Targeting the reversibly oxidized protein tyrosine phosphatase superfamily

Measuring the Reversible Oxidation of Protein Tyrosine Phosphatases Using a Modified Cysteinyl-Labeling Assay

The modified cysteinyl-labeling assay enables the labeling, enrichment, and detection of all members of the protein tyrosine phosphatase (PTP) superfamily that become reversibly oxidized in cells to facilitate phosphorylation-dependent signaling. In this chapter, we describe the method in detail and highlight the pitfalls of avoiding post-lysis oxidation of PTPs to measure the dynamic and transient oxidation and reduction of PTPs in cell signaling.

Protein disulfide isomerase A1 as a novel redox sensor in VEGFR2 signaling and angiogenesis

VEGFR2 signaling in endothelial cells (ECs) is regulated by reactive oxygen species (ROS) derived from NADPH oxidases (NOXs) and mitochondria, which plays an important role in postnatal angiogenesis. However, it remains unclear how highly diffusible ROS signal enhances VEGFR2 signaling and reparative angiogenesis. Protein disulfide isomerase A1 (PDIA1) functions as an oxidoreductase depending on the redox environment. We hypothesized that PDIA1 functions as a redox sensor to enhance angiogenesis. Here we showed that PDIA1 co-immunoprecipitated with VEGFR2 or colocalized with either VEGFR2 or an early endosome marker Rab5 at the perinuclear region upon stimulation of human ECs with VEGF. PDIA1 silencing significantly reduced VEGF-induced EC migration, proliferation and spheroid sprouting via inhibiting VEGFR2 signaling. Mechanistically, VEGF stimulation rapidly increased Cys-OH formation of PDIA1 via the NOX4-mitochondrial ROS axis. Overexpression of "redox-dead" mutant PDIA1 with replacement of the active four Cys residues with Ser significantly inhibited VEGF-induced PDIA1-CysOH formation and angiogenic responses via reducing VEGFR2 phosphorylation. Pdia1+/- mice showed impaired angiogenesis in developmental retina and Matrigel plug models as well as ex vivo aortic ring sprouting model. Study using hindlimb ischemia model revealed that PDIA1 expression was markedly increased in angiogenic ECs of ischemic muscles, and that ischemia-induced limb perfusion recovery and neovascularization were impaired in EC-specific Pdia1 conditional knockout mice. These results suggest that PDIA1 can sense VEGF-induced H2O2 signal via CysOH formation to promote VEGFR2 signaling and angiogenesis in ECs, thereby enhancing postnatal angiogenesis. The oxidized PDIA1 is a potential therapeutic target for treatment of ischemic vascular diseases.

Potential Contribution of the Intestinal Microbiome to Phenethylamine-Induced Hyperthermia

Phenethylamines (e.g., methamphetamine) are a common source of drug toxicity. Phenethylamine-induced hyperthermia (PIH) can activate a cascade of events that may result in rhabdomyolysis, coagulopathy, and even death. Here, we review recent evidence that suggests a potential link between the gut-brain axis and PIH. Within the preoptic area of the hypothalamus, phenethylamines lead to changes in catecholamine levels, that activate the sympathetic nervous system (SNS) and increase the peripheral levels of norepinephrine (NE), resulting in: (1) the loss of heat dissipation through α1 adrenergic receptor (α1-AR)-mediated vasoconstriction, (2) heat generation through β-AR activation and subsequent free fatty acid (FFA) activation of uncoupling proteins (UCPs) in brown and white adipose tissue, and (3) alteration of the gut microbiome and its link to the gut-brain axis. Recent studies have shown that phenethylamine derivatives can influence the composition of the gut microbiome and thus its metabolic potential. Phenethylamines increase the relative level of Proteuswhich has been linked to enhanced NE turnover. Bidirectional fecal microbial transplants (FMT) between PIH-tolerant and PIH-naïve rats demonstrated that the transplantation of gut microbiome can confer phenotypic hyperthermic and tolerant responses to phenethylamines. These phenethylamine-mediated changes in the gut microbiome were also associated with epigenetic changes in the mediators of thermogenesis. Given the significant role that the microbiome has been shown to play in the maintenance of body temperature, we outline current studies demonstrating the effects of phenethylamines on the gut microbiome and how these microbiome changes may mechanistically contribute to alterations in body temperature.

The Implication of STEP in Synaptic Plasticity and Cognitive Impairments in Alzheimer's Disease and Other Neurological Disorders

STriatal-Enriched protein tyrosine Phosphatase (STEP) is a tyrosine phosphatase that has been implicated in Alzheimer’s disease (AD), the most common form of dementia, and many other neurological diseases. The protein level and activity of STEP have been found to be elevated in most of these disorders, and specifically in AD as a result of dysregulation of different pathways including PP2B/DARPP32/PP1, PKA as well as impairments of both proteasomal and lysosomal systems. The upregulation in STEP leads to increased binding to, and dephosphorylation of, its substrates which are mainly found to be synaptic plasticity and thus learning and memory related proteins. These proteins include kinases like Fyn, Pyk2, ERK1/2 and both NMDA and AMPA receptor subunits GluN2B and GluA2. The dephosphorylation of these molecules results in inactivation of these kinases and internalization of NMDA and AMPA receptor complexes leading to synapse loss and cognitive impairments. In this study, we aim to review STEP regulation and its implications in AD as well as other neurological disorders and then summarize data on targeting STEP as therapeutic strategy in these diseases.

In Vitro Activity Assays to Quantitatively Assess the Endogenous Reversible Oxidation State of Protein Tyrosine Phosphatases in Cells

The reversible oxidation of protein tyrosine phosphatases (PTPs) impairs their ability to dephosphorylate substrates in vivo. This transient inactivation of PTPs occurs as their conserved catalytic cysteine residue reacts with cellular oxidants thereby abolishing the ability of this reactive cysteine to attack the phosphate of the target substrate. Hence, in vivo, the inhibition of specific PTPs in response to regulated and localized rises in cellular oxidants enables phospho-dependent signaling. We present assays that measure the endogenous activity of specific PTPs that become transiently inactivated in cells exposed to growth factors. Here, we describe the methods and highlight the pitfalls to avoid post-lysis oxidation of PTPs in order to assess the inactivation and the reactivation of PTPs targeted by cellular oxidants in signal transduction. © 2020 Wiley Periodicals LLC. Basic Protocol 1: Cell transfection (optional) Support Protocol: Preparation of degassed lysis buffers Basic Protocol 2: Cellular extraction in anaerobic conditions Basic Protocol 3: Enrichment and activity assay of specific PTPs Alternate Protocol: Measurement of active PTPs via direct cysteinyl labeling.

xCT (SLC7A11) expression confers intrinsic resistance to physical plasma treatment in tumor cells

Cold physical plasma is a partially ionized gas investigated as a new anticancer tool in selectively targeting cancer cells in monotherapy or in combination with therapeutic agents. Here, we investigated the intrinsic resistance mechanisms of tumor cells towards physical plasma treatment. When analyzing the dose-response relationship to cold plasma-derived oxidants in 11 human cancer cell lines, we identified four 'resistant' and seven 'sensitive' cell lines. We observed stable intracellular glutathione levels following plasma treatment only in the 'resistant' cell lines indicative of altered antioxidant mechanisms. Assessment of proteins involved in GSH metabolism revealed cystine-glutamate antiporter xCT (SLC7A11) to be significantly more abundant in the 'resistant' cell lines as compared to 'sensitive' cell lines. This decisive role of xCT was confirmed by pharmacological and genetic inhibition, followed by cold physical plasma treatment. Finally, microscopy analysis of ex vivo plasma-treated human melanoma punch biopsies suggested a correlation between apoptosis and basal xCT protein abundance. Taken together, our results demonstrate that xCT holds the potential as a biomarker predicting the sensitivity of tumor cells towards plasma treatment.

Regulation of PTP1B activation through disruption of redox-complex formation

We have identified a molecular interaction between the reversibly oxidized form of protein tyrosine phosphatase 1B (PTP1B) and 14-3-3ζ that regulates PTP1B activity. Destabilizing the transient interaction between 14-3-3ζ and PTP1B prevented PTP1B inactivation by reactive oxygen species and decreased epidermal growth factor receptor phosphorylation. Our data suggest that destabilizing the interaction between 14-3-3ζ and the reversibly oxidized and inactive form of PTP1B may establish a path to PTP1B activation in cells.

Activated Thiol Sepharose-based proteomic approach to quantify reversible protein oxidation

Reactive oxygen species (ROS) can act as second messengers in various signaling pathways, and abnormal oxidation contributes to multiple diseases, including cancer. Detecting and quantifying protein oxidation is crucial for a detailed understanding of reduction-oxidation reaction (redox) signaling. We developed an Activated Thiol Sepharose-based proteomic (ATSP) approach to quantify reversible protein oxidation. ATSP can enrich H2O2-sensitive thiol peptides, which are more likely to contain reactive cysteines involved in redox signaling. We applied our approach to analyze hereditary leiomyomatosis and renal cell carcinoma (HLRCC), a type of kidney cancer that harbors fumarate hydratase (FH)-inactivating mutations and has elevated ROS levels. Multiple proteins were oxidized in FH-deficient cells, including many metabolic proteins such as the pyruvate kinase M2 isoform (PKM2). Treatment of HLRCC cells with dimethyl fumarate or PKM2 activators altered PKM2 oxidation levels. Finally, we found that ATSP could detect Src homology region 2 domain-containing phosphatase-2 and PKM2 oxidation in cells stimulated with platelet-derived growth factor. This newly developed redox proteomics workflow can detect reversible oxidation of reactive cysteines and can be employed to analyze multiple physiologic and pathologic conditions.-Xu, Y., Andrade, J., Ueberheide, B., Neel, B. G. Activated Thiol Sepharose-based proteomic approach to quantify reversible protein oxidation.

Modulation of FLT3 signal transduction through cytoplasmic cysteine residues indicates the potential for redox regulation

Oxidative modification of cysteine residues has been shown to regulate the activity of several protein-tyrosine kinases. We explored the possibility that Fms-like tyrosine kinase 3 (FLT3), a hematopoietic receptor-tyrosine kinase, is subject to this type of regulation. An underlying rationale was that the FLT3 gene is frequently mutated in Acute Myeloid Leukemia patients, and resulting oncogenic variants of FLT3 with 'internal tandem duplications (FLT3ITD)' drive production of reactive oxygen in leukemic cells. FLT3 was moderately activated by treatment of intact cells with hydrogen peroxide. Conversely, FLT3ITD signaling was attenuated by cell treatments with agents inhibiting formation of reactive oxygen species. FLT3 and FLT3ITD incorporated DCP-Bio1, a reagent specifically reacting with sulfenic acid residues. Mutation of FLT3ITD cysteines 695 and 790 reduced DCP-Bio1 incorporation, suggesting that these sites are subject to oxidative modification. Functional characterization of individual FLT3ITD cysteine-to-serine mutants of all 8 cytoplasmic cysteines revealed phenotypes in kinase activity, signal transduction and cell transformation. Replacement of cysteines 681, 694, 695, 807, 925, and 945 attenuated signaling and blocked FLT3ITD-mediated cell transformation, whereas mutation of cysteine 790 enhanced activity of both FLT3ITD and wild-type FLT3. These effects were not related to altered FLT3ITD dimerization, but likely caused by changed intramolecular interactions. The findings identify the functional relevance of all cytoplasmic FLT3ITD cysteines, and indicate the potential for redox regulation of this clinically important oncoprotein.

Bicarbonate is essential for protein-tyrosine phosphatase 1B (PTP1B) oxidation and cellular signaling through EGF-triggered phosphorylation cascades

Protein-tyrosine phosphatases (PTPs) counteract protein tyrosine phosphorylation and cooperate with receptor-tyrosine kinases in the regulation of cell signaling. PTPs need to undergo oxidative inhibition for activation of cellular cascades of protein-tyrosine kinase phosphorylation following growth factor stimulation. It has remained enigmatic how such oxidation can occur in the presence of potent cellular reducing systems. Here, using in vitro biochemical assays with purified, recombinant protein, along with experiments in the adenocarcinoma cell line A431, we discovered that bicarbonate, which reacts with H₂O₂ to form the more reactive peroxymonocarbonate, potently facilitates H₂O₂-mediated PTP1B inactivation in the presence of thioredoxin reductase 1 (TrxR1), thioredoxin 1 (Trx1), and peroxiredoxin 2 (Prx2) together with NADPH. The cellular experiments revealed that intracellular bicarbonate proportionally dictates total protein phosphotyrosine levels obtained after stimulation with epidermal growth factor (EGF) and that bicarbonate levels directly correlate with the extent of PTP1B oxidation. In fact, EGF-induced cellular oxidation of PTP1B was completely dependent on the presence of bicarbonate. These results provide a plausible mechanism for PTP inactivation during cell signaling and explain long-standing observations that growth factor responses and protein phosphorylation cascades are intimately linked to the cellular acid-base balance.

Redox Signaling and Persistent Pulmonary Hypertension of the Newborn

Reactive oxygen species (ROS) are redox-signaling molecules that are critically involved in regulating endothelial cell functions, host defense, aging, and cellular adaptation. Mitochondria are the major sources of ROS and important sources of redox signaling in pulmonary circulation. It is becoming increasingly evident that increased mitochondrial oxidative stress and aberrant signaling through redox-sensitive pathways play a direct causative role in the pathogenesis of many cardiopulmonary disorders including persistent pulmonary hypertension of the newborn (PPHN). This chapter highlights redox signaling in endothelial cells, antioxidant defense mechanism, cell responses to oxidative stress, and their contributions to disease pathogenesis.

Altered Met receptor phosphorylation and LRP1-mediated uptake in cells lacking carbohydrate-dependent lysosomal targeting

Acid hydrolases utilize a carbohydrate-dependent mechanism for lysosomal targeting. These hydrolases acquire a mannose 6-phosphate tag by the action of the GlcNAc-1-phosphotransferase enzyme, allowing them to bind receptors and traffic to endosomes. Loss of GlcNAc-1-phosphotransferase results in hydrolase hypersecretion and profound lysosomal storage. Little, however, is known about how these cellular phenotypes affect the trafficking, activity, and localization of surface glycoproteins. To address this question, we profiled the abundance of surface glycoproteins in WT and CRISPR-mediated GNPTAB^-/- HeLa cells and identified changes in numerous glycoproteins, including the uptake receptor LRP1 and multiple receptor tyrosine kinases. Decreased cell surface LRP1 in GNPTAB^-/- cells corresponded with a reduction in its steady-state level and less amyloid-β-40 (Aβ40) peptide uptake. GNPTAB^-/- cells displayed elevated activation of several kinases including Met receptor. We found increased Met phosphorylation within both the kinase and the docking domains and observed that lower concentrations of pervanadate were needed to cause an increase in phospho-Met in GNPTAB^-/- cells. Together, these data suggested a decrease in the activity of the receptor and non-receptor protein-tyrosine phosphatases that down-regulate Met phosphorylation. GNPTAB^-/- cells exhibited elevated levels of reactive oxygen species, known to inactivate cell surface and cytosolic phosphatases by oxidation of active site cysteine residues. Consistent with this mode of action, peroxide treatment of parental HeLa cells elevated phospho-Met levels whereas antioxidant treatment of GNPTAB^-/- cells reduced phospho-Met levels. Collectively, these findings identify new mechanisms whereby impaired lysosomal targeting can impact the activity and recycling of receptors.

Molecular underpinnings of neurodegenerative disorders: striatal-enriched protein tyrosine phosphatase signaling and synaptic plasticity

This commentary focuses on potential molecular mechanisms related to the dysfunctional synaptic plasticity that is associated with neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Specifically, we focus on the role of striatal-enriched protein tyrosine phosphatase (STEP) in modulating synaptic function in these illnesses. STEP affects neuronal communication by opposing synaptic strengthening and does so by dephosphorylating several key substrates known to control synaptic signaling and plasticity. STEP levels are elevated in brains from patients with Alzheimer's and Parkinson's disease. Studies in model systems have found that high levels of STEP result in internalization of glutamate receptors as well as inactivation of ERK1/2, Fyn, Pyk2, and other STEP substrates necessary for the development of synaptic strengthening. We discuss the search for inhibitors of STEP activity that may offer potential treatments for neurocognitive disorders that are characterized by increased STEP activity. Future studies are needed to examine the mechanisms of differential and region-specific changes in STEP expression pattern, as such knowledge could lead to targeted therapies for disorders involving disrupted STEP activity.

Reversible oxidation controls the activity and oligomeric state of the mammalian phosphoglycolate phosphatase AUM

Redox-dependent switches of enzyme activity are emerging as important fine-tuning mechanisms in cell signaling. For example, protein tyrosine phosphatases employ a conserved cysteine residue for catalysis, which also renders them highly susceptible to reversible inactivation by oxidation. In contrast, haloacid dehalogenase (HAD)-type phosphatases perform catalysis via a phosphoaspartyltransferase reaction. The potential regulation of HAD phosphatases by reversible oxidation has not yet been explored. Here, we investigate the redox-sensitivity of the HAD-type phosphoglycolate phosphatase PGP, also known as AUM or glycerol-3-phosphate phosphatase. We show that recombinant, purified murine PGP is inhibited by oxidation and re-activated by reduction. We identify three reactive cysteine residues in the catalytic core domain of PGP (Cys35, Cys104 and Cys243) that mediate the reversible inhibition of PGP activity and the associated, redox-dependent conformational changes. Structural analysis suggests that Cys35 oxidation weakens van-der-Waals interactions with Thr67, a conserved catalytic residue required for substrate coordination. Cys104 and Cys243 form a redox-dependent disulfide bridge between the PGP catalytic core and cap domains, which may impair the open/close-dynamics of the catalytic cycle. In addition, we demonstrate that Cys297 in the PGP cap domain is essential for redox-dependent PGP oligomerization, and that PGP oxidation/oligomerization occurs in response to stimulation of cells with EGF. Finally, employing a modified cysteinyl-labeling assay, we show that cysteines of cellular PGP are transiently oxidized to sulfenic acids. Taken together, our findings establish that PGP, an aspartate-dependent HAD phosphatase, is transiently inactivated by reversible oxidation in cells.

Tailor-Made Protein Tyrosine Phosphatases: In Vitro Site-Directed Mutagenesis of PTEN and PTPRZ-B

In vitro site-directed mutagenesis (SDM) of protein tyrosine phosphatases (PTPs) is a commonly used approach to experimentally analyze PTP functions at the molecular and cellular level and to establish functional correlations with PTP alterations found in human disease. Here, using the tumor-suppressor PTEN and the receptor-type PTPRZ-B (short isoform from PTPRZ1 gene) phosphatases as examples, we provide a brief insight into the utility of specific mutations in the experimental analysis of PTP functions. We describe a standardized, rapid, and simple method of mutagenesis to perform single and multiple amino acid substitutions, as well as deletions of short nucleotide sequences, based on one-step inverse PCR and DpnI restriction enzyme treatment. This method of SDM is generally applicable to any other protein of interest.

ROS signaling and redox biology in endothelial cells

The purpose of this review is to provide an overview of redox mechanisms, sources and antioxidants that control signaling events in ECs. In particular, we describe which molecules are involved in redox signaling and how they influence the relationship between ECs and other vascular component with regard to angiogenesis. Recent and new tools to investigate physiological ROS signaling will be also discussed. Such findings are providing an overview of the ROS biology relevant for endothelial cells in the context of normal and pathological angiogenic conditions.

Protein S-glutathionylation: from current basics to targeted modifications

The interaction between antioxidant glutathione and the free thiol in susceptible cysteine residues of proteins leads to reversible protein S-glutathionylation. This reaction ensures cellular homeostasis control (as a common redox-dependent post-translational modification associated with signal transduction) and intervenes in oxidative stress-related cardiovascular pathology (as initiated by redox imbalance). The purpose of this review is to evaluate the recent knowledge on protein S-glutathionylation in terms of chemistry, broad cellular intervention, specific quantification, and potential for therapeutic exploitation. The data bases searched were Medline and PubMed, from 2009 to 2014 (term: glutathionylation). Protein S-glutathionylation ensures protection of protein thiols against irreversible over-oxidation, operates as a biological redox switch in both cell survival (influencing kinases and protein phosphatases pathways) and cell death (by potentiation of apoptosis), and cross-talks with phosphorylation and with S-nitrosylation. Collectively, protein S-glutathionylation appears as a valuable biomarker for oxidative stress, with potential for translation into novel therapeutic strategies.

Dephosphorylation of tyrosine 393 in argonaute 2 by protein tyrosine phosphatase 1B regulates gene silencing in oncogenic RAS-induced senescence

Oncogenic RAS (H-RAS(V12)) induces premature senescence in primary cells by triggering production of reactive oxygen species (ROS), but the molecular role of ROS in senescence remains elusive. We investigated whether inhibition of protein tyrosine phosphatases by ROS contributed to H-RAS(V12)-induced senescence. We identified protein tyrosine phosphatase 1B (PTP1B) as a major target of H-RAS(V12)-induced ROS. Inactivation of PTP1B was necessary and sufficient to induce premature senescence in H-RAS(V12)-expressing IMR90 fibroblasts. We identified phospho-Tyr 393 of argonaute 2 (AGO2) as a direct substrate of PTP1B. Phosphorylation of AGO2 at Tyr 393 inhibited loading with microRNAs (miRNAs) and thus miRNA-mediated gene silencing, which counteracted the function of H-RAS(V12)-induced oncogenic miRNAs. Overall, our data illustrate that premature senescence in H-RAS(V12)-transformed primary cells is a consequence of oxidative inactivation of PTP1B and inhibition of miRNA-mediated gene silencing.

Inhibitor of the tyrosine phosphatase STEP reverses cognitive deficits in a mouse model of Alzheimer's disease

STEP (STriatal-Enriched protein tyrosine Phosphatase) is a neuron-specific phosphatase that regulates N-methyl-D-aspartate receptor (NMDAR) and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR) trafficking, as well as ERK1/2, p38, Fyn, and Pyk2 activity. STEP is overactive in several neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease (AD). The increase in STEP activity likely disrupts synaptic function and contributes to the cognitive deficits in AD. AD mice lacking STEP have restored levels of glutamate receptors on synaptosomal membranes and improved cognitive function, results that suggest STEP as a novel therapeutic target for AD. Here we describe the first large-scale effort to identify and characterize small-molecule STEP inhibitors. We identified the benzopentathiepin 8-(trifluoromethyl)-1,2,3,4,5-benzopentathiepin-6-amine hydrochloride (known as TC-2153) as an inhibitor of STEP with an IC50 of 24.6 nM. TC-2153 represents a novel class of PTP inhibitors based upon a cyclic polysulfide pharmacophore that forms a reversible covalent bond with the catalytic cysteine in STEP. In cell-based secondary assays, TC-2153 increased tyrosine phosphorylation of STEP substrates ERK1/2, Pyk2, and GluN2B, and exhibited no toxicity in cortical cultures. Validation and specificity experiments performed in wild-type (WT) and STEP knockout (KO) cortical cells and in vivo in WT and STEP KO mice suggest specificity of inhibitors towards STEP compared to highly homologous tyrosine phosphatases. Furthermore, TC-2153 improved cognitive function in several cognitive tasks in 6- and 12-mo-old triple transgenic AD (3xTg-AD) mice, with no change in beta amyloid and phospho-tau levels.

Wild-type and mutant p53 differentially regulate NADPH oxidase 4 in TGF-β-mediated migration of human lung and breast epithelial cells

BACKGROUND

Transforming growth factor-beta (TGF-β) induces the epithelial-to-mesenchymal transition (EMT) leading to increased cell plasticity at the onset of cancer cell invasion and metastasis. Mechanisms involved in TGF-β-mediated EMT and cell motility are unclear. Recent studies showed that p53 affects TGF-β/SMAD3-mediated signalling, cell migration, and tumorigenesis. We previously demonstrated that Nox4, a Nox family NADPH oxidase, is a TGF-β/SMAD3-inducible source of reactive oxygen species (ROS) affecting cell migration and fibronectin expression, an EMT marker, in normal and metastatic breast epithelial cells. Our present study investigates the involvement of p53 in TGF-β-regulated Nox4 expression and cell migration.

METHODS

We investigated the effect of wild-type p53 (WT-p53) and mutant p53 proteins on TGF-β-regulated Nox4 expression and cell migration. Nox4 mRNA and protein, ROS production, cell migration, and focal adhesion kinase (FAK) activation were examined in three different cell models based on their p53 mutational status. H1299, a p53-null lung epithelial cell line, was used for heterologous expression of WT-p53 or mutant p53. In contrast, functional studies using siRNA-mediated knockdown of endogenous p53 were conducted in MDA-MB-231 metastatic breast epithelial cells that express p53-R280K and MCF-10A normal breast cells that have WT-p53.

RESULTS

We found that WT-p53 is a potent suppressor of TGF-β-induced Nox4, ROS production, and cell migration in p53-null lung epithelial (H1299) cells. In contrast, tumour-associated mutant p53 proteins (R175H or R280K) caused enhanced Nox4 expression and cell migration in both TGF-β-dependent and TGF-β-independent pathways. Moreover, knockdown of endogenous mutant p53 (R280K) in TGF-β-treated MDA-MB-231 metastatic breast epithelial cells resulted in decreased Nox4 protein and reduced phosphorylation of FAK, a key regulator of cell motility. Expression of WT-p53 or dominant-negative Nox4 decreased TGF-β-mediated FAK phosphorylation, whereas mutant p53 (R280K) increased phospho-FAK. Furthermore, knockdown of WT-p53 in MCF-10A normal breast epithelial cells increased basal Nox4 expression, whereas p53-R280K could override endogenous WT-p53 repression of Nox4. Remarkably, immunofluorescence analysis revealed MCF-10A cells expressing p53-R280K mutant showed an upregulation of Nox4 in both confluent and migrating cells.

CONCLUSIONS

Collectively, our findings define novel opposing functions for WT-p53 and mutant p53 proteins in regulating Nox4-dependent signalling in TGF-β-mediated cell motility.

Redox-mediated signal transduction by cardiovascular Nox NADPH oxidases

The only known function of the Nox family of NADPH oxidases is the production of reactive oxygen species (ROS). Some Nox enzymes show high tissue-specific expression and the ROS locally produced are required for synthesis of hormones or tissue components. In the cardiovascular system, Nox enzymes are low abundant and function as redox-modulators. By reacting with thiols, nitric oxide (NO) or trace metals, Nox-derived ROS elicit a plethora of cellular responses required for physiological growth factor signaling and the induction and adaptation to pathological processes. The interactions of Nox-derived ROS with signaling elements in the cardiovascular system are highly diverse and will be detailed in this article, which is part of a Special Issue entitled "Redox Signalling in the Cardiovascular System".

Redox molecular machines involved in tumor progression

SIGNIFICANCE

We herein review recent advances on the role exerted by protein redox machines engaged in tumor progression, focusing on cell adhesion and migration, regulation of transcriptional response, and tumor metabolic reprogramming, all features belonging to the new hallmarks of cancer.

RECENT ADVANCES

Several recent insights have reported that oxidative stress, either due to intracellular sources of oxidants, which are frequently deregulated in cancers or to microenvironment factors as hypoxia or stromal cell contact, plays a key role in tumor malignancy, as well as in metabolic pathways control. Indeed, many proteins behave as sensors of intracellular oxidative stress, including protein tyrosine kinases and phosphatases, transcription factors as p53, forkhead box class-Os, nuclear respiratory factor-2, nuclear factor-kB, hypoxia inducible factor, enzymes involved in glycolysis or penthose phosphate pathway as pyruvate kinase-M2 and adenylate monophosphate kinase, or DNA repair enzymes as Ataxia Teleangectasia Mutated. All these proteins have been reported to play essential roles during cancer progression and their sensitivity to oxidative stress has added new levels of complexity to the cancer field.

CRITICAL ISSUES

Main significant issues that need to be addressed in redox cancer biology are (i) sensitivity to a different level of oxidative stress of sensors, that is, they can respond to different oxidative insults/signals, and (ii) the real susceptibility of cancer cells to redox-based therapies due to the acknowledged plasticity of cancer cells to develop adoptive strategies.

FUTURE DIRECTIONS

Definitely, redox machines have the potentiality to develop into novel biomarkers and related target therapies should attain the goal of personalized medicine in the fight against cancer.

Receptor protein-tyrosine phosphatase α regulates focal adhesion kinase phosphorylation and ErbB2 oncoprotein-mediated mammary epithelial cell motility

We investigated the role of protein-tyrosine phosphatase α (PTPα) in regulating signaling by the ErbB2 oncoprotein in mammary epithelial cells. Using this model, we demonstrated that activation of ErbB2 led to the transient inactivation of PTPα, suggesting that attenuation of PTPα activity may contribute to enhanced ErbB2 signaling. Furthermore, RNAi-induced suppression of PTPα led to increased cell migration in an ErbB2-dependent manner. The ability of ErbB2 to increase cell motility in the absence of PTPα was characterized by prolonged interaction of GRB7 with ErbB2 and increased association of ErbB2 with a β1-integrin-rich complex, which depended on GRB7-SH2 domain interactions. Finally, suppression of PTPα resulted in increased phosphorylation of focal adhesion kinase on Tyr-407, which induced the recruitment of vinculin and the formation of a novel focal adhesion kinase complex in response to ErbB2 activation in mammary epithelial cells. Collectively, these results reveal a new role for PTPα in the regulation of motility of mammary epithelial cells in response to ErbB2 activation.

Selective activation of oxidized PTP1B by the thioredoxin system modulates PDGF-β receptor tyrosine kinase signaling

The inhibitory reversible oxidation of protein tyrosine phosphatases (PTPs) is an important regulatory mechanism in growth factor signaling. Studies on PTP oxidation have focused on pathways that increase or decrease reactive oxygen species levels and thereby affect PTP oxidation. The processes involved in reactivation of oxidized PTPs remain largely unknown. Here the role of the thioredoxin (Trx) system in reactivation of oxidized PTPs was analyzed using a combination of in vitro and cell-based assays. Cells lacking the major Trx reductase TrxR1 (Txnrd1(-/-)) displayed increased oxidation of PTP1B, whereas SHP2 oxidation was unchanged. Furthermore, in vivo-oxidized PTP1B was reduced by exogenously added Trx system components, whereas SHP2 oxidation remained unchanged. Trx1 reduced oxidized PTP1B in vitro but failed to reactivate oxidized SHP2. Interestingly, the alternative TrxR1 substrate TRP14 also reactivated oxidized PTP1B, but not SHP2. Txnrd1-depleted cells displayed increased phosphorylation of PDGF-β receptor, and an enhanced mitogenic response, after PDGF-BB stimulation. The TrxR inhibitor auranofin also increased PDGF-β receptor phosphorylation. This effect was not observed in cells specifically lacking PTP1B. Together these results demonstrate that the Trx system, including both Trx1 and TRP14, impacts differentially on the oxidation of individual PTPs, with a preference of PTP1B over SHP2 activation. The studies demonstrate a previously unrecognized pathway for selective redox-regulated control of receptor tyrosine kinase signaling.

Regulated expression of PTPRJ/CD148 and an antisense long noncoding RNA in macrophages by proinflammatory stimuli

PTPRJ/CD148 is a tyrosine phosphatase that has tumour suppressor-like activity. Quantitative PCR of various cells and tissues revealed that it is preferentially expressed in macrophage-enriched tissues. Within lymphoid tissues immunohistochemistry revealed that PTPRJ/CD148 co-localised with F4/80, indicating that macrophages most strongly express the protein. Macrophages express the highest basal level of ptprj, and this is elevated further by treatment with LPS and other Toll-like receptor ligands. In contrast, CSF-1 treatment reduced basal and stimulated Ptprj expression in human and mouse cells, and interferon also repressed Ptprj expression. We identified a 1006 nucleotide long noncoding RNA species, Ptprj-as1 that is transcribed antisense to Ptprj. Ptprj-as1 was highly expressed in macrophage-enriched tissue and was transiently induced by Toll-like receptor ligands with a similar time course to Ptprj. Finally, putative transcription factor binding sites in the promoter region of Ptprj were identified.

The anti-inflammatory compound BAY-11-7082 is a potent inhibitor of protein tyrosine phosphatases

The families of protein tyrosine phosphatases (PTPs) and protein tyrosine kinases (PTKs) function in a coordinated manner to regulate signal transduction events that are critical for cellular homeostasis. Aberrant tyrosine phosphorylation, resulting from disruption of either PTP or PTK function, has been shown to be the cause of major human diseases, including cancer and diabetes. Consequently, the characterization of small-molecule inhibitors of these kinases and phosphatases may not only provide molecular probes with which to define the significance of particular signaling events, but also may have therapeutic implications. BAY-11-7082 is an anti-inflammatory compound that has been reported to inhibit IκB kinase activity. The compound has an α,β-unsaturated electrophilic center, which confers the property of being a Michael acceptor; this suggests that it may react with nucleophilic cysteine-containing proteins, such as PTPs. In this study, we demonstrated that BAY-11-7082 was a potent, irreversible inhibitor of PTPs. Using mass spectrometry, we have shown that BAY-11-7082 inactivated PTPs by forming a covalent adduct with the active-site cysteine. Administration of the compound caused an increase in protein tyrosine phosphorylation in RAW 264 macrophages, similar to the effects of the generic PTP inhibitor sodium orthovanadate. These data illustrate that BAY-11-7082 is an effective pan-PTP inhibitor with cell permeability, revealing its potential as a new probe for chemical biology approaches to the study of PTP function. Furthermore, the data suggest that inhibition of PTP function may contribute to the many biological effects of BAY-11-7082 that have been reported to date.

New tricks from an old dog: mitochondrial redox signaling in cellular inflammation

Reactive oxygen species (ROS) such as superoxide (O(2)(-)) and hydrogen peroxide (H(2)O(2)) have long been implicated as pro-inflammatory, yet the sources of ROS and the molecular mechanisms by which they enhance inflammation have been less clear. Recent advances in the understanding of the molecular basis of inflammation mediated by the innate immune system have allowed these issues to be revisited. Although the Nox2 NADPH oxidases generate the bulk of ROS for antimicrobial host defense, recent studies have found that NADPH oxidase-dependent ROS production can actually dampen macrophage inflammatory responses to sterile pro-inflammatory stimuli. Instead, production of mitochondrial ROS has emerged as an important factor in both host defense and sterile inflammation. Excess mitochondrial ROS can be generated by either damage to the respiratory chain or by alterations of mitochondrial function such as those that increase membrane potential and reduce respiratory electron carriers. In autoinflammatory diseases, where key components of innate immune responses are activated by genetic mutations or environmental stimuli, inflammation has been found to be particularly sensitive to inhibition of mitochondrial ROS production. These findings have highlighted mitochondrial ROS as a novel generator of pro-inflammatory ROS and a potential therapeutic target in inflammatory diseases.

Regulation of A20 and other OTU deubiquitinases by reversible oxidation

Protein ubiquitination is a highly versatile post-translational modification that regulates as diverse processes as protein degradation and kinase activation. Deubiquitinases hydrolyse ubiquitin modifications from proteins and are hence key regulators of the ubiquitin system. Ovarian tumour deubiquitinases comprise a family of fourteen human enzymes, many of which regulate cellular signalling pathways. Ovarian tumour deubiquitinases are cysteine proteases that cleave polyubiquitin chains in vitro and in cells, but little is currently known about their regulation. Here we show that ovarian tumour deubiquitinases are susceptible to reversible oxidation of the catalytic cysteine residue. High-resolution crystal structures of the catalytic domain of A20 in four different oxidation states reveal that the reversible form of A20 oxidation is a cysteine sulphenic acid intermediate, which is stabilised by the architecture of the catalytic centre. Using chemical tools to detect sulphenic acid intermediates, we show that many ovarian tumour deubiquitinases undergo reversible oxidation upon treatment with H2O2, revealing a new mechanism to regulate deubiquitinase activity.

Cellular redox, epigenetics and diseases

Since the Central dogma of Molecular Biology was proposed about 40 years ago; our understanding of the intricacies of gene regulation has undergone tectonic shifts almost every decade. It is now widely accepted that the complexity of an organism is not directed by the sheer number of genes it carries but how they are decoded by a myriad of regulatory modules. Over the years, it has emerged that the organizations chromatins and its remodeling; splicing and polyadenylation of pre-mRNAs, stability and localization of mRNAs and modulation of their expression by non-coding and miRNAs play pivotal roles in metazoan gene expression. Nevertheless, in spite of tremendous progress in our understanding of all these mechanisms of gene regulation, the way these events are coordinated leading towards a highly defined proteome of a given cell type remains enigmatic. In that context, the structures of many metazoan genes cannot fully explain their pattern of expression in different tissues, especially during embryonic development and progression of various diseases. Further, numerous studies done during the past quarter of a century suggested that the heritable states of transcriptional activation or repression of a gene can be influenced by the covalent modifications of constituent bases and associated histones; its chromosomal context and long-range interactions between various chromosomal elements (Holliday 1987; Turner 1998; Lyon 1993). However, molecular dissection of these phenomena is largely unknown and is an exciting topic of research under the sub-discipline epigenetics (Gasser et al. 1998).

Annexin A1, formyl peptide receptor, and NOX1 orchestrate epithelial repair

N-formyl peptide receptors (FPRs) are critical regulators of host defense in phagocytes and are also expressed in epithelia. FPR signaling and function have been extensively studied in phagocytes, yet their functional biology in epithelia is poorly understood. We describe a novel intestinal epithelial FPR signaling pathway that is activated by an endogenous FPR ligand, annexin A1 (ANXA1), and its cleavage product Ac2-26, which mediate activation of ROS by an epithelial NADPH oxidase, NOX1. We show that epithelial cell migration was regulated by this signaling cascade through oxidative inactivation of the regulatory phosphatases PTEN and PTP-PEST, with consequent activation of focal adhesion kinase (FAK) and paxillin. In vivo studies using intestinal epithelial specific Nox1(-/-IEC) and AnxA1(-/-) mice demonstrated defects in intestinal mucosal wound repair, while systemic administration of ANXA1 promoted wound recovery in a NOX1-dependent fashion. Additionally, increased ANXA1 expression was observed in the intestinal epithelium and infiltrating leukocytes in the mucosa of ulcerative colitis patients compared with normal intestinal mucosa. Our findings delineate a novel epithelial FPR1/NOX1-dependent redox signaling pathway that promotes mucosal wound repair.

Redox regulation of cancer cell migration and invasion

Cancer cell migration and invasion are the initial steps in metastasis. Through a series of cellular events, including cytoskeletal remodeling resulting in phenotype changes and degradation of the extracellular matrix, cells are able to detach from the primary tumor and metastasize to distant sites. These changes occur in response to intracellular signaling mechanisms triggered via cell surface receptor stimulation or signal amplification within the cell. Amongst the active molecules that participate in relaying cellular signals are the reactive oxygen species (ROS). Initially identified to participate in defense mechanisms to ward off invading pathogens, ROS are now considered to have important roles in several other biological processes including cancer development. In this report, we review recent evidence pointing towards the involvement of ROS in tumor progression. We discuss the biology of ROS and their roles at different stages during the process of cancer cell migration and invasion.

Methods to monitor classical protein-tyrosine phosphatase oxidation

Reactive oxygen species (ROS), particularly hydrogen peroxide (H(2)O(2)), act as intracellular second messengers in many signaling pathways. Protein-tyrosine phosphatases (PTPs) are now believed to be important targets of ROS. PTPs contain a conserved catalytic cysteine with an unusually low pK(a). This property allows PTPs to execute nucleophilic attack on substrate phosphotyrosyl residues, but also renders them highly susceptible to oxidation. Reversible oxidation, which inactivates PTPs, is emerging as an important cellular regulatory mechanism and might contribute to human diseases, including cancer. Given their potential toxicity, it seems likely that ROS generation is highly controlled within cells to restrict oxidation to those PTPs that must be inactivated for signaling to proceed. Thus, identifying ROS-inactivated PTPs could be tantamount to finding the PTP(s) that critically regulate a specific signaling pathway. This article provides an overview of the methods currently available to identify and quantify PTP oxidation and outlines future challenges in redox signaling.

Redox balance dynamically regulates vascular growth and remodeling

Vascular growth and remodeling responses entail several complex biochemical, molecular, and cellular responses centered primarily on endothelial cell activation and function. Recent studies reveal that changes in endothelial cell redox status critically influence numerous cellular events that are important for vascular growth under different conditions. It has been known for some time that oxidative stress actively participates in many aspects of angiogenesis and vascular remodeling. Initial studies in this field were largely exploratory with minimal insight into specific molecular mechanisms and how these responses could be regulated. However, it is now clear that intracellular redox mechanisms involving hypoxia, NADPH oxidases (NOX), xanthine oxidase (XO), nitric oxide and its synthases, and intracellular antioxidant defense pathways collectively orchestrate a redox balance system whereby reactive oxygen and nitrogen species integrate cues controlling vascular growth and remodeling. In this review, we discuss key redox regulation pathways that are centrally important for vascular growth in tissue health and disease. Important unresolved questions and issues are also addressed that requires future investigation.

Mitochondrial thiols in antioxidant protection and redox signaling: distinct roles for glutathionylation and other thiol modifications

SIGNIFICANCE

The mitochondrial matrix contains much of the machinery at the heart of metabolism. This compartment is also exposed to a high and continual flux of superoxide, hydrogen peroxide, and related reactive species. To protect mitochondria from these sources of oxidative damage, there is an integrated set of thiol systems within the matrix comprising the thioredoxin/peroxiredoxin/methionine sulfoxide reductase pathways and the glutathione/glutathione peroxidase/glutathione-S-transferase/glutaredoxin pathways that in conjunction with protein thiols prevent much of this oxidative damage. In addition, the changes in the redox state of many components of these mitochondrial thiol systems may transduce and relay redox signals within and through the mitochondrial matrix to modulate the activity of biochemical processes.

RECENT ADVANCES

Here, mitochondrial thiol systems are reviewed, and areas of uncertainty are pointed out, focusing on recent developments in our understanding of their roles.

CRITICAL ISSUES

The areas of particular focus are on the multiple, overlapping roles of mitochondrial thiols and on understanding how these thiols contribute to both antioxidant defenses and redox signaling.

FUTURE DIRECTIONS

Recent technical progress in the identification and quantification of thiol modifications by redox proteomics means that many of the questions raised about the multiple roles of mitochondrial thiols can now be addressed.

Global proteomic assessment of the classical protein-tyrosine phosphatome and "Redoxome"

Protein-tyrosine phosphatases (PTPs), along with protein-tyrosine kinases, play key roles in cellular signaling. All Class I PTPs contain an essential active site cysteinyl residue, which executes a nucleophilic attack on substrate phosphotyrosyl residues. The high reactivity of the catalytic cysteine also predisposes PTPs to oxidation by reactive oxygen species, such as H(2)O(2). Reversible PTP oxidation is emerging as an important cellular regulatory mechanism and might contribute to diseases such as cancer. We exploited these unique features of PTP enzymology to develop proteomic methods, broadly applicable to cell and tissue samples, that enable the comprehensive identification and quantification of expressed classical PTPs (PTPome) and the oxidized subset of the PTPome (oxPTPome). We find that mouse and human cells and tissues, including cancer cells, display distinctive PTPomes and oxPTPomes, revealing additional levels of complexity in the regulation of protein-tyrosine phosphorylation in normal and malignant cells.

Regulation of protein tyrosine phosphatases by reversible oxidation

Oxidation of the catalytic cysteine of protein-tyrosine phosphatases (PTP), which leads to their reversible inactivation, has emerged as an important regulatory mechanism linking cellular tyrosine phosphorylation and signalling by reactive-oxygen or -nitrogen species (ROS, RNS). This review focuses on recent findings about the involved pathways, enzymes and biochemical mechanisms. Both the general cellular redox state and extracellular ligand-stimulated ROS production can cause PTP oxidation. Members of the PTP family differ in their intrinsic susceptibility to oxidation, and different types of oxidative modification of the PTP catalytic cysteine can occur. The role of PTP oxidation for physiological signalling processes as well as in different pathologies is described on the basis of well-investigated examples. Criteria to establish the causal involvement of PTP oxidation in a given process are proposed. A better understanding of mechanisms leading to selective PTP oxidation in a cellular context, and finding ways to pharmacologically modulate these pathways are important topics for future research.

Targeting the reversibly oxidized protein tyrosine phosphatase superfamily

Controlled production of reactive oxygen species leads to reversible oxidation of protein tyrosine phosphatases (PTPs) and has emerged as an important tier of regulation over phosphorylation-dependent signal transduction. We present a modified cysteinyl-labeling assay that detects reversible oxidation of members of each of the different PTP subclasses. Here, we describe the methods for enriching reversibly oxidized PTPs from complex protein extracts, illustrating the procedure in IMR90 fibroblasts.