Irreversible inactivation of protein kinase C by glutathione

Ouabain inhibitor rostafuroxin attenuates dextromethorphan-induced manic potential

Dextromethorphan (DM) abuse produces mania-like symptoms in humans. ERK/Akt signaling activation involved in manic potential can be attenuated by the inhibition of ouabain-like cardiac steroids. In this study, increased phosphorylations of ERK/Akt and hyperlocomotion induced by DM (30 mg/kg, i.p./day × 7) were significantly protected by the ouabain inhibitor rostafuroxin (ROSTA), suggesting that DM induces the manic potential. ROSTA significantly attenuated DM-induced protein kinase C δ (PKCδ) phosphorylation, GluN2B (i.e., MDA receptor subunit) expression, and phospho-PKCδ/GluN2B interaction. DM instantly upregulated the nuclear factor erythroid-2-related factor 2 (Nrf2)-dependent system. However, DM reduced Nrf2 nuclear translocation, Nrf2 DNA binding activity, γ-glutamylcysteine mRNA expression, and subsequent GSH/GSSG level and enhanced oxidative parameters following 1-h of administration. ROSTA, PKCδ inhibitor rottlerin, and GluN2B inhibitor traxoprodil significantly attenuated DM-induced alterations in Nrf2-related redox parameters and locomotor activity induced by DM in wild-type mice. Importantly, in PKCδ knockout mice, DM failed to alter the above parameters. Further, ROSTA and traxoprodil also failed to enhance PKCδ depletion effect, suggesting that PKCδ is a critical target for the anti-manic potential of ROSTA or GluN2B antagonism. Our results suggest that ROSTA inhibits DM-induced manic potential by attenuating ERK/Akt activation, GluN2B/PKCδ signalings, and Nrf2-dependent system.

Oxidative Stress Underlies the Ischemia/Reperfusion-Induced Internalization and Degradation of AMPA Receptors

Stroke is the fifth leading cause of death annually in the United States. Ischemic stroke occurs when a blood vessel supplying the brain is occluded. The hippocampus is particularly susceptible to AMPA receptor-mediated delayed neuronal death as a result of ischemic/reperfusion injury. AMPA receptors composed of a GluA2 subunit are impermeable to calcium due to a post-transcriptional modification in the channel pore of the GluA2 subunit. GluA2 undergoes internalization and is subsequently degraded following ischemia/reperfusion. The subsequent increase in the expression of GluA2-lacking, Ca2+-permeable AMPARs results in excitotoxicity and eventually delayed neuronal death. Following ischemia/reperfusion, there is increased production of superoxide radicals. This study describes how the internalization and degradation of GluA1 and GluA2 AMPAR subunits following ischemia/reperfusion is mediated through an oxidative stress signaling cascade. U251-MG cells were transiently transfected with fluorescently tagged GluA1 and GluA2, and different Rab proteins to observe AMPAR endocytic trafficking following oxygen glucose-deprivation/reperfusion (OGD/R), an in vitro model for ischemia/reperfusion. Pretreatment with Mn(III)tetrakis(1-methyl-4-pyridyl)porphyrin (MnTMPyP), a superoxide dismutase mimetic, ameliorated the OGD/R-induced, but not agonist-induced, internalization and degradation of GluA1 and GluA2 AMPAR subunits. Specifically, MnTMPyP prevented the increased colocalization of GluA1 and GluA2 with Rab5, an early endosomal marker, and with Rab7, a late endosomal marker, but did not affect the colocalization of GluA1 with Rab11, a marker for recycling endosomes. These data indicate that oxidative stress may play a vital role in AMPAR-mediated cell death following ischemic/reperfusion injury.

Protein kinase Cδ knockout mice are protected from cocaine-induced hepatotoxicity

We investigated whether protein kinase Cδ (PKCδ) mediates cocaine-induced hepatotoxicity in mice. Cocaine treatment (60 mg/kg, i.p.) significantly increased cleaved PKCδ expression in the liver of wild-type (WT) mice, and led to significant increases in oxidative parameters (i.e., reactive oxygen species, 4-hydroxylnonenal and protein carbonyl). These cocaine-induced oxidative burdens were attenuated by pharmacological (i.e., rottlerin) or genetic depletion of PKCδ. We also demonstrated that treatment with cocaine resulted in significant increases in nuclear factor erythroid-2-related factor 2 (Nrf-2) nuclear translocation and increased Nrf-2 DNA-binding activity in wild-type (WT) mice. These increases were more pronounced in the rottlerin-treated WT or PKCδ knockout mice than in the saline-treated WT mice. Although cocaine treatment increased Nrf-2 nuclear translocation, DNA binding activity, and γ-glutamyl cysteine ligases (i.e., GCLc and GCLm) mRNA expressions, while it reduced the glutathione level and GSH/GSSG ratio. These decreases were attenuated by PKCδ depletion. Cocaine treatment significantly increased alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels in the serum of WT mice signifying the hepatic damage. These increases were also attenuated by PKCδ depletion. In addition, cocaine-induced hepatic degeneration in WT mice was evident 1 d post-cocaine. At that time, cocaine treatment decreased Bcl-2 and Bcl-xL levels, and increased Bax, cytosolic cytochrome c, and cleaved caspase-3 levels. Pharmacological or genetic depletion of PKCδ significantly ameliorated the pro-apoptotic properties and hepatic degeneration. Therefore, our results suggest that inhibition of PKCδ, as well as activation of Nrf-2, is important for protecting against hepatotoxicity induced by cocaine.

Evolving mechanisms of vascular smooth muscle contraction highlight key targets in vascular disease

Vascular smooth muscle (VSM) plays an important role in the regulation of vascular function. Identifying the mechanisms of VSM contraction has been a major research goal in order to determine the causes of vascular dysfunction and exaggerated vasoconstriction in vascular disease. Major discoveries over several decades have helped to better understand the mechanisms of VSM contraction. Ca2+ has been established as a major regulator of VSM contraction, and its sources, cytosolic levels, homeostatic mechanisms and subcellular distribution have been defined. Biochemical studies have also suggested that stimulation of Gq protein-coupled membrane receptors activates phospholipase C and promotes the hydrolysis of membrane phospholipids into inositol 1,4,5-trisphosphate (IP3) and diacylglycerol (DAG). IP3 stimulates initial Ca2+ release from the sarcoplasmic reticulum, and is buttressed by Ca2+ influx through voltage-dependent, receptor-operated, transient receptor potential and store-operated channels. In order to prevent large increases in cytosolic Ca2+ concentration ([Ca2+]c), Ca2+ removal mechanisms promote Ca2+ extrusion via the plasmalemmal Ca2+ pump and Na+/Ca2+ exchanger, and Ca2+ uptake by the sarcoplasmic reticulum and mitochondria, and the coordinated activities of these Ca2+ handling mechanisms help to create subplasmalemmal Ca2+ domains. Threshold increases in [Ca2+]c form a Ca2+-calmodulin complex, which activates myosin light chain (MLC) kinase, and causes MLC phosphorylation, actin-myosin interaction, and VSM contraction. Dissociations in the relationships between [Ca2+]c, MLC phosphorylation, and force have suggested additional Ca2+ sensitization mechanisms. DAG activates protein kinase C (PKC) isoforms, which directly or indirectly via mitogen-activated protein kinase phosphorylate the actin-binding proteins calponin and caldesmon and thereby enhance the myofilaments force sensitivity to Ca2+. PKC-mediated phosphorylation of PKC-potentiated phosphatase inhibitor protein-17 (CPI-17), and RhoA-mediated activation of Rho-kinase (ROCK) inhibit MLC phosphatase and in turn increase MLC phosphorylation and VSM contraction. Abnormalities in the Ca2+ handling mechanisms and PKC and ROCK activity have been associated with vascular dysfunction in multiple vascular disorders. Modulators of [Ca2+]c, PKC and ROCK activity could be useful in mitigating the increased vasoconstriction associated with vascular disease.

PKCδ Knockout Mice Are Protected from Dextromethorphan-Induced Serotonergic Behaviors in Mice: Involvements of Downregulation of 5-HT1A Receptor and Upregulation of Nrf2-Dependent GSH Synthesis

We investigated whether a specific serotonin (5-HT) receptor-mediated mechanism was involved in dextromethorphan (DM)-induced serotonergic behaviors. We firstly observed that the activation of 5-HT_1A receptor, but not 5-HT_2A receptor, contributed to DM-induced serotonergic behaviors in mice. We aimed to determine whether the upregulation of 5-HT_1A receptor induced by DM facilitates the specific induction of certain PKC isoform, because previous reports suggested that 5-HT_1A receptor activates protein kinase C (PKC). A high dose of DM (80 mg/kg, i.p.) induced a selective induction of PKCδ out of PKCα, PKCβI, PKCβII, PKCξ, and PKCδ in the hypothalamus of wild-type (WT) mice. More importantly, 5-HT_1A receptor co-immunoprecipitated PKCδ in the presence of DM. Consistently, rottlerin, a pharmacological inhibitor of PKCδ, or PKCδ knockout significantly protected against increases in 5-HT_1A receptor gene expression, 5-HT turnover rate, and serotonergic behaviors induced by DM. Treatment with DM resulted in an initial increase in nuclear factor erythroid-2-related factor 2 (Nrf2) nuclear translocation and DNA-binding activity, γ-glutamylcysteine (GCL) mRNA expression, and glutathione (GSH) level. This compensative induction was further potentiated by rottlerin or PKCδ knockout. However, GCL mRNA and GSH/GSSG levels were decreased 6 and 12 h post-DM. These decreases were attenuated by PKCδ inhibition. Our results suggest that interaction between 5-HT_1A receptor and PKCδ is critical for inducing DM-induced serotonergic behaviors and that inhibition of PKCδ attenuates the serotonergic behaviors via downregulation of 5-HT_1A receptor and upregulation of Nrf2-dependent GSH synthesis.

PKCδ-dependent p47phox activation mediates methamphetamine-induced dopaminergic neurotoxicity

Protein kinase C (PKC) has been recognized to activate NADPH oxidase (PHOX). However, the interaction between PKC and PHOX in vivo remains elusive. Treatment with methamphetamine (MA) resulted in a selective increase in PKCδ expression out of PKC isoforms. PKCδ co-immunoprecipitated with p47phox, and facilitated phosphorylation and membrane translocation of p47phox. MA-induced increases in PHOX activity and reactive oxygen species were attenuated by knockout of p47phox or PKCδ. In addition, MA-induced impairments in the Nrf-2-related glutathione synthetic system were also mitigated by knockout of p47phox or PKCδ. Glutathione-immunoreactivity was co-localized in Iba-1-labeled microglial cells and in NeuN-labeled neurons, but not in GFAP-labeled astrocytes, reflecting the necessity for self-protection against oxidative stress by mainly microglia. Buthionine-sulfoximine, an inhibitor of glutathione biosynthesis, potentiated microglial activation and pro-apoptotic changes, leading to dopaminergic losses. These neurotoxic processes were attenuated by rottlerin, a pharmacological inhibitor of PKCδ, genetic inhibitions of PKCδ [i.e., PKCδ knockout mice (KO) and PKCδ antisense oligonucleotide (ASO)], or genetic inhibition of p47phox (i.e., p47phox KO or p47phox ASO). Rottlerin did not exhibit any additive effects against the protective activity offered by genetic inhibition of p47phox. Therefore, we suggest that PKCδ is a critical regulator for p47phox activation induced by MA, and that Nrf-2-dependent GSH induction via inhibition of PKCδ or p47phox, is important for dopaminergic protection against MA insult.

Glutathione Preconditioning Attenuates Ac-LDL–lnduced Macrophage Apoptosis via Protein Kinase C–Dependent Ac-LDL Trafficking

Oxidized low-density lipoprotein (ox-LDL) incorporation into intlmally resident vascular cells via scavenger receptors marks one of the early steps in atherosclerosis. Cellular apoptotic damage results from two major serial intracellular events: the binding and scavenger receptor-mediated uptake of oxldizable lipoproteins and the intracellular oxidative responses of accumulated lipoproteins. Most molecular approaches to prevent apoptotic damage have focused on singular events within the cascade of lipoprotein trafficking. To identify a multifocal strategy against LDL-induced apoptosis, we evaluated the role of cellular preconditioning by glutathione-ethyl ester (GSH-Et), a native redox regulator, in the prevention of the uptake and apoptotic effects of an oxldizable scavenger receptor-specific ligand, acetylated low-density lipoprotein (Ac-LDL). Our results indicate that GSH-Et–mediated protein kinase C (PKC) pathway modulation regulates Ac-LDL binding and incorporation into GSH-Et preconditioned cells and subsequently delays reactive oxygen intermediate generation and apoptotic conversion. The GSH-Et protective effects on apoptosis and Ac-LDL binding were reversed by calphostin C, a PKC inhibitor, and were accompanied by an increase in PKC phosphorylation. However, the rate of reactive oxygen intermediate accumulation was not increased following calphostin C treatment, suggesting that GSH-Et may play an important nonreactive oxygen-intermediate–based protective role in regulating apoptotic dynamics. Overall, we report on the novel role for GSH-Et preconditioning as a molecular strategy to limit lipoprotein entry Into the cells, which presents a proactive modality to prevent cellular apoptosis in contrast with the prevalent antioxidant approaches that treat damage retroactively.

"Oxygen Sensing" by Na,K-ATPase: These Miraculous Thiols

Control over the Na,K-ATPase function plays a central role in adaptation of the organisms to hypoxic and anoxic conditions. As the enzyme itself does not possess O2 binding sites its "oxygen-sensitivity" is mediated by a variety of redox-sensitive modifications including S-glutathionylation, S-nitrosylation, and redox-sensitive phosphorylation. This is an overview of the current knowledge on the plethora of molecular mechanisms tuning the activity of the ATP-consuming Na,K-ATPase to the cellular metabolic activity. Recent findings suggest that oxygen-derived free radicals and H2O2, NO, and oxidized glutathione are the signaling messengers that make the Na,K-ATPase "oxygen-sensitive." This very ancient signaling pathway targeting thiols of all three subunits of the Na,K-ATPase as well as redox-sensitive kinases sustains the enzyme activity at the "optimal" level avoiding terminal ATP depletion and maintaining the transmembrane ion gradients in cells of anoxia-tolerant species. We acknowledge the complexity of the underlying processes as we characterize the sources of reactive oxygen and nitrogen species production in hypoxic cells, and identify their targets, the reactive thiol groups which, upon modification, impact the enzyme activity. Structured accordingly, this review presents a summary on (i) the sources of free radical production in hypoxic cells, (ii) localization of regulatory thiols within the Na,K-ATPase and the role reversible thiol modifications play in responses of the enzyme to a variety of stimuli (hypoxia, receptors' activation) (iii) redox-sensitive regulatory phosphorylation, and (iv) the role of fine modulation of the Na,K-ATPase function in survival success under hypoxic conditions. The co-authors attempted to cover all the contradictions and standing hypotheses in the field and propose the possible future developments in this dynamic area of research, the importance of which is hard to overestimate. Better understanding of the processes underlying successful adaptation strategies will make it possible to harness them and use for treatment of patients with stroke and myocardial infarction, sleep apnoea and high altitude pulmonary oedema, and those undergoing surgical interventions associated with the interruption of blood perfusion.

Protein Kinase C as Regulator of Vascular Smooth Muscle Function and Potential Target in Vascular Disorders

Vascular smooth muscle (VSM) plays an important role in maintaining vascular tone. In addition to Ca2+-dependent myosin light chain (MLC) phosphorylation, protein kinase C (PKC) is a major regulator of VSM function. PKC is a family of conventional Ca2+-dependent α, β, and γ, novel Ca2+-independent δ, ɛ, θ, and η, and atypical ξ, and ι/λ isoforms. Inactive PKC is mainly cytosolic, and upon activation it undergoes phosphorylation, maturation, and translocation to the surface membrane, the nucleus, endoplasmic reticulum, and other cell organelles; a process facilitated by scaffold proteins such as RACKs. Activated PKC phosphorylates different substrates including ion channels, pumps, and nuclear proteins. PKC also phosphorylates CPI-17 leading to inhibition of MLC phosphatase, increased MLC phosphorylation, and enhanced VSM contraction. PKC could also initiate a cascade of protein kinases leading to phosphorylation of the actin-binding proteins calponin and caldesmon, increased actin-myosin interaction, and VSM contraction. Increased PKC activity has been associated with vascular disorders including ischemia-reperfusion injury, coronary artery disease, hypertension, and diabetic vasculopathy. PKC inhibitors could test the role of PKC in different systems and could reduce PKC hyperactivity in vascular disorders. First-generation PKC inhibitors such as staurosporine and chelerythrine are not very specific. Isoform-specific PKC inhibitors such as ruboxistaurin have been tested in clinical trials. Target delivery of PKC pseudosubstrate inhibitory peptides and PKC siRNA may be useful in localized vascular disease. Further studies of PKC and its role in VSM should help design isoform-specific PKC modulators that are experimentally potent and clinically safe to target PKC in vascular disease.

Hyperglycemia-Induced Oxidative-Nitrosative Stress Induces Inflammation and Neurodegeneration via Augmented Tuberous Sclerosis Complex-2 (TSC-2) Activation in Neuronal Cells

Diabetes is a systemic disease mainly characterized by chronic hyperglycemia and with extensive and long-lasting spiteful complications in central nervous systems (CNS). Astrocytes play an important role in the defense mechanism of CNS, with great ability of withstanding accumulation of toxic substances. Apart from functional disorders, hyperglycemia leads to slow progressive structural abnormalities in the CNS through oxidative stress pathways. However, the molecular mechanism by which neurons die under oxidative stress induced by high glucose (HG) remains largely unclear. Here, we report that HG-induced inflammation and neurodegeneration in brain tissues, brain astrocytes (C6), and pheochromocytoma (PC-12) cells are cultured in HG conditions. Our results show that the increases in phosphorylation of Akt and ERK1/2MAPK are associated with increased accumulations of reactive oxygen species (ROS) in neuronal cells, which simultaneously enhanced phosphorylations of tuberous sclerosis complex-2 (TSC-2) and mammalian target of rapamycin (mTOR) in the diabetic brain and in HG-exposed neuronal cells. Pharmacologic inhibition of Akt or ERK1/2 or siRNA-mediated gene silencing of TSC-2 suppressed the strong downregulation of TSC-2-mTOR activation. Findings of this study also demonstrate that HG resulted in phosphorylation of NF-κB, coinciding with the increased production of inflammatory mediators and activation of neurodegenerative markers. Pretreatment of cells with antioxidants, phosphoinositide3-kinase (PI3-K)/Akt, and ERK1/2 inhibitors significantly reduced HG-induced TSC-2 phosphorylation and restored NF-κB protein expression leading to decreased production of inflammatory mediators and neurodegenerative markers. These results illustrate that ROS functions as a key signaling component in the regulatory pathway induced by elevated glucose in neuronal cell activation leading to inflammation and neurodegeneration.

Protein kinase Cδ mediates trimethyltin-induced neurotoxicity in mice in vivo via inhibition of glutathione defense mechanism

We investigated whether protein kinase C (PKC) is involved in trimethyltin (TMT)-induced neurotoxicity. TMT treatment (2.8 mg/kg, i.p.) significantly increased PKCδ expression out of PKC isozymes (i.e., α, βI, βII, δ, and ς) in the hippocampus of wild-type (WT) mice. Consistently, treatment with TMT resulted in significant increases in cleaved PKCδ expression. Genetic or pharmacological inhibition (PKCδ knockout or rottlerin) was less susceptible to TMT-induced seizures than WT mice. TMT treatment increased glutathione oxidation, lipid peroxidation, protein oxidation, and levels of reactive oxygen species. These effects were more pronounced in the WT mice than in PKCδ knockout mice. In addition, the ability of TMT to induce nuclear translocation of Nrf2, Nrf2 DNA-binding activity, and upregulation of γ-glutamylcysteine ligase was significantly increased in the PKCδ knockout mice and rottlerin (10 or 20 mg/kg, p.o. × 6)-treated WT mice. Furthermore, neuronal degeneration (as shown by nuclear chromatin clumping and TUNEL staining) in WT mice was most pronounced 2 days after TMT. At the same time, TMT-induced inhibition of phosphoinositol 3-kinase (PI3K)/Akt signaling was evident, thereby decreasing phospho-Bad, expression of Bcl-xL and Bcl-2, and the interaction between phospho-Bad and 14-3-3 protein, and increasing Bax expression and caspase-3 cleavage were observed. Rottlerin or PKCδ knockout significantly protected these changes in anti- and pro-apoptotic factors. Importantly, treatment of the PI3K inhibitor LY294002 (0.8 or 1.6 µg, i.c.v.) 4 h before TMT counteracted protective effects (i.e., Nrf-2-dependent glutathione induction and pro-survival phenomenon) of rottlerin. Therefore, our results suggest that down-regulation of PKCδ and up-regulations of Nrf2-dependent glutathione defense mechanism and PI3K/Akt signaling are critical for attenuating TMT neurotoxicity.

Sublethal Pb exposure produces season-dependent effects on immune response, oxidative balance and investment in carotenoid-based coloration in red-legged partridges

Ingestion of lead (Pb) shot pellets constitutes the main cause of Pb poisoning in avifauna. We studied the effects of sublethal Pb exposure on immunity, carotenoid-based coloration, oxidative stress and trade-offs among these types of responses during spring and autumn in red-legged partridges (Alectoris rufa). We evaluated constitutive immunity testing lysozyme and natural antibody levels, and blood bactericidal and phagocytic activities. We studied induced immunity by testing PHA and humoral responses. We analyzed fecal parasite and bacterial abundance and oxidative stress biomarkers. Pb exposure in spring reduced natural antibody levels, whereas in autumn, it reduced lysozyme levels and increased phagocytic activity. Pb exposure increased PHA response in both seasons, and decreased T-independent humoral response in autumn. Pb exposure also increased noncoliform and decreased coliform Gram-negative gut bacteria. In spring, Pb exposure decreased antioxidant levels and increased coloration in males, whereas in autumn, it increased retinol levels but reduced coloration in both genders. Our results suggest that in spring, Pb-exposed females used antioxidants to cope with oxidative stress at the expense of coloration, whereas Pb-exposed males increased coloration, which may reflect an increased breeding investment. In autumn, both genders prioritized oxidative balance maintenance at the expense of coloration.

Regulation of hepatic EAAT-2 glutamate transporter expression in human liver cholestasis

AIM: To investigate the activity and expression of EAAT2 glutamate transporter in both in vitro and in vivo models of cholestasis.

METHODS: This study was conducted on human hepatoblastoma HepG2 cell cultures, the liver of bile duct ligated rats and human specimens from cholestatic patients. EAAT2 glutamate transporter activity and expression were analyzed using a substrate uptake assay, immunofluorescence, reverse transcription-polymerase chain reaction, and immunohistochemistry, respectively.

RESULTS: In HepG2 cells, cholestasis was mimicked by treating cells with the protein kinase C activator, phorbol 12-myristate 13-acetate. Under such conditions, EAAT2 transporter activity was decreased both at the level of substrate affinity and maximal transport velocity. The decreased uptake was correlated with intracellular translocation of EAAT2 molecules as demonstrated using immunofluorescence. In the liver of bile duct ligated rats, an increase in EAAT2 transporter protein expression in hepatocytes was demonstrated using immunohistochemistry. The same findings were observed in human liver specimens of cholestasis in which high levels of γ-glutamyl transpeptidase were documented in patients with biliary atresia and progressive familial intrahepatic cholestasis type 3.

CONCLUSION: This study demonstrates the alteration in glutamate handling by hepatocytes in liver cholestasis and suggests a potential cross-talk between glutamatergic and bile systems.

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.

S-glutathionylation regulates GTP-binding of Rac2

Phagocyte NADPH oxidase catalyzes the reduction of molecular oxygen to superoxide and is essential for defense against microbes. Rac2 is a low molecular weight GTP-binding protein that has been implicated in the regulation of phagocyte NADPH oxidase. Here we report that Cys(157) of Rac2 is a target of S-glutathionylation and that this modification is reversed by dithiothreitol as well as enzymatically by thioltransferase in the presence of GSH. S-glutathionylated Rac2 enhanced the binding of GTP, presumably due to structural alterations. These results elucidate the redox regulation of cysteine in Rac2 and a possible mechanism for regulating NADPH oxidase activation.

Protein kinase C: an attractive target for cancer therapy

Apoptosis plays an important role during all stages of carcinogenesis and the development of chemoresistance in tumor cells may be due to their selective defects in the intracellular signaling proteins, central to apoptotic pathways. Consequently, many studies have focused on rendering the chemotherapy more effective in order to prevent chemoresistance and pre-clinical and clinical data has suggested that protein kinase C (PKC) may represent an attractive target for cancer therapy. Therefore, a complete understanding of how PKC regulates apoptosis and chemoresistance may lead to obtaining a PKC-based therapy that is able to reduce drug dosages and to prevent the development of chemoresistance.

Redox control of protein kinase C: cell- and disease-specific aspects

Hormones, growth factors, electrical stimulation, and cell-cell interactions regulate numerous cellular processes by altering the levels of second messengers, thus influencing biochemical reactions inside the cells. The Protein Kinase C family (PKCs) is a group of serine/threonine kinases that are dependent on calcium (Ca(2+)), diacylglycerol, and phospholipids. Signaling pathways that induce variations on the levels of PKC activators have been implicated in the regulation of diverse cellular functions and, in turn, PKCs are key regulators of a plethora of cellular processes, including proliferation, differentiation, and tumorigenesis. Importantly, PKCs contain regions, both in the N-terminal regulatory domain and in the C-terminal catalytic domain, that are susceptible to redox modifications. In several pathophysiological conditions when the balance between oxidants, antioxidants, and alkylants is compromised, cells undergo redox stress. PKCs are cell-signaling proteins that are particularly sensitive to redox stress because modification of their redox-sensitive regions interferes with their activity and, thus, with their biological effects. In this review, we summarize the involvement of PKCs in health and disease and the importance of redox signaling in the regulation of this family of kinases.

NADPH oxidase-dependent reactive oxygen species mediate amplified TLR4 signaling and sepsis-induced mortality in Nrf2-deficient mice

Sepsis syndrome is characterized by a dysregulated inflammatory response to infection. NADPH oxidase-dependent reactive oxygen species (ROS) play significant roles in the pathophysiology of sepsis. We previously showed that disruption of Nrf2, a master regulator of antioxidant defenses, caused a dysregulation of innate immune response that resulted in greater mortality in a polymicrobial sepsis and LPS shock model; however, the underlying mechanisms are unclear. In the current study, compared with wild-type (Nrf2(+/+)) macrophages, we observed greater protein kinase C-induced NADPH oxidase-dependent ROS generation in Nrf2-disrupted (Nrf2(-/-)) macrophages that was modulated by glutathione levels. To address the NADPH oxidase-mediated hyperinflammatory response and sepsis-induced lung injury and mortality in Nrf2(-/-) mice, we used double knockout mice lacking Nrf2 and NADPH oxidase subunit, gp91(phox) (Nrf2(-/-)//gp91(phox-/-)). Compared with Nrf2(+/+) macrophages, LPS induced greater activation of TLR4 as evident by TLR4 surface trafficking and downstream recruitment of MyD88 and Toll/IL-1R domain-containing adaptor in Nrf2(-/-) macrophages that was diminished by ablation of gp91(phox). Similarly, phosphorylation of IkappaB and IFN regulatory factor 3 as well as cytokine expression was markedly higher in Nrf2(-/-) macrophages; whereas, it was similar in Nrf2(+/+) and Nrf2(-/-)//gp91(phox-/-). In vivo studies showed greater LPS-induced pulmonary inflammation in Nrf2(-/-) mice that was significantly reduced by ablation of gp91(phox). Furthermore, LPS shock and polymicrobial sepsis induced early and greater mortality in Nrf2(-/-) mice; whereas, Nrf2(-/-)//gp91(phox-/-) showed prolonged survival. Together, these results demonstrate that Nrf2 is essential for the regulation of NADPH oxidase-dependent ROS-mediated TLR4 activation and lethal innate immune response in sepsis.

Alpha-tocopherol protects against oxidative stress in the fragile X knockout mouse: an experimental therapeutic approach for the Fmr1 deficiency

Fragile X syndrome is the most common genetic cause of mental disability. The mechanisms underlying the pathogenesis remain unclear and specific treatments are still under development. Previous studies have proposed an abnormal hypothalamic-pituitary-adrenal axis and high cortisol levels are demonstrated in the fragile X patients. Additionally, we have previously described that NADPH-oxidase activation leads to oxidative stress in the brain, representing a pathological mechanism in the fragile X mouse model. Fmr1-knockout mice develop an altered free radical production, abnormal glutathione homeostasis, high lipid and protein oxidation, accompanied by stress-dependent behavioral abnormalities and pathological changes in the first months of postnatal life. Chronic pharmacological treatment with alpha-tocopherol reversed pathophysiological hallmarks including free radical overproduction, oxidative stress, Rac1 and alpha-PKC activation, macroorchidism, and also behavior and learning deficits. The restoration of the oxidative status in the fragile X mouse emerges as a new and promising approach for further therapeutic research in fragile X syndrome.

Myosin as a potential redox-sensor: an in vitro study

A balanced redox status is necessary to optimize force production in contractile apparatus, where free radicals generated by skeletal muscle are involved in some basic physiological processes like excitation-contraction coupling. Protein glutathionylation has a key role in redox regulation of proteins and signal transduction. Here we show that myosin is sensitive to in vitro glutathionylation and MALDI-TOF analysis identified three potential sites of glutathione binding, two of them locating on the myosin head. Glutathionylation of myosin has an important impact on the protein structure, as documented by the lower fluorescence quantum yield of glutathionylated myosin and its increased susceptibility to the proteolytic cleavage. Myosin function is also sensitive to glutathionylation, which modulates its ATPase activity depending on GSSG redox balance. Thus, like the phosphorylation/dephosphorylation cycle, glutathionylation may represent a mechanism by which glutathione modulates sarcomere functions depending on the tissue redox state, and myosin may constitute a muscle redox-sensor.

Glutathionylation regulates IkappaB

Although there has been considerable interest in the regulation of NFkappaB activation by glutathionylation, the possibility of IkappaB as a target for glutathionylation has not been investigated. We now report that Cys(189) of IkappaB alpha is a target for S-glutathionylation. This modification is reversed by thiols such as dithiothreitol and GSH. The glutathionylated IkappaB alpha appears to be significantly less susceptible than is native protein to phosphorylation by IkappaB kinase and casein kinase II, as well as to in vitro ubiquitination. This finding suggests that glutathionylation plays a regulatory role, presumably through structural alterations. HeLa cells treated with oxidant inducing GSH oxidation such as diamide showed the accumulation of glutathionylated IkappaB alpha. This mechanism suggests an alternative modification to the redox regulation of cysteine in IkappaB alpha and a possible mechanism in the regulation of NFkappaB activation.

Redox signalling in cardiovascular disease

Oxidative stress has almost universally and unequivocally been implicated in the pathogenesis of all major diseases, including those of the cardiovascular system. Oxidative stress in cells and cardiovascular biology was once considered only in terms of injury, disease and dysfunction. However, it is now appreciated that oxidants are also produced in healthy tissues, and they function as signalling molecules transmitting information throughout the cell. Conversely, when cells move to a more reduced state, as can occur when oxygen is limiting, this can also result in alterations in the function of biomolecules and subsequently cells. At the centre of this 'redox signalling' are oxidoreductive chemical reactions involving oxidants or reductants post translationally modifying proteins. These structural alterations allow changes in cellular redox state to be coupled to alterations in cell function. In this review, we consider aspects of redox signalling in the cardiovascular system, focusing on the molecular basis of redox sensing by proteins and the array of post-translational oxidative modifications that can occur. In addition, we discuss studies utilising proteomic methods to identify redox-sensitive cardiac proteins, as well as those using this technology more broadly to assess redox signalling in cardiovascular disease.

Inhibition of caspase-3 activity and activation by protein glutathionylation

Protein glutathionylation is a post-translational modification that may account for a broad mechanism of redox signaling. The caspase family of cysteine proteases represents a potential target for regulation by glutathionylation. To examine this, caspase proteins, derived from HL-60 cells after activation with actinomycin D, were incubated with GSSG. Total protein glutathionylation was enhanced and caspase-3 activity was inhibited in a dose- and time-dependent manner by GSSG. Caspase inhibition was reversible by thiol-specific reducing reagents. Proteolytic activation of caspases was also affected, as the activation of procaspase-3 and procaspase-9 in HL-60 cell extracts induced by cytochrome c and dATP was inhibited by pre-incubation with GSSG. When biotin-labeled GSSG was incubated with recombinant caspase-3, biotin label was found associated with both p12 and p17 subunits of active caspase-3 by non-reducing SDS-PAGE. Caspase-3 glutathionylation was confirmed by matrix assisted laser desorption ionization (MALDI) mass spectrometric analysis of GSSG-treated recombinant caspase-3. Specific sites of glutathionylation were identified as Cys(135) of the p17 protein (the active site) and Cys(45) of the p12 protein. These results indicate that glutathionylation of caspase can occur at physiologically relevant concentrations of GSSG and results in the inhibition of caspase activation and activity.

PKC signaling in oxidative hepatic damage

Protein kinase C (PKC) is a family of isoenzymes differently involved in cell response to injury and many studies describe their role as "stress sensors". Oxidative stress is strictly involved in the pathogenesis of chronic liver diseases including alcohol- or drug-induced hepatotoxicity, iron overload, hepatitis and hepatocarcinoma development, but molecular mechanisms are not really defined. A crucial role of PKC as a redox sensitive signaling molecule has been widely accepted.

Serum levels of S-glutathionylated proteins as a risk-marker for arteriosclerosis obliterans

BACKGROUND

Oxidative stress plays a role in the development of chronic peripheral arterial disease (PAD) because under these conditions redox regulation is impaired, inducing the S-glutathionylation of proteins. A method of estimating the levels of S-glutathionylated proteins has been developed using biotinylated glutathione S-transferase, which allows the study of their crucial role in the oxidative stress-related progression of PAD.

METHODS AND RESULTS

The serum levels of S-glutathionylated proteins were examined in 41 patients with arteriosclerosis obliterans (ASO) and 38 age-matched non-ASO patients using biotinylated glutathione S-transferase. The levels were higher in the patients with ASO, even early on, and positively correlated with the ankle/brachial index. In vitro, the levels of S-glutathionylated proteins were reduced in the presence of glutathione and glutaredoxin.

CONCLUSIONS

Serum levels of S-glutathionylated proteins are a sensitive risk-marker for ASO at an early stage.

Cytomodulation of interleukin-2 effect by L-2-oxothiazolidine-4-carboxylate on human malignant melanoma

Glutathione (GSH), the most prevalent intracellular non-protein thiol, plays an important role in the interleukin-2 (IL-2)-induced proliferative activity of normal and tumour cells expressing IL-2 receptor (IL-2R). In the present study, we investigate the effect of IL-2 on proliferation of the human melanoma A375 cell line, and the possible selective cytomodulation effect of this cytokine by L-2-oxothiazolidine-4-carboxylate (OTZ) on these melanoma cells and on human peripheral blood mononuclear cells (PBMCs). We found that recombinant IL-2 (rIL-2) significantly increased the proliferation rate of A375 melanoma cells, which was associated with an increase in GSH levels, the enhancement of IL-2Ralpha expression and the endogenous production of IL-2 in these tumour cells. In contrast, OTZ decreased GSH content and the proliferation rate of A375 cells, and abrogated the growth-promoting effects of rIL-2. Thus, compared to cells treated with rIL-2, pre-treatment with OTZ reduced IL-2Ralpha expression, and also decreased the consumption of rIL-2 and the endogenous secretion of IL-2 by these tumour cells. With regard to PBMCs, the combination of OTZ plus rIL-2 resulted in a more rapid and greater increase of IL-2Ralpha expression than rIL-2 alone, with the proliferation rate being similar in the first 24 h, but with a lower PBMC' count found thereafter compared to rIL-2 treatment alone. These results suggest that OTZ plays a crucial role in obtaining a selective cytomodulation of rIL-2, enabling it to exert its growth-promoting effect on normal cells, but not on melanoma cells, thereby possibly improving biochemotherapy with rIL-2.

Glutathione depletion modulates gene expression in HepG2 cells via activation of protein kinase C alpha

Buthionine sulphoximine (BSO; 1mM) resulted in the depletion of glutathione (GSH) in HepG2 cells to 17+/-1.5% within 24h. This was not associated with apoptotic or necrotic cell death over this time period. Use of a human (Phase 1) cDNA custom toxicology-array and a larger scale (>10,000 gene) Affymetrix U95Av2 array identified a total of 48 and 104 genes, respectively, with a statistically significant (and >1.5-fold) change in expression. A total of 64 differentially expressed genes (6 of which were confirmed by real-time polymerase chain reaction) were suggestive of protein kinase C (PKC) activation. Activation of PKC-alpha (but not betaI or delta) was demonstrated at 24 h through activity measurements and through Western blot analysis of membrane-associated PKC-alpha protein. Activation did not occur in the presence of additional gamma-glutamylcysteine to prevent GSH depletion. Activation of PKC-alpha by GSH-depletion may, at least in part, be mediated by thiol oxidation and may contribute to a survival signal. If sustained, the activation may be important in non-genotoxic carcinogenesis.

Reactive oxygen species: Biological stimuli of neuroblastoma cell response

Reactive oxygen species play a critical role in differentiation, proliferation and apoptosis acting as 'second messengers' able to regulate sulphydryl groups in signaling molecules as protein kinase C, a family of isoenzymes involved in many cellular responses and implicated in cell transformation. Neuroblastoma is characterised by the production of oxygen intermediates and L-buthionine-S,R-sulfoximine, a glutathione-depleting agent that has been tested in the clinics, exploits this biological peculiarity to induce cell death. The latter process is mediated by the oxidative activation of PKC delta which might be involved also in the production of reactive oxygen species, thus amplifying the apoptotic cascade.

REDOX REGULATION BY INTRINSIC SPECIES AND EXTRINSIC NUTRIENTS IN NORMAL AND CANCER CELLS

Cells in multicellular organisms are exposed to both endogenous oxidative stresses generated metabolically and to oxidative stresses that originate from neighboring cells and from other tissues. To protect themselves from oxidative stress, cells are equipped with reducing buffer systems (glutathione/GSH and thioredoxin/thioredoxin reductase) and have developed several enzymatic mechanisms against oxidants that include catalase, superoxide dismutase, and glutathione peroxidase. Other major extrinsic defenses (from the diet) include ascorbic acid, beta-carotene and other carotenoids, and selenium. Recent evidence indicates that in addition to their antioxidant function, several of these redox species and systems are involved in regulation of biological processes, including cellular signaling, transcription factor activity, and apoptosis in normal and cancer cells. The survival and overall well-being of the cell is dependent upon the balance between the activity and the intracellular levels of these antioxidants as well as their interaction with various regulatory factors, including Ref-1, nuclear factor-kappaB, and activating protein-1.

Ischemic preconditioning: a potential role for protein S-thiolation?

Oxidant stress plays a crucial role in the triggering of cardioprotection involving ischemic preconditioning (IPC). We have used biotin-tagged cysteine to probe for redox-modified proteins in IPC protocols. Cysteine was biotinylated and introduced into isolated rat hearts. S-Thiolated proteins were detected and quantified using nonreducing western blots probed with streptavidin-horseradish peroxidase. Controls (15 min of aerobic perfusion plus 5 min of 0.5 mM biotin-cysteine plus 5 min of aerobic perfusion) showed low-level protein S-thiolation. Hearts preconditioned with 5 min of ischemia and reperfused for 5 min with biotin-cysteine plus 5 min of aerobic perfusion showed increased thiolation (160%) that was fully blocked by the antioxidant mercaptopropionylglycine, which is also known to block IPC. "Preconditioning" agonists (phorbol 12-myristate 13-acetate or phenylephrine) or oxidants (hydrogen peroxide or diamide) administered during aerobic preparations to biotin-cysteine-loaded hearts induced efficient protein S-thiolation. Preconditioning agonist-induced S-thiolation was significantly attenuated by diphenyleneiodonium (a flavoprotein inhibitor) or by the protein kinase C inhibitor bisindolylmaleimide I. Additional studies testing the role of a Nox2-containing NAD(P)H oxidase as the source of the oxidant stress essential to the triggering IPC showed that protein S-thiolation was the same in wild-type and Nox2 knockout mice.

Reciprocal regulation of glutathione S-transferase spliceforms and the Drosophila c-Jun N-terminal kinase pathway components

In mammalian systems, detoxification enzymes of the GST (glutathione S-transferase) family regulate JNK (c-Jun N-terminal kinase) signal transduction by interaction with JNK itself or other proteins upstream in the JNK pathway. In the present study, we have studied GSTs and their interaction with components of the JNK pathway from Diptera. We have evaluated the effects of four Delta class Anopheles dirus GSTs, GSTD1-1, GSTD2-2, GSTD3-3 and GSTD4-4, on the activity of full-length recombinant Drosophila HEP (mitogen-activated protein kinase kinase 7; where HEP stands for hemipterous) and the Drosophila JNK, as well as the reciprocal effect of these kinases on GST activity. Interestingly, even though these four GSTs are alternatively spliced products of the same gene and share >60% identity, they exerted different effects on JNK activity. GSTD1-1 inhibited JNK activity, whereas the other three GST isoforms activated JNK. GSTD2-2, GSTD3-3 and GSTD4-4 were inhibited 50-80% by HEP or JNK but GSTD1-1 was not inhibited by JNK. However, there were some similarities in the actions of HEP and JNK on these GSTs. For example, binding constants for HEP or JNK inhibiting a GST were similar (20-70 nM). Furthermore, after incubation of the GSTs with JNK, both JNK and the GSTs changed catalytic properties. The substrate specificities of both GSTs and JNK were also altered after their co-incubation. In addition, glutathione modulated the effects of JNK on GST activity. These results emphasize that different GST spliceforms possess different properties, both in their catalytic function and in their regulation of signalling through the JNK pathway.

Detection of S-glutathionylated proteins by glutathione S-transferase overlay

Oxidative and nitrosative stress lead to the S-glutathionylation of proteins and subsequent functional impairment. Glutathione S-transferase (GST) from Schistosoma japonicum was found to bind to the glutathione moiety of S-glutathionylated proteins, thus establishing a convenient method for detecting S-glutathionylated proteins by biotinylated GST. Applications of this method to proteins that were prepared from cultured cells and blotted onto a membrane exhibited numerous positive bands, which were abolished by treatment with dithiothreitol. Treatment of a cellular extract with nitrosoglutathione led to enhanced staining of the bands in a dose-dependent manner. The method was also applicable for the histochemical detection of S-glutathionylated proteins in situ. The positive staining by biotin-GST became faint in the presence of S-glutathionylated ovalbumin, suggesting that the reaction is specific to S-glutathionylated proteins. Collectively, these data indicate that the method established here is simple and useful for detecting S-glutathionylated proteins on blotted membrane and in situ.

Heme oxygenase-1-mediated partial cytoprotective effect by NO on cadmium-induced cytotoxicity in C6 rat glioma cells

Heme oxygenase-1 (HO-1) is a 32-kDa stress induced enzyme that degrades heme to carbon monoxide (CO) and biliverdin. By employing RT-PCR and Western blotting techniques, we have examined the HO-1 induction in C6 glioma cells that were treated with cadmium chloride (CdCl(2)) or spermine NONOate (SPER/NO). By employing a cell viability assay, we have also examined the cytoprotective effect of HO-1 induction against the cytotoxicity caused by toxic dose of CdCl(2). In C6 glioma cells exposed to CdCl(2), expression of HO-1 (mRNA and protein) was increased in a dose- and time-dependent manner. Nitric oxide (NO) generated from SPER/NO very rapidly increased HO-1 mRNA expression in the C6 glioma cells. The induction of HO-1 by SPER/NO protected the cells from toxic dose of CdCl(2). The up-regulation of HO-1 mRNA expression by CdCl(2) was inhibited by a pre-incubation of the cells with actinomycin D, a potent inhibitor of mRNA transcription. Upon the inhibition of elevated HO-1 mRNA expression by the use of zinc protoporphyrin IX (ZnPP), an inhibitor of HO activity, the change of HO-1 mRNA expression by ZnPP was not observed. Thus, the glial cell may respond to CdCl(2) toxicity by enhancing the HO-1 expression in its effort to minimize the CdCl(2)-derived oxidative damage, and to survive. In the glioma cells, when the HO-1 expression was elevated by a prior incubation with SPER/NO, the cell viability against the cytotoxicity of CdCl(2) was significantly increased. When the results of our experiment are taken together, we discovered that NO provided a rapid enhancement of HO-1 expression, and it provided a protective effect against CdCl(2)-derived oxidative injury in the C6 rat glioma cells.

Regulation of mitochondrial NADP+-dependent isocitrate dehydrogenase activity by glutathionylation

Recently, we demonstrated that the control of mitochondrial redox balance and oxidative damage is one of the primary functions of mitochondrial NADP(+)-dependent isocitrate dehydrogenase (IDPm). Because cysteine residue(s) in IDPm are susceptible to inactivation by a number of thiol-modifying reagents, we hypothesized that IDPm is likely a target for regulation by an oxidative mechanism, specifically glutathionylation. Oxidized glutathione led to enzyme inactivation with simultaneous formation of a mixed disulfide between glutathione and the cysteine residue(s) in IDPm, which was detected by immunoblotting with anti-GSH IgG. The inactivated IDPm was reactivated enzymatically by glutaredoxin2 in the presence of GSH, indicating that the inactivated form of IDPm is a glutathionyl mixed disulfide. Mass spectrometry and site-directed mutagenesis further confirmed that glutathionylation occurs to a Cys(269) of IDPm. The glutathionylated IDPm appeared to be significantly less susceptible than native protein to peptide fragmentation by reactive oxygen species and proteolytic digestion, suggesting that glutathionylation plays a protective role presumably through the structural alterations. HEK293 cells and intact respiring mitochondria treated with oxidants inducing GSH oxidation such as H(2)O(2) or diamide showed a decrease in IDPm activity and the accumulation of glutathionylated enzyme. Using immunoprecipitation with anti-IDPm IgG and immunoblotting with anti-GSH IgG, we were also able to purify and positively identify glutathionylated IDPm from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated mice, a model for Parkinson's disease. The results of the current study indicate that IDPm activity appears to be modulated through enzymatic glutathionylation and deglutathionylation during oxidative stress.

Ocular Melanogenesis: The Role of Antioxidants

Given the propensity of a large number of melanogenic pathways that can be modulated by cellular redox status, a causal role of the deficiency of ocular pigments such as melanin in the pathogenesis of age-related macular degeneration and evidence that melanin production does occur in the adult eye, it seems not improbable that antioxidants (or agents that modify cellular redox status) may have melanin stimulatory (or inhibitory) effects that are superimposible on their effects as mere free radical scavengers. More empirical studies are needed to investigate this phenomenon so that antioxidant therapy may prove more beneficial to patients with ocular degenerative diseases.

Actin glutathionylation increases in fibroblasts of patients with Friedreich's ataxia: a potential role in the pathogenesis of the disease

Increasing evidence suggests that iron-mediated oxidative stress might underlie the development of neurodegeneration in Friedreich's ataxia (FRDA), an autosomal recessive ataxia caused by decreased expression of frataxin, a protein implicated in iron metabolism. In this study, we demonstrate that, in fibroblasts of patients with FRDA, the cellular redox equilibrium is shifted toward more protein-bound glutathione. Furthermore, we found that actin is glutathionylated, probably as a result of the accumulation of reactive oxygen species, generated by iron overload in the disease. Indeed, high-pressure liquid chromatography analysis of control fibroblasts in vivo treated with FeSO4 showed a significant increase in the protein-bound/free GSH ratio, and Western blot analysis indicated a relevant rise in glutathionylation. Actin glutathionylation contributes to impaired microfilament organization in FRDA fibroblasts. Rhodamine phalloidin staining revealed a disarray of actin filaments and a reduced signal of F-actin fluorescence. The same hematoxylin/eosin-stained cells showed abnormalities in size and shape. When we treated FRDA fibroblasts with reduced glutathione, we obtained a complete rescue of cytoskeletal abnormalities and cell viability. Thus, we conclude that oxidative stress may induce actin glutathionylation and impairment of cytoskeletal functions in FRDA fibroblasts.

A novel role of protein kinase C-δ in cell signaling triggered by glutathione depletion

Current evidence demonstrates that protein kinase C (PKC) belongs to a group of cell-signaling molecules that are sensitive targets for redox modifications and functional alterations that mediate oxidant-induced cellular responses. Our studies have demonstrated that diminished intracellular GSH was associated to inactivation of classic isoforms and increased activity of novel PKCs, and triggered molecular signals important for cell survival. Loss of GSH and oxidative damage are probably an early signaling event in apoptotic death, which is characterized by the activation of PKC-delta. Apoptotic process consequent to GSH depletion was inhibited by rottlerin, a PKC-delta-specific inhibitor, which exerted a negative effect on oxyradical production. Therefore, it may be concluded that PKC-delta activity is related to reactive oxygen species production and is involved in the pathway leading to apoptosis and growth arrest.

Role of PKC-delta activity in glutathione-depleted neuroblastoma cells

Protein kinases C (PKCs) are a family of isoenzymes sensitive to oxidative modifications and involved in the transduction signal pathways that regulate cell growth. As such, they can act as cellular sensors able to intercept intracellular redox changes and promote the primary adaptive cell response. In this study, we have demonstrated that PKC isoforms are specifically influenced by the amount of intracellular glutathione (GSH). The greatest GSH depletion is associated with a maximal reactive oxygen species (ROS) production and accompanied by an increase in the activity of the delta isoform and a concomitant inactivation of alpha. ROS generation induced early morphological changes in GSH-depleted neuroblastoma cells characterized, at the intracellular level, by the modulation of PKC-delta activity that was involved in the pathway leading to apoptosis. When cells were pretreated with rottlerin, their survival was improved by the ability of this compound to inhibit the activity of PKC-delta and to counteract ROS production. These results define a novel role of PKC-delta in the cell signaling pathway triggered by GSH loss normally associated with many neurodegenerative diseases and clinically employed in the treatment of neuroblastoma.

Reversible cysteine-targeted oxidation of proteins during renal oxidative stress

Biotin-cysteine was used to study protein S-thiolation in isolated rat kidneys subjected to ischemia and reperfusion. After 40 min of ischemia, total protein S-thiolation increased significantly (P < 0.05), by 311%, and remained significantly elevated (P < 0.05), 221% above control, after 5 min of postischemic reperfusion. Treatment of protein samples with 2-mercaptoethanol abolished the S-thiolation signals detected, consistent with the dependence of the signal on the presence of a disulfide bond. With the use of gel filtration chromatography followed by affinity purification with streptavidin-agarose, S-thiolated proteins were purified from CHAPS-soluble kidney homogenate. The proteins were then separated by SDS-PAGE and stained with Coomassie blue. With a combination of matrix-assisted laser desorption ionization time of flight mass spectrometry and LC/MS/MS analysis of protein bands digested with trypsin, a number of S-thiolation substrates were identified. These included the LDL receptor-related protein 2, ATP synthase alpha chain, heat shock protein 90 beta, hydroxyacid oxidase 3, serum albumin precursor, triose phosphate isomerase, and lamin. These represent proteins that may be functionally regulated by S-thiolation and thus could undergo a change in activity or function after renal ischemia and reperfusion.

Detection of elevated glutathione in meningiomas by quantitative in vivo 1H MRS

Glutathione has major roles in removing free radicals and toxins from normal tissues, but its presence in tumor cells hinders the effectiveness of many anticancer therapies. Analysis of short echo time brain tumor (1)H spectra at 1.5 T using a linear combination of metabolite spectra (LCModel) suggested a significant contribution of glutathione to meningioma spectra. By in vivo MRS (TE = 30 ms, TR = 2020 ms), reduced glutathione was found to be significantly elevated in meningiomas (3.3 +/- 1.5 mM, Mann Whitney, P < 0.005) compared to normal white matter (1.2 +/- 0.15 mM) and low-grade gliomas (1.0 +/- 0.26 mM), in agreement with published histofluorescence studies of tumor biopsies. Glx concentrations were also found to be elevated in meningiomas compared to astrocytomas or normal white matter, indicative of metabolic differences. The ability to noninvasively quantify reduced glutathione in vivo may aid selection of treatment therapies and also provide an indication of tumor aggressiveness.

The importance of glutathione in human disease

Reduced glutathione (GSH) is the most prevalent non-protein thiol in animal cells. Its de novo and salvage synthesis serves to maintain a reduced cellular environment and the tripeptide is a co-factor for many cytoplasmic enzymes and may also act as an important post-translational modification in a number of cellular proteins. The cysteine thiol acts as a nucleophile in reactions with both exogenous and endogenous electrophilic species. As a consequence, reactive oxygen species (ROS) are frequently targeted by GSH in both spontaneous and catalytic reactions. Since ROS have defined roles in cell signaling events as well as in human disease pathologies, an imbalance in expression of GSH and associated enzymes has been implicated in a variety of circumstances. Cause and effect links between GSH metabolism and diseases such as cancer, neurodegenerative diseases, cystic fibrosis (CF), HIV, and aging have been shown. Polymorphic expression of enzymes involved in GSH homeostasis influences susceptibility and progression of these conditions. This review provides an overview of the biological importance of GSH at the level of the cell and organism.

Thiol-inducing and immunoregulatory effects of flavonoids in peripheral blood mononuclear cells from patients with end-stage diabetic nephropathy

The cellular thiol status and its relationship to T-cell activation and cytokine synthesis of mononuclear cells was investigated in patients with end-stage diabetic nephropathy (ESDN) undergoing dialysis treatment. The functional effects of thiol repair by in vitro and in vivo treatment with flavonoids were elucidated. The thiol status of peripheral blood lymphocytes from 30 ESDN patients on hemodialysis and healthy controls was determined by flow cytometry. T-cell activation in response to pokeweed mitogen was analyzed by CD69 expression; cytokines were determined in cell culture supernatants. In result, compared to age-matched healthy subjects, a significant thiol deficiency in ESDN patients was obvious. The lowered total intracellular thiol levels correlated directly to a significant diminished T-cell activation and an elevated synthesis of TNF-alpha in the patient group. The treatment with flavonoids led to a restoration of the thiol status within 72 h in vitro and in vivo. This effect showed a biphasic kinetic that first utilized cell surface thiols and secondly intracellular thiols. In parallel, the T-cell activation was improved substantially along with a significant decrease in TNF-alpha release. These data provide the rational for clinical trials using flavonoids in ESDN to normalize immunoregulatory defects via restoration of the cellular thiol status.

Glyceraldehyde phosphate dehydrogenase oxidation during cardiac ischemia and reperfusion

OBJECTIVES

Protein S-glutathiolation is a predicted mechanism by which protein thiol groups are oxidized during the oxidative stress of ischaemia and reperfusion. We measured protein S-thiolation during ischaemia and reperfusion and investigated the effect of this oxidative modification on the function of GAPDH.

METHODS

Glutathione was biotinylated (biotin-GSH) and used to probe for protein S-glutathiolation in isolated rat hearts using non-reducing Western blots and streptavidin-HRP. Streptavidin-agarose was used to purify S-glutathiolated proteins and these were identified using N-terminal sequencing and database searching.

RESULTS

Little protein S-glutathiolation occurred in control preparations, but this increased 15-fold during reperfusion. Protein S-glutathiolation was attenuated by the antioxidant mercaptopropionylglycine and was shown to occur only during the firstminutes of reperfusion. Affinity purification of the S-glutathiolated proteins showed 20 dominant S-glutathiolation substrates. A dominant S-thiolated protein was N-terminally sequenced (VKVGVNGFG) and HPLC peptide mapping gave additional sequence nearer the site of oxidation (TGVFTTMEKA). The first sequence was the N-terminus of GAPDH, and the second a peptide from the same protein starting at residue 96. GAPDH was immunopurified from aerobic, ischemic or reperfused hearts. Maleimidofluorescein labeling of purified GAPDH provided an index of its reduced thiol status. In the absence of DTT, ischemia induced a reduction in the number of free thiols on GAPDH that was reversed on reperfusion. When treated with DTT, the free thiol status of GAPDH could be increased in ischemic but not reperfused samples. Ischemia induced a reduction in GAPDH activity that was partially restored by reperfusion. DTT-treatment reactivated ischemic GAPDH, but had little effect on the activity from reperfused tissue. Mass spectra acquired from aerobic GAPDH preparations were relatively simple whereas spectra from ischemic or reperfused preparations were highly complex, possibly indicative of oxidation by multiple oxidants.

CONCLUSIONS

Many proteins, including GAPDH, are targets for S-glutathiolation during cardiac oxidative stress. GAPDH oxidation is associated with a loss in reduced cysteine status that correlates with the inactivation of this enzyme.