produce a novel PTM via cGMP adduction, a process that we named protein S-guanylation. 8-Nitro-cGMP may regulate electrophilic signaling on the basis of its electrophilicity through induction of S-guanylation of redox sensor proteins. Examples include S-guanylation of the redox sensor protein Kelch-like ECH-associated protein 1 (Keap1), which leads to activation of NF-E2-related factor 2 (Nrf2)-dependent expression of antioxidant and cytoprotective genes. This S-guanylation-mediated activation of an antioxidant adaptive response may play an important role in cytoprotection during bacterial infections and oxidative stress. Identification of new redox-sensitive proteins as targets for S-guanylation may help development of novel therapeutics for oxidative stress- and inflammation-related disorders and vascular diseases as well as understanding of cellular protection against oxidative stress.

Constitutive nitric oxide synthase-mediated caspase-3 S-nitrosylation in ghrelin protection against Porphyromonas gingivalis-induced salivary gland acinar cell apoptosis

Recent advances in identifying the salivary constituents capable of influencing the oral mucosal inflammatory responses have brought to focus the importance of a peptide hormone, ghrelin. Here, we report on the involvement of ghrelin in controlling the apoptotic processes induced in sublingual salivary gland acinar cells by the lipopolysaccharide (LPS) of a periodontopathic bacterium, Porphyromonas gingivalis. We show that the countering effect of ghrelin on the LPS-induced acinar cell apoptosis was associated with the increase in constitutive nitric oxide synthase (cNOS) activity, and the reduction in caspase-3 and inducible nitric oxide synthase (iNOS). The loss in countering effect of ghrelin on the LPS-induced changes in apoptosis and caspase-3 activity was attained with Src kinase inhibitor, PP2, as well as Akt inhibitor, SH-5, and cNOS inhibitor, L-NAME, but not the iNOS inhibitor, 1400W. The effect of ghrelin on the LPS-induced changes in cNOS activity, moreover, was reflected in the increased cNOS phosphorylation that was sensitive to PP2 as well as SH-5. Furthermore, the ghrelin-induced up-regulation in cNOS activity was associated with the increase in caspase-3 S-nitrosylation that was susceptible to the blockage by SH-5 and L-NAME. The findings point to the involvement of ghrelin in Src/Akt kinase-mediated cNOS activation and the apoptogenic signal inhibition through the NO-induced caspase-3 S-nitrosylation.

Nitric oxide: promoter or suppressor of programmed cell death?

Nitric oxide (NO) is a short-lived gaseous free radical that predominantly functions as a messenger and effector molecule. It affects a variety of physiological processes, including programmed cell death (PCD) through cyclic guanosine monophosphate (cGMP)-dependent and - independent pathways. In this field, dominant discoveries are the diverse apoptosis networks in mammalian cells, which involve signals primarily via death receptors (extrinsic pathway) or the mitochondria (intrinsic pathway) that recruit caspases as effector molecules. In plants, PCD shares some similarities with animal cells, but NO is involved in PCD induction via interacting with pathways of phytohormones. NO has both promoting and suppressing effects on cell death, depending on a variety of factors, such as cell type, cellular redox status, and the flux and dose of local NO. In this article, we focus on how NO regulates the apoptotic signal cascade through protein S-nitrosylation and review the recent progress on mechanisms of PCD in both mammalian and plant cells.

Thioredoxins and glutaredoxins: unifying elements in redox biology

Since their discovery as a substrate for ribonucleotide reductase (RNR), the role of thioredoxin (Trx) and glutaredoxin (Grx) has been largely extended through their regulatory function. Both proteins act by changing the structure and activity of a broad spectrum of target proteins, typically by modifying redox status. Trx and Grx are members of families with multiple and partially redundant genes. The number of genes clearly increased with the appearance of multicellular organisms, in part because of new types of Trx and Grx with orthologs throughout the animal and plant kingdoms. The function of Trx and Grx also broadened as cells achieved increased complexity, especially in the regulation arena. In view of these progressive changes, the ubiquitous distribution of Trx and the wide occurrence of Grx enable these proteins to serve as indicators of the evolutionary history of redox regulation. In so doing, they add a unifying element that links the diverse forms of life to one another in an uninterrupted continuum. It is anticipated that future research will embellish this continuum and further elucidate the properties of these proteins and their impact on biology. The new information will be important not only to our understanding of the role of Trx and Grx in fundamental cell processes but also to future societal benefits as the proteins find new applications in a range of fields.

17beta-Estradiol induces protein S-nitrosylation in the endothelium

AIMS

Estrogen induces nitric oxide (NO) in the endothelium and appears to protect against inflammation and atherosclerosis. NO can induce post-translational protein modifications such as cysteine S-nitrosylation in the cellular proteins which may exert anti-inflammatory effects. However, whether estrogen can induce protein S-nitrosylation in the endothelium is not known. Given this background, we investigated the role of 17beta-estradiol (E2beta), the major form of estrogen in the body, on endothelial protein S-nitrosylation.

METHODS AND RESULTS

Experiments were performed in human umbilical vein endothelial cells (HUVECs). S-nitrosylation was detected by immunostaining for nitrosocysteine and further confirmed by biotin switch method. Ovariectomized 12-month-old Sprague-Dawley rats with/without estradiol supplementation were used for in vivo validation of findings. We found that physiologically relevant doses of E2beta increased protein S-nitrosylation in HUVECs through estrogen receptor-alpha (ERalpha) and endothelial nitric oxide synthase (eNOS). Interestingly, specific agonists for both ERalpha and ERbeta increased eNOS protein expression, while only the former could activate eNOS through phosphorylation. S-nitrosylation by E2beta prevented angiotensin II-induced upregulation of intercellular cell adhesion molecule-1, suggesting a potential anti-inflammatory mechanism. Finally, we showed that exogenous E2beta could increase endothelial S-nitrosylation in vivo in a rat model.

CONCLUSION

Our results demonstrate for the first time that E2beta increases protein S-nitrosylation in the vascular endothelium, which might be a novel pathway to mediate the protective effects on the vasculature.

Nitric oxide in cell survival: a janus molecule

Nitric oxide (NO), plays multiple roles in the nervous system. In addition to regulating proliferation, survival and differentiation of neurons, NO is involved in synaptic activity, neural plasticity, and memory function. Nitric oxide promotes survival and differentiation of neural cells and exerts long-lasting effects through regulation of transcription factors and modulation of gene expression. Signaling by reactive nitrogen species is carried out mainly by targeted modifications of critical cysteine residues in proteins, including S-nitrosylation and S-oxidation, as well as by lipid nitration. NO and other reactive nitrogen species are also involved in neuroinflammation and neurodegeneration, such as in Alzheimer disease, amyotrophic lateral sclerosis, Parkinson disease, multiple sclerosis, Friedreich ataxia, and Huntington disease. Susceptibility to NO and peroxynitrite exposure may depend on factors such as the intracellular reduced glutathione and cellular stress resistance signaling pathways. Thus, neurons, in contrast to astrocytes, appear particularly vulnerable to the effects of nitrosative stress. This article reviews the current understanding of the cytotoxic versus cytoprotective effects of NO in the central nervous system, highlighting the Janus-faced properties of this small molecule. The significance of NO in redox signaling and modulation of the adaptive cellular stress responses and its exciting future perspectives also are discussed.

Nitric oxide suppresses transforming growth factor-beta1-induced epithelial-to-mesenchymal transition and apoptosis in mouse hepatocytes

Nitric oxide (NO) is a multifunctional regulator that is implicated in various physiological and pathological processes. Here we report that administration of NO donor S-nitroso-N-acetylpenicillamine (SNAP) inhibited transforming growth factor-beta1 (TGF-beta1)-induced epithelial-to-mesenchymal transition (EMT) and apoptosis in mouse hepatocytes. Overexpression of inducible NO synthase (iNOS) by transfection of the iNOS-expressing vector, which increased NO production, also inhibited the TGF-beta1-induced EMT and apoptosis in these cells. Treatment of cells with proinflammatory mediators, including tumor necrosis factor (TNF)-alpha, interleukin (IL)-1beta, and interferon (IFN)-gamma, which increased the endogenous NO production, produced the same inhibitory effect. Furthermore, exogenous NO donor SNAP treatment caused a decrease in the intracellular adenosine triphosphate (ATP) levels. Consistently, depletion of intracellular ATP by mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP) inhibited the TGF-beta1-induced EMT and apoptosis, suggesting that an NO-induced decrease of ATP involved in the NO-mediated inhibition of TGF-beta1-induced EMT and apoptosis. NO and FCCP also inhibited TGF-beta1-induced STAT3 activation, suggesting that signal transducer and activator of transcription 3 inactivation is involved in the NO-induced effects on TGF-beta1-induced EMT and apoptosis.

CONCLUSION

Our study indicates that NO plays an important role in the inhibition of TGF-beta1-induced EMT and apoptosis in mouse hepatocytes through the downregulation of intracellular ATP levels. The data provide an insight into the in vivo mechanisms on the function of NO during the processes of both EMT and apoptosis.

Elevated neuronal nitric oxide synthase expression during ageing and mitochondrial energy production

This study evaluated the effect of ageing on brain mitochondrial function mediated through protein post-translational modifications. Neuronal nitric oxide synthase increased with age and this led to a discreet pattern of nitration of mitochondrial proteins. LC/MS/MS analyses identified the nitrated mitochondrial proteins as succinyl-CoA-transferase and F1-ATPase; the latter was nitrated at Tyr269, suggesting deficient ADP binding to the active site. Activities of succinyl-CoA-transferase, F1-ATPase and cytochrome oxidase decreased with age. The decreased activity of the latter cannot be ascribed to protein modifications and is most likely due to a decreased expression and assembly of complex IV. Mitochondrial protein post-translational modifications were associated with a moderately impaired mitochondrial function, as indicated by the decreased respiratory control ratios as a function of age and by the release of mitochondrial cytochrome c to the cytosol, thus supporting the amplification of apoptotic cascades.

Amino acids: metabolism, functions, and nutrition

Recent years have witnessed the discovery that amino acids (AA) are not only cell signaling molecules but are also regulators of gene expression and the protein phosphorylation cascade. Additionally, AA are key precursors for syntheses of hormones and low-molecular weight nitrogenous substances with each having enormous biological importance. Physiological concentrations of AA and their metabolites (e.g., nitric oxide, polyamines, glutathione, taurine, thyroid hormones, and serotonin) are required for the functions. However, elevated levels of AA and their products (e.g., ammonia, homocysteine, and asymmetric dimethylarginine) are pathogenic factors for neurological disorders, oxidative stress, and cardiovascular disease. Thus, an optimal balance among AA in the diet and circulation is crucial for whole body homeostasis. There is growing recognition that besides their role as building blocks of proteins and polypeptides, some AA regulate key metabolic pathways that are necessary for maintenance, growth, reproduction, and immunity. They are called functional AA, which include arginine, cysteine, glutamine, leucine, proline, and tryptophan. Dietary supplementation with one or a mixture of these AA may be beneficial for (1) ameliorating health problems at various stages of the life cycle (e.g., fetal growth restriction, neonatal morbidity and mortality, weaning-associated intestinal dysfunction and wasting syndrome, obesity, diabetes, cardiovascular disease, the metabolic syndrome, and infertility); (2) optimizing efficiency of metabolic transformations to enhance muscle growth, milk production, egg and meat quality and athletic performance, while preventing excess fat deposition and reducing adiposity. Thus, AA have important functions in both nutrition and health.

L-Glutamine or L-alanyl-L-glutamine prevents oxidant- or endotoxin-induced death of neonatal enterocytes

This study tested the hypothesis that L-glutamine (Gln) or L-alanyl-L-glutamine (Ala-Gln) prevents oxidant- or endotoxin-induced death of neonatal enterocytes. Enterocytes of neonatal pigs rapidly hydrolyzed Ala-Gln and utilized Gln. To determine whether Gln or Ala-Gln has a cytoprotective effect, IPEC-1 cells were cultured for 24 h in Gln-free Dulbecco's modified Eagle's-F12 Ham medium containing 0, 0.5, 2.0 or 5.0 mM Gln or Ala-Gln, and 0, 0.5 mM H(2)O(2) or 30 ng/ml lipopolysaccharide (LPS). Without Gln or Ala-Gln, H(2)O(2)- or LPS-treated cells exhibited almost complete death. Gln or Ala-Gln at 0.5, 2 and 5 mM dose-dependently reduced H(2)O(2)- or LPS-induced cell death by 14, 54 and 95%, respectively, whereas D: -glutamine, alanine, glutamate, ornithine, proline, glucosamine or nucleosides had no effect. To evaluate the effectiveness of Gln or Ala-Gln in vivo, 7-day-old piglets received one-week oral administration of Gln or Ala-Gln (3.42 mmol/kg body weight) twice daily and then a single intraperitoneal injection of LPS (0.1 mg/kg body weight); piglets were euthanized in 24 and 48 h to analyze intestinal apoptotic proteins and morphology. Administration of Gln or Ala-Gln to LPS-challenged piglets increased Gln concentrations in small-intestinal lumen and plasma, reduced intestinal expression of Toll-like receptor-4, active caspase-3 and NFkB, ameliorated intestinal injury, decreased rectal temperature, and enhanced growth performance. These results demonstrate a protective effect of Gln or Ala-Gln against H(2)O(2)- or LPS-induced enterocyte death. The findings support addition of Gln or Ala-Gln to current Gln-free pediatric amino acid solutions to prevent intestinal oxidative injury and inflammatory disease in neonates.