The phosphorylation targets of p47phox, a subunit of the respiratory burst oxidase. Functions of the individual target serines as evaluated by site-directed mutagenesis

Enhanced effect of limb remote ischemic postconditioning combined with paeoniflorin on alleviating cerebral ischemic injury via neutrophil NADPH pathway

BACKGROUND

Limb remote ischemic postconditioning (LRIP) and paeoniflorin (PF) both can ameliorate cerebral ischemia reperfusion (I/R) injury. At present, whether LRIP combined with PF can achieve better therapeutic effect is unknown.

PURPOSE

This study explored the alleviating effect and mechanism of LRIP in combination with PF on cerebral I/R injury in rats.

METHODS

Middle cerebral artery occlusion (MCAO) surgery was performed on rats except Sham group. Then PF (2.5 mg/kg, 5 mg/kg, 10 mg/kg) was administrated by intraperitoneal injection 10 min before the start of reperfusion. LRIP was operated on the left femoral artery at 0 h of reperfusion. Behavioral testing was used to assess neurological impairment, while TTC staining was used to examine infarct volume. Protein expression of MyD88, TRAF6, p38-MAPK and phosphorylation of p47phox in neutrophils from rat peripheral blood were tested by Western blot. Rat bone marrow neutrophils were extracted and incubated for 24 h with serum from rats after LRIP combined with PF. p38 MAPK inhibitor group was administrated SB203580 while the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor group was administrated Apocynin. Neutrophils were stimulated by fMLP (10 μM). Reactive oxygen species (ROS) production and protein expression of MyD88, TRAF6, p38 MAPK, and p47phox (ser 304 and ser 345) were detected.

RESULTS

LRIP combined with PF (5 mg/kg) reduced cerebral infarct volume, ameliorated neurological deficit score (NDS), decreased fMLP-stimulated ROS release and downregulated the protein expression of MyD88, TRAF6, p38-MAPK and phosphorylation of p47phox (ser 304 and ser 345) in neutrophils.

CONCLUSION

The protective effect of LRIP combined with PF on cerebral I/R injury was better than either alone. Taken together, we provided solid evidence to demonstrate that the combination of LRIP and PF had potential to alleviate cerebral I/R injury, which was regulated by MyD88-TRAF6-p38 MAPK pathway and neutrophil NADPH oxidase pathway.

The influence of sepsis on erythrocytes morphology: case report and literature review

This paper highlights a clinical case of sepsis caused by soft tissue infection. Peripheral blood smear, plasma value of inflammatory biomarkers and the white blood cells count were performed. Significant morphological changes were revealed through peripheral blood smear test two days after patient admission. Patient developed septic shock after the third day in intensive care unit (ICU). Laboratory results showed major morphological changes (erythrocytes deformity, abnormal neutrophils); these were correlated with elevated plasma value of interleukin-6 and procalcitonin.

Role of the phospholipid binding sites, PX of p47phox and PB region of Rac1, in the formation of the phagocyte NADPH oxidase complex NOX2

In phagocytes, superoxide anion (O2-), the precursor of reactive oxygen species, is produced by the NADPH oxidase complex to kill pathogens. Phagocyte NADPH oxidase consists of the transmembrane cytochrome b558 (cyt b558) and four cytosolic components: p40phox, p47phox, p67phox, and Rac1/2. The phagocyte activation by stimuli leads to activation of signal transduction pathways. This is followed by the translocation of cytosolic components to the membrane and their association with cyt b558 to form the active enzyme. To investigate the roles of membrane-interacting domains of the cytosolic proteins in the NADPH oxidase complex assembly and activity, we used giant unilamellar phospholipid vesicles (GUV). We also used the neutrophil-like cell line PLB-985 to investigate these roles under physiological conditions. We confirmed that the isolated proteins must be activated to bind to the membrane. We showed that their membrane binding was strengthened by the presence of the other cytosolic partners, with a key role for p47phox. We also used a fused chimera consisting of p47phox(aa 1-286), p67phox(aa 1-212) and Rac1Q61L, as well as mutated versions in the p47phox PX domain and the Rac polybasic region (PB). We showed that these two domains have a crucial role in the trimera membrane-binding and in the trimera assembly to cyt b558. They also have an impact on O2.- production in vitro and in cellulo: the PX domain strongly binding to GUV made of a mix of polar lipids; and the PB region strongly binding to the plasma membrane of neutrophils and resting PLB-985 cells.

Fisetin alleviates cellular senescence through PTEN mediated inhibition of PKCδ-NOX1 pathway in vascular smooth muscle cells

Reactive oxygen species (ROS) are a key risk factor of cellular senescence and age-related diseases, and protein kinase C (PKC) has been shown to activate NADPH oxidases (NOXs), which generate ROS. Although PKC activation induces oxidative stress, leading to the cellular dysfunction in various cell types, the correlation between PKC and senescence has not been reported in vascular smooth muscle cell (VSMC). Several studies have indicated cellular senescence is accompanied by phosphatase and tensin homolog (PTEN) loss and that an interaction exists between PTEN and PKC. Therefore, we aimed to determine whether PTEN and PKC are associated with VSMC senescence and to investigate the mechanism involved. We found hydrogen peroxide (H₂O₂) decreased PTEN expression and increased PKCδ phosphorylation. Moreover, H₂O₂ upregulated the NOX1 subunits, p22^phox and p47^phox, and induced VSMC senescence via p53-p21 signaling pathway. We identified PKCδ activation contributed to VSMC senescence through activation of NOX1 and ROS production. However, fisetin inhibited cellular senescence induced by the PTEN-PKCδ-NOX1-ROS signaling pathway, and this anti-aging effect was attributed to reduced ROS production caused by suppressing NOX1 activation. These results suggest that the PTEN-PCKδ signaling pathway is directly related to senescence via NOX1 activation and that the downregulation of PKCδ by flavonoids provides a potential means of treating age-associated diseases.

Impaired p47phox phosphorylation in neutrophils from patients with p67phox-deficient chronic granulomatous disease

Superoxide production by the phagocyte reduced NAD phosphate (NADPH) oxidase is essential for innate immunity as shown in chronic granulomatous disease (CGD), an immunodeficiency disease resulting from mutations in 1 of its genes. The NADPH oxidase is composed of 2 membrane proteins (gp91phox/NOX2 and p22phox) and 4 cytosolic proteins (p47phox, p67phox, p40phox, and Rac1/2). The phosphorylation of p47phox is required for NADPH oxidase activation in cells. As p47phox and p67phox can form a tight complex in cells, we hypothesized that p67phox could regulate p47phox phosphorylation. To investigate this hypothesis, we used phospho-specific antibodies against 5 major p47phox-phosphorylated sites (Ser304, Ser315, Ser320, Ser328, and Ser345) and neutrophils from healthy donors and from p67phox-/- CGD patients. Results showed that formyl-methionyl-leucyl-phenylalanine and phorbol myristate acetate induced a time- and a concentration-dependent phosphorylation of p47phox on Ser304, Ser315, Ser320, and Ser328 in healthy human neutrophils. Interestingly, in neutrophils and Epstein-Barr virus-transformed B lymphocytes from p67phox-/- CGD patients, phosphorylation of p47phox on serine residues was dramatically reduced. In COSphox cells, the presence of p67phox led to increased phosphorylation of p47phox. In vitro studies showed that recombinant p47phox was phosphorylated on Ser304, Ser315, Ser320, and Ser328 by different PKC isoforms and the addition of recombinant p67phox alone or in combination with p40phox potentiated this process. Thus, p67phox and p40phox are required for optimal p47phox phosphorylation on Ser304, Ser315, Ser320, and Ser328 in intact cells. Therefore, p67phox and p40phox are novel regulators of p47phox-phosphorylation.

Shear and Integrin Outside-In Signaling Activate NADPH-Oxidase 2 to Promote Platelet Activation

[Figure: see text].

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.

p47phox siRNA-Loaded PLGA Nanoparticles Suppress ROS/Oxidative Stress-Induced Chondrocyte Damage in Osteoarthritis

Osteoarthritis (OA) is the most common joint disorder that has had an increasing prevalence due to the aging of the population. Recent studies have concluded that OA progression is related to oxidative stress and reactive oxygen species (ROS). ROS are produced at low levels in articular chondrocytes, mainly by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, and ROS production and oxidative stress have been found to be elevated in patients with OA. The cartilage of OA-affected rat exhibits a significant induction of p47phox, a cytosolic subunit of the NADPH oxidase, similarly to human osteoarthritis cartilage. Therefore, this study tested whether siRNA p47phox that is introduced with poly (D,L-lactic-co-glycolic acid) (PLGA) nanoparticles (p47phox si_NPs) can alleviate chondrocyte cell death by reducing ROS production. Here, we confirm that p47phox si_NPs significantly attenuated oxidative stress and decreased cartilage damage in mono-iodoacetate (MIA)-induced OA. In conclusion, these data suggest that p47phox si_NPs may be of therapeutic value in the treatment of osteoarthritis.

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.

Redox Activation of Nox1 (NADPH Oxidase 1) Involves an Intermolecular Disulfide Bond Between Protein Disulfide Isomerase and p47phox in Vascular Smooth Muscle Cells

Objective- PDI (protein disulfide isomerase A1) was reported to support Nox1 (NADPH oxidase) activation mediated by growth factors in vascular smooth muscle cells. Our aim was to investigate the molecular mechanism by which PDI activates Nox1 and the functional implications of PDI in Nox1 activation in vascular disease. Approach and Results- Using recombinant proteins, we identified a redox interaction between PDI and the cytosolic subunit p47^phox in vitro. Mass spectrometry of crosslinked peptides confirmed redox-dependent disulfide bonds between cysteines of p47^phox and PDI and an intramolecular bond between Cys 196 and 378 in p47^phox. PDI catalytic Cys 400 and p47^phox Cys 196 were essential for the activation of Nox1 by PDI in vascular smooth muscle cells. Transfection of PDI resulted in the rapid oxidation of a redox-sensitive protein linked to p47^phox, whereas PDI mutant did not promote this effect. Mutation of p47^phox Cys 196, or the redox active cysteines of PDI, prevented Nox1 complex assembly and vascular smooth muscle cell migration. Proximity ligation assay confirmed the interaction of PDI and p47^phox in murine carotid arteries after wire injury. Moreover, in human atheroma plaques, a positive correlation between the expression of PDI and p47^phox occurred only in PDI family members with the a' redox active site. Conclusions- PDI redox cysteines facilitate Nox1 complex assembly, thus identifying a new mechanism through which PDI regulates Nox activity in vascular disease.

A Role for MK2 in Enhancing Neutrophil-Derived ROS Production and Aggravating Liver Ischemia/Reperfusion Injury

Increased inflammatory responses and enhanced reactive oxygen species contribute to hepatic ischemia/reperfusion (I/R) injury, however the modulatory mechanisms haven't been completely unveiled. Here, we report that genetic deficiency of MAPK-activated protein kinase 2 (MK2) protected against hepatic I/R injury and decreased hepatic neutrophil accumulation in MK2^−/− mice. Depletion of neutrophil attenuated hepatic I/R injury in wide type mice. In response to C5a stimulation, MK2^−/− neutrophils generated less superoxide in which both NADPH oxidase activation and p47^phox phosphorylation were decreased. Furthermore, Ser329 of p47^phox was identified for enhancement of superoxide production. The Ser329 phosphorylation was reduced in MK2^−/− neutrophils. To determine whether MK2 modulates hepatic I/R injury via activating neutrophils, we generated myeloid-specific MK2 deletion mice (MK2^Lyz2−KO) and liver I/R injury was reduced in MK2^Lyz2−KO mice. Our results indicate that MK2 augments hepatic I/R injury and induces ROS production with increased p47^phox phosphorylation and MK2 is a potential drug target for treating hepatic I/R injury.

NADPH oxidase activation in neutrophils: Role of the phosphorylation of its subunits

Neutrophils are key cells of innate immunity and during inflammation. Upon activation, they produce large amounts of superoxide anion (O₂ ^-. ) and ensuing reactive oxygen species (ROS) to kill phagocytized microbes. The enzyme responsible for O₂ ^-. production is called the phagocyte NADPH oxidase. This is a multicomponent enzyme system that becomes active after assembly of four cytosolic proteins (p47^phox , p67^phox , p40^phox and Rac2) with the transmembrane proteins (p22^phox and gp91^phox , which form the cytochrome b₅₅₈ ). gp91^phox represents the catalytic subunit of the NADPH oxidase and is also called NOX2. NADPH oxidase-derived ROS are essential for microbial killing and innate immunity; however, excessive ROS production induces tissue injury and prolonged inflammatory reactions that contribute to inflammatory diseases. Thus, NADPH oxidase activation must be tightly regulated in time and space to limit ROS production. NADPH oxidase activation is regulated by several processes such as phosphorylation of its components, exchange of GDP/GTP on Rac2 and binding of p47^phox and p40^phox to phospholipids. This review aims to provide new insights into the role of the phosphorylation of the NADPH oxidase components, that is gp91^phox , p22^phox , p47^phox , p67^phox and p40^phox , in the activation of this enzyme.

Organizers and activators: Cytosolic Nox proteins impacting on vascular function

NADPH oxidases of the Nox family are important enzymatic sources of reactive oxygen species (ROS) in the cardiovascular system. Of the 7 members of the Nox family, at least three depend for their activation on specific cytosolic proteins. These are p47phox and its homologue NoxO1 and p67phox and its homologue NoxA1. Also the Rho-GTPase Rac is important but as this protein has many additional functions, it will not be covered here. The Nox1 enzyme is preferentially activated by the combination of NoxO1 with NoxA1, whereas Nox2 gains highest activity with p47phox together with p67phox. As p47phox, different to NoxO1 contains an auto inhibitory region it has to be phosphorylated prior to complex formation. In the cardio-vascular system, all cytosolic Nox proteins are expressed but the evidence for their contribution to ROS production is not well established. Most data have been collected for p47phox, whereas NoxA1 has basically not yet been studied. In this article the specific aspects of cytosolic Nox proteins in the cardiovascular system with respect to Nox activation, their expression and their importance will be reviewed. Finally, it will be discussed whether cytosolic Nox proteins are suitable pharmacological targets to tamper with vascular ROS production.

NOX Activation by Subunit Interaction and Underlying Mechanisms in Disease

Nicotinamide adenine dinucleotide phosphate (NAPDH) oxidase (NOX) is an enzyme complex with the sole function of producing superoxide anion and reactive oxygen species (ROS) at the expense of NADPH. Vital to the immune system as well as cellular signaling, NOX is also involved in the pathologies of a wide variety of disease states. Particularly, it is an integral player in many neurological diseases, including stroke, TBI, and neurodegenerative diseases. Pathologically, NOX produces an excessive amount of ROS that exceed the body’s antioxidant ability to neutralize them, leading to oxidative stress and aberrant signaling. This prevalence makes it an attractive therapeutic target and as such, NOX inhibitors have been studied and developed to counter NOX’s deleterious effects. However, recent studies of NOX have created a better understanding of the NOX complex. Comprised of independent cytosolic subunits, p47-phox, p67-phox, p40-phox and Rac, and membrane subunits, gp91-phox and p22-phox, the NOX complex requires a unique activation process through subunit interaction. Of these subunits, p47-phox plays the most important role in activation, binding and translocating the cytosolic subunits to the membrane and anchoring to p22-phox to organize the complex for NOX activation and function. Moreover, these interactions, particularly that between p47-phox and p22-phox, are dependent on phosphorylation initiated by upstream processes involving protein kinase C (PKC). This review will look at these interactions between subunits and with PKC. It will focus on the interaction involving p47-phox with p22-phox, key in bringing the cytosolic subunits to the membrane. Furthermore, the implication of these interactions as a target for NOX inhibitors such as apocynin will be discussed as a potential avenue for further investigation, in order to develop more specific NOX inhibitors based on the inhibition of NOX assembly and activation.

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.

HIV Protease Inhibitor-Induced Cathepsin Modulation Alters Antigen Processing and Cross-Presentation

Immune recognition by T cells relies on the presentation of pathogen-derived peptides by infected cells, but the persistence of chronic infections calls for new approaches to modulate immune recognition. Ag cross-presentation, the process by which pathogen Ags are internalized, degraded, and presented by MHC class I, is crucial to prime CD8 T cell responses. The original degradation of Ags is performed by pH-dependent endolysosomal cathepsins. In this article, we show that HIV protease inhibitors (PIs) prescribed to HIV-infected persons variably modulate cathepsin activities in human APCs, dendritic cells and macrophages, and CD4 T cells, three cell subsets infected by HIV. Two HIV PIs acted in two complementary ways on cathepsin hydrolytic activities: directly on cathepsins and indirectly on their regulators by inhibiting Akt kinase activities, reducing NADPH oxidase 2 activation, and lowering phagolysosomal reactive oxygen species production and pH, which led to enhanced cathepsin activities. HIV PIs modified endolysosomal degradation and epitope production of proteins from HIV and other pathogens in a sequence-dependent manner. They altered cross-presentation of Ags by dendritic cells to epitope-specific T cells and T cell-mediated killing. HIV PI-induced modulation of Ag processing partly changed the MHC self-peptidome displayed by primary human cells. This first identification, to our knowledge, of prescription drugs modifying the regulation of cathepsin activities and the MHC-peptidome may provide an alternate therapeutic approach to modulate immune recognition in immune disease beyond HIV.

Carob pods (Ceratonia siliqua L.) inhibit human neutrophils myeloperoxidase and in vitro ROS-scavenging activity

Chromatographic profiles of aqueous extract of carob pods ((A) pulp and (B) seeds).

Molecular insights of p47phox phosphorylation dynamics in the regulation of NADPH oxidase activation and superoxide production

Phagocyte superoxide production by a multicomponent NADPH oxidase is important in host defense against microbial invasion. However inappropriate NADPH oxidase activation causes inflammation. Endothelial cells express NADPH oxidase and endothelial oxidative stress due to prolonged NADPH oxidase activation predisposes many diseases. Discovering the mechanism of NADPH oxidase activation is essential for developing novel treatment of these diseases. The p47^phox is a key regulatory subunit of NADPH oxidase; however, due to the lack of full protein structural information, the mechanistic insight of p47^phox phosphorylation in NADPH oxidase activation remains incomplete. Based on crystal structures of three functional domains, we generated a computational structural model of the full p47^phox protein. Using a combination of in silico phosphorylation, molecular dynamics simulation and protein/protein docking, we discovered that the C-terminal tail of p47^phox is critical for stabilizing its autoinhibited structure. Ser-379 phosphorylation disrupts H-bonds that link the C-terminal tail to the autoinhibitory region (AIR) and the tandem Src homology 3 (SH3) domains, allowing the AIR to undergo phosphorylation to expose the SH3 pocket for p22^phox binding. These findings were confirmed by site-directed mutagenesis and gene transfection of p47^phox−/− coronary microvascular cells. Compared with wild-type p47^phox cDNA transfected cells, the single mutation of S379A completely blocked p47^phox membrane translocation, binding to p22^phox and endothelial O₂^⨪ production in response to acute stimulation of PKC. p47^phox C-terminal tail plays a key role in stabilizing intramolecular interactions at rest. Ser-379 phosphorylation is a molecular switch which initiates p47^phox conformational changes and NADPH oxidase-dependent superoxide production by cells.

Evaluation of p47phox phosphorylation in human neutrophils using phospho-specific antibodies

Superoxide anions production by neutrophils plays a key role in host defense against pathogens and in inflammation. The enzyme responsible for this process is called the NADPH oxidase. It is a multicomponent enzyme comprised of a membrane-bound flavocytochrome b558 and several cytosolic proteins (p47phox, p67phox, p40phox, and p21rac1/2). The phosphorylation of p47phox is essential for the activation of the complex in intact cells. Until recently, analysis of the phosphorylation of p47phox in neutrophils required radioactive labeling, which implied the use of high amount of radioactive ((32)P)-orthophosphoric acid, high number of cells, and protein recovery by immunoprecipitation. In this study, we describe a radioactive-free technique to analyze the phosphorylation of p47phox in cell lysates, based on the use of phospho-specific antibodies, SDS-polyacrylamide gel electrophoresis (SDS-PAGE), and Western blotting. This technique could be used to quickly and easily study the phosphorylation of p47phox under different conditions, such as testing the effects of pharmacological agents in this process or assessing the activation status of neutrophils in situ.

Assessment of priming of the human neutrophil respiratory burst

Neutrophils play an essential role in host defense against microbial pathogens and in the inflammatory reaction. Upon activation, neutrophils produce reactive oxygen species (ROS) such as superoxide anion (O2 (∙-)), hydrogen peroxide (H2O2), and hypochlorous acid (HOCl), a process referred to as the respiratory burst. The enzyme responsible for this process is called the NADPH oxidase or respiratory burst oxidase. This multicomponent enzyme system is composed of two transmembrane proteins (p22phox and gp91phox/NOX2, which form the cytochrome b558), three cytosolic proteins (p47phox, p67phox, p40phox), and a GTPase (Rac1 or Rac2), which assemble at membrane sites upon cell activation. The NADPH oxidase is in a resting state in circulating neutrophils, and its activation can be induced by a large number of soluble and particulate agents such as the formylated peptide, formyl-methionyl-leucyl-phenylalanine (fMLF). This activation can be enhanced or "primed" by pro-inflammatory cytokines, LPS and other agents. Priming is a "double-edged sword" process as it contributes to a rapid and efficient elimination of the pathogens but can also induce the generation of large quantities of toxic ROS that can damage surrounding tissues and participate to inflammation. In this chapter, we describe the techniques used to measure priming of the NADPH oxidase in human neutrophils.

The oxidative burst reaction in mammalian cells depends on gravity

Gravity has been a constant force throughout the Earth’s evolutionary history. Thus, one of the fundamental biological questions is if and how complex cellular and molecular functions of life on Earth require gravity. In this study, we investigated the influence of gravity on the oxidative burst reaction in macrophages, one of the key elements in innate immune response and cellular signaling. An important step is the production of superoxide by the NADPH oxidase, which is rapidly converted to H₂O₂ by spontaneous and enzymatic dismutation. The phagozytosis-mediated oxidative burst under altered gravity conditions was studied in NR8383 rat alveolar macrophages by means of a luminol assay. Ground-based experiments in “functional weightlessness” were performed using a 2 D clinostat combined with a photomultiplier (PMT clinostat). The same technical set-up was used during the 13th DLR and 51st ESA parabolic flight campaign. Furthermore, hypergravity conditions were provided by using the Multi-Sample Incubation Centrifuge (MuSIC) and the Short Arm Human Centrifuge (SAHC). The results demonstrate that release of reactive oxygen species (ROS) during the oxidative burst reaction depends greatly on gravity conditions. ROS release is 1.) reduced in microgravity, 2.) enhanced in hypergravity and 3.) responds rapidly and reversible to altered gravity within seconds. We substantiated the effect of altered gravity on oxidative burst reaction in two independent experimental systems, parabolic flights and 2D clinostat / centrifuge experiments. Furthermore, the results obtained in simulated microgravity (2D clinorotation experiments) were proven by experiments in real microgravity as in both cases a pronounced reduction in ROS was observed. Our experiments indicate that gravity-sensitive steps are located both in the initial activation pathways and in the final oxidative burst reaction itself, which could be explained by the role of cytoskeletal dynamics in the assembly and function of the NADPH oxidase complex.

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.

Midazolam induces cellular apoptosis in human cancer cells and inhibits tumor growth in xenograft mice

Midazolam is a widely used anesthetic of the benzodiazepine class that has shown cytotoxicity and apoptosisinducing activity in neuronal cells and lymphocytes. This study aims to evaluate the effect of midazolam on growth of K562 human leukemia cells and HT29 colon cancer cells. The in vivo effect of midazolam was investigated in BALB/c-nu mice bearing K562 and HT29 cells human tumor xenografts. The results show that midazolam decreased the viability of K562 and HT29 cells by inducing apoptosis and S phase cell-cycle arrest in a concentration-dependent manner. Midazolam activated caspase-9, capspase-3 and PARP indicating induction of the mitochondrial intrinsic pathway of apoptosis. Midazolam lowered mitochondrial membrane potential and increased apoptotic DNA fragmentation. Midazolam showed reactive oxygen species (ROS) scavenging activity through inhibition of NADPH oxidase 2 (Nox2) enzyme activity in K562 cells. Midazolam caused inhibition of pERK1/2 signaling which led to inhibition of the anti-apoptotic proteins Bcl-XL and XIAP and phosphorylation activation of the pro-apoptotic protein Bid. Midazolam inhibited growth of HT29 tumors in xenograft mice. Collectively our results demonstrate that midazolam caused growth inhibition of cancer cells via activation of the mitochondrial intrinsic pathway of apoptosis and inhibited HT29 tumor growth in xenograft mice. The mechanism underlying these effects of midazolam might be suppression of ROS production leading to modulation of apoptosis and growth regulatory proteins. These findings present possible clinical implications of midazolam as an anesthetic to relieve pain during in vivo anticancer drug delivery and to enhance anticancer efficacy through its ROS-scavenging and pro-apoptotic properties.

Mechanosensitive microRNAs-role in endothelial responses to shear stress and redox state

Endothelial functions are highly regulated by imposed shear stress in vivo. The characteristics of shear stress determine mechanotransduction events that regulate phenotypic outcomes including redox and inflammatory states. Recent data indicate that microRNAs (miRs) in vascular endothelial cells play an essential role in shear stress-regulated endothelial responses. More specifically, atheroprotective pulsatile flow (PS) induces miRs that inhibit mediators of oxidative stress and inflammation while promoting those involved in maintaining vascular homeostasis. Conversely, oscillatory flow (OS) elicits the opposing networks. This is exemplified by the PS-responsive transcription factor Krüppel-like factor 2 (KLF2), which regulates miR expression but is also regulated by OS-sensitive miRs to ultimately regulate the oxidative and inflammatory state of the endothelium. In this review, we outline important findings demonstrating the multifaceted roles of shear stress-regulated miRs in endothelial redox and inflammatory balance. Furthermore, we discuss the use of algorithms in deciphering signaling networks differentially regulated by PS and OS.

Protein Kinase C Epsilon Contributes to NADPH Oxidase Activation in a Pre-Eclampsia Lymphoblast Cell Model

Pre-eclampsia is a pregnancy-specific disorder characterised by hypertension and proteinuria, which in severe cases results in multi-system disturbances. The maternal syndrome is associated with a pro-inflammatory state, consisting of leukocyte activation, which is thought to contribute to the widespread endothelial dysfunction. We previously showed increased activation of NADPH oxidase in pre-eclampsia, in both neutrophils and B-lymphoblast cell lines (B-LCLs). In this study, the mechanism by which NADPH oxidase activity is increased in pre-eclampsia was further investigated. NADPH oxidase activity was found to be increased in phorbol-12-myristate-13-acetate (PMA) stimulated B-LCLs isolated from women with pre-eclampsia. This correlated with an increase in protein kinase C (PKC) substrate phosphorylation, p47-phox phosphorylation (a regulatory component of NADPH oxidase) and p47-phox directed-kinase activity. Using ion exchange and hydroxyapatite chromatography we identified a major peak of PMA regulated p47-phox kinase activity. Chromatography fractions were probed for PKC isoforms. We found the major peak of p47-phox kinase activity could not be separated from the elution profile of PKC epsilon. Using a peptide inhibitor of PKC epsilon, PMA-induced reactive oxygen species (ROS) production could be reduced to that of a normal B-LCL. These data suggest a pro-inflammatory role for PKC epsilon in the pathogenesis of pre-eclampsia.

Oxidative stress induced by P2X7 receptor stimulation in murine macrophages is mediated by c-Src/Pyk2 and ERK1/2

BACKGROUND

Activation of ATP-gated P2X7 receptors (P2X7R) in macrophages leads to production of reactive oxygen species (ROS) by a mechanism that is partially characterized. Here we used J774 cells to identify the signaling cascade that couples ROS production to receptor stimulation.

METHODS

J774 cells and mP2X7-transfected HEK293 cells were stimulated with Bz-ATP in the presence and absence of extracellular calcium. Protein inhibitors were used to evaluate the physiological role of various kinases in ROS production. In addition, phospho-antibodies against ERK1/2 and Pyk2 were used to determine activation of these two kinases.

RESULTS

ROS generation in either J774 or HEK293 cells (expressing P2X7, NOX2, Rac1, p47phox and p67phox) was strictly dependent on calcium entry via P2X7R. Stimulation of P2X7R activated Pyk2 but not calmodulin. Inhibitors of MEK1/2 and c-Src abolished ERK1/2 activation and ROS production but inhibitors of PI3K and p38 MAPK had no effect on ROS generation. PKC inhibitors abolished ERK1/2 activation but barely reduced the amount of ROS produced by Bz-ATP. In agreement, the amount of ROS produced by PMA was about half of that produced by Bz-ATP.

CONCLUSIONS

Purinergic stimulation resulted in calcium entry via P2X7R and subsequent activation of the PKC/c-Src/Pyk2/ERK1/2 pathway to produce ROS. This signaling mechanism did not require PI3K, p38 MAPK or calmodulin.

GENERAL SIGNIFICANCE

ROS is generated in order to kill invading pathogens, thus elucidating the mechanism of ROS production in macrophages and other immune cells allow us to understand how our body copes with microbial infections.

NADPH oxidases in heart failure: poachers or gamekeepers?

SIGNIFICANCE

Oxidative stress is involved in the pathogenesis of heart failure but clinical antioxidant trials have been unsuccessful. This may be because effects of reactive oxygen species (ROS) depend upon their source, location, and concentration. Nicotinamide adenine dinucleotide phosphate oxidase (Nox) proteins generate ROS in a highly regulated fashion and modulate several components of the heart failure phenotype.

RECENT ADVANCES

Two Nox isoforms, Nox2 and Nox4, are expressed in the heart. Studies using gene-modified mice deficient in Nox2 activity indicate that Nox2 activation contributes to angiotensin II-induced cardiomyocyte hypertrophy, atrial fibrillation, and the development of interstitial fibrosis but may also positively modulate physiological excitation-contraction coupling. Nox2 contributes to myocyte death under stress situations and plays important roles in postmyocardial infarction remodeling, in part by modulating matrix metalloprotease activity. In contrast to Nox2, Nox4 is constitutively active at a low level and induces protective effects in the heart under chronic stress, for example, by maintaining myocardial capillary density. However, high levels of Nox4 could have detrimental effects.

CRITICAL ISSUES

The effects of Nox proteins during the development of heart failure likely depend upon the isoform, activation level, and cellular distribution, and may include beneficial as well as detrimental effects. More needs to be learnt about the precise regulation of abundance and biochemical activity of these proteins in the heart as well as the downstream signaling pathways that they regulate.

FUTURE DIRECTIONS

The development of specific approaches to target individual Nox isoforms and/or specific cell types may be important for the achievement of therapeutic efficacy in heart failure.

Conjugated equine estrogen treatment corrected the exacerbated aorta oxidative stress in ovariectomized spontaneously hypertensive rats

OBJECTIVE

The increased risk of cardiovascular diseases in postmenopausal women has been linked to the decrease in plasma estrogen levels. Preparation of conjugate equine estrogens (CEE) is one of the most routinely used hormone therapy in postmenopausal women. However, studies on the vascular effects of CEE are still sparse and the mechanism of action is not completely elucidated. In this context, we have determined the effects of CEE in the vascular oxidative stress observed in ovariectomyzed (OVX) spontaneously hypertensive rats (SHR). Mechanisms by which CEE interferes with redox-sensitive pathways and endothelial function were also determined.

RESULTS

Aortas from OVX rats exhibited increased generation of reactive oxygen species (ROS), NADPH oxidase activity and reduced catalase protein expression, compared to aortas from sham SHR. Endothelium-intact aortic rings from OVX were hyperreactive to NE when compared to Sham aortas. This hyperreactivity was corrected by superoxide dismutase (SOD), catalase, and endothelium removal. Treatment of OVX-SHR with CEE reduced vascular ROS generation, NADPH oxidase activity, enhanced SOD and catalase expression and also corrected the NE-hyperreactivity in aortic rings from OVX-SHR.

CONCLUSION

Our study indicates a potential benefit of CEE therapy through a mechanism that involves reduction in oxidative stress, improving endothelial function in OVX hypertensive rats.

Reactive oxygen species delay control of lymphocytic choriomeningitis virus

Cluster of differentiation (CD)8(+) T cells are like a double edged sword during chronic viral infections because they not only promote virus elimination but also induce virus-mediated immunopathology. Elevated levels of reactive oxygen species (ROS) have been reported during virus infections. However, the role of ROS in T-cell-mediated immunopathology remains unclear. Here we used the murine lymphocytic choriomeningitis virus to explore the role of ROS during the processes of virus elimination and induction of immunopathology. We found that virus infection led to elevated levels of ROS producing granulocytes and macrophages in virus-infected liver and spleen tissues that were triggered by the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Lack of the regulatory subunit p47phox of the NADPH oxidase diminished ROS production in these cells. While CD8(+) T cells exhibited ROS production that was independent of NADPH oxidase expression, survival and T-cell function was elevated in p47phox-deficient (Ncf1(-/-)) mice. In the absence of p47phox, enhanced T-cell immunity promoted virus elimination and blunted corresponding immunopathology. In conclusion, we find that NADPH-mediated production of ROS critically impairs the immune response, impacting elimination of virus and outcome of liver cell damage.

Phosphorylation of p47phox is required for receptor-mediated NADPH oxidase/NOX2 activation in Epstein-Barr virus-transformed human B lymphocytes

The phagocyte NADPH oxidase (NOX2) is known to be expressed in Epstein-Barr virus (EBV)-transformed human B lymphocytes. Phosphorylation of the NOX2 cytosolic subunit p47phox is required for phorbol myristate acetate (PMA)-induced NOX2 activation in EBV-transformed B lymphocytes, however the role of this process in receptor-mediated NOX2 activation is not known. Here, we used pansorbin which acts by cross linking cell surface IgG and transfected cells with mutated p47phox to address if the phosphorylation of this subunit is required for receptor-mediated NOX2 activation. We show that pansorbin induced NOX2 activation in a time and concentration-dependent manner, albeit at levels only of 20% of those induced by PMA. GF109203X, a PKC selective inhibitor, inhibited pansorbin as well as PMA-induced NOX2 activation. Using specific anti-phospho serine antibodies we showed that pansorbin induced p47phox phosphorylation on Ser304, 315, 320, 328, and 345 and kinetics of these phosphorylations preceed NOX2 activation. To determine whether the phosphorylation of p47phox is required for pansorbin-induced NOX2 activation, we transfected EBV-transformed lymphocytes deficent in p47phox with a plasmid expressing wild type p47phox or p47phox with all the phosphorylated serines mutated to alanines, p47phoxS(303-379)A. Results show that pansorbin-induced NOX2 activation was greatly decreased in lymphocytes expressing the mutant as compared to the wild-type p47phox. These results show that pansorbin induced p47phox phosphorylation on multiple sites in EBV-transformed B lymphocytes and this process is required for pansorbin-induced NADPH oxidase activation in these cells.

Cell signaling through protein kinase C oxidation and activation

Due to the growing importance of cellular signaling mediated by reactive oxygen species (ROS), proteins that are reversibly modulated by these reactant molecules are of high interest. In this context, protein kinases and phosphatases, which act coordinately in the regulation of signal transduction through the phosphorylation and dephosphorylation of target proteins, have been described to be key elements in ROS-mediated signaling events. The major mechanism by which these proteins may be modified by oxidation involves the presence of key redox-sensitive cysteine residues. Protein kinase C (PKC) is involved in a variety of cellular signaling pathways. These proteins have been shown to contain a unique structural feature that is susceptible to oxidative modification. A large number of scientific studies have highlighted the importance of ROS as a second messenger in numerous cellular processes, including cell proliferation, gene expression, adhesion, differentiation, senescence, and apoptosis. In this context, the goal of this review is to discuss the mechanisms by which PKCs are modulated by ROS and how these processes are involved in the cellular response.

Regulation of alveolar macrophage p40phox: hierarchy of activating kinases and their inhibition by PGE2

PGE(2), produced in the lung during infection with microbes such as Klebsiella pneumoniae, inhibits alveolar macrophage (AM) antimicrobial functions by preventing H(2)O(2) production by NADPH oxidase (NADPHox). Activation of the NADPHox complex is poorly understood in AMs, although in neutrophils it is known to be mediated by kinases including PI3K/Akt, protein kinase C (PKC) δ, p21-activated protein kinase (PAK), casein kinase 2 (CK2), and MAPKs. The p40phox cytosolic subunit of NADPHox has been recently recognized to function as a carrier protein for other subunits and a positive regulator of oxidase activation, a role previously considered unique to another subunit, p47phox. The regulation of p40phox remains poorly understood, and the effect of PGE(2) on its activation is completely undefined. We addressed these issues in rat AMs activated with IgG-opsonized K. pneumoniae. The kinetics of kinase activation and the consequences of kinase inhibition and silencing revealed a critical role for a PKCδ-PAK-class I PI3K/Akt1 cascade in the regulation of p40phox activation upon bacterial challenge in AMs; PKCα, ERK, and CK2 were not involved. PGE(2) inhibited the activation of p40phox, and its effects were mediated by protein kinase A type II, were independent of interactions with anchoring proteins, and were directed at the distal class I PI3K/Akt1 activation step. Defining the kinases that control AM p40phox activation and that are the targets for inhibition by PGE(2) provides new insights into immunoregulation in the infected lung.

Regulation of NAD(P)H oxidases by AMPK in cardiovascular systems

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are ubiquitously produced in cardiovascular systems. Under physiological conditions, ROS/RNS function as signaling molecules that are essential in maintaining cardiovascular function. Aberrant concentrations of ROS/RNS have been demonstrated in cardiovascular diseases owing to increased production or decreased scavenging, which have been considered common pathways for the initiation and progression of cardiovascular diseases such as atherosclerosis, hypertension, (re)stenosis, and congestive heart failure. NAD(P)H oxidases are primary sources of ROS and can be induced or activated by all known cardiovascular risk factors. Stresses, hormones, vasoactive agents, and cytokines via different signaling cascades control the expression and activity of these enzymes and of their regulatory subunits. But the molecular mechanisms by which NAD(P)H oxidase is regulated in cardiovascular systems remain poorly characterized. Investigations by us and others suggest that adenosine monophosphate-activated protein kinase (AMPK), as an energy sensor and modulator, is highly sensitive to ROS/RNS. We have also obtained convincing evidence that AMPK is a physiological suppressor of NAD(P)H oxidase in multiple cardiovascular cell systems. In this review, we summarize our current understanding of how AMPK functions as a physiological repressor of NAD(P)H oxidase.

Divergent effects of p47(phox) phosphorylation at S303-4 or S379 on tumor necrosis factor-α signaling via TRAF4 and MAPK in endothelial cells

OBJECTIVE

To define the mechanism of p47(phox) phosphorylation in regulating endothelial cell response to tumor necrosis factor-α (TNFα) stimulation.

METHODS AND RESULTS

We replaced 11 serines (303-4, 310, 315, 320, 328, 345, 348, 359, 370, and 379) with alanines and investigated their effects on TNFα (100 U/mL, 30 minutes)-induced acute O(2)(.-) production and mitogen-activated protein kinase phosphorylation in endothelial cells. Seven constructs, S303-4A (double), S310A, S315A, S328A, S345A, S370A, and S379A, significantly reduced the O(2)(.-) production, and 4 of them (S328A, S345A, S370A, and S379A) also inhibited TNFα-induced extracellular-signal-regulated kinase (ERK) 1/2 phosphorylation. Blocking the phosphorylation of S303-4 and S379 inhibited most effectively TNFα-induced O(2)(.-) production. However, phosphorylation of S303-4 was not required for TNFα-induced p47(phox) membrane translocation and binding to TNF receptor-associated factor 4, ERK1/2 activation, and subsequent vascular cell adhesion molecule-1 expression. Knockout of p47(phox) or knockdown of TNF receptor-associated factor 4 using siRNA abolished TNFα-induced ERK1/2 phosphorylation, and inhibition of ERK1/2 activation significantly reduced the TNFα-induced vascular cell adhesion molecule-1 expression.

CONCLUSIONS

Phosphorylation of p47(phox) at different serine sites plays distinct roles in endothelial cell response to TNFα stimulation. Double serine (S303-4) phosphorylation is crucial for acute O(2)(.-) production, but is not involved in TNFα signaling through TNF receptor-associated factor 4 and ERK1/2. p47(phox) requires serine phosphorylation at distinct sites to support specific signaling events in response to TNFα.

Adiponectin and its globular fragment differentially modulate the oxidative burst of primary human phagocytes

Adiponectin (Acrp30) belongs to the family of C1q/tumor necrosis factor α (TNFα)-related proteins. Acrp30 circulates as multimers of high, middle, and low molecular weight. In this study, we detected Acrp30 and its globular fragment (gAcrp30) in synovial fluid from rheumatoid arthritis patients. Intriguingly, the LMW form was more abundant in synovial fluid than in serum from both rheumatoid arthritis patients and healthy subjects. We also investigated the effects of Acrp30 and gAcrp30 on reactive oxygen species (ROS) production via the phagocytic NADPH oxidase. Acrp30 inhibited fMLF-induced ROS production by human phagocytes, whereas gAcrp30 enhanced it. gAcrp30's effect is additive with TNFα, whereas Acrp30 inhibited TNFα-induced priming. gAcrp30 enhanced NOX-2 expression at the plasma membrane, with a concomitant increase in p47(phox) phosphorylation. Selective inhibitors of p38 mitogen-activated protein kinase (MAPK) and extracellular signal-regulated kinase 1 (ERK1)/2 abrogated p47(phox) phosphorylation by gAcrp30. In contrast, p47(phox) phosphorylation was inhibited by Acrp30 in association with increased AMP-activated protein kinase (AMPK) phosphorylation in phagocytes. These results suggest that human phagocyte ROS production is regulated by different mechanisms selective for Acrp30 versus gAcrp30. An imbalance between gAcrp30 and higher molecular weight isoforms of Acrp30 might contribute to chronic inflammation by regulating NADPH oxidase.

The NADPH oxidase cytosolic component p67phox is constitutively phosphorylated in human neutrophils: Regulation by a protein tyrosine kinase, MEK1/2 and phosphatases 1/2A

Neutrophils play a key role in host defense and inflammation through the production of superoxide anion and other reactive oxygen species (ROS) by the enzyme complex NADPH oxidase. The cytosolic NADPH oxidase component, p67phox, has been shown to be phosphorylated in human neutrophils but the pathways involved in this process are largely unknown. In this study, we show that p67phox is constitutively phosphorylated in resting human neutrophils and that neutrophil stimulation with PMA further enhanced this phosphorylation. Inhibition of the constitutively active serine/threonine phosphatases type 1 and type 2A (PP1/2A) by calyculin A resulted in the enhancement of p67phox phosphorylation. Constitutive and calyculin A-induced phosphorylation of p67phox was completely inhibited by the protein tyrosine kinase inhibitor genistein and partially inhibited by the MEK1/2 inhibitor PD98059, but was unaffected by GF109203X, wortmannin and SB203580, inhibitors of PKC, PI3K and p38MAP kinase, respectively. Two-dimensional phosphopeptide mapping revealed that constitutive and calyculin A-induced p67phox phosphorylation occurred on the same major sites. Interestingly, calyculin A enhanced formyl-Met-Leu-Phe (fMLP)-induced superoxide production, while genistein inhibited this process. Taken together, these results suggest that (i) p67phox undergoes a continual cycle of phosphorylation/dephosphorylation in resting cells; (ii) p67phox phosphorylation is controlled by MEK1/2 and an upstream tyrosine kinase; (iii) PP1/2A directly or indirectly antagonize this process. Thus, these pathways could play a role in regulating ROS production by human neutrophils at inflammatory sites.

Lipopolysaccharide primes the respiratory burst of Atlantic salmon SHK-1 cells through protein kinase C-mediated phosphorylation of p47phox

The superoxide-producing NADPH oxidase complex of phagocytes plays a crucial role in host defenses against microbial infection. NADPH oxidase consists of a membrane heterodimeric protein, composed of gp91phox and p22phox, and the cytosolic proteins, p40phox, p47phox and p67phox. In the present study, we clone and sequence the full-length cDNAs coding for the Atlantic salmon (Salmo salar) phagocyte NADPH oxidase components, p47phox, p67phox and gp91phox, using a homology cloning approach. The sequences of these cDNAs showed that the S. salar p47phox, p67phox and gp91phox genes contained single open reading frames, which encoded predicted proteins of 413, 504 and 565 amino acids, respectively. Comparison of the deduced amino acid sequences showed that the S. salar p47phox, p67phox and gp91phox sequences shared 51, 45 and 68% identity with those of human components, respectively. Despite this relatively low homology between salmon and mammalian NADPH oxidase subunits, their functional domains are highly conserved. We also found that the mRNA levels of p47phox, p67phox and gp91phox expression were higher in immune-related tissues, such as kidney, spleen and gill. In addition, infection of the salmon macrophage cell line SHK-1 with Piscirickettsia salmonis induced the expression of p47phox, but had no effect on p67phox and gp91phox expression. Finally, we show for the first time in fish that activation of macrophages with lipopolysaccharide promotes the activation of protein kinase C, which in turn phosphorylates p47phox, leading to NADPH oxidase activation and reactive oxygen species generation. Collectively, these results suggest that the mechanisms of activation of phagocyte NADPH oxidase are well conserved from fish to mammals.

The prolyl isomerase Pin1 acts as a novel molecular switch for TNF-alpha-induced priming of the NADPH oxidase in human neutrophils

Neutrophils play a key role in host defense by releasing reactive oxygen species (ROS). However, excessive ROS production by neutrophil nicotinamide adenine dinucleotide phosphate (NADPH) oxidase can damage bystander tissues, thereby contributing to inflammatory diseases. Tumor necrosis factor-α (TNF-α), a major mediator of inflammation, does not activate NADPH oxidase but induces a state of hyperresponsiveness to subsequent stimuli, an action known as priming. The molecular mechanisms by which TNF-α primes the NADPH oxidase are unknown. Here we show that Pin1, a unique cis-trans prolyl isomerase, is a previously unrecognized regulator of TNF-α-induced NADPH oxidase hyperactivation. We first showed that Pin1 is expressed in neutrophil cytosol and that its activity is markedly enhanced by TNF-α. Inhibition of Pin1 activity with juglone or with a specific peptide inhibitor abrogated TNF-α-induced priming of neutrophil ROS production induced by N-formyl-methionyl-leucyl-phenylalanine peptide (fMLF). TNF-α enhanced fMLF-induced Pin1 and p47phox translocation to the membranes and juglone inhibited this process. Pin1 binds to p47phox via phosphorylated Ser345, thereby inducing conformational changes that facilitate p47phox phosphorylation on other sites by protein kinase C. These findings indicate that Pin1 is critical for TNF-α-induced priming of NADPH oxidase and for excessive ROS production. Pin1 inhibition could potentially represent a novel anti-inflammatory strategy.

NADPH oxidases are responsible for the failure of nitric oxide to inhibit migration of smooth muscle cells exposed to high glucose

Our previous studies showed that nitric oxide (NO) fails to inhibit migration of smooth muscle cells (SMC) exposed to high glucose (HG) because of oxidation of the most reactive cysteine, cysteine-674, on the sarco/endoplasmic reticulum ATPase, preventing its S-glutathiolation, thus blocking NO action. This study further addresses the sources of the oxidants responsible for the failure of NO to inhibit SMC migration in HG. NADPH oxidases are the major source of reactive oxygen species (ROS) in SMC. We used small interfering RNA or dominant-negative adenoviral vectors to target components of NADPH oxidase to study their individual roles by measuring serum-induced migration in the presence or absence of NO. In HG, the mRNA levels of Nox1 and Nox4 and the protein level of Nox4 were increased; knocking down Nox1 or Nox4 attenuated the ROS production and restored the inhibition of SMC migration by NO. Blockade of the activation of Rac1 or p47(phox) inhibited serum-induced migration and restored the inhibition of migration by NO. These data indicate that NADPH oxidases are responsible for the failure of NO to inhibit SMC migration caused by HG.

Regulation of TNF-induced oxygen radical production in human neutrophils: role of delta-PKC

In human neutrophils, TNF-elicited O(2)(-) production requires adherence and integrin activation. How this cooperative signaling between TNFRs and integrins regulates O(2)(-) generation has yet to be fully elucidated. Previously, we identified delta-PKC as a critical early regulator of TNF signaling in adherent neutrophils. In this study, we demonstrate that inhibition of delta-PKC with a dominant-negative delta-PKC TAT peptide resulted in a significant delay in the onset time of TNF-elicited O(2)(-) generation but had no effect on Vmax, indicating an involvement of delta-PKC in the initiation of O(2)(-) production. In contrast, fMLP-elicited O(2)(-) production in adherent and nonadherent neutrophils was delta-PKC-independent, suggesting differential regulation of O(2)(-) production. An important step in activation of the NADPH oxidase is phosphorylation of the cytosolic p47phox component. In adherent neutrophils, TNF triggered a time-dependent association of delta-PKC with p47phox, which was associated with p47phox phosphorylation, indicating a role for delta-PKC in regulating O(2)(-) production at the level of p47phox. Activation of ERK and p38 MAPK is also required for TNF-elicited O(2)(-) generation. TNF-mediated ERK but not p38 MAPK recruitment to p47phox was delta-PKC-dependent. delta-PKC activity is controlled through serine/threonine phosphorylation, and phosphorylation of delta-PKC (Ser643) and delta-PKC (Thr505) was increased significantly by TNF in adherent cells via a PI3K-dependent process. Thus, signaling for TNF-elicited O(2)(-) generation is regulated by delta-PKC. Adherence-dependent cooperative signaling activates PI3K signaling, delta-PKC phosphorylation, and delta-PKC recruitment to p47phox. delta-PKC activates p47phox by serine phosphorylation or indirectly through control of ERK recruitment to p47phox.

Emerging evidence for the importance of phosphorylation in the regulation of NADPH oxidases

The NADPH oxidase (Nox) enzyme family generates reactive oxygen species (ROS) that contribute to cell signaling, innate immune responses, proliferation, and transcription. The signaling mechanisms that regulate this important enzyme family are only beginning to be understood. Evidence is emerging which suggests that phosphorylation of Nox and/or their regulatory components may be important means of modulating their activity. We describe here the evidence for Nox regulation through the action of kinases, and speculate on how such regulatory mechanisms might contribute to the development of pathological disease states.

Punicic acid a conjugated linolenic acid inhibits TNFalpha-induced neutrophil hyperactivation and protects from experimental colon inflammation in rats

Background

Neutrophils play a major role in inflammation by releasing large amounts of ROS produced by NADPH-oxidase and myeloperoxidase (MPO). The proinflammatory cytokine TNFα primes ROS production through phosphorylation of the NADPH-oxidase subunit p47phox on Ser345. Conventional anti-inflammatory therapies remain partially successful and may have side effects. Therefore, regulation of neutrophil activation by natural dietary components represents an alternative therapeutic strategy in inflammatory diseases such as inflammatory bowel diseases. The aim of this study was to assess the effect of punicic acid, a conjugated linolenic fatty acid from pomegranate seed oil on TNFα-induced neutrophil hyperactivation in vitro and on colon inflammation in vivo.

Methodology and Principal Findings

We analyzed the effect of punicic acid on TNFα-induced neutrophil upregulation of ROS production in vitro and on TNBS-induced rat colon inflammation. Results show that punicic acid inhibited TNFα-induced priming of ROS production in vitro while preserving formyl-methionyl-leucyl-phenylalanine (fMLP)-induced response. This effect was mediated by the inhibition of Ser345-p47phox phosphorylation and upstream kinase p38MAPK. Punicic acid also inhibited fMLP- and TNFα+fMLP-induced MPO extracellular release from neutrophils. In vivo experiments showed that punicic acid and pomegranate seed oil intake decreased neutrophil-activation and ROS/MPO-mediated tissue damage as measured by F2-isoprostane release and protected rats from TNBS-induced colon inflammation.

Conclusions/Significance

These data show that punicic acid exerts a potent anti-inflammatory effect through inhibition of TNFα-induced priming of NADPH oxidase by targeting the p38MAPKinase/Ser345-p47phox-axis and MPO release. This natural dietary compound may provide a novel alternative therapeutic strategy in inflammatory diseases such as inflammatory bowel diseases.

p47phox, the phagocyte NADPH oxidase/NOX2 organizer: structure, phosphorylation and implication in diseases

Phagocytes such as neutrophils play a vital role in host defense against microbial pathogens. The anti-microbial function of neutrophils is based on the production of superoxide anion (O2 -), which generates other microbicidal reactive oxygen species (ROS) and release of antimicrobial peptides and proteins. The enzyme responsible for O2 - production is called the NADPH oxidase or respiratory burst oxidase. This multicomponent enzyme system is composed of two trans- membrane proteins (p22phox and gp91phox, also called NOX2, which together form the cytochrome b558) and four cytosolic proteins (p47phox, p67phox, p40phox and a GTPase Rac1 or Rac2), which assemble at membrane sites upon cell activation. NADPH oxidase activation in phagocytes can be induced by a large number of soluble and particulate agents. This process is dependent on the phosphorylation of the cytosolic protein p47phox. p47phox is a 390 amino acids protein with several functional domains: one phox homology (PX) domain, two src homology 3 (SH3) domains, an auto-inhibitory region (AIR), a proline rich domain (PRR) and has several phosphorylated sites located between Ser303 and Ser379. In this review, we will describe the structure of p47phox, its phosphorylation and discuss how these events regulate NADPH oxidase activation.

Regulation of the phagocyte NADPH oxidase activity: phosphorylation of gp91phox/NOX2 by protein kinase C enhances its diaphorase activity and binding to Rac2, p67phox, and p47phox

Neutrophils generate microbicidal oxidants through activation of a multicomponent enzyme called NADPH oxidase. During activation, the cytosolic NADPH oxidase components (p47(phox), p67(phox), p40(phox), and Rac2) translocate to the membranes, where they associate with flavocytochrome b(558), which is composed of gp91(phox)/NOX2 and p22(phox), to form the active system. During neutrophil stimulation, p47(phox), p67(phox), p40(phox), and p22(phox) are phosphorylated; however, the phosphorylation of gp91(phox)/NOX2 and its potential role have not been defined. In this study, we show that gp91(phox) is phosphorylated in stimulated neutrophils. The gp91(phox) phosphoprotein is absent in neutrophils from chronic granulomatous disease patients deficient in gp91(phox), which confirms that this phosphoprotein is gp91(phox). The protein kinase C inhibitor GF109203X inhibited phorbol 12-myristate 13-acetate-induced phosphorylation of gp91(phox), and protein kinase C (PKC) phosphorylated the recombinant gp91(phox)- cytosolic carboxy-terminal flavoprotein domain. Two-dimensional tryptic peptide mapping analysis showed that PKC phosphorylated the gp91(phox)-cytosolic tail on the same peptides that were phosphorylated on gp91(phox) in intact cells. In addition, PKC phosphorylation increased diaphorase activity of the gp91(phox) flavoprotein cytosolic domain and its binding to Rac2, p67(phox), and p47(phox). These results demonstrate that gp91(phox) is phosphorylated in human neutrophils by PKC to enhance its catalytic activity and assembly of the complex. Phosphorylation of gp91(phox)/NOX2 is a novel mechanism of NADPH oxidase regulation.