A metabolic enzyme for S-nitrosothiol conserved from bacteria to humans

Transnitrosylation: A Factor in Nitric Oxide-Mediated Penile Erection

INTRODUCTION

Nitric oxide (NO) signaling can be mediated not only through classic 3',5'-cyclic guanosine monophosphate but also through S-nitrosylation. However, the impact of S-nitrosylation on erectile function and in NO regulation and oxidative stress in the penis remains poorly understood.

AIMS

To characterize the role of S-nitrosoglutathione reductase (GSNOR), a major regulator of S-nitrosylation homeostasis, on erection physiology and on endothelial NO synthase (eNOS) function and oxidative-nitrosative stress in the penis.

METHODS

Adult GSNOR-deficient and wild-type (WT) mice were used. Erectile function was assessed in response to electrical stimulation of the cavernous nerve. Total NO in penile homogenates was measured by Griess reaction. Protein S-nitrosylation, eNOS phosphorylation on Ser-1177 (positive regulatory site), eNOS uncoupling, and markers of oxidative stress (4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine) in the penis were measured by western blot.

MAIN OUTCOME MEASURES

Erectile function, eNOS function, and oxidative stress in the penis of GSNOR-deficient mice.

RESULTS

Erectile function was intact in GSNOR-deficient mice. Total S-nitrosylated proteins were increased (P < .05) in the GSNOR(-/-) compared with WT mouse penis. Although eNOS phosphorylation on Ser-1177 did not differ between the GSNOR(-/-) and WT mouse penises at baseline, electrical stimulation of the cavernous nerve increased (P < .05) phosphorylated eNOS in the WT mouse penis but failed to increase phosphorylated eNOS in the GSNOR(-/-) mouse penis. Total NO production was decreased (P < .05), whereas eNOS uncoupling, 4-hydroxy-2-nonenal, malondialdehyde, and nitrotyrosine were increased (P < .05) in the GSNOR-deficient mouse penis compared with the WT mouse penis.

CONCLUSION

Transnitrosylation mechanisms play an important role in regulating NO bioactivity in the penis. Deficiency of GSNOR leads to eNOS dysfunction and increased oxidative damage, suggesting that homeostatic eNOS function in the penis is governed by transnitrosylation.

The role of S-nitrosoglutathione reductase (GSNOR) in human disease and therapy

S-nitrosoglutathione reductase (GSNOR), or ADH5, is an enzyme in the alcohol dehydrogenase (ADH) family. It is unique when compared to other ADH enzymes in that primary short-chain alcohols are not its principle substrate. GSNOR metabolizes S-nitrosoglutathione (GSNO), S-hydroxymethylglutathione (the spontaneous adduct of formaldehyde and glutathione), and some alcohols. GSNOR modulates reactive nitric oxide (•NO) availability in the cell by catalyzing the breakdown of GSNO, and indirectly regulates S-nitrosothiols (RSNOs) through GSNO-mediated protein S-nitrosation. The dysregulation of GSNOR can significantly alter cellular homeostasis, leading to disease. GSNOR plays an important regulatory role in smooth muscle relaxation, immune function, inflammation, neuronal development and cancer progression, among many other processes. In recent years, the therapeutic inhibition of GSNOR has been investigated to treat asthma, cystic fibrosis and interstitial lung disease (ILD). The direct action of •NO on cellular pathways, as well as the important regulatory role of protein S-nitrosation, is closely tied to GSNOR regulation and defines this enzyme as an important therapeutic target.

Evidence towards the involvement of nitric oxide in drought tolerance of sugarcane

Exogenous supply of nitric oxide (NO) increases drought tolerance in sugarcane plants. However, little is known about the role of NO produced by plants under water deficit. The aim of this study was to test the hypothesis that drought-tolerance in sugarcane is associated with NO production and metabolism, with the more drought-tolerant genotype presenting higher NO accumulation in plant tissues. The sugarcane genotypes IACSP95-5000 (drought-tolerant) and IACSP97-7065 (drought-sensitive) were submitted to water deficit by adding polyethylene glycol (PEG-8000) in nutrient solution to reduce the osmotic potential to -0.4 MPa. To evaluate short-time responses to water deficit, leaf and root samples were taken after 24 h under water deficit. The drought-tolerant genotype presented higher root extracellular NO content, which was accompanied by higher root nitrate reductase (NR) activity as compared to the drought-sensitive genotype under water deficit. In addition, the drought-tolerant genotype had higher leaf intracellular NO content than the drought-sensitive one. IACSP95-5000 exhibited decreases in root S-nitrosoglutathione reductase (GSNOR) activity under water deficit, suggesting that S-nitrosoglutathione (GSNO) is less degraded and that the drought-tolerant genotype has a higher natural reservoir of NO than the drought-sensitive one. Those differences in intracellular and extracellular NO contents and enzymatic activities were associated with higher leaf hydration in the drought-tolerant genotype as compared to the sensitive one under water deficit.

VEGF-A Stimulates STAT3 Activity via Nitrosylation of Myocardin to Regulate the Expression of Vascular Smooth Muscle Cell Differentiation Markers

Vascular endothelial growth factor A (VEGF-A) is a pivotal player in angiogenesis. It is capable of influencing such cellular processes as tubulogenesis and vascular smooth muscle cell (VSMC) proliferation, yet very little is known about the actual signaling events that mediate VEGF-A induced VSMC phenotypic switch. In this report, we describe the identification of an intricate VEGF-A-induced signaling cascade that involves VEGFR2, STAT3, and Myocardin. We demonstrate that VEGF-A promotes VSMC proliferation via VEGFR2/STAT3-mediated upregulating the proliferation of markers like Cyclin D1 and PCNA. Specifically, VEGF-A leads to nitrosylation of Myocardin, weakens its effect on promoting the expression of contractile markers and is unable to inhibit the activation of STAT3. These observations reinforce the importance of nitric oxide and S-nitrosylation in angiogenesis and provide a mechanistic pathway for VEGF-A-induced VSMC phenotypic switch. In addition, Myocardin, GSNOR and GSNO can create a negative feedback loop to regulate the VSMC phenotypic switch. Thus, the discovery of this interactive network of signaling pathways provides novel and unexpected therapeutic targets for angiogenesis-dependent diseases.

Adenosine A1 receptor activation increases myocardial protein S-nitrosothiols and elicits protection from ischemia-reperfusion injury in male and female hearts

Nitric oxide (NO) plays an important role in cardioprotection, and recent work from our group and others has implicated protein S-nitrosylation (SNO) as a critical component of NO-mediated protection in different models, including ischemic pre- and post-conditioning and sex-dependent cardioprotection. However, studies have yet to examine whether protein SNO levels are similarly increased with pharmacologic preconditioning in male and female hearts, and whether an increase in protein SNO levels, which is protective in male hearts, is sufficient to increase baseline protection in female hearts. Therefore, we pharmacologically preconditioned male and female hearts with the adenosine A1 receptor agonist N6-cyclohexyl adenosine (CHA). CHA administration prior to ischemia significantly improved functional recovery in both male and female hearts compared to baseline in a Langendorff-perfused heart model of ischemia-reperfusion injury (% of preischemic function ± SE: male baseline: 37.5±3.4% vs. male CHA: 55.3±3.2%; female baseline: 61.4±5.7% vs. female CHA: 76.0±6.2%). In a separate set of hearts, we found that CHA increased p-Akt and p-eNOS levels. We also used SNO-resin-assisted capture with LC-MS/MS to identify SNO proteins in male and female hearts, and determined that CHA perfusion induced a modest increase in protein SNO levels in both male (11.4%) and female (12.3%) hearts compared to baseline. These findings support a potential role for protein SNO in a model of pharmacologic preconditioning, and provide evidence to suggest that a modest increase in protein SNO levels is sufficient to protect both male and female hearts from ischemic injury. In addition, a number of the SNO proteins identified with CHA treatment were also observed with other forms of cardioprotective stimuli in prior studies, further supporting a role for protein SNO in cardioprotection.

Luminescent Strategies for Label-Free G-Quadruplex-Based Enzyme Activity Sensing

By catalyzing highly specific and tightly controlled chemical reactions, enzymes are essential to maintaining normal cellular physiology. However, aberrant enzymatic activity can be linked to the pathogenesis of various diseases. Therefore, the unusual activity of particular enzymes can represent testable biomarkers for the diagnosis or screening of certain diseases. In recent years, G-quadruplex-based platforms have attracted wide attention for the monitoring of enzymatic activities. In this Personal Account, we discuss our group's works on the development of G-quadruplex-based sensing system for enzyme activities by using mainly iridium(III) complexes as luminescent label-free probes. These studies showcase the versatility of the G-quadruplex for developing assays for a variety of different enzymes.

Balance between S-nitrosylation and denitrosylation modulates myoblast proliferation independently of soluble guanylyl cyclase activation

Nitric oxide (NO) contributes to myogenesis by regulating the transition between myoblast proliferation and fusion through cGMP signaling. NO can form S-nitrosothiols (RSNO), which control signaling pathways in many different cell types. However, neither the role of RSNO content nor its regulation by the denitrosylase activity of S-nitrosoglutathione reductase (GSNOR) during myogenesis is understood. Here, we used primary cultures of chick embryonic skeletal muscle cells to investigate whether changes in intracellular RSNO alter proliferation and fusion of myoblasts in the presence and absence of cGMP. Cultures were grown to fuse most of the myoblasts into myotubes, with and without S-nitrosocysteine (CysNO), 8-Br-cGMP, DETA-NO, or inhibitors for NO synthase (NOS), GSNOR, soluble guanylyl cyclase (sGC), or a combination of these, followed by analysis of GSNOR activity, protein expression, RSNO, cGMP, and cell morphology. Although the activity of GSNOR increased progressively over 72 h, inhibiting GSNOR (by GSNOR inhibitor - GSNORi - or by knocking down GSNOR with siRNA) produced an increase in RSNO and in the number of myoblasts and fibroblasts, accompanied by a decrease in myoblast fusion index. This was also detected with CysNO supplementation. Enhanced myoblast number was proportional to GSNOR inhibition. Effects of the GSNORi and GSNOR knockdown were blunted by NOS inhibition, suggesting their dependence on NO synthesis. Interestingly, GSNORi and GSNOR knockdown reversed the attenuated proliferation obtained with sGC inhibition in myoblasts, but not in fibroblasts. Hence myoblast proliferation is enhanced by increasing RSNO, and regulated by GSNOR activity, independently of cGMP production and signaling.

The Chaperone TRAP1 As a Modulator of the Mitochondrial Adaptations in Cancer Cells

Mitochondria can receive, integrate, and transmit a variety of signals to shape many biochemical activities of the cell. In the process of tumor onset and growth, mitochondria contribute to the capability of cells of escaping death insults, handling changes in ROS levels, rewiring metabolism, and reprograming gene expression. Therefore, mitochondria can tune the bioenergetic and anabolic needs of neoplastic cells in a rapid and flexible way, and these adaptations are required for cell survival and proliferation in the fluctuating environment of a rapidly growing tumor mass. The molecular bases of pro-neoplastic mitochondrial adaptations are complex and only partially understood. Recently, the mitochondrial molecular chaperone TRAP1 (tumor necrosis factor receptor associated protein 1) was identified as a key regulator of mitochondrial bioenergetics in tumor cells, with a profound impact on neoplastic growth. In this review, we analyze these findings and discuss the possibility that targeting TRAP1 constitutes a new antitumor approach.

Bacillus aryabhattai SRB02 tolerates oxidative and nitrosative stress and promotes the growth of soybean by modulating the production of phytohormones

Plant growth promoting rhizobacteria (PGPR) are diverse, naturally occurring bacteria that establish a close association with plant roots and promote the growth and immunity of plants. Established mechanisms involved in PGPR-mediated plant growth promotion include regulation of phytohormones, improved nutrient availability, and antagonistic effects on plant pathogens. In this study, we isolated a bacterium from the rhizospheric soil of a soybean field in Chungcheong buk-do, South Korea. Using 16S rRNA sequencing, the bacterium was identified as Bacillus aryabhattai strain SRB02. Here we show that this strain significantly promotes the growth of soybean. Gas chromatography-mass spectrometry analysis showed that SRB02 produced significant amounts of abscisic acid, indole acetic acid, cytokinin and different gibberellic acids in culture. SRB02-treated soybean plants showed significantly better heat stress tolerance than did untreated plants. These plants also produced consistent levels of ABA under heat stress and exhibited ABA-mediated stomatal closure. High levels of IAA, JA, GA12, GA4, and GA7, were recorded in SRB02-treated plants. These plants produced longer roots and shoots than those of control plants. B. aryabhattai SRB02 was found to be highly tolerant to oxidative stress induced by H2O2 and MV potentiated by high catalase (CAT) and superoxide dismutase (SOD) activities. SRB02 also tolerated high nitrosative stress induced by the nitric oxide donors GSNO and CysNO. Because of these attributes, B. aryabhattai SRB02 may prove to be a valuable resource for incorporation in biofertilizers and other soil amendments that seek to improve crop productivity.

Normalization of hemoglobin-based oxygen carrier-201 induced vasoconstriction: targeting nitric oxide and endothelin

Hemoglobin-based oxygen carrier (HBOC)-201 is a cell-free modified hemoglobin solution potentially facilitating oxygen uptake and delivery in cardiovascular disorders and hemorrhagic shock. Clinical use has been hampered by vasoconstriction in the systemic and pulmonary beds. Therefore, we aimed to 1) determine the possibility of counteracting HBOC-201-induced pressor effects with either adenosine (ADO) or nitroglycerin (NTG); 2) assess the potential roles of nitric oxide (NO) scavenging, reactive oxygen species (ROS), and endothelin (ET) in mediating the observed vasoconstriction; and 3) compare these effects in resting and exercising swine. Chronically instrumented swine were studied at rest and during exercise after administration of HBOC-201 alone or in combination with ADO. The role of NO was assessed by supplementation with NTG or administration of the eNOS inhibitor N^ω-nitro-l-arginine. Alternative vasoactive pathways were investigated via intravenous administration of the ET_A/ET_B receptor blocker tezosentan or a mixture of ROS scavengers. The systemic and to a lesser extent the pulmonary pressor effects of HBOC-201 could be counteracted by ADO; however, dosage titration was very important to avoid systemic hypotension. Similarly, supplementation of NO with NTG negated the pressor effects but also required titration of the dose. The pressor response to HBOC-201 was reduced after eNOS inhibition and abolished by simultaneous ET_A/ET_B receptor blockade, while ROS scavenging had no effect. In conclusion, the pressor response to HBOC-201 is mediated by vasoconstriction due to NO scavenging and production of ET. Further research should explore the effect of longer-acting ET receptor blockers to counteract the side effect of hemoglobin-based oxygen carriers.NEW & NOTEWORTHY Hemoglobin-based oxygen carrier (HBOC)-201 can disrupt hemodynamic homeostasis, mimicking some aspects of endothelial dysfunction, resulting in elevated systemic and pulmonary blood pressures. HBOC-201-induced vasoconstriction is mediated by scavenging nitric oxide (NO) and by upregulating endothelin (ET) production. Pressor effects can be prevented by adjuvant treatment with NO donors or direct vasodilators, such as nitroglycerin or adenosine, but dosages must be carefully monitored to avoid hypotension. However, hemodynamic normalization is more easily achieved via administration of an ET receptor blocker.

Shedding light on NO homeostasis: Light as a key regulator of glutathione and nitric oxide metabolisms during seedling deetiolation

Despite the significant impacts of light on nitric oxide (NO) levels in plants, the mechanism underlying the influence of this environmental factor on NO metabolism remains poorly understood. A critical mechanism controlling NO levels in plant cells relies on the S-nitrosylation of glutathione (GSH), giving rise to S-nitrosoglutathione (GSNO), which can be either stored or degraded depending on the cellular context. Here, we demonstrate that a strict balance is maintained between NO generation and scavenging during tomato (Solanum lycopersicum) seedling deetiolation. Given the absence of accurate methods in the literature to estimate NO scavenging in planta, we first developed a simple, robust system to continuously monitor the global in vivo NO scavenging by plant tissues. Then, using photomorphogenic tomato mutants, we demonstrated that the light-evoked de-etiolation is associated with a dramatic rise in NO content followed by a progressive increment in NO scavenging capacity of the tissues. Light-driven increments in NO scavenging rates coincided with pronounced rises in S-nitrosothiol content and GSNO reductase (GSNOR) activity, thereby suggesting that GSNO formation and subsequent removal via GSNOR might be key for controlling NO levels during seedling deetiolation. Accordingly, treatments with thiol-blocking compounds further indicated that thiol nitrosylation might be critically involved in the NO scavenging mechanism responsible for maintaining NO homeostasis during deetiolation. The impacts of both light and NO on the transcriptional profile of glutathione metabolic genes also revealed an independent but coordinated action of these signals on the regulation of key components of glutathione and GSNO metabolisms. Altogether, these data indicated that GSNO formation and subsequent removal might facilitate maintaining NO homeostasis during light-driven seedling deetiolation.

New Insights in Oxidant Biology in Asthma

Research over the past 30 years has identified mechanistic biochemical oxidation pathways that contribute to asthma pathophysiology. Redox imbalance is present in asthma and strongly linked to the pathobiology of airflow obstruction, airway hyperreactivity, and remodeling. High levels of reactive oxygen species, reactive nitrogen species, and oxidatively modified proteins in the lung, blood, and urine provide conclusive evidence for pathologic oxidation in asthma. Concurrent loss of antioxidants, such as superoxide dismutases and catalase, is attributed to redox modifications of the enzymes, and further amplifies the oxidative injury in the airway. The presence of high levels of urine bromotyrosine, an oxidation product of eosinophil peroxidase, identifies activated eosinophils, and shows promise for use as a noninvasive biomarker of poor asthma control.

Overexpression of E3 Ubiquitin Ligase Gene AdBiL Contributes to Resistance against Chilling Stress and Leaf Mold Disease in Tomato

Ubiquitination is a common regulatory mechanism, playing a critical role in diverse cellular and developmental processes in eukaryotes. However, a few reports on the functional correlation between E3 ubiquitin ligases and reactive oxygen species (ROS) or reactive nitrogen species (RNS) metabolism in response to stress are currently available in plants. In the present study, the E3 ubiquitin ligase gene AdBiL (Adi3 Binding E3 Ligase) was introduced into tomato line Ailsa Craig via Agrobacterium-mediated method. Transgenic lines were confirmed for integration into the tomato genome using PCR. Transcription of AdBiL in various transgenic lines was determined using real-time PCR. Evaluation of stress tolerance showed that T₁ generation of transgenic tomato lines showed only mild symptoms of chilling injury as evident by higher biomass accumulation and chlorophyll content than those of non-transformed plants. Compared with wild-type plants, the contents of AsA, AsA/DHA, GSH and the activity of GaILDH, γ-GCS and GSNOR were increased, while H₂O₂, [Formula: see text], MDA, NO, SNOs, and GSNO accumulations were significantly decreased in AdBiL overexpressing plants in response to chilling stress. Furthermore, transgenic tomato plants overexpressing AdBiL showed higher activities of enzymes such as G6PDH, 6PGDH, NADP-ICDH, and NADP-ME involved in pentose phosphate pathway (PPP). The transgenic tomato plants also exhibited an enhanced tolerance against the necrotrophic fungus Cladosporium fulvum. Tyrosine nitration protein was activated in the plants infected with leaf mold disease, while the inhibition could be recovered in AdBiL gene overexpressing lines. Taken together, our results revealed a possible physiological role of AdBiL in the activation of the key enzymes of AsA-GSH cycle, PPP and down-regulation of GSNO reductase, thereby reducing oxidative and nitrosative stress in plants. This study demonstrates an optimized transgenic strategy using AdBiL gene for crop improvement against biotic and abiotic stress factors.

Excessive Cellular S-nitrosothiol Impairs Endocytosis of Auxin Efflux Transporter PIN2

S-nitrosoglutathione reductase (GSNOR1) is the key enzyme that regulates cellular levels of S-nitrosylation across kingdoms. We have previously reported that loss of GSNOR1 resulted in impaired auxin signaling and compromised auxin transport in Arabidopsis, leading to the auxin-related morphological phenotypes. However, the molecular mechanism underpinning the compromised auxin transport in gsnor1-3 mutant is still unknown. Endocytosis of plasma-membrane (PM)-localized efflux PIN proteins play critical roles in auxin transport. Therefore, we investigate whether loss of GSNOR1 function has any effects on the endocytosis of PIN-FORMED (PIN) proteins. It was found that the endocytosis of either the endogenous PIN2 or the transgenically expressed PIN2-GFP was compromised in the root cells of gsnor1-3 seedlings relative to Col-0. The internalization of PM-associated PIN2 or PIN2-GFP into Brefeldin A (BFA) bodies was significantly reduced in gsnor1-3 upon BFA treatment in a manner independent of de novo protein synthesis. In addition, the exogenously applied GSNO not only compromised the endocytosis of PIN2-GFP but also inhibited the root elongation in a concentration-dependent manner. Taken together, our results indicate that, besides the reduced PIN2 level, one or more compromised components in the endocytosis pathway could account for the reduced endocytosis of PIN2 in gsnor1-3.

RhoA S-nitrosylation as a regulatory mechanism influencing endothelial barrier function in response to G+-bacterial toxins

Disruption of the endothelial barrier in response to Gram positive (G⁺) bacterial toxins is a major complication of acute lung injury (ALI) and can be further aggravated by antibiotics which stimulate toxin release. The integrity of the pulmonary endothelial barrier is mediated by the balance of disruptive forces such as the small GTPase RhoA, and protective forces including endothelium-derived nitric oxide (NO). How NO protects against the barrier dysfunction is incompletely understood and our goal was to determine whether NO and S-nitrosylation can modulate RhoA activity and whether this mechanism is important for G⁺ toxin-induced microvascular permeability. We found that the G⁺ toxin listeriolysin-O (LLO) increased RhoA activity and that NO and S-NO donors inhibit RhoA activity. RhoA was robustly S-nitrosylated as determined by biotin-switch and mercury column analysis. MS revealed that three primary cysteine residues are S-nitrosylated including cys16, cys20 and cys159. Mutation of these residues to serine diminished S-nitrosylation to endogenous NO and mutant RhoA was less sensitive to inhibition by S-NO. G⁺-toxins stimulated the denitrosylation of RhoA which was not mediated by S-nitrosoglutathione reductase (GSNOR), thioredoxin (TRX) or thiol-dependent enzyme activity but was instead stimulated directly by elevated calcium levels. Calcium-promoted the direct denitrosylation of WT but not mutant RhoA and mutant RhoA adenovirus was more effective than WT in disrupting the barrier integrity of human lung microvascular endothelial cells. In conclusion, we reveal a novel mechanism by which NO and S-nitrosylation reduces RhoA activity which may be of significance in the management of pulmonary endothelial permeability induced by G⁺-toxins.

Nitrosative Stress Response in Vibrio cholerae: Role of S-Nitrosoglutathione Reductase

Vibrio cholerae, the causative agent of cholera, poses serious threats to humans worldwide. V. cholerae faces host inflammatory response and encounters nitrosative stress before establishing successful colonization. It is not clear how V. cholerae combats nitric oxide and reactive nitrogen species. In the present study, we used three clinical strains of V. cholerae and tested their nitrosative stress response pattern towards sodium nitroprusside (SNP) and S-Nitrosoglutathione (GSNO). Among them, V. cholerae, belonging to both O1 and O139 serotypes, showed moderate resistance to SNP and GSNO. However, a V. cholerae strain belonging to non O1 and non O139 showed sensitivity to SNP but resistance towards GSNO. Reduced glutathione and glutathione reductase play a significant role to combat nitrosative stress in V. cholerae. This is the first report where we show the presence of GSNO reductase activity in V. cholerae and that it plays an important role to detoxify S-Nitrosoglutathione. GSNO reductase activity of V. cholerae was regulated by posttranslational modification through S-nitrosylation under in vitro conditions which could be reversed by dithiothreitol (DTT). In addition, we show that biofilm formation remained unaffected under nitrosative stress in V. cholerae.

Regulation of Anticancer Styrylpyrone Biosynthesis in the Medicinal Mushroom Inonotus obliquus Requires Thioredoxin Mediated Transnitrosylation of S-nitrosoglutathione Reductase

The medicinal macrofungus Inonotus obliquus widely utilized as folk medicine in Russia and Baltic countries is a source of phenylpropanoid-derived styrylpyrone polyphenols that can inhibit tumor proliferation. Insights into the regulatory machinery that controls I. obliquus styrylpyrone polyphenol biosynthesis will enable strategies to increase the production of these molecules. Here we show that Thioredoxin (Trx) mediated transnitrosylation of S-nitrosoglutathione reductase (GSNOR) underpins the regulation of styrylpyrone production, driven by nitric oxide (NO) synthesis triggered by P. morii coculture. NO accumulation results in the S-nitrosylation of PAL and 4CL required for the synthesis of precursor phenylpropanoids and styrylpyrone synthase (SPS), integral to the production of styrylpyrone, inhibiting their activities. These enzymes are targeted for denitrosylation by Trx proteins, which restore their activity. Further, this Trx S-nitrosothiol (SNO) reductase activity was potentiated following S-nitrosylation of Trx proteins at a non-catalytic cysteine (Cys) residue. Intriguingly, this process was counterbalanced by Trx denitrosylation, mediated by Trx-dependent transnitrosylation of GSNOR. Thus, unprecedented interplay between Trx and GSNOR oxidoreductases regulates the biosynthesis of styrylpyrone polyphenols in I. obliquus.

Role of sulfiredoxin as a peroxiredoxin-2 denitrosylase in human iPSC-derived dopaminergic neurons

Recent studies have pointed to protein S-nitrosylation as a critical regulator of cellular redox homeostasis. For example, S-nitrosylation of peroxiredoxin-2 (Prx2), a peroxidase widely expressed in mammalian neurons, inhibits both enzymatic activity and protective function against oxidative stress. Here, using in vitro and in vivo approaches, we identify a role and reaction mechanism of the reductase sulfiredoxin (Srxn1) as an enzyme that denitrosylates (thus removing -SNO) from Prx2 in an ATP-dependent manner. Accordingly, by decreasing S-nitrosylated Prx2 (SNO-Prx2), overexpression of Srxn1 protects dopaminergic neural cells and human-induced pluripotent stem cell (hiPSC)-derived neurons from NO-induced hypersensitivity to oxidative stress. The pathophysiological relevance of this observation is suggested by our finding that SNO-Prx2 is dramatically increased in murine and human Parkinson's disease (PD) brains. Our findings therefore suggest that Srxn1 may represent a therapeutic target for neurodegenerative disorders such as PD that involve nitrosative/oxidative stress.

S-Nitrosoglutathione Attenuates Airway Hyperresponsiveness in Murine Bronchopulmonary Dysplasia

Bronchopulmonary dysplasia (BPD) is characterized by lifelong obstructive lung disease and profound, refractory bronchospasm. It is observed among survivors of premature birth who have been treated with prolonged supplemental oxygen. Therapeutic options are limited. Using a neonatal mouse model of BPD, we show that hyperoxia increases activity and expression of a mediator of endogenous bronchoconstriction, S-nitrosoglutathione (GSNO) reductase. MicroRNA-342-3p, predicted in silico and shown in this study in vitro to suppress expression of GSNO reductase, was decreased in hyperoxia-exposed pups. Both pretreatment with aerosolized GSNO and inhibition of GSNO reductase attenuated airway hyperresponsiveness in vivo among juvenile and adult mice exposed to neonatal hyperoxia. Our data suggest that neonatal hyperoxia exposure causes detrimental effects on airway hyperreactivity through microRNA-342-3p-mediated upregulation of GSNO reductase expression. Furthermore, our data demonstrate that this adverse effect can be overcome by supplementing its substrate, GSNO, or by inhibiting the enzyme itself. Rates of BPD have not improved over the past two decades; nor have new therapies been developed. GSNO-based therapies are a novel treatment of the respiratory problems that patients with BPD experience.

Arabidopsis CaM1 and CaM4 Promote Nitric Oxide Production and Salt Resistance by Inhibiting S-Nitrosoglutathione Reductase via Direct Binding

Salt is a major threat to plant growth and crop productivity. Calmodulin (CaM), the most important multifunctional Ca2+ sensor protein in plants, mediates reactions against environmental stresses through target proteins; however, direct proof of the participation of CaM in salt tolerance and its corresponding signaling pathway in vivo is lacking. In this study, we found that AtCaM1 and AtCaM4 produced salt-responsive CaM isoforms according to real-time reverse transcription-polymerase chain reaction analyses; this result was verified based on a phenotypic analysis of salt-treated loss-of-function mutant and transgenic plants. We also found that the level of nitric oxide (NO), an important salt-responsive signaling molecule, varied in response to salt treatment depending on AtCaM1 and AtCaM4 expression. GSNOR is considered as an important and widely utilized regulatory component of NO homeostasis in plant resistance protein signaling networks. In vivo and in vitro protein-protein interaction assays revealed direct binding between AtCaM4 and S-nitrosoglutathione reductase (GSNOR), leading to reduced GSNOR activity and an increased NO level. Overexpression of GSNOR intensified the salt sensitivity of cam4 mutant plants accompanied by a reduced internal NO level, whereas a gsnor deficiency increased the salt tolerance of cam4 plants accompanied by an increased internal NO level. Physiological experiments showed that CaM4-GSNOR, acting through NO, reestablished the ion balance to increase plant resistance to salt stress. Together, these data suggest that AtCaM1 and AtCaM4 serve as signals in plant salt resistance by promoting NO accumulation through the binding and inhibition of GSNOR. This could be a conserved defensive signaling pathway in plants and animals.

The Effectors and Sensory Sites of Formaldehyde-responsive Regulator FrmR and Metal-sensing Variant

The DUF156 family of DNA-binding transcriptional regulators includes metal sensors that respond to cobalt and/or nickel (RcnR, InrS) or copper (CsoR) plus CstR, which responds to persulfide, and formaldehyde-responsive FrmR. Unexpectedly, the allosteric mechanism of FrmR from Salmonella enterica serovar Typhimurium is triggered by metals in vitro, and variant FrmR(E64H) gains responsiveness to Zn(II) and cobalt in vivo Here we establish that the allosteric mechanism of FrmR is triggered directly by formaldehyde in vitro Sensitivity to formaldehyde requires a cysteine (Cys(35) in FrmR) conserved in all DUF156 proteins. A crystal structure of metal- and formaldehyde-sensing FrmR(E64H) reveals that an FrmR-specific amino-terminal Pro(2) is proximal to Cys(35), and these residues form the deduced formaldehyde-sensing site. Evidence is presented that implies that residues spatially close to the conserved cysteine tune the sensitivities of DUF156 proteins above or below critical thresholds for different effectors, generating the semblance of specificity within cells. Relative to FrmR, RcnR is less responsive to formaldehyde in vitro, and RcnR does not sense formaldehyde in vivo, but reciprocal mutations FrmR(P2S) and RcnR(S2P), respectively, impair and enhance formaldehyde reactivity in vitro Formaldehyde detoxification by FrmA requires S-(hydroxymethyl)glutathione, yet glutathione inhibits formaldehyde detection by FrmR in vivo and in vitro Quantifying the number of FrmR molecules per cell and modeling formaldehyde modification as a function of [formaldehyde] demonstrates that FrmR reactivity is optimized such that FrmR is modified and frmRA is derepressed at lower [formaldehyde] than required to generate S-(hydroxymethyl)glutathione. Expression of FrmA is thereby coordinated with the accumulation of its substrate.

Rapid proteomic responses to a near-lethal heat stress in the salt marsh mussel Geukensia demissa

Acute heat stress perturbs cellular function on a variety of levels, leading to protein dysfunction and aggregation, oxidative stress and loss of metabolic homeostasis. If these challenges are not overcome quickly, the stressed organism can die. To better understand the earliest tissue-level responses to heat stress, we examined the proteomic response of gill from Geukensia demissa, an extremely eurythermal mussel from the temperate intertidal zone of eastern North America. We exposed 15°C-acclimated individuals to an acute near-lethal heat stress (45°C) for 1 h, and collected gill samples from 0 to 24 h of recovery. The changes in protein expression we found reveal a coordinated physiological response to acute heat stress: proteins associated with apoptotic processes were increased in abundance during the stress itself (i.e. at 0 h of recovery), while protein chaperones and foldases increased in abundance soon after (3 h). The greatest number of proteins changed abundance at 6 h; these included oxidative stress proteins and enzymes of energy metabolism. Proteins associated with the cytoskeleton and extracellular matrix also changed in abundance starting at 6 h, providing evidence of cell proliferation, migration and tissue remodeling. By 12 h, the response to acute heat stress was diminishing, with fewer stress and structural proteins changing in abundance. Finally, the proteins with altered abundances identified at 24 h suggest a return to the pre-stress anabolic state.

Nebivolol Acts as a S-Nitrosoglutathione Reductase Inhibitor

Background and Purpose:

Published data on nebivolol reveal selective β1 adrenergic selectively along with novel nitric oxide (NO)-dependent vasodilatory properties. However, the exact molecular mechanism is unknown. Protein S-nitrosylation constitutes a large part of the ubiquitous influence of NO on cellular signal transduction and is involved in a number of human diseases. More recently, protein denitrosylation has been shown to play a major role in controlling cellular S-nitrosylation (SNO). Several enzymes have been reported to catalyze the reduction of SNOs and are viewed as candidate denitrosylases. One of the first described is known as S-nitrosoglutathione reductase (GSNOR). Importantly, GSNOR has been shown to play a role in regulating SNO signaling downstream of the β-adrenergic receptor and is therefore operative in cellular signal transduction. Pharmacological inhibition or genetic deletion of GSNOR leads to enhanced vasodilation and characteristic of known effects of nebivolol. Structurally, nebivolol is similar to known inhibitors of GSNOR. Therefore, we hypothesize that some of the known effects of nebivolol may occur through this mechanism.

Experimental Approach:

Using cell culture systems, tissue organ bath, and intact animal models, we report that nebivolol treatment leads to a dose-dependent accumulation of nitrosothiols in cells, and this is associated with an enhanced vasodilation by S-nitrosoglutathione.

Key Results:

These data suggest a new mechanism of action of nebivolol that may explain in part the reported NO activity.

Conclusions and Implications:

Because exogenous mediators of protein SNO or denitrosylation can substantially affect the development or progression of disease, this may call for new utility of nebivolol.

Exogenous nitric oxide improves sugarcane growth and photosynthesis under water deficit

Nitric oxide (NO)-mediated redox signaling plays a role in alleviating the negative impact of water stress in sugarcane plants by improving root growth and photosynthesis. Drought is an environmental limitation affecting sugarcane growth and yield. The redox-active molecule nitric oxide (NO) is known to modulate plant responses to stressful conditions. NO may react with glutathione (GSH) to form S-nitrosoglutathione (GSNO), which is considered the main reservoir of NO in cells. Here, we investigate the role of NO in alleviating the effects of water deficit on growth and photosynthesis of sugarcane plants. Well-hydrated plants were compared to plants under drought and sprayed with mock (water) or GSNO at concentrations ranging from 10 to 1000 μM. Leaf GSNO sprayed plants showed significant improvement of relative water content and leaf and root dry matter under drought compared to mock-sprayed plants. Additionally, plants sprayed with GSNO (≥ 100 μM) showed higher leaf gas exchange and photochemical activity as compared to mock-sprayed plants under water deficit and after rehydration. Surprisingly, a raise in the total S-nitrosothiols content was observed in leaves sprayed with GSH or GSNO, suggesting a long-term role of NO-mediated responses to water deficit. Experiments with leaf discs fumigated with NO gas also suggested a role of NO in drought tolerance of sugarcane plants. Overall, our data indicate that the NO-mediated redox signaling plays a role in alleviating the negative effects of water stress in sugarcane plants by protecting the photosynthetic apparatus and improving shoot and root growth.

Nitrosative Stress, Hypernitrosylation, and Autoimmune Responses to Nitrosylated Proteins: New Pathways in Neuroprogressive Disorders Including Depression and Chronic Fatigue Syndrome

Nitric oxide plays an indispensable role in modulating cellular signaling and redox pathways. This role is mainly effected by the readily reversible nitrosylation of selective protein cysteine thiols. The reversibility and sophistication of this signaling system is enabled and regulated by a number of enzymes which form part of the thioredoxin, glutathione, and pyridoxine antioxidant systems. Increases in nitric oxide levels initially lead to a defensive increase in the number of nitrosylated proteins in an effort to preserve their function. However, in an environment of chronic oxidative and nitrosative stress (O&NS), nitrosylation of crucial cysteine groups within key enzymes of the thioredoxin, glutathione, and pyridoxine systems leads to their inactivation thereby disabling denitrosylation and transnitrosylation and subsequently a state described as "hypernitrosylation." This state leads to the development of pathology in multiple domains such as the inhibition of enzymes of the electron transport chain, decreased mitochondrial function, and altered conformation of proteins and amino acids leading to loss of immune tolerance and development of autoimmunity. Hypernitrosylation also leads to altered function or inactivation of proteins involved in the regulation of apoptosis, autophagy, proteomic degradation, transcription factor activity, immune-inflammatory pathways, energy production, and neural function and survival. Hypernitrosylation, as a consequence of chronically elevated O&NS and activated immune-inflammatory pathways, can explain many characteristic abnormalities observed in neuroprogressive disease including major depression and chronic fatigue syndrome/myalgic encephalomyelitis. In those disorders, increased bacterial translocation may drive hypernitrosylation and autoimmune responses against nitrosylated proteins.

S-nitrosomycothiol reductase and mycothiol are required for survival under aldehyde stress and biofilm formation in Mycobacterium smegmatis

We show that Mycobacterium smegmatis mutants disrupted in mscR, coding for a dual function S-nitrosomycothiol reductase and formaldehyde dehydrogenase, and mshC, coding for a mycothiol ligase and lacking mycothiol (MSH), are more susceptible to S-nitrosoglutathione (GSNO) and aldehydes than wild type. MSH is a cofactor for MscR, and both mshC and mscR are induced by GSNO and aldehydes. We also show that a mutant disrupted in egtA, coding for a γ-glutamyl cysteine synthetase and lacking in ergothioneine, is sensitive to nitrosative stress but not to aldehydes. In addition, we find that MSH and S-nitrosomycothiol reductase are required for normal biofilm formation in M. smegmatis, suggesting potential new therapeutic pathways to target to inhibit or disrupt biofilm formation. © 2016 IUBMB Life, 68(8):621-628, 2016.

S-nitrosylation of the Mitochondrial Chaperone TRAP1 Sensitizes Hepatocellular Carcinoma Cells to Inhibitors of Succinate Dehydrogenase

S-nitrosoglutathione reductase (GSNOR) represents the best-documented denitrosylase implicated in regulating the levels of proteins posttranslationally modified by nitric oxide on cysteine residues by S-nitrosylation. GSNOR controls a diverse array of physiologic functions, including cellular growth and differentiation, inflammation, and metabolism. Chromosomal deletion of GSNOR results in pathologic protein S-nitrosylation that is implicated in human hepatocellular carcinoma (HCC). Here we identify a metabolic hallmark of aberrant S-nitrosylation in HCC and exploit it for therapeutic gain. We find that hepatocyte GSNOR deficiency is characterized by mitochondrial alteration and by marked increases in succinate dehydrogenase (SDH) levels and activity. We find that this depends on the selective S-nitrosylation of Cys(501) in the mitochondrial chaperone TRAP1, which mediates its degradation. As a result, GSNOR-deficient cells and tumors are highly sensitive to SDH inhibition, namely to α-tocopheryl succinate, an SDH-targeting molecule that induced RIP1/PARP1-mediated necroptosis and inhibited tumor growth. Our work provides a specific molecular signature of aberrant S-nitrosylation in HCC, a novel molecular target in SDH, and a first-in-class therapy to treat the disease. Cancer Res; 76(14); 4170-82. ©2016 AACR.

Copper disrupts S-nitrosothiol signaling in activated BV2 microglia

Microglia, the primary resident immune cells of the central nervous system (CNS), responds rapidly to pathogens and injury by secreting immune mediators including nitric oxide (NO). The reaction of NO with the anti-oxidant glutathione forms S-nitrosoglutathione (GSNO), the major pool of biologic NO in the body. GSNO is degraded by GSNO reductase (GSNOR). Recently, we have shown that copper (Cu(I)) inhibits the release of NO in lipopolysaccharide (LPS)-stimulated BV2 microglia and induces BV2 microglia to acquire a mixed a profile with both pro- and anti-inflammatory characteristics. Since GSNOR is the critical enzyme in GSNO metabolism, we sought to determine whether Cu(I) affects GSNOR activity and S-nitrosothiol (SNO) accumulation in activated BV2 microglia. Our results show that GSNOR protein expression is reduced by Cu(I) treatment in LPS-stimulated BV2 microglia. Our results also show a decrease in S-nitrosothiol content despite a reduced GSNOR expression. This effect is most likely due to Cu(I) reacting with the central thiol of the SNO bond resulting in the degradation of SNO. A dose of 1 μM Cu(I) did not affect SNO protein accumulation in LPS-stimulated BV2 microglia, however, a dose of 100 μM Cu(I) inhibited SNO protein in accordance with inhibition of S-nitrosothiols. These data provide direct evidence that Cu(I) disrupts S-nitrosothiol homeostasis and NO metabolism, and, thus, provide new insights into the mechanisms involved in microglia-mediated-CNS disorders.

Sulfur Denitrosylation by an Engineered Trx-like DsbG Enzyme Identifies Nucleophilic Cysteine Hydrogen Bonds as Key Functional Determinant

Exposure of bacteria to NO results in the nitrosylation of cysteine thiols in proteins and low molecular weight thiols such as GSH. The cells possess enzymatic systems that catalyze the denitrosylation of these modified sulfurs. An important player in these systems is thioredoxin (Trx), a ubiquitous, cytoplasmic oxidoreductase that can denitrosylate proteins in vivo and S-nitrosoglutathione (GSNO) in vitro However, a periplasmic or extracellular denitrosylase has not been identified, raising the question of how extracytoplasmic proteins are repaired after nitrosative damage. In this study, we tested whether DsbG and DsbC, two Trx family proteins that function in reducing pathways in the Escherichia coli periplasm, also possess denitrosylating activity. Both DsbG and DsbC are poorly reactive toward GSNO. Moreover, DsbG is unable to denitrosylate its specific substrate protein, YbiS. Remarkably, by borrowing the CGPC active site of E. coli Trx-1 in combination with a T200M point mutation, we transformed DsbG into an enzyme highly reactive toward GSNO and YbiS. The pKa of the nucleophilic cysteine, as well as the redox and thermodynamic properties of the engineered DsbG are dramatically changed and become similar to those of E. coli Trx-1. X-ray structural insights suggest that this results from a loss of two direct hydrogen bonds to the nucleophilic cysteine sulfur in the DsbG mutant. Our results highlight the plasticity of the Trx structural fold and reveal that the subtle change of the number of hydrogen bonds in the active site of Trx-like proteins is the key factor that thermodynamically controls reactivity toward nitrosylated compounds.

Detection of S-Nitrosoglutathione Reductase Activity in Plants

S-nitrosoglutathione reductase (GSNOR) is considered a key enzyme in the regulation of intracellular levels of S-nitrosoglutathione and protein S-nitrosylation. As a part of nitric oxide catabolism, GSNOR catalyzes the irreversible decomposition of GSNO to oxidized glutathione. GSNOR is involved in the regulation of plant growth and development, mediated by NO-dependent signaling mechanisms, and is known to play important roles in plant responses to various abiotic and biotic stress conditions. Here we present optimized protocols to determine GSNOR enzyme activities in plant samples by spectrophotometric measurements and by activity staining after the native polyacrylamide gel electrophoresis.

S-Nitrosation of Conserved Cysteines Modulates Activity and Stability of S-Nitrosoglutathione Reductase (GSNOR)

The free radical nitric oxide (NO(•)) regulates diverse physiological processes from vasodilation in humans to gas exchange in plants. S-Nitrosoglutathione (GSNO) is considered a principal nitroso reservoir due to its chemical stability. GSNO accumulation is attenuated by GSNO reductase (GSNOR), a cysteine-rich cytosolic enzyme. Regulation of protein nitrosation is not well understood since NO(•)-dependent events proceed without discernible changes in GSNOR expression. Because GSNORs contain evolutionarily conserved cysteines that could serve as nitrosation sites, we examined the effects of treating plant (Arabidopsis thaliana), mammalian (human), and yeast (Saccharomyces cerevisiae) GSNORs with nitrosating agents in vitro. Enzyme activity was sensitive to nitroso donors, whereas the reducing agent dithiothreitol (DTT) restored activity, suggesting that catalytic impairment was due to S-nitrosation. Protein nitrosation was confirmed by mass spectrometry, by which mono-, di-, and trinitrosation were observed, and these signals were sensitive to DTT. GSNOR mutants in specific non-zinc-coordinating cysteines were less sensitive to catalytic inhibition by nitroso donors and exhibited reduced nitrosation signals by mass spectrometry. Nitrosation also coincided with decreased tryptophan fluorescence, increased thermal aggregation propensity, and increased polydispersity-properties reflected by differential solvent accessibility of amino acids important for dimerization and the shape of the substrate and coenzyme binding pockets as assessed by hydrogen-deuterium exchange mass spectrometry. Collectively, these data suggest a mechanism for NO(•) signal transduction in which GSNOR nitrosation and inhibition transiently permit GSNO accumulation.

Formaldehyde Stress Responses in Bacterial Pathogens

Formaldehyde is the simplest of all aldehydes and is highly cytotoxic. Its use and associated dangers from environmental exposure have been well documented. Detoxification systems for formaldehyde are found throughout the biological world and they are especially important in methylotrophic bacteria, which generate this compound as part of their metabolism of methanol. Formaldehyde metabolizing systems can be divided into those dependent upon pterin cofactors, sugar phosphates and those dependent upon glutathione. The more prevalent thiol-dependent formaldehyde detoxification system is found in many bacterial pathogens, almost all of which do not metabolize methane or methanol. This review describes the endogenous and exogenous sources of formaldehyde, its toxic effects and mechanisms of detoxification. The methods of formaldehyde sensing are also described with a focus on the formaldehyde responsive transcription factors HxlR, FrmR, and NmlR. Finally, the physiological relevance of detoxification systems for formaldehyde in bacterial pathogens is discussed.

Inorganic sulfur-nitrogen compounds: from gunpowder chemistry to the forefront of biological signaling

The reactions between inorganic sulfur and nitrogen-bearing compounds to form S-N containing species have a long history and, besides assuming importance in industrial synthetic processes, are of relevance to microbial metabolism; waste water treatment; aquatic, soil and atmospheric chemistry; and combustion processes. The recent discovery that hydrogen sulfide and nitric oxide exert often similar, sometimes mutually dependent effects in a variety of biological systems, and that the chemical interaction of these two species leads to formation of S-N compounds brought this chemistry to the attention of physiologists, biochemists and physicians. We here provide a perspective about the potential role of S-N compounds in biological signaling and briefly review their chemical properties and bioactivities in the context of the chronology of their discovery. Studies of the biological role of NO revealed why its chemistry is ideally suited for the tasks Nature has chosen for it; realising how the distinctive properties of sulfur can enrich this bioactivity does much to revive 'die Freude am experimentellen Spiel' of the pioneers in this field.

Characterization of the sex-dependent myocardial S-nitrosothiol proteome

Premenopausal women exhibit endogenous cardioprotective signaling mechanisms that are thought to result from the beneficial effects of estrogen, which we have shown to increase protein S-nitrosylation in the heart. S-nitrosylation is a labile protein modification that increases with a number of different forms of cardioprotection, including ischemic preconditioning. Herein, we sought to identify a potential role for protein S-nitrosylation in sex-dependent cardioprotection. We utilized a Langendorff-perfused mouse heart model of ischemia-reperfusion injury with male and female hearts, and S-nitrosylation-resin-assisted capture with liquid chromatography tandem mass spectrometry to identify S-nitrosylated proteins and modification sites. Consistent with previous studies, female hearts exhibited resilience to injury with a significant increase in functional recovery compared with male hearts. In a separate set of hearts, we identified a total of 177 S-nitrosylated proteins in female hearts at baseline compared with 109 S-nitrosylated proteins in male hearts. Unique S-nitrosylated proteins in the female group included the F1FO-ATPase and cyclophilin D. We also utilized label-free peptide analysis to quantify levels of common S-nitrosylated identifications and noted that the S-nitrosylation of sarcoplasmic/endoplasmic reticulum Ca(2+)-ATPase 2a was nearly 70% lower in male hearts compared with female, with no difference in expression. Furthermore, we found a significant increase in endothelial nitric oxide synthase expression, phosphorylation, and total nitric oxide production in female hearts compared with males, likely accounting for the enhanced S-nitrosylation protein levels in female hearts. In conclusion, we identified a number of novel S-nitrosylated proteins in female hearts that are likely to contribute to sex-dependent cardioprotection.

Protein S-nitrosylation in photosynthetic organisms: A comprehensive overview with future perspectives

BACKGROUND

The free radical nitric oxide (NO) and derivative reactive nitrogen species (RNS) play essential roles in cellular redox regulation mainly through protein S-nitrosylation, a redox post-translational modification in which specific cysteines are converted to nitrosothiols.

SCOPE OF VIEW

This review aims to discuss the current state of knowledge, as well as future perspectives, regarding protein S-nitrosylation in photosynthetic organisms.

MAJOR CONCLUSIONS

NO, synthesized by plants from different sources (nitrite, arginine), provides directly or indirectly the nitroso moiety of nitrosothiols. Biosynthesis, reactivity and scavenging systems of NO/RNS, determine the NO-based signaling including the rate of protein nitrosylation. Denitrosylation reactions compete with nitrosylation in setting the levels of nitrosylated proteins in vivo.

GENERAL SIGNIFICANCE

Based on a combination of proteomic, biochemical and genetic approaches, protein nitrosylation is emerging as a pervasive player in cell signaling networks. Specificity of protein nitrosylation and integration among different post-translational modifications are among the major challenges for future experimental studies in the redox biology field. This article is part of a Special Issue entitled: Plant Proteomics--a bridge between fundamental processes and crop production, edited by Dr. Hans-Peter Mock.

Altered S-nitrosothiol homeostasis provides a survival advantage to breast cancer cells in HER2 tumors and reduces their sensitivity to trastuzumab

The monoclonal antibody trastuzumab against HER2/neu, which is overexpressed in 15-20% of breast cancers, has clinical efficacy but many patients do not respond to initial treatment or develop resistance during treatment. Nitric oxide (NO) regulates cell signaling by targeting specific cysteine residues in proteins, forming S-nitrosothiols (SNO) in a process known as S-nitrosylation. We previously reported that molecular characteristics in breast cancer may dictate the tumor response to impaired SNO homeostasis. In the present study, we explored the role of SNO homeostasis in HER2 breast tumors. The antiproliferative action of trastuzumab in HER2-overexpressing BT-474 and SKBR-3 cells was suppressed when S-nitrosoglutathione reductase (GSNOR/ADH5) activity, which plays a key role in SNO homeostasis, was specifically inhibited with the pyrrole derivative compound N6022. Moreover, GSNOR inhibition restored the activation of survival signaling pathways involved in the resistance to anti-HER2 therapies (AKT, Src and c-Abl kinases and TrkA/NRTK1, TrkB/NRTK2, EphA1 and EphA3 receptors) and reduced the apoptotic effect of trastuzumab. Accordingly, GSNOR inhibition augmented the S-nitrosylation of apoptosis-related proteins, including Apaf-1, pSer73/63 c-Jun, calcineurin subunit α and HSF1. In agreement with in vitro data, immunohistochemical analyses of 51 breast tumors showed that HER2 expression was associated with lower expression of GSNOR protein. Moreover, gene expression analysis confirmed that high ADH5/GSNOR gene expression was associated with high patient survival rates in HER2 tumors. In conclusion, our data provide evidence of molecular mechanisms contributing to the progression of HER2+ breast cancers and could facilitate the development of therapeutic options to counteract resistance to anti-HER2 therapies.

Antioxidant Systems are Regulated by Nitric Oxide-Mediated Post-translational Modifications (NO-PTMs)

Nitric oxide (NO) is a biological messenger that orchestrates a plethora of plant functions, mainly through post-translational modifications (PTMs) such as S-nitrosylation or tyrosine nitration. In plants, hundreds of proteins have been identified as potential targets of these NO-PTMs under physiological and stress conditions indicating the relevance of NO in plant-signaling mechanisms. Among these NO protein targets, there are different antioxidant enzymes involved in the control of reactive oxygen species (ROS), such as H2O2, which is also a signal molecule. This highlights the close relationship between ROS/NO signaling pathways. The major plant antioxidant enzymes, including catalase, superoxide dismutases (SODs) peroxiredoxins (Prx) and all the enzymatic components of the ascorbate-glutathione (Asa-GSH) cycle, have been shown to be modulated to different degrees by NO-PTMs. This mini-review will update the recent knowledge concerning the interaction of NO with these antioxidant enzymes, with a special focus on the components of the Asa-GSH cycle and their physiological relevance.

Protein S-Nitrosylation as a Therapeutic Target for Neurodegenerative Diseases

At physiological levels, nitric oxide (NO) contributes to the maintenance of normal neuronal activity and survival, thus serving as an important regulatory mechanism in the central nervous system. By contrast, accumulating evidence suggests that exposure to environmental toxins or the normal aging process can trigger excessive production of reactive oxygen/nitrogen species (such as NO), contributing to the etiology of several neurodegenerative diseases. We highlight here protein S-nitrosylation, resulting from covalent attachment of an NO group to a cysteine thiol of the target protein, as a ubiquitous effector of NO signaling in both health and disease. We review our current understanding of this redox-dependent post-translational modification under neurodegenerative conditions, and evaluate how targeting dysregulated protein S-nitrosylation can lead to novel therapeutics.

Augmentation of CFTR maturation by S-nitrosoglutathione reductase

S-nitrosoglutathione (GSNO) reductase regulates novel endogenous S-nitrosothiol signaling pathways, and mice deficient in GSNO reductase are protected from airways hyperreactivity. S-nitrosothiols are present in the airway, and patients with cystic fibrosis (CF) tend to have low S-nitrosothiol levels that may be attributed to upregulation of GSNO reductase activity. The present study demonstrates that 1) GSNO reductase activity is increased in the cystic fibrosis bronchial epithelial (CFBE41o(-)) cells expressing mutant F508del-cystic fibrosis transmembrane regulator (CFTR) compared with the wild-type CFBE41o(-) cells, 2) GSNO reductase expression level is increased in the primary human bronchial epithelial cells expressing mutant F508del-CFTR compared with the wild-type cells, 3) GSNO reductase colocalizes with cochaperone Hsp70/Hsp90 organizing protein (Hop; Stip1) in human airway epithelial cells, 4) GSNO reductase knockdown with siRNA increases the expression and maturation of CFTR and decreases Stip1 expression in human airway epithelial cells, 5) increased levels of GSNO reductase cause a decrease in maturation of CFTR, and 6) a GSNO reductase inhibitor effectively reverses the effects of GSNO reductase on CFTR maturation. These studies provide a novel approach to define the subcellular location of the interactions between Stip1 and GSNO reductase and the role of S-nitrosothiols in these interactions.

Quantitative proteomics analysis reveals that S-nitrosoglutathione reductase (GSNOR) and nitric oxide signaling enhance poplar defense against chilling stress

NO acts as the essential signal to enhance poplar tolerance to chilling stress via antioxidant enzyme activities and protein S -nitrosylation modification, NO signal is also strictly controlled by S -nitrosoglutathione reductase and nitrate reductase to avoid the over-accumulation of reactive nitrogen species. Poplar (Populus trichocarpa) are fast growing woody plants with both ecological and economic value; however, the mechanisms by which poplar adapts to environmental stress are poorly understood. In this study, we used isobaric tags for relative and absolute quantification proteomic approach to characterize the response of poplar exposed to cold stress. We identified 114 proteins that were differentially expressed in plants exposed to cold stress. In particular, some of the proteins are involved in reactive oxygen species (ROS) and reactive nitrogen species (RNS) metabolism. Further physiological analysis showed that nitric oxide (NO) signaling activated a series of downstream defense responses. We further demonstrated that NO activated antioxidant enzyme activities and S-nitrosoglutathione reductase (GSNOR) activities, which would reduce ROS and RNS toxicity and thereby enhance poplar tolerance to cold stress. Suppressing NO accumulation or GSNOR activity aggravated cold damage to poplar leaves. Moreover, our results showed that RNS can suppress the activities of GSNOR and NO nitrate reductase (NR) by S-nitrosylation to fine-tune the NO signal and modulate ROS levels by modulating the S-nitrosylation of ascorbate peroxidase protein. Hence, our data demonstrate that NO signaling activates multiple pathways that enhance poplar tolerances to cold stress, and that NO signaling is strictly controlled through protein post-translational modification by S-nitrosylation.

Nitrogen chemistry and lung physiology

The versatile chemistry of nitrogen is important to pulmonary physiology. Indeed, almost all redox forms of nitrogen are relevant to pulmonary physiology and to pathophysiology. Here we review the relevance to pulmonary biology of (a) elemental nitrogen; (b) reduced forms of nitrogen such as amines, ammonia, and hydroxylamine; and (c) oxidized forms of nitrogen such as the nitroxyl anion, the nitric oxide free radical, and S-nitrosothiols. Our focus is on oxidized nitrogen in the form of S-nitrosothiol bond-containing species, which are now appreciated to be important to every type of cell-signaling process in the lung. We also review potential clinical applications of nitrogen oxide biochemistry. These principles are being translated into clinical practice as diagnostic techniques and therapies for a range of pulmonary diseases including asthma, cystic fibrosis, adult respiratory distress syndrome, primary ciliary dyskinesia, and pulmonary hypertension.

S-Nitrosylation of Sarcomeric Proteins Depresses Myofilament Ca2+)Sensitivity in Intact Cardiomyocytes

AIMS

The heart responds to physiological and pathophysiological stress factors by increasing its production of nitric oxide (NO), which reacts with intracellular glutathione to form S-nitrosoglutathione (GSNO), a protein S-nitrosylating agent. Although S-nitrosylation protects some cardiac proteins against oxidative stress, direct effects on myofilament performance are unknown. We hypothesize that S-nitrosylation of sarcomeric proteins will modulate the performance of cardiac myofilaments.

RESULTS

Incubation of intact mouse cardiomyocytes with S-nitrosocysteine (CysNO, a cell-permeable low-molecular-weight nitrosothiol) significantly decreased myofilament Ca(2+) sensitivity. In demembranated (skinned) fibers, S-nitrosylation with 1 μM GSNO also decreased Ca(2+) sensitivity of contraction and 10 μM reduced maximal isometric force, while inhibition of relaxation and myofibrillar ATPase required higher concentrations (≥ 100 μM). Reducing S-nitrosylation with ascorbate partially reversed the effects on Ca(2+) sensitivity and ATPase activity. In live cardiomyocytes treated with CysNO, resin-assisted capture of S-nitrosylated protein thiols was combined with label-free liquid chromatography-tandem mass spectrometry to quantify S-nitrosylation and determine the susceptible cysteine sites on myosin, actin, myosin-binding protein C, troponin C and I, tropomyosin, and titin. The ability of sarcomere proteins to form S-NO from 10-500 μM CysNO in intact cardiomyocytes was further determined by immunoblot, with actin, myosin, myosin-binding protein C, and troponin C being the more susceptible sarcomeric proteins.

INNOVATION AND CONCLUSIONS

Thus, specific physiological effects are associated with S-nitrosylation of a limited number of cysteine residues in sarcomeric proteins, which also offer potential targets for interventions in pathophysiological situations.