Novel redox-dependent regulation of NOX5 by the tyrosine kinase c-Abl

NADPH Oxidases: From Molecular Mechanisms to Current Inhibitors

NADPH oxidases (NOXs) form a family of electron-transporting membrane enzymes whose main function is reactive oxygen species (ROS) generation. Strong evidence suggests that ROS produced by NOX enzymes are major contributors to oxidative damage under pathologic conditions. Therefore, blocking the undesirable actions of these enzymes is a therapeutic strategy for treating various pathological disorders, such as cardiovascular diseases, inflammation, and cancer. To date, identification of selective NOX inhibitors is quite challenging, precluding a pharmacologic demonstration of NOX as therapeutic targets in vivo. The aim of this Perspective is to furnish an updated outlook about the small-molecule NOX inhibitors described over the last two decades. Structures, activities, and in vitro/in vivo specificity are discussed, as well as the main biological assays used.

Functional interactions between NADPH oxidase 5 and actin

NADPH oxidase 5 (NOX5) is a transmembrane oxidative signaling enzyme which produces superoxide in response to intracellular calcium flux. Increasing evidence indicates that NOX5 is involved in a variety of physiological processes as well as human disease, however, details of NOX5 signaling pathways and targets of NOX5 mediated oxidative modifications remain poorly resolved. Actin dynamics have previously been shown to be modulated by oxidative modification, however, a direct connection to NOX5 expression and activity has not been fully explored. Here we show that NOX5 and actin interact in the cell, and each modulate the activity of the other. Using actin effector molecules jasplakinolide, cytochalasin D and latrunculin A, we show that changes in actin dynamics affect NOX5 superoxide production. In tandem, NOX5 oxidatively modifies actin, and shifts the ratio of filamentous to monomeric actin. Finally, we show that knockdown of NOX5 in the pancreatic cancer cell line PSN-1 impairs cell migration. Together our findings indicate an important link between actin dynamics and oxidative signaling through NOX5.

Redox Regulation to Modulate Phosphorylation Events in Human Spermatozoa

Significance: Spermatozoa are complex and compartmentalized cells that undergo capacitation, a series of biochemical and morphological changes to acquire the ability to fertilize oocytes. Reactive oxygen species (ROS) have a prominent dual role in capacitation. At physiological levels, ROS regulate numerous cellular processes, including increases of cyclic adenosine monophosphate, calcium, and activation of phosphorylation events needed for capacitation. On the contrary, at high concentrations that do not impair sperm viability, ROS can cause loss of motility and inhibition of capacitation. Higher ROS concentrations promote oxidation of lipids, proteins, and DNA leading to cell death, and these damages have been associated with male infertility. Critical Issues: When incubated under specific conditions, spermatozoa can produce low and controlled amounts of ROS that are not harmful but instead regulate numerous cellular processes, including the phosphorylation of tyrosine, serine, and threonine residues in critical proteins needed for sperm capacitation. Here, we outline the complex redox signaling in human spermatozoa needed to achieve fertility and the role of ROS as physiological mediators that trigger phosphorylation cascades. Moreover, we illustrate the importance of various phosphoproteins in spermatozoa capacitation, viability, and hyperactive motility. Future Directions: Further studies to elucidate the different phosphorylation players during sperm capacitation and acrosome reaction (the regulated exocytotic event that releases proteolytic enzymes allowing the spermatozoon to penetrate the zona pellucida and fertilize the oocyte) are essential to understand how the spermatozoon acquires the fertilizing ability to fertilize the oocyte. This knowledge will serve to develop novel diagnostic tools and therapy for male infertility. Antioxid. Redox Signal. 37, 437-450.

Central role of c-Src in NOX5- mediated redox signalling in vascular smooth muscle cells in human hypertension

AIMS

NOX-derived reactive oxygen species (ROS) are mediators of signalling pathways implicated in vascular smooth muscle cell (VSMC) dysfunction in hypertension. Among the numerous redox-sensitive kinases important in VSMC regulation is c-Src. However, mechanisms linking NOX/ROS to c-Src are unclear, especially in the context of oxidative stress in hypertension. Here, we investigated the role of NOX-induced oxidative stress in VSMCs in human hypertension focusing on NOX5, and explored c-Src, as a putative intermediate connecting NOX5-ROS to downstream effector targets underlying VSMC dysfunction.

METHODS AND RESULTS

VSMC from arteries from normotensive (NT) and hypertensive (HT) subjects were studied. NOX1,2,4,5 expression, ROS generation, oxidation/phosphorylation of signalling molecules, and actin polymerization and migration were assessed in the absence and presence of NOX5 (melittin) and Src (PP2) inhibitors. NOX5 and p22phox-dependent NOXs (NOX1-4) were down-regulated using NOX5 siRNA and p22phox-siRNA approaches. As proof of concept in intact vessels, vascular function was assessed by myography in transgenic mice expressing human NOX5 in a VSMC-specific manner. In HT VSMCs, NOX5 was up-regulated, with associated oxidative stress, hyperoxidation (c-Src, peroxiredoxin, DJ-1), and hyperphosphorylation (c-Src, PKC, ERK1/2, MLC20) of signalling molecules. NOX5 siRNA reduced ROS generation in NT and HT subjects. NOX5 siRNA, but not p22phox-siRNA, blunted c-Src phosphorylation in HT VSMCs. NOX5 siRNA reduced phosphorylation of MLC20 and FAK in NT and HT. In p22phox- silenced HT VSMCs, Ang II-induced phosphorylation of MLC20 was increased, effects blocked by melittin and PP2. NOX5 and c-Src inhibition attenuated actin polymerization and migration in HT VSMCs. In NOX5 transgenic mice, vascular hypercontractilty was decreased by melittin and PP2.

CONCLUSION

We define NOX5/ROS/c-Src as a novel feedforward signalling network in human VSMCs. Amplification of this system in hypertension contributes to VSMC dysfunction. Dampening the NOX5/ROS/c-Src pathway may ameliorate hypertension-associated vascular injury.

Calmodulin binding to the dehydrogenase domain of NADPH oxidase 5 alters its oligomeric state

Superoxide generated by NADPH Oxidase 5 (Nox5) is regulated by Ca²⁺ through the interaction of its self-contained Ca²⁺ binding domain and dehydrogenase domain (DH). Recently, calmodulin (CaM) has been reported to enhance the Ca²⁺ sensitivity of Nox5 by binding to the CaM-binding domain sequence (CMBD), in which the interaction between CaM and Nox5 is largely unclear. Here, we used the CMBD peptide and truncated DH constructs, and separately studied their interaction with CaM by fluorescence, calorimetry, and dynamic light scattering. Our results revealed that each half-domain of CaM binds one CMBD peptide with a binding constant near 10⁶ M^-1 and a binding enthalpy change of −3.81 kcal/mol, consistent with an extended 1:2 CaM:CMBD structure. However, the recombinant truncated DH proteins exist as oligomers, possibly trimer and tetramer. The oligomeric states are concentration and salt dependent. CaM binding appears to stabilize the DH dimer complexed with CaM. The thermodynamics of CaM binding to the DH is comparable to the peptide-based study except that the near unity binding stoichiometry and a large conformational change were observed. Our result suggests that the oligomeric states of Nox5, mediated by its DH domain and CaM, may be important for its superoxide-generating activity.

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Calmodulin (CaM) binds two peptides corresponding to the CaM-binding domain (CMBD) in Nox5.

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Solution characterization suggests that the CMBD-bound Ca²⁺-CaM is in the extended form.

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The truncated dehydrogenase domains (DHs) were expressed as trimer and tetramer.

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The CaM binding to Nox5's DH kinetically stabilizes the dimer formation with unity stoichiometry.

Pathophysiology and Therapeutic Potential of NADPH Oxidases in Ischemic Stroke-Induced Oxidative Stress

Stroke is a leading cause of death and disability in humans. The excessive production of reactive oxygen species (ROS) is an important contributor to oxidative stress and secondary brain damage after stroke. Nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, an enzyme complex consisting of membrane subunits and cytoplasmic subunits, regulates neuronal maturation and cerebrovascular homeostasis. However, NADPH oxidase overproduction contributes to neurotoxicity and cerebrovascular disease. NADPH oxidase has been implicated as the principal source of ROS in the brain, and numerous studies have shown that the knockout of NADPH exerts a protective effect in the model of ischemic stroke. In this review, we summarize the mechanism of activation of the NADPH oxidase family members, the pathophysiological effects of NADPH oxidase isoforms in ischemic stroke, and the studies of NADPH oxidase inhibitors to explore potential clinical applications.

The protein kinase A negatively regulates reactive oxygen species production by phosphorylating gp91phox/NOX2 in human neutrophils

Superoxide anion production by neutrophils is essential for host defense against microbes. Superoxide anion generates other reactive oxygen species (ROS) that are very toxic for microbes and host cells, therefore their excessive production could induce inflammatory reactions and tissue injury. Cyclic adenosine monophosphate (cAMP) elevating agents are considered to be physiological inhibitors of superoxide production by neutrophils but the mechanisms involved in this inhibitory effect are poorly understood. Superoxide is produced by the phagocyte NADPH oxidase, a complex enzyme composed of two membrane subunits, gp91^phox or NOX2 and p22^phox, and four cytosolic components p47^phox, p67^phox, p40^phox, and Rac2. Except Rac2, these proteins are known to be phosphorylated upon neutrophil stimulation. Here we show that forskolin, an activator of the adenylate cyclase-cAMP-PKA pathway, induced phosphorylation of gp91phox/NOX2 and inhibited fMLF-induced NADPH oxidase activation in human neutrophils. H89, a PKA inhibitor prevented the forskolin-induced phosphorylation of gp91phox and restored NADPH oxidase activation. Furthermore, PKA phosphorylated the recombinant gp91phox/NOX2-cytosolic C-terminal region in vitro only on a few specific peptides containing serine residues, as compared to PKC. Interestingly, phosphorylation of NOX2-Cter by PKA alone did not induce interaction with the cytosolic components p47^phox, p67^phox and Rac2, however it induced inhibition of PKC-induced interaction. Furthermore, PKA alone did not induce NOX2 electron transfer activity, however it inhibited PKC-induced activation. These results suggest that PKA phosphorylates NOX2 in human neutrophils, a process essential to limit ROS production and inflammation under physiological conditions. Our data identify the cAMP-PKA-NOX2-axis as a critical gatekeeper of neutrophil ROS production.

Membranous NOX5-derived ROS oxidizes and activates local Src to promote malignancy of tumor cells

Reactive oxygen species (ROS) localized at the precise subcellular compartments are essential for regulating the activity of signaling proteins. Furthermore, ROS are master regulators of tumor malignant progression that respond to a diverse set of environmental stress, especially hypoxia. NADPH oxidases (NOXs) appear to be activated within discrete subcellular compartments to facilitate local ROS production. However, the subcellular function of NOXs in hypoxic tumor is still unclear. In this study, we demonstrated that NOX5 was greatly upregulated in clinical esophageal squamous cell carcinoma (ESCC) tumors, ESCC cell lines or primary ESCC cells, and elevated NOX5 was correlated to malignancy of ESCC tumors and poor prognosis. NOX5 induced the malignant progression of ESCC by activating Src, especially under hypoxic condition. Mechanistically, we showed that hypoxia promoted the interaction between NOX5 and Pyk2 on cell membrane via facilitating Ca²⁺-mediated Pyk2 Tyr⁴⁰² site phosphorylation. Subsequently, Pyk2 acted as a scaffold for c-Abl phosphorylating the catalytic domain of NOX5 Tyr^476/478 sites, which in turn upregulated hydrogen peroxide (H₂O₂) inside the Pyk2/NOX5 complex to oxidize and activate local Src. These findings provide insights into the biological significance of NOX5 in the development of ESCC.

Dynamic regulation of NADPH oxidase 5 by intracellular heme levels and cellular chaperones

NADPH oxidase 5 (NOX5) is a transmembrane signaling enzyme that produces superoxide in response to elevated cytosolic calcium. In addition to its association with numerous human diseases, NOX5 has recently been discovered to play crucial roles in the immune response and cardiovascular system. Details of NOX5 maturation, and specifically its response to changes in intracellular heme levels have remained unclear. Here we establish an experimental system in mammalian cells that allows us to probe the influence of heme availability on ROS production by NOX5. We identified a mode of dynamic regulatory control over NOX5 activity through modulation of its heme saturation and oligomeric state by intracellular heme levels and Hsp90 binding. This regulatory mechanism allows for fine-tuning and reversible modulation of NOX5 activity in response to stimuli.

On the mechanism of calcium-dependent activation of NADPH oxidase 5 (NOX5)

It is now accepted that reactive oxygen species (ROS) are not only dangerous oxidative agents but also chemical mediators of the redox cell signaling and innate immune response. A central role in ROS-controlled production is played by the NADPH oxidases (NOXs), a group of seven membrane-bound enzymes (NOX1-5 and DUOX1-2) whose unique function is to produce ROS. Here, we describe the regulation of NOX5, a widespread family member present in cyanobacteria, protists, plants, fungi, and the animal kingdom. We show that the calmodulin-like regulatory EF-domain of NOX5 is partially unfolded and detached from the rest of the protein in the absence of calcium. In the presence of calcium, the C-terminal lobe of the EF-domain acquires an ordered and more compact structure that enables its binding to the enzyme dehydrogenase (DH) domain. Our spectroscopic and mutagenesis studies further identified a set of conserved aspartate residues in the DH domain that are essential for NOX5 activation. Altogether, our work shows that calcium induces an unfolded-to-folded transition of the EF-domain that promotes direct interaction with a conserved regulatory region, resulting in NOX5 activation.

The potential effect of imatinib against hypercholesterolemia induced atherosclerosis, endothelial dysfunction and hepatic injury in rabbits

AIMS

Imatinib is an effective tyrosine kinase inhibitor which has different therapeutic actions. The recent work demonstrated the possible beneficial effects of imatinib on the progression of atherosclerosis, endothelial dysfunction, and hypercholesterolemia-associated liver damage in rabbits.

MAIN METHODS

Animals had been distributed in 4 groups: group 1 (non-treated): animals fed regular diet; group 2 high cholesterol [HC]: animals fed 1% cholesterol supplemented diet for 30 days; group 3 (HC-Imatinib): animals fed 1% cholesterol supplemented diet+imatinib (0.01 g/kg daily, p.o) for 30 days; group 4 (Imatinib): animals fed regular diet with imatinib (0.01 g/kg daily, p.o). After thirty days, tissue samples and blood were isolated to be detected biochemically, histologically, and for in vitro analysis.

KEY FINDINGS

HC exhibited significant elevations in serum lipid parameters, CRP, ALT, AST and ALP. Additionally, HC induced significant increases for aortic and hepatic MDA, aortic NO and hepatic PDGFR-β, while significantly exhibited reductions in aortic and hepatic GSH, SOD and hepatic PPARγ1. Moreover, HC produced impairment in ACh-enhanced aortic relaxation and aortic pathological changes. Histopathological examination of HC-fed rabbits revealed hepatic steatosis compared with non-treated group. Imatinib administration exhibited significant decreases in serum lipid parameters, CRP, ALT, AST and ALP. Additionally, imatinib induced significant decreases for aortic and hepatic MDA, aortic NO and hepatic PDGFR-β, while significantly exhibited elevations in aortic and hepatic GSH, SOD and hepatic PPARγ1 compared with HC animals. Furthermore, imatinib significantly protected against HC produced attenuation in ACh-induced aortic relaxation and pathological changes in aortic and hepatic tissues. Interestingly, imatinib could return serum CRP, ALP, hepatic SOD and PDGFR-β to basal values.

SIGNIFICANCE

The recent observation reports that imatinib could have beneficial effect against atherosclerosis progression, vascular malfunction, and liver damage in high cholesterol diet (HCD)-fed rabbits.

Calcium Signaling Commands Phagosome Maturation Process

Phagosome-lysosome (P-L) fusion is one of the central immune-effector responses of host. It is known that phagosome maturation process is associated with numerous signaling cascades and among these, important role of calcium (Ca²⁺) signaling has been realized recently. Ca²⁺ plays key roles in actin rearrangement, activation of NADPH oxidase and protein kinase C (PKC). Involvement of Ca²⁺ in these cellular processes directs phagosomal maturation process. Some of the intracellular pathogens have acquired the strategies to modulate Ca²⁺ associated pathways to block P-L fusion process. In this review we have described the mechanism of Ca²⁺ signals that influence P-L fusion by controlling ROS, actin and PKC signaling cascades. We have also discussed the strategies implemented by the intracellular pathogens to manipulate Ca²⁺ signaling to consequently subvert P-L fusion. A detail study of factors associated in manipulating Ca²⁺ signaling may provide new insights for the development of therapeutic tools for more effective treatment options against infectious diseases.

NADPH oxidase in the vasculature: Expression, regulation and signalling pathways; role in normal cardiovascular physiology and its dysregulation in hypertension

The last 20-25 years have seen an explosion of interest in the role of NADPH oxidase (NOX) in cardiovascular function and disease. In vascular smooth muscle and endothelium, NOX generates reactive oxygen species (ROS) that act as second messengers, contributing to the control of normal vascular function. NOX activity is altered in response to a variety of stimuli, including G-protein coupled receptor agonists, growth-factors, perfusion pressure, flow and hypoxia. NOX-derived ROS are involved in smooth muscle constriction, endothelium-dependent relaxation and smooth muscle growth, proliferation and migration, thus contributing to the fine-tuning of blood flow, arterial wall thickness and vascular resistance. Through reversible oxidative modification of target proteins, ROS regulate the activity of protein tyrosine phosphatases, kinases, G proteins, ion channels, cytoskeletal proteins and transcription factors. There is now considerable, but somewhat contradictory evidence that NOX contributes to the pathogenesis of hypertension through oxidative stress. Specific NOX isoforms have been implicated in endothelial dysfunction, hyper-contractility and vascular remodelling in various animal models of hypertension, pulmonary hypertension and pulmonary arterial hypertension, but also have potential protective effects, particularly NOX4. This review explores the multiplicity of NOX function in the healthy vasculature and the evidence for and against targeting NOX for antihypertensive therapy.

Evaluation of the NOX5 protein expression and oxidative stress in sperm from asthenozoospermic men compared to normozoospermic men

PURPOSE

NADPH oxidase 5 (NOX5), the main isoform of NOX in spermatozoa, has been recognized as the main active generators of reactive oxygen species (ROS), including superoxide anion (O ₂ ^-. ) and hydrogen peroxide (H₂O₂). ROS have been shown to play important roles in many physiological and pathological conditions in spermatozoa. The present study aims to investigate the alterations of NOX5 protein expression and oxidative stress (OS) status in asthenozoospermic men compared to normozoospermic men.

METHODS

Semen samples were collected from 25 asthenozoospermic men and 28 normozoospermic men. In this study, NOX5 protein expression was evaluated by Western blotting. An OS status was evaluated by measuring of ROS (O ₂ ^-. and H₂O₂), DNA damage and plasma membrane integrity in spermatozoa.

RESULTS

The protein expression of NOX5 (p < 0.0001) was remarkably higher in asthenozoospermic men in comparison to normozoospermic men. In addition, the percentages of intracellular O ₂ ^-. (p < 0.0001), H₂O₂ (p < 0.0001) in viable spermatozoa, apoptotic sperm cells with altered plasma membrane (p < 0.001) and DNA damage (p = 0.001) were significantly increased in asthenozoospermic men compared to normozoospermic men.

CONCLUSIONS

The present study provides evidence that the overexpression of NOX5 protein may induce excessive ROS production and oxidative stress damages to DNA and plasma membrane integrity in asthenozoospermic men.

Podocyte NADPH Oxidase 5 Promotes Renal Inflammation Regulated by the Toll-Like Receptor Pathway

AIMS

Oxidative stress associated with a proinflammatory state occurs in endothelial dysfunction, hypertension, chronic kidney disease, and diabetes. The NADPH oxidase (Nox) family of reactive oxygen species (ROS) generating enzymes is implicated in these processes, yet little information regarding the role of Nox5 is available. Our aim was to investigate the role of Nox5 in promoting renal inflammation and identify mechanisms regulating its activity.

RESULTS

Mice with podocyte-specific Nox5 (Nox5^pod+) expression demonstrated greater glomerular inflammation and increased expression of Toll-like receptors (TLRs) and proinflammatory cytokines. In a lipopolysaccharide (LPS) model of acute kidney injury, Nox5^pod+ and control littermates exhibited increased TLR and Nox1 expression. Compared with control littermates, Nox5^pod+ animals developed greater glomerular inflammation and ROS production. Immortalized human podocytes (hPODs) incubated with LPS demonstrated TLR induction, increased Nox5 expression, and enhanced ROS production. Inhibition of interleukin-1 receptor-associated kinases (IRAK)-1 and -4 that lie downstream of TLR inhibited LPS-induced ROS production. Interaction between IRAK1 and Nox5 was confirmed by coimmunoprecipitation. Furthermore, LPS treatment of hPODs resulted in phosphorylation of threonine residue(s) in Nox5 that was attenuated by an IRAK1/4 inhibitor. Innovation and Conclusion: These results are the first to demonstrate that Nox5 is a downstream target of the TLR pathway and that Nox5-derived ROS may be modulated by IRAK1/4 activity. Nox5-derived ROS in podocytes can promote a proinflammatory state in the kidney via induction of cytokine expression and upregulation of TLRs leading to a feed-forward loop in which TLR activation enhances Nox5-mediated ROS production.

NOX5: Molecular biology and pathophysiology

NEW FINDINGS

What is the topic of this review? This review provides a comprehensive overview of Nox5 from basic biology to human disease and highlights unique features of this Nox isoform What advances does it highlight? Major advances in Nox5 biology relate to crystallization of the molecule and new insights into the pathophysiological role of Nox5. Recent discoveries have unravelled the crystal structure of Nox5, the first Nox isoform to be crystalized. This provides new opportunities to develop drugs or small molecules targeted to Nox5 in an isoform-specific manner, possibly for therapeutic use. Moreover genome wide association studies (GWAS) identified Nox5 as a new blood pressure-associated gene and studies in mice expressing human Nox5 in a cell-specific manner have provided new information about the (patho) physiological role of Nox5 in the cardiovascular system and kidneys. Nox5 seems to be important in the regulation of vascular contraction and kidney function. In cardiovascular disease and diabetic nephropathy, Nox5 activity is increased and this is associated with increased production of reactive oxygen species and oxidative stress implicated in tissue damage.

ABSTRACT

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (Nox), comprise seven family members (Nox1-Nox5 and dual oxidase 1 and 2) and are major producers of reactive oxygen species in mammalian cells. Reactive oxygen species are crucially involved in cell signalling and function. All Noxs share structural homology comprising six transmembrane domains with two haem-binding regions and an NADPH-binding region on the intracellular C-terminus, whereas their regulatory systems, mechanisms of activation and tissue distribution differ. This explains the diverse function of Noxs. Of the Noxs, NOX5 is unique in that rodents lack the gene, it is regulated by Ca2+ , it does not require NADPH oxidase subunits for its activation, and it is not glycosylated. NOX5 localizes in the perinuclear and endoplasmic reticulum regions of cells and traffics to the cell membrane upon activation. It is tightly regulated through numerous post-translational modifications and is activated by vasoactive agents, growth factors and pro-inflammatory cytokines. The exact pathophysiological significance of NOX5 remains unclear, but it seems to be important in the physiological regulation of sperm motility, vascular contraction and lymphocyte differentiation, and NOX5 hyperactivation has been implicated in cardiovascular disease, kidney injury and cancer. The field of NOX5 biology is still in its infancy, but with new insights into its biochemistry and cellular regulation, discovery of the NOX5 crystal structure and genome-wide association studies implicating NOX5 in disease, the time is now ripe to advance NOX5 research. This review provides a comprehensive overview of our current understanding of NOX5, from basic biology to human disease, and highlights the unique characteristics of this enigmatic Nox isoform.

Vascular Biology of Superoxide-Generating NADPH Oxidase 5-Implications in Hypertension and Cardiovascular Disease

SIGNIFICANCE

NADPH oxidases (Noxs), of which there are seven isoforms (Nox1-5, Duox1/Duox2), are professional oxidases functioning as reactive oxygen species (ROS)-generating enzymes. ROS are signaling molecules important in physiological processes. Increased ROS production and altered redox signaling in the vascular system have been implicated in the pathophysiology of cardiovascular diseases, including hypertension, and have been attributed, in part, to increased Nox activity. Recent Advances: Nox1, Nox2, Nox4, and Nox5 are expressed and functionally active in human vascular cells. While Nox1, Nox2, and Nox4 have been well characterized in models of cardiovascular disease, little is known about Nox5. This may relate to the lack of experimental models because rodents lack NOX5. However, recent studies have advanced the field by (i) elucidating mechanisms of Nox5 regulation, (ii) identifying Nox5 variants, (iii) characterizing Nox5 expression, and (iv) discovering the Nox5 crystal structure. Moreover, studies in human Nox5-expressing mice have highlighted a putative role for Nox5 in cardiovascular disease.

CRITICAL ISSUES

Although growing evidence indicates a role for Nox-derived ROS in cardiovascular (patho)physiology, the exact function of each isoform remains unclear. This is especially true for Nox5.

FUTURE DIRECTIONS

Future directions should focus on clinically relevant studies to discover the functional significance of Noxs, and Nox5 in particular, in human health and disease. Two important recent studies will impact future directions. First, Nox5 is the first Nox to be crystallized. Second, a genome-wide association study identified Nox5 as a novel blood pressure-associated gene. These discoveries, together with advancements in Nox5 biology and biochemistry, will facilitate discovery of drugs that selectively target Noxs to interfere in uncontrolled ROS generation.

Carcinogenesis and Reactive Oxygen Species Signaling: Interaction of the NADPH Oxidase NOX1-5 and Superoxide Dismutase 1-3 Signal Transduction Pathways

SIGNIFICANCE

Reduction/oxidation (redox) balance could be defined as an even distribution of reduction and oxidation complementary processes and their reaction end products. There is a consensus that aberrant levels of reactive oxygen species (ROS), commonly observed in cancer, stimulate primary cell immortalization and progression of carcinogenesis. However, the mechanism how different ROS regulate redox balance is not completely understood. Recent Advances: In the current review, we have summarized the main signaling cascades inducing NADPH oxidase NOX1-5 and superoxide dismutase (SOD) 1-3 expression and their connection to cell proliferation, immortalization, transformation, and CD34+ cell differentiation in thyroid, colon, lung, breast, and hematological cancers.

CRITICAL ISSUES

Interestingly, many of the signaling pathways activating redox enzymes or mediating the effect of ROS are common, such as pathways initiated from G protein-coupled receptors and tyrosine kinase receptors involving protein kinase A, phospholipase C, calcium, and small GTPase signaling molecules.

FUTURE DIRECTIONS

The clarification of interaction of signal transduction pathways could explain how cells regulate redox balance and may even provide means to inhibit the accumulation of harmful levels of ROS in human pathologies.

Regulation of NADPH Oxidases by G Protein-Coupled Receptors

SIGNIFICANCE

G protein-coupled receptors (GPCR) are the largest group of cell surface receptors, which link cells to their environment. Reactive oxygen species (ROS) can act as important cellular signaling molecules. The family of NADPH oxidases generates ROS in response to activated cell surface receptors. Recent Advances: Various signaling pathways linking GPCRs and activation of NADPH oxidases have been characterized.

CRITICAL ISSUES

Still, a more detailed analysis of G proteins involved in the GPCR-mediated activation of NADPH oxidases is needed. In addition, a more precise discrimination of NADPH oxidase activation due to either upregulation of subunit expression or post-translational subunit modifications is needed. Also, the role of noncanonical modulators of NADPH oxidase activation in the response to GPCRs awaits further analyses.

FUTURE DIRECTIONS

As GPCRs are one of the most popular classes of investigational drug targets, further detailing of G protein-coupled mechanisms in the activation mechanism of NADPH oxidases as well as better understanding of the link between newly identified NADPH oxidase interaction partners and GPCR signaling will provide new opportunities for improved efficiency and decreased off target effects of therapies targeting GPCRs.

Guidelines for the Detection of NADPH Oxidases by Immunoblot and RT-qPCR

The identification of NADPH oxidase (NOX) isoforms in tissues is essential for interpreting experiments and for next step decisions regarding cell lines, animal models, and targeted drug design. Two basic methods, immunoblotting and reverse transcriptase-quantitative polymerase chain reaction (RT-qPCR), are important to monitor NOX protein and messenger RNA (mRNA) levels, respectively, for a range of investigations from understanding cell signaling events to judging NOX inhibitor efficacies. For many other genes that are expressed in high abundance, these methods may seem rather simple. However, detecting the low expression levels of endogenous NOX/DUOX is difficult and can be frustrating, so some guidelines would be helpful to those who are facing difficulties. One reason why detection is so difficult is the limited availability of vetted NOX/DUOX antibodies. Many of the commercial antibodies do not perform well in our hands, and dependable antibodies, often generated by academic laboratories, are in limited supply. Another problem is the growing trend in the NOX literature to omit end-user validation of antibodies by not providing appropriate positive and negative controls. With regard to NOX mRNA levels, knockdown of NOX/DUOX has been reported in cell lines with very low endogenous expression (C _q values ≥30) or in cell lines devoid of the targeted NOX isoform (e.g., NOX4 expression in NCI-60 cancer cell panel cell line 786-0). These publications propagate misinformation and hinder progress in understanding NOX/DUOX function. This chapter provides overdue guidelines on how to validate a NOX antibody and provides general methodologies to prepare samples for optimal detection. It also includes validated methodology to perform RT-qPCR for the measurement of NOX mRNA levels, and we suggest that RT-qPCR should be performed prior to embarking on NOX protein detection.

The Molecular Regulation and Functional Roles of NOX5

NOX (NADPH oxidases) are a family of NADPH-dependent transmembrane enzymes that synthesize superoxide and other reactive oxygen species. There are seven isoforms (NOX1-5 and DUOX1-2) which derive from a common ancestral NOX. NOX enzymes are distinguished by different modes of activation, the types of ROS that are produced, the cell types where they are expressed, and distinct functional roles. NOX5 was one of the earliest eukaryotic Nox enzymes to evolve and ironically the last isoform to be discovered in humans. In the time since its discovery, our knowledge of the regulation of NOX5 has expanded tremendously, and we now have a more comprehensive understanding of the molecular mechanisms underlying NOX5-dependent ROS production. In contrast, the cell types where NOX5 is robustly expressed and its functional significance in health and disease remain an underdeveloped area. The goal of this chapter is to provide an up-to-date overview of the mechanisms regulating NOX5 function and its importance in human physiology and pathophysiology.

Nox2 Activity Is Required in Obesity-Mediated Alteration of Bone Remodeling

Despite increasing evidence suggesting a role for NADPH oxidases (Nox) in bone pathophysiology, whether Nox enzymes contribute to obesity-mediated bone remodeling remains to be clearly elucidated. Nox2 is one of the predominant Nox enzymes expressed in the bone marrow microenvironment and is a major source of ROS generation during inflammatory processes. It is also well recognized that a high-fat diet (HFD) induces obesity, which negatively impacts bone remodeling. In this work, we investigated the effect of Nox2 loss of function on obesity-mediated alteration of bone remodeling using wild-type (WT) and Nox2-knockout (KO) mice fed with a standard lab chow diet (SD) as a control or a HFD as an obesity model. Bone mineral density (BMD) of mice was assessed at the beginning and after 3 months of feeding with SD or HFD. Our results show that HFD increased bone mineral density to a greater extent in KO mice than in WT mice without affecting the total body weight and fat mass. HFD also significantly increased the number of adipocytes in the bone marrow microenvironment of WT mice as compared to KO mice. The bone levels of proinflammatory cytokines and proosteoclastogenic factors were also significantly elevated in WT-HFD mice as compared to KO-HFD mice. Furthermore, the in vitro differentiation of bone marrow cells into osteoclasts was significantly increased when using bone marrow cells from WT-HFD mice as compared to KO-HFD mice. Our data collectively suggest that Nox2 is implicated in HFD-induced deleterious bone remodeling by enhancing bone marrow adipogenesis and osteoclastogenesis.

Stressing the (Epi)Genome: Dealing with Reactive Oxygen Species in Cancer

SIGNIFICANCE

Growing evidence indicates cross-talk between reactive oxygen species (ROS) and several key epigenetic processes such as DNA methylation, histone modifications, and miRNAs in normal physiology and human pathologies including cancer. This review focuses on how ROS-induced oxidative stress, metabolic intermediates, and epigenetic processes influence each other in various cancers. Recent Advances: ROS alter chromatin structure and metabolism that impact the epigenetic landscape in cancer cells. Several site-specific DNA methylation changes have been identified in different cancers and are discussed in the review. We also discuss the interplay of epigenetic enzymes and miRNAs in influencing malignant transformation in an ROS-dependent manner.

CRITICAL ISSUES

Loss of ROS-mediated signaling mostly by epigenetic regulation may promote tumorigenesis. In contrast, augmented oxidative stress because of high ROS levels may precipitate epigenetic alterations to effect various phases of carcinogenesis. We address both aspects in the review.

FUTURE DIRECTIONS

Several drugs targeting ROS are under various stages of clinical development. Recent analysis of human cancers has revealed pervasive deregulation of the epigenetic machinery. Thus, a better understanding of the cross-talk between ROS and epigenetic alterations in cancer could lead to the identification of new drug targets and more effective treatment modalities.

T Cell Receptor-Independent, CD31/IL-17A-Driven Inflammatory Axis Shapes Synovitis in Juvenile Idiopathic Arthritis

T cells are considered autoimmune effectors in juvenile idiopathic arthritis (JIA), but the antigenic cause of arthritis remains elusive. Since T cells comprise a significant proportion of joint-infiltrating cells, we examined whether the environment in the joint could be shaped through the inflammatory activation by T cells that is independent of conventional TCR signaling. We focused on the analysis of synovial fluid (SF) collected from children with oligoarticular and rheumatoid factor-negative polyarticular JIA. Cytokine profiling of SF showed dominance of five molecules including IL-17A. Cytometric analysis of the same SF samples showed enrichment of αβT cells that lacked both CD4 and CD8 co-receptors [herein called double negative (DN) T cells] and also lacked the CD28 costimulatory receptor. However, these synovial αβT cells expressed high levels of CD31, an adhesion molecule that is normally employed by granulocytes when they transit to sites of injury. In receptor crosslinking assays, ligation of CD31 alone on synovial CD28^nullCD31⁺ DN αβT cells effectively and sufficiently induced phosphorylation of signaling substrates and increased intracytoplasmic stores of cytokines including IL-17A. CD31 ligation was also sufficient to induce RORγT expression and trans-activation of the IL-17A promoter. In addition to T cells, SF contained fibrocyte-like cells (FLC) expressing IL-17 receptor A (IL-17RA) and CD38, a known ligand for CD31. Stimulation of FLC with IL-17A led to CD38 upregulation, and to production of cytokines and tissue-destructive molecules. Addition of an oxidoreductase analog to the bioassays suppressed the CD31-driven IL-17A production by T cells. It also suppressed the downstream IL-17A-mediated production of effectors by FLC. The levels of suppression of FLC effector activities by the oxidoreductase analog were comparable to those seen with corticosteroid and/or biologic inhibitors to IL-6 and TNFα. Collectively, our data suggest that activation of a CD31-driven, αβTCR-independent, IL-17A-mediated T cell-FLC inflammatory circuit drives and/or perpetuates synovitis. With the notable finding that the oxidoreductase mimic suppresses the effector activities of synovial CD31⁺CD28^null αβT cells and IL-17RA⁺CD38⁺ FLC, this small molecule could be used to probe further the intricacies of this inflammatory circuit. Such bioactivities of this small molecule also provide rationale for new translational avenue(s) to potentially modulate JIA synovitis.

A data mining approach for identifying pathway-gene biomarkers for predicting clinical outcome: A case study of erlotinib and sorafenib

A novel data mining procedure is proposed for identifying potential pathway-gene biomarkers from preclinical drug sensitivity data for predicting clinical responses to erlotinib or sorafenib. The analysis applies linear ridge regression modeling to generate a small (N~1000) set of baseline gene expressions that jointly yield quality predictions of preclinical drug sensitivity data and clinical responses. Standard clustering of the pathway-gene combinations from gene set enrichment analysis of this initial gene set, according to their shared appearance in molecular function pathways, yields a reduced (N~300) set of potential pathway-gene biomarkers. A modified method for quantifying pathway fitness is used to determine smaller numbers of over and under expressed genes that correspond with favorable and unfavorable clinical responses. Detailed literature-based evidence is provided in support of the roles of these under and over expressed genes in compound efficacy. RandomForest analysis of potential pathway-gene biomarkers finds average treatment prediction errors of 10% and 22%, respectively, for patients receiving erlotinib or sorafenib that had a favorable clinical response. Higher errors were found for both compounds when predicting an unfavorable clinical response. Collectively these results suggest complementary roles for biomarker genes and biomarker pathways when predicting clinical responses from preclinical data.

The emerging role of NADPH oxidase NOX5 in vascular disease

Oxidative stress is a consequence of up-regulation of pro-oxidant enzyme-induced reactive oxygen species (ROS) production and concomitant depletion of antioxidants. Elevated levels of ROS act as an intermediate and are the common denominator for various diseases including diabetes-associated macro-/micro-vascular complications and hypertension. A range of enzymes are capable of generating ROS, but the pro-oxidant enzyme family, nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs), are the only enzymes known to be solely dedicated to ROS generation in the vascular tissues, kidney, aortas and eyes. While there is convincing evidence for a role of NOX1 in vascular and eye disease and for NOX4 in renal injury, the role of NOX5 in disease is less clear. Although NOX5 is highly up-regulated in humans in disease, it is absent in rodents. Thus, so far it has not been possible to study NOX5 in traditional mouse or rat models of disease. In the present review, we summarize and critically analyse the emerging evidence for a pathophysiological role of NOX5 in disease including the expression, regulation and molecular and cellular mechanisms which have been demonstrated to be involved in NOX5 activation.

NOX5-L can stimulate proliferation and apoptosis depending on its levels and cellular context, determining cancer cell susceptibility to cisplatin

The NADPH oxidase, NOX5, is known to stimulate cell proliferation in some cancers by generating reactive oxygen species (ROS). We show here that the long form of NOX5 (NOX5-L) also promotes cell death, and thus determines the balance of proliferation and death, in skin, breast and lung cancer cells. Moderate expression of NOX5-L induced cell proliferation accompanied by AKT and ERK phosphorylation, whereas an increase in NOX5-L above a certain threshold promoted cancer cell death accompanied by caspase-3 activation. Notably, cisplatin treatment increased NOX5-L levels through CREB activation and enhanced NOX5-L activity through augmentation of Ca²⁺ release and c-Abl expression, ultimately triggering ROS-mediated cancer cell death—a distinct pathway absent in normal cells. These results indicate that NOX5-L determines cellular responses in a concentration- and context-dependent manner.

Diabetes and Kidney Disease: Role of Oxidative Stress

Intrarenal oxidative stress plays a critical role in the initiation and progression of diabetic kidney disease (DKD). Enhanced oxidative stress results from overproduction of reactive oxygen species (ROS) in the context of concomitant, insufficient antioxidant pathways. Renal ROS production in diabetes is predominantly mediated by various NADPH oxidases (NOXs), but a defective antioxidant system as well as mitochondrial dysfunction may also contribute. Recent Advances: Effective agents targeting the source of ROS generation hold the promise to rescue the kidney from oxidative damage and prevent subsequent progression of DKD. Critical Issues and Future Directions: In the present review, we summarize and critically analyze molecular and cellular mechanisms that have been demonstrated to be involved in NOX-induced renal injury in diabetes, with particular focus on the role of increased glomerular injury, the development of albuminuria, and tubulointerstitial fibrosis, as well as mitochondrial dysfunction. Furthermore, novel agents targeting NOX isoforms are discussed. Antioxid. Redox Signal. 25, 657-684.

Regulation of breast tumorigenesis through acid sensors

The low extracellular pH in the microenvironment has been shown to promote tumor growth and metastasis; however, the underlying mechanism is poorly understood. Particularly, little is known how the tumor cell senses the acidic signal to activate the acidosis-mediated signaling. In this study, we show that breast cancer cells express acid-sensing ion channel 1 (ASIC1), a proton-gated cation channel primarily expressed in the nervous system. RNA interference, knockout and rescue experiments demonstrate a critical role for ASIC1 in acidosis-induced reactive oxidative species and NF-κB activation, two key events for tumorigenesis. Mechanistically, ASIC1 is required for acidosis-mediated signaling through calcium influx. We show that as a cytoplasmic membrane protein, ASIC1 is also associated with mitochondria, suggesting that ASIC1 may regulate mitochondrial calcium influx. Importantly, interrogation of the Cancer Genome Atlas breast invasive carcinoma data set indicates that alterations of ASIC1 alone or combined with other 4 ASIC genes are significantly correlated with poor patient survival. Furthermore, ASIC1 inhibitors cause a significant reduction of tumor growth and tumor load. Together, these results suggest that ASIC1 contributes to breast cancer pathogenesis in response to acidic tumor microenvironments, and ASIC1 may serve as a prognostic marker and a therapeutic target for breast cancer.

Oxidation of Са2+-Binding Domain of NADPH Oxidase 5 (NOX5): Toward Understanding the Mechanism of Inactivation of NOX5 by ROS

NOX5 protein, one of the most active generators of reactive oxygen species (ROS), plays an important role in many processes, including regulation of cell growth, death and differentiation. Because of its central role in ROS generation, it needs to be tightly regulated to guarantee cellular homeostasis. Contrary to other members of NADPH-oxidases family, NOX5 has its own regulatory calcium-binding domain and thus could be activated directly by calcium ions. While several mechanisms of activation have been described, very little is known about the mechanisms that could prevent the overproduction of ROS by NOX5. In the present study using calorimetric methods and circular dichroism we found that oxidation of cysteine and methionine residues of NOX5 decreases binding of Ca²⁺ ions and perturbs both secondary and tertiary structure of protein. Our data strongly suggest that oxidation of calcium-binding domain of NOX5 could be implicated in its inactivation, serving as a possible defense mechanism against oxidative stress.

Redox signaling, Nox5 and vascular remodeling in hypertension

Purpose of review

Extensive data indicate a role for reactive oxygen species (ROS) and redox signaling in vascular damage in hypertension. However, molecular mechanisms underlying these processes remain unclear, but oxidative post-translational modification of vascular proteins is critical. This review discusses how proteins are oxidatively modified and how redox signaling influences vascular smooth muscle cell growth and vascular remodeling in hypertension. We also highlight Nox5 as a novel vascular ROS-generating oxidase.

Recent findings

Oxidative stress in hypertension leads to oxidative imbalance that affects vascular cell function through redox signaling. Many Nox isoforms produce ROS in the vascular wall, and recent findings show that Nox5 may be important in humans. ROS regulate signaling by numerous processes including cysteine oxidative post-translational modification such as S-nitrosylation, S-glutathionylation and sulfydration. In vascular smooth muscle cells, this influences cellular responses to oxidative stimuli promoting changes from a contractile to a proliferative phenotype.

Summary

In hypertension, Nox-induced ROS production is increased, leading to perturbed redox signaling through oxidative modifications of vascular proteins. This influences mitogenic signaling and cell cycle regulation, leading to altered cell growth and vascular remodeling in hypertension.

Nox5 stability and superoxide production is regulated by C-terminal binding of Hsp90 and CO-chaperones

Heat shock protein 90 (Hsp90) is a molecular chaperone that orchestrates the folding and stability of proteins that regulate cellular signaling, proliferation and inflammation. We have previously shown that Hsp90 controls the production of reactive oxygen species by modulating the activity of Noxes1-3 and 5, but not Nox4. The goal of the current study was to define the regions on Nox5 that bind Hsp90 and determine how Hsp90 regulates enzyme activity. In isolated enzyme activity assays, we found that Hsp90 inhibitors selectively decrease superoxide, but not hydrogen peroxide, production. The addition of Hsp90 alone only modestly increases Nox5 enzyme activity but in combination with the co-chaperones, Hsp70, HOP, Hsp40, and p23 it robustly stimulated superoxide, but not hydrogen peroxide, production. Proximity ligation assays reveal that Nox5 and Hsp90 interact in intact cells. In cell lysates using a co-IP approach, Hsp90 binds to Nox5 but not Nox4, and the degree of binding can be influenced by calcium-dependent stimuli. Inhibition of Hsp90 induced the degradation of full length, catalytically inactive and a C-terminal fragment (aa398-719) of Nox5. In contrast, inhibition of Hsp90 did not affect the expression levels of N-terminal fragments (aa1-550) suggesting that Hsp90 binding maintains the stability of C-terminal regions. In Co-IP assays, Hsp90 was bound only to the C-terminal region of Nox5. Further refinement using deletion analysis revealed that the region between aa490-550 mediates Hsp90 binding. Converse mapping experiments show that the C-terminal region of Nox5 bound to the M domain of Hsp90 (aa310-529). In addition to Hsp90, Nox5 bound other components of the foldosome including co-chaperones Hsp70, HOP, p23 and Hsp40. Silencing of HOP, Hsp40 and p23 reduced Nox5-dependent superoxide. In contrast, increased expression of Hsp70 decreased Nox5 activity whereas a mutant of Hsp70 failed to do so. Inhibition of Hsp90 results in the loss of higher molecular weight complexes of Nox5 and decreased interaction between monomers. Collectively these results show that the C-terminal region of Nox5 binds to the M domain of Hsp90 and that the binding of Hsp90 and select co-chaperones facilitate oligomerization and the efficient production of superoxide.

Amelioration of experimentally induced diabetic nephropathy and renal damage by nilotinib

Diabetes mellitus is an ever growing world-wide health problem. The patient has to stick to a firm life-long therapeutic regimen, otherwise diabetic complications will develop. Diabetic nephropathy (DN) is one of the most common diabetic complications and it requires careful medical attendance. Nilotinib hydrochloride is a protein tyrosine kinase inhibitor reported to have numerous therapeutic efficacies besides being an anticancer. In the current study, single I.P. streptozotocin (50 mg/kg) injection was used to induce type I diabetes mellitus in male Sprague-Dawley rats. After 8 weeks, significant deterioration of renal function with urinary excretion of nephrin, podocalyxin, and albumin was observed. Daily oral administration of nilotinib (20 mg/kg) for 8 weeks significantly improved signs of DN on all investigated scales. On a biochemical scale, kidney functions, albuminuria, urinary nephrin, podocalyxin excretion, and host oxidant/antioxidant balance significantly improved. Kidney content of nitric oxide, expression of toll-like receptors 4 and NF-κB/p65 activity significantly declined as well. On a histopathological scale, α-smooth muscle actin and nestin expression significantly declined. Meanwhile, area of fibrosis significantly declined as seen with significant reduction in accumulation of extracellular matrix components and kidney content of collagen. Ultimately, such improvements were accompanied by significant restoration of normal kidney physiology and function. In conclusion, nilotinib can hinder progression of DN through various mechanisms. Reduction of oxidative stress, enhancement of host antioxidant defense system, reduction of inflammation, angiogenesis, tissue hypoxia, and pro-fibrogenic biomarker expression can be implicated in the beneficial therapeutic outcome observed with nilotinib therapy.

The NADPH oxidase NOX5 protects against apoptosis in ALK-positive anaplastic large-cell lymphoma cell lines

Reactive oxygen species (ROS) are key modulators of apoptosis and carcinogenesis. One of the important sources of ROS is NADPH oxidases (NOXs). The isoform NOX5 is highly expressed in lymphoid tissues, but it has not been detected in any common Hodgkin or non-Hodgkin lymphoma cell lines. In diverse, nonlymphoid malignant cells NOX5 exerts an antiapoptotic effect. Apoptosis suppression is the hallmark feature of a rare type of lymphoma, termed anaplastic lymphoma kinase-positive (ALK(+)) anaplastic large-cell lymphoma (ALCL), and a major factor in the therapy resistance and relapse of ALK(+) ALCL tumors. We applied RT-PCR and Western blot analysis to detect NOX5 expression in three ALK(+) ALCL cell lines (Karpas-299, SR-786, SUP-M2). We investigated the role of NOX5 in apoptosis by small-interfering RNA (siRNA)-mediated gene silencing and chemical inhibition of NOX5 using FACS analysis and examining caspase 3 cleavage in Karpas-299 cells. We used immunohistochemistry to detect NOX5 in ALK(+) ALCL pediatric tumors. NOX5 mRNA was uniquely detected in ALK(+) ALCL cells, whereas cell lines of other lymphoma classes were devoid of NOX5. Transfection of NOX5-specific siRNA and chemical inhibition of NOX5 abrogated calcium-induced superoxide production and increased caspase 3-mediated apoptosis in Karpas-299 cells. Immunohistochemistry revealed focal NOX5 reactivity in pediatric ALK(+) ALCL tumor cells. These results indicate that NOX5-derived ROS contribute to apoptosis blockage in ALK(+) ALCL cell lines and suggest NOX5 as a potential pharmaceutical target to enhance apoptosis and thus to suppress tumor progression and prevent relapse in pediatric ALK(+) ALCL patients that resist classical therapeutic approaches.

Nox2 mediates skeletal muscle insulin resistance induced by a high fat diet

Inflammation and oxidative stress through the production of reactive oxygen species (ROS) are consistently associated with metabolic syndrome/type 2 diabetes. Although the role of Nox2, a major ROS-generating enzyme, is well described in host defense and inflammation, little is known about its potential role in insulin resistance in skeletal muscle. Insulin resistance induced by a high fat diet was mitigated in Nox2-null mice compared with wild-type mice after 3 or 9 months on the diet. High fat feeding increased Nox2 expression, superoxide production, and impaired insulin signaling in skeletal muscle tissue of wild-type mice but not in Nox2-null mice. Exposure of C2C12 cultured myotubes to either high glucose concentration, palmitate, or H2O2 decreases insulin-induced Akt phosphorylation and glucose uptake. Pretreatment with catalase abrogated these effects, indicating a key role for H2O2 in mediating insulin resistance. Down-regulation of Nox2 in C2C12 cells by shRNA prevented insulin resistance induced by high glucose or palmitate but not H2O2. These data indicate that increased production of ROS in insulin resistance induced by high glucose in skeletal muscle cells is a consequence of Nox2 activation. This is the first report to show that Nox2 is a key mediator of insulin resistance in skeletal muscle.

3-nitrotyrosine modified proteins in atherosclerosis

Cardiovascular disease is the leading cause of premature death worldwide, and atherosclerosis is the main contributor. Lipid-laden macrophages, known as foam cells, accumulate in the subendothelial space of the lesion area and contribute to consolidate a chronic inflammatory environment where oxygen and nitrogen derived oxidants are released. Oxidatively modified lipids and proteins are present both in plasma as well as atherosclerotic lesions. A relevant oxidative posttranslational protein modification is the addition of a nitro group to the hydroxyphenyl ring of tyrosine residues, mediated by nitric oxide derived oxidants. Nitrotyrosine modified proteins were found in the lesion and also in plasma from atherosclerotic patients. Despite the fact of the low yield of nitration, immunogenic, proatherogenic, and prothrombotic properties acquired by 3-nitrotyrosine modified proteins are in agreement with epidemiological studies showing a significant correlation between the level of nitration found in plasma proteins and the prevalence of cardiovascular disease, supporting the usefulness of this biomarker to predict the outcome and to take appropriate therapeutic decisions in atherosclerotic disease.

NADPH oxidases: a perspective on reactive oxygen species production in tumor biology

SIGNIFICANCE

Reactive oxygen species (ROS) promote genomic instability, altered signal transduction, and an environment that can sustain tumor formation and growth. The NOX family of NADPH oxidases, membrane-bound epithelial superoxide and hydrogen peroxide producers, plays a critical role in the maintenance of immune function, cell growth, and apoptosis. The impact of NOX enzymes in carcinogenesis is currently being defined and may directly link chronic inflammation and NOX ROS-mediated tumor formation.

RECENT ADVANCES

Increased interest in the function of NOX enzymes in tumor biology has spurred a surge of investigative effort to understand the variability of NOX expression levels in tumors and the effect of NOX activity on tumor cell proliferation. These initial efforts have demonstrated a wide variance in NOX distribution and expression levels across numerous cancers as well as in common tumor cell lines, suggesting that much remains to be discovered about the unique role of NOX-related ROS production within each system. Progression from in vitro cell line studies toward in vivo tumor tissue screening and xenograft models has begun to provide evidence supporting the importance of NOX expression in carcinogenesis.

CRITICAL ISSUES

A lack of universally available, isoform-specific antibodies and animal tumor models of inducible knockout or over-expression of NOX isoforms has hindered progress toward the completion of in vivo studies.

FUTURE DIRECTIONS

In vivo validation experiments and the use of large, existing gene expression data sets should help define the best model systems for studying the NOX homologues in the context of cancer.

Nox NADPH oxidases and the endoplasmic reticulum

SIGNIFICANCE

Understanding isoform- and context-specific subcellular Nox reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase compartmentalization allows relevant functional inferences. This review addresses the interplay between Nox NADPH oxidases and the endoplasmic reticulum (ER), an increasingly evident player in redox pathophysiology given its role in redox protein folding and stress responses.

RECENT ADVANCES

Catalytic/regulatory transmembrane subunits are synthesized in the ER and their processing includes folding, N-glycosylation, heme insertion, p22phox heterodimerization, as shown for phagocyte Nox2. Dual oxidase (Duox) maturation also involves the regulation by ER-resident Duoxa2. The ER is the activation site for some isoforms, typically Nox4, but potentially other isoforms. Such location influences redox/Nox-mediated calcium signaling regulation via ER targets, such as sarcoendoplasmic reticulum calcium ATPase (SERCA). Growing evidence suggests that Noxes are integral signaling elements of the unfolded protein response during ER stress, with Nox4 playing a dual prosurvival/proapoptotic role in this setting, whereas Nox2 enhances proapoptotic signaling. ER chaperones such as protein disulfide isomerase (PDI) closely interact with Noxes. PDI supports growth factor-dependent Nox1 activation and mRNA expression, as well as migration in smooth muscle cells, and PDI overexpression induces acute spontaneous Nox activation.

CRITICAL ISSUES

Mechanisms of PDI effects include possible support of complex formation and RhoGTPase activation. In phagocytes, PDI supports phagocytosis, Nox activation, and redox-dependent interactions with p47phox. Together, the results implicate PDI as possible Nox organizer.

FUTURE DIRECTIONS

We propose that convergence between Noxes and ER may have evolutive roots given ER-related functional contexts, which paved Nox evolution, namely calcium signaling and pathogen killing. Overall, the interplay between Noxes and the ER may provide relevant insights in Nox-related (patho)physiology.

Mucosal reactive oxygen species are required for antiviral response: role of Duox in influenza a virus infection

AIMS

Influenza A virus (IAV), a major airborne pathogen, is closely associated with significant morbidity and mortality. The primary target for influenza virus replication is the respiratory epithelium, which reacts to infection by mounting a multifaceted antiviral response. A part of this mucosal host defense is the generation of reactive oxygen species (ROS) by NADPH oxidases. Duox1 and Duox2 are the main ROS-producing enzymes in the airway epithelium, but their contribution to mammalian host defense is still ill defined.

RESULTS

To gain a better understanding of Duox function in respiratory tract infections, human differentiated lung epithelial cells and an animal model were used to monitor the effect of epithelial ROS on IAV propagation. IAV infection led to coordinated up-regulation of Duox2 and Duox-mediated ROS generation. Interference with H2O2 production and ROS signaling by oxidase inhibition or H2O2 decomposition augmented IAV replication. A nuclear pool of Duox enzymes participated in the regulation of the spliceosome, which is critical for alternative splicing of viral transcripts and controls the assembly of viable virions. In vivo silencing of Duox increased the viral load on intranasal infection with 2009 pandemic H1N1 influenza virus.

INNOVATION

This is the first study conclusively linking Duox NADPH oxidases with the antiviral mammalian immune response. Further, ROS generated by Duox enzymes localized adjacent to nuclear speckles altered the splicing of viral genes.

CONCLUSION

Duox-derived ROS are host protective and essential for counteracting IAV replication.

Origin of the phagocytic respiratory burst and its role in gut epithelial phagocytosis in a basal chordate

The vertebrate phagocytic respiratory burst (PRB) is a highly specific and efficient mechanism for reactive oxygen species (ROS) production. This mechanism is mediated by NADPH oxidase 2 (NOX2) and used by vertebrate phagocytic leukocytes to destroy internalized microbes. Here we demonstrate the presence of the PRB in a basal chordate, the amphioxus Branchiostoma belcheri tsingtauense (bbt). We show that using the antioxidant NAC to scavenge the production of ROS significantly decreased the survival rates of infected amphioxus, indicating that ROS are indispensable for efficient antibacterial responses. Amphioxus NOX enzymes and cytosolic factors were found to colocalize in the epithelial cells of the gill, intestine, and hepatic cecum and could be upregulated after exposure to microbial pathogens. The ROS production in epithelial cell lysates could be reconstructed by supplementing recombinant cytosolic factors, including bbt-p47phox, bbt-p67phox, bbt-p47phox, and bbt-Rac; the restored ROS production could be inhibited by anti-bbt-NOX2 and anti-bbt-p67phox antibodies. We also reveal that the gut epithelial lining cells of the amphioxus are competent at bacterial phagocytosis, and there is evidence that the PRB machinery could participate in the initiation of this phagocytic process. In conclusion, we report the presence of the classical PRB machinery in nonvertebrates and provide the first evidence for the possible role of PRB in epithelial cell immunity and phagocytosis.

Unique role of NADPH oxidase 5 in oxidative stress in human renal proximal tubule cells

NADPH oxidases are the major sources of reactive oxygen species in cardiovascular, neural, and kidney cells. The NADPH oxidase 5 (NOX5) gene is present in humans but not rodents. Because Nox isoforms in renal proximal tubules (RPTs) are involved in the pathogenesis of hypertension, we tested the hypothesis that NOX5 is differentially expressed in RPT cells from normotensive (NT) and hypertensive subjects (HT). We found that NOX5 mRNA, total NOX5 protein, and apical membrane NOX5 protein were 4.2±0.7-fold, 5.2±0.7-fold, and 2.8±0.5-fold greater in HT than NT. Basal total NADPH oxidase activity was 4.5±0.2-fold and basal NOX5 activity in NOX5 immunoprecipitates was 6.2±0.2-fold greater in HT than NT (P=<0.001, n=6-14/group). Ionomycin increased total NOX and NOX5 activities in RPT cells from HT (P<0.01, n=4, ANOVA), effects that were abrogated by pre-treatment of the RPT cells with diphenylene-iodonium or superoxide dismutase. Silencing NOX5 using NOX5-siRNA decreased NADPH oxidase activity (-45.1±3.2% vs. mock-siRNA, n=6-8) in HT. D1-like receptor stimulation decreased NADPH oxidase activity to a greater extent in NT (-32.5±1.8%) than HT (-14.8±1.8). In contrast to the marked increase in expression and activity of NOX5 in HT, NOX1 mRNA and protein were minimally increased in HT, relative to NT; total NOX2 and NOX4 proteins were not different between HT and NT, while the increase in apical RPT cell membrane NOX1, NOX2, and NOX4 proteins in HT, relative to NT, was much less than those observed with NOX5. Thus, we demonstrate, for the first time, that NOX5 is expressed in human RPT cells and to greater extent than the other Nox isoforms in HT than NT. We suggest that the increased expression of NOX5, which may be responsible for the increased oxidative stress in RPT cells in human essential hypertension, is caused, in part, by a defective renal dopaminergic system.

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.

Reactive oxygen species, vascular Noxs, and hypertension: focus on translational and clinical research

SIGNIFICANCE

Reactive oxygen species (ROS) are signaling molecules that are important in physiological processes, including host defense, aging, and cellular homeostasis. Increased ROS bioavailability and altered redox signaling (oxidative stress) have been implicated in the onset and/or progression of chronic diseases, including hypertension.

RECENT ADVANCES

Although oxidative stress may not be the only cause of hypertension, it amplifies blood pressure elevation in the presence of other pro-hypertensive factors, such as salt loading, activation of the renin-angiotensin-aldosterone system, and sympathetic hyperactivity, at least in experimental models. A major source for ROS in the cardiovascular-renal system is a family of nicotinamide adenine dinucleotide phosphate oxidases (Noxs), including the prototypic Nox2-based Nox, and Nox family members: Nox1, Nox4, and Nox5.

CRITICAL ISSUES

Although extensive experimental data support a role for increased ROS levels and altered redox signaling in the pathogenesis of hypertension, the role in clinical hypertension is unclear, as a direct causative role of ROS in blood pressure elevation has yet to be demonstrated in humans. Nevertheless, what is becoming increasingly evident is that abnormal ROS regulation and aberrant signaling through redox-sensitive pathways are important in the pathophysiological processes which is associated with vascular injury and target-organ damage in hypertension.

FUTURE DIRECTIONS

There is a paucity of clinical information related to the mechanisms of oxidative stress and blood pressure elevation, and a few assays accurately measure ROS directly in patients. Such further ROS research is needed in humans and in the development of adequately validated analytical methods to accurately assess oxidative stress in the clinic.

Characterization of NADPH oxidase 5 expression in human tumors and tumor cell lines with a novel mouse monoclonal antibody

Reactive oxygen species generated by NADPH oxidase 5 (Nox5) have been implicated in physiological and pathophysiological signaling pathways, including cancer development and progression. However, because immunological tools are lacking, knowledge of the role of Nox5 in tumor biology has been limited; the expression of Nox5 protein across tumors and normal tissues is essentially unknown. Here, we report the characterization and use of a mouse monoclonal antibody against a recombinant Nox5 protein (bp 600-746) for expression profiling of Nox5 in human tumors by tissue microarray analysis. Using our novel antibody, we also report the detection of endogenous Nox5 protein in human UACC-257 melanoma cells. Immunofluorescence, confocal microscopy, and immunohistochemical techniques were employed to demonstrate Nox5 localization throughout UACC-257 cells, with perinuclear enhancement. Tissue microarray analysis revealed, for the first time, substantial Nox5 overexpression in several human cancers, including those of prostate, breast, colon, lung, brain, and ovary, as well as in malignant melanoma and non-Hodgkin lymphoma; expression in most nonmalignant tissues was negative to weak. This validated mouse monoclonal antibody will promote further exploration of the functional significance of Nox5 in human pathophysiology, including tumor cell growth and proliferation.

Fulvene-5 inhibition of Nadph oxidases attenuates activation of epithelial sodium channels in A6 distal nephron cells

Nadph oxidase 4 is an important cellular source of reactive oxygen species (ROS) generation in the kidney. Novel antioxidant drugs, such as Nox4 inhibitor compounds, are being developed. There is, however, very little experimental evidence for the biological role and regulation of Nadph oxidase isoforms in the kidney. Herein, we show that Fulvene-5 is an effective inhibitor of Nox-generated ROS and report the role of Nox isoforms in activating epithelial sodium channels (ENaC) in A6 distal nephron cells via oxidant signaling and cell stretch activation. Using single-channel patch-clamp analysis, we report that Fulvene-5 blocked the increase in ENaC activity that is typically observed with H2O2 treatment of A6 cells: average ENaC NPo values decreased from a baseline level of 1.04 ± 0.18 (means ± SE) to 0.25 ± 0.08 following Fulvene-5 treatment. H2O2 treatment failed to increase ENaC activity in the presence of Fulvene-5. Moreover, Fulvene-5 treatment of A6 cells blocked the osmotic cell stretch response of A6 cells, indicating that stretch activation of Nox-derived ROS plays an important role in ENaC regulation. Together, these findings indicate that Fulvene-5, and perhaps other classes of antioxidant inhibitors, may represent a novel class of compounds useful for the treatment of pathological disorders stemming from inappropriate ion channel activity, such as hypertension.