Redox-dependent Post-translational Modification Research Articles

An evolutionary view of the function of CC-type glutaredoxins in plant development and adaptation to the environment.

Land plants have to face an oxidizing, heterogeneous, and fast changing environment. Redox-dependent post-translational modifications emerge as a critical component of plant responses to stresses. Among the thiol oxidoreductase superfamily, class III CC-type glutaredoxins (called ROXYs) are land plant specific, and their evolutionary history is highly dynamic. Angiosperms encode many isoforms, classified into five subgroups (Aα, Aβ, Bα, Bβ, Bγ) that probably evolved from five common ancestral ROXYs, with higher evolutionary dynamics in the Bγ subgroup compared with the other subgroups. ROXYs can modulate the transcriptional activity of TGA transcription factor target genes, although their biochemical function is still debated. ROXYs participate in the control of proper plant development and reproduction, and are mainly negative regulators of plant responses to biotic and abiotic stresses. This suggests that most ROXYs could play essential and conserved functions in resetting redox-dependent changes in transcriptional activity upon stress signaling to ensure the responsiveness of the system and/or avoid exaggerated responses that could lead to major defects in plant growth and reproduction. In Arabidopsis Bγ members acquired important functions in responses to nitrogen availability and endogenous status, but the rapid and independent evolution of this subclass might suggest that this function results from neofunctionalization, specifically observed in core eudicots.

Endogenous S-nitrosocysteine proteomic inventories identify a core of proteins in heart metabolic pathways

Protein cysteine residues are essential for protein folding, participate in enzymatic catalysis, and coordinate the binding of metal ions to proteins. Enzymatically catalyzed and redox-dependent post-translational modifications of cysteine residues are also critical for signal transduction and regulation of protein function and localization. S-nitrosylation, the addition of a nitric oxide equivalent to a cysteine residue, is a redox-dependent modification. In this study, we curated and analyzed four different studies that employed various chemoselective platforms coupled to mass spectrometry to precisely identify S-nitrosocysteine residues in mouse heart proteins. Collectively 1974 S-nitrosocysteine residues in 761 proteins were identified and 33.4% were identified in two or more studies. A core of 75 S-nitrosocysteine residues in 44 proteins were identified in all four studies. Bioinformatic analysis of each study indicated a significant enrichment of mitochondrial proteins participating in metabolism. Regulatory proteins in glycolysis, TCA cycle, oxidative phosphorylation and ATP production, long chain fatty acid β-oxidation, and ketone and amino acid metabolism constitute the major functional pathways impacted by protein S-nitrosylation. In the cardiovascular system, nitric oxide signaling regulates vasodilation and cardiac muscle contractility. The meta-analysis of the proteomic data supports the hypothesis that nitric oxide signaling via protein S-nitrosylation is also a regulator of cardiomyocyte metabolism that coordinates fuel utilization to maximize ATP production. As such, protein cysteine S-nitrosylation represents a third functional dimension of nitric oxide signaling in the cardiovascular system to ensure optimal cardiac function.

Characterization of cellular oxidative stress response by stoichiometric redox proteomics.

The thiol redox proteome refers to all proteins whose cysteine thiols are subjected to various redox-dependent posttranslational modifications (PTMs) including S-glutathionylation (SSG), S-nitrosylation (SNO), S-sulfenylation (SOH), and S-sulfhydration (SSH). These modifications can impact various aspects of protein function such as activity, binding, conformation, localization, and interactions with other molecules. To identify novel redox proteins in signaling and regulation, it is highly desirable to have robust redox proteomics methods that can provide global, site-specific, and stoichiometric quantification of redox PTMs. Mass spectrometry (MS)-based redox proteomics has emerged as the primary platform for broad characterization of thiol PTMs in cells and tissues. Herein, we review recent advances in MS-based redox proteomics approaches for quantitative profiling of redox PTMs at physiological or oxidative stress conditions and highlight some recent applications. Considering the relative maturity of available methods, emphasis will be on two types of modifications: 1) total oxidation (i.e., all reversible thiol modifications), the level of which represents the overall redox state, and 2) S-glutathionylation, a major form of reversible thiol oxidation. We also discuss the significance of stoichiometric measurements of thiol PTMs as well as future perspectives toward a better understanding of cellular redox regulatory networks in cells and tissues.

Arabidopsis thaliana alcohol dehydrogenase is differently affected by several redox modifications.

In plant cells, many stresses, including low oxygen availability, result in a higher production of reactive oxygen species (ROS) and reactive nitrogen species (RNS). These molecules can lead to redox-dependent post-translational modification of proteins Cys residues. Here, we studied the effect of different redox modifications on alcohol dehydrogenase (ADH) from Arabidopsis thaliana. ADH catalyzes the last step of the ethanol fermentation pathway used by plants to cope with energy deficiency during hypoxic stress. Arabidopsis suspension cell cultures showed decreased ADH activity upon exposure to H2O2, but not to the thiol oxidizing agent diamide. We purified recombinant ADH and observed a significant decrease in the enzyme activity by treatments with H2O2 and diethylamine NONOate (DEA/NO). Treatments leading to the formation of a disulfide bond between ADH and glutathione (protein S-glutathionylation) had no negative effect on the enzyme activity. LC-MS/MS analysis showed that Cys47 and Cys243 could make a stable disulfide bond with glutathione, suggesting redox sensitivity of these residues. Mutation of ADH Cys47 to Ser caused an almost complete loss of the enzyme activity while the Cys243 to Ser mutant had increased specific activity. Incubation of ADH with NAD+ or NADH prevented inhibition of the enzyme by H2O2 or DEA/NO. These results suggest that binding of ADH with its cofactors may limit availability of Cys residues to redox modifications. Our study demonstrates that ADH from A. thaliana is subject to different redox modifications. Implications of ADH sensitivity to ROS and RNS during hypoxic stress conditions are discussed.

Quantitative proteomic characterization of redox-dependent post-translational modifications on protein cysteines.

Protein thiols play a crucial role in redox signaling, in the regulation of enzymatic activity and protein function, and in maintaining redox homeostasis in living systems. The unique chemical reactivity of the thiol group makes protein cysteines susceptible to reactions with reactive oxygen and nitrogen species that form various reversible and irreversible post-translational modifications (PTMs). The reversible PTMs in particular are major components of redox signaling and are involved in the regulation of various cellular processes under physiological and pathological conditions. The biological significance of these redox PTMs in both healthy and disease states has been increasingly recognized. Herein, we review recent advances in quantitative proteomic approaches for investigating redox PTMs in complex biological systems, including general considerations of sample processing, chemical or affinity enrichment strategies, and quantitative approaches. We also highlight a number of redox proteomic approaches that enable effective profiling of redox PTMs for specific biological applications. Although technical limitations remain, redox proteomics is paving the way to a better understanding of redox signaling and regulation in both healthy and disease states.

The Measurement of Reversible Redox Dependent Post-translational Modifications and Their Regulation of Mitochondrial and Skeletal Muscle Function.

Mitochondrial oxidative stress is a common feature of skeletal myopathies across multiple conditions; however, the mechanism by which it contributes to skeletal muscle dysfunction remains controversial. Oxidative damage to proteins, lipids, and DNA has received the most attention, yet an important role for reversible redox post-translational modifications (PTMs) in pathophysiology is emerging. The possibility that these PTMs can exert dynamic control of muscle function implicates them as a mechanism contributing to skeletal muscle dysfunction in chronic disease. Herein, we discuss the significance of thiol-based redox dependent modifications to mitochondrial, myofibrillar, and excitation-contraction (EC) coupling proteins with an emphasis on how these changes could alter skeletal muscle performance under chronically stressed conditions. A major barrier to a better mechanistic understanding of the role of reversible redox PTMs in muscle function is the technical challenges associated with accurately measuring the changes of site-specific redox PTMs. Here we will critically review current approaches with an emphasis on sample preparation artifacts, quantitation, and specificity. Despite these challenges, the ability to accurately quantify reversible redox PTMs is critical to understanding the mechanisms by which mitochondrial oxidative stress contributes to skeletal muscle dysfunction in chronic diseases.

OP35 - Mitochondrial oxidative stress in skeletal muscle and cardiac aging

Mitochondrial dysfunction plays an important role in many chronic diseases, including aging. However the role of oxidative stress in this dysfunction remains controversial. We tested whether mitochondrial oxidative stress underlies not only mitochondrial deficits, but also declines in performance of skeletal and cardiac muscle in aged mice. Direct manipulation of mitochondrial H 2 O 2 (mtH 2 O 2 ) production by lifelong overexpression of mitochondrial targeted catalase reduced mitochondrial deficits in aged skeletal muscle and protected against age-related declines in cardiac function. To test whether manipulating mitochondrial oxidative stress late in life could reverse deficits in aged skeletal muscle and heart we used a novel mitochondrial targeted peptide, SS-31, that interacts with cardiolipin on the inner mitochondrial membrane. SS-31 reduces mtH 2 O 2 production in dysfunctional aged mitochondria and improved glutathione redox status while not affecting young healthy mitochondria. Acute (1 hr) and 8 week treatment with SS-31 had similar effects on mitochondrial function and skeletal muscle performance. Both treatments reversed age-related declines in in vivo maximal mitochondrial ATP production and efficiency of oxidative phosphorylation (P/O) while increasing muscle fatigue resistance. Treatment for 8 weeks also reversed cardiac dysfunction, especially diastolic dysfunction. These improvements in skeletal muscle and cardiac function translated to improved treadmill endurance capacity in the aged mice. These results reveal a dynamic relationship between mitochondrial deficits and the redox environment of the cell that affects function in these tissues. To examine the mechanisms underlying this interaction we are examining the effect of manipulating mitochondrial oxidant production on the thiol redox proteome. Aging is associated with increased S-glutathionylation of the thiol proteome in aged skeletal muscle. Treatment with SS-31 partially reverses many of these age-related changes, including proteins involved in E-C coupling, muscle contraction, and protein quality control. These results demonstrate that mitochondrial oxidant production alters redox dependent post-translational modifications throughout the muscle thereby providing a potential mechanism linking mitochondrial oxidative stress to loss of muscle function with age. Furthermore, we demonstrate that reversing this mitochondrial oxidative stress can rapidly improve function highlighting the interaction between mitochondria and cellular redox environment as an attractive target to improve health in the elderly.

S‐Glutathionylation promotes HSP90 degradation under oxidative stress

S‐Glutathionylation, a redox‐dependent post‐translational modification, alters protein activity and stability in response to various stimuli. Heat shock protein 90 (HSP90), a ubiquitous chaperone, is known to interact with numerous proteins to regulate multiple cellular processes, especially in cell proliferation and cell cycle progression. The increased level of HSP90 is known as a hallmark in tumor cells and tissues, revealing the importance of HSP90 in tumorigenesis. Accumulating evidences indicated that the protein degradation of HSP90 is controlled by ubiquitin proteasome system. We herein report the site‐specific S‐glutathionylation of HSP90 in vivo and in vitro. The level of HSP90 was obviously decreased after the treatment with hydrogen peroxide or oxidized glutathione (GSSG), owing to the proteasome‐mediated degradation. Further gel filtration and CD spectrometric analyses indicated that S‐glutathionylation is the trigger to alter the quaternary and secondary structure of HSP90, respectively. Taken together, these results support the idea that S‐glutathionylation causes structure alterations in HSP90 and promotes the subsequent degradation. Since high level of HSP90 is associated with drug resistance of tumors and cancer reoccurrence, the findings on the S‐glutathionylation and subsequent protein degradation of HSP90 would shed light on the therapeutic potential in cancer therapy.

Glutathionylation of the Aquaporin-2 Water Channel: A Novel Post-Translational Modification Modulated by the Oxidative Stress

Aquaporin-2 (AQP2) is the vasopressin-regulated water channel that controls renal water reabsorption and urine concentration. AQP2 undergoes different regulated post-translational modifications, including phosphorylation and ubiquitylation, which are fundamental for controlling AQP2 cellular localization, stability, and function. The relationship between AQP2 and S-glutathionylation is of potential interest because reactive oxygen species (ROS), produced under renal failure or nephrotoxic drugs, may influence renal function as well as the expression and the activity of different transporters and channels, including aquaporins. Here, we show for the first time that AQP2 is subjected to S-glutathionylation in kidney and in HEK-293 cells stably expressing AQP2. S-Glutathionylation is a redox-dependent post-translational modification controlling several signal transduction pathways and displaying an acute effect on free cytosolic calcium concentration. Interestingly, we found that in fresh kidney slices, the increased AQP2 S-glutathionylation correlated with tert-butyl hydroperoxide-induced ROS generation. Moreover, we also found that cells expressing wild-type human calcium-sensing receptor (hCaSR-wt) and its gain of function (hCaSR-R990G; hCaSR-N124K) had a significant decrease in AQP2 S-glutathionylation secondary to reduced ROS levels and reduced basal intracellular calcium concentration compared with mock cells. Together, these new findings provide fundamental insight into cell biological aspects of AQP2 function and may be relevant to better understand and explain pathological states characterized by an oxidative stress and AQP2-dependent water reabsorption disturbs.

The glutaredoxin/S-glutathionylation axis regulates interleukin-17A-induced proinflammatory responses in lung epithelial cells in association with S-glutathionylation of nuclear factor κB family proteins

Interleukin-17A (IL-17A) is a newly emerging player in the pathogenesis of chronic lung diseases that amplifies inflammatory responses and promotes tissue remodeling. Stimulation of lung epithelial cells with IL-17A leads to activation of the transcription factor nuclear factor κB (NF-κB), a key player in the orchestration of lung inflammation. We have previously demonstrated the importance of the redox-dependent posttranslational modification S-glutathionylation in limiting activation of NF-κB and downstream gene induction. Under physiological conditions, the enzyme glutaredoxin 1 (Grx1) acts to deglutathionylate NF-κB proteins, which restores functional activity. In this study, we sought to determine the impact of S-glutathionylation on IL-17A-induced NF-κB activation and expression of proinflammatory mediators. C10 mouse lung alveolar epithelial cells or primary mouse tracheal epithelial cells exposed to IL-17A show rapid activation of NF-κB and the induction of proinflammatory genes. Upon IL-17A exposure, sulfenic acid formation and S-glutathionylated proteins increased. Assessment of S-glutathionylation of NF-κB pathway components revealed S-glutathionylation of RelA (RelA-SSG) and inhibitory κB kinase α (IKKα-SSG) after stimulation with IL-17A. SiRNA-mediated ablation of Grx1 increased both RelA-SSG and IKKα-SSG and acutely increased nuclear content of RelA and tended to decrease nuclear RelB. SiRNA-mediated ablation or genetic ablation of Glrx1 decreased the expression of the NF-κB-regulated genes KC and CCL20 in response to IL-17A, but conversely increased the expression of IL-6. Last, siRNA-mediated ablation of IKKα attenuated nuclear RelA and RelB content and decreased expression of KC and CCL20 in response to IL-17A. Together, these data demonstrate a critical role for the S-glutathionylation/Grx1 redox axis in regulating IKKα and RelA S-glutathionylation and the responsiveness of epithelial cells to IL-17A.

Mild oxidative stress induces S-glutathionylation of STAT3 and enhances chemosensitivity of tumoural cells to chemotherapeutic drugs

STAT3 is a transcription factor constitutively activated in a variety of cancers that has a critical role in the inhibition of apoptosis and induction of chemoresistance. Inhibition of the STAT3 signaling pathway suppresses cell survival signals and leads to apoptosis in cancer cells, suggesting that direct inhibition of STAT3 function is a viable therapeutic approach. Herein, we identify the naturally occurring sesquiterpene lactone cynaropicrin as a potent inhibitor of both IL-6-inducible and constitutive STAT3 activation (IC50=12μM). Cynaropicrin, which contains an α-β-unsaturated carbonyl moiety and acts as potent Michael reaction acceptor, induces a rapid drop in intracellular glutathione (GSH) concentration, thereby triggering S-glutathionylation of STAT3. Furthermore, glutathione ethylene ester, the cell permeable form of GSH, reverts the inhibitory action of cynaropicrin on STAT3 tyrosine phosphorylation. These findings suggest that this sesquiterpene lactone is able to induce redox-dependent post-translational modification of cysteine residues of STAT3 protein to regulate its function. STAT3 inhibition led to the suppression of two anti-apoptotic genes, Bcl-2 and survivin, in DU145 cells that constitutively express active STAT3. This event may be responsible for the decline in cell viability after cynaropicrin treatment. As revealed by PI/annexin-V staining, PARP cleavage, and DNA ladder formation, cynaropicrin cytotoxicity is mediated by apoptosis. Finally, cynaropicrin displayed a slight to strong synergism with two well-established chemotherapeutic drugs, cisplatin and docetaxel. Taken together our studies suggest that cynaropicrin suppresses the STAT3 pathway, leading to the down-regulation of STAT3-dependent gene expression and chemosensitization of tumour cells to chemotherapy.

Abstract P234: S-nitrosylation of Cyclophilin D Attenuates Mitochondrial Permeability Transition Pore Opening: A Critical Role for Cysteine 203 Residue

S-nitrosylation (SNO), a reversible, redox-dependent post-translational modification, has emerged as an important mechanism for dynamic regulation of many proteins. Our previous studies have shown that protein S-nitrosylation (SNO) plays a protective role in myocardial ischemia/reperfusion (IR) injury. The primary mediator of cell death in I/R injury is activation of the mitochondrial permeability transition pore (mPTP). Using a proteomic approach, we have previously found that cyclophilin D (CypD), a critical mPTP regulator, can be SNO on cysteine 203 (C203). To investigate whether SNO of CypD might attenuate mPTP activation, we mutated cysteine 203 of CypD, to a serine residue (C203S) and determined its effects on mPTP opening by assessing H 2 O 2 -induced mPTP opening using the calcein AM-cobalt chloride quenching method. Treatment of CypD -/- mouse embryonic fibroblasts (MEFs) with H 2 O 2 resulted loss in an ≈50 % loss of mPTP opening as compared to WT MEFs (n=5, p<0.05), consistent with the protective role of CypD in mPTP activation. Addition of a nitric oxide donor, GSNO, to CypD -/- MEFs did not further reduce mPTP opening; however, WT MEFs treated GSNO attenuated mPTP opening by half. To elucidate the role of SNO of C203 on CypD, we infected CypD -/- MEFs with a C203S-CypD vector. C203S-CypD re-constituted MEFs were also resistant to mPTP opening in the presence or absence of GSNO. This suggests that C203 is required for mPTP activation. To determine whether in vivo expression of C203S-CypD would alter mPTP opening, we generated adenovirus vectors encoding WT CypD or mutated C203S-CypD and injected these viral particles into CypD -/- mice via tail-vein. Mitochondria isolated from livers of CypD -/- mice or mice expressing C203S-CypD were resistant to Ca 2+ -induced swelling as compared to WT CypD reconstituted mice. In summary, our results indicate that C203 of CypD is required for mPTP opening and for the first time shows that SNO of C203 on CypD acts to attenuate mPTP activation.

Two Naturally Occurring Terpenes, Dehydrocostuslactone and Costunolide, Decrease Intracellular GSH Content and Inhibit STAT3 Activation

The main purpose of the present study is to envisage the molecular mechanism of inhibitory action ofdehydrocostuslactone (DCE) andcostunolide (CS), two naturally occurring sesquiterpene lactones, towards the activation of signal transducer and activator of transcription 3 (STAT3). We report that, in human THP-1 cell line, they inhibit IL-6-elicited tyrosine phosphorylation of STAT3 and its DNA binding activity with EC50 of 10 µM with concomitantdown-regulation ofthe phosphorylation of the tyrosine Janus kinases JAK1, JAK2 and Tyk2. Furthermore, these compounds that contain an α-β-unsatured carbonyl moiety and function as potent Michael reaction acceptor, induce a rapid drop in intracellular glutathione (GSH) concentration by direct interaction with it, thereby triggering S-glutathionylation of STAT3. Dehydrocostunolide (HCS), the reduced form of CS lacking only the α-β-unsaturated carbonyl group, fails to exert any inhibitory action. Finally, the glutathione ethylene ester (GEE), the cell permeable GSH form, reverts the inhibitory action of DCE and CS on STAT3 tyrosine phosphorylation. We conclude that these two sesquiterpene lactones are able to induce redox-dependent post-translational modification of cysteine residues of STAT3 protein in order to regulate its function.

Transduction of redox signaling by electrophile-protein reactions.

Over the last 50 years, the posttranslational modification (PTM) of proteins has emerged as a central mechanism for cells to regulate metabolism, growth, differentiation, cell-cell interactions, and immune responses. By influencing protein structure and function, PTM leads to a multiplication of proteome diversity. Redox-dependent PTMs, mediated by environmental and endogenously generated reactive species, induce cell signaling responses and can have toxic effects in organisms. PTMs induced by the electrophilic by-products of redox reactions most frequently occur at protein thiols; other nucleophilic amino acids serve as less favorable targets. Advances in mass spectrometry and affinity-chemistry strategies have improved the detection of electrophile-induced protein modifications both in vitro and in vivo and have revealed a high degree of amino acid and protein selectivity of electrophilic PTM. The identification of biological targets of electrophiles has motivated further study of the functional impact of various PTM reactions on specific signaling pathways and how this might affect organisms.

Glutaredoxin Regulates Autocrine and Paracrine Proinflammatory Responses in Retinal Glial (Müller) Cells

Protein S-glutathionylation is a reversible redox-dependent post-translational modification. Many cellular functions and signal transduction pathways involve proteins whose cysteine-dependent activities are modulated by glutathionylation. Glutaredoxin (Grx1) plays a key role in such regulation because it is a specific and efficient catalyst of deglutathionylation. We recently reported an increase in Grx1 in retinae of diabetic rats and in rat retinal Müller glial cells (rMC-1) cultured in high glucose. This up-regulation of Grx1 was concomitant with NFkappaB activation and induction of intercellular adhesion molecule-1 (ICAM-1). This proinflammatory response was replicated by adenoviral-directed up-regulation of Grx1 in cells in normal glucose. The site of regulation of NFkappaB was localized to the cytoplasm, where IkappaB kinase (IKK) is a master regulator of NFkappaB activation. In the current study, inhibition of IKK activity abrogated the increase in ICAM-1 induced by high glucose or by adenoviral-directed up-regulation of Grx1. Conditioned medium from the Müller cells overexpressing Grx1 was added to fresh cultures of Müller or endothelial cells and elicited increases in the Grx1 and ICAM-1 proteins in these cells. These effects correlate with a novel finding that secretion of interleukin-6 was elevated in the cultures of Grx overexpressing cells. Also, pure interleukin-6 increased Grx1 and ICAM-1 in the rMC-1 cells. Thus, Grx1 appears to play an important role in both autocrine and paracrine proinflammatory responses. Furthermore, IKKbeta isolated from Müller cells in normal glucose medium was found to be glutathionylated on Cys-179. Hence Grx-mediated activation of IKK via deglutathionylation may play a central role in diabetic complications in vivo where Grx1 is increased.

Protein Tyrosine Phosphorylation and Reversible Oxidation: Two Cross-Talking Posttranslation Modifications

In addition to protein phosphorylation, redox-dependent posttranslational modification of proteins is emerging as a key signaling system, conserved throughout evolution, and influencing many aspects of cellular homeostasis. Recent data have provided new insight about the interplay between phosphorylation- and redox-dependent signaling, and reactive oxygen species have been included among intracellular signal transducers of growth factor and extracellular matrix receptors. Both tyrosine phosphorylation and thiol oxidation are reversible and dynamic, and this review will particularly focus on the cross-talk between these posttranslational protein regulatory means. Although these modifications share their reversibility, their effects on enzymatic activity of protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) may be even opposite. Indeed, while tyrosine phosphorylation is frequently correlated to enzyme activation, thiol oxidation leads to inactivation of PTPs and to superactivation of PTKs. Several papers describe that both these modifications occur during the same input, (i.e., cell proliferation and motility induced by numerous growth factors and cytokines). The review will discuss several aspects of phosphorylation\oxidation interplay, describing both convergent and divergent features of the integrated and coordinated function of PTPs and PTKs during signaling.