Tetratricopeptide repeat (TPR) motifs of p67(phox) participate in interaction with the small GTPase Rac and activation of the phagocyte NADPH oxidase

NADPH Oxidase 3: Beyond the Inner Ear

Reactive oxygen species (ROS) were formerly known as mere byproducts of metabolism with damaging effects on cellular structures. The discovery and description of NADPH oxidases (Nox) as a whole enzyme family that only produce this harmful group of molecules was surprising. After intensive research, seven Nox isoforms were discovered, described and extensively studied. Among them, the NADPH oxidase 3 is the perhaps most underrated Nox isoform, since it was firstly discovered in the inner ear. This stigma of Nox3 as "being only expressed in the inner ear" was also used by me several times. Therefore, the question arose whether this sentence is still valid or even usable. To this end, this review solely focuses on Nox3 and summarizes its discovery, the structural components, the activating and regulating factors, the expression in cells, tissues and organs, as well as the beneficial and detrimental effects of Nox3-mediated ROS production on body functions. Furthermore, the involvement of Nox3-derived ROS in diseases progression and, accordingly, as a potential target for disease treatment, will be discussed.

Palmitoylation-dependent regulation of cardiomyocyte Rac1 signaling activity and minor effects on cardiac hypertrophy

S-palmitoylation is a reversible lipid modification catalyzed by 23 S-acyltransferases with a conserved zinc finger aspartate-histidine-histidine-cysteine (zDHHC) domain that facilitates targeting of proteins to specific intracellular membranes. Here we performed a gain-of-function screen in the mouse and identified the Golgi-localized enzymes zDHHC3 and zDHHC7 as regulators of cardiac hypertrophy. Cardiomyocyte-specific transgenic mice overexpressing zDHHC3 show cardiac disease, and S-acyl proteomics identified the small GTPase Rac1 as a novel substrate of zDHHC3. Notably, cardiomyopathy and congestive heart failure in zDHHC3 transgenic mice is preceded by enhanced Rac1 S-palmitoylation, membrane localization, activity, downstream hypertrophic signaling, and concomitant induction of all Rho family small GTPases whereas mice overexpressing an enzymatically dead zDHHC3 mutant show no discernible effect. However, loss of Rac1 or other identified zDHHC3 targets Gαq/11 or galectin-1 does not diminish zDHHC3-induced cardiomyopathy, suggesting multiple effectors and pathways promoting decompensation with sustained zDHHC3 activity. Genetic deletion of Zdhhc3 in combination with Zdhhc7 reduces cardiac hypertrophy during the early response to pressure overload stimulation but not over longer time periods. Indeed, cardiac hypertrophy in response to 2 weeks of angiotensin-II infusion is not diminished by Zdhhc3/7 deletion, again suggesting other S-acyltransferases or signaling mechanisms compensate to promote hypertrophic signaling. Taken together, these data indicate that the activity of zDHHC3 and zDHHC7 at the cardiomyocyte Golgi promote Rac1 signaling and maladaptive cardiac remodeling, but redundant signaling effectors compensate to maintain cardiac hypertrophy with sustained pathological stimulation in the absence of zDHHC3/7.

A correlation between oxidative stress and diabetic retinopathy: An updated review

Oxidative stress (OS) is a cytopathic outcome of excessively generated reactive oxygen species (ROS), down regulated antioxidant defense signaling pathways, and the imbalance between the produced radicals and their clearance. It plays a role in the genesis of several illnesses, especially hyperglycemia and its effects. Diabetic retinal illness, a micro vascular side effect of the condition, is the prime reason of diabetic related blindness. The OS (directly or indirectly) is associated with diabetic retinopathy (DR) and related consequences. The OS is responsible to induce and interfere the metabolic signaling pathways to enhance influx of the polyol cascades and hexosamine pathways, stimulate Protein Kinase-C (PKC) variants, and accumulate advanced glycation end products (AGEs). Additionally, the inequity between the scavenging and generation of ROS is caused by the epigenetic alteration caused by hyperglycemia that suppresses the antioxidant defense system. Induced by an excessive buildup of ROS, retinal changes in structure and function include mitochondrial damage, cellular death, inflammation, and lipid peroxidation. Therefore, it is crucial to comprehend and clarify the mechanisms connected to oxidative stress that underlie the development of DR.

The role of NADPH oxidases in infectious and inflammatory diseases

Nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) are enzymes that generate superoxide or hydrogen peroxide from molecular oxygen utilizing NADPH as an electron donor. There are seven enzymes in the NOX family: NOX1-5 and dual oxidase (DUOX) 1-2. NOX enzymes in humans play important roles in diverse biological functions and vary in expression from tissue to tissue. Importantly, NOX2 is involved in regulating many aspects of innate and adaptive immunity, including regulation of type I interferons, the inflammasome, phagocytosis, antigen processing and presentation, and cell signaling. DUOX1 and DUOX2 play important roles in innate immune defenses at epithelial barriers. This review discusses the role of NOX enzymes in normal physiological processes as well as in disease. NOX enzymes are important in autoimmune diseases like type 1 diabetes and have also been implicated in acute lung injury caused by infection with SARS-CoV-2. Targeting NOX enzymes directly or through scavenging free radicals may be useful therapies for autoimmunity and acute lung injury where oxidative stress contributes to pathology.

Regulation of NADPH Oxidase-Mediated Superoxide Production by Acetylation and Deacetylation

Oral treatment of apolipoprotein E-knockout (ApoE-KO) mice with the putative sirtuin 1 (SIRT1) activator resveratrol led to a reduction of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activity in the heart. In contrast, the SIRT1 inhibitor EX527 enhanced the superoxide production in isolated human polymorphonuclear granulocytes. In human monocytic THP-1 cells, phorbol ester-stimulated superoxide production was enhanced by inhibitors of histone deacetylases (HDACs; including quisinostat, trichostatin A (TSA), PCI34051, and tubastatin A) and decreased by inhibitors of histone acetyltransferases [such as garcinol, curcumin, and histone acetyltransferase (HAT) Inhibitor II]. These results indicate that protein acetylation and deacetylation may represent crucial mechanisms regulating NADPH oxidase-mediated superoxide production. In cell-free systems, incubation of recombinant Rac1 with SIRT1 resulted in decreased Rac1 acetylation. Mass spectrometry analyses identified lysine 166 (K166) in Rac1 as a residue targeted by SIRT1. Deacetylation of Rac1 by SIRT1 markedly reduced the interaction of Rac1 with p67phox in in vitro assays. Computational modeling analyses revealed that K166 deacetylation of Rac1 led to a 5-fold reduction in its binding affinity to guanosine-5'-triphosphate, and a 21-fold decrease in its binding potential to p67phox. The latter is crucial for Rac1-mediated recruitment of p67phox to the membrane and for p67phox activation. In conclusion, both SIRT1 and non-sirtuin deacetylases play a role in regulating NADPH oxidase activity. Rac1 can be directly deacetylated by SIRT1 in a cell-free system, leading to an inhibition of Rac1-p67phox interaction. The downstream targets of non-sirtuin deacetylases are still unknown. The in vivo significance of these findings needs to be investigated in future studies.

Rac-dependent feedforward autoactivation of NOX2 leads to oxidative burst

NADPH oxidase 2 (NOX2) produces the superoxide anion radical (O₂⁻), which has functions in both cell signaling and immune defense. NOX2 is a multimeric-protein complex consisting of several protein subunits including the GTPase Rac. NOX2 uniquely facilitates an oxidative burst, which is described by initially slow O₂⁻ production, which increases over time. The NOX2 oxidative burst is considered critical to immune defense because it enables expedited O₂⁻ production in response to infections. However, the mechanism of the initiation and progression of this oxidative burst and its implications for regulation of NOX2 have not been clarified. In this study, we show that the NOX2 oxidative burst is a result of autoactivation of NOX2 coupled with the redox function of Rac. NOX2 autoactivation begins when active Rac triggers NOX2 activation and the subsequent production of O₂⁻, which in turn activates redox-sensitive Rac. This activated Rac further activates NOX2, amplifying the feedforward cycle and resulting in a NOX2-mediated oxidative burst. Using mutagenesis-based kinetic and cell analyses, we show that enzymatic activation of Rac is exclusively responsible for production of the active Rac trigger that initiates NOX2 autoactivation, whereas redox-mediated Rac activation is the main driving force of NOX2 autoactivation and contributes to generation of ∼98% of the active NOX2 in cells. The results of this study provide insight into the regulation of NOX2 function, which could be used to develop therapeutics to control immune responses associated with dysregulated NOX2 oxidative bursts.

NOX2 Activation in COVID-19: Possible Implications for Neurodegenerative Diseases

Coronavirus disease 2019 (COVID-19) is a rapidly spreading contagious infectious disease caused by the pathogen severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), that primarily affects the respiratory tract as well as the central nervous system (CNS). SARS-CoV-2 infection occurs through the interaction of the viral protein Spike with the angiotensin II receptor (ACE 2), leading to an increase of angiotensin II and activation of nicotinamide adenine dinucleotide phosphate oxidase2 (NOX2), resulting in the release of both reactive oxygen species (ROS) and inflammatory molecules. The purpose of the review is to explain that SARS-CoV-2 infection can determine neuroinflammation that induces NOX2 activation in microglia. To better understand the role of NOX2 in inflammation, an overview of its involvement in neurodegenerative diseases (NDs) such as Parkinson’s disease (PD), Alzheimer’s disease (AD), and amyotrophic lateral sclerosis (ALS) is provided. To write this manuscript, we performed a PubMed search to evaluate the possible relationship of SARS-CoV-2 infection in NOX2 activation in microglia, as well as the role of NOX2 in NDs. Several studies highlighted that NOX2 activation in microglia amplifies neuroinflammation. To date, there is no clinical treatment capable of counteracting its activation, however, NOX2 could be a promising pharmaceutical target useful for both the treatment and prevention of NDs and COVID-19 treatment.

The molecular basis of Rac-GTP action-promoting binding of p67phox to Nox2 by disengaging the β hairpin from downstream residues

p67^phox fulfils a key role in the assembly/activation of the NADPH oxidase by direct interaction with Nox2. We proposed that Rac-GTP serves both as a carrier of p67^phox to the membrane and an inducer of a conformational change enhancing its affinity for Nox2. This study provides evidence for the latter function: (i) oxidase activation was inhibited by p67^phox peptides (106-120) and (181-195), corresponding to the β hairpin and to a downstream region engaged in intramolecular bonds with the β hairpin, respectively; (ii) deletion of residues 181-193 and point mutations Q115R or K181E resulted in selective binding of p67^phox to Nox2 peptide (369-383); (iii) both deletion and point mutations led to a change in p67^phox , expressed in increased apparent molecular weights; (iv) p67^phox was bound to p67^phox peptide (181-195) and to a cluster of peptides (residues 97-117), supporting the participation of selected residues within these sequences in intramolecular bonds; (v) p67^phox failed to bind to Nox2 peptide (369-383), following interaction with Rac1-GTP, but a (p67^phox -Rac1-GTP) chimera exhibited marked binding to the peptide, similar to that of p67^phox deletion and point mutants; and (vi) size exclusion chromatography of the chimera revealed its partition in monomeric and polymeric forms, with binding to Nox2 peptide (369-383) restricted to polymers. The molecular basis of Rac-GTP action entails unmasking of a previously hidden Nox2-binding site in p67^phox , following disengagement of the β hairpin from more C-terminal residues. The domain in Nox2 binding the "modified" p67^phox comprises residues within the 369-383 sequence in the cytosolic dehydrogenase region.

Second Report of Chronic Granulomatous Disease in Jordan: Clinical and Genetic Description of 31 Patients From 21 Different Families, Including Families From Lybia and Iraq

Chronic granulomatous Disease (CGD) is a rare innate immunodeficiency disorder caused by mutations in one of the six genes (CYBA, CYBB, NCF1, NCF2, NCF4, and CYBC1/EROS) encoding the superoxide-producing nicotinamide adenine dinucleotide phosphate (NADPH)—oxidase complex in phagocytes. In the Western population, the most prevalent form of CGD (about two-thirds of all cases) is the X-linked form (X-CGD) caused by mutations in CYBB. The autosomal recessive forms (AR-CGD), due to mutations in the other genes, collectively account for the remaining one-third of CGD cases. We investigated the clinical and molecular features of 22 Jordanian, 7 Libyan, and 2 Iraqi CGD patients from 21 different families. In addition, 11 sibling patients from these families were suspected to have been died from CGD as suggested by their familial and clinical history. All patients except 9 were children of consanguineous parents. Most of the patients suffered from AR-CGD, with mutations in CYBA, NCF1, and NCF2, encoding p22^phox, p47^phox, and p67^phox proteins, respectively. AR-CGD was the most frequent form, in Jordan probably because consanguineous marriages are common in this country. Only one patient from non-consanguineous parents suffered from an X91⁰ CGD subtype (0 indicates no protein expression). AR67⁰ CGD and AR22⁰ CGD appeared to be the most frequently found sub-types but also the most severe clinical forms compared to AR47⁰ CGD. As a geographical clustering of 11 patients from eight Jordanian families exhibited the c.1171_1175delAAGCT mutation in NCF2, segregation analysis with nine polymorphic markers overlapping NCF2 indicates that a common ancestor has arisen ~1,075 years ago.

NADPH Oxidases Are Required for Full Platelet Activation In Vitro and Thrombosis In Vivo but Dispensable for Plasma Coagulation and Hemostasis

OBJECTIVE

Using 3KO (triple NOX [NADPH oxidase] knockout) mice (ie, NOX1-/-/NOX2-/-/NOX4-/-), we aimed to clarify the role of this family of enzymes in the regulation of platelets in vitro and hemostasis in vivo. Approach and Results: 3KO mice displayed significantly reduced platelet superoxide radical generation, which was associated with impaired platelet aggregation, adhesion, and thrombus formation in response to the key agonists collagen and thrombin. A comparison with single-gene knockouts suggested that the phenotype of 3KO platelets is the combination of the effects of the genetic deletion of NOX1 and NOX2, while NOX4 does not show any significant function in platelet regulation. 3KO platelets displayed significantly higher levels of cGMP-a negative platelet regulator that activates PKG (protein kinase G). The inhibition of PKG substantially but only partially rescued the defective phenotype of 3KO platelets, which are responsive to both collagen and thrombin in the presence of the PKG inhibitors KT5823 or Rp-8-pCPT-cGMPs, but not in the presence of the NOS (NO synthase) inhibitor L-NG-monomethyl arginine. In vivo, triple NOX deficiency protected against ferric chloride-driven carotid artery thrombosis and experimental pulmonary embolism, while hemostasis tested in a tail-tip transection assay was not affected. Procoagulatory activity of platelets (ie, phosphatidylserine surface exposure) and the coagulation cascade in platelet-free plasma were normal.

CONCLUSIONS

This study indicates that inhibiting NOXs has strong antithrombotic effects partially caused by increased intracellular cGMP but spares hemostasis. NOXs are, therefore, pharmacotherapeutic targets to develop new antithrombotic drugs without bleeding side effects.

Rho GTPase regulation of reactive oxygen species generation and signalling in platelet function and disease

Platelets are master regulators and effectors of haemostasis with increasingly recognized functions as mediators of inflammation and immune responses. The Rho family of GTPase members Rac1, Cdc42 and RhoA are known to be major components of the intracellular signalling network critical to platelet shape change and morphological dynamics, thus playing a major role in platelet spreading, secretion and thrombus formation. Initially linked to the regulation of actomyosin contraction and lamellipodia formation, recent reports have uncovered non-canonical functions of platelet RhoGTPases in the regulation of reactive oxygen species (ROS), where intrinsically generated ROS modulate platelet function and contribute to thrombus formation. Platelet RhoGTPases orchestrate oxidative processes and cytoskeletal rearrangement in an interconnected manner to regulate intracellular signalling networks underlying platelet activity and thrombus formation. Herein we review our current knowledge of the regulation of platelet ROS generation by RhoGTPases and their relationship with platelet cytoskeletal reorganization, activation and function.

The NADPH Oxidase Family and Its Inhibitors

Significance: The oxidative stress, resulting from an imbalance in the production and scavenging of reactive oxygen species (ROS), is known to be involved in the development and progression of several pathologies. The excess of ROS production is often due to an overactivation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOX) and for this reason these enzymes became promising therapeutic targets. However, even if NOX are now well characterized, the development of new therapies is limited by the lack of highly isoform-specific inhibitors. Recent Advances: In the past decade, several groups and laboratories have screened thousands of molecules to identify new specific inhibitors with low off-target effects. These works have led to the characterization of several new potent NOX inhibitors; however, their specificity varies a lot depending on the molecules. Critical Issues: Here, we are reviewing more than 25 known NOX inhibitors, focusing mainly on the newly identified ones such as APX-115, NOS31, Phox-I1 and 2, GLX7013114, and GSK2795039. To have a better overall view of these molecules, the inhibitors were classified according to their specificity, from pan-NOX inhibitors to highly isoform-specific ones. We are also presenting the use of these compounds both in vitro and in vivo. Future Directions: Several of these new molecules are potent and very specific inhibitors that could be good candidates for the development of new drugs. Even if the results are very promising, most of these compounds were only validated in vitro or in mice models and further investigations will be required before using them as potential therapies.

ROS in Platelet Biology: Functional Aspects and Methodological Insights

Reactive oxygen species (ROS) and mitochondria play a pivotal role in regulating platelet functions. Platelet activation determines a drastic change in redox balance and in platelet metabolism. Indeed, several signaling pathways have been demonstrated to induce ROS production by NAPDH oxidase (NOX) and mitochondria, upon platelet activation. Platelet-derived ROS, in turn, boost further ROS production and consequent platelet activation, adhesion and recruitment in an auto-amplifying loop. This vicious circle results in a platelet procoagulant phenotype and apoptosis, both accounting for the high thrombotic risk in oxidative stress-related diseases. This review sought to elucidate molecular mechanisms underlying ROS production upon platelet activation and the effects of an altered redox balance on platelet function, focusing on the main advances that have been made in platelet redox biology. Furthermore, given the increasing interest in this field, we also describe the up-to-date methods for detecting platelets, ROS and the platelet bioenergetic profile, which have been proposed as potential disease biomarkers.

Role of Skeletal Muscle in Insulin Resistance and Glucose Uptake

The skeletal muscle is the largest organ in the body, by mass. It is also the regulator of glucose homeostasis, responsible for 80% of postprandial glucose uptake from the circulation. Skeletal muscle is essential for metabolism, both for its role in glucose uptake and its importance in exercise and metabolic disease. In this article, we give an overview of the importance of skeletal muscle in metabolism, describing its role in glucose uptake and the diseases that are associated with skeletal muscle metabolic dysregulation. We focus on the role of skeletal muscle in peripheral insulin resistance and the potential for skeletal muscle-targeted therapeutics to combat insulin resistance and diabetes, as well as other metabolic diseases like aging and obesity. In particular, we outline the possibilities and pitfalls of the quest for exercise mimetics, which are intended to target the molecular mechanisms underlying the beneficial effects of exercise on metabolic disease. We also provide a description of the molecular mechanisms that regulate skeletal muscle glucose uptake, including a focus on the SNARE proteins, which are essential regulators of glucose transport into the skeletal muscle. © 2020 American Physiological Society. Compr Physiol 10:785-809, 2020.

p67phox -derived self-assembled peptides prevent Nox2 NADPH oxidase activation by an auto-inhibitory mechanism

Activation of the Nox2-dependent NADPH oxidase is the result of a conformational change in Nox2 induced by interaction with the cytosolic component p67^phox . In preliminary work we identified a cluster of overlapping 15-mer synthetic peptides, corresponding to p67^phox residues 259-279, which inhibited oxidase activity in an in vitro, cell-free assay, but the results did not point to a competitive mechanism. We recently identified an auto-inhibitory intramolecular bond in p67^phox , one extremity of which was located within the 259-279 sequence, and we hypothesized that inhibition by exogenous peptides might mimic intrinsic auto-inhibition. In this study, we found that: (i) progressive N- and C-terminal truncation of inhibitory p67^phox peptides, corresponding to residues 259-273 and 265-279, revealed that inhibitory ability correlated with the presence of residues ²⁶⁵ NIVFVL²⁷⁰ , exposed at either the N- or C-termini of the peptides; (ii) inhibition of oxidase activity was associated exclusively with self-assembled peptides, which pelleted upon centrifugation at 12,000 ×g; (iii) self-assembled p67^phox peptides inhibited oxidase activity by specific binding of p67^phox and the ensuing depletion of this component, essential for interaction with Nox2; and (iv) peptides subjected to scrambling or reversing the order of residues in NIVFVL retained the propensity for self-assembly, oxidase inhibitory ability, and specific binding of p67^phox , indicating that the dominant parameter was the hydrophobic character of five of the six residues. This appears to be the first description of inhibition of oxidase activity by self-assembled peptides derived from an oxidase component, acting by an auto-inhibitory mechanism.

A novel variant in the neutrophil cytosolic factor 2 (NCF2) gene results in severe disseminated BCG infectious disease: A clinical report and literature review

Background

Chronic granulomatous disease (CGD) is a rare primary immunodeficiency disorder (PID) affecting NADPH oxidase activity. The rarest form of the disease is considered to be caused by NCF2 gene bi‐allelic variant. Here, we report the clinical and molecular characterization of a patient presenting with early‐onset severe disease due to bi‐allelic NCF2 variant.

Methods

Gene mutational analysis was performed by whole‐exome and Sanger sequencing.

Results

The patient presented with a history of fever and rash since the age of 1 month, followed by destructive osteomyelitis and necrotizing lymphadenopathy. The patient received the Bacillus Calmette‐Guérin (BCG) vaccine at birth; she was subsequently diagnosed with disseminated BCG infection. Whole‐exome sequencing identified a private (unreported) homozygous variant in NCF2 (c.290C > A) that results in a nonconservative change, p.Ala97Asp, in the p67^phox protein. The variant is located in the third helix of the TRP domain, which is crucial for the binding of GTPase RAC2 to the NADPH oxidase complex.

Conclusion

We identified a novel NCF2 variant located in the region interacting with RAC2 that is linked to a severe and early CGD phenotype in the setting of disseminated BCG infection. Our findings support postponing BCG vaccination until 6–12 months of age and after PID assessment.

The Emerging Roles of Nicotinamide Adenine Dinucleotide Phosphate Oxidase 2 in Skeletal Muscle Redox Signaling and Metabolism

Significance: Skeletal muscle is a crucial tissue to whole-body locomotion and metabolic health. Reactive oxygen species (ROS) have emerged as intracellular messengers participating in both physiological and pathological adaptations in skeletal muscle. A complex interplay between ROS-producing enzymes and antioxidant networks exists in different subcellular compartments of mature skeletal muscle. Recent evidence suggests that nicotinamide adenine dinucleotide phosphate (NADPH) oxidases (NOXs) are a major source of contraction- and insulin-stimulated oxidants production, but they may paradoxically also contribute to muscle insulin resistance and atrophy. Recent Advances: Pharmacological and molecular biological tools, including redox-sensitive probes and transgenic mouse models, have generated novel insights into compartmentalized redox signaling and suggested that NOX2 contributes to redox control of skeletal muscle metabolism. Critical Issues: Major outstanding questions in skeletal muscle include where NOX2 activation occurs under different conditions in health and disease, how NOX2 activation is regulated, how superoxide/hydrogen peroxide generated by NOX2 reaches the cytosol, what the signaling mediators are downstream of NOX2, and the role of NOX2 for different physiological and pathophysiological processes. Future Directions: Future research should utilize and expand the current redox-signaling toolbox to clarify the NOX2-dependent mechanisms in skeletal muscle and determine whether the proposed functions of NOX2 in cells and animal models are conserved into humans.

The β2-adrenergic receptor-ROS signaling axis: An overlooked component of β2AR function?

β2-Adrenergic receptor (β2AR) agonists are clinically used to elicit rapid bronchodilation for the treatment of bronchospasms in pulmonary diseases such as asthma and COPD, both of which exhibit characteristically high levels of reactive oxygen species (ROS); likely secondary to over-expression of ROS generating enzymes and chronically heightened inflammation. Interestingly, β2AR has long-been linked to ROS, yet the involvement of ROS in β2AR function has not been as vigorously studied as other aspects of β2AR signaling. Herein, we discuss the existing body of evidence linking β2AR activation to intracellular ROS generation and importantly, the role of ROS in regulating β2AR function. The reciprocal interplay of the β2AR and ROS appear to endow this receptor with the ability to self-regulate signaling efficacy and ligand binding, hereby unveiling a redox-axis that may be unfavorably altered in pathological states contributing to both disease progression and therapeutic drug responses.

Fas-associated factor 1 mediates NADPH oxidase-induced reactive oxygen species production and proinflammatory responses in macrophages against Listeria infection

Fas-associated factor 1 is a death-promoting protein that induces apoptosis by interacting with the Fas receptor. Until now, FAF1 was reported to interact potentially with diverse proteins and to function as a negative and/or positive regulator of several cellular possesses. However, the role of FAF1 in defense against bacterial infection remains unclear. Here, we show that FAF1 plays a pivotal role in activating NADPH oxidase in macrophages during Listeria monocytogenes infection. Upon infection by L. monocytogenes, FAF1 interacts with p67phox (an activator of the NADPH oxidase complex), thereby facilitating its stabilization and increasing the activity of NADPH oxidase. Consequently, knockdown or ectopic expression of FAF1 had a marked effect on production of ROS, proinflammatory cytokines, and antibacterial activity, in macrophages upon stimulation of TLR2 or after infection with L. monocytogenes. Consistent with this, FAF1^gt/gt mice, which are knocked down in FAF1, showed weaker inflammatory responses than wild-type mice; these weaker responses led to increased replication of L. monocytogenes. Collectively, these findings suggest that FAF1 positively regulates NADPH oxidase-mediated ROS production and antibacterial defenses.

Phagocytic NADPH oxidase plays a pivotal role in generating reactive oxygen species (ROS) and in defense against bacterial infections such as L. monocytogenes. ROS eliminate phagocytosed bacteria directly and are implicated in transduction of signals that mediate inflammatory responses. Here, we show that the apoptotic protein FAF1 regulates ROS production in macrophages by regulating phagocytic NADPH oxidase activity upon infection by L. monocytogenes. FAF1 interacts directly with and stabilizes p67phox, a regulatory protein of the phagocytic NADPH oxidase complex, to induce ROS production during L. monocytogenes infection. Production of ROS leads to release of proinflammatory cytokines, chemokines and, ultimately, to bacterial clearance. Interestingly, FAF1^gt/gt mice deficient in FAF1 expression exhibit weakened inflammatory responses and are thus more vulnerable to bacterial infection than FAF1^+/+ mice. This study reveals that FAF1 is a crucial regulator that induces inflammatory responses to bacterial infection via ROS production.

Dominant activating RAC2 mutation with lymphopenia, immunodeficiency, and cytoskeletal defects

Ras-related C3 botulinum toxin substrate 2 (RAC2), through interactions with reduced NAD phosphate oxidase component p67 phox , activates neutrophil superoxide production, whereas interactions with p21-activated kinase are necessary for fMLF-induced actin remodeling. We identified 3 patients with de novo RAC2[E62K] mutations resulting in severe T- and B-cell lymphopenia, myeloid dysfunction, and recurrent respiratory infections. Neutrophils from RAC2[E62K] patients exhibited excessive superoxide production, impaired fMLF-directed chemotaxis, and abnormal macropinocytosis. Cell lines transfected with RAC2[E62K] displayed characteristics of active guanosine triphosphate (GTP)-bound RAC2 including enhanced superoxide production and increased membrane ruffling. Biochemical studies demonstrated that RAC2[E62K] retains intrinsic GTP hydrolysis; however, GTPase-activating protein failed to accelerate hydrolysis resulting in prolonged active GTP-bound RAC2. Rac2+/E62K mice phenocopy the T- and B-cell lymphopenia, increased neutrophil F-actin, and excessive superoxide production seen in patients. This gain-of-function mutation highlights a specific, nonredundant role for RAC2 in hematopoietic cells that discriminates RAC2 from the related, ubiquitous RAC1.

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.

Mammalian NADPH Oxidases

Reactive oxygen species (ROS) are highly reactive oxygen derivatives. Initially, they were considered as metabolic by-products (of mitochondria in particular), which consistently lead to aging and disease. Over the last decades, however, it became increasingly apparent that virtually all eukaryotic cells possess specifically ROS-producing enzymes, namely, NOX NADPH oxidases. In most mammals, there are seven NOX isoforms: three closely related isoforms, NOX1, 2, 3, which are activated by cytoplasmic subunits; NOX4, which appears to be constitutively active; and the EF-hand-containing Ca²⁺-activated isoforms NOX5 and DUOX1 and 2. Loss-of-function mutations in NOX genes can lead to serious human disease. NOX2 deficiency leads to primary immune deficiency, while DUOX2 deficiency presents as congenital hypothyroidism. Nox-deficient mice provide important tools to explore the physiological functions of various NADPH oxidases as a loss of function in Nox2, Nox3, and Duox2 leads to a spontaneous phenotype. The genetic absence of Nox1, Nox4, and Duox1 does not result in an obvious mouse phenotype (the NOX5 gene is absent in rodents and can therefore not be studied using knockout mice). Since the discovery of the NOX family at the turn of the millennium, much progress in understanding the biochemistry and the physiology of NOX has been made; however many questions remain unanswered to date. This chapter is an overview of our present knowledge on mammalian NOX/DUOX enzymes.

Soluble Regulatory Proteins for Activation of NOX Family NADPH Oxidases

NOX family NADPH oxidases deliberately produce reactive oxygen species and thus contribute to a variety of biological functions. Of seven members in the human family, the three oxidases NOX2, NOX1, and NOX3 form a heterodimer with p22^phox and are regulated by soluble regulatory proteins: p47^phox, its related organizer NOXO1; p67^phox, its related activator NOXA1; p40^phox; and the small GTPase Rac. Activation of the phagocyte oxidase NOX2 requires p47^phox, p67^phox, and GTP-bound Rac. In addition to these regulators, p40^phox plays a crucial role when NOX2 is activated during phagocytosis. On the other hand, NOX1 activation prefers NOXO1 and NOXA1, although Rac is also involved. NOX3 constitutively produces superoxide, which is enhanced by regulatory proteins such as p47^phox, NOXO1, and p67^phox. Here we describe mechanisms for NOX activation with special attention to the soluble regulatory proteins.

Arachidonic Acid and Nitroarachidonic: Effects on NADPH Oxidase Activity

Arachidonic acid (AA) is a polyunsaturated fatty acid that participates in the inflammatory response mainly through bioactive-lipids formation in macrophages and also in the phagocytic NADPH oxidase 2 (NOX2) activation. NOX2 is the enzyme responsible for a huge superoxide formation in macrophages, essential to eliminate pathogens inside the phagosome. The oxidase is an enzymatic complex comprised of a membrane-bound flavocytochrome b ₅₅₈ (gp91^phox/p22^phox), three cytosolic subunits (p47^phox, p40^phox and p67^phox) and a Rac-GTPase. The enzyme becomes active when macrophages are exposed to appropriate stimuli that trigger the phosphorylation of cytosolic subunits and its migration to plasmatic membrane to form the active complex. It is proposed that AA stimulates NOX2 activity through AA interaction with different components of the NADPH oxidase complex. In inflammatory conditions, there is an increase in reactive oxygen and nitrogen species that results in the production of nitrated derivatives of AA, such as nitroarachidonic acid (NO₂-AA). NO₂-AA is capable to inhibit NOX2 activity by interfering with p47^phox migration to the membrane without affecting phosphorylation of cytosolic proteins. Also, NO₂-AA is capable to interact with protein disulfide isomerase (PDI), which is involved on NOX2 active complex formation. It has been demonstrated that NO₂-AA forms a covalent adduct with PDI that could prevent the interaction with NOX2 and it would explain the inhibitory effects of the fatty acid upon NOX2. Together, current data indicate that AA is an important activator of NOX2 formed in the early events of the inflammatory response, leading to a massive production of oxidants that may, in turn, promote NO₂-AA formation and shutting down the oxidative burst. Hence, AA and its derivatives could have antagonistic roles on NOX2 activity regulation.

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.

Insights into the NOX NADPH Oxidases Using Heterologous Whole Cell Assays

Assays based on ectopic expression of NOX NADPH oxidase subunits in heterologous mammalian cells are an important approach for investigating features of this family of enzymes. These model systems have been used to analyze the biosynthesis and functional domains of NOX enzyme components as well as their regulation and cellular activities. This chapter provides an overview of the basic principles and applications of heterologous whole cell assays in studying NOX NADPH oxidases.

Small molecule targeting the Rac1-NOX2 interaction prevents collagen-related peptide and thrombin-induced reactive oxygen species generation and platelet activation

Essentials Reactive oxygen species (ROS) generation by NOX2 plays a critical role in platelet activation. Rac1 regulation of NOX2 is important for ROS generation. Small molecule inhibitor of the Rac1-p67phox interaction prevents platelet activation. Pharmacologic targeting of Rac1-NOX2 axis can be a viable approach for antithrombotic therapy.

SUMMARY

Background Platelets from patients with X-linked chronic granulomatous disease or mice deficient in nicotinamide adenine dinucleotide (phosphate) (NAD(P)H) oxidase isoform NOX2 exhibit diminished reactive oxygen species (ROS) generation and platelet activation. Binding of Rac1 GTPase to p67phox plays a critical role in NOX2 activation by facilitating the assembly of the NOX2 enzyme complex. Objective We tested the hypothesis that Phox-I, a rationally designed small molecule inhibitor of Rac-p67phox interaction, may serve as an antithrombosis agent by suppressing ROS production and platelet activation. Results Collagen-related peptide (CRP) induced ROS generation in a time-dependent manner. Platelets from Rac1-/- mice or human platelets treated with NSC23766, a specific Rac inhibitor, produced significantly less ROS in response to CRP. Treatment of platelets with Phox-I inhibited diverse CRP-induced responses, including: (i) ROS generation; (ii) release of P-selectin; (iii) secretion of ATP; (iv) platelet aggregation; and (v) phosphorylation of Akt. Similarly, incubation of platelets with Phox-I inhibited thrombin-induced: (i) secretion of ATP; (ii) platelet aggregation; (iii) rise in cytosolic calcium; and (iv) phosphorylation of Akt. In mouse models, intraperitoneal administration of Phox-I inhibited: (i) collagen-induced platelet aggregation without affecting the tail bleeding time and (ii) in vivo platelet adhesion/accumulation at the laser injury sites on the saphenous vein without affecting the time for complete cessation of blood loss. Conclusions Small molecule targeting of the Rac1-p67phox interaction may present an antithrombosis regimen by preventing GPVI- and non-GPVI-mediated NOX2 activation, ROS generation and platelet function without affecting the bleeding time.

N-Formyl Peptide Receptors Induce Radical Oxygen Production in Fibroblasts Derived From Systemic Sclerosis by Interacting With a Cleaved Form of Urokinase Receptor

Systemic sclerosis (SSc) is a chronic autoimmune disease characterized by fibrosis, alteration in the microvasculature and immunologic abnormalities. It has been hypothesized that an abnormal redox state could regulate the persistent fibrotic phenotype in SSc patients. N-Formyl peptide receptors (FPRs) are chemotactic receptors overexpressed in fibroblasts derived from SSc patients. In this study, we demonstrated that stimulation of FPRs promotes the generation of reactive oxygen species (ROS) in skin fibroblasts. In fibroblast cells, ROS production was due to FPRs interaction with the urokinase receptor (uPAR) and to β₁ integrin engagement. FPRs cross-talk with uPAR and integrins led to Rac1 and ERKs activation. FPRs stimulation increased gp91phox and p67phox expression as well as the direct interaction between GTP-Rac1 and p67phox, thus promoting assembly and activation of the NADPH oxidase complex. FPRs functions occur through interaction with a specific domain of uPAR (residues ₈₈SRSRY₉₂) that can be exposed on the cell membrane by protease-mediated receptor cleavage. Immunohistochemistry analysis with a specific anti-SRSRY antibody showed increased expression of uPAR in a cleaved form, which exposes the SRSRY sequence at its N-terminus (DIIDIII-uPAR88–92) in skin biopsies from SSc patients. As expected by the increased expression of both FPRs and DII-DIII-uPAR_88-92, fibroblasts derived from SSc patients showed a significantly increase in ROS generation both at a basal level than after FPRs stimulation, as compared to fibroblasts from normal subjects. C37, a small molecule blocking the interaction between FPRs and uPAR, and selumetinib, a clinically approved MAPKK/ERK inhibitor, significantly inhibited FPRs-mediated ROS production in fibroblasts derived from SSc patients. Thus, FPRs, through the interaction with the uPA/uPAR system, can induce ROS generation in fibroblasts by activating the NADPH oxidase, playing a role in the alteration of the redox state observed in SSc.

PlexinD1 signaling controls morphological changes and migration termination in newborn neurons

Newborn neurons maintain a very simple, bipolar shape, while they migrate from their birthplace toward their destinations in the brain, where they differentiate into mature neurons with complex dendritic morphologies. Here, we report a mechanism by which the termination of neuronal migration is maintained in the postnatal olfactory bulb (OB). During neuronal deceleration in the OB, newborn neurons transiently extend a protrusion from the proximal part of their leading process in the resting phase, which we refer to as a filopodium-like lateral protrusion (FLP). The FLP formation is induced by PlexinD1 downregulation and local Rac1 activation, which coincide with microtubule reorganization and the pausing of somal translocation. The somal translocation of resting neurons is suppressed by microtubule polymerization within the FLP The timing of neuronal migration termination, controlled by Sema3E-PlexinD1-Rac1 signaling, influences the final positioning, dendritic patterns, and functions of the neurons in the OB These results suggest that PlexinD1 signaling controls FLP formation and the termination of neuronal migration through a precise control of microtubule dynamics.

Structural complexity and functional diversity of plant NADPH oxidases

Plant NADPH oxidases also known as respiratory burst oxidase homologs (Rbohs) are a family of membrane-bound enzymes that play diverse roles in the defense response and morphogenetic processes via regulated generation of reactive oxygen species. Rbohs are associated with a variety of functions, although the reason for this is not clear. To evaluate using bioinformatics, the possible mechanisms for the observed functional diversity within the plant kingdom, 127 Rboh protein sequences representing 26 plant species were analyzed. Multiple clusters were identified with gene duplications that were both dicot as well as monocot-specific. The N-terminal sequences were observed to be highly variable. The conserved cysteine (equivalent of Cys890) in C-terminal of AtRbohD suggested that the redox-based modification like S-nitrosylation may regulate the activity of other Rbohs. Three-dimensional models corresponding to the N-terminal domain for Rbohs from Arabidopsis thaliana and Oryza sativa were constructed and molecular dynamics studies were carried out to study the role of Ca2+ in the folding of Rboh proteins. Certain mutations indicated possibly affect the structure and function of the plant NADPH oxidases, thereby providing the rationale for further experimental validation.

Conversion of NOX2 into a constitutive enzyme in vitro and in living cells, after its binding with a chimera of the regulatory subunits

During the phagocytosis of pathogens by phagocyte cells, the NADPH oxidase complex is activated to produce superoxide anion, a precursor of microbial oxidants. The activated NADPH oxidase complex from phagocytes consists in two transmembrane proteins (Nox2 and p22^phox) and four cytosolic proteins (p40^phox, p47^phox, p67^phox and Rac1-2). In the resting state of the cells, these proteins are dispersed in the cytosol, the membrane of granules and the plasma membrane. In order to synchronize the assembly of the cytosolic subunits on the membrane components of the oxidase, a fusion of the cytosolic proteins p47^phox, p67^phox and Rac1 named trimera was constructed. The trimera investigated in this paper is composed of the p47^phox segment 1-286, the p67^phox segment 1-212 and the mutated Rac1(Q61L). We demonstrate that the complex trimera-cyt b₅₅₈ is functionally comparable to the one containing the separated subunits. Each of the subunits p47^phox, p67^phox and Rac1Q61L has kept its own activating property. The trimera is produced in an activated conformation as seen by circular dichroism. However, the presence of amphiphile is still necessary in a cell-free system to trigger superoxide anion production. The COS7^gp91-p22 cells expressing the trimera produce continuously superoxide anion at high rate. This constitutive activity in cells can be of particular interest for understanding the NADPH oxidase functioning independently of signaling pathways.

Neutrophils to the ROScue: Mechanisms of NADPH Oxidase Activation and Bacterial Resistance

Reactive oxygen species (ROS) generated by NADPH oxidase play an important role in antimicrobial host defense and inflammation. Their deficiency in humans results in recurrent and severe bacterial infections, while their unregulated release leads to pathology from excessive inflammation. The release of high concentrations of ROS aids in clearance of invading bacteria. Localization of ROS release to phagosomes containing pathogens limits tissue damage. Host immune cells, like neutrophils, also known as PMNs, will release large amounts of ROS at the site of infection following the activation of surface receptors. The binding of ligands to G-protein-coupled receptors (GPCRs), toll-like receptors, and cytokine receptors can prime PMNs for a more robust response if additional signals are encountered. Meanwhile, activation of Fc and integrin directly induces high levels of ROS production. Additionally, GPCRs that bind to the bacterial-peptide analog fMLP, a neutrophil chemoattractant, can both prime cells and trigger low levels of ROS production. Engagement of these receptors initiates intracellular signaling pathways, resulting in activation of downstream effector proteins, assembly of the NADPH oxidase complex, and ultimately, the production of ROS by this complex. Within PMNs, ROS released by the NADPH oxidase complex can activate granular proteases and induce the formation of neutrophil extracellular traps (NETs). Additionally, ROS can cross the membranes of bacterial pathogens and damage their nucleic acids, proteins, and cell membranes. Consequently, in order to establish infections, bacterial pathogens employ various strategies to prevent restriction by PMN-derived ROS or downstream consequences of ROS production. Some pathogens are able to directly prevent the oxidative burst of phagocytes using secreted effector proteins or toxins that interfere with translocation of the NADPH oxidase complex or signaling pathways needed for its activation. Nonetheless, these pathogens often rely on repair and detoxifying proteins in addition to these secreted effectors and toxins in order to resist mammalian sources of ROS. This suggests that pathogens have both intrinsic and extrinsic mechanisms to avoid restriction by PMN-derived ROS. Here, we review mechanisms of oxidative burst in PMNs in response to bacterial infections, as well as the mechanisms by which bacterial pathogens thwart restriction by ROS to survive under conditions of oxidative stress.

Inhibitory Effects of Echinochrome A, Isolated from Shell of the Sea Urchin Anthocidaris crassispina, on Antigen-Stimulated Degranulation in Rat Basophilic Leukemia RBL-2H3 Cells through Suppression of Lyn Activation

Echinochrome A (Echi-A) was isolated from the sea urchin Anthocidaris crassispina and its structure determined using 1D and 2D-NMR. In the present study, we examined the inhibitory effect of Echi-A on antigen-stimulated degranulation in rat basophilic leukemia RBL-2H3 cells, which were suppressed in a dose dependent manner. The antigens bind to the high affinity immunoglobulin E receptor, which is expressed on the surface of mast cells and basophils and activate intracellular signal transduction, resulting in the release of biologically active mediators such as histamine. In order to disclose the inhibitory mechanisms of degranulation by Echi-A, we examined the elevation in intracellular Ca2+ concentration ([Ca2+]i), production levels of intracellular reactive oxygen species (ROS) and early intracellular signaling events. Both elevation of [Ca2+]i and intracellular ROS production were markedly suppressed in cells treated with Echi-A. Echi-A also suppressed the activation of Lyn, Syk, and PLCγ1/2 in antigen-stimulated cells. These results indicated that inhibition of antigen-stimulated degranulation in RBL-2H3 cells by Echi-A is mainly due to the inactivation of Lyn/Syk/PLCγ signaling pathways. Our findings suggest that Echi-A could be a beneficial agent for alleviating the symptoms of type I allergy.

Nox1 in cardiovascular diseases: regulation and pathophysiology

Since its discovery in 1999, a number of studies have evaluated the role of Nox1 NADPH oxidase in the cardiovascular system. Nox1 is activated in vascular cells in response to several different agonists, with its activity regulated at the transcriptional level as well as by NADPH oxidase complex formation, protein stabilization and post-translational modification. Nox1 has been shown to decrease the bioavailability of nitric oxide, transactivate the epidermal growth factor receptor, induce pro-inflammatory signalling, and promote cell migration and proliferation. Enhanced expression and activity of Nox1 under pathologic conditions results in excessive production of reactive oxygen species and dysregulated cellular function. Indeed, studies using genetic models of Nox1 deficiency or overexpression have revealed roles for Nox1 in the pathogenesis of cardiovascular diseases ranging from atherosclerosis to hypertension, restenosis and ischaemia/reperfusion injury. These data suggest that Nox1 is a potential therapeutic target for vascular disease, and drug development efforts are ongoing to identify a specific bioavailable inhibitor of Nox1.

The Role of NADPH Oxidases (NOXs) in Liver Fibrosis and the Activation of Myofibroblasts

Chronic liver injury, resulted from different etiologies (e.g., virus infection, alcohol abuse, nonalcoholic steatohepatitis (NASH) and cholestasis) can lead to liver fibrosis characterized by the excess accumulation of extracellular matrix (ECM) proteins (e.g., type I collagen). Hepatic myofibroblasts that are activated upon liver injury are the key producers of ECM proteins, contributing to both the initiation and progression of liver fibrosis. Hepatic stellate cells (HSCs) and to a lesser extent, portal fibroblast, are believed to be the precursor cells that give rise to hepatic myofibroblasts in response to liver injury. Although, much progress has been made toward dissecting the lineage origin of myofibroblasts, how these cells are activated and become functional producers of ECM proteins remains incompletely understood. Activation of myofibroblasts is a complex process that involves the interactions between parenchymal and non-parenchymal cells, which drives the phenotypic change of HSCs from a quiescent stage to a myofibroblastic and active phenotype. Accumulating evidence has suggested a critical role of NADPH oxidase (NOX), a multi-component complex that catalyzes reactions from molecular oxygen to reactive oxygen species (ROS), in the activation process of hepatic myofibroblasts. NOX isoforms, including NOX1, NOX2 and NOX4, and NOX-derived ROS, have all been implicated to regulate HSC activation and hepatocyte apoptosis, both of which are essential steps for initiating liver fibrosis. This review highlights the importance of NOX isoforms in hepatic myofibroblast activation and the progression of liver fibrosis, and also discusses the therapeutic potential of targeting NOXs for liver fibrosis and associated hepatic diseases.

FgNoxR, a regulatory subunit of NADPH oxidases, is required for female fertility and pathogenicity in Fusarium graminearum

Fusarium graminearum is a filamentous fungal pathogen that causes wheat Fusarium head blight. In this study, we identified FgNoxR, a regulatory subunit of NADPH oxidases (Nox) in F. graminearum, and found that it plays an important role in the pathogenicity of F. graminearum. FgNoxR is localized on punctate structures throughout the cytoplasm in aerial hyphae while these structures tend to accumulate at or near the plasma membrane, septa and hyphal tips in germinated conidia. Deletion of the FgNOXR gene results in reduced conidiation and germination. Importantly, sexual development is totally abolished in the FgNOXR deletion mutant. In addition, the disease lesion of FgNOXR deletion mutant is limited to the inoculated spikelets of wheat heads. Finally, FgNoxR interacts with FgRac1 and FgNoxA, and all three proteins are required for female fertility. Taken together, our data indicate that FgNoxR contributes to conidiation, sexual reproduction and pathogenesis in F. graminearum.

Clinical Application of NOX Activity and Other Oxidative Biomarkers in Cardiovascular Disease: A Critical Review

SIGNIFICANCE

The oxidative stress theory of atherosclerosis is based on the assumption that the production of reactive oxidant species (ROS) by blood, as well as resident cells of the artery wall, elicits the formation of oxidized low-density lipoproteins (ox-LDL), which, in turn, promotes a series of inflammatory responses, ultimately leading to atherosclerotic plaque. This theory prompted the development of new laboratory methodologies that aimed at assessing the relationship between oxidative stress and clinical progression of human atherosclerosis.

CRITICAL ISSUES

Markers assessing the oxidation of phospholipid and protein components of LDL were among the first to be developed. Clinical trials included cross-sectional as well as retrospective and prospective studies that, however, provided equivocal results. Thus, clear evidence that oxidative biomarkers add more to the risk stratification by common atherosclerotic risk factors is still lacking.

RECENT ADVANCES

More recently, the analysis of oxidative stress focused on enzymatic pathways generating ROS, such as NADPH oxidase and myeloperoxidase (MPO). Experimental and clinical studies suggest that both enzymes may be implicated in promoting atherosclerotic disease. Novel laboratory methodologies have been, therefore, developed to study NADPH oxidase and MPO in patients with stable atherosclerosis as well as in patients with acute coronary and cerebro-vascular syndromes.

FUTURE DIRECTIONS

This review will analyze the strengths and weaknesses of the current methodology to study these enzymes in human atherosclerosis with particular regard to their clinical application in several settings of cardiovascular disease. Clinical methodology and results of previous studies with regard to markers of LDL oxidation have also been reviewed as a useful background for the future development of clinical trials.

The Role of PB1 Domain Proteins in Endothelial Cell Dysfunction and Disease

SIGNIFICANCE

There are a limited number of proteins containing the Phox-Bem1 (PB1) protein interaction domain, and almost all of them play some role in endothelial cell (EC) function, health, and homeostasis.

RECENT ADVANCES

Most of these proteins have been shown to physically interact through PB1-PB1 binding and, as such, are linked together to form complexes that are responsive to hemodynamic force. These complexes range from redox regulation to inflammation to autophagy and back, and they employ multiple feedback mechanisms that are reliant on PB1 domain proteins.

CRITICAL ISSUES

Pathologic roles for PB1 domain-containing proteins have been demonstrated in multiple diseases, including vascular disease, cancer, liver disease, and myriad other concerns. Findings cited in this review show that dimerization of PB1 proteins exerts novel effects on EC function that may be important in multiple cardiovascular diseases, including atherosclerosis, thrombosis, inflammation, and hypertension.

FUTURE DIRECTIONS

As mechanistic understanding of the component pathways (redox regulation, cell polarity, inflammation, atheroprotection, and autophagy) is continually increasing, the larger picture of how these pathways interact with one another is evolving rapidly. We can now evaluate the PB1 domain proteins as a family in the context of multiple phenotypic readouts in EC function as well as evaluate them as drug targets against disease.

AMPylation of Rho GTPases subverts multiple host signaling processes

Rho GTPases are frequent targets of virulence factors as they are keystone signaling molecules. Herein, we demonstrate that AMPylation of Rho GTPases by VopS is a multifaceted virulence mechanism that counters several host immunity strategies. Activation of NFκB, Erk, and JNK kinase signaling pathways were inhibited in a VopS-dependent manner during infection with Vibrio parahaemolyticus. Phosphorylation and degradation of IKBα were inhibited in the presence of VopS as was nuclear translocation of the NFκB subunit p65. AMPylation also prevented the generation of superoxide by the phagocytic NADPH oxidase complex, potentially by inhibiting the interaction of Rac and p67. Furthermore, the interaction of GTPases with the E3 ubiquitin ligases cIAP1 and XIAP was hindered, leading to decreased degradation of Rac and RhoA during infection. Finally, we screened for novel Rac1 interactions using a nucleic acid programmable protein array and discovered that Rac1 binds to the protein C1QA, a protein known to promote immune signaling in the cytosol. Interestingly, this interaction was disrupted by AMPylation. We conclude that AMPylation of Rho Family GTPases by VopS results in diverse inhibitory consequences during infection beyond the most obvious phenotype, the collapse of the actin cytoskeleton.

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.

The crystal structure of the plant small GTPase OsRac1 reveals its mode of binding to NADPH oxidase

Rac/Rop proteins are Rho-type small GTPases that act as molecular switches in plants. Recent studies have identified these proteins as key components in many major plant signaling pathways, such as innate immunity, pollen tube growth, and root hair formation. In rice, the Rac/Rop protein OsRac1 plays an important role in regulating the production of reactive oxygen species (ROS) by the NADPH oxidase OsRbohB during innate immunity. However, the molecular mechanism by which OsRac1 regulates OsRbohB remains unknown. Here, we report the crystal structure of OsRac1 complexed with the non-hydrolyzable GTP analog guanosine 5'-(β,γ-imido)triphosphate at 1.9 Å resolution; this represents the first active-form structure of a plant small GTPase. To elucidate the ROS production in rice cells, structural information was used to design OsRac1 mutants that displayed reduced binding to OsRbohB. Only mutations in the OsRac1 Switch I region showed attenuated interactions with OsRbohB in vitro. In particular, Tyr(39) and Asp(45) substitutions suppressed ROS production in rice cells, indicating that these residues are critical for interaction with and activation of OsRbohB. Structural comparison of active-form OsRac1 with AtRop9 in its GDP-bound inactive form showed a large conformational difference in the vicinity of these residues. Our results provide new insights into the molecular mechanism of the immune response through OsRac1 and the various cellular responses associated with plant Rac/Rop proteins.

Arachidonic acid induces direct interaction of the p67(phox)-Rac complex with the phagocyte oxidase Nox2, leading to superoxide production

The phagocyte NADPH oxidase Nox2, heterodimerized with p22(phox) in the membrane, is dormant in resting cells but becomes activated upon cell stimulation to produce superoxide, a precursor of microbicidal oxidants. Nox2 activation requires two switches to be turned on simultaneously: a conformational change of the cytosolic protein p47(phox) and GDP/GTP exchange on the small GTPase Rac. These proteins, in an active form, bind to their respective targets, p22(phox) and p67(phox), leading to productive oxidase assembly at the membrane. Although arachidonic acid (AA) efficiently activates Nox2 both in vivo and in vitro, the mechanism has not been fully understood, except that AA induces p47(phox) conformational change. Here we show that AA elicits GDP-to-GTP exchange on Rac at the cellular level, consistent with its role as a potent Nox2 activator. However, even when constitutively active forms of p47(phox) and Rac1 are both expressed in HeLa cells, superoxide production by Nox2 is scarcely induced in the absence of AA. These active proteins also fail to effectively activate Nox2 in a cell-free reconstituted system without AA. Without affecting Rac-GTP binding to p67(phox), AA induces the direct interaction of Rac-GTP-bound p67(phox) with the C-terminal cytosolic region of Nox2. p67(phox)-Rac-Nox2 assembly and superoxide production are both abrogated by alanine substitution for Tyr-198, Leu-199, and Val-204 in the p67(phox) activation domain that localizes the C-terminal to the Rac-binding domain. Thus the "third" switch (AA-inducible interaction of p67(phox)·Rac-GTP with Nox2) is required to be turned on at the same time for Nox2 activation.

Role of the Rho GTPase Rac in the activation of the phagocyte NADPH oxidase: outsourcing a key task

The superoxide-generating NADPH oxidase of phagocytes consists of the membrane-associated cytochrome b 558 (a heterodimer of Nox2 and p22(phox)) and 4 cytosolic components: p47(phox), p67(phox), p40(phox), and the small GTPase, Rac, in complex with RhoGDI. Superoxide is produced by the NADPH-driven reduction of molecular oxygen, via a redox gradient located in Nox2. Electron flow in Nox2 is initiated by interaction with cytosolic components, which translocate to the membrane, p67(phox) playing the central role. The participation of Rac is expressed in the following sequence: (1) Translocation of the RacGDP-RhoGDI complex to the membrane; (2) Dissociation of RacGDP from RhoGDI; (3) GDP to GTP exchange on Rac, mediated by a guanine nucleotide exchange factor; (4) Binding of RacGTP to p67(phox); (5) Induction of a conformational change in p67(phox), promoting interaction with Nox2. The particular involvement of Rac in NADPH oxidase assembly serves as a paradigm for signaling by Rho GTPases, in general.

Role of Rac GTPase activating proteins in regulation of NADPH oxidase in human neutrophils

Precise spatiotemporal regulation of O2(-)-generating NADPH oxidases (Nox) is a vital requirement. In the case of Nox1-3, which depend on the small GTPase Rac, acceleration of GTP hydrolysis by GTPase activating protein (GAP) could represent a feasible temporal control mechanism. Our goal was to investigate the molecular interactions between RacGAPs and phagocytic Nox2 in neutrophilic granulocytes. In structural studies we revealed that simultaneous interaction of Rac with its effector protein p67(phox) and regulatory protein RacGAP was sterically possible. The effect of RacGAPs was experimentally investigated in a cell-free O2(-)-generating system consisting of isolated membranes and recombinant p47(phox) and p67(phox) proteins. Addition of soluble RacGAPs decreased O2(-) production and there was no difference in the effect of four RacGAPs previously identified in neutrophils. Depletion of membrane-associated RacGAPs had a selective effect: a decrease in ARHGAP1 or ARHGAP25 level increased O2(-) production but a depletion of ARHGAP35 had no effect. Only membrane-localized RacGAPs seem to be able to interact with Rac when it is assembled in the Nox2 complex. Thus, in neutrophils multiple RacGAPs are involved in the control of O2(-) production by Nox2, allowing selective regulation via different signaling pathways.

Platelet NOX, a novel target for anti-thrombotic treatment

There is a growing body of evidence to suggest that reactive oxidant species (ROS) including O2-, OH- or H2O2 act as second messengers to activate platelets via 1) calcium mobilisation, 2) nitric oxide (NO) inactivation, and 3) interaction with arachidonic to give formation of isoprostanes. Among the enzymes generating ROS formation NOX2, the catalytic core of NADPH oxidase (NOX), plays a prominent role as shown by the almost absent ROS production by platelets taken from patients with hereditary deficiency of NOX2. Experimental and clinical studies provided evidence that NOX2 is implicated in platelet activation. Thus, impaired platelet activation has been detected in patients with NOX2 hereditary deficiency. Similarly, normal platelets added with NOX2 specific inhibitors disclosed impaired platelet activation along with ROS down-regulation. Accordingly, animals prone to atherosclerosis treated with apocynin, a NOX inhibitor, showed reduced platelet adhesion and atherosclerotic plaque. Furthermore, a significant association between NOX2 up-regulation and platelet activation has been detected in patients at athero-thrombotic risk, but a cause-effect relationship needs to be established. These findings may represent a rationale to plan interventional trials with NOX inhibitors to establish if blocking NOX2 or other NOX isoforms may represent a novel anti-platelet approach.

Assembly of NADPH oxidase in human neutrophils is modulated by the opacity-associated protein expression State of Neisseria gonorrhoeae

Neisseria gonorrhoeae (the gonococcus, Gc) triggers a potent inflammatory response and recruitment of neutrophils to the site of infection. Gc survives exposure to neutrophils despite these cells' antimicrobial products, such as reactive oxygen species (ROS). ROS production in neutrophils is initiated by NADPH oxidase, which converts oxygen into superoxide. The subunits of NADPH oxidase are spatially separated between granules (gp91(phox)/p22(phox)) and the cytoplasm (p47(phox), p67(phox), and p40(phox)). Activation of neutrophils promotes the coassembly of NADPH oxidase subunits at phagosome and/or plasma membranes. While Gc-expressing opacity-associated (Opa) proteins can induce neutrophils to produce ROS, Opa-negative (Opa-) Gc does not stimulate neutrophil ROS production. Using constitutively Opa- and OpaD-positive (OpaD+) Gc bacteria in strain FA1090, we now show that the difference in ROS production levels in primary human neutrophils between these backgrounds can be attributed to differential assembly of NADPH oxidase. Neutrophils infected with Opa- Gc showed limited translocation of NADPH oxidase cytoplasmic subunits to cellular membranes, including the bacterial phagosome. In contrast, these subunits rapidly translocated to neutrophil membranes following infection with OpaD+ Gc. gp91(phox) and p22(phox) were recruited to Gc phagosomes regardless of bacterial Opa expression. These results suggest that Opa- Gc interferes with the recruitment of neutrophil NADPH oxidase cytoplasmic subunits to membranes, in particular, the p47(phox) "organizing" subunit, to prevent assembly of the holoenzyme, resulting in an absence of the oxidative burst.

Interaction of NuMA protein with the kinesin Eg5: its possible role in bipolar spindle assembly and chromosome alignment

Bipolar spindle assembly in mitotic cells is a prerequisite to ensure correct alignment of chromosomes for their segregation to each daughter cell; spindle microtubules are tethered at plus ends to chromosomes and focused at minus ends to either of the two spindle poles. NuMA (nuclear mitotic apparatus protein) is present solely in the nucleus in interphase cells, but relocalizes during mitosis to the spindle poles to play a crucial role in spindle assembly via focusing spindle microtubules to each pole. In the present study we show that the kinesin-5 family motor Eg5 is a protein that directly interacts with NuMA, using a proteomics approach and various binding assays both in vivo and in vitro. During mitosis Eg5 appears to interact with NuMA in the vicinity of the spindle poles, whereas the interaction does not occur in interphase cells, where Eg5 is distributed throughout the cytoplasm but NuMA exclusively localizes to the nucleus. Slight, but significant, depletion of Eg5 in HeLa cells by RNA interference results in formation of less-focused spindle poles with misaligned chromosomes in metaphase; these phenotypes are similar to those induced by depletion of NuMA. Since NuMA is less accumulated at the spindle poles in Eg5-depleted cells, Eg5 probably contributes to spindle assembly via regulating NuMA localization. Furthermore, depletion of cytoplasmic dynein induces mislocalization of NuMA and phenotypes similar to those observed in NuMA-depleted cells, without affecting Eg5 localization to the spindles. Thus dynein appears to control NuMA function in conjunction with Eg5.