Hsp90 regulates NADPH oxidase activity and is necessary for superoxide but not hydrogen peroxide production

NRROS negatively regulates reactive oxygen species during host defence and autoimmunity

Reactive oxygen species (ROS) produced by phagocytes are essential for host defence against bacterial and fungal infections. Individuals with defective ROS production machinery develop chronic granulomatous disease. Conversely, excessive ROS can cause collateral tissue damage during inflammatory processes and therefore needs to be tightly regulated. Here we describe a protein, we termed negative regulator of ROS (NRROS), which limits ROS generation by phagocytes during inflammatory responses. NRROS expression in phagocytes can be repressed by inflammatory signals. NRROS-deficient phagocytes produce increased ROS upon inflammatory challenges, and mice lacking NRROS in their phagocytes show enhanced bactericidal activity against Escherichia coli and Listeria monocytogenes. Conversely, these mice develop severe experimental autoimmune encephalomyelitis owing to oxidative tissue damage in the central nervous system. Mechanistically, NRROS is localized to the endoplasmic reticulum, where it directly interacts with nascent NOX2 (also known as gp91(phox) and encoded by Cybb) monomer, one of the membrane-bound subunits of the NADPH oxidase complex, and facilitates the degradation of NOX2 through the endoplasmic-reticulum-associated degradation pathway. Thus, NRROS provides a hitherto undefined mechanism for regulating ROS production--one that enables phagocytes to produce higher amounts of ROS, if required to control invading pathogens, while minimizing unwanted collateral tissue damage.

Regulation of NADPH oxidase 5 by protein kinase C isoforms

NADPH oxidase5 (Nox5) is a novel Nox isoform which has recently been recognized as having important roles in the pathogenesis of coronary artery disease, acute myocardial infarction, fetal ventricular septal defect and cancer. The activity of Nox5 and production of reactive oxygen species is regulated by intracellular calcium levels and phosphorylation. However, the kinases that phosphorylate Nox5 remain poorly understood. Previous studies have shown that the phosphorylation of Nox5 is PKC dependent, but this contention was based on the use of pharmacological inhibitors and the isoforms of PKC involved remain unknown. Thus, the major goals of this study were to determine whether PKC can directly regulate Nox5 phosphorylation and activity, to identify which isoforms are involved in the process, and to understand the functional significance of this pathway in disease. We found that a relatively specific PKCα inhibitor, Ro-32-0432, dose-dependently inhibited PMA-induced superoxide production from Nox5. PMA-stimulated Nox5 activity was significantly reduced in cells with genetic silencing of PKCα and PKCε, enhanced by loss of PKCδ and the silencing of PKCθ expression was without effect. A constitutively active form of PKCα robustly increased basal and PMA-stimulated Nox5 activity and promoted the phosphorylation of Nox5 on Ser490, Thr494, and Ser498. In contrast, constitutively active PKCε potently inhibited both basal and PMA-dependent Nox5 activity. Co-IP and in vitro kinase assay experiments demonstrated that PKCα directly binds to Nox5 and modifies Nox5 phosphorylation and activity. Exposure of endothelial cells to high glucose significantly increased PKCα activation, and enhanced Nox5 derived superoxide in a manner that was in prevented by a PKCα inhibitor, Go 6976. In summary, our study reveals that PKCα is the primary isoform mediating the activation of Nox5 and this maybe of significance in our understanding of the vascular complications of diabetes and other diseases with increased ROS production.

Curcumin: a double hit on malignant mesothelioma

Inflammation is a key mediator in the development of malignant mesothelioma, which has a dismal prognosis and poor therapeutic strategies. Curcumin, a naturally occurring polyphenol in turmeric, has been shown to possess anticarcinogenic properties through its anti-inflammatory effects. Inflammasomes, a component of inflammation, control the activation of caspase-1 leading to pyroptosis and processing of proinflammatory cytokines, interleukin (IL)-1β and IL-18. In the present study, we investigate the role of curcumin in pyroptotic cell death of malignant mesothelioma cells. Using in vitro models with mouse and human malignant mesothelioma cells, curcumin is shown to induce pyroptosis through activation of caspase-1 and increased release of high-mobility group box 1 (HMGB1) without processing of IL-1β and IL-18. Absence of IL-1β processing in response to curcumin-mediated caspase-1 activation is attributed to blockade of pro-IL-1β priming through inhibition of the NF-κB pathway. Furthermore, curcumin's cytotoxicity in malignant mesothelioma cells is demonstrated to be dependent on pyroptosis as inhibition of caspase-1 resulted in protection against curcumin-induced cell death. We also demonstrate that curcumin-mediated caspase-1 activation is oxidant dependent by using N-acetyl-L-cysteine (NAC) to inhibit pyroptosis. PCR array analysis using the human inflammasome template revealed that curcumin significantly downregulated levels of inflammasome-related gene expression involved in inflammation, e.g., NF-κB, toll-like receptors (TLR), and IL-1β. Our data indicate that curcumin has a double effect on malignant mesothelioma cells through induction of pyroptosis while subsequently protecting against inflammation.

New roles for old pathways? A circuitous relationship between reactive oxygen species and cyclo-oxygenase in hypertension

Elevated production of prostanoids from the constitutive (COX-1) or inducible (COX-2) cyclo-oxygenases has been involved in the alterations in vascular function, structure and mechanical properties observed in cardiovascular diseases, including hypertension. In addition, it is well known that production of ROS (reactive oxygen species) plays an important role in the impaired contractile and vasodilator responses, vascular remodelling and altered vascular mechanics of hypertension. Of particular interest is the cross-talk between NADPH oxidase and mitochondria, the main ROS sources in hypertension, which may represent a vicious feed-forward cycle of ROS production. In recent years, there is experimental evidence showing a relationship between ROS and COX-derived products. Thus ROS can activate COX and the COX/PG (prostaglandin) synthase pathways can induce ROS production through effects on different ROS generating enzymes. Additionally, recent evidence suggests that the COX-ROS axis might constitute a vicious circle of self-perpetuating vasoactive products that have a pathophysiological role in altered vascular contractile and dilator responses and hypertension development. The present review discusses the current knowledge on the role of oxidative stress and COX-derived prostanoids in the vascular alterations observed in hypertension, highlighting new findings indicating that these two pathways act in concert to induce vascular dysfunction.

Cytokine-induced oxidative stress in cardiac inflammation and heart failure-how the ubiquitin proteasome system targets this vicious cycle

The ubiquitin proteasome system (UPS) is critical for the regulation of many intracellular processes necessary for cell function and survival. The absolute requirement of the UPS for the maintenance of protein homeostasis and thereby for the regulation of protein quality control is reflected by the fact that deviation of proteasome function from the norm was reported in cardiovascular pathologies. Inflammation is a major factor contributing to cardiac pathology. Herein, cytokines induce protein translation and the production of free radicals, thereby challenging the cellular protein equilibrium. Here, we discuss current knowledge on the mechanisms of UPS-functional adaptation in response to oxidative stress in cardiac inflammation. The increasing pool of oxidant-damaged degradation-prone proteins in cardiac pathology accounts for the need for enhanced protein turnover by the UPS. This process is accomplished by an up-regulation of the ubiquitylation machinery and the induction of immunoproteasomes. Thereby, the inflamed heart muscle is cleared from accumulating misfolded proteins. Current advances on immunoproteasome-specific inhibitors in this field question the impact of the proteasome as a therapeutic target in heart failure.

NADPH Oxidases NOXs and DUOXs as putative targets for cancer therapy

Reactive oxygen species (ROS) form a class of molecules with both positive and negative impacts on cellular health. Negatively, ROS may react with cellular constituents including proteins, lipids, and DNA to generate an array of oxidative lesions. These lesions may compromise genome stability which is critical for long-term cellular homeostasis and healthy progeny. Paradoxically, ROS also function as strong signalling molecules that mediate various growth-related responses, so their presence is also essential for cellular metabolism. While ROS are generated in an unregulated manner by physical stresses such as exposure to ionizing radiation and biochemical malfunctions such as mitochondrial leakage, cells also contain the NADPH oxidases NOXs and DUOXs, which specifically generate ROS in a wide variety of tissues. While the NOXs/DUOXs may be involved in maintaining optimal cellular redox levels, there is also accumulating evidence that NADPH oxidases-derived ROS may elevate the risk for genomic instability and cancer. Cancer cells may produce high levels of ROS, and in some cases, the source of these ROS has been linked to NOX/DUOX deregulation as reported for prostate cancer (NOX1 and NOX5), melanoma and glioblastoma (NOX4) among others. In addition, recent studies reveal that targeting NADPH oxidases with NOXs inhibitors may impair tumor growth in vivo; indicating that these proteins may be useful targets in future clinical strategies to fight cancer. This review provides an overview of the current knowledge concerning these enzymes, their roles in cancer, and their potential as targets in future cancer therapies.

Neuroprotective mechanisms of the standardized extract of Bacopa monniera in a paraquat/diquat-mediated acute toxicity

Parkinson's disease (PD) is one of the most common age related neurodegenerative disease and affects millions of people worldwide. Strong evidence suggests a role for oxidative stress and mitochondrial dysfunctions in the pathogenesis of PD. Recent epidemiologic and toxicological studies have shown that environmental factors, especially herbicides such as paraquat and diquat represent one of the primary classes of neurotoxic agents associated with PD. The objective of our study was to investigate the neuroprotective effects of the standardized extract of Bacopa monniera (BM) against paraquat/diquat-induced toxicity and to elucidate the mechanisms underlying this protection. Our results showed that a pre-treatment with the BM extract, from 20.0μg/ml, protected the rat dopaminergic PC12 cell line against paraquat/diquat-induced toxicity in various cell survival assays. We demonstrated that BM pre-treatment, from 5.0μg/ml, could prevent the generation of intracellular reactive oxygen species (ROS), decreased mitochondrial superoxide levels and depolarized the mitochondria. BM pre-treatment also increased tyrosine hydroxylase (TH) levels and antioxidant defense systems such as γ-glutamylcysteine synthetase (γ-GCS) and thioredoxin1 (Trx1) levels. Furthermore, BM pre-treatment prevented the activation of Akt and heat shock protein90 (HSP90) proteins. Thus, our findings demonstrated that BM can protect PC12 cells through modulating cellular redox pathways which are altered in PD and could have a therapeutic application in the prevention of PD.

17-AAG kills intracellular Leishmania amazonensis while reducing inflammatory responses in infected macrophages

Background

Leishmaniasis is a neglected endemic disease with a broad spectrum of clinical manifestations. Pentavalent antimonials have been the treatment of choice for the past 70 years and, due to the emergence of resistant cases, the efficacy of these drugs has come under scrutiny. Second-line drugs are less efficacious, cause a range of side effects and can be costly. The formulation of new generations of drugs, especially in developing countries, has become mandatory.

Methodology/Principal Findings

We investigated the anti-leishmanial effect of 17-(allylamino)-17-demethoxygeldanamycin (17-AAG), an HSP90 inhibitor, in vitro. This inhibitor is currently in clinical trials for cancer treatment; however, its effects against intracellular Leishmania remain untested. Macrophages infected with L. amazonensis were treated with 17-AAG (25–500 nM) and parasite load was quantified using optical microscopy. Parasite load declined in 17-AAG-treated macrophages in a dose- and time-dependent manner. Intracellular parasite death became irreversible after 4 h of treatment with 17-AAG, and occurred independent of nitric oxide (NO) and superoxide (O₂⁻) production. Additionally, intracellular parasite viability was severely reduced after 48 h of treatment. Interestingly, treatment with 17-AAG reduced pro-inflammatory mediator production, including TNF-α, IL-6 and MCP-1, yet IL-12 remained unaffected. Electron microscopy revealed morphological alterations, such as double-membrane vacuoles and myelin figures at 24 and 48 h after 17-AAG treatment.

Conclusions/Significance

The HSP90 inhibitor, 17-AAG, possesses high potency under low dosage and reduces both pro-inflammatory and oxidative molecule production. Therefore, further studies are warranted to investigate this inhibitor’s potential in the development of new generations of anti-leishmanials.

From form to function: the role of Nox4 in the cardiovascular system

The NADPH oxidase (Nox) family of proteins is comprised of seven members, including Noxes1–5 and the Duoxes 1 and 2. Nox4 is readily distinguished from the other Nox isoforms by its high level of expression in cardiovascular tissues and unique enzymatic properties. Nox4 is constitutively active and the amount of reactive oxygen species (ROS) contributed by Nox4 is primarily regulated at the transcriptional level although there is recent evidence for post-translational control. Nox4 emits a different pattern of ROS and its subcellular localizations, tissue distribution and influence over signaling pathways is different from the other Nox enzymes. Previous investigations have revealed that Nox4 is involved in oxygen sensing, vasomotor control, cellular proliferation, differentiation, migration, apoptosis, senescence, fibrosis, and angiogenesis. Elevated expression of Nox4 has been reported in a number of cardiovascular diseases, including atherosclerosis, pulmonary fibrosis, and hypertension, cardiac failure and ischemic stroke. However, many important questions remain regarding the functional significance of Nox4 in health and disease, including the role of Nox4 subcellular localization and its downstream targets. The goal of this review is to summarize the recent literature on the genetic and enzymatic regulation, subcellular localization, signaling pathways, and the role of Nox4 in cardiovascular disease states.

Opposing actions of heat shock protein 90 and 70 regulate nicotinamide adenine dinucleotide phosphate oxidase stability and reactive oxygen species production

OBJECTIVE

Excessive reactive oxygen species contribute to vascular dysfunction. We have previously shown that heat shock protein (Hsp90) inhibitors potently suppress Nox 1 to 3 and 5, and the goals of this study were to identify how molecular chaperones regulate Nox function.

METHODS AND RESULTS

In vitro, protein expression of Nox 1 to 2, 5 was decreased by Hsp90 inhibitors in multiple cell types (human pulmonary artery endothelial cells, neutrophils, macrophages, and human saphenous vein). In mice treated with Hsp90 inhibitors, Nox1 expression was reduced in lung along with reduced reactive oxygen species from leukocytes. Elevated reactive oxygen species production in obese (db/db) aorta was suppressed by Hsp90 inhibition. Hsp90 inhibitors did not alter Nox5 micro RNA levels, and proteasome inhibition prevented Nox2 and 5 protein degradation and increased ubiquitin incorporation. Inhibition of Hsp90 upregulated the expression of Hsp70 and Hsp70-bound Nox2, 5 and promoted degradation. Silencing Hsp70 prevented Hsp90 inhibitor-mediated degradation of Nox5. The Hsp70-regulated ubiquitin ligase, carboxyl terminus of Hsp70-interacting protein (CHIP), also bound Nox5 and promoted increased Nox5 ubiquitination and degradation. The chaperone binding and ubiquitination domains of CHIP were required, and the silencing of CHIP blunted Hsp90 inhibitor-mediated degradation of Nox2 and 5.

CONCLUSIONS

We conclude that Hsp90 binds to and regulates Nox protein stability. These actions are opposed by Hsp70 and CHIP, which promote the ubiquitination and degradation of Nox proteins and reduce reactive oxygen species production.

The type of DUOX-dependent ROS production is dictated by defined sequences in DUOXA

A deliberate generation of ROS is now recognized to be achieved by specific NADPH oxidases (NOX). Dual oxidases (DUOXs) are Ca(2+)-activated NOXs and operate as H(2)O(2)-generators in various tissues. A tight regulation is however required to avoid ROS overproduction that can rapidly be harmful to biological systems. DUOX activator (DUOXA) proteins act as organizing elements for surface expression and activity of the DUOX enzymes. To study DUOX activation by the maturation factors, chimeric DUOXA proteins were generated by replacing particular domains between DUOXA1 and DUOXA2. Their impact on DUOX function and membrane expression were explored in a reconstituted heterologous cell system composed of COS-7 cells. We have shown that the COOH-terminal end of DUOXA1 is responsible for DUOX1-dependent H(2)O(2) generation. The NH(2)-terminal tail of DUOXA2 is critical to specify the type of ROS released by DUOX2, hydrogen peroxide or superoxide. Native DUOXA2 would constrain DUOX2 to produce H(2)O(2). However, alterations of the DUOXA2 NH(2)-terminal domain modify DUOX2 activity triggering superoxide leaking. Our results demonstrate that specific domains of the DUOX maturation factors promote the activation of DUOXs as well as the type of ROS generated by the oxidases.

The NOX toolbox: validating the role of NADPH oxidases in physiology and disease

Reactive oxygen species (ROS) are cellular signals but also disease triggers; their relative excess (oxidative stress) or shortage (reductive stress) compared to reducing equivalents are potentially deleterious. This may explain why antioxidants fail to combat diseases that correlate with oxidative stress. Instead, targeting of disease-relevant enzymatic ROS sources that leaves physiological ROS signaling unaffected may be more beneficial. NADPH oxidases are the only known enzyme family with the sole function to produce ROS. Of the catalytic NADPH oxidase subunits (NOX), NOX4 is the most widely distributed isoform. We provide here a critical review of the currently available experimental tools to assess the role of NOX and especially NOX4, i.e. knock-out mice, siRNAs, antibodies, and pharmacological inhibitors. We then focus on the characterization of the small molecule NADPH oxidase inhibitor, VAS2870, in vitro and in vivo, its specificity, selectivity, and possible mechanism of action. Finally, we discuss the validation of NOX4 as a potential therapeutic target for indications including stroke, heart failure, and fibrosis.

The 1027th target candidate in stroke: Will NADPH oxidase hold up?

As recently reviewed, 1026 neuroprotective drug candidates in stroke research have all failed on their road towards validation and clinical translation, reasons being quality issues in preclinical research and publication bias. Quality control guidelines for preclinical stroke studies have now been established. However, sufficient understanding of the underlying mechanisms of neuronal death after stroke that could be possibly translated into new therapies is lacking. One exception is the hypothesis that cellular death is mediated by oxidative stress. Oxidative stress is defined as an excess of reactive oxygen species (ROS) derived from different possible enzymatic sources. Among these, NADPH oxidases (NOX1-5) stand out as they represent the only known enzyme family that has no other function than to produce ROS. Based on data from different NOX knockout mouse models in ischemic stroke, the most relevant isoform appears to be NOX4. Here we discuss the state-of-the-art of this target with respect to stroke and open questions that need to be addressed on the path towards clinical translation.

Biochemistry, physiology, and pathophysiology of NADPH oxidases in the cardiovascular system

The NADPH oxidase (Nox) enzymes are critical mediators of cardiovascular physiology and pathophysiology. These proteins are expressed in virtually all cardiovascular cells, and regulate such diverse functions as differentiation, proliferation, apoptosis, senescence, inflammatory responses and oxygen sensing. They target a number of important signaling molecules, including kinases, phosphatases, transcription factors, ion channels, and proteins that regulate the cytoskeleton. Nox enzymes have been implicated in many different cardiovascular pathologies: atherosclerosis, hypertension, cardiac hypertrophy and remodeling, angiogenesis and collateral formation, stroke, and heart failure. In this review, we discuss in detail the biochemistry of Nox enzymes expressed in the cardiovascular system (Nox1, 2, 4, and 5), their roles in cardiovascular cell biology, and their contributions to disease development.

Nitric oxide reduces NADPH oxidase 5 (Nox5) activity by reversible S-nitrosylation

The NADPH oxidases (Noxs) are a family of transmembrane oxidoreductases that produce superoxide and other reactive oxygen species (ROS). Nox5 was the last of the conventional Nox isoforms to be identified and is a calcium-dependent enzyme that does not depend on accessory subunits for activation. Recently, Nox5 was shown to be expressed in human blood vessels and therefore the goal of this study was to determine whether nitric oxide (NO) can modulate Nox5 activity. Endogenously produced NO potently inhibited basal and stimulated Nox5 activity and this inhibition was reversible with chronic, but not acute, exposure to L-NAME. Nox5 activity was reduced by NO donors, iNOS, and eNOS and in endothelial cells and LPS-stimulated smooth muscle cells in a manner dependent on NO concentration. ROS production was diminished by NO in an isolated enzyme activity assay replete with surplus calcium and NADPH. There was no evidence for NO-dependent changes in tyrosine nitration, glutathiolation, or phosphorylation of Nox5. In contrast, there was evidence for the increased nitrosylation of Nox5 as determined by the biotin-switch assay and mass spectrometry. Four S-nitrosylation sites were identified and of these, mutation of C694 dramatically lowered Nox5 activity, NO sensitivity, and biotin labeling. Furthermore, coexpression of the denitrosylation enzymes thioredoxin 1 and GSNO reductase prevented NO-dependent inhibition of Nox5. The potency of NO against other Nox enzymes was in the order Nox1 ≥ Nox3 > Nox5 > Nox2, whereas Nox4 was refractory. Collectively, these results suggest that endogenously produced NO can directly S-nitrosylate and inhibit the activity of Nox5.

HSP90 inhibition by 17-DMAG attenuates oxidative stress in experimental atherosclerosis

AIMS

Reactive oxygen species (ROS) participate in atherogenesis through different mechanisms including oxidative stress and inflammation. Proteins implicated in both processes, such as mitogen-activated protein kinase kinase (MEK) and some NADPH oxidase (NOX) subunits, are heat shock protein-90 (HSP90) client proteins. In this work, we investigated the antioxidant properties of the HSP90 inhibitor, 17-dimethylaminoethylamino-17-demethoxygeldanamycin (17-DMAG) in experimental atherosclerosis.

METHODS AND RESULTS

Treatment of ApoE(-/-) mice with 17-DMAG (2 mg/kg every 2 days for 10 weeks) decreased ROS levels and extracellular signal-regulated kinase (ERK) activation in aortic plaques compared with control animals. Accordingly, treatment of rat vascular smooth muscle cells (VSMCs) with 17-DMAG increased HSP27 and HSP70 and inhibited ERK activation. Interestingly, 17-DMAG diminished NADPH oxidase dependent ROS production in VSMCs and monocytes. In addition, a marked reduction in NADPH oxidase dependent ROS production was observed with HSP90siRNA and the opposite pattern with HSP70siRNA. 17-DMAG also diminished the expression of Nox1 and Nox organizer-1 (Noxo1) in VSMCs and monocytes. Interestingly, 17-DMAG was able to modulate ROS-induced monocyte to macrophage differentiation. Finally, higher expression of Nox1 and Noxo1 was found in the inflammatory region of human atherosclerotic plaques, colocalizing with VSMCs, macrophages, and ROS-producing cells.

CONCLUSION

Our results suggest that HSP90 inhibitors interfere with oxidative stress and modulate experimental atherosclerosis development through reduction in pro-oxidative factors.

Expression and functional significance of NADPH oxidase 5 (Nox5) and its splice variants in human blood vessels

The expression and functional significance of NADPH oxidase 5 (Nox5) and its five isoforms in vascular cells is poorly understood. The goal of this study was to determine whether Nox5-α, -β, -δ, -γ, and -ε (short) are expressed in human blood vessels and evaluate their respective functions. Nox5 mRNA and protein were detected in human blood vessels, cultured human vascular smooth muscle (HVSMC) and endothelium, but not fibroblasts. The most abundant isoforms were α and β, whereas δ and γ were not detected. Nox5-α and -β produced reactive oxygen species (ROS), but -δ, -γ, and -ε were not catalytically active. Coexpression of the active Nox5 isoforms with inactive Nox5 variants suppressed ROS production, and coimmunoprecipitation revealed that Nox5-β binds the inactive ε variant, which may account for reduced ROS production. In HVSMC, angiotensin II, endothelin-1 and TNF-α increased endogenous Nox5 mRNA levels, while adenovirus-mediated overexpression of Nox5 promoted p38 MAPK, JAK2, JNK, and ERK1/2 phosphorylation in endothelial cells (EC), but only increased ERK1/2 phosphorylation in HVSMC. At higher levels of Nox5, there was evidence of increased apoptosis in EC, but not in HVSMC, as detected by the presence of cleaved caspase-3 and cleaved poly(ADP-ribose)polymerase. Although catalytically inactive, Nox5-ε potently activated ERK in HVSMC, and increased expression of Nox5-ε promoted HVSMC proliferation. Nox5 is expressed in human blood vessels. The Nox5-α and -β splice variants are the major isoforms that are expressed and the only variants capable of ROS production. Nox5-ε can inhibit Nox5 activity and activate ERK and HVSMC proliferation.