cAMP-response element-binding protein mediates acid-induced NADPH oxidase NOX5-S expression in Barrett esophageal adenocarcinoma cells

IL-4 and IL-13 induce equivalent expression of traditional M2 markers and modulation of reactive oxygen species in human macrophages

In cardiovascular disease, pathological and protective roles are reported for the Th2 cytokines IL-4 and IL-13, respectively. We hypothesised that differential effects on macrophage function are responsible. Type I and II receptor subunit (IL-2Rγ, IL-4Rα and IL-13Rα1) and M2 marker (MRC-1, CCL18, CCL22) expression was assessed via RT-qPCR in IL-4- and IL-13-treated human primary macrophages. Downstream signalling was evaluated via STAT1, STAT3 and STAT6 inhibitors, and IL-4- and IL-13-induced reactive oxygen species (ROS) generation assessed. IL-4 and IL-13 exhibited equivalent potency and efficacy for M2 marker induction, which was attenuated by STAT3 inhibition. Both cytokines enhanced PDBu-stimulated superoxide generation however this effect was 17% greater with IL-4 treatment. Type I IL-4 receptor expression was increased on M1-like macrophages but did not lead to a differing ability of these cytokines to modulate M1-like macrophage superoxide production. Overall, this study did not identify major differences in the ability of IL-4 and IL-13 to modulate macrophage function, suggesting that the opposing roles of these cytokines in cardiovascular disease are likely to be via actions on other cell types. Future studies should directly compare IL-4 and IL-13 in vivo to more thoroughly investigate the therapeutic validity of selective targeting of these cytokines.

The Oxidative Stress and Nervous Distress Connection in Gastrointestinal Disorders

Oxidative stress is increasingly recognized as a central player in a range of gastrointestinal (GI) disorders, as well as complications stemming from therapeutic interventions. This article presents an overview of the mechanisms of oxidative stress in GI conditions and highlights a link between oxidative insult and disruption to the enteric nervous system (ENS), which controls GI functions. The dysfunction of the ENS is characteristic of a spectrum of disorders, including neurointestinal diseases and conditions such as inflammatory bowel disease (IBD), diabetic gastroparesis, and chemotherapy-induced GI side effects. Neurons in the ENS, while essential for normal gut function, appear particularly vulnerable to oxidative damage. Mechanistically, oxidative stress in enteric neurons can result from intrinsic nitrosative injury, mitochondrial dysfunction, or inflammation-related pathways. Although antioxidant-based therapies have shown limited efficacy, recognizing the multifaceted role of oxidative stress in GI diseases offers a promising avenue for future interventions. This comprehensive review summarizes the literature to date implicating oxidative stress as a critical player in the pathophysiology of GI disorders, with a focus on its role in ENS injury and dysfunction, and highlights opportunities for the development of targeted therapeutics for these diseases.

Epigenetic Alterations from Barrett's Esophagus to Esophageal Adenocarcinoma

Barrett's esophagus (BE) is a disease entity that is a sequela of chronic gastroesophageal reflux disease that may result in esophageal adenocarcinoma (EAC) due to columnar epithelial dysplasia. The histological degree of dysplasia is the sole biomarker frequently utilized by clinicians. However, the cost of endoscopy and the fact that the degree of dysplasia does not progress in many patients with BE diminish the effectiveness of histological grading as a perfect biomarker. Multiple or more quantitative biomarkers are required by clinicians since early diagnosis is crucial in esophageal adenocancers, which have a high mortality rate. The presence of epigenetic factors in the early stages of this neoplastic transformation holds promise as a predictive biomarker. In this review, current studies on DNA methylations, histone modifications, and noncoding RNAs (miRNAs) that have been discovered during the progression from BE dysplasia to EAC were collated.

Structure, regulation, and physiological functions of NADPH oxidase 5 (NOX5)

NOX5 is the last member of the NADPH oxidase (NOXs) family to be identified and presents some specific characteristics differing from the rest of the NOXs. It contains four Ca²⁺ binding domains at the N-terminus and its activity is regulated by the intracellular concentration of Ca²⁺. NOX5 generates superoxide (O₂^•-) using NADPH as a substrate, and it modulates functions related to processes in which reactive oxygen species (ROS) are involved. Those functions appear to be detrimental or beneficial depending on the level of ROS produced. For example, the increase in NOX5 activity is related to the development of various oxidative stress-related pathologies such as cancer, cardiovascular, and renal diseases. In this context, pancreatic expression of NOX5 can negatively alter insulin action in high-fat diet-fed transgenic mice. This is consistent with the idea that the expression of NOX5 tends to increase in response to a stimulus or a stressful situation, generally causing a worsening of the pathology. On the other hand, it has also been suggested that it might have a positive role in preparing the body for metabolic stress, for example, by inducing a protective adipose tissue adaptation to the excess of nutrients supplied by a high-fat diet. In this line, its endothelial overexpression can delay lipid accumulation and insulin resistance development in obese transgenic mice by inducing the secretion of IL-6 followed by the expression of thermogenic and lipolytic genes. However, as NOX5 gene is not present in rodents and human NOX5 protein has not been crystallized, its function is still poorly characterized and further extensive research is required.

Ca2+ -binding-region-dependent cell surface localization of NADPH oxidase Nox5

Six gene splice variants of superoxide-generating NADPH oxidase 5 (Nox5) have been identified in humans, and they differ in the sequence of their N-terminal cytoplasmic domains, which comprise four EF-hand motifs. Here, we demonstrated that the Ca²⁺ -dependent association and dissociation between the N- and C-terminal cytoplasmic domains of the Nox5β variant are affected by the alanine substitution of the conserved Ile-113 or Leu-115 at the connecting loop between the third and fourth EF-hand motifs. These substitutions impair the cell surface localization of Nox5β. In addition, the Nox5ε/S variant, lacking all EF-hand motifs, does not localize to the plasma membrane. Thus, the Ca²⁺ -sensitive intramolecular interaction determines the Nox5 subcellular localization, that is, whether Nox5 variants generate superoxide in the extracellular or intracellular space.

Natural Bioactive Compounds Targeting NADPH Oxidase Pathway in Cardiovascular Diseases

Cardiovascular disease (CVD) is the leading cause of death worldwide, in both developed and developing countries. According to the WHO report, the morbidity and mortality caused by CVD will continue to rise with the estimation of death going up to 22.2 million in 2030. NADPH oxidase (NOX)-derived reactive oxygen species (ROS) production induces endothelial nitric oxide synthase (eNOS) uncoupling and mitochondrial dysfunction, resulting in sustained oxidative stress and the development of cardiovascular diseases. Seven distinct members of the family have been identified of which four (namely, NOX1, 2, 4 and 5) may have cardiovascular functions. Currently, the treatment and management plan for patients with CVDs mainly depends on the drugs. However, prolonged use of prescribed drugs may cause adverse drug reactions. Therefore, it is crucial to find alternative treatment options with lesser adverse effects. Natural products have been gaining interest as complementary therapy for CVDs over the past decade due to their wide range of medicinal properties, including antioxidants. These might be due to their potent active ingredients, such as flavonoid and phenolic compounds. Numerous natural compounds have been demonstrated to have advantageous effects on cardiovascular disease via NADPH cascade. This review highlights the potential of natural products targeting NOX-derived ROS generation in treating CVDs. Emphasis is put on the activation of the oxidases, including upstream or downstream signalling events.

Modulation of Reactive Oxygen Species in Cancers: Recent Advances

Oxidation-reduction reactions played a significant role in the chemical evolution of life forms on oxygenated earth. Cellular respiration is dependent on such redox reactions, and any imbalance leads to the accumulation of reactive oxygen species (ROS), resulting in both chronic and acute illnesses. According to the International Agency for Research on Cancer (IARC), by 2040, the global burden of new cancer cases is expected to be around 27.5 million, with 16.3 million cancer deaths due to an increase in risk factors such as unhealthy lifestyle, environmental factors, aberrant gene mutations, and resistance to therapies. ROS play an important role in cellular signalling, but they can cause severe damage to tissues when present at higher levels. Elevated and chronic levels of ROS are pertinent in carcinogenesis, while several therapeutic strategies rely on altering cellular ROS to eliminate tumour cells as they are more susceptible to ROS-induced damage than normal cells. Given this selective targeting potential, therapies that can effectively modulate ROS levels have been the focus of intense research in recent years. The current review describes biologically relevant ROS, its origins in solid and haematological cancers, and the current status of evolving antioxidant and pro-oxidant therapies in cancers.

PbAc Triggers Oxidation and Apoptosis via the PKA Pathway in NRK-52E Cells

This study aimed to investigate the mechanism of the lead exposure-induced oxidative stress and apoptosis of renal tubular epithelial cells. We explored the effects of lead acetate (PbAc) on the oxidation and apoptosis of renal proximal tubular cells (NRK-52E) through in vitro experiments. Results showed that PbAc induced dose-dependent reactive oxygen species (ROS) accumulation in NRK-52E cells, and the activities of superoxide dismutase (SOD) and glutathione (GSH) decreased, whereas the malondialdehyde (MDA) content increased. Under the exposure of 40 and 80 μM PbAc, the mRNA level of B cell lymphoma-2 (Bcl-2) in the cells decreased, the mRNA levels of Bcl-2-associated X protein (Bax) and caspase-3 increased, and apoptosis was obvious. Furthermore, the nicotinamide adenine dinucleotide phosphate oxidase 4 (Nox4) activity was enhanced by PbAc in a dose-dependent manner. The mRNA levels of protein kinase A (PKA) were upregulated by PbAc. H-89, a PKA inhibitor, suppressed PKA activation, ROS accumulation, and Nox4 activity in NRK-52E cells. Our results indicated that PbAc potentially stimulated oxidative stress and apoptosis in NRK-52E cells by increasing Nox4-dependent ROS production via the PKA signaling pathway.

NADPH Oxidases (NOX): An Overview from Discovery, Molecular Mechanisms to Physiology and Pathology

The reactive oxygen species (ROS)-producing enzyme NADPH oxidase (NOX) was first identified in the membrane of phagocytic cells. For many years, its only known role was in immune defense, where its ROS production leads to the destruction of pathogens by the immune cells. NOX from phagocytes catalyzes, via one-electron trans-membrane transfer to molecular oxygen, the production of the superoxide anion. Over the years, six human homologs of the catalytic subunit of the phagocyte NADPH oxidase were found: NOX1, NOX3, NOX4, NOX5, DUOX1, and DUOX2. Together with the NOX2/gp91phox component present in the phagocyte NADPH oxidase assembly itself, the homologs are now referred to as the NOX family of NADPH oxidases. NOX are complex multidomain proteins with varying requirements for assembly with combinations of other proteins for activity. The recent structural insights acquired on both prokaryotic and eukaryotic NOX open new perspectives for the understanding of the molecular mechanisms inherent to NOX regulation and ROS production (superoxide or hydrogen peroxide). This new structural information will certainly inform new investigations of human disease. As specialized ROS producers, NOX enzymes participate in numerous crucial physiological processes, including host defense, the post-translational processing of proteins, cellular signaling, regulation of gene expression, and cell differentiation. These diversities of physiological context will be discussed in this review. We also discuss NOX misregulation, which can contribute to a wide range of severe pathologies, such as atherosclerosis, hypertension, diabetic nephropathy, lung fibrosis, cancer, or neurodegenerative diseases, giving this family of membrane proteins a strong therapeutic interest.

The Impact of Oxidative Stress in Human Pathology: Focus on Gastrointestinal Disorders

Accumulating evidence shows that oxidative stress plays an essential role in the pathogenesis and progression of many diseases. The imbalance between the production of reactive oxygen species (ROS) and the antioxidant systems has been extensively studied in pulmonary, neurodegenerative cardiovascular disorders; however, its contribution is still debated in gastrointestinal disorders. Evidence suggests that oxidative stress affects gastrointestinal motility in obesity, and post-infectious disorders by favoring the smooth muscle phenotypic switch toward a synthetic phenotype. The aim of this review is to gain insight into the role played by oxidative stress in gastrointestinal pathologies (GIT), and the involvement of ROS in the signaling underlying the muscular alterations of the gastrointestinal tract (GIT). In addition, potential therapeutic strategies based on the use of antioxidants for the treatment of inflammatory gastrointestinal diseases are reviewed and discussed. Although substantial progress has been made in identifying new techniques capable of assessing the presence of oxidative stress in humans, the biochemical-molecular mechanisms underlying GIT mucosal disorders are not yet well defined. Therefore, further studies are needed to clarify the mechanisms through which oxidative stress-related signaling can contribute to the alteration of the GIT mucosa in order to devise effective preventive and curative therapeutic strategies.

Regulation of Metabolic Processes by Hydrogen Peroxide Generated by NADPH Oxidases

Hydrogen peroxide (H2O2) is an important oxidizing molecule that regulates the metabolisms of aerobic organisms. Redox signaling comprises physiological oxidative stress (eustress), while excessive oxidative stress causes damage to molecules. The main enzymatic generators of H2O2 are nicotinamide adenine dinucleotide phosphate oxidases or NADPH oxidases (NOXs) and mitochondrial respiratory chains, as well as various oxidases. The NOX family is constituted of seven enzyme isoforms that produce a superoxide anion (O2−), which can be converted to H2O2 by superoxide dismutase or spontaneously. H2O2 passes through the membranes by some aquaporins (AQPs), known as peroxyporins. It diffuses through cells and tissues to initiate cellular effects, such as proliferation, the recruitment of immune cells, and cell shape changes. Therefore, it has been proposed that H2O2 has the same importance as Ca2+ or adenosine triphosphate (ATP) to act as modulators in signaling and the metabolism. The present overview focuses on the metabolic processes of liver and adipose tissue, regulated by the H2O2 generated by NOXs.

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.

Distinct Redox Signalling following Macrophage Activation Influences Profibrotic Activity

Aims

To date, the ROS-generating capacities of macrophages in different activation states have not been thoroughly compared. This study is aimed at determining the nature and levels of ROS generated following stimulation with common activators of M1 and M2 macrophages and investigating the potential for this to impact fibrosis.

Results

Human primary and THP-1 macrophages were treated with IFN-γ+LPS or IL-4-activating stimuli, and mRNA expression of established M1 (CXCL11, CCR7, IL-1β) and M2 (MRC-1, CCL18, CCL22) markers was used to confirm activation. Superoxide generation was assessed by L-012-enhanced chemiluminescence and was increased in both M(IFN-γ+LPS) and M(IL-4) macrophages, as compared to unpolarised macrophages (MΦ). This signal was attenuated with NOX2 siRNA. Increased expression of the p47phox and p67phox subunits of the NOX2 oxidase complex was evident in M(IFN-γ+LPS) and M(IL-4) macrophages, respectively. Amplex Red and DCF fluorescence assays detected increased hydrogen peroxide generation following stimulation with IL-4, but not IFN-γ+LPS. Coculture with human aortic adventitial fibroblasts revealed that M(IL-4), but not M(IFN-γ+LPS), enhanced fibroblast collagen 1 protein expression. Macrophage pretreatment with the hydrogen peroxide scavenger, PEG-catalase, attenuated this effect.

Conclusion

We show that superoxide generation is not only enhanced with stimuli associated with M1 macrophage activation but also with the M2 stimulus IL-4. Macrophages activated with IL-4 also exhibited enhanced hydrogen peroxide generation which in turn increased aortic fibroblast collagen production. Thus, M2 macrophage-derived ROS is identified as a potentially important contributor to aortic fibrosis.

Effect of Proton Pump Inhibitor Therapy on NOX5, mPGES1 and iNOS expression in Barrett's Esophagus

Acid reflux may contribute to the progression from Barrett’s esophagus (BE) to esophageal adenocarcinoma (EA). However, it is not clear whether the molecular changes present in BE patients are reversible after proton pump inhibitor (PPI) treatment. In this study we examined whether PPI treatment affects NOX5, microsomal prostaglandin E synthase (mPGES)-1 and inducible nitric oxide synthase (iNOS) expression. We found that NADPH oxidase 5 (NOX5), mPGES-1 and iNOS were significantly increased in BE mucosa. One-month PPI treatment significantly decreased NOX5, mPGES1 and iNOS. In BAR-T cells, NOX5 mRNA and p16 promoter methylation increased after pulsed acid treatment in a time-dependent manner. Four or eight-week-acid induced increase in NOX5 mRNA, NOX5 protein and p16 methylation may be reversible. Twelve-week acid treatment also significantly increased NOX5, mPGES1 and iNOS mRNA expression. However, twelve-week-acid-induced changes only partially restored or did not recover at all after the cells were cultured at pH 7.2 for 8 weeks. We conclude that NOX5, mPGES1 and iNOS may be reversible after PPI treatment. Short-term acid-induced increase in NOX5 expression and p16 methylation might be reversible, whereas long-term acid-induced changes only partially recovered 8 weeks after removal of acid treatment.

The tumor suppressive roles of ARHGAP25 in lung cancer cells

Aim

Several Rho GTPase-activating proteins (Rho GAPs) have been proved to serve as tumor suppressors in diverse human cancers. Among them, ARHGAP25 has also been found to be associated with hematopoietic cells and regulate phagocytosis. Little is known about the role of ARHGAP25 in lung cancer cells.

Methods

Quantitative real-time PCR and Western blot were used to measure the expression levels of ARHGAP25. The ability of cell growth and mobility were measured by cell proliferation and Transwell assays. Chromatin immunoprecipitation and luciferase assay were conducted to identify the transcriptional regulation.

Results

Lung cancer tissues had much lower expression level of ARHGAP25 compared to non-cancerous specimens as well as for lung cancer cells. Cell growth and mobility were strongly reduced when ARHGAP25 was overexpressed. Further, significantly negative correlation between ARHGAP25 expression and Wnt signaling pathway was observed. Overexpression of ARHGAP25 reduced the expression of β-catenin and matrix metalloproteinase-7. ARHGAP25 knockdown effect of increased abilities of cell proliferation, migration and invasion could be reversed by adding XAV939 inhibitor. The promoter site of ARHGAP25 could be bound with HOXA4. HOXA4 could regulate the transcriptional activity of ARHGAP25.

Conclusions

This study suggests that ARHGAP25 may inhibit lung cancer cell growth, migration and invasion through Wnt/β-catenin signaling pathway and its transcriptional activity can be regulated by HOXA4.

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.

Periprostatic Adipose Tissue Favors Prostate Cancer Cell Invasion in an Obesity-Dependent Manner: Role of Oxidative Stress

Prostate gland is surrounded by periprostatic adipose tissue (PPAT), which is increasingly believed to play a paracrine role in prostate cancer progression. Our previous work demonstrates that adipocytes promote homing of prostate cancer cells to PPAT and that this effect is upregulated by obesity. Here, we show that once tumor cells have invaded PPAT (mimicked by an in vitro model of coculture), they establish a bidirectional crosstalk with adipocytes, which promotes tumor cell invasion. Indeed, tumor cells induce adipocyte lipolysis and the free fatty acids (FFA) released are taken up and stored by tumor cells. Incubation with exogenous lipids also stimulates tumor cell invasion, underlining the importance of lipid transfer in prostate cancer aggressiveness. Transferred FFAs (after coculture or exogenous lipid treatment) stimulate the expression of one isoform of the pro-oxidant enzyme NADPH oxidase, NOX5. NOX5 increases intracellular reactive oxygen species (ROS) that, in turn, activate a HIF1/MMP14 pathway, which is responsible for the increased tumor cell invasion. In obesity, tumor-surrounding adipocytes are more prone to activate the depicted signaling pathway and to induce tumor invasion. Finally, the expression of NOX5 and MMP14 is upregulated at the invasive front of human tumors where cancer cells are in close proximity to adipocytes and this process is amplified in obese patients, underlining the clinical relevance of our results. IMPLICATIONS: Our work emphasizes the key role of adjacent PPAT in prostate cancer dissemination and proposes new molecular targets for the treatment of obese patients exhibiting aggressive diseases.

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.

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.

G Protein-Coupled Estrogen Receptor Protects From Angiotensin II-Induced Increases in Pulse Pressure and Oxidative Stress

Our previous work showed that the G protein-coupled estrogen receptor (GPER) is protective in the vasculature and kidneys during angiotensin (Ang) II-dependent hypertension by inhibiting oxidative stress. The goal of the current study was to assess the impact of GPER deletion on sex differences in Ang II-induced hypertension and oxidative stress. Male and female wildtype and GPER knockout mice were implanted with radiotelemetry probes for measurement of baseline blood pressure before infusion of Ang II (700 ng/kg/min) for 2 weeks. Mean arterial pressure was increased to the same extent in all groups, but female wildtype mice were protected from Ang II-induced increases in pulse pressure, aortic wall thickness, and Nox4 mRNA. In vitro studies using vascular smooth muscle cells found that pre-treatment with the GPER agonist G-1 inhibited Ang II-induced ROS and NADP/NADPH. Ang II increased while G-1 decreased Nox4 mRNA and protein. The effects of Ang II were blocked by losartan and Nox4 siRNA, while the effects of G-1 were inhibited by adenylyl cyclase inhibition and mimicked by phosphodiesterase inhibition. We conclude that during conditions of elevated Ang II, GPER via the cAMP pathway suppresses Nox4 transcription to limit ROS production and prevent arterial stiffening. Taken together with our previous work, this study provides insight into how acute estrogen signaling via GPER provides cardiovascular protection during Ang II hypertension and potentially other diseases characterized by increased oxidative stress.

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.

NADPH oxidase 5 promotes proliferation and fibrosis in human hepatic stellate cells

NADPH oxidase (Nox) variants Nox1, Nox2 and Nox4 are implicated in the progression of liver fibrosis. However, the role of Nox5 is not yet known, mainly due to the lack of this enzyme in rat and mouse genomes. Here we describe the expression and functional relevance of Nox5 in the human cell line of hepatic stellate cells (HSC) LX-2. Under basal conditions, three long (Nox5-L: Nox5α, -β, and -δ) and a short (Nox5-S or Nox5ε) splice variants were detected, which were silenced with specific siRNAs for Nox5. The most abundant isoform was Nox5-S, accounting for more than 90% of Nox5 protein. Overexpression of Nox5β generated reactive oxygen species (ROS) in the presence of calcium, as judged by the production of hydrogen peroxide, L-012 luminescence and cytochrome c reduction. Nox5ε did not generated ROS under these conditions, and a reduced ROS production was observed when co-expressed with Nox5β. In contrast, dihydroethidium oxidation was increased by Nox5β or Nox5ε, suggesting that Nox5ε induced intracellular oxidative stress by an unknown mechanism. Functional studies showed that both Nox5β and Nox5ε stimulated the proliferation of LX-2 cells and the collagen type I levels, while Nox5 siRNAs inhibited these effects. Interestingly, TGF-β and angiotensin II upregulated Nox5 expression, which was reduced in cells pre-incubated with catalase. Further studies silencing Nox5 in TGF-β-treated cells resulted in a reduction of collagen levels via p38 MAPK. Collectively, these results show for the first time that Nox5 can play a relevant role in the proliferation and fibrosis on human HSC.

NADPH oxidase 5 (NOX5)-induced reactive oxygen signaling modulates normoxic HIF-1α and p27Kip1 expression in malignant melanoma and other human tumors

NADPH oxidase 5 (NOX5) generated reactive oxygen species (ROS) have been implicated in signaling cascades that regulate cancer cell proliferation. To evaluate and validate NOX5 expression in human tumors, we screened a broad range of tissue microarrays (TMAs), and report substantial overexpression of NOX5 in malignant melanoma and cancers of the prostate, breast, and ovary. In human UACC-257 melanoma cells that possesses high levels of functional endogenous NOX5, overexpression of NOX5 resulted in enhanced cell growth, increased numbers of BrdU positive cells, and increased γ-H2AX levels. Additionally, NOX5-overexpressing (stable and inducible) UACC-257 cells demonstrated increased normoxic HIF-1α expression and decreased p27Kip1 expression. Similarly, increased normoxic HIF-1α expression and decreased p27Kip1 expression were observed in stable NOX5-overexpressing clones of KARPAS 299 human lymphoma cells and in the human prostate cancer cell line, PC-3. Conversely, knockdown of endogenous NOX5 in UACC-257 cells resulted in decreased cell growth, decreased HIF-1α expression, and increased p27Kip1 expression. Likewise, in an additional human melanoma cell line, WM852, and in PC-3 cells, transient knockdown of endogenous NOX5 resulted in increased p27Kip1 and decreased HIF-1α expression. Knockdown of endogenous NOX5 in UACC-257 cells resulted in decreased Akt and GSK3β phosphorylation, signaling pathways known to modulate p27Kip1 levels. In summary, our findings suggest that NOX5 expression in human UACC-257 melanoma cells could contribute to cell proliferation due, in part, to the generation of high local concentrations of extracellular ROS that modulate multiple pathways that regulate HIF-1α and networks that signal through Akt/GSK3β/p27Kip1 .

Paradoxical roles of dual oxidases in cancer biology

Dysregulated oxidative metabolism is a well-recognized aspect of cancer biology, and many therapeutic strategies are based on targeting cancers by altering cellular redox pathways. The NADPH oxidases (NOXes) present an important enzymatic source of biological oxidants, and the expression and activation of several NOX isoforms are frequently dysregulated in many cancers. Cell-based studies have demonstrated a role for several NOX isozymes in controlling cell proliferation and/or cell migration, further supporting a potential contributing role for NOX in promoting cancer. While various NOX isoforms are often upregulated in cancers, paradoxical recent findings indicate that dual oxidases (DUOXes), normally prominently expressed in epithelial lineages, are frequently suppressed in epithelial-derived cancers by epigenetic mechanisms, although the functional relevance of such DUOX silencing has remained unclear. This review will briefly summarize our current understanding regarding the importance of reactive oxygen species (ROS) and NOXes in cancer biology, and focus on recent observations indicating the unique and seemingly opposing roles of DUOX enzymes in cancer biology. We will discuss current knowledge regarding the functional properties of DUOX, and recent studies highlighting mechanistic consequences of DUOX1 loss in lung cancer, and its consequences for tumor invasiveness and current anticancer therapy. Finally, we will also discuss potentially unique roles for the DUOX maturation factors. Overall, a better understanding of mechanisms that regulate DUOX and the functional consequences of DUOX silencing in cancer may offer valuable new diagnostic insights and novel therapeutic opportunities.

Activation of NADPH oxidases leads to DNA damage in esophageal cells

Gastroesophageal reflux disease (GERD) is the strongest known risk factor for esophageal adenocarcinoma. In the center of tumorigenic events caused by GERD is repeated damage of esophageal tissues by the refluxate. In this study, we focused on a genotoxic aspect of exposure of esophageal cells to acidic bile reflux (BA/A). Analyzing cells generated from patients with Barrett's esophagus and human esophageal specimens, we found that BA/A cause significant DNA damage that is mediated by reactive-oxygen species. ROS originate from mitochondria and NADPH oxidases. We specifically identified NOX1 and NOX2 enzymes to be responsible for ROS generation. Inhibition of NOX2 and NOX1 with siRNA or chemical inhibitors significantly suppresses ROS production and DNA damage induced by BA/A. Mechanistically, our data showed that exposure of esophageal cells to acidic bile salts induces phosphorylation of the p47^phox subunit of NOX2 and its translocation to the cellular membrane. This process is mediated by protein kinase C, which is activated by BA/A. Taken together, our studies suggest that inhibition of ROS induced by reflux can be a useful strategy for preventing DNA damage and decreasing the risk of tumorigenic transformation caused by GERD.

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.

ROS signalling in the biology of cancer

Increased reactive oxygen species (ROS) production has been detected in various cancers and has been shown to have several roles, for example, they can activate pro-tumourigenic signalling, enhance cell survival and proliferation, and drive DNA damage and genetic instability. Counterintuitively ROS can also promote anti-tumourigenic signalling, initiating oxidative stress-induced tumour cell death. Tumour cells express elevated levels of antioxidant proteins to detoxify elevated ROS levels, establish a redox balance, while maintaining pro-tumourigenic signalling and resistance to apoptosis. Tumour cells have an altered redox balance to that of their normal counterparts and this identifies ROS manipulation as a potential target for cancer therapies. This review discusses the generation and sources of ROS within tumour cells, the regulation of ROS by antioxidant defence systems, as well as the effect of elevated ROS production on their signalling targets in cancer. It also provides an insight into how pro- and anti-tumourigenic ROS signalling pathways could be manipulated in the treatment of cancer.

Redox signaling in the gastrointestinal tract

Redox signaling regulates physiological self-renewal, proliferation, migration and differentiation in gastrointestinal epithelium by modulating Wnt/β-catenin and Notch signaling pathways mainly through NADPH oxidases (NOXs). In the intestine, intracellular and extracellular thiol redox status modulates the proliferative potential of epithelial cells. Furthermore, commensal bacteria contribute to intestine epithelial homeostasis through NOX1- and dual oxidase 2-derived reactive oxygen species (ROS). The loss of redox homeostasis is involved in the pathogenesis and development of a wide diversity of gastrointestinal disorders, such as Barrett's esophagus, esophageal adenocarcinoma, peptic ulcer, gastric cancer, ischemic intestinal injury, celiac disease, inflammatory bowel disease and colorectal cancer. The overproduction of superoxide anion together with inactivation of superoxide dismutase are involved in the pathogenesis of Barrett's esophagus and its transformation to adenocarcinoma. In Helicobacter pylori-induced peptic ulcer, oxidative stress derived from the leukocyte infiltrate and NOX1 aggravates mucosal damage, especially in HspB+ strains that downregulate Nrf2. In celiac disease, oxidative stress mediates most of the cytotoxic effects induced by gluten peptides and increases transglutaminase levels, whereas nitrosative stress contributes to the impairment of tight junctions. Progression of inflammatory bowel disease relies on the balance between pro-inflammatory redox-sensitive pathways, such as NLRP3 inflammasome and NF-κB, and the adaptive up-regulation of Mn superoxide dismutase and glutathione peroxidase 2. In colorectal cancer, redox signaling exhibits two Janus faces: On the one hand, NOX1 up-regulation and derived hydrogen peroxide enhance Wnt/β-catenin and Notch proliferating pathways; on the other hand, ROS may disrupt tumor progression through different pro-apoptotic mechanisms. In conclusion, redox signaling plays a critical role in the physiology and pathophysiology of gastrointestinal tract.

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.

Silencer-of-Death Domain Mediates Acid-Induced Decrease in Cell Apoptosis in Barrett's Associated Esophageal Adenocarcinoma Cells

We have shown that NADPH oxidase (NOX)5-S may mediate the acid-induced decrease in cell apoptosis. However, mechanisms of NOX5-S-dependent decrease in cell apoptosis are not fully understood. In this study, we found that silencer-of-death domain (SODD) was significantly increased in esophageal adenocarcinoma (EA) tissues, EA cell lines FLO and OE33, and a dysplastic cell line CP-B. Strong SODD immunostaining was significantly higher in low-grade dysplasia (66.7%), high-grade dysplasia (81.2%), and EA (71.2%) than in Barrett's mucosa (10.5%). Acid treatment significantly increased SODD protein and mRNA expression and promoter activity in FLO cells, an increase that was significantly decreased by the knockdown of NOX5-S and nuclear factor κB (NF-κB)1 p50 with their small interfering RNAs. Similarly, acid-induced increase of SODD mRNA was blocked by knockdown of NOX5-S and p50 in a BE cell line CP-A. Overexpression of NOX5-S significantly increased SODD protein expression in FLO cells. Moreover, overexpression of NOX5-S or p50 significantly increased the SODD promoter activity and decreased the caspase 9 activity or apoptosis. NOX5-S overexpression-induced increase in SODD promoter activity was significantly decreased by knockdown of p50. In addition, acid treatment significantly decreased the caspase 9 activity, a decrease that was significantly inhibited by knockdown of SODD. Furthermore, chromatin immunoprecipitation assay showed that NF-κB1 p50 bound to SODD genomic DNA containing a NF-κB-binding element GGGGACACCCT. This binding element was further confirmed by a gel mobility shift assay. We conclude that acid-induced increase in SODD expression and decrease in cell apoptosis may depend on the activation of NOX5-S and NF-κB1 p50 in FLO cells.

Bile acid receptor TGR5, NADPH Oxidase NOX5-S and CREB Mediate Bile Acid-Induced DNA Damage In Barrett's Esophageal Adenocarcinoma Cells

The mechanisms whereby bile acid reflux may accelerate the progression from Barrett’s esophagus (BE) to esophageal adenocarcinoma (EA) are not fully understood. In this study we found that bile acid taurodeoxycholic acid (TDCA) significantly increased the tail moment (TM) and histone H2AX phosphorylation in FLO-1 EA cells, an increase which was significantly decreased by knockdown of TGR5. Overexpression of TGR5 significantly increased TDCA-induced TM increase and H2AX phosphorylation. In addition, NADPH oxidase inhibitor diphenylene iodonium significantly inhibited the TDCA-induced increase in TM and H2AX phosphorylation. TDCA-induced increase in TM and H2AX phosphorylation was significantly decreased by knockdown of NOX5-S and overexpression of NOX5-S significantly increased TDCA-induced increase in the tail moment and H2AX phosphorylation. Furthermore, TDCA significantly increased cAMP response element binding protein (CREB) phosphorylation in FLO-1 cells. Knockdown of CREB significantly decreased TDCA-induced increase in NOX5-S mRNA and the tail moment. Conversely, overexpression of CREB significantly increased TDCA-induced TM increase. We conclude that TDCA-induced DNA damage may depend on the activation of TGR5, CREB and NOX5-S. It is possible that in Barrett’s patients bile acids may activate NOX5-S and increase reactive oxygen species (ROS) production via activation of TGR5 and CREB. NOX5-S-derived ROS may cause DNA damage, thereby contributing to the progression from BE to EA.

Tuberin regulates reactive oxygen species in renal proximal cells, kidney from rodents, and kidney from patients with tuberous sclerosis complex

Reactive oxygen species (ROS) are an important endogenous source of DNA damage and oxidative stress in all cell types. Deficiency in tuberin resulted in increased oxidative DNA damage in renal cells. In this study, the role of tuberin in the regulating of ROS and NADPH oxidases was investigated. Formation of ROS and activity of NADPH oxidases were significantly higher in mouse embryonic fibroblasts and in primary culture of rat renal proximal tubular epithelial tuberin‐deficient cells compared to wild‐type cells. In addition, expression of NADPH oxidase (Nox)1, Nox2, and Nox4 (Nox isoforms) was higher in mouse embryonic fibroblasts and renal proximal tubular epithelial tuberin‐deficient cells compared to wild‐type cells. Furthermore, activity levels of NADPH oxidases and protein expression of all Nox isoforms were higher in the renal cortex of rat deficient in tuberin. However, treatment of tuberin‐deficient cells with rapamycin showed significant decrease in protein expression of all Nox. Significant increase in protein kinase C βII expression was detected in tuberin‐deficient cells, whereas inhibition of protein kinase C βII by bisindolylmaleimide I resulted in decreased protein expression of all Nox isoforms. In addition, treatment of mice deficient in tuberin with rapamycin resulted in significant decrease in all Nox protein expression. Moreover, protein and mRNA expression of all Nox were highly expressed in tumor kidney tissue of patients with tuberous sclerosis complex compared to control kidney tissue of normal subjects. These data provide the first evidence that tuberin plays a novel role in regulating ROS generation, NADPH oxidase activity, and Nox expression that may potentially be involved in development of kidney tumor in patients with tuberous sclerosis complex.

Cloning, Characteristics, and Functional Analysis of Rabbit NADPH Oxidase 5

Background: Nox5 was the last member of the Nox enzyme family to be identified. Functionally distinct from the other Nox isoforms, our understanding of its physiological significance has been hampered by the absence of Nox5 in mouse and rat genomes. Nox5 is present in the genomes of other species such as the rabbit that have broad utility as models of cardiovascular disease. However, the mRNA sequence, characteristics, and functional analysis of rabbit Nox5 has not been fully defined and were the goals of the current study.

Methods: Rabbit Nox5 was amplified from rabbit tissue, cloned, and sequenced. COS-7 cells were employed for expression and functional analysis via Western blotting and measurements of superoxide. We designed and synthesized miRNAs selectively targeting rabbit Nox5. The nucleotide and amino acid sequences of rabbit Nox5 were aligned with those of putative rabbit isoforms (X1, X2, X3, and X4). A phylogenetic tree was generated based on the mRNA sequence for Nox5 from rabbit and other species.

Results: Sequence alignment revealed that the identified rabbit Nox5 was highly conserved with the predicted sequence of rabbit Nox5. Cell based experiments reveal that rabbit Nox5 was robustly expressed and produced superoxide at rest and in a calcium and PMA-dependent manner that was susceptible to superoxide dismutase and the flavoprotein inhibitor, DPI. miRNA-1 was shown to be most effective in down-regulating the expression of rabbit Nox5. Phylogenetic analysis revealed a close relationship between rabbit and armadillo Nox5. Rabbit Nox5 was relatively closely related to human Nox5, but lies in a distinct cluster.

Conclusion: Our study establishes the suitability of the rabbit as a model organism to further our understanding of the role of Nox5 in cardiovascular and other diseases and provides new information on the genetic relationship of Nox5 genes in different species.

Overview of major molecular alterations during progression from Barrett's esophagus to esophageal adenocarcinoma

Esophageal adenocarcinoma (EAC) develops in the sequential transformation of normal epithelium into metaplastic epithelium, called Barrett's esophagus (BE), then to dysplasia, and finally cancer. BE is a common condition in which normal stratified squamous epithelium of the esophagus is replaced with an intestine-like columnar epithelium, and it is the most prominent risk factor for EAC. This review aims to impartially systemize the knowledge from a large number of publications that describe the molecular and biochemical alterations occurring over this progression sequence. In order to provide an unbiased extraction of the knowledge from the literature, a text-mining methodology was used to select genes that are involved in the BE progression, with the top candidate genes found to be TP53, CDKN2A, CTNNB1, CDH1, GPX3, and NOX5. In addition, sample frequencies across analyzed patient cohorts at each stage of disease progression are summarized. All six genes are altered in the majority of EAC patients, and accumulation of alterations correlates well with the sequential progression of BE to cancer, indicating that the text-mining method is a valid approach for gene prioritization. This review discusses how, besides being cancer drivers, these genes are functionally interconnected and might collectively be considered a central hub of BE progression.

Rho Kinase ROCK2 Mediates Acid-Induced NADPH Oxidase NOX5-S Expression in Human Esophageal Adenocarcinoma Cells

Mechanisms of the progression from Barrett’s esophagus (BE) to esophageal adenocarcinoma (EA) are not fully understood. We have shown that NOX5-S may be involved in this progression. However, how acid upregulates NOX5-S is not well known. We found that acid-induced increase in NOX5-S expression was significantly decreased by the Rho kinase (ROCK) inhibitor Y27632 in BE mucosal biopsies and FLO-1 EA cells. In addition, acid treatment significantly increased the Rho kinase activity in FLO-1 cells. The acid-induced increase in NOX5-S expression and H₂O₂ production was significantly decreased by knockdown of Rho kinase ROCK2, but not by knockdown of ROCK1. Conversely, the overexpression of the constitutively active ROCK2, but not the constitutively active ROCK1, significantly enhanced the NOX5-S expression and H₂O₂ production. Moreover, the acid-induced increase in Rho kinase activity and in NOX5-S mRNA expression was blocked by the removal of calcium in both FLO-1 and OE33 cells. The calcium ionophore A23187 significantly increased the Rho kinase activity and NOX5-S mRNA expression. We conclude that acid-induced increase in NOX5-S expression and H₂O₂ production may depend on the activation of ROCK2, but not ROCK1, in EA cells. The acid-induced activation of Rho kinase may be mediated by the intracellular calcium increase. It is possible that persistent acid reflux present in BE patients may increase the intracellular calcium, activate ROCK2 and thereby upregulate NOX5-S. High levels of reactive oxygen species derived from NOX5-S may cause DNA damage and thereby contribute to the progression from BE to EA.

DUOX2 Expression Is Increased in Barrett Esophagus and Cancerous Tissues of Stomach and Colon

Aim. To detect the expression of dual oxidase (DUOX) 2 in Barrett esophagus, gastric cancer, and colorectal cancer (CRC). Materials and Methods. The endoscopic biopsies were collected from patients with Barrett esophagus, while the curative resection tissues were obtained from patients with gastric cancer, CRC, or hepatic carcinoma. The DUOX2 protein and mRNA levels were detected with immunohistochemistry (IHC) and real-time quantitative PCR (qPCR). The correlation of DUOX2 expression with clinicopathological parameters of tumors was identified. Results. Low levels of DUOX2 mRNA were detected in Barrett esophagus and the adjacent normal tissues, and there was no difference between these two groups. DUOX2 protein was found in Barrett esophagus and undetectable in the normal epithelium. The DUOX2 mRNA and protein levels in the gastric cancer and CRC were increased compared to the adjacent nonmalignant tissues. The elevated DUOX2 in the gastric cancer was significantly associated with smoking history. In CRC tissues, the DUOX2 protein expression level in stages II–IV was significantly higher than that in stage I. In both hepatic carcinoma and the adjacent nonmalignant tissue, the DUOX2 was virtually undetectable. Conclusion. DUOX2 in Barrett esophagus, gastric cancer, and CRC may be involved in the tumorigenesis of these tissues.

Barrett's esophagus: recent insights into pathogenesis and cellular ontogeny

Esophageal adenocarcinoma (EAC) has increased 6-fold in its incidence in the last 2 decades. Evidence supports the hypothesis of stepwise progression from normal squamous epithelium → reflux esophagitis → metaplasia (Barrett's esophagus, BE) → dysplasia → adenocarcinoma. The precursor, BE, stands as the bridge connecting the widespread but naive reflux disease and the rare but fatal EAC. The step of metaplasia from squamous to intestine-like columnar phenotype is perhaps pivotal in promoting dysplastic vulnerability. It is widely accepted that chronic inflammation because of gastroesophageal reflux disease leads to the development of metaplasia, however the precise molecular mechanism is yet to be discovered. Additionally, how this seemingly adaptive change in the cellular phenotype promotes dysplasia remains a mystery. This conceptual void is deterring further translational research and clouding clinical decision making. This article critically reviews theories on the pathogenesis of Barrett's esophagus and the various controversies surrounding its diagnosis. We further discuss unanswered questions and future directions, which are vital in formulating effective preventive and therapeutic guidelines for Barrett's esophagus.

Superoxide-Generating Nox5α Is Functionally Required for the Human T-Cell Leukemia Virus Type 1-Induced Cell Transformation Phenotype

Human T-cell leukemia virus type 1 (HTLV-1) is associated with adult T-cell leukemia (ATL) and transforms T cells in vitro. To our knowledge, the functional role of reactive oxygen species (ROS)-generating NADPH oxidase 5 (Nox5) in HTLV-1 transformation remains undefined. Here, we found that Nox5α expression was upregulated in 88% of 17 ATL patient samples but not in normal peripheral blood T cells. Upregulation of the Nox5α variant was transcriptionally sustained by the constitutive Janus family tyrosine kinase (Jak)-STAT5 signaling pathway in interleukin-2 (IL-2)-independent HTLV-1-transformed cell lines, including MT1 and MT2, whereas it was transiently induced by the IL-2-triggered Jak-STAT5 axis in uninfected T cells. A Nox inhibitor, diphenylene iodonium, and antioxidants such as N-acetyl cysteine blocked proliferation of MT1 and MT2 cells. Ablation of Nox5α by small interfering RNAs abrogated ROS production, inhibited cellular activities, including proliferation, migration, and survival, and suppressed tumorigenicity in immunodeficient NOG mice. The findings suggest that Nox5α is a key molecule for redox-signal-mediated maintenance of the HTLV-1 transformation phenotype and could be a potential molecular target for therapeutic intervention in cancer development.

IMPORTANCE

HTLV-1 is the first human oncogenic retrovirus shown to be associated with ATL. Despite the extensive study over the years, the mechanism underlying HTLV-1-induced cell transformation is not fully understood. In this study, we addressed the expression and function of ROS-generating Nox family genes in HTLV-1-transformed cells. Our report provides the first evidence that the upregulated expression of Nox5α is associated with the pathological state of ATL peripheral blood mononuclear cells and that Nox5α is an integral component of the Jak-STAT5 signaling pathway in HTLV-1-transformed T cells. Nox5α-derived ROS are critically involved in the regulation of cellular activities, including proliferation, migration, survival, and tumorigenicity, in HTLV-1-transformed cells. These results indicate that Nox5α-derived ROS are functionally required for maintenance of the HTLV-1 transformation phenotype. The finding provides new insight into the redox-dependent mechanism of HTLV-1 transformation and raises an intriguing possibility that Nox5α serves as a potential molecular target to treat HTLV-1-related leukemia.

Long-term methionine-diet induced mild hyperhomocysteinemia associated cardiac metabolic dysfunction in multiparous rats

Mild hyperhomocysteinemia (HHcy, clinically defined as less than 30 μmol/L) is an independent cardiovascular disease (CVD) risk factor, and is associated with many complications during pregnancy, such as preeclampsia (PE). The aim of this study was to assess the effect of long-term mild HHcy on cardiac metabolic function of multiparous rats. Female rats were mated 3 to 4 times and were fed with methionine in drinking water to increase plasma Hcy (2.9 ± 0.3 to 10.5 ± 2.3 μmol/L) until termination. This caused significant increase of heart weight/body weight (0.24 ± 0.01 to 0.27 ± 0.01 g/100 g) and left ventricle weight (0.69 ± 0.03 to 0.78 ± 0.01 g). Superoxide production was increased by 2.5-fold in HHcy hearts using lucigenin chemiluminescence. The ability of bradykinin and carbachol to regulate myocardial oxygen consumption (MVO₂) in vitro was impaired by 59% and 66% in HHcy heart, and it was restored by ascorbic acid (AA), tempol, or apocynin (Apo). Protein expression of p22^phox subunit of NAD(P)H oxidase was increased by 2.6-fold, but there were no changes in other NAD(P)H oxidase subunits, NOSs or SODs. Microarray revealed 1518 genes to be differentially regulated (P < 0.05). The mRNA level of NAD(P)H oxidase subunits, NOSs or SODs remained unchanged. In conclusion, long-term mild HHcy increases cardiac superoxide mainly through regulation of p22^phox component of the NAD(P)H oxidase and impairs the ability of NO to regulate MVO₂ in heart of multiparous mothers.

Selective killing of K-ras-transformed pancreatic cancer cells by targeting NAD(P)H oxidase

Introduction

Oncogenic activation of the K-ras gene occurs in >90% of pancreatic ductal carcinoma and plays a critical role in the pathogenesis of this malignancy. Increase of reactive oxygen species (ROS) has also been observed in a wide spectrum of cancers. This study aimed to investigate the mechanistic association between K-ras–induced transformation and increased ROS stress and its therapeutic implications in pancreatic cancer.

Methods

ROS level, NADPH oxidase (NOX) activity and expression, and cell invasion were examined in human pancreatic duct epithelial E6E7 cells transfected with K-ras^G12V compared with parental E6E7 cells. The cytotoxic effect and antitumor effect of capsaicin, a NOX inhibitor, were also tested in vitro and in vivo.

Results

K-ras transfection caused activation of the membrane-associated redox enzyme NOX and elevated ROS generation through the phosphatidylinositol 3′-kinase (PI3K) pathway. Importantly, capsaicin preferentially inhibited the enzyme activity of NOX and induced severe ROS accumulation in K-ras–transformed cells compared with parental E6E7 cells. Furthermore, capsaicin effectively inhibited cell proliferation, prevented invasiveness of K-ras–transformed pancreatic cancer cells, and caused minimum toxicity to parental E6E7 cells. In vivo, capsaicin exhibited antitumor activity against pancreatic cancer and showed oxidative damage to the xenograft tumor cells.

Conclusions

K-ras oncogenic signaling causes increased ROS stress through NOX, and abnormal ROS stress can selectively kill tumor cells by using NOX inhibitors. Our study provides a basis for developing a novel therapeutic strategy to effectively kill K-ras–transformed cells through a redox-mediated mechanism.

NADPH oxidases and cancer

The mechanism by which reactive oxygen species (ROS) are produced by tumour cells remained incompletely understood until the discovery over the last 15 years of the family of NADPH oxidases (NOXs 1–5 and dual oxidases DUOX1/2) which are structural homologues of gp91phox, the major membrane-bound component of the respiratory burst oxidase of leucocytes. Knowledge of the roles of the NOX isoforms in cancer is rapidly expanding. Recent evidence suggests that both NOX1 and DUOX2 species produce ROS in the gastrointestinal tract as a result of chronic inflammatory stress; cytokine induction (by interferon-γ, tumour necrosis factor α, and interleukins IL-4 and IL-13) of NOX1 and DUOX2 may contribute to the development of colorectal and pancreatic carcinomas in patients with inflammatory bowel disease and chronic pancreatitis, respectively. NOX4 expression is increased in pre-malignant fibrotic states which may lead to carcinomas of the lung and liver. NOX5 is highly expressed in malignant melanomas, prostate cancer and Barrett's oesophagus-associated adenocarcinomas, and in the last it is related to chronic gastro-oesophageal reflux and inflammation. Over-expression of functional NOX proteins in many tissues helps to explain tissue injury and DNA damage from ROS that accompany pre-malignant conditions, as well as elucidating the potential mechanisms of NOX-related damage that contribute to both the initiation and the progression of a wide range of solid and haematopoietic malignancies.

ROS signaling by NADPH oxidase 5 modulates the proliferation and survival of prostate carcinoma cells

Prostate cancer (PCa) is the most commonly diagnosed cancer and second leading cause of male cancer death in Western nations. Thus, new treatment modalities are urgently needed. Elevated production of reactive oxygen species (ROS) by NADPH oxidase (Nox) enzymes is implicated in tumorigenesis of the prostate and other tissues. However, the identity of the Nox enzyme(s) involved in prostate carcinogenesis remains largely unknown. Analysis of radical prostatectomy tissue samples and benign and malignant prostate epithelial cell lines identified Nox5 as an abundantly expressed Nox isoform. Consistently, immunohistochemical staining of a human PCa tissue microarray revealed distinct Nox5 expression in epithelial cells of benign and malignant prostatic glands. shRNA‐mediated knockdown of Nox5 impaired proliferation of Nox5‐expressing (PC‐3, LNCaP) but not Nox5‐negative (DU145) PCa cell lines. Similar effects were observed upon ROS ablation via the antioxidant N‐acetylcysteine confirming ROS as the mediators. In addition, Nox5 silencing increased apoptosis of PC‐3 cells. Concomitantly, protein kinase C zeta (PKCζ) protein levels and c‐Jun N‐terminal kinase (JNK) phosphorylation were reduced. Moreover, the effect of Nox5 knockdown on PC‐3 cell proliferation could be mimicked by pharmacological inhibition of JNK. Collectively, these data indicate that Nox5 is expressed at functionally relevant levels in the human prostate and clinical PCa. Moreover, findings herein suggest that Nox5‐derived ROS and subsequent depletion of PKCζ and JNK inactivation play a critical role in modulating intracellular signaling cascades involved in the proliferation and survival of PCa cells. © 2014 The Authors. Molecular Carcinogenesis published by Wiley Periodicals, Inc.

NADPH oxidases: an overview from structure to innate immunity-associated pathologies

Oxygen-derived free radicals, collectively termed reactive oxygen species (ROS), play important roles in immunity, cell growth, and cell signaling. In excess, however, ROS are lethal to cells, and the overproduction of these molecules leads to a myriad of devastating diseases. The key producers of ROS in many cells are the NOX family of NADPH oxidases, of which there are seven members, with various tissue distributions and activation mechanisms. NADPH oxidase is a multisubunit enzyme comprising membrane and cytosolic components, which actively communicate during the host responses to a wide variety of stimuli, including viral and bacterial infections. This enzymatic complex has been implicated in many functions ranging from host defense to cellular signaling and the regulation of gene expression. NOX deficiency might lead to immunosuppression, while the intracellular accumulation of ROS results in the inhibition of viral propagation and apoptosis. However, excess ROS production causes cellular stress, leading to various lethal diseases, including autoimmune diseases and cancer. During the later stages of injury, NOX promotes tissue repair through the induction of angiogenesis and cell proliferation. Therefore, a complete understanding of the function of NOX is important to direct the role of this enzyme towards host defense and tissue repair or increase resistance to stress in a timely and disease-specific manner.

Bidirectional regulation between TMEFF2 and STAT3 may contribute to Helicobacter pylori-associated gastric carcinogenesis

The transmembrane protein with epidermal growth factor and two follistatin motifs 2 (TMEFF2) is a single-pass transmembrane protein, and it is downregulated in human gastric cancer and levels correlate with tumor progression and time of survival. However, the mechanism of its dysregulation in gastric cancer is little known. Here we investigate its regulatory mechanism and the bidirectional regulation between TMEFF2 and STAT3 in gastric carcinogenesis. TMEFF2 expression was decreased after Helicobacter pylori (H. pylori) infection in vivo and in vitro. STAT3 directly binds to the promoter of TMEFF2 and regulates H. pylori-induced TMEFF2 downregulation in normal gastric GES-1 cells and gastric cancer AGS cells. Conversely, TMEFF2 may suppress the phosphorylation of STAT3 and TMEFF2-induced downregulation of STAT3 phosphorylation may depend on SHP-1. A highly inverse correlation between the expression of TMEFF2 and pSTAT3 was also revealed in gastric tissues. We now show the deregulation mechanism of TMEFF2 in gastric carcinogenesis and identify TMEFF2 as a new target gene of STAT3. The phosphorylation of STAT3 may be negatively regulated by TMEFF2, and the bidirectional regulation between TMEFF2 and STAT3 may contribute to H. pylori-associated gastric carcinogenesis.

Impact of Nox5 polymorphisms on basal and stimulus-dependent ROS generation

Nox5 is an EF-hand containing, calcium-dependent isoform of the NADPH oxidase family of reactive oxygen species (ROS) generating enzymes. Altered expression and activity of Nox5 has been reported in cardiovascular diseases and cancers but the absence of Nox5 in rodents has precluded a greater understanding of its physiological and pathophysiological roles. Multiple polymorphisms have been identified within the coding sequence of human Nox5, but whether this translates into altered enzyme function is unknown. Herein, we have generated 15 novel mutants of Nox5β to evaluate the effect of exonic SNPs on basal and stimulated enzyme activity. Compared to the WT enzyme, ROS production was unchanged or slightly modified in the majority of mutants, but significantly decreased in 7. Focusing on M77K, Nox5 activity was dramatically reduced in unstimulated cells and following challenge with both calcium- and phosphorylation-dependent stimuli despite equivalent levels of expression. The M77K mutation did not influence the Nox5 phosphorylation or the ability to bind Hsp90, but in cell-free assays with excess co-factors and calcium, ROS production was dramatically reduced. A more conservative substitution M77V arising from another SNP yielded a different profile of enzyme activity and suggests a critical role of M77 in calcium-dependent ROS production. Two C-terminal mutants, R530H and G542R, were observed that had little to no activity and relatively high minor allele frequency (MAF). In conclusion, we have identified 7 missense SNPs in Nox5 that result in little or no enzyme activity. Whether humans with dysfunctional Nox5 variants have altered physiology or disease remains to be determined.

NADPH oxidase-generated reactive oxygen species are required for stromal cell-derived factor-1α-stimulated angiogenesis

OBJECTIVE

Reactive oxygen species (ROS) act as signaling molecules during angiogenesis; however, the mechanisms used for such signaling events remain unclear. Stromal cell-derived factor-1α (SDF-1α) is one of the most potent angiogenic chemokines. Here, we examined the role of ROS in the regulation of SDF-1α-dependent angiogenesis.

APPROACH AND RESULTS

Bovine aortic endothelial cells were treated with SDF-1α, and intracellular ROS generation was monitored. SDF-1α treatment induced bovine aortic endothelial cell migration and ROS generation, with the majority of ROS generated by bovine aortic endothelial cells at the leading edge of the migratory cells. Antioxidants and nicotinamide adenine dinucleotide phosphate oxidase (NOX) inhibitors blocked SDF-1α-induced endothelial migration. Furthermore, knockdown of either NOX5 or p22phox (a requisite subunit for NOX1/2/4 activation) significantly impaired endothelial motility and tube formation, suggesting that multiple NOXs regulate SDF-1α-dependent angiogenesis. Our previous study demonstrated that c-Jun N-terminal kinase 3 activity is essential for SDF-1α-dependent angiogenesis. Here, we identified that NOX5 is the dominant NOX required for SDF-1α-induced c-Jun N-terminal kinase 3 activation and that NOX5 and MAP kinase phosphatase 7 (MKP7; the c-Jun N-terminal kinase 3 phosphatase) associate with one another but decrease this interaction on SDF-1α treatment. Furthermore, MKP7 activity was inhibited by SDF-1α, and this inhibition was relieved by NOX5 knockdown, indicating that NOX5 promotes c-Jun N-terminal kinase 3 activation by blocking MKP7 activity.

CONCLUSIONS

We conclude that NOX is required for SDF-1α signaling and that intracellular redox balance is critical for SDF-1α-induced endothelial migration and angiogenesis.

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.

Role of intracellular calcium and NADPH oxidase NOX5-S in acid-induced DNA damage in Barrett's cells and Barrett's esophageal adenocarcinoma cells

Mechanisms whereby acid reflux may accelerate the progression from Barrett's esophagus (BE) to esophageal adenocarcinoma (EA) are not fully understood. Acid and reactive oxygen species (ROS) have been reported to cause DNA damage in Barrett's cells. We have previously shown that NADPH oxidase NOX5-S is responsible for acid-induced H2O2 production in Barrett's cells and in EA cells. In this study we examined the role of intracellular calcium and NADPH oxidase NOX5-S in acid-induced DNA damage in a Barrett's EA cell line FLO and a Barrett's cell line CP-A. We found that pulsed acid treatment significantly increased tail moment in FLO and CP-A cells and histone H2AX phosphorylation in FLO cells. In addition, acid treatment significantly increased intracellular Ca(2+) in FLO cells, an increase that is blocked by Ca(2+)-free medium with EGTA and thapsigargin. Acid-induced increase in tail moment was significantly decreased by NADPH oxidase inhibitor diphenylene iodonium in FLO cells, and by blockade of intracellular Ca(2+) increase or knockdown of NOX5-S with NOX5 small-interfering RNA (siRNA) in FLO and CP-A cells. Acid-induced increase in histone H2AX phosphorylation was significantly decreased by NOX5 siRNA in FLO cells. Conversely, overexpression of NOX5-S significantly increased tail moment and histone H2AX phosphorylation in FLO cells. We conclude that pulsed acid treatment causes DNA damage via increase of intracellular calcium and activation of NOX5-S. It is possible that in BE acid reflux increases intracellular calcium, activates NOX5-S, and increases ROS production, which causes DNA damage, thereby contributing to the progression from BE to EA.