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

A fluorescently tagged C-terminal fragment of p47phox detects NADPH oxidase dynamics during phagocytosis

The assembly of cytosolic p47(phox) and p67(phox) with flavocytochrome b(558) at the membrane is crucial for activating the leukocyte NADPH oxidase that generates superoxide for microbial killing. p47(phox) and p67(phox) are linked via a high-affinity, tail-to-tail interaction involving a proline-rich region (PRR) and a C-terminal SH3 domain (SH3b), respectively, in their C-termini. This interaction mediates p67(phox) translocation in neutrophils, but is not required for oxidase activity in model systems. Here we examined phagocytosis-induced NADPH oxidase assembly, showing the sequential recruitment of YFP-tagged p67(phox) to the phagosomal cup, and, after phagosome internalization, a probe for PI(3)P followed by a YFP-tagged fragment derived from the p47(phox) PRR. This fragment was recruited in a flavocytochrome b(558)-dependent, p67(phox)-specific, and PI(3)P-independent manner. These findings indicate that p47PRR fragment probes the status of the p67(phox) SH3b domain and suggest that the p47(phox)/p67(phox) tail-to-tail interaction is disrupted after oxidase assembly such that the p67(phox)-SH3b domain becomes accessible. Superoxide generation was sustained within phagosomes, indicating that this change does not correlate with loss of enzyme activity. This study defines a sequence of events during phagocytosis-induced NADPH oxidase assembly and provides experimental evidence that intermolecular interactions within this complex are dynamic and modulated after assembly on phagosomes.

AMP-activated kinase may suppress NADPH oxidase activation in vascular tissues

Activation of AMP-activated kinase (AMPK) suppresses NF-kappaB-mediated transcription in endothelial cells exposed to palmitate or TNF-alpha; it also impedes angiotensin II-driven proliferation in vascular smooth muscle cells. These phenomena become predictable if we postulate that AMPK can inhibit activation of NADPH oxidase. Such an effect would make sense from a homeostatic perspective, and moreover there is direct evidence that AMPK suppresses NADPH oxidase activation in neutrophils. New evidence that sub-pathological levels of peroxynitrite can activate AMPK suggest that this enzyme may act as an "early warning signal" for oxidant stress; inhibiting NADPH oxidase would constitute a rational feedback response to such a signal.

Dihydroxyoctadecamonoenoate esters inhibit the neutrophil respiratory burst

The leukotoxins [9(10)-and 12(13)-EpOME] are produced by activated inflammatory leukocytes such as neutrophils. High EpOME levels are observed in disorders such as acute respiratory distress syndrome and in patients with extensive burns.Although the physiological significance of the EpOMEs remains poorly understood,in some systems, the EpOMEs act as a protoxin,with their corresponding epoxide hydrolase metabolites,9,10-and 12,13-DiHOME, specifically exerting toxicity.Both the EpOMEs and the DiHOMEs were also recently shown to have neutrophil chemotactic activity.We evaluated whether the neutrophil respiratory burst,a surge of oxidant production thought to play an important role in limiting certain bacterial and fungal infections,is modulated by members of the EpOME metabolic pathway.We present evidence that the DiHOMEs suppress the neutrophil respiratory burst by a mechanism distinct from that of respiratory burst inhibitors such as cyclosporin H or lipoxin A4,which inhibit multiple aspects of neutrophil activation.

Priming of the neutrophil NADPH oxidase activation: role of p47phox phosphorylation and NOX2 mobilization to the plasma membrane

Neutrophils play an essential role in host defense against microbial pathogens and in the inflammatory reaction. Upon activation, neutrophils produce superoxide anion (O*2), which generates other reactive oxygen species (ROS) such as hydrogen peroxide (H2O2), hydroxyl radical (OH*) and hypochlorous acid (HOCl), together with microbicidal peptides and proteases. The enzyme responsible for O2* production is called the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase or respiratory burst oxidase. This multicomponent enzyme system is composed of two trans-membrane 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. NADPH oxidase activation in phagocytes can be induced by a large number of soluble and particulate factors. Three major events accompany NAPDH oxidase activation: (1) protein phosphorylation, (2) GTPase activation, and (3) translocation of cytosolic components to the plasma membrane to form the active enzyme. Actually, the neutrophil NADPH oxidase exists in different states: resting, primed, activated, or inactivated. The resting state is found in circulating blood neutrophils. The primed state can be induced by neutrophil adhesion, pro-inflammatory cytokines, lipopolysaccharide, and other agents and has been characterized as a "ready to go" state, which results in a faster and higher response upon exposure to a second stimulus. The active state is found at the inflammatory or infection site. Activation is induced by the pathogen itself or by pathogen-derived formylated peptides and other agents. Finally, inactivation of NADPH oxidase is induced by anti-inflammatory agents to limit inflammation. 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 by hyperactivation of the NADPH oxidase, which can damage surrounding tissues and participate to inflammation. In order to avoid extensive damage to host tissues, NADPH oxidase priming and activation must be tightly regulated. In this review, we will discuss some of the mechanisms of NADPH oxidase priming in neutrophils and the relevance of this process to physiology and pathology.

NADPH oxidase: recent evidence for its role in erectile dysfunction

Important roles for reactive oxygen species (ROS) in physiology and pathophysiology have been increasingly recognized. Under normal conditions, ROS serve as signaling molecules in the regulation of cellular functions. However, enhanced ROS production as a result of the activation of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase contributes significantly to the pathogeneses of vascular diseases. Although it has become evident that increased ROS is associated with erectile dysfunction (ED), the sources of ROS in the penis remain largely unknown. In recent years, emergent evidence suggests the possible role of NADPH oxidase in inducing ED. In this review, we examine the relationship between ROS and ED in different disease models and discuss the current evidence basis for NADPH oxidase-derived ROS in ED.

Stimulus-dependent regulation of the phagocyte NADPH oxidase by a VAV1, Rac1, and PAK1 signaling axis

The p21-activated kinase-1 (PAK1) is best known for its role in the regulation of cytoskeletal and transcriptional signaling pathways. We show here in the microglia cell line Ra2 that PAK1 regulates NADPH oxidase (NOX-2) activity in a stimulus-specific manner. Thus, conditional expression of PAK1 dominant-positive mutants enhanced, whereas dominant-negative mutants inhibited, NADPH oxidase-mediated superoxide generation following formyl-methionyl-leucylphenylalanine or phorbol 12-myristate 13-acetate stimulation. Both Rac1 and the GTP exchange factor VAV1 were required as upstream signaling proteins in the formyl-methionyl-leucyl-phenylalanine-induced activation of endogenous PAK1. In contrast, PAK1 mutants had no effect on superoxide generation downstream of FcgammaR signaling during phagocytosis of IgG-immune complexes. We further present evidence that the effect of PAK1 on the respiratory burst is mediated through phosphorylation of p47(Phox), and we show that expression of a p47(Phox) (S303D/S304D/S320D) mutant, which mimics phosphorylation by PAK1, induced basal superoxide generation in vivo. In contrast PAK1 substrates LIMK-1 or RhoGDI are not likely to contribute to the PAK1 effect on NADPH oxidase activation. Collectively, our findings define a VAV1-Rac1-PAK1 signaling axis in mononuclear phagocytes regulating superoxide production in a stimulus-dependent manner.

Constitutive NADPH oxidase and increased mitochondrial respiratory chain activity regulate chemokine gene expression

Alveolar macrophages, which generate high levels of reactive oxygen species, especially O(2)(*-), are involved in the recruitment of neutrophils to sites of inflammation and injury in the lung, and the generation of chemotactic proteins triggers this cellular recruitment. In this study, we asked whether O(2)(*-) generation in alveolar macrophages had a role in the expression of chemokines. Specifically, we hypothesized that O(2)(*-) generation is necessary for chemokine expression in alveolar macrophages after TNF-alpha stimulation. We found that alveolar macrophages have high constitutive NADPH oxidase activity that was not increased by TNF-alpha, but TNF-alpha increased the activity of the mitochondrial respiratory chain. In addition, the mitochondrial respiratory chain increased O(2)(*-) generation if the NADPH oxidase was inhibited. O(2)(*-) generation was necessary for macrophage inflammatory protein-2 (MIP-2) gene expression, because inhibition of NADPH oxidase or the mitochondrial respiratory chain or overexpression of Cu,Zn-superoxide dismutase significantly inhibited expression of MIP-2. TNF-alpha activated the ERK MAP kinase, and ERK activity was essential for chemokine gene expression. In addition, overexpression of the MEK1-->ERK pathway significantly increased IL-8 expression, and a small interfering RNA to the NADPH oxidase inhibited ERK- and TNF-alpha-induced chemokine expression. Collectively, these results suggest that in alveolar macrophages, O(2)(*-) generation mediates chemokine expression after TNF-alpha stimulation in an ERK-dependent manner.

Platelet particle formation by anti GPIIIa49-66 Ab, Ca2+ ionophore A23187, and phorbol myristate acetate is induced by reactive oxygen species and inhibited by dexamethasone blockade of platelet phospholipase A2, 12-lipoxygenase, and NADPH oxidase

An HIV antibody (Ab) against platelet integrin GPIIIa49-66 induces complement-independent platelet particle formation by the elaboration of reactive oxygen species (ROS) downstream of the activation of the platelet NADPH oxidase by the 12-lipoxygenase (12-LO) product 12(S)-HETE. To determine whether other inducers of platelet particle formation also function via the induction of ROS, we examined the effects of the Ca(2+) ionophore A23187 and phorbol myristate acetate (PMA). Both agents induced oxidative platelet particle formation in an identical fashion as Ab, requiring Ca(2+) flux and 12(S)-HETE production as well as intact NADPH oxidase and 12-LO pathways. Since HIV-ITP patients with this Ab correct their platelet counts with dexamethasone (Dex), we examined the role of this steroid in this unique autoimmune disorder. Dex at therapeutic concentrations inhibited Ab-, A23187-, or PMA-induced platelet particle formation by inhibiting platelet PLA(2), 12-LO, and NADPH oxidase. The operational requirement of translocation of PLA(2), 12-LO, and NADPH oxidase components (p67 phox) from cytosol to membrane for induction of ROS was both inhibited and partially reversed by Dex in platelets. We conclude that (1) platelet particle formation can be induced by the generation of ROS; and (2) platelet PLA(2), 12-LO, NADPH oxidase, and cytosol membrane translocation, requirements for ROS production, are inhibited by Dex.

Selective roles for alpha-PKC in positive signaling for O-(2) generation and calcium mobilization but not elastase release in differentiated HL60 cells

Protein kinase C (PKC) isotypes and Ca2+ mobilization have been implicated in phagocytic cell functions such as O(-)(2) generation. Ca/DG-dependent alpha-PKC and beta-PKC have similar substrate specificities and cofactor requirements in vitro. However it is not known if these isotypes play redundant or unique roles in the intact cell. In the present study, a role for alpha-PKC in positive signaling for fMet-Leu-Phe- and PMA-activated O(-)(2) generation was probed using an siRNA strategy in HL60 cells differentiated to a neutrophilic phenotype (dHL60 cells). A selective decrease in alpha-PKC in dHL60 cells attenuated O(-)(2) generation but not degranulation, and reduced ligand-induced phosphorylation of p47phox as previously shown for beta-PKC. However alpha-PKC, unlike beta-PKC, was a positive regulator of fMet-Leu-Phe-triggered Ca2+ uptake via SOCC (Store Operated Calcium Channels). The ability of a selective SOCC inhibitor, MRS1845, to decrease fMet-Leu-Phe induced Ca2+ uptake and O(-)(2) generation confirmed that Ca2+ uptake via SOCC was required for O(-)(2) generation. These results indicate that alpha-PKC and beta-PKC are required for optimal O(-)(2) generation, but play different roles in Ca2+ signaling for phagocytic responses such as O(-)(2) generation.

The antimicrobial peptide parabutoporin competes with p47(phox) as a PKC-substrate and inhibits NADPH oxidase in human neutrophils

We investigated parabutoporin (PP), an antimicrobial scorpion peptide, to understand its inhibition on NADPH oxidase in human PMN. We show that PP is a good substrate for all PKC-isotypes, implicated in the activation of NADPH oxidase, and acts as a potent competitive inhibitor of in vitro p47(phox)-phosphorylation by PKC-alpha, -betaI, -betaII and -delta, but not PKC-zeta. In PMN, PP also inhibits the PMA-stimulated phosphorylation of p47(phox) and its subsequent translocation. In contrast, PP affects the PKC-independent activation to a much lesser degree. This indicates that PP inhibits the activation of NADPH oxidase at submicromolar concentrations in a strongly PKC-dependent manner.

PtdIns3P binding to the PX domain of p40phox is a physiological signal in NADPH oxidase activation

The production of reactive oxygen species by the NADPH oxidase complex of phagocytes plays a critical role in our defence against bacterial and fungal infections. The PX domains of two oxidase components, p47(phox) and p40(phox), are known to bind phosphoinositide products of PI3Ks but the physiological roles of these interactions are unclear. We have created mice which carry an R58A mutation in the PX domain of their p40(phox) gene, which selectively prevents binding to PtdIns3P. p40(phoxR58A/R58A) embryos do not develop normally but p40(phoxR58A/-) mice are viable and neutrophils from these animals exhibit significantly reduced oxidase responses compared to those from their p40(phox+/-) siblings (e.g. 60% reduced in response to phagocytosis of Staphylococcus aureus). Wortmannin inhibition of the S. aureus oxidase response correlates with inhibition of phagosomal PtdIns3P accumulation and overlaps with the reduction in this response caused by the R58A mutation, suggesting PI3K regulation of this response is substantially dependent on PtdIns3P-binding to p40(phox). p40(phoxR58A/-) mice are significantly compromised in their ability to kill S. aureus in vivo, defining the physiological importance of this interaction.

Nox2, Ca2+, and protein kinase C play a role in angiotensin II-induced free radical production in nucleus tractus solitarius

The dorsomedial portion of the nucleus tractus solitarius (dmNTS) is the site of termination of baroreceptor and cardiorespiratory vagal afferents and plays a critical role in cardiovascular regulation. Angiotensin II (Ang II) is a powerful signaling molecule in dmNTS neurons and exerts some of its biological effects by modulating Ca(2+) currents via reactive oxygen species (ROS) derived from reduced nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase. We investigated whether a Nox2-containing NADPH oxidase is the source of the Ang II-induced ROS production and whether the signaling mechanisms of its activation require intracellular Ca(2+) or protein kinase C (PKC). Second-order dmNTS neurons were anterogradely labeled with 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide transported from the vagus and isolated from the brain stem. ROS production was assessed in 4-(4-[didecylamino]styryl)-N-methylpyridinium iodide-positive dmNTS neurons using the fluorescent dye 6-carboxy-2',7'-dichlorodihydro-fluorescein di(acetoxymethyl ester). Ang II (3 to 2000 nmol/L) increased ROS production in dmNTS neurons (EC(50)=38.3 nmol/L). The effect was abolished by the ROS scavenger Mn (III) porphyrin 5,10,20-tetrakis (benzoic acid) porphyrin manganese (III), the Ang II type 1 receptor antagonist losartan, or the NADPH oxidase inhibitors apocynin or gp91ds-tat. Ang II failed to increase ROS production or to potentiate L-type Ca(2+) currents in dmNTS neurons of mice lacking Nox2. The PKC inhibitor GF109203X or depletion of intracellular Ca(2+) attenuated Ang II-elicited ROS production. We conclude that the powerful effects of Ang II on Ca(2+) currents in dmNTS neurons are mediated by PKC activation leading to ROS production via Nox2. Thus, a Nox2-containing NADPH oxidase is the critical link between Ang II and the enhancement of Ca(2+) currents that underlie the actions of Ang II on central autonomic regulation.

Small-angle X-ray scattering reveals an extended organization for the autoinhibitory resting state of the p47(phox) modular protein

In response to microbial infection, neutrophiles promote the assembly of the NADPH oxidase complex in order to produce superoxide anions. This reaction is activated by the association of cytosolic factors, p47(phox), p67(phox), p40(phox), and a small G protein Rac with the membranous heterodimeric flavocytochrome b(558), composed of gp91(phox) and p22(phox). In the activation process, p47(phox) plays a central role as the target of phosphorylations and as a scaffolding protein conducting the translocation and assembly of cytosolic factors onto the membranous components. The PX and tandem SH3s of p47(phox) have been highlighted as being key determinants for the interaction with membrane lipids and the p22(phox) component, respectively. In the resting state, the two corresponding interfaces are thought to be masked allowing its cytoplasmic localization. However, the resting state modular organization of p47(phox) and its autoinhibition mode are still not fully understood despite available structural information on separate modules. More precisely, it raises the question of the mutual arrangement of the PX domain and the tandem SH3 domains in the resting state. To address this question, we have engaged a study of the entire p47(phox) molecule in solution using small-angle X-ray scattering. Despite internal autoinhibitory interactions, p47(phox) adopts an extended conformation. First insights about the domain arrangement in whole p47(phox) can be derived. Our data allow to discard the usual representation of a globular and compact autoinhibited resting state.

A specific p47phox -serine phosphorylated by convergent MAPKs mediates neutrophil NADPH oxidase priming at inflammatory sites

Neutrophil NADPH oxidase plays a key role in host defense and in inflammation by releasing large amounts of superoxide and other ROSs. Proinflammatory cytokines such as GM-CSF and TNF-alpha prime ROS production by neutrophils through unknown mechanisms. Here we used peptide sequencing by tandem mass spectrometry to show that GM-CSF and TNF-alpha induce phosphorylation of Ser345 on p47phox, a cytosolic component of NADPH oxidase, in human neutrophils. As Ser345 is located in the MAPK consensus sequence, we tested the effects of MAPK inhibitors. Inhibitors of the ERK1/2 pathway abrogated GM-CSF-induced phosphorylation of Ser345, while p38 MAPK inhibitor abrogated TNF-alpha-induced phosphorylation of Ser345. Transfection of HL-60 cells with a mutated p47phox (S345A) inhibited GM-CSF- and TNF-alpha-induced priming of ROS production. This event was also inhibited in neutrophils by a cell-permeable peptide containing a TAT-p47phox-Ser345 sequence. Furthermore, ROS generation, p47phox-Ser345 phosphorylation, and ERK1/2 and p38 MAPK phosphorylation were increased in synovial neutrophils from rheumatoid arthritis (RA) patients, and TAT-Ser345 peptide inhibited ROS production by these primed neutrophils. This study therefore identifies convergent MAPK pathways on Ser345 that are involved in GM-CSF- and TNF-alpha-induced priming of neutrophils and are activated in RA. Inhibition of the point of convergence of these pathways might serve as a novel antiinflammatory strategy.

A comprehensive map of the toll-like receptor signaling network

Recognition of pathogen-associated molecular signatures is critically important in proper activation of the immune system. The toll-like receptor (TLR) signaling network is responsible for innate immune response. In mammalians, there are 11 TLRs that recognize a variety of ligands from pathogens to trigger immunological responses. In this paper, we present a comprehensive map of TLRs and interleukin 1 receptor signaling networks based on papers published so far. The map illustrates the possible existence of a main network subsystem that has a bow-tie structure in which myeloid differentiation primary response gene 88 (MyD88) is a nonredundant core element, two collateral subsystems with small GTPase and phosphatidylinositol signaling, and MyD88-independent pathway. There is extensive crosstalk between the main bow-tie network and subsystems, as well as feedback and feedforward controls. One obvious feature of this network is the fragility against removal of the nonredundant core element, which is MyD88, and involvement of collateral subsystems for generating different reactions and gene expressions for different stimuli.

Regulation of NADPH oxidases: the role of Rac proteins

The role for reactive oxygen species (ROS) in cellular (patho)physiology, in particular in signal transduction, is increasingly recognized. The family of NADPH oxidases (NOXes) plays an important role in the production of ROS in response to receptor agonists such as growth factors or inflammatory cytokines that signal through the Rho-like small GTPases Rac1 or Rac2. The phagocyte oxidase (gp91phox/NOX2) is the best characterized family member, and its mode of activation is relatively well understood. Recent work has uncovered novel and increasingly complex modes of control of the NOX2-related proteins. Some of these, including NOX2, have been implicated in various aspects of (cardio)vascular disease, including vascular smooth muscle and endothelial cell hypertrophy and proliferation, inflammation, and atherosclerosis. This review focuses on the role of the Rac1 and Rac2 GTPases in the activation of the various NOX family members.

Subcellular targeting of oxidants during endothelial cell migration

Endogenous oxidants participate in endothelial cell migration, suggesting that the enzymatic source of oxidants, like other proteins controlling cell migration, requires precise subcellular localization for spatial confinement of signaling effects. We found that the nicotinamide adenine dinucleotide phosphate reduced (NADPH) oxidase adaptor p47^phox and its binding partner TRAF4 were sequestered within nascent, focal complexlike structures in the lamellae of motile endothelial cells. TRAF4 directly associated with the focal contact scaffold Hic-5, and the knockdown of either protein, disruption of the complex, or oxidant scavenging blocked cell migration. An active mutant of TRAF4 activated the NADPH oxidase downstream of the Rho GTPases and p21-activated kinase 1 (PAK1) and oxidatively modified the focal contact phosphatase PTP-PEST. The oxidase also functioned upstream of Rac1 activation, suggesting its participation in a positive feedback loop. Active TRAF4 initiated robust membrane ruffling through Rac1, PAK1, and the oxidase, whereas the knockdown of PTP-PEST increased ruffling independent of oxidase activation. Our data suggest that TRAF4 specifies a molecular address within focal complexes that is targeted for oxidative modification during cell migration.

A region C-terminal to the proline-rich core of p47phox regulates activation of the phagocyte NADPH oxidase by interacting with the C-terminal SH3 domain of p67phox

Activation of the phagocyte NADPH oxidase requires the regulatory proteins p47(phox) and p67(phox), each harboring two SH3 domains. p67(phox) interacts with p47(phox) via simultaneous binding of the p67(phox) C-terminal SH3 domain to both the proline-rich region (PRR) of amino acid residues 360-369 and its C-terminally flanking region of p47(phox); the role of the interaction in oxidase regulation has not been fully understood. Here we show that the p47(phox)-p67(phox) interaction is disrupted not only by deletion of the PRR but also by substitution for basic residues in the extra-PRR (K383E/K385E). The substitution impaired oxidase activation partially in vitro and much more profoundly in vivo, indicating the significance of the p47(phox) extra-PRR. Replacement of Ser-379 in the extra-PRR, a residue known to undergo phosphorylation in stimulated cells, by aspartate attenuates the interaction and thus results in a defective superoxide production, suggesting that phosphorylation of Ser-379 is involved in oxidase regulation.

Alternative mRNA splice forms of NOXO1: differential tissue expression and regulation of Nox1 and Nox3

The activity of gp91phox, the catalytic subunit of the superoxide-generating respiratory burst oxidase, is stimulated by the regulatory subunits p47phox, p67phox and the small GTPase Rac. Novel homologs of p47phox and p67phox (NOXO1 and NOXA1, respectively) were recently identified and are implicated in the regulation of the gp91phox homologs Nox1 and Nox3. Herein, we report four splice forms of human NOXO1. NOXO1beta is the major mRNA splice form in human colon and fetal liver while NOXO1gamma was the majority species in testis. Neither the alpha nor delta forms were expressed in significant amounts in any tissue tested. Splice forms were generated by alternative splicing of the two ends of exon 3 of the NOXO1 gene, and resulted in differences in the PX domain. The PX domain is known to bind inositol lipids, but the expressed, purified PX domains from NOXO1beta and NOXO1gamma bound these lipids with the same specificity and affinity. NOXO1beta and NOXO1gamma both activated Nox1, but NOXO1gamma showed a poorer ability to activate Nox3 compared with NOXO1beta. These data suggest different tissue localizations and functions for NOXO1beta and NOXO1gamma in regulating Nox family members.

Interleukin 8 dimerization as a mechanism for regulation of neutrophil adherence-dependent oxidant production

Interleukin 8 (IL-8), a member of the CXC subfamily of chemoattractant cytokines, induces a range of functional responses in human neutrophils via its interactions with two high-affinity cell-surface receptors, CXCR1 and CXCR2. Like other CXC chemokines, IL-8 forms homodimers at physiologic concentrations. Monomers and dimers bind to CXC receptors with high affinity and induce various functions. Binding to glycosaminoglycans decreases the dimerization constant, enhancing surface-bound dimer formation. However, a specific role for IL-8 dimerization has not been identified. We explored the hypothesis that certain neutrophil responses to IL-8 were induced primarily by the IL-8 dimers. To this end, two dimerization-deficient IL-8 mutant proteins, M3 and M4, were used in various functional assays. In contrast to native IL-8, these proteins existed primarily as monomers at micromolar concentrations. The mutants retained high-affinity binding to both CXC receptors and potently induced neutrophil calcium flux, chemotaxis, and elastase release. In contrast to native IL-8, neither mutant inhibited tumor necrosis factor alpha-induced oxidant production. Additionally, M4 was less effective than native IL-8 at desensitizing neutrophil migration. These data suggest that although IL-8 dimers or monomers are sufficient for several neutrophil functions, dimers may participate in suppression of specific surface-dependent neutrophil responses.

Effects of p47 C Terminus Phosphorylations on Binding Interactions with p40 and p67

The neutrophil NADPH oxidase produces superoxide anions in response to infection. This reaction is activated by association of cytosolic factors, p47phox and p67phox, and a small G protein Rac with the membranous flavocytochrome b558. Another cytosolic factor, p40phox, is associated to the complex and is reported to play regulatory roles. Initiation of the NADPH oxidase activation cascade has been reported as consecutive to phosphorylation on serines 359/370 and 379 of the p47phox C terminus. These serines surround a polyproline motif that can interact with the Src homology 3 (SH3) module of p40phox (SH3p40) or the C-terminal SH3 of p67phox (C-SH3p67). The latter one presents a higher affinity in the resting state for p47phox. A change in SH3 binding preference following phosphorylation has been postulated earlier. Here we report the crystal structures of SH3p40 alone or in complex with a 12-residue proline-rich region of p47phox at 1.46 angstrom resolution. Using intrinsic tryptophan fluorescence measurements, we compared the affinity of the strict polyproline motif and the whole C terminus peptide with both SH3p40 and C-SH3p67. These data reveal that SH3p40 can interact with a consensus polyproline motif but also with a noncanonical motif of the p47phox C terminus. The electrostatic surfaces of both SH3 are very different, and therefore the binding preference for C-SH3p67 can be attributed to the polyproline motif recognition and particularly to the Arg-368p47 binding mode. The noncanonical motif contributes equally to interaction with both SH3. The influence of serine phosphorylation on residues 359/370 and 379 on the affinity for both SH3 domains has been checked. We conclude that contrarily to previous suggestions, phosphorylation of Ser-359/370 does not modify the SH3 binding affinity for both SH3, whereas phosphorylation of Ser-379 has a destabilizing effect on both interactions. Other mechanisms than a phosphorylation induced switch between the two SH3 must therefore take place for NADPH oxidase activation cascade to start.

Activation and assembly of the NADPH oxidase: a structural perspective

The NADPH oxidase of professional phagocytes is a crucial component of the innate immune response due to its fundamental role in the production of reactive oxygen species that act as powerful microbicidal agents. The activity of this multi-protein enzyme is dependent on the regulated assembly of the six enzyme subunits at the membrane where oxygen is reduced to superoxide anions. In the resting state, four of the enzyme subunits are maintained in the cytosol, either through auto-inhibitory interactions or through complex formation with accessory proteins that are not part of the active enzyme complex. Multiple inputs are required to disrupt these inhibitory interactions and allow translocation to the membrane and association with the integral membrane components. Protein interaction modules are key regulators of NADPH oxidase assembly, and the protein-protein interactions mediated via these domains have been the target of numerous studies. Many models have been put forward to describe the intricate network of reversible protein interactions that regulate the activity of this enzyme, but an all-encompassing model has so far been elusive. An important step towards an understanding of the molecular basis of NADPH oxidase assembly and activity has been the recent solution of the three-dimensional structures of some of the oxidase components. We will discuss these structures in the present review and attempt to reconcile some of the conflicting models on the basis of the structural information available.

p47(phox) PX domain of NADPH oxidase targets cell membrane via moesin-mediated association with the actin cytoskeleton

Activation of phagocytic NADPH oxidase requires association of its cytosolic subunits with the membrane-bound flavocytochrome. Extensive phosphorylation of the p47(phox) subunit of NADPH oxidase marks the initiation of this activation process. The p47(phox) subunit then translocates to the plasma membrane, bringing the p67(phox) subunit to cytochrome b558 to form the active NADPH oxidase complex. However, the detailed mechanism for targeting the p47(phox) subunit to the cell membrane during activation still remains unclear. Here, we show that the p47(phox) PX domain is responsible for translocating the p47(phox) subunit to the plasma membrane for subsequent activation of NADPH oxidase. We also demonstrate that translocation of the p47(phox) PX domain to the plasma membrane is not due to interactions with phospholipids but rather to association with the actin cytoskeleton. This association is mediated by direct interaction between the p47(phox) PX domain and moesin.

Stimulators of AMP-activated protein kinase inhibit the respiratory burst in human neutrophils

In the present study, we have examined the potential ability of 5'-AMP-activated protein kinase (AMPK) to modulate NADPH oxidase activity in human neutrophils. AMPK activated with either 5'-aminoimidazole-4-carboxamide ribonucleoside (AICAR) or with 5'-AMP significantly attenuated both phorbol 12-myristate 13-acetate (PMA) and formyl methionyl leucyl phenylalanine-stimulated superoxide anion O2- release by human neutrophils, consistently with a reduced translocation to the cell membrane and phosphorylation of a cytosolic component of NADPH oxidase, namely p47phox. AMPK was found to be present in human neutrophils and to become phosphorylated in response to either AICAR or other stimulators of its enzyme activity. Furthermore, AICAR also strongly reduced PMA-dependent H2O2 release, and induced the phosphorylation of c-jun N-terminal kinase 1 (p46), p38 mitogen-activated protein kinase and extracellular signal-regulated kinase. Present data demonstrate for the first time that the activation of AMPK, in states of low cellular energy charge (such as under high levels of 5'-AMP) or other signals, could be a factor contributing to reduce the host defense mechanisms.

The NADPH oxidase of professional phagocytes--prototype of the NOX electron transport chain systems

The NADPH oxidase is an electron transport chain in "professional" phagocytic cells that transfers electrons from NADPH in the cytoplasm, across the wall of the phagocytic vacuole, to form superoxide. The electron transporting flavocytochrome b is activated by the integrated function of four cytoplasmic proteins. The antimicrobial function of this system involves pumping K+ into the vacuole through BKCa channels, the effect of which is to elevate the vacuolar pH and activate neutral proteases. A number of homologous systems have been discovered in plants and lower animals as well as in man. Their function remains to be established.

Complement-independent Ab-induced peroxide lysis of platelets requires 12-lipoxygenase and a platelet NADPH oxidase pathway

Antiplatelet GPIIIa49-66 Ab of HIV-related thrombocytopenic patients induces thrombocytopenia and platelet fragmentation by the generation of peroxide and other reactive oxygen species (ROS). Here we report the presence of a functional platelet NADPH oxidase pathway that requires activation by the platelet 12-lipoxygenase (12-LO) pathway to fragment platelets. A new Ab-mediated mechanism is described in which the platelet 12-LO product, 12(S)-HETE activates the NADPH oxidase pathway to generate ROS.

NAD(P)H Oxidase-derived H2O2 Signals Chloride Channel Activation in Cell Volume Regulation and Cell Proliferation

Cellular swelling triggers the activation of Cl(-) channels (volume-sensitive outwardly rectifying (VSOR) Cl(-) channels) in many cell types. Ensuing regulatory volume decrease has been considered the primary function of these channels. However, Cl(-) channels, which share functional properties with volume-sensitive Cl(-) channels, have been shown to be involved in other physiological processes, including cell proliferation and apoptosis, raising the question of their physiological roles and the signal transduction pathways involved in their activation. Here we report that exogenously applied H(2)O(2) elicited VSOR Cl(-) channel activation. Furthermore, activation of these channels was found to be coupled to NAD(P)H oxidase activity. Also, epidermal growth factor, known to increase H(2)O(2) production, activated Cl(-) channels with properties identical to swelling-sensitive Cl(-) channels. It is concluded that NAD(P)H oxidase-derived H(2)O(2) is the common signal transducing molecule that mediates the activation of these ubiquitously expressed anion channels under a variety of physiological conditions.

Molecular basis of phosphorylation-induced activation of the NADPH oxidase

The multi-subunit NADPH oxidase complex plays a crucial role in host defense against microbial infection through the production of reactive oxygen species. Activation of the NADPH oxidase requires the targeting of a cytoplasmic p40-p47-p67(phox) complex to the membrane bound heterodimeric p22-gp91(phox) flavocytochrome. This interaction is prevented in the resting state due to an auto-inhibited conformation of p47(phox). The X-ray structure of the auto-inhibited form of p47(phox) reveals that tandem SH3 domains function together to maintain the cytoplasmic complex in an inactive form. Further structural and biochemical data show that phosphorylation of p47(phox) activates a molecular switch that relieves the inhibitory intramolecular interaction. This permits p47(phox) to interact with the cytoplasmic tail of p22(phox) and initiate formation of the active, membrane bound enzyme complex.

Modulation of p47PHOX activity by site-specific phosphorylation: Akt-dependent activation of the NADPH oxidase

The leukocyte NADPH oxidase catalyzes the reduction of oxygen to O(2)(-) at the expense of NADPH. Extensive phosphorylation of the oxidase subunit p47(PHOX) occurs during the activation of the enzyme in intact cells. p47(PHOX) carrying certain serine-to-alanine mutations fails to support NADPH oxidase activity in intact cells, suggesting that the phosphorylation of specific serines on p47(PHOX) is required for the activation of the oxidase. Earlier studies with both intact cells and a kinase-dependent, cell-free system have suggested that protein kinase C can phosphorylate those serines of p47(PHOX) whose phosphorylation is necessary for its activity. Work with inhibitors suggested that a phosphatidylinositol 3-kinase-dependent pathway also can activate the oxidase. Phosphorylation of p47(PHOX) by Akt (protein kinase B), whose activation depends on phosphatidylinositol 3-kinase, could be the final step in such a pathway. We now find that Akt activates the oxidase in vitro by phosphorylating serines S304 and S328 of p47(PHOX). These results suggest that Akt could participate in the activation of the leukocyte NADPH oxidase.

Induction of colonic epithelial cell apoptosis by p47-dependent oxidants

Exogenous oxidants appear capable of initiating both proliferative and death signals, but the role of endogenous oxidants in either tumorigenesis or tumor suppression is unclear. We found that expression of the NAD(P)H oxidase adapter p47(phox) was suppressed in human colon carcinoma specimens relative to adjacent normal colon. Overexpression of p47(phox) increased apoptosis in colon cancer cell lines independent of p53 and mismatch-repair competency. p47(phox) was found to interact with the c-Abl adapter Abl interactor-1 (ABI-1), and p47(phox) coprecipitated with both ABI-1 and c-Abl. Ectopic expression of p47(phox) in colon cancer cells increased oxidant production with phosphorylation and activation of nuclear c-Abl and consequent apoptosis. Colonic epithelial p47(phox) may be specifically targeted to a c-Abl-containing complex that serves a physiologic tumor suppressing function.

NADPH oxidase priming and p47phox phosphorylation in neutrophils from synovial fluid of patients with rheumatoid arthritis and spondylarthropathy

Superoxide anion (O2(o)-)production by neutrophil NADPH oxidase participates in arthritic joint lesion formation. Proinflammatory cytokines such as tumor necrosis factor alpha (TNFalpha), interleukin 8 (IL-8) and granulocyte/macrophage-colony stimulating factor (GM-CSF) have a priming effect on neutrophil NADPH oxidase activity. NADPH oxidase activation is dependent on phosphorylation of p47phox, a cytosolic component of the enzyme. We studied O2(o)-production and p47phox phosphorylation in synovial fluid (SF) from patients with rheumatoid arthritis (RA) and spondylarthropathy (SpA) according to TNFalpha, IL-8 and GM-CSF levels. O2(o)-production by neutrophils isolated from SF of all the arthritis patients (RA and SpA) was higher than that of circulating resting neutrophils and when stimulated with fMLP or PMA. In addition, p47phox was partially phosphorylated in SF neutrophils compared to circulating neutrophils. High levels of TNFalpha and IL-8 (but not GM-CSF) are detected in patient's SF (compared to circulating blood levels). TNFalpha levels were significantly higher in RA than in SpA SF. These results suggest that increased NADPH oxidase activity could be involved in arthritic joint inflammation through increased p47phox phosphorylation. This could be the result of the presence of high levels of priming agents such as TNFalpha and IL-8 but not GM-CSF.

Phosphorylation of p47phox sites by PKC alpha, beta II, delta, and zeta: effect on binding to p22phox and on NADPH oxidase activation

Production of superoxide anions by the multicomponent enzyme of human neutrophil NADPH oxidase is accompanied by extensive phosphorylation of p47(phox), one of its cytosolic components. p47(phox) is an excellent substrate for protein kinase C (PKC), but the respective contribution of each PKC isoform to this process is not clearly defined. In this study, we found that PKC isoforms known to be present in human neutrophils (PKC alpha, beta, delta, and zeta) phosphorylate p47(phox) in a time- and concentration-dependent manner, with apparent K(m) values of 10.33, 3.37, 2.37, and 2.13 microM for PKC alpha, beta II, delta, and zeta, respectively. Phosphopeptide mapping of p47(phox) showed that, as opposed to PKC zeta, PKC alpha, beta II, and delta are able to phosphorylate all the major PKC sites. The use of p47(phox) mutants identified serines 303, 304, 315, 320, 328, 359, 370, and 379 as targets of PKC alpha, beta II, and delta. Comparison of the intensity of phosphopeptides suggests that Ser 328 is the most phosphorylated serine. The ability of each PKC isoform to induce p47(phox) to associate with p22(phox) was tested by using an overlay technique; the results showed that all the PKC isoforms that were studied induce p47(phox) binding to the cytosolic fragment of p22(phox). In addition, PKC alpha, beta II, delta, and zeta were able to induce production of superoxide anions in a cell-free system using recombinant cytosolic proteins. Surprisingly, PKC zeta, which phosphorylates a subset of selective p47(phox) sites, induced stronger activation of the NADPH oxidase. Taken together, these results suggest that PKC alpha, beta II, delta, and zeta expressed in human neutrophils can individually phosphorylate p47(phox) and induce both its translocation and NADPH oxidase activation. In addition, phosphorylation of some serines could have an inhibitory effect on oxidase activation.

Creation of a genetic system for analysis of the phagocyte respiratory burst: high-level reconstitution of the NADPH oxidase in a nonhematopoietic system

The phagocyte nicotinamide adenine dinucleotide phosphate (reduced form) (NADPH) oxidase was functionally reconstituted in monkey kidney COS-7 cells by transfection of essential subunits, gp91(phox), p22(phox), p47(phox), and p67(phox). COS-7 cells express the essential small guanosine 5'-triphosphatase, Rac1. Transgenic COS-phox cells were capable of arachidonic acid-induced NADPH oxidase activity up to 80% of that of human neutrophils, and of phorbol myristate acetate (PMA)-induced activity up to 20% of that of neutrophils. Expression of all 4 phox components was required for enzyme activity, and enzyme activation was associated with membrane translocation of p47(phox), p67(phox), and Rac1. Expression of p47(phox) Ser303Ala/Ser304Ala or Ser379Ala phosphorylation-deficient mutants resulted in significantly impaired NAPDH oxidase activity, compared with expression of wild-type p47(phox) or the p47(phox) Ser303Glu/Ser304Glu phosphorylation mimic, suggesting that p47(phox) phosphorylation contributes to enzyme activity in the COS system, as is the case in neutrophils. Hence, COS-phox cells should be useful as a new whole-cell model that is both capable of high-level superoxide production and readily amenable to genetic manipulation for investigation of NADPH oxidase function. PMA-elicited superoxide production in COS-phox cells was regulated by activation of protein kinase C (PKC) and Rac. Although COS-7 cells differ from human neutrophils in PKC isoform expression, transient expression of major neutrophil isoforms in COS-phox cells did not increase PMA-induced superoxide production, suggesting that endogenous isoforms were not rate limiting. Val204 in p67(phox), previously shown to be required for NADPH oxidase activity under cell-free conditions, was found to be essential for superoxide production by intact COS-phox cells, on the basis of transfection studies using a p67(phox) (Val204Ala) mutant.

The activity of leukocyte NADPH oxidase: regulation by p47PHOX cysteine and serine residues

The leukocyte NADPH oxidase is regulated chiefly by phosphorylation of the serines of p47(PHOX), one of its cytosolic subunits. Its activity is also regulated, however, by the four cysteines of the same subunit, as indicated by the replacement of those cysteines by alanines.

The neutrophil NADPH oxidase

The NADPH oxidase of phagocytes catalyzes the conversion of oxygen to O2(-). This multicomponent enzyme complex contains five essential protein components, two in the membrane and three in the cytosol. Unassembled and inactive in resting phagocytes, the oxidase becomes active after translocation of cytosolic components to the membrane to assemble a functional oxidase. Multiple factors regulate its assembly and activity, thus serving to maintain this highly reactive system under spatial and temporal control until recruited for antimicrobial or proinflammatory events. The recent identification of homologs of one of the membrane components in nonphagocytic cells will expand understanding of the biological contexts in which this system may function.

TNFalpha activates c-Jun amino terminal kinase through p47(phox)

Reactive oxygen intermediates have been implicated in the transduction of TNFalpha signals, although the source of such oxidants has not been established. We found that activation of ECV-304 cells by TNFalpha was accompanied by a transient burst of oxidants and activation of JNK, both of which were suppressed by two distinct inhibitors of the phagocyte NADPH oxidase and the thiol antioxidant N-acetyl cysteine (NAC). We cloned partial and full-length cDNA sequences from ECV-304 cells and human umbilical vein endothelial cells (HUVEC), respectively, for p47(phox), demonstrating that these nonphagocytic cells express this adapter protein known to specifically initiate assembly of the NADPH oxidase in professional phagocytes. A mutant p47(phox), defective in the first Src homology 3 (SH3) domain (p47W(193)R), diminished JNK activation by TNFalpha. Surprisingly, p47(phox) resided entirely in the particulate, not cytosolic, fraction of cells. Immunostaining suggested partial colocalization with cytoskeletal elements, and cytoskeletal disrupters decreased both oxidant production and JNK activation by TNFalpha. A p47-GFP fusion protein localized to the cortical cytoskeleton in living cells; further, stimulation of cells with TNFalpha caused a marked concentration of p47-GFP in membrane ruffles, actin-rich structures associated with intense respiratory burst activity in stimulated neutrophils. We conclude that nonphagocytic cells express p47(phox), which appears to localize to the cytoskeleton and participate in TNFalpha signaling. We speculate that this physical targeting may prove important in conferring signal specificity and enhancing signaling efficiency of unstable oxidants.

Phosphorylation of the leucocyte NADPH oxidase subunit p47(phox) by casein kinase 2: conformation-dependent phosphorylation and modulation of oxidase activity

The leucocyte NADPH oxidase of neutrophils is a membrane-bound enzyme that catalyses the reduction of oxygen to O(-)(2) at the expense of NADPH. The enzyme is dormant in resting neutrophils but becomes active when the cells are exposed to the appropriate stimuli. During oxidase activation, the highly basic cytosolic oxidase component p47(phox) becomes phosphorylated on several serines and migrates to the plasma membrane. Protein kinase CK2 is an essential serine/threonine kinase present in all eukaryotic organisms. The leucocyte NADPH oxidase subunit p47(phox) has several putative CK2 phosphorylation sites. In the present study, we report that CK2 is able to catalyse the phosphorylation of p47(phox) in vitro. Phosphoamino acid analysis of phosphorylated p47(phox) by CK2 indicated that the phosphorylation occurs on serine residues. CNBr mapping and phosphorylation of peptides containing the putative site of CK2 indicated that the main phosphorylated residues are Ser-208 and Ser-283 in the Src homology 3 (SH3) domains, and Ser-348 in the C-terminal domain of p47(phox). Dependence of phosphorylation on the conformation of p47(phox) is supported by the finding that p47(phox) undergoes better phosphorylation by CK2 in the presence of arachidonic acid, a known activator of NADPH oxidase which induces conformational changes in p47(phox). In addition, 5,6-dichloro-1-beta-o-ribofuranosyl benzimidazole, a CK2 inhibitor, potentiates formyl-Met-Leu-Phe-induced NADPH oxidase activity in DMSO-differentiated HL-60 cells. Taken together, we propose that CK2 is the p47(phox) kinase, and that phosphorylation of p47(phox) by CK2 regulates the deactivation of NADPH oxidase.

Intracellular pool of IL-10 receptors in specific granules of human neutrophils: differential mobilization by proinflammatory mediators

IL-10 has a wide range of effects tending to control inflammatory responses. We used flow cytometry to study IL-10 binding at the polymorphonuclear neutrophil (PMN) surface and its modulation by various proinflammatory agents. Little IL-10 bound to the surface of resting PMN. However, binding was strongly increased after stimulation with LPS and proinflammatory cytokines such as TNF and GM-CSF. IL-1 and IL-8 did not significantly modify IL-10 binding. Cycloheximide had no effect on TNF-induced IL-10 binding, strongly suggesting the release of a pre-existing pool of IL-10R rather than de novo receptor synthesis by PMN. This was confirmed by the inhibitory effect of pentoxifylline, an inhibitor of degranulation. The existence of an intracellular pool of IL-10R was shown by flow cytometry, immunocytochemical staining, and Western blotting with several anti-human IL-10R Abs. In subcellular fractions of resting PMN, IL-10R was mainly located in the specific granule fraction, and was absent from azurophil granules and cytosol. We also tested the mobilization of specific granules by measuring the release of lactoferrin, their reference marker. The differential effects of the proinflammatory agents on IL-10 binding matched their effects on lactoferrin release and may therefore be related to differential mobilization of specific granules by these agents. Furthermore, the kinetics of TNF-induced up-regulation of IL-10 binding to PMN ran parallel to the kinetics of the inhibitory effect of IL-10 on the oxidative burst, suggesting a key role of IL-10R mobilization from specific granules to the membranes in optimal regulation of inflammatory responses.

The neutrophil: function and regulation in innate and humoral immunity

The neutrophil is a critical effector cell in humoral and innate immunity and plays vital roles in phagocytosis and bacterial killing. Discussed here are the neutrophil components necessary for these processes and the diseases in which these components are either lacking or dysfunctional, illustrating that normal neutrophil function is vital for health.

Roles for beta II-protein kinase C and RACK1 in positive and negative signaling for superoxide anion generation in differentiated HL60 cells

beta-Protein kinase (PKC) is essential for ligand-initiated assembly of the NADPH oxidase for generation of superoxide anion (O(2)). Neutrophils and neutrophilic HL60 cells contain both betaI and betaII-PKC, isotypes that are derived by alternate splicing. betaI-PKC-positive and betaI-PKC null HL60 cells generated equivalent amounts of O(2) in response to fMet-Leu-Phe and phorbol myristate acetate. However, antisense depletion of betaII-PKC from betaI-PKC null cells inhibited ligand-initiated O(2) generation. fMet-Leu-Phe triggered association of a cytosolic NADPH oxidase component, p47(phox), with betaII-PKC but not with RACK1, a binding protein for betaII-PKC. Thus, RACK1 was not a component of the signaling complex for NADPH oxidase assembly. Inhibition of beta-PKC/RACK1 association by an inhibitory peptide or by antisense depletion of RACK1 enhanced O(2) generation. Therefore, betaII-PKC but not betaI-PKC is essential for activation of O(2) generation and plays a positive role in signaling for NADPH oxidase activation in association with p47(phox). In contrast, RACK1 is involved in negative signaling for O(2) generation. RACK1 binds to betaII-PKC but not with the p47(phox).betaII-PKC complex. RACK1 may divert betaII-PKC to other signaling pathways requiring beta-PKC for signal transduction. Alternatively, RACK1 may sequester betaII-PKC to down-regulate O(2) generation.

Mutational analysis of patients with p47-phox-deficient chronic granulomatous disease: The significance of recombination events between the p47-phox gene (NCF1) and its highly homologous pseudogenes

OBJECTIVE

The aim of this study was to determine the molecular basis of p47-phox-deficient chronic granulomatous disease (CGD), the most common autosomal recessive form of the disease. CGD is an inherited condition characterized by defective oxygen radical production due to defects in the phagocyte nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Mutational analysis of p47-phox-deficient CGD patients previously demonstrated that the majority of patients have a GT dinucleotide (Delta GT) deletion at the start of exon 2, a signature sequence also observed in the highly homologous pseudogenes of NCF1.

MATERIALS AND METHODS

We performed genetic analysis of NCF1 and its pseudogenes using genomic DNA in 29 p47-phox-deficient CGD patients from 22 separate families. First-strand cDNA analysis was performed in 17 of the 29 patients.

RESULTS

We confirmed the significance of the Delta GT mutation; in 27 of 29 patients, only the Delta GT sequence was detectable. All but one of the 27 had at least one additional signature sequence, specific to the pseudogene, in either intron 1 and/or intron 2. We extended our analysis to look at signature sequence differences in exons 6 and 9 and detected both the wild-type and pseudogene sequences in all patients tested.

CONCLUSIONS

Although detection of only Delta GT sequence accounts for over 85% of affected patients, the molecular basis is most likely due to partial cross-over events between the wild-type and pseudogene(s) of p47-phox at different recombination sites. Our results suggest that complete gene conversion or deletion of the p47-phox gene (NCF1) occurs rarely, if it all.

Protein kinase C zeta phosphorylates a subset of selective sites of the NADPH oxidase component p47phox and participates in formyl peptide-mediated neutrophil respiratory burst

Generation of superoxide anion by the multiprotein complex NADPH phagocyte oxidase is accompanied by extensive phosphorylation of its 47-kDa protein component, p47(phox), a major cytosolic component of this oxidase. Protein kinase C zeta (PKC zeta), an atypical PKC isoform expressed abundantly in human polymorphonuclear leukocytes (PMN), translocates to the PMN plasma membrane upon stimulation by the chemoattractant fMLP. We investigated the role of PKC zeta in p47(phox) phosphorylation and in superoxide anion production by human PMN. In vitro incubation of recombinant p47(phox) with recombinant PKC zeta induced a time- and concentration-dependent phosphorylation of p47(phox) with an apparent K(m) value of 2 microM. Phosphopeptide mapping analysis of p47(phox) showed that PKC zeta phosphorylated fewer selective sites in comparison to "conventional" PKCs. Serine 303/304 and serine 315 were identified as targets of PKC zeta by site-directed mutagenesis. Stimulation of PMN by fMLP induced a rapid and sustained plasma membrane translocation of PKC zeta that correlated to that of p47(phox). A cell-permeant-specific peptide antagonist of PKC zeta inhibited both fMLP-induced phosphorylation of p47(phox) and its membrane translocation. The antagonist also inhibited the fMLP-induced production of oxidant (IC(50) of 10 microM), but not that induced by PMA. The inhibition of PKC zeta expression in HL-60 neutrophil-like cells using antisense oligonucleotides (5 and 10 microM) inhibited fMLP-promoted oxidant production (27 and 50%, respectively), but not that induced by PMA. In conclusion, p47(phox) is a substrate for PKC zeta and participates in the signaling cascade between fMLP receptors and NADPH oxidase activation.

The mitogen-activated protein kinase extracellular signal-regulated kinase 1/2 pathway is involved in formyl-methionyl-leucyl-phenylalanine-induced p47phox phosphorylation in human neutrophils

Phosphorylation of p47 phagocyte oxidase, (p47(phox)), one of the NADPH oxidase components, is essential for the activation of this enzyme and for superoxide production. p47(phox) is phosphorylated on multiple serine residues, but the kinases involved in this process in vivo remain to be characterized. We examined the role of extracellular signal-regulated kinase (ERK1/2) and p38 mitogen-activated protein kinase in p47(phox) phosphorylation. Inhibition of ERK1/2 activation by PD98059, a specific inhibitor of ERK kinase 1/2, inhibited the fMLP-induced phosphorylation of p47(phox). However, PD98059 weakly affected PMA-induced p47(phox) phosphorylation, even though ERK1/2 activation was abrogated. This effect was confirmed using U0126, a second ERK kinase inhibitor. Unlike PD98059 and U0126, the p38 mitogen-activated protein kinase inhibitor SB203580 did not inhibit the phosphorylation of p47(phox) induced either by fMLP or by PMA. Two-dimensional phosphopeptide mapping analysis showed that, in fMLP-induced p47(phox) phosphorylation, PD98059 affected the phosphorylation of all the major phosphopeptides, suggesting that ERK1/2 may regulate p47(phox) phosphorylation either directly or indirectly via other kinases. In PMA-induced p47(phox) phosphorylation, GF109203X, a protein kinase C inhibitor, strongly inhibits p47(phox) phosphorylation. However, in fMLP-induced p47(phox) phosphorylation, PD98059 and GF109203X partially inhibited the phosphorylation of p47(phox) when tested alone, and exerted additive inhibitory effects on p47(phox) phosphorylation when tested together. These results show for the first time that the ERK1/2 pathway participates in the phosphorylation of p47(phox). Furthermore, they strongly suggest that p47(phox) is targeted by several kinase cascades in intact neutrophils activated by fMLP and is therefore a converging point for ERK1/2 and protein kinase C.

C-terminal region of the cytosolic subunit p47(phox) is a primary target of conformational change during the activation of leukocyte NADPH oxidase

The leukocyte NADPH oxidase of neutrophils is a membrane-bound enzyme that catalyzes the production of O(2(-)) from oxygen using NADPH as the electron donor. During activation, the cytosolic oxidase components p47(phox) and p67(phox), each containing two Src homology 3 (SH3) domains, migrate to the plasma membrane, where they associate with cytochrome b(558), a membrane-integrated flavohemoprotein, to assemble the active oxidase. Oxidase activation can be mimicked in a cell-free system using an anionic amphiphile, such as sodium dodecyl sulfate or arachidonic acid and the phosphorylation of p47(phox )with protein kinase C. Activators of the oxidase in vitro cause exposure of p47(phox)-SH3, which has probably been masked by the C-terminal region of this protein in a resting state. We show here that the total protein steady-state intrinsic fluorescence exhibited by the tryptophan residues of p47(phox) substantially decreased when N-terminal truncated p47(phox)-SH3-C was treated with anionic amphiphiles or phosphorylated with protein kinase C. This finding was similar to the results obtained with full-length p47(phox). However, the fluorescence of C-terminal truncated p47(phox)-N-SH3 and both C-terminal and N-terminal truncated p47(phox)-SH3 were not altered by the activators. These results indicate that the C-terminal region of p47(phox) is a primary target of the conformational change during the activation of NADPH oxidase.

Arachidonic acid and phosphorylation synergistically induce a conformational change of p47phox to activate the phagocyte NADPH oxidase

The superoxide-producing phagocyte NADPH oxidase can be activated by arachidonic acid (AA) or by phosphorylation of p47(phox) under cell-free conditions. The molecular mechanism underlying the activation, however, has remained largely unknown. Here we demonstrate that AA, at high concentrations (50-100 micrometer), induces direct interaction between the oxidase factors p47(phox) and p22(phox) in parallel with superoxide production. The interaction, being required for the oxidase activation, is mediated via the Src homology 3 (SH3) domains of p47(phox) (p47-(SH3)(2)), which are intramolecularly masked in a resting state. We also show that AA disrupts complexation of p47-(SH3)(2) with its intramolecular target fragment (amino acids 286-340) without affecting association of p47-(SH3)(2) with p22(phox), indicating that the disruption plays a crucial role in the induced interaction with p22(phox). Phosphorylation of p47(phox) by protein kinase C partially replaces the effects of AA; treatment of the SH3 target fragment with PKC in vitro results in a completely impaired interaction with p47-(SH3)(2), and the same treatment of the full-length p47(phox) leads to both interaction with p22(phox) and oxidase activation without AA, but to a lesser extent. Furthermore, phosphorylated p47(phox) effectively binds to p22(phox) and activates the oxidase in the presence of AA at low concentrations (1-5 micrometer), where an unphosphorylated protein only slightly supports superoxide production. Thus AA, at high concentrations, fully induces the interaction of p47(phox) with p22(phox) by itself, whereas, at low concentrations, AA synergizes with phosphorylation of p47(phox) to facilitate the interaction, thereby activating the NADPH oxidase.

Genetic, biochemical, and clinical features of chronic granulomatous disease

The reduced nicotinamide dinucleotide phosphate (NADPH) oxidase complex allows phagocytes to rapidly convert O2 to superoxide anion which then generates other antimicrobial reactive oxygen intermediates, such as H2O2, hydroxyl anion, and peroxynitrite anion. Chronic granulomatous disease (CGD) results from a defect in any of the 4 subunits of the NADPH oxidase and is characterized by recurrent life-threatening bacterial and fungal infections and abnormal tissue granuloma formation. Activation of the NADPH oxidase requires translocation of the cytosolic subunits p47phox (phagocyte oxidase), p67phox, and the low molecular weight GT-Pase Rac, to the membrane-bound flavocytochrome, a heterodimer composed of the heavy chain gp91phox and the light chain p22phox. This complex transfers electrons from NADPH on the cytoplasmic side to O2 on the vacuolar or extracellular side, thereby generating superoxide anion. Activation of the NADPH oxidase requires complex rearrangements between the protein subunits, which are in part mediated by noncovalent binding between src-homology 3 domains (SH3 domains) and proline-rich motifs. Outpatient management of CGD patients relies on the use of prophylactic antibiotics and interferon-gamma. When infection is suspected, aggressive effort to obtain culture material is required. Treatment of infections involves prolonged use of systemic antibiotics, surgical debridement when feasible, and, in severe infections, use of granulocyte transfusions. Mouse knockout models of CGD have been created in which to examine aspects of pathophysiology and therapy. Gene therapy and bone marrow transplantation trials in CGD patients are ongoing and show great promise.

Genomic structure of the human p47-phox (NCF1) gene

The cytosolic factor p47-phox, encoded by the NCF1 gene, is an essential component of the phagocyte NADPH-oxidase system. Upon activation of this multicomponent system, p47-phox translocates to the membrane and participates in the electron transfer from NADPH to molecular oxygen. A deficiency or absence of p47-phox is the most common autosomal form of chronic granulomatous disease (CGD). We have cloned and characterized the NCF1 gene from four bacteriophage clones, a P1 clone and genomic DNA from normal individuals. The gene is 15,236 base pairs long and includes 11 exons. It is 98.6% homologous in sequence to at least one pseudogene that maps to the same region of chromosome 7q11.23. Slightly more than half (50.37%) of the wild-type NCF1 gene consists of repetitive elements. In particular, the density of Alu sequences is high (1.4 Alu/kb); there are 21 Alu repeats interspersed through 10 introns. These findings are consistent with the observation that recombination events between the wild-type gene and its highly homologous pseudogenes account for the majority of potentially lethal mutations in p47-phox-deficient chronic granulomatous disease. Analysis of 1.96 kb of sequence 5' of the start of translation revealed a high homology (99.6%) between wild-type and pseudogene clones. Characterization of NCF1 establishes a foundation for detailed molecular analysis of p47-phox-deficient CGD patients as well as for the study of the regulation of the NCF1 gene and pseudogenes, both of which are present as full-length transcripts in normal individuals.