Interactions between the components of the human NADPH oxidase: intrigues in the phox family

The human NADPH oxidase is a very intriguing enzyme; although its catalytic unit is retained within cytochrome b558, various additional proteins are required for activity of the NADPH oxidase. In the past few years substantial progress has been made to elucidate the protein-protein interactions and the activation events involved. The following facts have become evident: (1) activation of rac and subsequent interaction with p67-phox is crucial for the interaction of p67-phox with cytochrome b558, and probably with gp91-phox; (2) p47-phox interacts with p22-phox, and phosphorylation of 379Ser of p47-phox is obligatory for this event; (3) p47-phox and p67-phox regulate each other's translocation in a positive sense (see also reference 71). To put it differently: it is vital to gain insight in the intrigues within the phox family and associated characters to fully understand NADPH oxidase activation.

Genomic structure, chromosomal localization, start of transcription, and tissue expression of the human p40-phox, a new component of the nicotinamide adenine dinucleotide phosphate-oxidase complex

p40-phox is a newly isolated cytosolic component of the nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase that copurifies with p67-phox. Although its function is not well defined, preliminary evidence indicates that it is a component of the cytosolic complex. We report the characterization of the human p40-phox gene, which is single copy and spans approximately 18 kb with 10 exons. Based on fluorescent in situ hybridization (FISH) studies and analysis of somatic hybrid cell lines, the chromosomal location of p40-phox is human chromosome 22q13.1. The start of transcription has been mapped to bp -156. The expression of p40-phox message is restricted to hematopoietic cells. In addition to identifying the mRNA transcript on Northern blot analysis in cells known to express components of the NADPH-oxidase, polymorphonuclear leukocytes, monocytes, B lymphoblastoid cell lines, and eosinophils, p40-phox is also expressed in two other cell types of white cell lineage, mast cells, and basophils. In addition, the mRNA for p40-phox is expressed in megakaryocytic cells, but not in erythroid cells.

High-level reconstitution of respiratory burst activity in a human X-linked chronic granulomatous disease (X-CGD) cell line and correction of murine X-CGD bone marrow cells by retroviral-mediated gene transfer of human gp91phox

The X-linked form of chronic granulomatous disease (X-CGD) results from mutations in the gene encoding gp91phox, a 91-kD membrane glycoprotein that is the larger subunit of the respiratory burst oxidase cytochrome b. In this study, a new retroviral vector for expression of human gp91phox, MSCV-h91Neo, based on murine stem cell virus vectors, was evaluated using a human X-CGD myeloid cell line (X-CGD PLB-985 cells) and murine bone marrow cells. Expression of recombinant gp91phox in transduced X-CGD PLB-985 cells was substantially improved compared with levels achieved previously using a different retroviral construct, and respiratory burst oxidase activity was fully reconstituted in the majority of clones analyzed. Expression of gp91phox transcripts was also observed in primary and secondary murine colony-forming unit-spleen derived from transduced bone marrow cells. Furthermore, respiratory burst activity was restored to granulocyte-monocyte progeny of transduced X-CGD mice bone marrow cells cultured in vitro. This observation is the first reported use of gene transfer to correct the enzymatic defect in murine CGD phagocytes and is also consistent with the high conservation of the oxidase complex among different species. Taken together, these data suggest that the MSCV-h91Neo vector may be useful for gene replacement therapy in X-linked CGD, in which high-level reconstitution of phagocyte oxidase activity may be important for full correction of phagocyte microbicidal function.

Two-exon skipping due to a point mutation in p67-phox--deficient chronic granulomatous disease

The cytosolic 67-kD protein in phagocytes (p67-phox) and B lymphocytes is one of essential components of the superoxide-generating system in these cells, and its defect causes an autosomal recessive type of chronic granulomatous disease (CGD). We performed mutation analysis of p67-phox mRNA from a CGD patient who lacks the protein and found an in-frame deletion from nucleotide 694 to 879, which corresponds to the entire sequence of exons 8 and 9. This sequence encodes one of two Src homology 3 domains and a part of proline-rich domain in p67-phox and lack of these domains seem to have influenced stability of this protein. To know causative reason for the deletion, we analyzed genomic DNA for p67-phox using two sets of primers that covered exons 8 and 9 with adjacent introns. The DNA fragments from the patient were shown to be same in length as those from control. However, the single-strand conformation-polymorphism analysis of the fragments showed that a patient's specimen that included the splice junction of exon 9 exhibited different mobility from the control. By sequencing of the fragment, a homozygous G to A replacement at position +1 of intron 9 was found to be a sole mutation, which reduced the matching score of the splicing sequence to the consensus calculated according to the formula proposed by Shapiro and Senapathy (Nucleic Acids Res 15:7155, 1987). The reduced matching score at the splice doner site (5' splice site) of intron 9 and the original low matching score at the acceptor site (3' splice site) of intron 7 may explain the skipping of exon 8 and 9, and another predicted mechanism is discussed on the basis of Shapiro and Senapathy's hypothesis.

Interactions between the components of the human NADPH oxidase: a review about the intrigues in the phox family

When microorganisms invade the body, they encounter a large asssortment of defense mechanisms. Among these, phagocytes play an important role in the process of killing pathogens. This event is mediated by two important processes, viz. activation of the NADPH oxidase enzyme, which leads to the production of toxic oxygen metabolites, and fusion of intracellular granules with the phagosome (the vesicle that contains the ingested micro-organisms), which causes release of the toxic granule contents into this vesicle. The human NADPH oxidase is a very complex enzyme, in two ways: 1. it exists of at least 6 components: cytochrome b558 (a heterodimer comprised of gp91-phox and p22-phox), p47-phox, p67-phox, p40-phox, rac and Rap1A, and 2. there are multiple signal transduction pathways leading to activation of the NADPH oxidase. The most likely reason for this complexity is the toxicity of the oxygen radicals produced by the active NADPH oxidase; these compounds are not only harmful to the invading pathogens, but also to the surrounding tissues. This latter effect is enforced by the activation of metalloproteases released by neutrophils and by oxidation of protease inhibitors by oxygen metabolites. Therefore, an improper activation of the NADPH oxidase must be prevented at all costs and, when the infection has been cleared, a rapid deactivation mechanism is imperative. In this review, the interaction between the different components of the NADPH oxidase and the activation of these proteins will be discussed.

Functional reconstitution of oxidase activity in X-linked chronic granulomatous disease by retrovirus-mediated gene transfer

The feasibility of correction of the disease phenotype by gene gene transfer was investigated in cells of four patients with X-linked chronic granulomatous disease. These patients carry point mutations of the gp91-phox gene, encoding for the large subunit of the catalytic core of the phagocytic cell NADPH oxidase. A retroviral vector expressing the gp91-phox protein was constructed and used to transduce lymphoblastoid cell lines established from the patients. Several transduced lymphoblastoid cell clones were investigated for mRNA and protein expression, and for functional reconstitution of oxidase activity. Although extensive quantitative variability was detected among different clones, functional reconstitution of O2- production was obtained in most cases, with oxidase function within the same range as in B cell lines derived from normal individuals. The same vector was also used for transduction of hematopoietic precursors from bone marrow or peripheral blood either with or without enrichment for CD34+ cells. A comprehensive analysis was performed on differentiated myeloid colonies, to evaluate the efficiency of transduction, the levels of gp91-phox expression, and the extent of functional reconstitution of oxidase activity. A high efficiency of transduction was obtained in most experiments, with 60-100% of colonies containing proviral DNA. Among the transduced colonies, an extensive variability in the levels of expression of the transduced gene and of functional restoration of NADPH oxidase activity was observed. These results represent a step toward the development of a gene therapy protocol for these patients.

Cloning of murine gp91phox cDNA and functional expression in a human X-linked chronic granulomatous disease cell line

The phagocyte cytochrome b558, a heterodimer comprised of gp91phox and p22phox, is a flavocytochrome that mediates the transfer of electrons from NADPH to molecular oxygen in the respiratory burst oxidase. The human gene encoding the glycosylated gp91phox subunit is the site of mutations in X-linked chronic granulomatous disease (CGD). Reverse transcriptase-polymerase chain reaction was used to obtain a full-length clone for the murine gp91phox cDNA, which was 87% identical to the human gp91phox cDNA. The encoded murine protein had 39 amino acids out of 570 that differed from the human, many of which were conservative substitutions. Nonconservative replacements occurred in hydrophilic regions outside of domains previously implicated in binding to NADPH, flavin, and the cytosolic oxidase subunit p47phox. Some substitutions altered potential N-glycosylation sites, which is likely to explain why the glycosylated murine protein migrates with an apparent molecular mass of 58 kD instead of 91 kD as seen for the human protein. Expression of murine gp91phox in a human myeloid cell line with a null gp91phox allele using a mammalian expression plasmid or a retroviral vector rescued stable expression of the p22phox subunit and fully reconstituted respiratory burst activity. This suggests that the murine gp91phox subunit forms a functional cytochrome b558 heterodimer with human oxidase subunits, consistent with the high degree of identity between the mouse and human proteins in domains implicated in cytochrome function.

The NADPH oxidase and chronic granulomatous disease

Chronic granulomatous disease (CGD) is characterized by severe, protracted and often fatal infection, which results from a failure of the NADPH oxidase enzyme system in the patient's phagocytes to produce superoxide. The NADPH oxidase enzyme system is composed of a number of interacting components, the absence of any one of which causes failure of the system as a whole. Investigation of individuals with CGD has led to the identification of the different protein components and the genes coding for them. CGD is particularly well suited to treatment by gene therapy and is likely to be one of the earliest monogenic conditions to be successfully treated in this way.

Hypoxic induction of gene expression in chronic granulomatous disease-derived B-cell lines: oxygen sensing is independent of the cytochrome b558-containing nicotinamide adenine dinucleotide phosphate oxidase

Reduced oxygenation of a variety of cells results in transcriptional upregulation of several genes, including the hematopoietic hormone erythropoietin, the angiogenic vascular endothelial growth factor (VEGF), and glycolytic enzymes such as aldolase. Recently, the heme protein cytochrome b558 of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase complex has been proposed as a key component of the oxygen-sensing mechanism. Cytochrome b558 consists of the p22phox and gp91phox subunits and is essential for superoxide generation in phagocytes and B lymphocytes. Mutations in these subunits result in cytochrome b558-negative chronic granulomatous disease (cytb- CGD), an inherited disorder in humans characterized by reduced microbicidal activity due to deficient superoxide generation. To test whether NADPH oxidase is involved in oxygen sensing, we exposed wild-type B-cell lines as well as cytb- CGD-derived B cell lines, deficient in either p22phox or gp91phox, to hypoxia (1% oxygen) or CoCl2 (100 mumol/L) and compared the mRNA levels of VEGF and aldolase with the untreated controls. Northern blot analysis revealed unimpaired basal and inducible expression of VEGF and aldolase mRNA in all four cytb- CGD-derived B-cell lines compared with wild-type cells. Furthermore, reconstitution of cytochrome b558 expression in cytb- CGD-derived B cells by transfection with p22phox or gp91phox expression vectors did not modify VEGF and aldolase mRNA expression. Thus, cytochrome b558 of the NADPH oxidase complex appears not to be essential for hypoxia-activated gene expression and can be excluded as a candidate for the putative universal oxygen sensor.

A bicistronic retrovirus vector containing a picornavirus internal ribosome entry site allows for correction of X-linked CGD by selection for MDR1 expression

Chronic granulomatous disease (CGD) is an inherited hematologic disorder involving failure of phagocytic cell oxidase to produce superoxide (O2-.), resulting in recurrent infections. The success of retrovirus gene therapy for hematopoietic diseases will be limited both by the efficiency of ex vivo transduction of target cells and by the ability of corrected cells to replace uncorrected cells in vivo. Using MFG-based retrovirus vectors containing oxidase genes, we have previously demonstrated in vitro correction of CGD, but transduction rates were low. In the present study we explore a strategy for providing a selective growth advantage to transduced cells, while retaining the single promoter feature of MFG responsible for high virus titer and enhanced protein production. We constructed a bicistronic retrovirus producing a single mRNA encoding both the therapeutic gene for the X-linked form of CGD (X-CGD), gp91phox, and the selectable human multidrug resistance gene, MDR1 linked together by the encephalomyocarditis virus internal ribosome entry site (IRES). As a control we constructed a bicistronic vector with the polio virus IRES element and using the bacterial neomycin resistance gene (neor) as the selective element. In Epstein-Barr virus transformed B (EBV-B) cells from an X-CGD patient, a tissue culture model of CGD, we show correction of the CGD defect and complete normalization of the cell population using either of these vectors and appropriate selection (vincristine for MDR1 and G418 for neor). Using a chemiluminescence assay of O2-. production, populations of cells transduced with either vector demonstrated initial correction levels of from less than 0.1% up to 2.7% of normal EBV-B cell oxidase activity. With either construct, cell growth under appropriate selection enriched the population of transduced cells, resulting in correction of X-CGD EBV-B cells to a level of O2-. production equalling or exceeding that of normal EBV-B cells. These studies show that a therapeutic gene can be linked to a resistance gene by an IRES element, allowing for selective enrichment of cells expressing the therapeutic gene. Furthermore, the use of MDR1 as a selective element in our studies validates an important approach to gene therapy that could allow in vivo selection and is generalizable to a number of therapeutic settings.

Genotype-dependent variability in flow cytometric evaluation of reduced nicotinamide adenine dinucleotide phosphate oxidase function in patients with chronic granulomatous disease

We studied phagocyte reduced nicotinamide adenine dinucleotide phosphate function to evaluate production of reactive oxygen species in both X-linked and autosomal forms of chronic granulomatous disease. We found a consistent and significant difference between the activated granulocyte response of the X-linked (gp91-phagocyte oxidase) form of chronic granulomatous disease (n = 18) and that of the most common autosomal recessive (p47-phagocyte oxidase) form of the disease (n = 17). The data indicate that mutations in the p47-phagocyte oxidase component of the reduced nicotinamide adenine dinucleotide phosphate oxidase component do not completely prevent oxidation despite severe defects in superoxide generation.

Safety and effectiveness of long-term interferon gamma therapy in patients with chronic granulomatous disease

In chronic granulomatous disease (CGD), diminished or absent neutrophil NADPH oxidase function leads to recurrent pyogenic infections and granuloma formation. In a recent randomized, placebo-controlled trail, short-term prophylactic use of recombinant human interferon gamma (rIFN-gamma 1b) reduced the risk of serious infection in CGD patients by 67%, The current study evaluated the safety and effectiveness of long-term rIFN-gamma therapy in CGD patients. Patients were treated three times weekly with rIFN-gamma and evaluated semiannually. Serious infections (requiring hospitalization and parenteral antibiotic therapy), adverse clinical events, and measures of growth and development were noted. Thirty patients were evaluated for 12 months. The total average duration of rIFN-gamma therapy was 2.5 years. Three patients developed a total of four serious infections (0.13 infections per patient year). This rate compare favorably with rates of 1.10 and 0.38 infections per patient year found in the placebo and rIFN-gamma groups, respectively, during a previous study. Common adverse events were fever (23%), diarrhea (13%), and flu-like illness (13%). No serious adverse event was attributable to rIFN-gamma therapy and no obvious effects on growth and development were observed. rIFN-gamma is a safe and effective adjunctive therapy for reducing the frequency and severity of serious infections in CGD patients.

Cell-free activation of neutrophil NADPH oxidase by a phosphatidic acid-regulated protein kinase

The phosphorylation-dependent mechanisms regulating activation of the human neutrophil respiratory-burst enzyme, NADPH oxidase, have not been elucidated. We have shown that phosphatidic acid (PA) and diacylglycerol (DG), products of phospholipase activation, synergize to activate NADPH oxidase in a cell-free system. We now report that activation by PA plus DG involves protein kinase activity, unlike other cell-free system activators. NADPH oxidase activation by PA plus DG is reduced approximately 70% by several protein kinase inhibitors [1-(5-isoquinolinesulfonyl)piperazine, staurosporine, GF-109203X]. Similarly, depletion of ATP by dialysis reduces PA plus DG-mediated NADPH oxidase activation by approximately 70%. Addition of ATP, but not a nonhydrolyzable ATP analog, to the dialyzed system restores activation levels to normal. In contrast, these treatments have little effect on NADPH oxidase activation by arachidonic acid or SDS plus DG. PA plus DG induces the phosphorylation of a number of endogenous proteins. Phosphorylation is largely mediated by PA, not DG. A predominant substrate is p47-phox, a phosphoprotein component of NADPH oxidase. Phosphorylation of p47-phox precedes activation of NADPH oxidase and is markedly reduced by the protein kinase inhibitors. In contrast, arachidonic acid alone or SDS plus DG is a poor activator of protein phosphorylation in the cell-free system. Thus, PA induces activation of one or more protein kinases that regulate NADPH oxidase activation in a cell-free system. This cell-free system will be useful for identifying a functionally important PA-activated protein kinase(s) and for dissecting the phosphorylation-dependent mechanisms responsible for NADPH oxidase activation.

Functional reconstitution of the NADPH-oxidase by adeno-associated virus gene transfer

Chronic granulomatous disease (CGD) comprises a heterogeneous group of inherited conditions characterized biochemically by disordered function of a unique multicomponent enzyme system present in phagocytic cells, the NADPH-oxidase. Clinically, it is characterized by recurrent bacterial and fungal infections that are relatively resistant to treatment by conventional means. Curative bone marrow transplantation has been successfully achieved in a small number of cases, but the wider application of this procedure is limited by availability of suitable donor material. Somatic gene therapy would overcome this problem, and several groups have now shown correction of the biochemical defect in hematopoietic cells by retrovirus-mediated gene transfer. However, the failure of the current generation of retroviral vectors to efficiently transduce quiescent cells greatly restricts their potential for gene transfer to pluripotent hematopoietic stem cells. Given these limitations, we have constructed vectors based on adeno-associated virus and used these to transfer a functional copy of the p47phox gene to immortalized B cells derived from patients with p47phox-deficient autosomal recessive CGD. We show stable expression of protein and restoration of NADPH-oxidase function in these cells in the absence of selection. Adeno-associated virus vectors may overcome some of the limitations of retroviral gene delivery systems and may therefore be a useful vehicle for curative gene therapy of CGD and other primary immunodeficiencies.

Phagocytic NADPH oxidase and its role in chronic granulomatous disease

Chronic granulomatous disease is an inherited disease manifest as recurrent bacterial and fungal infections. Although extremely rare, in the absence of long-term treatment it can be lead to death at an early age. Even though the disease was first described almost 40 years ago it is only recently that the enzymatic defects which cause the disease have been well characterised, allowing an instructive classification of the disorder and paving the way for advances in gene therapy as a lasting cure.

A variant X-linked chronic granulomatous disease patient (X91+) with partially functional cytochrome b

Genetic analysis of a patient with the variant cytochrome b-245-positive form of chronic granulomatous disease revealed a missense mutation resulting in a Arg54-->Ser substitution in the gp91phox subunit of cytochrome b-245. As a consequence, although no O2- is made, NADPH oxidase-associated FAD accepts electrons from NADPH in the cell-free activation system and becomes reduced. The reduced flavin exhibits normal levels of iodonitrotetrazolium violet diaphorase activity, and the patient's neutrophils exhibit high levels of intracellular oxidant production and show a low level of NBT staining in the NBT slide test. Thus, this mutation appears to render the heme center of NADPH oxidase present but nonfunctional, while leaving the flavin center fully functional.

The respiratory burst oxidase

The respiratory burst oxidase catalyzes the production of O2- by activated phagocytes and B lymphocytes. Activation is accomplished by any number of signal transduction pathways, and involves protein kinase C, MAP kinase, or both, and perhaps lipid-mediated pathways. Failure of O2- production is characteristic of chronic granulomatous disease, an inherited disorder of phagocyte function. A number of new mutations responsible for chronic granulomatous disease have been reported. O2- production is also altered in other diseases, most notably certain hematologic malignancies.

Chronic granulomatous disease and glutathione peroxidase deficiency, revisited

We have restudied two kindreds that formed the basis of the original report of autosomal recessive chronic granulomatous disease (CGD) associated with leukocyte glutathione peroxidase deficiency. Case 1 from the original study and the surviving brother of the originally reported case 2 both have severe CGD, with no detectable respiratory burst activity in purified intact neutrophils. However, their leukocytes exhibit normal glutathione peroxidase enzyme activity and gene expression. Examination of phagocyte nicotinamide adenine dinucleotide phosphate (NADPH)-oxidase components known to be defective in CGD reveals no detectable cytochrome b558 nor any membrane activity in a cell-free NADPH oxidase assay system. Molecular analysis of the genes encoding cytochrome b558 subunits shows, in case 1, a C-->T substitution at nucleotide 688 of the gene encoding the gp91-phox subunit of cytochrome b558, resulting in a termination signal in place of Arginine-226. Levels of gp91-phox mRNA are markedly decreased despite normal levels of gene transcription, indicating a post-transcriptional effect of the nonsense mutation on mRNA processing or stability. The X-linked form of CGD developed in this cytogenetically normal female due to the uniform inactivation of the normal X chromosome in her granulocytes, indicated by the expression in her granulocyte mRNA of only one allele of a glucose-6-phosphate dehydrogenase polymorphisms for which she is heterozygous in genomic DNA. Case 2 (of the present study) has distinct mutations in each allele of the p22-phox gene.(ABSTRACT TRUNCATED AT 250 WORDS)

The superoxide-generating system of human neutrophils possesses a novel diaphorase activity. Evidence for distinct regulation of electron flow within NADPH oxidase by p67-phox and p47-phox

A dye reductase activity, independent of the production of superoxide, is induced in membranes prepared from stimulated human neutrophils or during activation of NADPH oxidase in a cell-free system. This diaphorase activity was greater under anaerobic as opposed to aerobic conditions. The activity has an absolute requirement for the membrane components of the oxidase, but does not appear to have an absolute dependence for the 47-kDa cytosolic factor p47-phox, suggesting the oxidase can be converted to a partial state of activation in the absence of this factor. The dye-reductase activity was inhibited at low concentration by the oxidase inhibitor, diphenylene iodonium. The electron acceptor, iodonitrotetrazolium violet (2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyltetrazolium chloride) is both a substrate and a mixed inhibitor of NADPH oxidation.

A point mutation in gp91-phox of cytochrome b558 of the human NADPH oxidase leading to defective translocation of the cytosolic proteins p47-phox and p67-phox

The superoxide-forming NADPH oxidase of human phagocytes is composed of membrane-bound and cytosolic proteins which, upon cell activation, assemble on the plasma membrane to form the active enzyme. Patients suffering from chronic granulomatous disease (CGD) are defective in one of the following components: p47-phox and p67-phox, residing in the cytosol of resting phagocytes, and gp91-phox and p22-phox, constituting the membrane-bound cytochrome b558. In an X-linked CGD patient we identified a novel missense mutation predicting an Asp-->Gly substitution at residue 500 of gp91-phox, associated with normal amounts of nonfunctional cytochrome b558 in the patient's neutrophils. In PMA-stimulated neutrophils and in a cell-free translocation assay with neutrophil membranes and cytosol, the association of the cytosolic proteins p47-phox and p67-phox with the membrane fraction of the patient was strongly disturbed. Furthermore, a synthetic peptide mimicking domain 491-504 of gp91-phox inhibited NADPH oxidase activity in the cell-free assay (IC50 about 10 microM), and the translocation of p47-phox and p67-phox in the cell-free translocation assay. We conclude that residue 500 of gp91-phox resides in a region critical for stable binding of p47-phox and p67-phox.

A novel cytosolic component, p40phox, of respiratory burst oxidase associates with p67phox and is absent in patients with chronic granulomatous disease who lack p67phox

Cytosolic components of human neutrophils, p47phox and p67phox, deficiencies of which lead to chronic granulomatous disease (CGD), potentiate respiratory burst oxidase translocating from cytosol to membrane upon cell stimulation. In this report we describe a novel cytosolic component, p40phox, which consistently behaves with p67phox through immunoprecipitation and column works, and is missing in patients with CGD who lack p67phox. Although actin has been reported to be involved in O2- generation, the p40phox profile did not correspond to that of actin. The tight association between p40phox and p67phox was not affected by treatment with a mixture of deoxycholate and Nonidet P-40, until subjected to SDS-PAGE. Addition of recombinant p67phox to cytosol did not produce any additional p40phox in the immunoprecipitate, unlike the additive increment in the band of p67phox. These results suggest that p40phox forms a complex with p67phox in a molar ratio of 1:1, without any free p40phox in the cytosol.