Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:1.6.3.1 (NADPH oxidase)
11,281 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The formation of oxygen radicals by phagocytic cells occurs through the activation of a multiple-component NADPH oxidase system. An unidentified low molecular weight GTP-binding protein has been proposed to modulate the activity of the NADPH oxidase. The low molecular weight GTP-binding proteins undergo posttranslational processing, including an initial covalent incorporation of an isoprenyl group. To test whether such an isoprenylation reaction might be required for the activity of the oxidase, we utilized compactin and lovastatin as inhibitors of the isoprenylation pathway. Treatment of DMSO-differentiated HL-60 cells with compactin produced a concentration-dependent inhibition of O2- formation in response to FMLP or phorbol myristate acetate. Cell viability was not affected nor was normal differentiation of the HL-60 cells into a neutrophil-like cell. The inhibitory effect of compactin was specifically prevented by addition of exogenous mevalonic acid to the HL-60 cells, indicating that the inhibitory effects of the drug were due to blockade of the pathway leading to isoprenoid synthesis. Addition of cholesterol, ubiquinone, or dolichol, which are also downstream products of the isoprenoid pathway, did not override the inhibitory effects of the drug. Subcellular fractions were prepared from compactin-treated cells, and the location of the compactin-sensitive factor was determined by complementation analysis in a cell-free NADPH oxidase system. The inhibited factor was localized to the HL-60 cytosol. These data suggest that an isoprenoid pathway intermediate is necessary for activation of the phagocyte NADPH oxidase. This is likely to represent the requirement for an isoprenoid moiety in the posttranslational modification of a low molecular weight GTP-binding protein. Our studies provide support for the involvement of such a low molecular weight GTP-binding protein in NADPH oxidase activation.
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PMID:Isoprenoid metabolism is required for stimulation of the respiratory burst oxidase of HL-60 cells. 131 Jun 93

Human neutrophils and other phagocytes generate superoxide anion (O2-) as a means of destroying ingested microorganisms. O2- is produced by an NADPH-consuming oxidase composed of membrane and cytosolic components. Activation of the NADPH oxidase is absolutely dependent upon GTP, indicating the requirement for a GTP-binding protein in this process. We have utilized a five-step chromatographic procedure to isolate a GTP-binding protein from human neutrophil cytosol which can stimulate NADPH oxidase activity in a cell-free assay. Oxidase enhancing activity was shown to coisolate with this GTP-binding component, which was purified to apparent homogeneity. The GTP-binding protein was identified as Rac 2 by immunological reactivity and amino acid sequencing. Thus, Rac 2 appears to be a third cytosolic component required for human neutrophil NADPH oxidase activation. Recombinant Rac 2 was shown to bind guanine nucleotides in a Mg(2+)-dependent fashion. GDP dissociation rates were determined and shown to be regulated by the free Mg2+ concentration. Rac 2 was found to possess the highest rate of intrinsic GTP hydrolysis of any of the characterized members of the Ras superfamily. The biochemical properties of Rac 2 indicate it is likely to be subject to regulatory cofactors in vivo.
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PMID:Purification and characterization of Rac 2. A cytosolic GTP-binding protein that regulates human neutrophil NADPH oxidase. 133 Oct 90

Activation of neutrophils was recently reported to be accompanied by large changes in their Cl- content [J. B. Myers, H. F. Cantiello, J. H. Schwartz, and A. I. Tauber. Am. J. Physiol. 259 (Cell Physiol. 28): C531-C540, 1990]. The significance of these ionic changes to the immune response has not been studied. To evaluate the role of intracellular [Cl-], the anionic composition of the cytosol was varied in human neutrophils permeabilized by electroporation or by treatment with streptolysin O. In Cl(-)-rich media, permeabilized but otherwise untreated cells remained quiescent, resembling unstimulated intact cells. In contrast, suspension of permeabilized cells in Cl(-)-depleted media elicited protein phosphorylation, actin polymerization, secretion of lysozyme, and a respiratory burst. The latter was demonstrated by several criteria to be mediated by the NADPH oxidase. The responses observed in Cl(-)-depleted media were insensitive to pretreatment of the cells with pertussis toxin but were inhibited by addition of GDP or by omission of ATP. The data suggest that an early event in signal transduction, common to several effectors, is sensitive to the ionic composition of the cytosol. This component, possibly a GTP-binding protein, may be affected by the anion concentration changes reported to occur during physiological stimulation of neutrophils.
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PMID:Activation of permeabilized neutrophils: role of anions. 163 84

A major action of the microbicidal system of human neutrophils is the formation of superoxide anion (O2-) by a multicomponent oxidase that transfers electrons from the reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) to molecular oxygen. The mechanism of assembly and activation of the oxidase from its cytosolic and membrane-bound components is unknown, but may require the activity of a guanosine 5'-triphosphate (GTP)-binding component. A cytosolic GTP-binding protein (Gox) that regulates the NADPH oxidase of neutrophils was identified. Gox was purified and shown to augment the rate of O2- production in a cell-free oxidase activation system. Sequence analysis of peptide fragments from Gox identified it as Rac 2, a member of the Ras superfamily of GTP-binding proteins. Antibody to a peptide derived from the COOH-terminus of Rac 2 inhibited O2- generation in a concentration-dependent manner. These results suggest that Rac 2 is a regulatory component of the human neutrophil NADPH oxidase, and provide new insights into the mechanism by which this oxygen radical-generating system is regulated.
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PMID:Regulation of phagocyte oxygen radical production by the GTP-binding protein Rac 2. 166 Jan 88

Activation of the membrane-associated NADPH oxidase in intact human neutrophils requires a receptor-associated heterotrimeric GTP-binding protein that is sensitive to pertussis toxin. Activation of this NADPH oxidase by arachidonate in a cell-free system requires an additional downstream pertussis toxin-insensitive G protein (Gabig, T. G., English, D., Akard, L. P., and Schell, M. J. (1987) (J. Biol. Chem. 262, 1685-1690) that is located in the cytosolic fraction of unstimulated cells (Gabig, T. G., Eklund, E. A., Potter, G. B., and Dykes, J. R. (1990) J. Immunol. 145, 945-951). In the present study, immunodepletion of G proteins from the cytosolic fraction of unstimulated neutrophils resulted in a loss of the ability to activate NADPH oxidase in the membrane fraction. The activity in immunodepleted cytosol was fully reconstituted by a partially purified fraction from neutrophil cytosol that contained a 21-kDa GTP-binding protein. Purified human recombinant Krev-1 p21 also completely reconstituted immunodepleted cytosol whereas recombinant human H-ras p21 or yeast RAS GTP-binding proteins had no reconstitutive activity. Rabbit antisera raised against a synthetic peptide corresponding to the effector region of Krev-1 (amino acids 31-43) completely inhibited cell-free NADPH oxidase activation, and this inhibition was blocked by the synthetic 31-43 peptide. An inhibitory monoclonal antibody specific for ras p21 amino acids 60-77 (Y13-259) had no effect on cell-free NADPH oxidase activation. Activation of the NADPH oxidase in intact neutrophils by stimulation with phorbol myristate acetate caused a marked increase in the amount of membrane-associated antigen recognized by 151 antiserum on Western blot. Thus a G protein in the cytosol of unstimulated neutrophils antigenically and functionally related to Krev-1 may be the downstream effector G protein for NADPH oxidase activation. This system represents a unique model to study molecular interactions of a ras-like G protein.
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PMID:Resolution of a low molecular weight G protein in neutrophil cytosol required for NADPH oxidase activation and reconstitution by recombinant Krev-1 protein. 190 90

Upon engagement of chemoattractant receptors, neutrophils generate inositol trisphosphate and diacylglycerol (DG) by means of a phosphatidylinositol-specific phospholipase C (PI-PLC) which is regulated by a GTP-binding protein(s). We have previously reported (Reibman, J., H. M. Korchak, L. B. Vosshall, K. A. Haines, A. M. Rich, and G. Weissmann. 1988. J. Biol. Chem. 263:6322-6328) a biphasic rise in DG after exposure of neutrophils to the chemoattractant FMLP: a rapid (less than or equal to 15 s) phase ("triggering") and a slow (greater than or equal to 30 s) phase ("activation"). These derive from distinct intracellular lipid pools. To study the source of rapid and slow DG, we have used a unique probe, protein I, a porin that is the major outer membrane protein of Neisseria gonorrhoeae. Treatment of neutrophils with protein I inhibits exocytosis and homotypic cell adhesion provoked by FMLP without inhibiting assembly of the NADPH oxidase responsible for O2-. generation. DG turnover in PMN labeled with [3H]arachidonate and [14C]glycerol was profoundly altered by protein I. Whereas the rapid peak of DG was only modestly diminished (FMLP vs. FMLP plus protein I = DG labeled with [3H]arachidonic acid (3H-a.a.-DG): 142 +/- 14% SEM vs. 125 +/- 22%; DG labeled with the glycerol backbone with [14C]glycerol (D-14C-G): 125 +/- 10% SEM vs. 107 +/- 8.5% SEM), the slow rise in both 3H-a.a.-DG and D-14C-G was essentially abolished. Moreover, treatment of neutrophils with 4-4'-diisothiocyanatostilbene-2,2'-disulfonic acid (DIDS), which, like protein I, inhibits exocytosis without affecting O2-. generation also inhibited slow DG. However, protein phosphorylation and dephosphorylation (47phox, 66phox) were unaffected in the absence of slow DG. To determine the source of the slow DG, we have analyzed radiolabeled phospholipid (PL) turnover after FMLP +/- protein I (P.I.). Treatment of PMN with FMLP (0.1 microM) resulted in breakdown of phosphatidylcholine (PC), beginning at 30 s, and reaching a nadir at 60 s (3H-PC = 59 +/- 10.2% SEM of resting, 14C-PC = 57 +/- 6.4%). Protein I (0.25 microM) significantly inhibited PC turnover after FMLP ([3H]PC = 95 +/- 5.6% and [14C]PC = 86 +/- 8.4% of resting at 60 s), but failed to alter the metabolism of 3H- or 14C-phosphatidylinositol after FMLP (91 +/- 19.6 and 88 +/- 16.5% vs. 92 +/- 9.2 and 91 +/- 16% at 60 s).(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Effects of protein I of Neisseria gonorrhoeae on neutrophil activation: generation of diacylglycerol from phosphatidylcholine via a specific phospholipase C is associated with exocytosis. 190 86

The dormant O2(-)-generating oxidase in plasma membranes from unstimulated neutrophils becomes activated in the presence of arachidonate and a multicomponent cytosolic fraction. This process is stimulated by nonhydrolyzable GTP analogues and may involve a pertussis toxin insensitive GTP-binding protein. Our studies were designed to characterize the putative GTP-binding protein, localizing it to either membrane or cytosolic fraction in this system. Exposure of the isolated membrane fraction to guanosine-5'-(3-O-thio)triphosphate (GTP gamma S), with or without arachidonate, had no effect on subsequent NADPH oxidase activation by the cytosolic fraction. Preexposure of the cytosolic fraction to GTP gamma S alone did not enhance activation of the membrane oxidase. However, preexposure of the cytosol to GTP gamma S then arachidonate caused a four-fold enhancement of its ability to activate the membrane oxidase. This enhancement was evident after removal of unbound GTP gamma S and arachidonate, and was not augmented by additional GTP gamma S during membrane activation. A reconstitution assay was developed for cytosolic component(s) responsible for the GTP gamma S effect. Cytosol preincubated with GTP gamma 35S then arachidonate was fractionated by anion exchange chromatography. A single peak of protein-bound GTP gamma 35S was recovered that had reconstitutive activity. Cytosol preincubated with GTP gamma 35S alone was similarly fractionated and the same peak of protein-bound GTP gamma 35S was observed. However, this peak had no reconstitutive activity. We conclude that the GTP-binding protein regulating this cellfree system is located in the cytosolic fraction. The GTP gamma S-liganded form of this protein may be activated or stabilized by arachidonate.
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PMID:A neutrophil GTP-binding protein that regulates cell free NADPH oxidase activation is located in the cytosolic fraction. 211 50

In phagocytes, activation of the respiratory burst by chemoattractants requires ATP and involves a pertussis toxin-sensitive G protein. ATP is also required for the response elicited in permeabilized neutrophils by nonhydrolyzable GTP analogs, indicating that at least one of the ATP-dependent steps lies downstream of the receptor-coupled G protein(s). A respiratory burst can also be produced in a reconstituted cell-free system by addition of arachidonic acid. Most investigators find this response to be independent of ATP, yet stimulated by GTP analogs, implying that the ATP-dependent steps observed in the unbroken cells must precede the guanine nucleotide-requiring event. To resolve this apparent discrepancy, we studied the ATP and guanine nucleotide dependence of the oxidative response elicited by arachidonic acid in electrically permeabilized human neutrophils. Two components of the response were apparent: one was ATP-dependent, the other ATP-independent. The ATP-dependent component was partially inhibited by staurosporine, suggesting involvement of protein kinase C. This kinase signals activation of the NADPH oxidase without intervening G proteins, since stimulation by phorbol ester was unaffected by guanosine 5'-(beta-thio)diphosphate (GDP beta S). Although nonhydrolyzable GTP analogs failed to stimulate the oxidase in the absence of ATP, the ATP-independent response stimulated by arachidonic acid was found to require GTP or one of its analogs and to be inhibited by GDP beta S. The relative potency of the guanine nucleotides to support the arachidonic acid response in the absence of ATP (5'-guanylyl imidodiphosphate (GMP-PNP) greater than or equal to guanosine 5'-(gamma-thio)triphosphate GTP gamma S) greater than or equal to (GTP) differed from their efficacy to stimulate the burst in the presence of ATP (GTP gamma S greater than GMP-PNP much greater than GTP). These observations suggest the involvement of two distinct GTP-binding proteins in oxidase activation: a receptor-coupled, heterotrimeric, pertussis toxin-sensitive G protein, and a second GTP-binding protein(s) located downstream of the ATP-requiring steps, which may lie in close proximity to the NADPH oxidase. This secondary GTP-binding protein could be part of the pathway activated by chemoattractants, but does not mediate stimulation via protein kinase C. Therefore multiple parallel routes may exist for activation of the NADPH oxidase.
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PMID:ATP and guanine nucleotide dependence of neutrophil activation. Evidence for the involvement of two distinct GTP-binding proteins. 216 41

The role of the activation of phosphoinositide turnover and of the increase in cytosolic free calcium, [Ca2+]i, in the phagocytosis and associated activation of the respiratory burst was investigated. We report the results obtained on the phagocytosis of yeast cells mediated by Con A in normal and in Ca2+-depleted human neutrophils. In normal neutrophils the phagocytosis was associated with a respiratory burst, a stimulation in the formation of [3H] inositol phosphates and [32P]phosphatidic acid, the release of [3H]arachidonic acid, and a rise in [Ca2+]i. Ca2+-depleted neutrophils are able to perform the phagocytosis of yeast cells mediated by Con A and to activate the respiratory burst without stimulation of [3H]inositol phosphates and [32P]phosphatidic acid formation, [3H]arachidonic acid release, and rise in [Ca2+]i. In both normal and Ca2+-depleted neutrophils the phagocytosis and the associated respiratory burst, 1) were inhibited by cytochalasin B; 2) were insensitive to H-7, an inhibitor of protein kinase C; and 3) did not involve GTP-binding protein sensitive to pertussis toxin. These findings indicate that the activation of phosphoinositide turnover, the liberation of arachidonic acid, the rise in [Ca2+]i, and the activity of protein kinase C are not necessarily required for ingestion of Con A-opsonized particles and for associated activation of the NADPH oxidase, the enzyme responsible for the respiratory burst. The molecular mechanisms of these phosphoinositide and Ca2+-independent responses are discussed.
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PMID:Studies on molecular regulation of phagocytosis in neutrophils. Con A-mediated ingestion and associated respiratory burst independent of phosphoinositide turnover, rise in [Ca2+]i, and arachidonic acid release. 253 59

Polymorphonuclear leukocytes (PMNL) release superoxide anions formed by a membrane-bound NADPH oxidase induced by stimulations. Properties of the inducers and their antagonists indicate that Ca2+, GTP-binding protein (G-protein), phospholipase C and Ca2+, phospholipid-dependent protein kinase (C-kinase) are mainly associated with the stimulation of receptors. Low concentrations of ATP induce the oxidase accompanied by the increase in the intracellular Ca2+ due to the flux from the medium and the storage site. ATP-gamma-S, UTP and ITP are effective but mononucleotides, dinucleotides, GTP and CTP are not. Leukotriene B4 (LTB4) which acts as a chemotactic agent and the inducer of the NADPH oxidase is catabolized. It is hydroxylated by a specific cytochrome P450 and then oxidized to a carboxy derivative by a cytosolic alcohol dehydrogenase and a microsomal aldehyde dehydrogenase in PMNL. Active NADPH oxidase was obtained by incubating membrane and cytosolic components of resting PMNL in the presence of sodium dodecyl sulfate (SDS). Two cytosolic components were obtained by an affinity chromatography on 2',5'-ADP Sepharose. One component is active in the presence of GTP or GTP-gamma-S and the other component in the presence of another cytosolic fraction.
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PMID:Metabolism of stimulated polymorphonuclear leukocytes. 254 77


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