Nitrosylation: the next phosphorylation?

Vascular nitric oxide resistance in type 2 diabetes

Vascular nitric oxide (NO•) resistance, manifested by an impaired vasodilator function of NO• in both the macro- and microvessels, is a common state in type 2 diabetes (T2D) associated with developing cardiovascular events and death. Here, we summarize experimental and human evidence of vascular NO• resistance in T2D and discuss its underlying mechanisms. Human studies indicate a ~ 13-94% decrease in the endothelium (ET)-dependent vascular smooth muscle (VSM) relaxation and a 6-42% reduced response to NO• donors, i.e., sodium nitroprusside (SNP) and glyceryl trinitrate (GTN), in patients with T2D. A decreased vascular NO• production, NO• inactivation, and impaired responsiveness of VSM to NO• [occurred due to quenching NO• activity, desensitization of its receptor soluble guanylate cyclase (sGC), and/or impairment of its downstream pathway, cyclic guanosine monophosphate (cGMP)-protein kinase G (PKG)] are the known mechanisms underlying the vascular NO• resistance in T2D. Hyperglycemia-induced overproduction of reactive oxygen species (ROS) and vascular insulin resistance are key players in this state. Therefore, upregulating vascular NO• availability, re-sensitizing or bypassing the non-responsive pathways to NO•, and targeting key vascular sources of ROS production may be clinically relevant pharmacological approaches to circumvent T2D-induced vascular NO• resistance.

Insulin secretion: The nitric oxide controversy

Nitric oxide (NO) is a gas that serves as a ubiquitous signaling molecule participating in physiological activities of various organ systems. Nitric oxide is produced in the endocrine pancreas and contributes to synthesis and secretion of insulin. The potential role of NO in insulin secretion is disputable - both stimulatory and inhibitory effects have been reported. Available data indicate that effects of NO critically depend on its concentration. Different isoforms of NO synthase (NOS) control this and have the potential to decrease or increase insulin secretion. In this review, the role of NO in insulin secretion as well as the possible reasons for discrepant findings are discussed. A better understanding of the role of NO system in the regulation of insulin secretion may facilitate the development of new therapeutic strategies in the management of diabetes.

Nitric oxide: To be or not to be an endocrine hormone?

Nitric oxide (NO), a highly reactive gasotransmitter, is critical for a number of cellular processes and has multiple biological functions. Due to its limited lifetime and diffusion distance, NO has been mainly believed to act in autocrine/paracrine fashion. The increasingly recognized effects of pharmacologically delivered and endogenous NO at a distant site have changed the conventional wisdom and introduced NO as an endocrine signalling molecule. The notion is greatly supported by the detection of a number of NO adducts and their circulatory cycles, which in turn contribute to the transport and delivery of NO bioactivity, remote from the sites of its synthesis. The existence of endocrine sites of synthesis, negative feedback regulation of biosynthesis, integrated storage and transport systems, having an exclusive receptor, that is, soluble guanylyl cyclase (sGC), and organized circadian rhythmicity make NO something beyond a simple autocrine/paracrine signalling molecule that could qualify for being an endocrine signalling molecule. Here, we discuss hormonal features of NO from the classical endocrine point of view and review available knowledge supporting NO as a true endocrine hormone. This new insight can provide a new framework within which to reinterpret NO biology and its clinical applications.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Urban Particulate Matter-Induced Decomposition of S-Nitrosoglutathione Relevant to Aberrant Nitric Oxide Biological Signaling

Exposure to airborne particulate matter (PM) is associated with hazardous effects on human health. Soluble constituents of PM may be released in biological fluids and disturb the precisely tuned nitric oxide signaling processes. The influence of aqueous extracts from two types of airborne urban PM (SRM 1648a, a commercially available sample, and KR PM2.5, a sample collected "in-house" in Krakow, Poland) on the stability of S-nitrosoglutathione (GSNO) was investigated. The particle interfaces had no direct effect on the studied reaction, but extracts obtained from both samples facilitated NO release from GSNO. The effectiveness of NO release was significantly affected by glutathione (GSH) and ascorbic acid (AscA). Examination of the combined influence of Cu²⁺ , Fe³⁺ , and reductants on GSNO stability revealed copper to be the main GSNO decomposing species. Computational models of nitrosothiols interacting with metal oxide substrates and solvated metal ions support these claims. The study stresses the importance of the interplay between metal ions and biological reductants in S-nitrosothiols decomposition.

Regulation of vascular tone homeostasis by NO and H2S: Implications in hypertension

Nitric oxide (NO) and hydrogen sulfide (H2S) are two gasotransmitters that are produced in the vasculature and contribute to the regulation of vascular tone. NO and H2S are synthesized in both vascular smooth muscle and endothelial cells; NO functions primarily through the sGC/cGMP pathway, and H2S mainly through activation of the ATP-dependent potassium channels; both leading to relaxation of vascular smooth muscle cells. A deficit in the NO/H2S homeostasis is involved in the pathogenesis of various cardiovascular diseases, especially hypertension. It is now becoming increasingly clear that there are important interactions between NO and H2S and that have a profound impact on vascular tone and this may provide insights into the new therapeutic interventions. The aim of this review is to provide a better understanding of individual and interactive roles of NO and H2S in vascular biology. Overall, available data indicate that both NO and H2S contribute to vascular (patho)physiology and in regulating blood pressure. In addition, boosting NO and H2S using various dietary sources or donors could be a hopeful therapeutic strategy in the management of hypertension.

Anti-obesity and anti-diabetic effects of nitrate and nitrite

Prevalence of obesity is increasing worldwide and type 2 diabetes to date is the most devastating complication of obesity. Decreased nitric oxide bioavailability is a feature of obesity and diabetes that links these two pathologies. Nitric oxide is synthesized both by nitric oxide synthase enzymes from l-arginine and nitric oxide synthase-independent from nitrate/nitrite. Nitric oxide production from nitrate/nitrite could potentially be used for nutrition-based therapy in obesity and diabetes. Nitric oxide deficiency also contributes to pathogeneses of cardiovascular disease and hypertension, which are associated with obesity and diabetes. This review summarizes pathways for nitric oxide production and focuses on the anti-diabetic and anti-obesity effects of the nitrate-nitrite-nitric oxide pathway. In addition to increasing nitric oxide production, nitrate and nitrite reduce oxidative stress, increase adipose tissue browning, have favorable effects on nitric oxide synthase expression, and increase insulin secretion, all effects that are potentially promising for management of obesity and diabetes. Based on current data, it could be suggested that amplifying the nitrate-nitrite-nitric oxide pathway is a diet-based strategy for increasing nitric oxide bioavailability and the management of these two interlinked conditions. Adding nitrate/nitrite to drugs that are currently used for managing diabetes (e.g. metformin) and possibly anti-obesity drugs may also enhance their efficacy.

Analysis of reactive oxygen and nitrogen species generated in three liquid media by low temperature helium plasma jet

In order to identify aqueous species formed in Plasma activated media (PAM), quantitative investigations of reactive oxygen and nitrogen species (ROS, RNS) were performed and compared to Milli-Q water and culture media without and with Fetal Calf Serum. Electron paramagnetic resonance, fluorometric and colorimetric analysis were used to identify and quantify free radicals generated by helium plasma jet in these liquids. Results clearly show the formation of ROS such as hydroxyl radical, superoxide anion radical and singlet oxygen in order of the micromolar range of concentrations. Nitric oxide, hydrogen peroxide and nitrite-nitrate anions (in range of several hundred micromolars) are the major species observed in PAM. The composition of the medium has a major impact on the pH of the solution during plasma treatment, on the stability of the different RONS that are produced and on their reactivity with biomolecules. To emphasize the interactions of plasma with a complex medium, amino acid degradation by means of mass spectrometry was also investigated using methionine, tyrosine, tryptophan and arginine. All of these components such as long lifetime RONS and oxidized biological compounds may contribute to the cytotoxic effect of PAM. This study provides mechanistic insights into the mechanisms involved in cell death after treatment with PAM.

S-Nitrosoglutathione ameliorates acute renal dysfunction in a rat model of lipopolysaccharide-induced sepsis

OBJECTIVE

Sepsis induces an inflammatory response that results in acute renal failure (ARF). The current study is to evaluate the role of S-Nitrosoglutathione (GSNO) in renoprotection from lipopolysaccharide (LPS)-induced sepsis.

METHODS

Rats were divided to three groups. First group received LPS (5 mg/kg body weight), second group was treated with LPS + GSNO (50 μg/kg body weight), and third group was administered with vehicle (saline). They were sacrificed on day 1 and 3 post-LPS injection. Serum levels of nitric oxide (NO), creatinine and blood urea nitrogen (BUN) were analysed. Tissue morphology, T lymphocyte infiltrations, and the expression of inflammatory (TNF-α, iNOS) and anti-inflammatory (IL-10) mediators as well as glutathione (GSH) levels were determined.

KEY FINDING

Lipopolysaccharide significantly decreased body weight and increased cellular T lymphocyte infiltration, caspase-3 and iNOS and decreased PPAR-γ in renal tissue. NO, creatinine and BUN were significantly elevated after LPS challenge, and they significantly decreased after GSNO treatment. TNF-α level was found significantly increased in LPS-treated serum and kidney. GSNO treatment of LPS-challenged rats decreased caspase-3, iNOS, TNF-α, T lymphocyte infiltration and remarkably increased levels of IL-10, PPAR-γ and GSH.

CONCLUSION

GSNO can be used as a renoprotective agent for the treatment of sepsis-induced acute kidney injury.

Protein S-nitrosylation: specificity and identification strategies in plants

The role of nitric oxide (NO) as a major regulator of plant physiological functions has become increasingly evident. To further improve our understanding of its role, within the last few years plant biologists have begun to embrace the exciting opportunity of investigating protein S-nitrosylation, a major reversible NO-dependent post-translational modification (PTM) targeting specific Cys residues and widely studied in animals. Thanks to the development of dedicated proteomic approaches, in particular the use of the biotin switch technique (BST) combined with mass spectrometry, hundreds of plant protein candidates for S-nitrosylation have been identified. Functional studies focused on specific proteins provided preliminary comprehensive views of how this PTM impacts the structure and function of proteins and, more generally, of how NO might regulate biological plant processes. The aim of this review is to detail the basic principle of protein S-nitrosylation, to provide information on the biochemical and structural features of the S-nitrosylation sites and to describe the proteomic strategies adopted to investigate this PTM in plants. Limits of the current approaches and tomorrow's challenges are also discussed.

Nitric oxide-matrix metaloproteinase-9 interactions: biological and pharmacological significance--NO and MMP-9 interactions

Nitric oxide (NO) and matrix metalloproteinase 9 (MMP-9) levels are found to increase in inflammation states and in cancer, and their levels may be reciprocally modulated. Understanding interactions between NO and MMP-9 is of biological and pharmacological relevance and may prove crucial in designing new therapeutics. The reciprocal interaction between NO and MMP-9 have been studied for nearly twenty years but to our knowledge, are yet to be the subject of a review. This review provides a summary of published data regarding the complex and sometimes contradictory effects of NO on MMP-9. We also analyse molecular mechanisms modulating and mediating NO-MMP-9 interactions. Finally, a potential therapeutic relevance of these interactions is presented.

Identification of nitric oxide as an endogenous inhibitor of 26S proteasomes in vascular endothelial cells

The 26S proteasome plays a fundamental role in almost all eukaryotic cells, including vascular endothelial cells. However, it remains largely unknown how proteasome functionality is regulated in the vasculature. Endothelial nitric oxide (NO) synthase (eNOS)-derived NO is known to be essential to maintain endothelial homeostasis. The aim of the present study was to establish the connection between endothelial NO and 26S proteasome functionality in vascular endothelial cells. The 26S proteasome reporter protein levels, 26S proteasome activity, and the O-GlcNAcylation of Rpt2, a key subunit of the proteasome regulatory complex, were assayed in 26S proteasome reporter cells, human umbilical vein endothelial cells (HUVEC), and mouse aortic tissues isolated from 26S proteasome reporter and eNOS knockout mice. Like the other selective NO donors, NO derived from activated eNOS (by pharmacological and genetic approach) increased O-GlcNAc modification of Rpt2, reduced proteasome chymotrypsin-like activity, and caused 26S proteasome reporter protein accumulation. Conversely, inactivation of eNOS reversed all the effects. SiRNA knockdown of O-GlcNAc transferase (OGT), the key enzyme that catalyzes protein O-GlcNAcylation, abolished NO-induced effects. Consistently, adenoviral overexpression of O-GlcNAcase (OGA), the enzyme catalyzing the removal of the O-GlcNAc group, mimicked the effects of OGT knockdown. Finally, compared to eNOS wild type aortic tissues, 26S proteasome reporter mice lacking eNOS exhibited elevated 26S proteasome functionality in parallel with decreased Rpt2 O-GlcNAcylation, without changing the levels of Rpt2 protein. In conclusion, the eNOS-derived NO functions as a physiological suppressor of the 26S proteasome in vascular endothelial cells.

Redox proteomics: from bench to bedside

In general protein posttranslation modifications (PTMs) involve the covalent addition of functional groups or molecules to specific amino acid residues in proteins. These modifications include phosphorylation, glycosylation, S-nitrosylation, acetylation, lipidation, among others (Angew Chem Int Ed Engl 44(45):7342-7372, 2005). Although other amino acids can undergo different kinds of oxidative posttranslational modifications (oxPTMs) (Exp Gerontol 36(9):1495-1502, 2001), in this chapter oxPTM will be considered specifically related to Cysteine oxidation, and redox proteomics here is translated as a comprehensive investigation of oxPTMs, in biological systems, using diverse technical approaches. Protein Cysteine residues are not the only amino acid that can be target for oxidative modifications in proteins (Exp Gerontol 36(9):1495-1502, 2001; Biochim Biophys Acta 1814(12):1785-1795, 2011), but certainly it is among the most reactive amino acid (Nature 468(7325):790-795, 2010). Interestingly, it is one of the least abundant amino acid, but it often occurs in the functional sites of proteins (J Mol Biol 404(5):902-916, 2010). In addition, the majority of the Cysteine oxidations are reversible, indicating potential regulatory mechanism of proteins. The global analysis of oxPTMs has been increasingly recognized as an important area of proteomics, because not only maps protein caused by reactive oxygen species (ROS) and reactive nitrogen species (RNS), but also explores protein modulation involving ROS/RNS. Furthermore, the tools and strategies to study this type oxidation are also very abundant and developed, offering high degree of accuracy on the results. As a consequence, the redox proteomics field focuses very much on analyzing Cysteine oxidation in proteins under several experimental conditions and diseases states. Therefore, the identification and localization of oxPTMs within cellular milieu became critical to understand redox regulation of proteins in physiological and pathological conditions, and consequently an important information to develop better strategies for treatment and prevention of diseases associated with oxidative stress.There is a wide range of techniques available to investigate oxPTMs, including gel-based and non-gel-based separation approaches to be combined with sophisticated methods of detection, identification, and quantification of these modifications. The strategies and approaches to study oxPTMs and the respective applications related to physiological and pathological conditions will be discussed in more detail in this chapter.

Efficient nitrosation of glutathione by nitric oxide

Nitrosothiols are increasingly regarded as important participants in a range of physiological processes, yet little is known about their biological generation. Nitrosothiols can be formed from the corresponding thiols by nitric oxide in a reaction that requires the presence of oxygen and is mediated by reactive intermediates (NO₂ or N₂O₃) formed in the course of NO autoxidation. Because the autoxidation of NO is second order in NO, it is extremely slow at submicromolar NO concentrations, casting doubt on its physiological relevance. In this paper we present evidence that at submicromolar NO concentrations the aerobic nitrosation of glutathione does not involve NO autoxidation but a reaction that is first order in NO. We show that this reaction produces nitrosoglutathione efficiently in a reaction that is strongly stimulated by physiological concentrations of Mg(2+). These observations suggest that direct aerobic nitrosation may represent a physiologically relevant pathway of nitrosothiol formation.

Auxin induces redox regulation of ascorbate peroxidase 1 activity by S-nitrosylation/denitrosylation balance resulting in changes of root growth pattern in Arabidopsis

S-Nitrosylation of Cys residues is one of the molecular mechanisms driven by nitric oxide (NO) for regulating biological functions of key proteins. While the studies on S-nitrosylation of Cys residues have served for identifying SNO proteomes, the physiological relevance of protein S-nitrosylation/denitrosylation remains poorly understood. In this study, it is shown that auxin influences the balance of S-nitrosylated/denitrosylated proteins in roots of Arabidopsis seedlings. 2D-PAGE allowed the identification of ascorbate peroxidase 1 (APX1) as target of auxin-induced denitrosylation in roots. Auxin causes APX1 denitrosylation and partial inhibition of APX1 activity in Arabidopsis roots. In agreement, the S-nitrosylated form of recombinant APX1 expressed in Escherichia coli is more active than the denitrosylated form. Consistently, Arabidopsis apx1 mutants have increased H₂O₂ accumulation in roots, shorter roots, and less sensitivity to auxin than the wild type. It is postulated that an auxin-regulated counterbalance of APX1 S-nitrosylation/denitrosylation contributes to a fine-tuned control of root development and determination of root architecture.

Methods for detection and characterization of protein S-nitrosylation

Reversible protein S-nitrosylation, defined as the covalent addition of a nitroso moiety to the reactive thiol group on a cysteine residue, has received increasing recognition as a critical post-translational modification that exerts ubiquitous influence in a wide range of cellular pathways and physiological processes. Due to the lability of the S-NO bond, which is a dynamic modification, and the low abundance of endogenously S-nitrosylated proteins in vivo, unambiguous identification of S-nitrosylated proteins and S-nitrosylation sites remains methodologically challenging. In this review, we summarize recent advancements and the use of state-of-art approaches for the enrichment, systematic identification and quantitation of S-nitrosylation protein targets and their modification sites at the S-nitrosoproteome scale. These advancements have facilitated the global identification of >3000 S-nitrosylated proteins that are associated with wide range of human diseases. These strategies hold promise to site-specifically unravel potential molecular targets and to change S-nitrosylation-based pathophysiology, which may further the understanding of the potential role of S-nitrosylation in diseases.

Is S-nitrosylation of cochlear proteins a critical factor in cisplatin-induced ototoxicity?

S-nitrosylation is a redox-sensitive protein modification, which is a highly specific, but reversible mechanism that regulates several signal transduction cascades. Oxidative stress plays a causal role in the ototoxic effects of an anti-neoplastic drug, cisplatin. Despite emerging evidence implicating nitroxidative stress as a critical factor in cisplatin toxicity, the significance of the cochlear protein S-nitrosylation in cisplatin ototoxicity is yet to be understood. In the present study, a 16-mg/kg dose of cisplatin, induced a significant shift in the amplitudes of distortion product otoacoustic emissions, a measure of outer hair cell activity, in Wistar rats, 3 days post-treatment. These ototoxic effects were accompanied by significant increases in the S-nitrosylation of at least three cochlear proteins. Biological significance of these S-nitrosylated proteins was indicated by their immunolocalization in organ of Corti, stria vascularis, and spiral ganglions, which are known cochlear targets of cisplatin toxicity. In addition, co-treatment with Trolox, an inhibitor of peroxynitrite, attenuated cisplatin-induced S-nitrosylation of cochlear proteins and prevented the associated hearing loss. The cisplatin-induced S-nitrosylation of inner ear proteins, their sensitive cochlear localization, and their potential association with cisplatin-induced hearing loss suggests that S-nitrosylation of cochlear proteins might play a crucial role in mediating cisplatin ototoxicity.

MDA-7/IL-24 induces Bcl-2 denitrosylation and ubiquitin-degradation involved in cancer cell apoptosis

MDA-7/IL-24 was involved in the specific cancer apoptosis through suppression of Bcl-2 expression, which is a key apoptosis regulatory protein of the mitochondrial death pathway. However, the underlying mechanisms of this regulation are unclear. We report here that tumor-selective replicating adenovirus ZD55-IL-24 leads to Bcl-2 S-denitrosylation and concomitant ubiquitination, which take part in the 26S proteasome degradation. IL-24-siRNA completely blocks Bcl-2 ubiquitination via reversion of Bcl-2 S-denitrosylation and protects it from proteasomal degradation which confirmed the significant role of MDA-7/IL-24 in regulating posttranslational modification of Bcl-2 in cancer cells. Nitric oxide (NO) is a key regulator of protein S-nitrosylation and denitrosylation. The NO donor, sodium nitroprusside (SNP), down-regulates Bcl-2 S-denitrosylation, attenuates Bcl-2 ubiquitination and subsequently counteracts MDA-7/IL-24 induced cancer cell apoptosis, whereas NO inhibitor 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxy-3-oxide (PTIO) shows the opposite effect. At the same time, these NO modulators fail to affect Bcl-2 phosphorylation, suggesting that NO regulates Bcl-2 stability in a phosphorylation-independent manner. In addition, Bcl-2 S-nitrosylation reduction induced by ZD55-IL-24 was attributed to both iNOS decrease and TrxR1 increase. iNOS-siRNA facilitates Bcl-2 S-denitrosylation and ubiquitin-degradation, whereas the TrxR1 inhibitor auranofin prevents Bcl-2 from denitrosylation and ubiquitination, thus restrains the caspase signal pathway activation and subsequent cancer cell apoptosis. Taken together, our studies reveal that MDA-7/IL-24 induces Bcl-2 S-denitrosylation via regulation of iNOS and TrxR1. Moreover, denitrosylation of Bcl-2 results in its ubiquitination and subsequent caspase protease family activation, as a consequence, apoptosis susceptibility. These findings provide a novel insight into MDA-7/IL-24 induced growth inhibition and carcinoma apoptosis.

Endothelial nitric oxide and 15-lipoxygenase-1 metabolites independently mediate relaxation of the rabbit aorta

Endothelial 15-lipoxygenase-1 (15-LO-1) metabolites of arachidonic acid (AA), 11,12,15-trihydroxyeicosatrienoic acid (THETA) and 15-hydroxy-11,12-epoxyeicosatrienoic acid (HEETA) and nitric oxide (NO) mediate relaxations to acetylcholine (ACH). However, interactions between NO and the 15-LO-1 pathway have not been explored. Therefore, the effect of physiological and pharmacological concentrations of NO on 15-LO activity and relaxation was studied in rabbit aorta. In indomethacin-treated aortic rings, maximal ACH relaxations of 91.3±4.0%, decreased to 54.5±3.0% by the NO synthase inhibitor, nitro-l-arginine (LNA), to 49.8±3% by the guanylate cyclase (GC) inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one, to 63.7±4.9% by the lipoxygenase (LO) inhibitor, nordihydroguaiaretic acid (NDGA) and were completely inhibited by the combination of LNA and NDGA. AA relaxations were not affected by GC inhibition but were reduced by LO inhibition. The NO donor, dipropylenetriamine-NONOate (DPTA) caused concentration-related relaxations (EC(50)=4.7×10(-6)M). Aortic metabolism of (14)C-AA to THETA and HEETA was not altered by EC(50) concentrations of DPTA but were reduced 10-fold by 10(-3)M DPTA. In LNA-treated aorta, DPTA (3×10(-6)M) caused relaxations of 38.2.5±4%. Maximum relaxations to ACH did not differ in the presence and absence 3×10(-6)M DPTA (49.5±5% and 44.2±4%, respectively). These results indicate that NO and 15-LO-1 act in parallel to mediate ACH relaxations and NO does not alter 15-LO-1 activity.

Mechanisms of xylanase-induced nitric oxide and phosphatidic acid production in tomato cells

The second messenger nitric oxide (NO), phosphatidic acid (PA) and reactive oxygen species (ROS) are involved in the plant defense response during plant-pathogen interactions. NO has been shown to participate in PA production in response to the pathogen-associated molecular pattern xylanase in tomato cell suspensions. Defense responses downstream of PA include ROS production. The goal of this work was to study the signaling mechanisms involved in PA production during the defense responses triggered by xylanase and mediated by NO in the suspension-cultured tomato cells. We analyzed the participation of protein kinases, guanylate cyclase and the NO-mediated posttranslational modification S-nitrosylation, by means of pharmacology and biochemistry. We showed that NO, PA and ROS levels are significantly diminished by treatment with the general protein kinase inhibitor staurosporine. This indicates that xylanase-induced protein phosphorylation events might be the important components leading to NO formation, and hence for the downstream regulation of PA and ROS levels. When assayed, a guanylate cyclase inhibitor or a cGMP analog did not alter the PA accumulation. These results suggest that a cGMP-mediated pathway is not involved in xylanase-induced PA formation. Finally, the inhibition of protein S-nitrosylation did not affect NO formation but compromised PA and ROS production. Data collectively indicate that upon xylanase perception, cells activate a protein kinase pathway required for NO formation and that, S-nitrosylation-dependent mechanisms are involved in downstream signaling leading to PA and ROS.

Pathogen-specific TLR2 protein activation programs macrophages to induce Wnt-beta-catenin signaling

Innate immunity recognizes and resists various pathogens; however, the mechanisms regulating pathogen versus nonpathogen discrimination are still imprecisely understood. Here, we demonstrate that pathogen-specific activation of TLR2 upon infection with Mycobacterium bovis BCG, in comparison with other pathogenic microbes, including Salmonella typhimurium and Staphylococcus aureus, programs macrophages for robust up-regulation of signaling cohorts of Wnt-β-catenin signaling. Signaling perturbations or genetic approaches suggest that infection-mediated stimulation of Wnt-β-catenin is vital for activation of Notch1 signaling. Interestingly, inducible NOS (iNOS) activity is pivotal for TLR2-mediated activation of Wnt-β-catenin signaling as iNOS(-/-) mice demonstrated compromised ability to trigger activation of Wnt-β-catenin signaling as well as Notch1-mediated cellular responses. Intriguingly, TLR2-driven integration of iNOS/NO, Wnt-β-catenin, and Notch1 signaling contributes to its capacity to regulate the battery of genes associated with T(Reg) cell lineage commitment. These findings reveal a role for differential stimulation of TLR2 in deciding the strength of Wnt-β-catenin signaling, which together with signals from Notch1 contributes toward the modulation of a defined set of effector functions in macrophages and thus establishes a conceptual framework for the development of novel therapeutics.

Flux of nitric oxide between the necrotrophic pathogen Botrytis cinerea and the host plant

Nitric oxide (NO) production by Botrytis cinerea and the effect of externally supplied NO were studied during saprophytic growth and plant infection. Fluorescence analysis with 4,5-diaminofluorescein diacetate and electrochemical studies were conducted in vitro between 4 and 20 h of incubation and in planta between 15 and 75 h post-inoculation. The production of NO by B. cinerea in vitro was detected inside the germinating spores and mycelium and in the surrounding medium. In planta production of NO showed a large variation that was dependent on the host plant and developmental stage of the infection. The induced production of NO was detected from 16 h of in vitro incubation in response to externally added NO. The production of NO by B. cinerea is probably modulated to promote fungal colonization of the plant tissue. The production of NO which diffuses outside the fungal cells and the induction of NO production by exogenous NO open up the possibility of NO cross-talk between the fungus and the plant. Finally, the existence of an NO concentration threshold is proposed, which may increase or reduce the plant defence against necrotrophic fungal pathogens.

Proteomic and mass spectroscopic quantitation of protein S-nitrosation differentiates NO-donors

Protein S-nitrosation has been argued to be the most important signaling pathway mediating the bioactivity of NO. This post-translational modification of protein thiols is the result of chemical nitrosation of cysteine residues. The term NO-donors covers very different chemical classes, from clinical therapeutics to probes of routine use in chemical biology; their different chemistry is predicted to result in distinctive biology regulated by protein S-nitrosation. To measure the extent of protein S-nitrosation by NO-donors, a proteomic mass spectrometry method was developed, which quantitates free thiol versus nitrosothiol for each modified cysteine residue, coined d-Switch. This method is adapted from the biotin switch (BST) method, used extensively to identify S-nitrosated proteins in complex biological mixtures; however, BST does not quantitate free thiol. Since glutathione-S-transferase P1-1 (GST-P1) has been proposed to be a biological "NO-carrier", GST-P1 was used as a reporter protein. The 5 different chemical classes of NO-donors compared by d-Switch demonstrated very different profiles of protein S-nitrosation and response to O(2) and cysteine, although all NO-donors were oxidants toward GST-P1. The low limits of detection and the ability to use established MS database searching allowed facile generalization of the d-Switch method. Therefore after incubation of neuronal cell cultures with nitrosothiol, it was possible to quantitate not only S-nitrosation of GST-P1 but also many other proteins, including novel targets such as ubiquitin carboxyl-terminal esterase L1 (UCHL1). Moreover, d-Switch also allowed identification of non-nitrosated proteins and quantitation of degree of nitrosation for individual protein thiols.

Emerging roles of nitric oxide in neurodegeneration

Nitric oxide (NO) is a gaseous signaling molecule which has physiological and pathological roles in the cell. Under normal conditions, NO is produced by nitric oxide synthase (NOS) and can induce physiological responses such as vasodilation. However, over-activation of NOS has been linked to a number of human pathological conditions. For instance, most neurodegenerative disorders are marked by the presence of nitrated protein aggregates. How nitrosative stress leads to neurodegeneration is not clear, but various studies suggest that increased nitrosative stress causes protein nitration which then leads to protein aggregation. Protein aggregates are highly toxic to neurons and can promote neurodegeneration. In addition to inducing protein aggregation, recent studies show that nitrosative stress can also compromise a number of neuroprotective pathways by modifying activities of certain proteins through S-nitrosylation. These findings suggest that increased nitrosative stress can contribute to neurodegeneration through multiple pathways.

Nitric oxide is involved in Mycobacterium bovis bacillus Calmette-Guérin-activated Jagged1 and Notch1 signaling

Pathogenic mycobacteria have evolved unique strategies to survive within the hostile environment of macrophages. Modulation of key signaling cascades by NO, generated by the host during infection, assumes critical importance in overall cell-fate decisions. We show that NO is a critical factor in Mycobacterium bovis bacillus Calmette-Guérin-mediated Notch1 activation, as the generation of activated Notch1 or expression of Notch1 target genes matrix metalloproteinase-9 (MMP-9) or Hes1 was abrogated in macrophages derived from inducible NO synthase (iNOS) knockout (iNOS(-/-)), but not from wild-type, mice. Interestingly, expression of the Notch1 ligand Jagged1 was compromised in M. bovis bacillus Calmette-Guérin-stimulated iNOS(-/-) macrophages, and loss of Jagged1 expression or Notch1 signaling could be rescued by NO donors. Signaling perturbations or genetic approaches implicated that robust expression of MMP-9 or Hes1 required synergy and cross talk between TLR2 and canonical Notch1-PI3K cascade. Further, CSL/RBP-Jk contributed to TLR2-mediated expression of MMP-9 or Hes1. Correlative evidence shows that, in a murine model for CNS tuberculosis, this mechanism operates in vivo only in brains derived from WT but not from iNOS(-/-) mice. Importantly, we demonstrate the activation of Notch1 signaling in vivo in granulomatous lesions in the brains of Mycobacterium tuberculosis-infected human patients with tuberculous meningitis. Current investigation identifies NO as a pathological link that modulates direct cooperation of TLR2 with Notch1-PI3K signaling or Jagged1 to regulate specific components of TLR2 responses. These findings provide new insights into mechanisms by which Notch1, TLR2, and NO signals are integrated in a cross talk that modulates a defined set of effector functions in macrophages.

Inhibition of nitric oxide synthesis during induced cholestasis ameliorates hepatocellular injury by facilitating S-nitrosothiol homeostasis

Cholestatic liver injury following extra- or intrahepatic bile duct obstruction causes nonparenchymal cell proliferation and matrix deposition leading to end-stage liver disease and cirrhosis. In cholestatic conditions, nitric oxide (NO) is mainly produced by a hepatocyte-inducible NO synthase (iNOS) as a result of enhanced inflow of endotoxins to the liver and also by accumulation of bile salts in hepatocytes and subsequent hepatocellular injury. This study was aimed to investigate the role of NO and S-nitrosothiol (SNO) homeostasis in the development of hepatocellular injury during cholestasis induced by bile duct ligation (BDL) in rats. Male Wistar rats (200-250 g) were divided into four groups (n=10 each), including sham-operated (SO), bile duct-ligated (BDL), tauroursodeoxycholic acid (TUDCA, 50 mg/kg) and S-methylisothiourea (SMT, 25 mg/kg) treated. After 7 days, BDL rats showed elevated serum levels of gamma-glutamiltranspeptidase, aspartate aminotransferase, alanine aminotransferase, LDH, and bilirubin, bile duct proliferation and fibrosis, compared with the SO group. TUDCA treatment did not significantly alter these parameters, but the iNOS inhibitor SMT ameliorated hepatocellular injury, as shown by lower levels of circulating hepatic enzymes and bilirubin, and a decreased grade of bile duct proliferation and fibrosis. Both TUDCA and SMT treatments reversed Mrp2 canalicular pump expression to control levels. However, only SMT treatment significantly lowered the increased levels of plasma NO and S-nitrosation (S-nitrosylation) of liver proteins in BDL rats. Moreover, BDL resulted in a reduction of the S-nitrosoglutathione reductase (GSNOR/Adh5) enzymatic activity and a downregulation of the GSNOR/Adh5 mRNA expression that was reverted by SMT, but not TUDCA, treatment. A total of 25 liver proteins, including S-adenosyl methionine synthetase, betaine-homocysteine S-methyltransferase, Hsp90 and protein disulfide isomerase, were found to be S-nitrosated in BDL rats. In conclusion, the inhibition of NO production during induced cholestasis ameliorates hepatocellular injury. This effect is in part mediated by the improvement of cell proficiency in maintaining SNO homeostasis.

Molecular mechanisms of 4-hydroxy-2-nonenal and acrolein toxicity: nucleophilic targets and adduct formation

Acrolein and 4-hydroxy-2-nonenal (HNE) are byproducts of lipid peroxidation and are thought to play central roles in various traumatic injuries and disease states that involve cellular oxidative stress, for example, spinal cord trauma, diabetes, and Alzheimer's disease. In this review, we will discuss the chemical attributes of acrolein and HNE that determine their toxicities. Specifically, these aldehydes are classified as type 2 alkenes and are characterized by an alpha,beta-unsaturated carbonyl structure. This structure is a conjugated system that contains mobile pi-electrons. The carbonyl oxygen atom is electronegative and can promote the withdrawal of mobile electron density from the beta-carbon atom causing regional electron deficiency. On the basis of this type of electron polarizability, both acrolein and HNE are considered to be soft electrophiles that preferentially form 1,4-Michael type adducts with soft nucleophiles. Proteomic, quantum mechanical, and kinetic data will be presented, indicating that cysteine sulfhydryl groups are the primary soft nucleophilic targets of acrolein and HNE. This is in contrast to nitrogen groups on harder biological nucleophiles such as lysine or histidine residues. The toxicological outcome of adduct formation is not only dependent upon residue selectivity but also the importance of the targeted amino acid in protein function or structure. In attempting to discern the toxicological significance of a given adduct, we will consider the normal roles of cysteine, lysine, and histidine residues in proteins and the relative merits of corresponding adducts in the manifestations of diseases or toxic states. Understanding the molecular actions of acrolein and HNE could provide insight into many pathogenic conditions that involve initial cellular oxidative stress and could, thereby, offer new efficacious avenues of pharmacological defense.

Bacterial nitric oxide detoxification prevents host cell S-nitrosothiol formation: a novel mechanism of bacterial pathogenesis

S-nitrosylation is an important mediator of multiple nitric oxide-dependent biological processes, including eukaryotic cellular events such as macrophage apoptosis and proinflammatory signaling. Many pathogenic bacteria possess NO detoxification mechanisms, such as the nitric oxide reductase (NorB) of Neisseria meningitidis and the flavohemoglobins (Hmp) of Salmonella enterica and Escherichia coli, which serve to protect the microorganism from nitrosative stress within the intracellular environment. In this study, we demonstrate that expression of meningococcal NorB increases the rate at which low-molecular-weight S-nitrosothiol (SNO) decomposes in vitro. To determine whether this effect occurs in cells during infection by bacteria, we induced SNO formation in murine macrophages by activation with lipopolysaccharide and γ-interferon and observed a reduced abundance of SNO during coincubation with N. meningitidis, S. enterica, or E. coli. In each case, this effect was shown to be dependent on bacterial NO detoxification genes, which act to prevent SNO formation through the removal of NO. This may represent a novel mechanism of host cell injury by bacteria.—Laver, J. R., Stevanin, T. M., Messenger, S. L., Dehn Lunn, A., Lee, M. E., Moir, J. W. B., Poole, R. K., Read, R. C. Bacterial nitric oxide detoxification prevents host cell S-nitrosothiol formation: a novel mechanism of bacterial pathogenesis.

Nitric oxide and nitric oxide synthase isoforms in the normal, hypertrophic, and failing heart

Nitric oxide (NO) produced in the heart by nitric oxide synthase (NOS) is a highly reactive signaling molecule and an important modulator of myocardial function. NOS catalyzes the conversion of L: -arginine to L: -citrulline and NO but under particular circumstances reactive oxygen species (ROS) can be formed instead of NO (uncoupling). In the heart, three NOS isoforms are present: neuronal NOS (nNOS, NOS1) and endothelial NOS (eNOS, NOS3) are constitutively present enzymes in distinct subcellular locations within cardiomyocytes, whereas inducible NOS (iNOS, NOS2) is absent in the healthy heart, but its expression is induced by pro-inflammatory mediators. In the tissue, NO has two main effects: (i) NO stimulates the activity of guanylate cyclase, leading to cGMP generation and activation of protein kinase G, and (ii) NO nitrosylates tyrosine and thiol-groups of cysteine in proteins. Upon nitrosylation, proteins may change their properties. Changes in (i) NOS expression and activity, (ii) subcellular compartmentation of NOS activity, and (iii) the occurrence of uncoupling may lead to multiple NO-induced effects, some of which being particularly evident during myocardial overload as occurs during aortic constriction and myocardial infarction. Many of these NO-induced effects are considered to be cardioprotective but particularly if NOS becomes uncoupled, formation of ROS in combination with a low NO bioavailability predisposes for cardiac damage.

S-nitrosation of proteins duringd-galactosamine-induced cell death in human hepatocytes

Nitric oxide (NO) participates in the cell death induced by d-Galactosamine (d-GalN) in hepatocytes, and NO-derived reactive oxygen intermediates are critical contributors to protein modification and hepatocellular injury. It is anticipated that S-nitrosation of proteins will participate in the mechanisms leading to cell death in d-GalN-treated human hepatocytes. In the present study, d-GalN-induced cell death was related to augmented levels of NO production and S-nitrosothiol (SNO) content. The biotin switch assay confirmed that d-GalN increased the levels of S-nitrosated proteins in human hepatocytes. S-nitrosocysteine (CSNO) enhanced protein S-nitrosation and altered cell death parameters that were related to S-nitrosation of the executioner caspase-3. Fifteen S-nitrosated proteins participating in metabolism, antioxidative defense and cellular homeostasis were identified in human hepatocytes treated with CSNO. Among them, seven were also identified in d-GalN-treated hepatocytes. The results here reported underline the importance of the alteration of SNO homeostasis during d-GalN-induced cell death in human hepatocytes.

Exogenous nitric oxide induces protection during hemorrhagic shock

INTRODUCTION

This study analyzed the systemic and microvascular hemodynamic changes related to increased nitric oxide (NO) availability during the early phase of hemorrhagic shock. Hemodynamic responses to hemorrhagic shock were studied in the hamster window chamber.

MATERIALS AND METHODS

Exogenous NO was administered in the form of nitrosothiols (nitrosylated glutathione, GSNO) and was given prior the onset of hemorrhage. Moderate hemorrhage was induced by arterial controlled bleeding of 50% of the blood volume, and the hypovolemic shock was followed over 90 min.

RESULTS

Animals pre-treated with GSNO maintained systemic and microvascular conditions during hypovolemic hemorrhagic shock, when compared to animal treated with glutathione (GSH) or the Sham group. Low concentrations of NO released during the early phase of hypovolemic shock from GSNO mitigated arteriolar vasoconstriction, increased capillary perfusion and venous return, and improved cardiac function (recovered of blood pressure and stabilized heart rate). GSNO's effect on resistance vessels influenced intravascular pressure redistribution and blood flow, preventing tissue ischemia.

DISCUSSION

Increases in NO availability during the early phase of hypovolemic shock could preserve cardiac function and microvascular perfusion, sustaining organ function. Direct translation into a clinical scenario may be limited, although the pathophysiological importance of NO in the early phase of hypovolemia is clearly highlighted here.

M. bovis BCG induced expression of COX-2 involves nitric oxide-dependent and -independent signaling pathways

In a multifaceted immunity to mycobacterial infection, induced expression of cyclooxygenase-2 (COX-2) by Mycobacterium bovis bacillus Calmette-Guerin (BCG) may act as an important influencing factor for the effective host immunity. We here demonstrate that M. bovis BCG-triggered TLR2-dependent signaling leads to COX-2 and PGE2 expression in vitro in macrophages and in vivo in mice. Further, the presence of PGE2 could be demonstrated in sera or cerebrospinal fluid of tuberculosis patients. The induced COX-2 expression in macrophages is dependent on NF-kappaB activation, which is mediated by inducible NO synthase (iNOS)/NO-dependent participation of the members of Notch1-PI-3K signaling cascades as well as iNOS-independent activation of ERK1/2 and p38 MAPKs. Inhibition of iNOS activity abrogated the M. bovis BCG ability to trigger the generation of Notch1 intracellular domain (NICD), a marker for Notch1 signaling activation, as well as activation of the PI-3K signaling cascade. On the contrary, treatment of macrophages with 3-morpholinosydnonimine, a NO donor, resulted in a rapid increase in generation of NICD, activation of PI-3K pathway, as well as the expression of COX-2. Stable expression of NICD in RAW 264.7 macrophages resulted in augmented expression of COX-2. Further, signaling perturbations suggested the involvement of the cross-talk of Notch1 with members with the PI-3K signaling cascade. These results implicate the dichotomous nature of TLR2 signaling during M. bovis BCG-triggered expression of COX-2. In this perspective, we propose the involvement of iNOS/NO as one of the obligatory, early, proximal signaling events during M. bovis BCG-induced COX-2 expression in macrophages.

The structural basis of gas-responsive transcription by the human nuclear hormone receptor REV-ERBbeta

Heme is a ligand for the human nuclear receptors (NR) REV-ERBalpha and REV-ERBbeta, which are transcriptional repressors that play important roles in circadian rhythm, lipid and glucose metabolism, and diseases such as diabetes, atherosclerosis, inflammation, and cancer. Here we show that transcription repression mediated by heme-bound REV-ERBs is reversed by the addition of nitric oxide (NO), and that the heme and NO effects are mediated by the C-terminal ligand-binding domain (LBD). A 1.9 A crystal structure of the REV-ERBbeta LBD, in complex with the oxidized Fe(III) form of heme, shows that heme binds in a prototypical NR ligand-binding pocket, where the heme iron is coordinately bound by histidine 568 and cysteine 384. Under reducing conditions, spectroscopic studies of the heme-REV-ERBbeta complex reveal that the Fe(II) form of the LBD transitions between penta-coordinated and hexa-coordinated structural states, neither of which possess the Cys384 bond observed in the oxidized state. In addition, the Fe(II) LBD is also able to bind either NO or CO, revealing a total of at least six structural states of the protein. The binding of known co-repressors is shown to be highly dependent upon these various liganded states. REV-ERBs are thus highly dynamic receptors that are responsive not only to heme, but also to redox and gas. Taken together, these findings suggest new mechanisms for the systemic coordination of molecular clocks and metabolism. They also raise the possibility for gas-based therapies for the many disorders associated with REV-ERB biological functions.

Molecular mechanisms and clinical implications of reversible protein S-glutathionylation

Sulfhydryl chemistry plays a vital role in normal biology and in defense of cells against oxidants, free radicals, and electrophiles. Modification of critical cysteine residues is an important mechanism of signal transduction, and perturbation of thiol-disulfide homeostasis is an important consequence of many diseases. A prevalent form of cysteine modification is reversible formation of protein mixed disulfides (protein-SSG) with glutathione (GSH). The abundance of GSH in cells and the ready conversion of sulfenic acids and S-nitroso derivatives to S-glutathione mixed disulfides suggests that reversible S-glutathionylation may be a common feature of redox signal transduction and regulation of the activities of redox sensitive thiol-proteins. The glutaredoxin enzyme has served as a focal point and important tool for evolution of this regulatory mechanism, because it is a specific and efficient catalyst of protein-SSG deglutathionylation. However, mechanisms of control of intracellular Grx activity in response to various stimuli are not well understood, and delineation of specific mechanisms and enzyme(s) involved in formation of protein-SSG intermediates requires further attention. A large number of proteins have been identified as potentially regulated by reversible S-glutathionylation, but only a few studies have documented glutathionylation-dependent changes in activity of specific proteins in a physiological context. Oxidative stress is a hallmark of many diseases which may interrupt or divert normal redox signaling and perturb protein-thiol homeostasis. Examples involving changes in S-glutathionylation of specific proteins are discussed in the context of diabetes, cardiovascular and lung diseases, cancer, and neurodegenerative diseases.

Nitrite-nitric oxide control of mitochondrial respiration at the frontier of anoxia

Actively respiring animal and plant tissues experience hypoxia because of mitochondrial O(2) consumption. Controlling oxygen balance is a critical issue that involves in mammals hypoxia-inducible factor (HIF) mediated transcriptional regulation, cytochrome oxidase (COX) subunit adjustment and nitric oxide (NO) as a mediator in vasodilatation and oxygen homeostasis. In plants, NO, mainly derived from nitrite, is also an important signalling molecule. We describe here a mechanism by which mitochondrial respiration is adjusted to prevent a tissue to reach anoxia. During pea seed germination, the internal atmosphere was strongly hypoxic due to very active mitochondrial respiration. There was no sign of fermentation, suggesting a down-regulation of O(2) consumption near anoxia. Mitochondria were found to finely regulate their surrounding O(2) level through a nitrite-dependent NO production, which was ascertained using electron paramagnetic resonance (EPR) spin trapping of NO within membranes. At low O(2), nitrite is reduced into NO, likely at complex III, and in turn reversibly inhibits COX, provoking a rise to a higher steady state level of oxygen. Since NO can be re-oxidized into nitrite chemically or by COX, a nitrite-NO pool is maintained, preventing mitochondrial anoxia. Such an evolutionarily conserved mechanism should have an important role for oxygen homeostasis in tissues undergoing hypoxia.

Assessment of the nitrosylation process

PURPOSE OF REVIEW

To understand the principles and limits of the methodologies used for the measurement of S-nitrosylated proteins.

RECENT FINDINGS

Among methods for studying protein S-nitrosylation, chemoluminescence and biotin switch assay have rapidly gained popularity. However, recent findings have attempted to highlight potential pitfalls for these methods. Many assays for biological S-nitrosylated proteins are used near the limit of detection and pretreatment of the biological samples can modify the S-NO bond. These results suggest that additional controls are essential in order to identify S-nitrosylated proteins and results should be quantitatively validated using more than one methodology.

SUMMARY

Protein S-nitrosylation is emerging as a key mechanism by which nitric oxide regulates cell signalling. This review focuses on existing methodologies for the measurement of S-nitrosylated proteins in biological matrices and the potential pitfalls of each method.

Nitric oxide-mediated modulation of calcium/calmodulin-dependent protein kinase II

The mechanisms of NO inhibition of CaMK [Ca2+/CaM (calmodulin)-dependent protein kinase] II activity were studied. In rat pituitary tumour GH3 cells, TRH [thyrotrophin (TSH)-releasing hormone]-stimulated phosphorylation of nNOS [neuronal NOS (NO synthase)] at Ser847 was sensitive to an inhibitor of CaMKs, KN-93, and was enhanced by inhibition of nNOS with 7NI (7-nitroindazole). Enzyme activity of CaMKII following in situ treatment with 7NI was also increased. The in vitro activity of CaMKII was inhibited by co-incubation either with nNOS and L-arginine or with NO donors SNAP (S-nitroso-N-acetyl-DL-penicillamine) and DEA-NONOate [diethylamine-NONOate (diazeniumdiolate)]. Once inhibited by these treatments, CaMKII was observed to undergo full reactivation on the addition of a reducing reagent, DTT (dithiothreitol). In transfected cells expressing CaMKII and nNOS, treatment with the calcium ionophore A23187 further revealed nNOS phosphorylation at Ser847, which was enhanced by 7NI and CaMKII S-nitrosylation. Mutated CaMKII (C6A), in which Cys6 was substituted with an alanine residue, was refractory to 7NI-induced enhancement of nNOS phosphorylation or to CaMKII S-nitrosylation. Furthermore, we could identify Cys6 as a direct target for S-nitrosylation of CaMKII using MS. In addition, treatment with glutamate caused an increase in CaMKII S-nitrosylation in rat hippocampal slices. This glutamate-induced S-nitrosylation was blocked by 7NI. These results suggest that inactivation of CaMKII mediated by S-nitrosylation at Cys6 may contribute to NO-induced neurotoxicity in the brain.

Nitric oxide-induced resistance or sensitization to death in tumor cells

This report summarizes the present state of our knowledge pertaining to the NO-induced resistance or sensitization of tumor cell death. The effects of NO and its synergy with members of the TNF family, with cytotoxic drugs, and with ionizing radiations have been investigated. The dual effect of NO-induced resistance or sensitization and the underlying molecular mechanisms are discussed.

S-nitrosylated proteins of a medicinal CAM plant Kalanchoe pinnata- ribulose-1,5-bisphosphate carboxylase/oxygenase activity targeted for inhibition

Nitric oxide (NO) is a signaling molecule that affects a myriad of processes in plants. However, the mechanistic details are limited. NO post-translationally modifies proteins by S-nitrosylation of cysteines. The soluble S-nitrosoproteome of a medicinal, crassulacean acid metabolism (CAM) plant, Kalanchoe pinnata, was purified using the biotin switch technique. Nineteen targets were identified by MALDI-TOF mass spectrometry, including proteins associated with carbon, nitrogen and sulfur metabolism, the cytoskeleton, stress and photosynthesis. Some were similar to those previously identified in Arabidopsis thaliana, but kinesin-like protein, glycolate oxidase, putative UDP glucose 4-epimerase and putative DNA topoisomerase II had not been identified as targets previously for any organism. In vitro and in vivo nitrosylation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), one of the targets, was confirmed by immunoblotting. Rubisco plays a central role in photosynthesis, and the effect of S-nitrosylation on its enzymatic activity was determined using NaH14CO3. The NO-releasing compound S-nitrosoglutathione inhibited its activity in a dose-dependent manner suggesting Rubisco inactivation by nitrosylation for the first time.

S-Nitrosylation - another biological switch like phosphorylation?

Nitric oxide (NO) has emerged as a key-signaling molecule affecting plant growth and development right from seed germination to cell death. It is now being considered as a new plant hormone. NO is predominantly produced by nitric oxide synthase (NOS) in animal systems. NOS converts L-arginine (substrate) to citrulline and NO is a byproduct of the reaction. However, a similar biosynthetic mechanism is still not fully established in plants as NOS is still to be purified. First plant NOS gene (AtNOS1) was cloned from Arabidopsis suggesting the existence of NOS in plants. It was shown to be involved in hormonal signaling, stomatal closure, flowering, pathogen defense response, oxidative stress, senescence and salt tolerance. However, recent studies have raised critical questions/concerns about its substantial role in NO biosynthesis. Despite the ever increasing number of NO responses observed, little is known about the signal transduction pathway(s) and mechanisms by which NO interacts with different components and results in altered cellular activities. A brief overview is presented here. Proteins are one of the major bio-molecule besides DNA, RNA and lipids which are modified by NO and its derivatives. S-nitrosylation is a ubiquitous NO mediated posttranslational modification that might regulate broad spectrum of proteins. In this review S-nitrosylation formation, catabolism and its biological significance is discussed to present the current scenario of this modification in plants.

Mechanisms of reversible protein glutathionylation in redox signaling and oxidative stress

Reversible protein S-glutathionylation (protein-SSG) is an important post-translational modification, providing protection of protein cysteines from irreversible oxidation and serving to transduce redox signals. Analogous to phosphatases, glutaredoxin (GRx) enzymes catalyze deglutathionylation of proteins, regulating diverse intracellular signaling pathways. Recently, other enzymes have been reported to exhibit deglutathionylating activity, but their contribution to intracellular protein deglutathionylation is uncertain. Currently, no enzyme has been shown to serve as a catalyst of S-glutathionylation in situ, although potential prototypes are reported, including human GRx1 and the pi isoform of glutathione-S-transferase (GSTpi). Further insight into cellular mechanisms of protein glutathionylation and deglutathionylation will enrich our understanding of redox signal transduction and potentially identify new therapeutic targets for diseases in which oxidative stress perturbs normal redox signaling. Accordingly, this review focuses primarily on mechanisms of catalysis in mammalian systems.

A new principle for information storage in an enzymatic pathway model

Strong experimental evidence indicates that protein kinase and phosphatase (KP) cycles are critical to both the induction and maintenance of activity-dependent modifications in neurons. However, their contribution to information storage remains controversial, despite impressive modeling efforts. For instance, plasticity models based on KP cycles do not account for the maintenance of plastic modifications. Moreover, bistable KP cycle models that display memory fail to capture essential features of information storage: rapid onset, bidirectional control, graded amplitude, and finite lifetimes. Here, we show in a biophysical model that upstream activation of KP cycles, a ubiquitous mechanism, is sufficient to provide information storage with realistic induction and maintenance properties: plastic modifications are rapid, bidirectional, and graded, with finite lifetimes that are compatible with animal and human memory. The maintenance of plastic modifications relies on negligible reaction rates in basal conditions and thus depends on enzyme nonlinearity and activation properties of the activity-dependent KP cycle. Moreover, we show that information coding and memory maintenance are robust to stochastic fluctuations inherent to the molecular nature of activity-dependent KP cycle operation. This model provides a new principle for information storage where plasticity and memory emerge from a single dynamic process whose rate is controlled by neuronal activity. This principle strongly departs from the long-standing view that memory reflects stable steady states in biological systems, and offers a new perspective on memory in animals and humans.

S-nitrosylation-induced conformational change in blackfin tuna myoglobin

S-nitrosylation is a post-translational protein modification that can alter the function of a variety of proteins. Despite the growing wealth of information that this modification may have important functional consequences, little is known about the structure of the moiety or its effect on protein tertiary structure. Here we report high-resolution x-ray crystal structures of S-nitrosylated and unmodified blackfin tuna myoglobin, which demonstrate that in vitro S-nitrosylation of this protein at the surface-exposed Cys-10 directly causes a reversible conformational change by "wedging" apart a helix and loop. Furthermore, we have demonstrated in solution and in a single crystal that reduction of the S-nitrosylated myoglobin with dithionite results in NO cleavage from the sulfur of Cys-10 and rebinding to the reduced heme iron, showing the reversibility of both the modification and the conformational changes. Finally, we report the 0.95-A structure of ferrous nitrosyl myoglobin, which provides an accurate structural view of the NO coordination geometry in the context of a globin heme pocket.

Nitric-oxide synthase: A cytochrome P450 family foster child

Nitric-oxide synthase (NOS), the enzyme responsible for mammalian NO generation, is no cytochrome P450, but there are striking similarities between both enzymes. First and foremost, both are heme-thiolate proteins, employing the same prosthetic group to perform similar chemistry. Moreover, they share the same redox partner, a diflavoprotein reductase, which in the case of NOS is incorporated with the oxygenase in one polypeptide chain. There are, however, also conspicuous differences, such as the presence in NOS of the additional cofactor tetrahydrobiopterin, which is applied as an auxiliary electron donor to prevent decay of the oxyferrous complex to ferric heme and superoxide. In this review similarities and differences between NOS and cytochrome P450 are analyzed in an attempt to explain why NOS requires BH4 and why NO synthesis is not catalyzed by a member of the cytochrome P450 family.

Oxidative-nitrosative stress and post-translational protein modifications: implications to lung structure-function relations. Arginase modulates NF-kappaB activity via a nitric oxide-dependent mechanism

NF-kappaB is a versatile transcription factor that regulates a wide array of processes, including inflammation and survival, and plays a critical role in the etiology of inflammatory lung diseases. Nitric oxide (NO) has been suggested to play an antiinflammatory role through S-nitrosation of components of NF-kappaB pathway. NO production can be modulated by changing the availability of its substrate, L-arginine. Arginases compete with NO synthases (NOSs) for their common substrate, L-arginine, and thereby have the potential to alter the signaling function of NO. The goal of the present study was to determine the impact of arginase manipulation on NO, and subsequent effects on NF-kappaB activation, in lung epithelial cells. Our results demonstrate that reduction of arginase activity enhanced cellular content of NO and S-nitrosated proteins, and resulted in decreases in TNF-alpha- or LPS-stimulated NF-kappaB DNA binding and transcriptional activity, in association with enhanced S-nitrosation of p50. The effects of arginase inhibition on NF-kappaB were reversed by the generic NOS inhibitor, N-omega-nitro-L-arginine methyl ester (L-NAME), suggesting a causal role for NO in the attenuation of NF-kappaB induced by arginase suppression. Conversely, overexpression of arginase I decreased cellular S-nitrosothiol content and enhanced IkappaB kinase activity and NF-kappaB DNA binding, and decreased S-nitrosation of p50. Collectively, our data point to a regulatory mechanism wherein NF-kappaB is controlled through arginase-dependent regulation of NO levels, which may impact on chronic inflammatory diseases that are accompanied by NF-kappaB activation and upregulation of arginases.