Stimulation of a histone H4 protein kinase in Triton X-100 lysates of rabbit peritoneal neutrophils pretreated with chemotactic factors. Effect of fMet-Leu-Phe and partial characterization of the protein kinase

The renaturable 69- and 63-kDa protein kinases that undergo rapid activation in chemoattractant-stimulated guinea pig neutrophils are p21-activated kinases

Neutrophils stimulated with the chemoattractant fMet-Leu-Phe (fMLP) are known to exhibit rapid activation of four protein kinases with molecular masses of approximately 69, approximately 63, approximately 49, and approximately 40-kDa. Activation of these kinases is blocked by antagonists of phosphatidylinositol 3-kinase and type 1 and/or type 2A protein phosphatases. These enzymes can be detected by their ability to undergo renaturation and catalyze the phosphorylation of a peptide substrate that corresponds to amino acid residues 297-331 of the 47-kDa subunit of the NADPH-oxidase complex fixed within a gel. In this report, we demonstrate that an antibody generated to a fusion protein containing amino acid residues 175-306 of p21-activated protein kinase 1 (Pak1) reacts with three proteins in guinea pig neutrophils with molecular masses in the 60-70-kDa range during Western blotting. This antibody immunoprecipitates both the 69- and 63-kDa renaturable kinases from lysates of stimulated cells along with a minor 60-kDa kinase. No activities were observed for any of these enzymes in immunoprecipitates from unstimulated neutrophils. However, addition of ATP and activated Rac 1 or Cdc42 to immunoprecipitates from unstimulated cells resulted in the stimulation of two renaturable kinases with molecular masses in the 69- and 63-kDa range. These immunoprecipitates also contained two novel protein kinases with masses of approximately49 and 40 kDa that were selectively activated by Cdc42. In contrast, the 69- and 63-kDa kinases were not immunoprecipitated from lysates of stimulated neutrophils with an antibody to Pak2 or with nonimmune serum. These data indicate that the renaturable 69- and 63-kDa kinases are Paks and reveal some of the upstream events that are necessary for the rapid activation of this family of protein kinases in neutrophils.

In vitro activation of a 60-70 kDa histone H4 protein kinase from neutrophils by limited proteolysis

Neutrophils stimulated with the chemotactic peptide fMet-Leu-Phe (fMLP) are known to exhibit a rapid and transient activation of a histone H4 kinase that may function in a stimulatory pathway downstream of phosphatidylinositol 3-kinase. The activity of this histone kinase in unstimulated neutrophils and cells treated with 1.0 microM fMLP for 10 sec was 8.8 +/- 5 and 43 +/- 2 pmol P/min per 10(7) cells, respectively. In this paper, we report that unstimulated neutrophils contain a latent H4 kinase in the 100,000 x g soluble fraction that can be markedly activated by treatment with trypsin. The values for the untreated and trypsin treated enzyme were 5.5 +/- 1.0 and 63.6 +/- 18 pmol P/min per 10(7) cell-equivalents, respectively. This kinase was insensitive to a selective antagonist of protein kinase C (i.e., 50 microM 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7)) but completely blocked by 100 nM staurosporine. Only a single peak of activity was observed for this enzyme when the 100,000 x g supernatant fraction was fractionated on either an exclusion (KW-803) or an anion exchange column (DEAE), or during isoelectric focusing. The molecular weight of the latent kinase was 64 +/- 6 kDa and the isoelectric point was 7.6 +/- 0.1. During all fractionation procedures, the H4 kinase co-chromatographed with a trypsin-activated kinase that catalyzed the phosphorylation of a peptide which corresponds to residues 297-331 of the 47 kDa subunit of the NADPH-oxidase complex (p47-phox). The properties of the trypsin-activated H4 kinase from unstimulated neutrophils are very similar to those reported for this enzyme from fMLP-stimulated cells.

Chemoattractant-induced activation of vacuolar H+ pumps and of an H(+)-selective conductance in neutrophils

Upon binding to their receptors on the surface of neutrophils, chemotactic peptides elicit a burst of metabolic activity. The excess acid generated by this burst must be rapidly extruded in order to maintain intracellular pH and preserve normal microbicidal responses. Recently, H(+)-pumping vacuolar-type ATPases (V-pumps) and a H(+)-selective conductance were described in the membrane of neutrophils. However, these systems are virtually quiescent in resting cells. In this report, we analyzed whether the V-pumps and the conductance become active and contribute to pH regulation following cell activation by chemoattractants. Formyl-Met-Leu-Phe (fMLP) was found to stimulate V-pumps, as assessed by the appearance of bafilomycin-sensitive H+ extrusion. Concomitantly, the chemoattractant also activated the H+ conductance, detected as a voltage-dependent and Zn(2+)-sensitive net H+ efflux. In both cases, activation was prevented by treatment with competing antagonistic peptides or with pertussis toxin, implying mediation by a receptor coupled to a heterotrimeric G protein. The signalling pathways downstream of the G proteins were also investigated. Stimulation of neither the V-pump nor the conductance required activation of protein kinase C. An elevation of cytosolic calcium ([Ca2+]i) comparable to that induced by fMLP did not suffice to trigger either transporter. Moreover activation of the conductance remained unaffected when the chemoattractant-induced increase in [Ca2+]i was precluded. In contrast, stimulation of the V-pump was substantially (approximately 50%) depressed when [Ca2+]i was prevented from rising. Tyrosine phosphorylation of several polypeptides accompanies stimulation by fMLP. Prevention of phosphotyrosine accumulation resulted in a pronounced inhibition of H(+)-pumping and of the H+ conductance. Together, these data indicate that engagement of surface receptors by chemotactic peptides can lead to stimulation of two voltage-sensitive pH regulatory pathways, a pump and a conductance, by a pathway that requires tyrosine phosphorylation. Both pathways are capable of sizable H+ extrusion, thereby contributing to pH regulation during the metabolic burst.

Regulation of human leukocyte p21-activated kinases through G protein--coupled receptors

The Rac guanosine 5'-triphosphate (GTP)-binding proteins regulate oxidant production by phagocytic leukocytes. Two Ste20-related p21-activated kinases (PAKs) were identified as targets of Rac in human neutrophils. Activity of the approximately 65- and approximately 68-kilodalton PAKs was rapidly stimulated by chemoattractants acting through pertussis toxin-sensitive heterotrimeric GTP-binding proteins (G proteins). Native and recombinant PAKs phosphorylated the p47phox reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase component in a Rac-GTP-dependent manner. The action of PAKs during phagocyte activation by G protein-coupled pathways may contribute to regulation of NADPH oxidase activity.

Antagonists of phosphatidylinositol 3-kinase block activation of several novel protein kinases in neutrophils

Several novel protein kinases are known to be rapidly activated in neutrophils stimulated with the chemoattractant fMet-Leu-Phe (fMLP). These kinases include a histone H4 protein kinase and several renaturable kinases with molecular masses of about 69, 63, 49, and 40 kDa. The renaturable kinases can catalyze the phosphorylation of a peptide that corresponds to residues 297-331 of the 47-kDa subunit of the NADPH-oxidase system (p47-phox). Previous studies have indicated that the activation of all of these protein kinases involves an uncharacterized stimulatory pathway and/or novel second messenger. The studies reported herein were undertaken to determine if phosphatidylinositol 3-kinase (PI3-K) is a component of this pathway. We report that certain chromosome derivatives (e.g. 2-(4-morpholinyl)-8-phenylchromone (LY294002)) and wortmannin, which inhibit PI3-K by distinct mechanisms, blocked activation of all of these novel kinases. These antagonists also inhibited the phosphorylation of p47-phox (about 50%) and O2.- release (about 80%) in cells stimulated with fMLP, but not with 4 beta-phorbol 12-myristate 13-acetate. A strong correlation exists between the amounts of these antagonists required to produce 50% inhibition of PI3-K in vitro and O2.- release in vivo. In contrast, a single atom substitution of LY294002 produced a compound (LY303511) that did not inhibit PI3-K. Compound LY303511 did not appreciably inhibit the activation of the novel protein kinases or O2.- generation. These data strongly suggest that PI3-K is involved in the activation of several novel protein kinases in neutrophils, one or more of which may be involved in O2.- release.

Serine/threonine kinase activation in human neutrophils: relationship to tyrosine phosphorylation

Tyrosine phosphorylation is among the earliest responses of neutrophils to chemotactic peptides. Tyrosine phosphorylated proteins comigrate with serine/threonine kinases of 65 and 72 kDa (PK65 and PK72), which are activated concomitantly by the chemoattractants. Studies were designed to test whether tyrosine phosphorylation is required for activation of PK65 and PK72. Pretreatment of cells with the tyrosine kinase inhibitors erbstatin or genistein prevented both phosphotyrosine accumulation and activation of PK65 and PK72. In nondenaturing lysates, PK65 and PK72 became spontaneously inactivated in parallel with rapid endogenous tyrosine dephosphorylation. Spontaneous dephosphorylation and inactivation of PK65 and PK72 were prevented in denatured lysates. Under these conditions, dephosphorylation could be induced by exogenous phosphotyrosine phosphatase 1B. PK65 and PK72 activation persisted despite virtually complete tyrosine dephosphorylation. Moreover, immunoprecipitation experiments indicated that PK65 and PK72 are not themselves tyrosine phosphorylated. We concluded that tyrosine phosphorylation is a necessary upstream event in the activation of the serine/threonine kinases. However, once the posttranslational modification that renders PK65 and PK72 active has occurred, tyrosine phosphorylation is no longer required for maintenance of their kinase activity.

Wortmannin and 1-butanol block activation of a novel family of protein kinases in neutrophils

Neutrophils contain four uncharacterized protein kinases with molecular masses of ca. 69, 63, 49 and 40 kDa that are rapidly activated upon stimulation of these cells with the chemoattractant fMet-Leu-Phe [Ding, J. and Badwey, J.A. (1993) J. Biol. Chem. 268, 17326-17333]. We now report that wortmannin and 1-butanol block activation of all four of these kinases. These reagents are known to inhibit superoxide generation in neutrophils stimulated with this agonist. Wortmannin inhibits phosphatidylinositol 3-kinase and blocks activation of phospholipase D, whereas 1-butanol can reduce the generation of phosphatidate in cells by serving as a substrate for phospholipase D. These data suggest that phosphatidylinositol 3-kinase and phospholipase D may be involved in the activation of several novel protein kinases in neutrophils and that one or more of these kinases is/are involved in superoxide release.

Modulation of leukotriene B4 and platelet-activating factor binding to neutrophils

Preincubation of human neutrophils with the human hormone granulocyte-macrophage colony-stimulating factor (GM-CSF) inhibits the specific binding of leukotriene B4 ([3H]LTB4) but not the nonmetabolizable bioactive platelet-activating factor ([3H]C-PAF) to intact cells. This inhibition requires that the GM-CSF interacts with intact cells. The action of GM-CSF is not prevented by pertussis toxin. Moreover, the rise in calcium produced by LTB4 but not by PAF is also inhibited in human neutrophils pretreated with GM-CSF. Interestingly, neither the inhibitory action of GM-CSF on [3H]LTB4 binding or LTB4-induced calcium rise nor the potentiation of superoxide production by GM-CSF is reduced by inhibitors of arachidonic acid metabolism by the lipoxygenase pathway. In contrast, preincubation of human neutrophils with either the chemotactic factor formyl-methionyl-leucyl-phenylalanine (fMet-Leu-Phe) or the active phorbol ester, phorbol 12-myristate 13-acetate (PMA), inhibits the binding of both [3H]LTB4 and [3H]C-PAF to intact cells. The inhibitory actions of GM-CSF, PMA, and fMet-Leu-Phe require that they interact with the intact cells; their actions cannot be reproduced in plasma membrane preparations. The effects of both GM-CSF and fMet-Leu-Phe cannot be prevented by the protein kinase C inhibitor staurosporine. The mechanisms of fMet-Leu-Phe and GM-CSF actions are probably not mediated through the release of LTB4 by the cells. Interestingly, this new action, unlike other reported effects of GM-CSF, is not mediated through a pertussis toxin-sensitive G protein (Gi alpha 2). This indicates that not all GM-CSF receptors are coupled to Gi alpha 2.

Stimulation of a histone H4 protein kinase in Triton X-100 lysates of rabbit peritoneal neutrophils pretreated with chemotactic factors: lack of requirements of calcium mobilization and protein kinase C activation

The characteristics of the activation of a histone H4 kinase activity in Triton X-100 lysates of rabbit peritoneal neutrophils pretreated with fMet-Leu-Phe were studied: The activation of the kinase was a) inhibited by the antagonist of formylpeptide, t-Boc-(Phe-Leu)2(-)-Phe, b) completely inhibited by pertussis toxin pretreatment, c) not affected by the pretreatment of neutrophils with an activator of protein kinase C, phorbol-12-myristate-13-acetate, or an inhibitor of protein kinase C, 1-(5-isoquinoline-sulfonyl)-2-methyl-piperazine, and d) not inhibited in the cells preloaded with the intracellular calcium chelators, bis-(o-aminophenoxy)-ethane-N,N,N',N'-tetra acetic acid acetoxymethyl-ester (BAPTA/AM). These results suggest that the stimulus-induced activation of H4 kinase requires functional receptor and GTP-binding protein but neither calcium mobilization nor protein kinase C activation.

Protein phosphorylation associated with the stimulation of neutrophils. Modulation of superoxide production by protein kinase C and calcium

Neutrophils and other phagocytic cells of the immune system possess a superoxide-generating oxidase system which is essential for the efficient killing of microbes. The system is activated by a wide variety of stimuli, some of which operate through pathways involving protein kinase C (PKC), while others appear not to. The PKC-dependent pathway is probably the major signal transduction route for most of the stimuli. Alterations in cellular Ca2+ and diglyceride levels can have a pronounced stimulatory effect on this pathway by their ability to synergistically activate PKC. This review discusses PKC, the different interactions of this kinase with the plasmalemma that are important in superoxide production, the synergy between Ca2+ and diglyceride, and the nature of the phosphoproteins involved. Evidence supporting the existence of the PKC-independent pathway is also reviewed.