Endogenous, regulatory cysteine sulfenylation of ERK kinases in response to proliferative signals

GAPDH inhibition mediated by thiol oxidation in human airway epithelial cells exposed to an environmental peroxide

Intracellular redox homeostasis in the airway epithelium is closely regulated through adaptive signaling and metabolic pathways. However, inhalational exposure to xenobiotic stressors such as secondary organic aerosols (SOA) can alter intracellular redox homeostasis. Isoprene hydroxy hydroperoxide (ISOPOOH), a ubiquitous volatile organic compound derived from the atmospheric photooxidation of biogenic isoprene, is a major contributor to SOA. We have previously demonstrated that exposure of human airway epithelial cells (HAEC) to ISOPOOH induces oxidative stress through multiple mechanisms including lipid peroxidation, glutathione oxidation, and alterations of glycolytic metabolism. Using dimedone-based reagents and copper catalyzed azo-alkynyl cycloaddition to tag intracellular protein thiol oxidation, we demonstrate that exposure of HAEC to micromolar levels of ISOPOOH induces reversible oxidation of cysteinyl thiols in multiple intracellular proteins, including GAPDH, that was accompanied by a dose-dependent loss of GAPDH enzymatic activity. These results demonstrate that ISOPOOH induces an oxidative modification of intracellular proteins that results in loss of GAPDH activity, which ultimately impacts the dynamic regulation of the intracellular redox homeostatic landscape in HAEC.

Redox signaling-mediated tumor extracellular matrix remodeling: pleiotropic regulatory mechanisms

BACKGROUND

The extracellular matrix (ECM), a fundamental constituent of all tissues and organs, is crucial for shaping the tumor microenvironment. Dysregulation of ECM remodeling has been closely linked to tumor initiation and progression, where specific signaling pathways, including redox signaling, play essential roles. Reactive oxygen species (ROS) are risk factors for carcinogenesis whose excess can facilitate the oxidative damage of biomacromolecules, such as DNA and proteins. Emerging evidence suggests that redox effects can aid the modification, stimulation, and degradation of ECM, thus affecting ECM remodeling. These alterations in both the density and components of the ECM subsequently act as critical drivers for tumorigenesis. In this review, we provide an overview of the functions and primary traits of the ECM, and it delves into our current understanding of how redox reactions participate in ECM remodeling during cancer progression. We also discuss the opportunities and challenges presented by clinical strategies targeting redox-controlled ECM remodeling to overcome cancer.

CONCLUSIONS

The redox-mediated ECM remodeling contributes importantly to tumor survival, progression, metastasis, and poor prognosis. A comprehensive investigation of the concrete mechanism of redox-mediated tumor ECM remodeling and the combination usage of redox-targeted drugs with existing treatment means may reveal new therapeutic strategy for future antitumor therapies.

Hydrogen peroxide-dependent oxidation of ERK2 within its D-recruitment site alters its substrate selection

Extracellular signal-regulated kinases 1 and 2 (ERK1/2) are dysregulated in many pervasive diseases. Recently, we discovered that ERK1/2 is oxidized by signal-generated hydrogen peroxide in various cell types. Since the putative sites of oxidation lie within or near ERK1/2's ligand-binding surfaces, we investigated how oxidation of ERK2 regulates interactions with the model substrates Sub-D and Sub-F. These studies revealed that ERK2 undergoes sulfenylation at C159 on its D-recruitment site surface and that this modification modulates ERK2 activity differentially between substrates. Integrated biochemical, computational, and mutational analyses suggest a plausible mechanism for peroxide-dependent changes in ERK2-substrate interactions. Interestingly, oxidation decreased ERK2's affinity for some D-site ligands while increasing its affinity for others. Finally, oxidation by signal-generated peroxide enhanced ERK1/2's ability to phosphorylate ribosomal S6 kinase A1 (RSK1) in HeLa cells. Together, these studies lay the foundation for examining crosstalk between redox- and phosphorylation-dependent signaling at the level of kinase-substrate selection.

Essential role of the CD docking motif of MPK4 in plant immunity, growth, and development

MAPKs are universal eukaryotic signaling factors whose functioning is assumed to depend on the recognition of a common docking motif (CD) by its activators, substrates, and inactivators. We studied the role of the CD domain of Arabidopsis MPK4 by performing interaction studies and determining the ligand-bound MPK4 crystal structure. We revealed that the CD domain of MPK4 is essential for interaction and activation by its upstream MAPKKs MKK1, MKK2, and MKK6. Cys181 in the CD site of MPK4 was shown to become sulfenylated in response to reactive oxygen species in vitro. To test the function of C181 in vivo, we generated wild-type (WT) MPK4-C181, nonsulfenylatable MPK4-C181S, and potentially sulfenylation mimicking MPK4-C181D lines in the mpk4 knockout background. We analyzed the phenotypes in growth, development, and stress responses, revealing that MPK4-C181S has WT activity and complements the mpk4 phenotype. By contrast, MPK4-C181D cannot be activated by upstream MAPKK and cannot complement the phenotypes of mpk4. Our findings show that the CD motif is essential and is required for activation by upstream MAPKK for MPK4 function. Furthermore, growth, development, or immunity functions require upstream activation of the MPK4 protein kinase.

H2S regulates redox signaling downstream of cardiac β-adrenergic receptors in a G6PD-dependent manner

Stimulating β-adrenergic receptors (β-AR) culminates in pathological hypertrophy - a condition underlying multiple cardiovascular diseases (CVDs). The ensuing signal transduction network appears to involve mutually communicating phosphorylation-cascades and redox signaling modules, although the regulators of redox signaling processes remain largely unknown. We previously showed that H₂S-induced Glucose-6-phosphate dehydrogenase (G6PD) activity is critical for suppressing cardiac hypertrophy in response to adrenergic stimulation. Here, we extended our findings and identified novel H₂S-dependent pathways constraining β-AR-induced pathological hypertrophy. We demonstrated that H₂S regulated early redox signal transduction processes - including suppression of cue-dependent production of reactive oxygen species (ROS) and oxidation of cysteine thiols (R-SOH) on critical signaling intermediates (including AKT1/2/3 & ERK1/2). Consistently, the maintenance of intracellular levels of H₂S dampened the transcriptional signature associated with pathological hypertrophy upon β-AR-stimulation, as demonstrated by RNA-seq analysis. We further prove that H₂S remodels cell metabolism by promoting G6PD activity to enforce changes in the redox state that favor physiological cardiomyocyte growth over pathological hypertrophy. Thus, our data suggest that G6PD is an effector of H₂S-mediated suppression of pathological hypertrophy and that the accumulation of ROS in the G6PD-deficient background can drive maladaptive remodeling. Our study reveals an adaptive role for H₂S relevant to basic and translational studies. Identifying adaptive signaling mediators of the β-AR-induced hypertrophy may reveal new therapeutic targets and routes for CVD therapy optimization.

Profiling protein targets of cellular toxicant exposure

Environmental agents of exposure can damage proteins, affecting protein function and cellular protein homeostasis. Specific residues are inherently chemically susceptible to damage from individual types of exposure. Amino acid content is not completely predictive of protein susceptibility, as secondary, tertiary, and quaternary structures of proteins strongly influence the reactivity of the proteome to individual exposures. Because we cannot readily predict which proteins will be affected by which chemical exposures, mass spectrometry-based proteomic strategies are necessary to determine the protein targets of environmental toxins and toxicants. This review describes the mechanisms by which environmental exposure to toxins and toxicants can damage proteins and affect their function, and emerging omic methodologies that can be used to identify the protein targets of a given agent. These methods include target identification strategies that have recently revolutionized the drug discovery field, such as activity-based protein profiling, protein footprinting, and protein stability profiling technologies. In particular, we highlight the necessity of multiple, complementary approaches to fully interrogate how protein integrity is challenged by individual exposures.

Harnessing redox signaling to overcome therapeutic-resistant cancer dormancy

Dormancy occurs when cells preserve viability but stop proliferating, which is considered an important cause of tumor relapse, which may occur many years after clinical remission. Since the life cycle of dormant cancer cells is affected by both intracellular and extracellular factors, gene mutation or epigenetic regulation of tumor cells may not fully explain the mechanisms involved. Recent studies have indicated that redox signaling regulates the formation, maintenance, and reactivation of dormant cancer cells by modulating intracellular signaling pathways and the extracellular environment, which provides a molecular explanation for the life cycle of dormant tumor cells. Indeed, redox signaling regulates the onset of dormancy by balancing the intrinsic pathways, the extrinsic environment, and the response to therapy. In addition, redox signaling sustains dormancy by managing stress homeostasis, maintaining stemness and immunogenic equilibrium. However, studies on dormancy reactivation are still limited, partly explained by redox-mediated activation of lipid metabolism and the transition from the tumor microenvironment to inflammation. Encouragingly, several drug combination strategies based on redox biology are currently under clinical evaluation. Continuing to gain an in-depth understanding of redox regulation and develop specific methods targeting redox modification holds the promise to accelerate the development of strategies to treat dormant tumors and benefit cancer patients.

Chemical Inhibition of Apurinic-Apyrimidinic Endonuclease 1 Redox and DNA Repair Functions Affects the Inflammatory Response via Different but Overlapping Mechanisms

The presence of oxidized DNA lesions, such as 7,8-dihydro-8-oxoguanine (8-oxoG) and apurinic/apyrimidinic sites (AP sites), has been described as epigenetic signals that are involved in gene expression control. In mammals, Apurinic-apyrimidinic endonuclease 1/Redox factor-1 (APE1/Ref-1) is the main AP endonuclease of the base excision repair (BER) pathway and is involved in active demethylation processes. In addition, APE1/Ref-1, through its redox function, regulates several transcriptional factors. However, the transcriptional control targets of each APE1 function are not completely known. In this study, a transcriptomic approach was used to investigate the effects of chemical inhibition of APE1/Ref-1 redox or DNA repair functions by E3330 or methoxyamine (MX) in an inflammatory cellular model. Under lipopolysaccharide (LPS) stimulation, both E3330 and MX reduced the expression of some cytokines and chemokines. Interestingly, E3330 treatment reduced cell viability after 48 h of the treatment. Genes related to inflammatory response and mitochondrial processes were downregulated in both treatments. In the E3330 treatment, RNA processing and ribosome biogenesis genes were downregulated, while they were upregulated in the MX treatment. Furthermore, in the E3330 treatment, the cellular stress response was the main upregulated process, while the cellular macromolecule metabolic process was observed in MX-upregulated genes. Nuclear respiratory factor 1 (NRF1) was predicted to be a master regulator of the downregulated genes in both treatments, while the ETS transcription factor ELK1 (ELK1) was predicted to be a master regulator only for E3330 treatment. Decreased expression of ELK1 and its target genes and a reduced 28S/18S ratio were observed, suggesting impaired rRNA processing. In addition, both redox and repair functions can affect the expression of NRF1 and GABPA target genes. The master regulators predicted for upregulated genes were YY1 and FLI1 for the E3330 and MX treatments, respectively. In summary, the chemical inhibition of APE1/Ref-1 affects gene expression regulated mainly by transcriptional factors of the ETS family, showing partial overlap of APE1 redox and DNA repair functions, suggesting that these activities are not entirely independent. This work provides a new perspective on the interaction between APE1 redox and DNA repair activity in inflammatory response modulation and transcription.

A walk-through MAPK structure and functionality with the 30-year-old yeast MAPK Slt2

Mitogen-activated protein kinases (MAPKs) are evolutionarily conserved signaling proteins involved in the regulation of most eukaryotic cellular processes. They are downstream components of essential signal transduction pathways activated by the external stimuli, in which the signal is conveyed through phosphorylation cascades. The excellent genetic and biochemical tractability of simple eukaryotes such as Saccharomyces cerevisiae has significantly contributed to gain fundamental information into the physiology of these key proteins. The budding yeast MAPK Slt2 was identified 30 years ago and was later revealed as a fundamental element of the cell wall integrity (CWI) pathway, one of the five MAPK routes of S. cerevisiae. As occurs with other MAPKs, whereas Slt2 displays the core typical structural traits of eukaryotic protein kinases, it also features conserved domains among MAPKs that allow an exquisite spatio-temporal regulation of their activity and binding to activating kinases, downregulatory phosphatases, or nuclear transcription factors. Additionally, Slt2 bears a regulatory extra C-terminal tail unique among S. cerevisiae MAPKs. Here, we review the structural and functional basis for the signaling role of Slt2 in the context of the molecular architecture of this important family of protein kinases.

Signaling diversity enabled by Rap1-regulated plasma membrane ERK with distinct temporal dynamics

A variety of different signals induce specific responses through a common, extracellular-signal regulated kinase (ERK)-dependent cascade. It has been suggested that signaling specificity can be achieved through precise temporal regulation of ERK activity. Given the wide distrubtion of ERK susbtrates across different subcellular compartments, it is important to understand how ERK activity is temporally regulated at specific subcellular locations. To address this question, we have expanded the toolbox of Förster Resonance Energy Transfer (FRET)-based ERK biosensors by creating a series of improved biosensors targeted to various subcellular regions via sequence specific motifs to measure spatiotemporal changes in ERK activity. Using these sensors, we showed that EGF induces sustained ERK activity near the plasma membrane in sharp contrast to the transient activity observed in the cytoplasm and nucleus. Furthermore, EGF-induced plasma membrane ERK activity involves Rap1, a noncanonical activator, and controls cell morphology and EGF-induced membrane protrusion dynamics. Our work strongly supports that spatial and temporal regulation of ERK activity is integrated to control signaling specificity from a single extracellular signal to multiple cellular processes.

Introduction to approaches and tools for the evaluation of protein cysteine oxidation

Oxidative modifications of cysteine thiols in cellular proteins are pivotal to the way signal-stimulated reactive oxygen species are sensed and elicit appropriate or sometimes pathological responses, but the dynamic and often transitory nature of these modifications offer a challenge to the investigator trying to identify such sites and the responses they elicit. A number of reagents and workflows have been developed to identify proteins undergoing oxidation and to query the timing, extent and location of such modifications, as described in this minireview. While no approach is perfect to capture all the redox information in a functioning cell, best practices described herein can enable considerable insights into the "redox world" of cells and organisms.

Mining for protein S-sulfenylation in Arabidopsis uncovers redox-sensitive sites

Hydrogen peroxide (H₂O₂) is an important messenger molecule for diverse cellular processes. H₂O₂ oxidizes proteinaceous cysteinyl thiols to sulfenic acid, also known as S-sulfenylation, thereby affecting the protein conformation and functionality. Although many proteins have been identified as S-sulfenylation targets in plants, site-specific mapping and quantification remain largely unexplored. By means of a peptide-centric chemoproteomics approach, we mapped 1,537 S-sulfenylated sites on more than 1,000 proteins in Arabidopsis thaliana cells. Proteins involved in RNA homeostasis and metabolism were identified as hotspots for S-sulfenylation. Moreover, S-sulfenylation frequently occurred on cysteines located at catalytic sites of enzymes or on cysteines involved in metal binding, hinting at a direct mode of action for redox regulation. Comparison of human and Arabidopsis S-sulfenylation datasets provided 155 conserved S-sulfenylated cysteines, including Cys181 of the Arabidopsis MITOGEN-ACTIVATED PROTEIN KINASE4 (AtMAPK4) that corresponds to Cys161 in the human MAPK1, which has been identified previously as being S-sulfenylated. We show that, by replacing Cys181 of recombinant AtMAPK4 by a redox-insensitive serine residue, the kinase activity decreased, indicating the importance of this noncatalytic cysteine for the kinase mechanism. Altogether, we quantitatively mapped the S-sulfenylated cysteines in Arabidopsis cells under H₂O₂ stress and thereby generated a comprehensive view on the S-sulfenylation landscape that will facilitate downstream plant redox studies.

Curcumin induces secretion of glucagon-like peptide-1 through an oxidation-dependent mechanism

Curcumin shows antiglycemic effects in animals. Curcumin is chemically unstable at physiological pH, and its oxidative degradation products were shown to contribute to its anti-inflammatory effects. Since the degradation products may also contribute to other effects, we analyzed their role in the antiglycemic activity of curcumin. We quantified curcumin-induced release of glucagon-like peptide 1 (GLP-1) from mouse STC-1 cells that represent enteroendocrine L-cells as a major source of this anti-diabetic hormone. Curcumin induced secretion of GLP-1 in a dose-dependent manner. Two chemically stable analogues of curcumin that do not readily undergo degradation, were less active while two unstable analogues were active secretagogues. Chromatographically isolated spiroepoxide, an unstable oxidative metabolite of curcumin with anti-inflammatory activity, also induced secretion of GLP-1. Stable compounds like the final oxidative metabolite bicyclopentadione, and the major plasma metabolite, curcumin-glucuronide, were inactive. GLP-1 secretion induced by curcumin and its oxidative degradation products was associated with activation of PKC, ERK, and CaM kinase II. Since activity largely correlated with instability of curcumin and the analogues, we tested the extent of covalent binding to proteins in STC-1 cells and found it occurred with similar affinity as N-ethylmaleimide, indicating covalent binding occurred with nucleophilic cysteine residues. These results suggest that oxidative metabolites of curcumin are involved in the antiglycemic effects of curcumin. Our findings support the hypothesis that curcumin functions as a pro-drug requiring oxidative activation to reveal its bioactive metabolites that act by binding to target proteins thereby causing a change in function.

NOX4 (NADPH Oxidase 4) and Poldip2 (Polymerase δ-Interacting Protein 2) Induce Filamentous Actin Oxidation and Promote Its Interaction With Vinculin During Integrin-Mediated Cell Adhesion

Objective- Actin cytoskeleton assembly and organization, as a result of focal adhesion (FA) formation during cell adhesion, are dependent on reactive oxygen species and the cellular redox environment. Poldip2 (polymerase δ-interacting protein 2), a novel regulator of NOX4 (NADPH oxidase 4), plays a significant role in reactive oxygen species production and cytoskeletal remodeling. Thus, we hypothesized that endogenous reactive oxygen species derived from Poldip2/NOX4 contribute to redox regulation of actin and cytoskeleton assembly during integrin-mediated cell adhesion. Approach and Results- Using vascular smooth muscle cells, we verified that hydrogen peroxide (H₂O₂) levels increase during integrin-mediated cell attachment as a result of activation of NOX4. Filamentous actin (F-actin) was oxidized by sulfenylation during cell attachment, with a peak at 3 hours (0.80±0.04 versus 0.08±0.13 arbitrary units at time zero), which was enhanced by overexpression of Poldip2. Depletion of Poldip2 or NOX4 using siRNA, or scavenging of endogenous H₂O₂ with catalase, inhibited F-actin oxidation by 78±26%, 99±1%, and 98±1%, respectively. To determine the consequence of F-actin oxidation, we examined the binding of F-actin to vinculin, a protein involved in FA complexes that regulates FA maturation. Vinculin binding during cell adhesion as well as migration capacity were inhibited after transfection with actin containing 2 oxidation-resistant point mutations (C272A and C374A). Silencing of Poldip2 or NOX4 also impaired actin-vinculin interaction, which disturbed maturation of FAs and inhibited cell migration. Conclusions- These results suggest that integrin engagement during cell attachment activates Poldip2/Nox4 to oxidize actin, which modulates FA assembly.

Mass Spectrometry in Advancement of Redox Precision Medicine

Redox (portmanteau of reduction-oxidation) reactions involve the transfer of electrons between chemical species in biological processes fundamental to life. It is of outmost importance that cells maintain a healthy redox state by balancing the action of oxidants and antioxidants; failure to do so leads to a multitude of diseases including cancer, diabetes, fibrosis, autoimmune diseases, and cardiovascular and neurodegenerative diseases. From the perspective of precision medicine, it is therefore beneficial to interrogate the redox phenotype of the individual-similar to the use of genomic sequencing-in order to design tailored strategies for disease prevention and treatment. This chapter provides an overview of redox metabolism and focuses on how mass spectrometry (MS) can be applied to advance our knowledge in redox biology and precision medicine.

Extra-mitochondrial Cu/Zn superoxide dismutase (Sod1) is dispensable for protection against oxidative stress but mediates peroxide signaling in Saccharomyces cerevisiae

Cu/Zn Superoxide Dismutase (Sod1) is a highly conserved and abundant metalloenzyme that catalyzes the disproportionation of superoxide radicals into hydrogen peroxide and molecular oxygen. As a consequence, Sod1 serves dual roles in oxidative stress protection and redox signaling by both scavenging cytotoxic superoxide radicals and producing hydrogen peroxide that can be used to oxidize and regulate the activity of downstream targets. However, the relative contributions of Sod1 to protection against oxidative stress and redox signaling are poorly understood. Using the model unicellular eukaryote, Baker's yeast, we found that only a small fraction of the total Sod1 pool is required for protection against superoxide toxicity and that this pool is localized to the mitochondrial intermembrane space. On the contrary, we find that much larger amounts of extra-mitochondrial Sod1 are critical for peroxide-mediated redox signaling. Altogether, our results force the re-evaluation of the physiological role of bulk Sod1 in redox biology; namely, we propose that the vast majority of Sod1 in yeast is utilized for peroxide-mediated signaling rather than superoxide scavenging.

H2O2 oxidation of cysteine residues in c-Jun N-terminal kinase 2 (JNK2) contributes to redox regulation in human articular chondrocytes

Reactive oxygen species (ROS), in particular H₂O₂, regulate intracellular signaling through reversible oxidation of reactive protein thiols present in a number of kinases and phosphatases. H₂O₂ has been shown to regulate mitogen-activated protein kinase (MAPK) signaling depending on the cellular context. We report here that in human articular chondrocytes, the MAPK family member c-Jun N-terminal kinase 2 (JNK2) is activated by fibronectin fragments and low physiological levels of H₂O₂ and inhibited by oxidation due to elevated levels of H₂O₂ The kinase activity of affinity-purified, phosphorylated JNK2 from cultured chondrocytes was reversibly inhibited by 5-20 μm H₂O₂ Using dimedone-based chemical probes that react specifically with sulfenylated cysteines (RSOH), we identified Cys-222 in JNK2, a residue not conserved in JNK1 or JNK3, as a redox-reactive site. MS analysis of human recombinant JNK2 also detected further oxidation at Cys-222 and other cysteines to sulfinic (RSO₂H) or sulfonic (RSO₃H) acid. H₂O₂ treatment of JNK2 resulted in detectable levels of peptides containing intramolecular disulfides between Cys-222 and either Cys-213 or Cys-177, without evidence of dimer formation. Substitution of Cys-222 to alanine rendered JNK2 insensitive to H₂O₂ inhibition, unlike C177A and C213A variants. Two other JNK2 variants, C116A and C163A, were also resistant to oxidative inhibition. Cumulatively, these findings indicate differential regulation of JNK2 signaling dependent on H₂O₂ levels and point to key cysteine residues regulating JNK2 activity. As levels of intracellular H₂O₂ rise, a switch occurs from activation to inhibition of JNK2 activity, linking JNK2 regulation to the redox status of the cell.

The dual role of Reactive Oxygen Species in autoimmune and inflammatory diseases: evidence from preclinical models

Reactive oxygen species (ROS) are created in cells during oxidative phosphorylation by the respiratory chain in the mitochondria or by the family of NADPH oxidase (NOX) complexes. The first discovered and most studied of these complexes, NOX2, mediates the oxidative burst in phagocytes. ROS generated by NOX2 are dreadful weapons: while being essential to kill ingested pathogens they can also cause degenerative changes on tissue if production and release are not balanced by sufficient detoxification. In the last fifteen years evidence has been accumulating that ROS are also integral signaling molecules and are important for regulating autoimmunity and immune-mediated inflammatory diseases. It seems that an accurate redox balance is necessary to sustain an immune state that both prevents the development of overt autoimmunity (the bright side of ROS) and minimizes collateral tissue damage (the dark side of ROS). Herein, we review studies from rodent models of arthritis, lupus, and neurodegenerative diseases that show that low NOX2-derived ROS production is linked to disease and elaborate on the underlying cellular and molecular mechanisms and the translation of these results to disease in humans.

Pathways crossing mammalian and plant sulfenomic landscapes

Reactive oxygen species (ROS) and especially hydrogen peroxide, are potent signaling molecules that activate cellular defense responses. Hydrogen peroxide can provoke reversible and irreversible oxidative posttranslational modifications on cysteine residues of proteins that act in diverse signaling circuits. The initial oxidation product of cysteine, sulfenic acid, has emerged as a biologically relevant posttranslational modification, because it is the primary sulfur oxygen modification that precedes divergent series of additional adaptations. In this review, we focus on the functional consequences of sulfenylation for both mammalian and plant proteins. Furthermore, we created compendia of sulfenylated proteins in human and plants based on mass spectrometry experiments, thereby defining the current plant and human sulfenomes. To assess the evolutionary conservation of sulfenylation, the sulfenomes of human and plants were compared based on protein homology. In total, 185 human sulfenylated proteins showed homology to sulfenylated plant proteins and the conserved sulfenylation targets participated in specific biological pathways and metabolic processes. Comprehensive functional studies of sulfenylation remains a future challenge, with multiple candidates suggested by mass spectrometry awaiting scrutinization.

Vascular Nox (NADPH Oxidase) Compartmentalization, Protein Hyperoxidation, and Endoplasmic Reticulum Stress Response in Hypertension

Vascular Nox (NADPH oxidase)-derived reactive oxygen species and endoplasmic reticulum (ER) stress have been implicated in hypertension. However, relationships between these processes are unclear. We hypothesized that Nox isoforms localize in a subcellular compartment-specific manner, contributing to oxidative and ER stress, which influence the oxidative proteome and vascular function in hypertension. Nox compartmentalization (cell fractionation), O₂^- (lucigenin), H₂O₂ (amplex red), reversible protein oxidation (sulfenylation), irreversible protein oxidation (protein tyrosine phosphatase, peroxiredoxin oxidation), and ER stress (PERK [protein kinase RNA-like endoplasmic reticulum kinase], IRE1α [inositol-requiring enzyme 1], and phosphorylation/oxidation) were studied in spontaneously hypertensive rat (SHR) vascular smooth muscle cells (VSMCs). VSMC proliferation was measured by fluorescence-activated cell sorting, and vascular reactivity assessed in stroke-prone SHR arteries by myography. Noxs were downregulated by short interfering RNA and pharmacologically. In SHR, Noxs were localized in specific subcellular regions: Nox1 in plasma membrane and Nox4 in ER. In SHR, oxidative stress was associated with increased protein sulfenylation and hyperoxidation of protein tyrosine phosphatases and peroxiredoxins. Inhibition of Nox1 (NoxA1ds), Nox1/4 (GKT137831), and ER stress (4-phenylbutyric acid/tauroursodeoxycholic acid) normalized SHR vascular reactive oxygen species generation. GKT137831 reduced IRE1α sulfenylation and XBP1 (X-box binding protein 1) splicing in SHR. Increased VSMC proliferation in SHR was normalized by GKT137831, 4-phenylbutyric acid, and STF083010 (IRE1-XBP1 disruptor). Hypercontractility in the stroke-prone SHR was attenuated by 4-phenylbutyric acid. We demonstrate that protein hyperoxidation in hypertension is associated with oxidative and ER stress through upregulation of plasmalemmal-Nox1 and ER-Nox4. The IRE1-XBP1 pathway of the ER stress response is regulated by Nox4/reactive oxygen species and plays a role in the hyperproliferative VSMC phenotype in SHR. Our study highlights the importance of Nox subcellular compartmentalization and interplay between cytoplasmic reactive oxygen species and ER stress response, which contribute to the VSMC oxidative proteome and vascular dysfunction in hypertension.

Chemical methods for mapping cysteine oxidation

Methods to characterise oxidative modifications of cysteine help clarify their role in protein function in both healthy and diseased cells.