Significance of phosphorylation/dephosphorylation of 46K protein(s) in regulation of superoxide anion production in intact guinea pig polymorphonuclear leukocytes

Phosphorylation of myeloid-related proteins MRP-14 and MRP-8 during human neutrophil activation

The myeloid-related proteins MRP-14 and MRP-8 and also p6, three calcium-binding proteins of the S100 family, translocate to the membrane during human neutrophil activation with stimuli known to require extracellular calcium for activity. When phorbol 12-myristate 13-acetate (PMA, an extracellular calcium-independent stimulus) is used, no translocation is observed. To characterize further the mechanisms involved in their translocation, phosphorylation of these proteins was studied. Three isoforms of MRP-14 were markedly phosphorylated in the membrane and in the cytosol upon activation with extracellular calcium-dependent stimuli, such as opsonized zymosan, the calcium ionophore A23187, N-formylmethionylleucylphenylalanine in the presence of cytochalasin B and arachidonic acid, or upon extracellular calcium-independent stimulation (PMA). In no case were p6 and a fourth, more basic isoform of MRP-14, phosphorylated. In PMA-activated cells, a phosphorylated acidic isoform of MRP-8 was detected in the cytosol only. However, phosphorylated MRP-8 represented only a small fraction of total MRP-8. Cgp 41251, an inhibitor of protein kinase C (PKC), completely inhibited the phosphorylation of MRP-8, and decreased cytosolic MRP-14 phosphorylation. To test whether phosphorylated MRP-8 could translocate, A23187, which induces translocation of the three S100 proteins, was added after PMA activation. This resulted in translocation of 18% +/- 5% of phosphorylated MRP-14 and 19% +/- 1% of only nonphosphorylated MRP-8. However, upon inhibition of PKC, translocation of MRP-14 and MRP-8 was increased up to 38% +/- 7% and 34% +/- 3% respectively. This suggests a putative role of phosphorylation and/or of PKC in the modulation of MRP-14 and MRP-8 translocation to the membrane.

Identification of a 64-kDa protein phosphorylated with glucose in human polymorphonuclear leukocytes in a cell-free system

We previously reported that a 64-kDa protein (p64) in human polymorphonuclear leukocytes (PMN) was phosphorylated with [gamma-32P]ATP under a micromolar concentration of glucose in a cell-free system. The present paper presents the results of analysis of phosphorylation reaction and the identification of phosphoprotein. The findings that p64 was also phosphorylated with glucose-6-[32P]phosphate and that phosphorylation was inhibited with mannoheptulose suggested that the reaction was mediated by hexokinase. In fact, it was found that [32P]phosphate in glucose-6-[32P]phosphate was incorporated into either p64 or rabbit muscle phosphoglucomutase and that glucose-6-phosphate formation from glucose and ATP was detected in over 100-kDa fraction of PMN cytosol. These results showed that p64 was phosphoglucomutase in PMN and that phosphate incorporation into p64 was a conversion of a phosphate group in glucose-6-phosphate produced by hexokinase. It was further demonstrated by analysis of two-dimensional electrophoresis that p64 phosphorylated with glucose induction was different from another 64-kDa protein phosphorylated by stimulation with formyl-methionyl-leucyl-phenylalanine in vivo.

Stimulation of superoxide anion production in guinea pig polymorphonuclear leukocytes by hypotonic conditions in combination with protein kinase C activators

Conditions for superoxide anion (O2-) production were examined in guinea pig polymorphonuclear leukocytes (PMNL). When PMNL were suspended in the hypotonic medium, O2- production was significantly enhanced by concurrent treatment with low concentrations of 1-oleoyl-2-acetylglycerol (OAG), a cell-permeable protein kinase C activator. Such hypotonicity or OAG alone had little effect on the production. Other protein kinase C activators also markedly enhanced O2- production in combination with hypotonicity, but not in the isotonic medium. Protein kinase C inhibitors, H-7 and staurosporine, dose-dependently inhibited the production. These observations indicate that protein kinase C participates in such synergistic O2- production with hypotonicity. Phosphorylation of 46-kDa protein(s), which was commonly enhanced in paralleled with an activation of NADPH oxidase in guinea pig PMNL, was increased by treatment with 10 microM OAG, but the phosphorylation was little altered by hypotonic treatment. Intracellular calcium concentration, arachidonate release, and 1,2-diacylglycerol and phosphoinositide concentrations were slightly altered by hypotonic treatment. A change in phosphatidate (PA) production in PMNL was induced by hypotonic treatment either by itself or in combination with OAG treatment. These results suggest that the combination of cell membrane changes by hypotonic treatment accompanied by the increase in PA and 46-kDa protein phosphorylation by protein kinase C provides the conditions required for a marked increase in O2- production. Hypotonicity may be a good tool for studying the mechanism of priming in the activation of NADPH oxidase.

Different abilities of two types of Fc gamma receptor on guinea-pig macrophages to trigger the intracellular Ca2+ mobilization and O2- generation

When exposed to hen ovalbumin (OA)-complexed IgG antibodies, guinea-pig macrophages undergo O2- generation and a rapid rise in the intracellular concentration of free Ca2+ ((Ca2+]i). These responses were found to depend on the IgG isotype of antibodies used; OA-complexed IgG2 antibody (OA gamma 2) induced these responses 3-5 times more intensively than did OA-complexed IgG1 antibody (OA gamma 1). The inhibitory effects of monoclonal antibody to Fc gamma receptor for IgG2 alone (Fc gamma 2R) and that to Fc gamma receptor for both IgG1 and IgG2 (Fc gamma 1/gamma 2R) showed that Fc gamma 2R triggered both an increase in [Ca2+]i and activation of the respiratory burst NADPH oxidase more effectively than did Fc gamma 1/gamma 2R. As the number of Fc gamma 2R molecules per macrophage is about one-half that of Fc gamma 1/gamma 2R molecules, the ability of Fc gamma 2R to trigger these responses may be much higher than that of Fc gamma 1/gamma 2R. This difference between their abilities was further demonstrated by measuring the responses induced by cross-linking of Fc gamma 2R or Fc gamma 1/gamma 2R molecules. In addition, the O2- generation with OA gamma 1 was found to be enhanced with cytochalasin B, and to be lowered by depletion of the intracellular Ca2+ of macrophages with Ionomycin and EGTA, though cytochalasin B and the Ca2+ depletion did not affect the O2- generation with OA gamma 2. These results suggest that the mechanisms of Fc gamma 2- and Fc gamma 1/gamma 2 R-mediated signal transmission leading to activation of the NADPH oxidase also differ from each other.

Involvement of membrane charges in constituting the active form of NADPH oxidase in guinea pig polymorphonuclear leukocytes

NADPH oxidase activity in a membrane fraction prepared from phorbol 12-myristate 13-acetate (PMA)-stimulated guinea pig polymorphonuclear leukocytes (PMNL) was inhibited by positively charged myristylamine. The inhibitory effect of myristylamine was significantly suppressed by simultaneous addition of a negatively charged fatty acid, such as myristic acid. However, the suppression by myristylamine was not sufficiently restored when myristic acid was added later. On the other hand, pretreatment of PMA-stimulated PMNL with glutaraldehyde, a protein crosslinking reagent, stabilized NADPH oxidase activity against inhibition by myristylamine, but not against that by p-chloromercuribenzenesulfonic acid. In a cell-free system of reconstituted plasma membrane and cytosolic fractions prepared from unstimulated PMNL, arachidonic acid-stimulated NADPH oxidase activity was also inhibited by myristylamine. During the activation of NADPH oxidase by PMA in intact PMNL and by arachidonic acid in the cell-free system, cytosolic activation factor(s) translocated to plasma membranes. The bound cytosolic activation factor(s) was released from the membranes by myristylamine, accompanied by a loss of NADPH oxidase activity. It is plausible from these results that the inhibitory effect of alkylamine on NADPH oxidase is due to induction of the decoupling and/or dissociation of the cytosolic activation component(s) from the activated NADPH oxidase complex by increments of positive charges in the membranes, and that the glutaraldehyde treatment prevents the dissociation of component(s).

Glucose-stimulated phosphorylation of the 64-kDa protein of human polymorphonuclear leukocytes in a cell-free system

Glucose-stimulated phosphorylation of 64-kDa protein using a greater than 30 kDa fraction of human polymorphonuclear leukocytes in a dose-dependent fashion with 33 microM for maximum stimulation and 1.4 microM for ED50. None of the glucose derivatives and metabolites of glycolysis stimulated phosphorylation, but glucose-1-phosphate, glucose-6-phosphate, fructose-6-phosphate and fructose-1,6-diphosphate inhibited the glucose-stimulated phosphorylation, strongly suggesting phosphorylation by glucose-regulated protein kinase. Cyclic nucleotides and the protein kinase inhibitors H-7, H-8, W-7 and staurosporine did not affect phosphorylation.

Continuous phosphorylation of both the 47 and the 49 kDa proteins occurs during superoxide production by neutrophils

Neutrophils stimulated with 4 beta-phorbol 12-myristate 13-acetate release large quantities of superoxide (O2-) and exhibit an intense phosphorylation of two proteins with molecular masses of approx. 47 and 49 kDa. Treatment of unstimulated cells with antagonists of protein kinase C (e.g., staurosporine; 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7)) is known to inhibit both of these phenomena upon stimulation. These antagonists of PKC also cause a rapid cessation of O2- release when added to cells that are already stimulated. In this paper, we report that the addition of staurosporine or H-7 to stimulated neutrophils resulted in a rapid loss of 32P from both the 47 and the 49 kDa phosphoprotein bands, as detected by autoradiography. This suggests that these two proteins may be regulated by a continual cycle of phosphorylation and dephosphorylation in the stimulated cell, with the phosphorylation reactions predominating, or undergo a rapid degradation subsequent to phosphorylation. Either explanation is consistent with the view that protein kinase C activity is necessary to both initiate and maintain O2- production in neutrophils stimulated with tumor promoters.

Effect of glutaraldehyde on NADPH oxidase system of guinea pig polymorphonuclear leukocytes

In an attempt to elucidate properties and activation mechanisms of the NADPH oxidase system, which is known to be responsible for the production of superoxide anion (O2-) in cell membranes of polymorphonuclear leukocytes (PMNL), intact guinea pig PMNL were treated with glutaraldehyde, a protein crosslinking reagent, before or after stimulation with phorbol 12-myristate 13-acetate (PMA). Then, PMNL were disrupted and NADPH oxidase activity was measured. After the treatment of resting PMNL with glutaraldehyde, NADPH oxidase was no longer activated by PMA. On the other hand, the NADPH oxidase activity enhanced by PMA in advance was markedly retained by the glutaraldehyde treatment of such PMA-stimulated PMNL as compared to that in untreated cells. Similar retention by glutaraldehyde of the stimulated NADPH oxidase activity was observed in PMNL stimulated by formyl-methionyl-leucyl-phenylalanine (FMLP) and cytochalasin D. Furthermore, the oxidase activity of glutaraldehyde-treated PMNL was stable during incubation at 37 degrees C, the half life of the oxidase activity of the treated PMNL being more than 90 min whereas that of the untreated PMNL is about 15 min. This ability of the glutaraldehyde treatment to retain the activity was also observed against inactivation by high concentrations of NaCl and by positively charged alkylamine.

Cloning of the cDNA and functional expression of the 47-kilodalton cytosolic component of human neutrophil respiratory burst oxidase

Neutrophil NADPH oxidase is a multicomponent enzyme that is activated to generate superoxide anion and is defective in the cells of patients with chronic granulomatous disease. It requires both membrane and cytosolic components, the latter including 47- and 67-kDa proteins recognized by the polyclonal antiserum B-1. Immunoscreening of an induced HL-60 lambda ZAP cDNA library yielded seven cross-hybridizing cDNAs encoding the 47-kDa component. Fusion proteins of 22-50 kDa were recognized by B-1. Antiserum against a fusion protein recognized a 47-kDa protein in normal neutrophils but not in those from patients with autosomal chronic granulomatous disease who lack the 47-kDa cytosolic oxidase component. In a cell-free NADPH oxidase system full-length and C-terminal fusion proteins augmented superoxide generation and reconstituted the cytosolic defect of a patient missing the 47-kDa protein. The cDNA hybridized with a 1.4-kilobase mRNA from induced HL-60 cells. The longest cDNA contained an open reading frame encoding a protein of 41,440 Da with a calculated pI of 10.4, an N-terminal glycine, sites favorable for phosphorylation, a nucleotide binding domain, and a region of homology to the src protein kinases, phospholipase C, and alpha-fodrin. These structural features are pertinent to proposed functional roles of the protein in the respiratory burst oxidase.

Concanavalin A stimulation of O2 consumption in electropermeabilized neutrophils via a pertussis toxin-insensitive G protein

Electropermeabilized human neutrophils were used to investigate the possible role of G-proteins in the respiratory burst elicited by concanavalin A (Con A). The Con A-induced activation of the NADPH oxidase was not inhibited by either pertussis toxin or cholera toxin. However, the burst was inhibited by GDP and GDP beta S providing evidence for the involvement of a G-protein(s). O2 consumption in Con A-stimulated cells was dependent on both ATP and Mg2+. ATP could be substituted by ATP gamma S but not by the non-hydrolyzable analog AMP-PNP, suggesting involvement of phosphotransferase reactions. It is concluded that at least two distinct types of G-proteins are capable of inducing the respiratory burst in neutrophils and that accumulation of phosphorylated intermediates may be essential for activation of the respiratory burst by the lectin.

Phosphorylation of both 47 and 49kDa proteins accompanies superoxide release by neutrophils

Neutrophils stimulated with activators of protein kinase C (i.e., 4 beta-phorbol 12-myristate 13-acetate; sn-1,2-dioctanoylglycerol) exhibit a dramatic, dose-dependent incorporation of 32P[Pi] into two proteins with molecular weights of ca. 47 and 49kDa. Proteins of the same molecular weights are also labelled when the cells are stimulated with a chemotactic peptide. However, with the latter stimulus, labelling of the 47kDa species is transient whereas that of the 49kDa entity persists. Labelling of both proteins always accompanied the release of O2-stimulated by these agents. The kinetics of labelling are compatible with the involvement of both phosphoproteins in the stimulation of these cells.

Arachidonic acid release is closely related to the Fc gamma receptor-mediated superoxide generation in macrophages

Stimulation of macrophages with IgG2 immune complexes induced dose-dependently the O2- generation and the release of arachidonic acid and its metabolites. This Fc gamma R-mediated O2- generation was inhibited by a phospholipase A2 inhibitor, 4-p-bromophenacyl bromide (4-pBPB), in parallel to the dose-dependent inhibition of arachidonic acid release. The main arachidonic acid metabolites released were shown to be prostaglandin E2 and thromboxane B2 and blocking of the production of these metabolites by indomethacin did not inhibit the O2- generation. Inhibition of the Fc gamma R-mediated O2- generation and the arachidonic acid release by the C-kinase inhibitor, 1-(5-isoquinolinesulfonyl)-2-methylpiperazine (H-7), was less intense than by 4-pBPB. These results support the previously proposed hypothesis that arachidonic acid acts as an intracellular activator of the Fc gamma R-mediated O2- generation in macrophages. Although the C-kinase activation may also contribute to the activation of the O2--generating system, arachidonic acid release appears to play a major role in Fc gamma R-mediated O2- generation. In contrast, activation of C-kinase seems to be contributing mainly in the induction of both the arachidonic acid release and O2- generation by 12-o-tetradecanoylphorbol 13-acetate (TPA). Furthermore, suboptimal concentrations of TPA and arachidonate were found to act synergistically to stimulate O2- generation and the inhibition study suggested a positive synergism between C-kinase and arachidonic acid release to induce O2- generation. This synergistic action may have general importance in receptor-mediated O2- generation.

Protein phosphorylation and the respiratory burst

The exposure of 32P-loaded neutrophils to any of a variety of activating agents induces changes in the levels of phosphorylation of a large number of phosphoproteins. The uptake of phosphate by one set of phosphoproteins in particular, a family whose members migrate at Mr 48K with near neutral pI values, appears to be closely related to the activation of the respiratory burst oxidase, the O2--producing enzyme of phagocytes that is responsible for the generation of microbicidal oxidants by these cells. Evidence for the relationship between the phosphorylation of these proteins and the activation of the respiratory burst oxidase has been furnished by kinetic studies as well as by studies on protein phosphorylation in neutrophils from patients with chronic granulomatous disease, a group of inherited disorders affecting this oxidase. The details of this relationship are obscure, although the evidence suggests that these phosphoproteins act in substoichiometric amounts with respect to the oxidase.

Synergism of phosphorylation of 46K protein(s) and arachidonate release in the induction of superoxide anion production in guinea pig polymorphonuclear leukocytes

The phosphorylation of 46K protein(s), which was generally observed in parallel with an activation of NADPH oxidase of guinea pig polymorphonuclear leukocytes (PMNL) in our previous studies (N. Okamura et al. (1984) Arch. Biochem. Biophys. 228, 270-277; T. Ohtsuka et al. (1987) J. Biochem. 101, 897-903), was increased by treatment with 1-oleoyl-2-acetylglycerol (OAG), even at low concentrations at which both superoxide anion (O2-) production and arachidonate release were little induced. On the other hand, exposure of PMNL to low concentrations of a calcium ionophore, A23187, stimulated arachidonate release without causing substantial O2- production and increase in phosphorylation of 46K protein(s). Simultaneous addition of the above-mentioned suboptimal concentrations of both OAG and A23187 markedly enhanced O2- production in PMNL. This enhancing effect may be ascribable to the increase in the phosphorylation of 46K protein(s) and arachidonate release, which are induced by the addition of OAG and A23187, respectively. Another arachidonate-releasing agent, N-formyl-methionylleucyl-phenylalanine (FMLP), also stimulated O2- production in accordance with an increase in the arachidonate release and protein phosphorylation. Simultaneous addition of OAG significantly enhanced the FMLP-induced O2- production, presumably by maintaining the 46K protein phosphorylation which would facilitate the effect of arachidonate released by FMLP. Thus, the present results suggest that phosphorylation of 46K protein(s) and arachidonate release synergistically induce O2- production in PMNL, although either of them alone hardly induces the production.

Further evidence for the involvement of the phosphorylation of 46K protein(s) in the regulation of superoxide anion production in guinea pig polymorphonuclear leukocytes

Treatment of guinea pig polymorphonuclear leukocytes (PMNL) with arachidonate at concentrations of less than 20 microM induced slight stimulation of superoxide anion (O2-) production with little enhancement of the phosphorylation of the 46K protein(s). The stimulation of the phosphorylation of those protein(s) has been observed in parallel with an activation of NADPH oxidase in our previous studies (N. Okamura et al. (1984) Arch. Biochem. Biophys. 228, 270-277; T. Ohtsuka et al. (1986) Biochem. Biophys. Acta 888, 332-337; T. Ohtsuka et al. (1987) J. Biochem. 101, 897-903). On the other hand, the phosphorylation of the same protein(s) was increased by the treatment of PMNL with 10 microM 1-oleoyl-2-acetylglycerol (OAG), a permeable diacylglycerol, with little change in O2- production. Treatment of PMNL with a combination of such low concentrations of arachidonate and OAG, induced marked increase in O2- production in accordance with the increase in the phosphorylation of 46K protein(s) which was probably due to OAG action. Thus, it is likely that this protein phosphorylation is a prerequisite or regulatory to the stimulation of the O2- production by arachidonate in PMNL.