Clinical and functional spectrum of RAC2-related immunodeficiency.

ABSTRACT: Mutations in the small Rho-family guanosine triphosphate hydrolase RAC2, critical for actin cytoskeleton remodeling and intracellular signal transduction, are associated with neonatal severe combined immunodeficiency (SCID), infantile neutrophilic disorder resembling leukocyte adhesion deficiency (LAD), and later-onset combined immune deficiency (CID). We investigated 54 patients (23 previously reported) from 37 families yielding 15 novel RAC2 missense mutations, including one present only in homozygosity. Data were collected from referring physicians and literature reports with updated clinical information. Patients were grouped by presentation: neonatal SCID (n = 5), infantile LAD-like disease (n = 5), or CID (n = 44). Disease correlated to RAC2 activity: constitutively active RAS-like mutations caused neonatal SCID, dominant-negative mutations caused LAD-like disease, whereas dominant-activating mutations caused CID. Significant T- and B-lymphopenia with low immunoglobulins were seen in most patients; myeloid abnormalities included neutropenia, altered oxidative burst, impaired neutrophil migration, and visible neutrophil macropinosomes. Among 42 patients with CID with clinical data, upper and lower respiratory infections and viral infections were common. Twenty-three distinct RAC2 mutations, including 15 novel variants, were identified. Using heterologous expression systems, we assessed downstream effector functions including superoxide production, p21-activated kinase 1 binding, AKT activation, and protein stability. Confocal microscopy showed altered actin assembly evidenced by membrane ruffling and macropinosomes. Altered protein localization and aggregation were observed. All tested RAC2 mutant proteins exhibited aberrant function; no single assay was sufficient to determine functional consequence. Most mutants produced elevated superoxide; mutations unable to support superoxide formation were associated with bacterial infections. RAC2 mutations cause a spectrum of immune dysfunction, ranging from early onset SCID to later-onset combined immunodeficiencies depending on RAC2 activity. This trial was registered at www.clinicaltrials.gov as #NCT00001355 and #NCT00001467.

Interpretation of Dihydrorhodamine-1,2,3 Flow Cytometry in Chronic Granulomatous Disease: an Atypical Exemplar.

PURPOSE: This is a functional characterization of a novel CYBA variant associated with normal DHR flow cytometry. Chronic granulomatous disease (CGD) is an inborn error of immunity characterized by recurrent bacterial and fungal infections and dysregulated inflammatory responses due to defective phagocytic cell function leading to the formation of granulomas. CGD patients have pathogenic variants in any of the five components of the phagocytic NADPH oxidase, which transfers electrons through the phagosomal membrane and produces superoxide upon bacterial uptake. Here, we report a pediatric female patient with a novel homozygous missense variant (c.293C > T, p.(Ser98Leu)) in CYBA, encoding the p22phox protein, associated with autosomal recessive CGD. METHODS AND RESULTS: The patient presented with severe recurrent pneumonia. Specific pathogens identified included Burkholderia and Serratia species suggesting neutrophil functional abnormalities; however, the dihydrorhodamine-1,2,3 (DHR) flow cytometric and cytochrome c reduction assays for neutrophil respiratory burst fell within the low side of the normal range. Western blot and flow cytometric analysis of individual NADPH oxidase components revealed reduced levels of p22phox and gp91phoxphox proteins. The pathological consequence of the p.Ser98Leu variant was further evaluated in heterologous expression systems, which confirmed reduced p22phox protein stability and oxidase activity. CONCLUSIONS: Although this patient did not exhibit all the classic features of CGD, such as granulomas and skin infections, she had recurrent pneumonias with oxidant-sensitive pathognomonic organisms, resulting in appropriate targeted CGD testing. This case emphasizes the need to contextually interpret laboratory data, especially using clinical findings to direct additional assessments including genetic analysis.

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.

Duox1 Regulates Primary B Cell Function under the Influence of IL-4 through BCR-Mediated Generation of Hydrogen Peroxide.

Engagement of the BCR with Ags triggers signaling pathways for commitment of B lymphocyte responses that can be regulated, in part, by reactive oxygen species. To investigate the functional relevance of reactive oxygen species produced in primary B cells, we focused on the role of the hydrogen peroxide generator Duox1 in stimulated splenic B cells under the influence of the TH2 cytokine IL-4. We found that H2O2 production in wild type (WT) and Nox2-deficient CD19+ B cells was boosted concomitantly with enhanced expression of Duox1 following costimulation with BCR agonists together with IL-4, whereas stimulated Duox1-/- cells showed attenuated H2O2 release. We examined whether Duox1-derived H2O2 contributes to proliferative activity and Ig isotype production in CD19+ cells upon BCR stimulation. Duox1-/- CD19+ B cells showed normal responses of Ig production but a higher rate of proliferation than WT or Nox2-deficient cells. Furthermore, we demonstrated that the H2O2 scavenger catalase mimics the effect of Duox1 deficiency by enhancing proliferation of WT CD19+ B cells in vitro. Results from immunized mice reflected the in vitro observations: T cell-independent Ag induced increased B cell expansion in germinal centers from Duox1-/- mice relative to WT and Nox2-/- mice, whereas immunization with T cell-dependent or -independent Ag elicited normal Ig isotype secretion in the Duox1 mutant mice. These observations, obtained both by in vitro and in vivo approaches, strongly suggest that Duox1-derived hydrogen peroxide negatively regulates proliferative activity but not Ig isotype production in primary splenic CD19+ B cells.

Heterozygous activating mutation in RAC2 causes infantile-onset combined immunodeficiency with susceptibility to viral infections.

Here we describe a 10-year-old girl with combined immunodeficiency presenting as recurring chest infections, lung disease and herpetic skin infections. The patient experienced two hematopoietic stem cell transplantations and despite full chimerism, she developed bone marrow aplasia due to adenovirus infection and died at post-transplant day 86. Immunologic investigation revealed low numbers of TRECs/KRECs, a severe reduction of memory B cells, absence of isohemagglutinins, and low IgG levels. Whole exome sequencing (WES) identified a novel heterozygous mutation in RAC2(c.275A > C, p.N92 T). Flow cytometric investigation of neutrophil migration demonstrated an absence of chemotaxis to fMLP. Cell lines transfected with RAC2 [N92 T] displayed characteristics of active GTP-bound RAC2 including enhanced NADPH oxidase-derived superoxide production both at rest and in response to PMA. Our findings broaden the clinical picture of RAC2 dysfunction, showing that some individuals can present with a combined immunodeficiency later in childhood rather than a congenital neutrophil disease.

The extracellular A-loop of dual oxidases affects the specificity of reactive oxygen species release.

NADPH oxidase (Nox) family proteins produce superoxide (O2 (⨪)) directly by transferring an electron to molecular oxygen. Dual oxidases (Duoxes) also produce an O2 (⨪) intermediate, although the final species secreted by mature Duoxes is H2O2, suggesting that intramolecular O2 (⨪) dismutation or other mechanisms contribute to H2O2 release. We explored the structural determinants affecting reactive oxygen species formation by Duox enzymes. Duox2 showed O2 (⨪) leakage when mismatched with Duox activator 1 (DuoxA1). Duox2 released O2 (⨪) even in correctly matched combinations, including Duox2 + DuoxA2 and Duox2 + N-terminally tagged DuoxA2 regardless of the type or number of tags. Conversely, Duox1 did not release O2 (⨪) in any combination. Chimeric Duox2 possessing the A-loop of Duox1 showed no O2 (⨪) leakage; chimeric Duox1 possessing the A-loop of Duox2 released O2 (⨪). Moreover, Duox2 proteins possessing the A-loops of Nox1 or Nox5 co-expressed with DuoxA2 showed enhanced O2 (⨪) release, and Duox1 proteins possessing the A-loops of Nox1 or Nox5 co-expressed with DuoxA1 acquired O2 (⨪) leakage. Although we identified Duox1 A-loop residues (His(1071), His(1072), and Gly(1074)) important for reducing O2 (⨪) release, mutations of these residues to those of Duox2 failed to convert Duox1 to an O2 (⨪)-releasing enzyme. Using immunoprecipitation and endoglycosidase H sensitivity assays, we found that the A-loop of Duoxes binds to DuoxA N termini, creating more stable, mature Duox-DuoxA complexes. In conclusion, the A-loops of both Duoxes support H2O2 production through interaction with corresponding activators, but complex formation between the Duox1 A-loop and DuoxA1 results in tighter control of H2O2 release by the enzyme complex.

Release of cystic fibrosis airway inflammatory markers from Pseudomonas aeruginosa-stimulated human neutrophils involves NADPH oxidase-dependent extracellular DNA trap formation.

Cystic fibrosis (CF) airways are characterized by bacterial infections, excess mucus production, and robust neutrophil recruitment. The main CF airway pathogen is Pseudomonas aeruginosa. Neutrophils are not capable of clearing the infection. Neutrophil primary granule components, myeloperoxidase (MPO) and human neutrophil elastase (HNE), are inflammatory markers in CF airways, and their increased levels are associated with poor lung function. Identifying the mechanism of MPO and HNE release from neutrophils is of high clinical relevance for CF. In this article, we show that human neutrophils release large amounts of neutrophil extracellular traps (NETs) in the presence of P. aeruginosa. Bacteria are entangled in NETs and colocalize with extracellular DNA. MPO, HNE, and citrullinated histone H4 are all associated with DNA in Pseudomonas-triggered NETs. Both laboratory standard strains and CF isolates of P. aeruginosa induce DNA, MPO, and HNE release from human neutrophils. The increase in peroxidase activity of neutrophil supernatants after Pseudomonas exposure indicates that enzymatically active MPO is released. P. aeruginosa induces a robust respiratory burst in neutrophils that is required for extracellular DNA release. Inhibition of the cytoskeleton prevents Pseudomonas-initiated superoxide production and DNA release. NADPH oxidase inhibition suppresses Pseudomonas-induced release of active MPO and HNE. Blocking MEK/ERK signaling results in only minimal inhibition of DNA release induced by Pseudomonas. Our data describe in vitro details of DNA, MPO, and HNE release from neutrophils activated by P. aeruginosa. We propose that Pseudomonas-induced NET formation is an important mechanism contributing to inflammatory conditions characteristic of CF airways.

Plasmodium falciparum merozoite surface protein 1 blocks the proinflammatory protein S100P.

The malaria parasite, Plasmodium falciparum, and the human immune system have coevolved to ensure that the parasite is not eliminated and reinfection is not resisted. This relationship is likely mediated through a myriad of host-parasite interactions, although surprisingly few such interactions have been identified. Here we show that the 33-kDa fragment of P. falciparum merozoite surface protein 1 (MSP1(33)), an abundant protein that is shed during red blood cell invasion, binds to the proinflammatory protein, S100P. MSP1(33) blocks S100P-induced NFκB activation in monocytes and chemotaxis in neutrophils. Remarkably, S100P binds to both dimorphic alleles of MSP1, estimated to have diverged >27 Mya, suggesting an ancient, conserved relationship between these parasite and host proteins that may serve to attenuate potentially damaging inflammatory responses.

Histamine stimulates hydrogen peroxide production by bronchial epithelial cells via histamine H1 receptor and dual oxidase.

Oxidative stress has been implicated in the pathogenesis of bronchial asthma. Besides granulocytes, the airway epithelium can produce large amounts of reactive oxygen species and can contribute to asthma-related oxidative stress. Histamine is a major inflammatory mediator present in large quantities in asthmatic airways. Whether histamine triggers epithelium-derived oxidative stress is unknown. We therefore aimed at characterizing human airway epithelial H2O2 production stimulated by histamine. We found that air-liquid interface cultures of primary human bronchial epithelial cells (BECs) and an immortalized BEC model (Cdk4/hTERT HBEC) produce H2O2 in response to histamine. The main source of airway epithelial H2O2 is an NADPH dual oxidase, Duox1. Out of the four histamine receptors (H1R-H4R), H1R has the highest expression in BECs and mediates the H2O2-producing effects of histamine. IL-4 induces Duox1 gene and protein expression levels and enhances histamine-induced H2O2 production by epithelial cells. Using HEK-293 cells expressing Duox1 or Duox2 and endogenous H1R, histamine triggers an immediate intracellular calcium signal and H2O2 release. Overexpression of H1R further increases the oxidative output of Duox-expressing HEK-293 cells. Our observations show that BECs respond to histamine with Duox-mediated H2O2 production. These findings reveal a mechanism that could be an important contributor to oxidative stress characteristic of asthmatic airways, suggesting novel therapeutic targets for treating asthmatic airway disease.

NLRP3 inflammasome activation and interleukin-1ß release in macrophages require calcium but are independent of calcium-activated NADPH oxidases.

OBJECTIVE AND DESIGN: We studied the involvement of calcium and calcium-activated NADPH oxidases in NLRP3 inflammasome activation and IL-1ß release to better understand inflammasome signaling in macrophages. MATERIAL OR SUBJECTS: Human volunteer blood donors were recruited to isolate monocytes to differentiate them into macrophages. Wild-type or DUOX1-deficient C57/B6 mice were used to prepare bone marrow-derived macrophages. TREATMENT: Murine or human macrophages were treated in vitro with NLRP3 inflammasome agonists (ATP, silica crystals) or calcium agonists (thapsigargin, ionomycin) in calcium-containing or calcium-free medium. METHODS: Intracellular calcium changes were followed by measuring FURA2-based fluorescence. Gene expression changes were measured by quantitative real-time PCR. Protein expression was assessed by western blotting. Enzymatic activity was measured by fluorescence caspase-1 activity assay. IL-1ß release was determined by ELISA. ELISA data were analyzed by ANOVA and Tukey's post hoc test. RESULTS: Our data show that calcium is essential for IL-1ß release in human macrophages. Increases in cytosolic calcium alone lead to IL-1ß secretion. Calcium removal blocks caspase-1 activation. Human macrophages express Duox1, a calcium-regulated NADPH oxidase that produces reactive oxygen species. However, Duox1-deficient murine macrophages show normal IL-1ß release. CONCLUSIONS: Human macrophage inflammasome activation and IL-1ß secretion requires calcium but does not involve NADPH oxidases.

Case Report: Profound newborn leukopenia related to a novel RAC2 variant.

We report the case of a 1-week-old male born full-term, who had two inconclusive severe combined immunodeficiency (SCID) newborn screens and developed scalp cellulitis and Escherichia coli bacteremia. He did not pass early confirmatory hearing screens. Initial blood counts and lymphocyte flow cytometry revealed profound neutropenia and lymphopenia with a T-/B-/NK- phenotype. Red blood cell adenosine deaminase 1 activity was within normal limits. A presumptive diagnosis of reticular dysgenesis was considered. Granulocyte colony-stimulating factor was started, but there was no improvement in neutrophil counts. Subsequent lymphocyte flow cytometry at around 4 weeks of age demonstrated an increase in T-, B- and NK-cell numbers, eliminating suspicion for SCID and raising concern for congenital neutropenia and bone marrow failure syndromes. Genetic testing revealed a novel variant in RAC2 [c.181C>A (p.Gln61Lys)] (Q61K). RAC2, a Ras-related GTPase, is the dominant RAC protein expressed in hematopoietic cells and is involved with various downstream immune-mediated responses. Pathogenic RAC2 variants show significant phenotypic heterogeneity (spanning from neutrophil defects to combined immunodeficiency) across dominant, constitutively activating, dominant activating, dominant negative, and autosomal recessive subtypes. Given the identification of a novel variant, functional testing was pursued to evaluate aberrant pathways described in other RAC2 pathogenic variants. In comparison to wild-type RAC2, the Q61K variant supported elevated superoxide production under both basal and PMA-stimulated conditions, increased PAK1 binding, and enhanced plasma membrane ruffling, consistent with other dominant, constitutively active mutations. This case highlights the diagnostic challenge associated with genetic variants identified via next-generation sequencing panels and the importance of functional assays to confirm variant pathogenicity.

BTK drives neutrophil activation for sterilizing antifungal immunity.

We describe a previously-unappreciated role for Bruton's tyrosine kinase (BTK) in fungal immune surveillance against aspergillosis, an unforeseen complication of BTK inhibitors (BTKi) used for treating B-cell lymphoid malignancies. We studied BTK-dependent fungal responses in neutrophils from diverse populations, including healthy donors, BTKi-treated patients, and X-linked agammaglobulinemia patients. Upon fungal exposure, BTK was activated in human neutrophils in a TLR2-, Dectin-1-, and FcγR-dependent manner, triggering the oxidative burst. BTK inhibition selectively impeded neutrophil-mediated damage to Aspergillus hyphae, primary granule release, and the fungus-induced oxidative burst by abrogating NADPH oxidase subunit p40phox and GTPase RAC2 activation. Moreover, neutrophil-specific Btk deletion in mice enhanced aspergillosis susceptibility by impairing neutrophil function, not recruitment or lifespan. Conversely, GM-CSF partially mitigated these deficits by enhancing p47phox activation. Our findings underline the crucial role of BTK signaling in neutrophils for antifungal immunity and provide a rationale for GM-CSF use to offset these deficits in susceptible patients.

Peroxiredoxin 6 translocates to the plasma membrane during neutrophil activation and is required for optimal NADPH oxidase activity.

Neutrophils provide the first line of defense against microbial invasion in part through production of reactive oxygen species (ROS) which is mediated through activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase generating superoxide anion (O2-). The phagocyte oxidase (phox) has multiple protein components that assemble on the plasma membrane in stimulated neutrophils. We recently described a protein in neutrophils, peroxiredoxin 6 (Prdx6), which has both peroxidase and phospholipase A2 (PLA2) activities and enhances oxidase activity in an SDS-activated, cell-free system. The function of Prdx6 in phox activity is further investigated. In reconstituted phox-competent K562 cells, siRNA-mediated suppression of Prdx6 resulted in decreased NADPH oxidase activity in response to formyl-methionyl-leucyl-phenylalanine (fMLP) or phorbol myristate acetate (PMA). In neutrophils stimulated with PMA, Prdx6 translocated to plasma membrane as demonstrated by Western blot and confocal microscopy. Translocation of Prdx6 in phox competent K562 cells required both p67phox and p47phox. In addition, plasma membrane from PMA-stimulated, oxidase competent K562 cells with siRNA-mediated Prdx6 suppression contained less p47phox and p67phox compared to cells in which Prdx6 was not decreased. Cell-free oxidase assays showed that recombinant Prdx6 did not alter the Km for NADPH, but increased the Vmax for O2- production in a saturable, Prdx6 concentration-dependent manner. Recombinant proteins with mutations in Prdx (C47S) and phospholipase (S32A) activity both enhanced cell-free phox activity to the same extent as wild type protein. Prdx6 supports retention of the active oxidase complex in stimulated plasma membrane, and results with mutant proteins imply that Prdx6 serves an additional biochemical or structural role in supporting optimal NADPH oxidase activity.

Double-stranded RNA induces shedding of the 34-kDa soluble TNFR1 from human airway epithelial cells via TLR3-TRIF-RIP1-dependent signaling: roles for dual oxidase 2- and caspase-dependent pathways.

TNF, an important mediator of inflammatory and innate immune responses, can be regulated by binding to soluble TNF receptors. The 55-kDa type 1 TNFR (TNFR1), the key receptor for TNF signaling, is released to the extracellular space by two mechanisms, the inducible cleavage and shedding of 34-kDa soluble TNFR1 (sTNFR1) ectodomains and the constitutive release of full-length 55-kDa TNFR1 within exosome-like vesicles. The aim of this study was to identify and characterize TLR signaling pathways that mediate TNFR1 release to the extracellular space. To our knowledge, we demonstrate for the first time that polyinosinic-polycytidylic acid [poly (I:C)], a synthetic dsRNA analogue that signals via TLR3, induces sTNFR1 shedding from human airway epithelial (NCI-H292) cells, whereas ligands for other microbial pattern recognition receptors, including TLR4, TLR7, and nucleotide-binding oligomerization domain containing 2, do not. Furthermore, poly (I:C) selectively induces the cleavage of 34-kDa sTNFR1 ectodomains but does not enhance the release of full-length 55-kDa TNFR1 within exosome-like vesicles. RNA interference experiments demonstrated that poly (I:C)-induced sTNFR1 shedding is mediated via activation of TLR3-TRIF-RIP1 signaling, with subsequent activation of two downstream pathways. One pathway involves the dual oxidase 2-mediated generation of reactive oxygen species, and the other pathway is via the caspase-mediated activation of apoptosis. Thus, the ability of dsRNA to induce the cleavage and shedding of the 34-kDa sTNFR1 from human bronchial epithelial cells represents a novel mechanism by which innate immune responses to viral infections are modulated.

Mutant p53 and NOX4 are modulators of a CCL5-driven pro-migratory secretome.

Previously, we showed wild-type (WT) and mutant (mt) forms of p53 differentially regulate ROS generation by NADPH oxidase-4 (NOX4). We found that WT-p53 suppresses TGF-ß-induced NOX4, ROS production, and cell migration, whereas tumor-associated mt-p53 proteins enhance NOX4 expression and cell migration by TGF-ß/SMAD3-dependent mechanisms. In this study, we investigated the role of mutant p53-induced NOX4 on the cancer cell secretome and the effects NOX4 signaling have on the tumor microenvironment (TME). We found conditioned media collected from H1299 lung epithelial cells stably expressing either mutant p53-R248Q or R273H promotes the migration and invasion of naïve H1299 cells and chemotactic recruitment of THP-1 monocytes. These effects were diminished with conditioned media from cells co-transfected with dominant negative NOX4 (P437H). We utilized immunoblot-based cytokine array analysis to identify factors in mutant p53 H1299 cell conditioned media that promote cell migration and invasion. We found CCL5 was significantly reduced in conditioned media from H1299 cells co-expressing p53-R248Q and dominant negative NOX4. Moreover, neutralization of CCL5 reduced autocrine-mediated H1299 cell mobility. Furthermore, CCL5 and TGF-beta from M2-polarized macrophages have a significant role in crosstalk and H1299 cell migration and invasion. Collectively, our findings provide further insight into NOX4-based communication in the tumor microenvironment and its potential as a therapeutic target affecting metastatic disease progression.

NOX1 and PRDX6 synergistically support migration and invasiveness of hepatocellular carcinoma cells through enhanced NADPH oxidase activity.

The NADPH oxidase 1 (NOX1) complex formed by proteins NOX1, p22phox, NOXO1, NOXA1, and RAC1 plays an important role in the generation of superoxide and other reactive oxygen species (ROS) which are involved in normal and pathological cell functions due to their effects on diverse cell signaling pathways. Cell migration and invasiveness are at the origin of tumor metastasis during cancer progression which involves a process of cellular de-differentiation known as the epithelial-mesenchymal transition (EMT). During EMT cells lose their polarized epithelial phenotype and express mesenchymal marker proteins that enable cytoskeletal rearrangements promoting cell migration, expression and activation of matrix metalloproteinases (MMPs), tissue remodeling, and cell invasion during metastasis. In this work, we explored the importance of the peroxiredoxin 6 (PRDX6)-NOX1 enzyme interaction leading to NOXA1 protein stabilization and increased levels of superoxide produced by NOX in hepatocarcinoma cells. This increase was accompanied by higher levels of N-cadherin and MMP2, correlating with a greater capacity for cell migration and invasiveness of SNU475 hepatocarcinoma cells. The increase in superoxide and the associated downstream effects on cancer progression were suppressed when phospholipase A2 or peroxidase activities of PRDX6 were abolished by site-directed mutagenesis, reinforcing the importance of these catalytic activities in supporting NOX1-based superoxide generation. Overall, these results demonstrate a clear functional cooperation between NOX1 and PRDX6 catalytic activities which generate higher levels of ROS production, resulting in a more aggressive tumor phenotype.

Loss of PRDX6 Aborts Proliferative and Migratory Signaling in Hepatocarcinoma Cell Lines.

Peroxiredoxin 6 (PRDX6), the only mammalian 1-Cys member of the peroxiredoxin family, has peroxidase, phospholipase A2 (PLA2), and lysophosphatidylcholine (LPC) acyltransferase (LPCAT) activities. It has been associated with tumor progression and cancer metastasis, but the mechanisms involved are not clear. We constructed an SNU475 hepatocarcinoma cell line knockout for PRDX6 to study the processes of migration and invasiveness in these mesenchymal cells. They showed lipid peroxidation but inhibition of the NRF2 transcriptional regulator, mitochondrial dysfunction, metabolic reprogramming, an altered cytoskeleton, down-regulation of PCNA, and a diminished growth rate. LPC regulatory action was inhibited, indicating that loss of both the peroxidase and PLA2 activities of PRDX6 are involved. Upstream regulators MYC, ATF4, HNF4A, and HNF4G were activated. Despite AKT activation and GSK3ß inhibition, the prosurvival pathway and the SNAI1-induced EMT program were aborted in the absence of PRDX6, as indicated by diminished migration and invasiveness, down-regulation of bottom-line markers of the EMT program, MMP2, cytoskeletal proteins, and triggering of the "cadherin switch". These changes point to a role for PRDX6 in tumor development and metastasis, so it can be considered a candidate for antitumoral therapies.

Development of an improved and specific inhibitor of NADPH oxidase 2 to treat traumatic brain injury.

NADPH oxidases (NOX's), and the reactive oxygen species (ROS) they produce, play an important role in host defense, thyroid hormone synthesis, apoptosis, gene regulation, angiogenesis and other processes. However, overproduction of ROS by these enzymes is associated with cardiovascular disease, fibrosis, traumatic brain injury (TBI) and other diseases. Structural similarities between NOX's have complicated development of specific inhibitors. Here, we report development of NCATS-SM7270, a small molecule optimized from GSK2795039, that inhibited NOX2 in primary human and mouse granulocytes. NCATS-SM7270 specifically inhibited NOX2 and had reduced inhibitory activity against xanthine oxidase in vitro. We also studied the role of several NOX isoforms during mild TBI (mTBI) and demonstrated that NOX2 and, to a lesser extent, NOX1 deficient mice are protected from mTBI pathology, whereas injury is exacerbated in NOX4 knockouts. Given the pathogenic role played by NOX2 in mTBI, we treated mice transcranially with NCATS-SM7270 after injury and revealed a dose-dependent reduction in mTBI induced cortical cell death. This inhibitor also partially reversed cortical damage observed in NOX4 deficient mice following mTBI. These data demonstrate that NCATS-SM7270 is an improved and specific inhibitor of NOX2 capable of protecting mice from NOX2-dependent cell death associated with mTBI.

Cooperation of p40(phox) with p47(phox) for Nox2-based NADPH oxidase activation during Fcγ receptor (FcγR)-mediated phagocytosis: mechanism for acquisition of p40(phox) phosphatidylinositol 3-phosphate (PI(3)P) binding.

During activation of the phagocyte (Nox2-based) NADPH oxidase, the cytoplasmic Phox complex (p47(phox)-p67(phox)-p40(phox)) translocates and associates with the membrane-spanning flavocytochrome b(558). It is unclear where (in cytoplasm or on membranes), when (before or after assembly), and how p40(phox) acquires its PI(3)P-binding capabilities. We demonstrated that in addition to conformational changes induced by H(2)O(2) in the cytoplasm, p40(phox) acquires PI(3)P-binding through direct or indirect membrane targeting. We also found that p40(phox) is essential when p47(phox) is partially phosphorylated during FcγR-mediated oxidase activation; however, p40(phox) is less critical when p47(phox) is adequately phosphorylated, using phosphorylation-mimicking mutants in HEK293(Nox2/FcγRIIa) and RAW264.7(p40/p47KD) cells. Moreover, PI binding to p47(phox) is less important when the autoinhibitory PX-PB1 domain interaction in p40(phox) is disrupted or when p40(phox) is targeted to membranes. Furthermore, we suggest that high affinity PI(3)P binding of the p40(phox) PX domain is critical during its accumulation on phagosomes, even when masked by the PB1 domain in the resting state. Thus, in addition to mechanisms for directly acquiring PI(3)P binding in the cytoplasm by H(2)O(2), p40(phox) can acquire PI(3)P binding on targeted membranes in a p47(phox)-dependent manner and functions both as a "carrier" of the cytoplasmic Phox complex to phagosomes and an "adaptor" of oxidase assembly on phagosomes in cooperation with p47(phox), using positive feedback mechanisms.