Protein kinase C isoforms in human neutrophil cytoplasts

In Vitro Neutrophil Migration Requires Protein Kinase C-Delta (δ-PKC)-Mediated Myristoylated Alanine-Rich C-Kinase Substrate (MARCKS) Phosphorylation

Dysregulated release of neutrophil reactive oxygen species and proteolytic enzymes contributes to both acute and chronic inflammatory diseases. Therefore, molecular regulators of these processes are potential targets for new anti-inflammatory therapies. We have shown previously that myristoylated alanine-rich C-kinase substrate (MARCKS), a well-known actin binding protein and protein kinase C (PKC) substrate, is a key regulator of neutrophil functions. In the current study, we investigate the role of PKC-mediated MARCKS phosphorylation in neutrophil migration and adhesion in vitro. We report that treatment of human neutrophils with the δ-PKC inhibitor rottlerin significantly attenuates f-Met-Leu-Phe (fMLF)-induced MARCKS phosphorylation (IC50=5.709 μM), adhesion (IC50=8.4 μM), and migration (IC50=6.7 μM), while α-, β-, and ζ-PKC inhibitors had no significant effect. We conclude that δ-PKC-mediated MARCKS phosphorylation is essential for human neutrophil migration and adhesion in vitro. These results implicate δ-PKC-mediated MARCKS phosphorylation as a key step in the inflammatory response of neutrophils.

PKCβII acts downstream of chemoattractant receptors and mTORC2 to regulate cAMP production and myosin II activity in neutrophils

mTORC2 has been shown to be involved in cytoskeletal regulation, but the mechanisms by which this takes place are poorly understood. This study shows that PKCβII is specifically required for mTORC2-dependent activation of adenylyl cyclase 9 and back retraction during neutrophil chemotaxis to chemoattractants.

Chemotaxis is a process by which cells polarize and move up a chemical gradient through the spatiotemporal regulation of actin assembly and actomyosin contractility, which ultimately control front protrusions and back retractions. We previously demonstrated that in neutrophils, mammalian target of rapamycin complex 2 (mTORC2) is required for chemoattractant-mediated activation of adenylyl cyclase 9 (AC9), which converts ATP into cAMP and regulates back contraction through MyoII phosphorylation. Here we study the mechanism by which mTORC2 regulates neutrophil chemotaxis and AC9 activity. We show that inhibition of protein kinase CβII (PKCβII) by CPG53353 or short hairpin RNA knockdown severely inhibits chemoattractant-induced cAMP synthesis and chemotaxis in neutrophils. Remarkably, PKCβII-inhibited cells exhibit specific and severe tail retraction defects. In response to chemoattractant stimulation, phosphorylated PKCβII, but not PKCα, is transiently translocated to the plasma membrane, where it phosphorylates and activates AC9. mTORC2-mediated PKCβII phosphorylation on its turn motif, but not its hydrophobic motif, is required for membrane translocation of PKCβII. Inhibition of mTORC2 activity by Rictor knockdown not only dramatically decreases PKCβII activity, but it also strongly inhibits membrane translocation of PKCβII. Together our findings show that PKCβII is specifically required for mTORC2-dependent AC9 activation and back retraction during neutrophil chemotaxis.

Protein kinase C isoforms in neutrophil adhesion and activation

Neutrophils are the first line of defense against bacterial and mycotic pathogens. In order to reach the pathogens, neutrophils need to transmigrate through the vascular endothelium and migrate to the site of infection. Defense strategies against pathogens include phagocytosis, production and release of oxygen radicals through the oxidative burst, and degranulation of antimicrobial and inflammatory molecules. Protein kinase C (PKC)-δ is required for full assembly of NADPH oxidase and activation of the respiratory burst. Neutrophils also express PKC-α and -β, which may be involved in adhesion, degranulation and phagocytosis, but the evidence is not conclusive yet. This review focuses on the potential impact of protein kinase C isoforms on neutrophil adhesion and activation.

The tripeptide feG regulates the production of intracellular reactive oxygen species by neutrophils

BACKGROUND

The D-isomeric form of the tripeptide FEG (feG) is a potent anti-inflammatory agent that suppresses type I hypersensitivity (IgE-mediated allergic) reactions in several animal species. One of feG's primary actions is to inhibit leukocyte activation resulting in loss of their adhesive and migratory properties. Since activation of neutrophils is often associated with an increase in respiratory burst with the generation of reactive oxygen species (ROS), we examined the effect of feG on the respiratory burst in neutrophils of antigen-sensitized rats. A role for protein kinase C (PKC) in the actions of feG was evaluated by using selective isoform inhibitors for PKC.

RESULTS

At 18 h after antigen (ovalbumin) challenge of sensitized Sprague-Dawley rats a pronounced neutrophilia occurred; a response that was reduced in animals treated with feG (100 microg/kg). With antigen-challenged animals the protein kinase C (PKC) activator, PMA, significantly increased intracellular ROS of circulating neutrophils, as determined by flow cytometry using the fluorescent probe dihydrorhodamine-123. This increase was prevented by treatment with feG at the time of antigen challenge. The inhibitor of PKCdelta, rottlerin, which effectively prevented intracellular ROS production by circulating neutrophils of animals receiving a naïve antigen, failed to inhibit PMA-stimulated ROS production if the animals were challenged with antigen. feG treatment, however, re-established the inhibitory effects of the PKCdelta inhibitor on intracellular ROS production. The extracellular release of superoxide anion, evaluated by measuring the oxidative reduction of cytochrome C, was neither modified by antigen challenge nor feG treatment. However, hispidin, an inhibitor of PKCbeta, inhibited the release of superoxide anion from circulating leukocytes in all groups of animals. feG prevented the increased expression of the beta1-integrin CD49d on the circulating neutrophils elicited by antigen challenge.

CONCLUSION

feG reduces the capacity of circulating neutrophils to generate intracellular ROS consequent to an allergic reaction by preventing the deregulation of PKCdelta. This action of feG may be related to the reduction in antigen-induced up-regulation of CD49d expression on circulating neutrophils.

Involvement of protein kinase Cdelta in the activation of NADPH oxidase and the phagocytosis of neutrophils

This experiment was performed to clarify the role of protein kinase C (PKC) delta in NADPH oxidase-dependent O(2-) production and actin polymerization followed by phagocytosis in neutrophils. Bovine neutrophils and human neutrophil-like differentiated HL-60 (dHL-60) cells were stimulated with serum-opsonized zymosan (OZ) and fMet-Leu-Phe (fMLP), respectively. Rottlerin, a specific inhibitor of PKCdelta, attenuated the production of O(2-) from NADPH oxidase in both neutrophils and dHL-60 cells. However, it did not inhibit the translocation of p47(phox) from the cytosol to the membrane in either type of cell or the phosphorylation of p47(phox) in dHL-60 cells. GF109203X (GFX), an inhibitor of cPKC, attenuated not only the production of O(2-) but also the translocation of p47(phox) in both cells. Furthermore, rottlerin significantly attenuated the ingestion of opsonized particles and the formation of F-actin in OZ-stimulated neutrophils, whereas, GFX did not affect those phagocytic processes. These results suggest that both PKCdelta and cPKC regulate NADPH oxidase through different pathways, but only PKCdelta regulates the phagocytic function in neutrophils.

Impaired NADPH oxidase activity in Rac2-deficient murine neutrophils does not result from defective translocation of p47phox and p67phox and can be rescued by exogenous arachidonic acid

Rac2 is a hematopoietic-specific Rho-GTPase that plays a stimulus-specific role in regulating reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase activation and other functional responses in neutrophils. In this study, rac2-/- neutrophils were shown to have significantly decreased NADPH oxidase activity and actin remodeling in response to exogenous arachidonic acid (AA), as previously observed for phorbol 12-myristate 13-acetate (PMA) or formyl-Met-Leu-Phe (fMLP) as agonists. PMA-, fMLP-, or AA-induced translocation of p47phox and p67phox to the plasma membrane was not impaired in rac2-/- neutrophils. Combined stimulation of rac2-/- neutrophils with exogenous AA and PMA had a synergistic effect on NADPH oxidase activity, and superoxide production increased to a level that was at least as high as wild-type cells and had no effect on fMLP-elicited enzyme activity. Membrane translocation of p47phox and p67phox as well as Rac1 activation was not increased further by combined PMA and AA stimulation. Inhibitor studies were consistent with important roles for phorbol ester-activated protein kinase C (PKC) isoforms and an atypical isoform, PKCzeta, in superoxide production by wild-type and rac2-/- neutrophils stimulated with AA and PMA. In addition, PMA-stimulated release of AA and cytoplasmic phospholipase A2 expression in rac2-/- neutrophils were similar to wild-type, suggesting that deficient AA production by PMA-stimulated rac2-/- neutrophils does not explain the effect of exogenous AA on oxidase activity. Although not required for translocation of p47phox and p67phox, Rac2 is necessary for optimal activity of the assembled oxidase complex, an effect that can be replaced by exogenous AA, which may act directly or via an exogenous AA-induced mediator.

Regulation of matrix metalloproteinase-9 (MMP-9) in TNF-stimulated neutrophils: novel pathways for tertiary granule release

Matrix metalloproteinase-9 (MMP-9) is present in the tertiary granules of neutrophils and is rapidly released following stimulation. We examined the pathways that regulate tumor necrosis factor (TNF)-mediated MMP-9 release and found this to be dependent on the TNF receptor I. TNF rapidly activated extracellular signal-regulated kinase and p38 mitogen-activated protein kinases, but neither of these pathways was critical for MMP-9 release. Many neutrophil responses to TNF require beta2-integrin-dependent signaling and subsequent Src family kinase activation. In contrast, we found that MMP-9 release from tertiary granules was only partially affected by blocking beta2-integrin-mediated adhesion. Similarly, blocking Src family kinases with the inhibitor PP2 only attenuated TNF-induced MMP-9 release. Blocking beta2-integrin-mediated adhesion and Src family kinases did not result in additive inhibition of MMP-9 release. In contrast, inhibiting protein kinase C (PKC) with a pan-specific inhibitor blocked greater than 85% of MMP-9 release. Inhibitors against specific PKC isoforms suggested a role for PKC alpha and PKC delta in maximal MMP-9 release. These data suggest that MMP-9 release from tertiary granules uses beta2-integrin-independent signaling pathways. Furthermore, PKC isoforms play a critical role in regulating tertiary granule release.

Protein kinase C-independent pathway for NADPH oxidase activation in guinea pig peritoneal polymorphonuclear leukocytes by cytochalasin D

Cytochalasin D (CD) induced production of the superoxide radical (O(2)(-)) in guinea pig polymorphonuclear leukocytes (PMNs). The protein kinase C (PKC) inhibitor GF109203X (GFX) was rarely without effect on CD-induced O(2)(-) production. CD as well as PMA induced the translocation of p47(phox) to the membrane fraction, and this translocation was slightly decreased by GFX. Moreover, the inhibitory effect of a PKCzeta antagonist with sequences based on the endogenous PKCzeta pseudosubstrate region was weaker than the inhibitory effect on N-formyl-methionyl-leucyl-phenylalanine (fMLP)-induced O(2)(-) production. On the other hand, the production of O(2)(-) induced by CD was more strongly suppressed by the PLD inhibitor ethanol and phosphatidylinositol 3-kinase (PI3-K) inhibitor wortmannin than that induced by fMLP, and the activation of phospholipase D (PLD) by CD was restrained by wortmannin. These findings suggest that NADPH oxidase is activated by CD through a PKC-independent signaling pathway in PMNs, and this pathway involves the activation of PLD through PI3-K.

SELECTIVE ACTIVATION OF PROTEIN KINASE C DELTA IN HUMAN NEUTROPHILS FOLLOWING ISCHEMIA REPERFUSION OF SKELETAL MUSCLE

Circulatory neutrophils are known to be critical mediators of inflammation and oxidative stress during ischemia reperfusion (I/R) injury. Recent studies have shown an important role for protein kinase C (PKC) in neutrophil survival and function. Activation of specific isotypes of PKC are known to be involved in membrane alteration and motility, oxidative phosphorylation, and apoptosis modulation of neutrophils. However, the role of PKC in neutrophil responses to I/R in the clinical setting has not been studied. In this study, we examined the neutrophil activation of PKC induced by tourniquet-controlled I/R of skeletal muscle in humans. We found that I/R rapidly activates and translocates PKC delta, but not any of the classical forms of PKC (alpha or beta) from cytosol to the particulate fraction of neutrophils. Particulate translocation of PKC delta is sustained up to 4 h after reperfusion and is associated with kinase activity. Postreperfusion activation of PKC delta in neutrophils signals proapoptosis, but does not cause immediate cell death (as revealed by neutrophil morphology study and DNA-laddering assay). This study indicates that calcium-independent novel PKC delta (nPKC delta) might be predominantly involved in regulating membrane functions and survival of neutrophils associated with post-I/R-induced inflammatory oxidative stress.

Eosinophil Major Basic Protein Stimulates Neutrophil Superoxide Production by a Class IAPhosphoinositide 3-Kinase and Protein Kinase C-ζ-Dependent Pathway

Eosinophil major basic protein (MBP) is an effective stimulus for neutrophil superoxide (O(2)(-)) production, degranulation, and IL-8 production. In this study we evaluated the participation of phosphoinositide 3-kinase (PI3K) and PI3K-associated signaling events in neutrophil activation by MBP. Inhibition of PI3K activity blocked MBP-stimulated O(2)(-) production, but not degranulation or IL-8 production. Measurement of Akt phosphorylation at Ser(473) and Thr(308) confirmed that MBP stimulated PI3K activity and also demonstrated indirectly activation of phosphoinositide-dependent kinase-1 by MBP. Genistein and the Src kinase family inhibitor, 4-amino-5-(4-methyphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine, inhibited MBP-stimulated phosphorylation of Akt. 4-Amino-5-(4-methyphenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine also inhibited MBP-stimulated O(2)(-) production. MBP stimulated phosphorylation and translocation of the p85 subunit of class I(A) PI3K, but not translocation of the p110gamma subunit of class I(B) PI3K, to the neutrophil membrane. Inhibition of protein kinase Czeta (PKCzeta) inhibited MBP-stimulated O(2)(-) production. Measurement of phosphorylated PKCzeta (Thr(410)) and PKCdelta (Thr(505)) confirmed that PKCzeta, but not PKCdelta, is activated in MBP-stimulated neutrophils. The time courses for phosphorylation and translocation of the p85 subunit of class I(A) PI3K, activation of Akt, and activation of PKCzeta were similar. Moreover, inhibition of PI3K activity inhibited MBP-induced activation of PKCzeta. We conclude that MBP stimulates a Src kinase-dependent activation of class I(A) PI3K and, in turn, activation of PKCzeta in neutrophils, which contributes to the activation of NADPH oxidase and the resultant O(2)(-) production in response to MBP stimulation.

Neutrophil apoptosis is delayed by trauma patients' plasma via a mechanism involving proinflammatory phospholipids and protein kinase C

BACKGROUND

Delayed apoptosis of primed neutrophils (PMNs) may facilitate PMN-mediated tissue injury leading to multiple organ failure (MOF). We previously reported delayed apoptosis and priming of PMNs in severely injured patients at risk for MOF. Our in vitro and in vivo data have implicated phospholipids in PMN cytotoxicity following trauma and shock. The phospholipid signaling pathway remains to be elucidated, but may involve protein kinase C (PKC). We hypothesized that circulating platelet-activating factor (PAF) and PAF-like proinflammatory phospholipids mediate delayed postinjury PMN apoptosis and that PKC is integral to the signaling pathway.

METHODS

Blood was drawn from severely injured patients (n = 6; mean injury severity score = 21 and transfusion = 10 units) at 6 h postinjury. The plasma fraction was isolated and incubated (5% CO(2), 37 degrees C, 24 h) with PMNs harvested from healthy volunteers. Some PMNs were preincubated with a PAF receptor antagonist (WEB 2170, 400 microM) or a PKC inhibitor (Bis I, 1 microM). Apoptotic index (% PMNs undergoing apoptosis) was assessed morphologically.

RESULTS

Trauma patients' plasma delayed PMN apoptosis compared with plasma from controls. The PMN apoptotic index was not altered by WEB 2170 or Bis I alone; however, WEB 2170 or Bis I pretreatment abrogated delayed PMN apoptosis in response to trauma patients' plasma.

CONCLUSION

Trauma patients' plasma delays apoptosis of PMNs. Our data implicate PAF-like phospholipids in this effect, and PKC appears to be integral in the signaling process. Further elucidation of specific lipids and signaling pathways may reveal clinically accessible therapeutic targets to prevent PMN-mediated hyperinflammation.

Fosfomycin inhibits neutrophil function via a protein kinase C-dependent signaling pathway

We investigated effects of fosfomycin (FOM) on neutrophil function, specifically the oxidative burst and adhesion molecule expression (CD11b/CD18, or MAC-1) using flow cytometry assay. Preincubation of polymorphonuclear leukocytes (PMNL) with FOM from 1 to 100 microg/ml prior to stimulation by phorbol 12-myristate 13-acetate (PMA, 2 ng/ml) significantly suppressed the oxidative burst in a concentration-dependent manner. However, FOM did not affect the oxidative burst of PMNL stimulated by a chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (FMLP). Stimulation with PMA (2 ng/ml) caused a rapid up-regulation of CD11b surface expression on PMNL, followed by time-dependent loss of this receptor. FOM also suppressed loss of CD11b in PMNL stimulated by PMA. FOM then inhibits the PMA-induced oxidative burst and CD11b epitope loss in PMNL. The suppressive effect appears to be mediated by the protein kinase C-dependent signaling pathway.

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.

Ethanol increases superoxide anion production stimulated with 4beta-phorbol 12-myristate 13-acetate in human polymorphonuclear leukocytes. Involvement of protein kinase C

Stimulation of human polymorphonuclear leukocytes (PMNs) with PMA initiates a cascade of events leading to the production and release of superoxide anion (O-2), a major component in anti-bacterial defense. Generation of O-2 by PMA-stimulated PMNs occurs through the translocation and activation of protein kinase C (PKC). In this study, using freshly isolated PMNs, we examined the effect of ethanol on this response to PMA. Our results show that the basal production of O-2 was not affected by ethanol. In contrast, the response induced by PMA was potentiated by ethanol. This potentiation was observed even at high doses of PMA (200 nM) which alone had stimulated the O-2 response maximally. This enhanced response was not due to an increase of PMA uptake by PMNs. The maximal effect was obtained when the cells were preincubated with 80 mM of ethanol before PMA stimulation. Measurement of PKC activity in the cytosolic and membrane fractions showed that pretreatment of PMNs with ethanol increased twofold the PMA-stimulated PKC activity in the membrane fraction. Furthermore, Western blot analysis verified that this increase in PKC activity in the membrane fraction was linked to an increase in the translocation of PKC-alpha and -beta isoforms to the membrane. These results suggest that ethanol potentiates PMA-induced O-2 production through increasing PKC translocation and activity in PMNs.

Spontaneous neutrophil apoptosis involves caspase 3-mediated activation of protein kinase C-delta

Neutrophils are short-lived leukocytes that die by apoptosis. Whereas stress-induced apoptosis is mediated by the p38 mitogen-activated protein (MAP) kinase pathway (Frasch, S. C., Nick, J. A., Fadok, V. A., Bratton, D. L., Worthen, G. S., and Henson, P. M. (1998) J. Biol. Chem. 273, 8389-8397), signals regulating spontaneous neutrophil apoptosis have not been fully determined. In this study we found increased activation of protein kinase C (PKC)-beta and -delta in neutrophils undergoing spontaneous apoptosis, but we show that only activation of PKC-delta was directly involved in the induction of apoptosis. PKC-delta can be proteolytically activated by caspase 3. We detected the 40-kDa caspase-generated fragment of PKC-delta in apoptotic neutrophils and showed that the caspase 3 inhibitor Asp-Glu-Val-Asp-fluoromethylketone prevented generation of the 40-kDa PKC-delta fragment and delayed neutrophil apoptosis. In a cell-free system, removal of PKC-delta by immunoprecipitation reduced DNA fragmentation, whereas loss of PKC-alpha, -beta, or -zeta had no significant effect. Rottlerin and LY379196 inhibit PKC-delta and PKC-beta, respectively. Only Rottlerin was able to delay neutrophil apoptosis. Inhibitors of MAP-ERK kinase 1 (PD98059) or p38 MAP kinase (SB202190) had no effect on neutrophil apoptosis, and activation of p42/44 and p38 MAP kinase did not increase in apoptotic neutrophils. We conclude that spontaneous neutrophil apoptosis involves activation of PKC-delta but is MAP kinase-independent.

A phosphatidic acid-activated protein kinase and conventional protein kinase C isoforms phosphorylate p22(phox), an NADPH oxidase component

Using a phosphorylation-dependent cell-free system to study NADPH oxidase activation (McPhail, L. C., Qualliotine-Mann, D., and Waite, K. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 7931-7935), we previously showed that p47(phox), a cytosolic NADPH oxidase component, is phosphorylated. Now, we show that p22(phox), a subunit of the NADPH oxidase component flavocytochrome b(558), also is phosphorylated. Phosphorylation is selectively activated by phosphatidic acid (PA) versus other lipids and occurs on a threonine residue in p22(phox). We identified two protein kinase families capable of phosphorylating p22(phox): 1) a potentially novel, partially purified PA-activated protein kinase(s) known to phosphorylate p47(phox) and postulated to mediate the phosphorylation-dependent activation of NADPH oxidase by PA and 2) conventional, but not novel or atypical, isoforms of protein kinase C (PKC). In contrast, all classes of PKC isoforms could phosphorylate p47(phox). In a gel retardation assay both the phosphatidic acid-dependent kinase and conventional PKC isoforms phosphorylated all molecules of p22(phox). These findings suggest that phosphorylation of p22(phox) by conventional PKC and/or a novel PA-activated protein kinase regulates the activation/assembly of NADPH oxidase.

Protein Kinase C (PKC) Isoforms Translocate to Triton-Insoluble Fractions in Stimulated Human Neutrophils: Correlation of Conventional PKC with Activation of NADPH Oxidase

The responses of human neutrophils (PMN) involve reorganization and phosphorylation of cytoskeletal components. We investigated the translocation of protein kinase C (PKC) isoforms to PMN cytoskeletal (Triton-insoluble) fractions, in conjunction with activation of the respiratory burst enzyme NADPH oxidase. In resting PMN, PKC-δ (29%) and small amounts of PKC-α (0.6%), but not PKC-βII, were present in cytoskeletal fractions. Upon stimulation with the PKC agonist PMA, the levels of PKC-α, PKC-βII, and PKC-δ increased in the cytoskeletal fraction, concomitant with a decrease in the noncytoskeletal (Triton-soluble) fractions. PKC-δ maximally associated with cytoskeletal fractions at 160 nM PMA and then declined, while PKC-α and PKC-βII plateaued at 300 nM PMA. Translocation of PKC-δ was maximal by 2 min and sustained for at least 10 min. Translocation of PKC-α and PKC-βII was biphasic, plateauing at 2–3 min and then increasing up to 10 min. Under maximal stimulation conditions, PKC isoforms were entirely cytoskeletal associated. Translocation of the NADPH oxidase component p47phox to the cytoskeletal fraction correlated with translocation of PKC-α and PKC-βII, but not with translocation of PKC-δ. Oxidase activity in cytoskeletal fractions paralleled translocation of PKC-α, PKC-βII, and p47phox. Stimulation with 1,2-dioctanoylglycerol resulted in little translocation of PKC isoforms or p47phox, and in minimal oxidase activity. We conclude that conventional PKC isoforms (PKC-α and/or PKC-βII) may regulate PMA-stimulated cytoskeletal association and activation of NADPH oxidase. PKC-δ may modulate other PMN responses that involve cytoskeletal components.

Stimulus-induced selective association of actin-associated proteins (alpha-actinin) and protein kinase C isoforms with the cytoskeleton of human neutrophils

We report a selective, differential stimulus-dependent enrichment of the actin-associated protein alpha-actinin and of isoforms of the signaling enzyme protein kinase C (PKC) in the neutrophil cytoskeleton. Chemotactic peptide, activators of PKC, and cell adhesion all induce a significant increase in the amount of cytoskeletal alpha-actinin and actin. Increased association of PKCbetaI and betaII with the cytoskeletal fraction of stimulated cells was also observed, with phorbol ester being more effective than chemotactic peptide. A fraction of phosphatase 2A was constitutively associated with the cytoskeleton independent of cell activation. None of the stimuli promoted association of vinculin or myosin II with the cytoskeleton. Phosphatase inhibitors okadaic acid and calyculin A prevented increases in cytoskeletal actin, alpha-actinin, and PKCbetaII induced by phorbol ester, suggesting the requirement for phosphatase activity in these events. Increases in cytoskeletal alpha-actinin and PKCbetaII showed differing sensitivity to agents that prevent actin polymerization (cytochalasin D, latrunculin A). Latrunculin A (1 microM) completely blocked PMA-induced increases in cytoskeletal alpha-actinin but reduced cytoskeletal recruitment of PKCbetaII only by 16%. Higher concentrations of latrunculin A (4 microM), which almost abolished the cytoskeletal actin pool, reduced cytoskeletal PKCbetaII by 43%. In conclusion, a selective enrichment of cytoskeletal and signaling proteins in the cytoskeleton of human neutrophils is induced by specific stimuli.

Analysis of the PKC-gamma-related immunocrossreactive region of a novel leukocyte protein gamma-rp

The newly discovered gamma-PKC-related-protein of human leukocytes (gamma-rp) crossreacts with a polyclonal antibody preparation originally designed to be specific for PKC-gamma (gammaMb-Ab). As this antibody is currently the only suitable probe for gamma-rp, we sought to characterize the binding of the two proteins. We determined that the gamma Mg-Ab does not recognize the native form of gamma-rp. However, with denaturing immunoblots of gamma-rp, we found that 1) the crossreactive gamma-rp epitope differs somewhat from that of classic rat brain PKC-gamma, but probably only to the degree of the rat/human PKC species difference; 2) the previously reported doublet bands of gamma-rp represent a single protein with cell-stimulus inducible modifications; 3) antibodies present in the gammaMg-Ab pool bind to two separate sites within the gamma-rp epitope; 4) access to one binding site is conformationally restricted, even after protein denaturation; 5) agonist-induced modification of gamma-rp does not significantly affect the total amount of gamma Mg-Ab that it can bind, but 6) does significantly affect the rate of antibody binding to one site. This investigation defines the appropriate experimental use of our antibody, and the significance of these findings for the future study and cloning of gamma-rp is discussed.

Stimulation of p38 phosphorylation and activity by arachidonic acid in HeLa cells, HL60 promyelocytic leukemic cells, and human neutrophils. Evidence for cell type-specific activation of mitogen-activated protein kinases

Although it is well appreciated that arachidonic acid, a second messenger molecule that is released by ligand-stimulated phospholipase A2, stimulates a wide range of cell types, the mechanisms that mediate the actions of arachidonic acid are still poorly understood. We now report that arachidonic acid stimulated the appearance of dual-phosphorylated (active) p38 mitogen-activated protein kinase as detected by Western blotting in HeLa cells, HL60 cells, human neutrophils, and human umbilical vein endothelial cells but not Jurkat cells. An increase in p38 kinase activity caused by arachidonic acid was also observed. Further studies with neutrophils show that the stimulation of p38 dual phosphorylation by arachidonic acid was transient, peaking at 5 min, and was concentration-dependent. The effect of arachidonic acid was not affected by either nordihydroguaiaretic acid, an inhibitor of the 5-, 12-, and 15-lipoxygenases or by indomethacin, an inhibitor of cyclooxygenase. Arachidonic acid also stimulated the phosphorylation and/or activity of the extracellular signal-regulated protein kinase and of c-jun N-terminal kinase in a cell-type-specific manner. An examination of the mechanisms through which arachidonic acid stimulated the phosphorylation/activity of p38 and extracellular signal-regulated protein kinase in neutrophils revealed an involvement of protein kinase C. Thus, arachidonic acid stimulated the translocation of protein kinase C alpha, betaI, and betaII to a particulate fraction, and the effects of arachidonic acid on mitogen-activated protein kinase phosphorylation/activity were partially inhibited by GF109203X, an inhibitor of protein kinase C. This study is the first to demonstrate that a polyunsaturated fatty acid causes the dual phosphorylation and activation of p38.

Superoxide production in human neutrophils: evidence for signal redundancy and the involvement of more than one PKC isoenzyme class

Selective protein kinase C (PKC) activators and inhibitors and a physiological agonist, fMLP, were used to study superoxide production and PKC isoenzyme activation in human neutrophils. The data show that the classical PKC isoenzymes, alpha and beta, were activated by TPA and at a time prior to NADPH oxidase complex assembly. fMLP induced activation of PKC-beta over a similar time course. Inhibition of c-PKCs reduced, but did not block, TPA-induced superoxide production completely, suggesting additional PKC isoenzymes were involved beyond NADPH oxidase assembly. PKC inhibitors were unable to inhibit fMLP-induced superoxide generation, indicative of signal redundancy in the induction of superoxide generation in human neutrophils.

An apparently novel protein of human leukocytes, reactive with an antibody to protein kinase C-gamma, is rapidly modified upon cell activation: initial characterization in neutrophils and their cytoplasts

On immunoblots of human neutrophil cytoplasts (U-CYT), a previously undescribed 97 kDa protein was revealed by intense and selective reaction with an antibody that was initially raised to recognize PKC-gamma. Denoted "gamma-rp" for gamma-related protein, this acidic cytosolic protein somewhat resembled the classic forms of PKC in several biochemical respects. Appearing as a doublet on low-percentage SDS-PAGE gels, both its mobility and staining pattern were rapidly altered by treatment of U-CYT with either phorbol ester or chemotactic peptide. Whole neutrophil gamma-rp was detectable only after TCA precipitation of intact cells. It was also detectable in human platelets, lymphocytes, and neutrophil-like differentiated HL60 cells, but not in fibroblasts, erythrocytes, monocytes, or monocyte-like differentiated HL60 cells. Our data suggest that gamma-rp merits further study as a potential participant in cellular activation, and as a possible structural or functional relative of PKC.

Effects of multidrug resistance-related ATP-binding-cassette transporter proteins on the cytoskeletal activity of cytochalasins

Cytochalasins are microfilament-active mould metabolites, widely utilized to study the involvement of the actin cytoskeleton in cellular processes as well as in genotoxicity and cell kinetic research. In this study we have investigated whether multidrug-resistance phenotypes, caused by overexpression of the ATP-binding-cassette transporter proteins P-glycoprotein (P-gp) or multidrug-resistance-associated protein (MRP), influence the microfilament-depolymerizing effect of cytochalasins. Using four well-characterized multidrug-resistance cell models, we have shown that both the microfilament-disrupting (phalloidine staining) and the cytotoxic (MTT-assay) activity of cytochalasins are reduced in parallel with increased P-gp expression and restorable by P-gp-modulating agents. This also applied to the cytochalasin D-mediated induction of polykaryons (microscopic evaluation) which arise as a consequence of impaired cytokinesis but unaffected karyokinesis. The reduced cellular activity of cytochalasins in P-gp-positive cell lines was correlated with decreased intracellular accumulation ([3H]cytochalasin B accumulation) which was also restorable by P-gp modulators. Moreover, the dose-dependent inhibition of P-gp photoaffinity labeling ([3H]-azidopine) suggested cytochalasins as P-gp-binding agents. In contrast, MRP overexpression had no effect on either cytochalasin microfilament activity or cytotoxicity. In conclusion, data indicate that the microfilament-destructive effects of cytochalasins are impaired due to a reduction of the intracellular cytochalasin accumulation by P-gp but not by MRP. Results are discussed with regard to P-gp as a resistance factor when cytochalasins are utilized to study microfilament dynamics, cell cycle kinetics or chromosomal damage. Moreover, the polykaryon-inducing activity of cytochalasin D is suggested as a specific indicator for a P-gp-mediated multidrug-resistance phenotype and the reversing potency of chemosensitizers.

The N-formyl peptide receptor: a model for the study of chemoattractant receptor structure and function

N-formyl peptides, such as fMet-Leu-Phe, are one of the most potent chemoattractants for phagocytic leukocytes. The interaction of N-formyl peptides with their specific cell surface receptors has been studied extensively and used as a model system for the characterization of G-protein-coupled signal transduction in phagocytes. The cloning of the N-formyl peptide receptor cDNA from several species and the identification of homologous genes have allowed detailed studies of structural and functional aspects of the receptor. Recent findings that the receptor is expressed in nonhematopoietic cells and that nonformylated peptides can activate the receptor suggest potentially novel functions and the existence of additional ligands for this receptor.

Evidence for the involvement of protein kinase C inhibition by norathyriol in the reduction of phorbol ester-induced neutrophil superoxide anion generation and aggregation

Norathyriol, a xanthone aglycone, inhibited superoxide anion (O2-) generation and O2 consumption in phorbol 12-myristate 13-acetate (PMA)-activated rat neutrophils in a concentration-dependent manner. In addition, norathyriol inhibited PMA- but enhanced formylmethionyl-leucyl-phenylalanine (fMLP)-induced neutrophil aggregation. Norathyriol suppressed neutrophil cytosolic protein kinase C as well as rat brain protein kinase C over the same range of concentrations at which it inhibited the respiratory burst. Norathyriol did not affect [3H]phorbol 12,13-dibutyrate ([3H]PDB) binding to neutrophil cytosolic protein kinase C, but effectively attenuated trypsin-treated rat brain protein kinase C activity. Moreover, norathyriol was found to be a noncompetitive inhibitor with respect to ATP and peptide substrate (N-terminal acetylated, amino acid sequence 4-14 of the myelin basic protein, Ac-MBP-(4-14)). Unlike staurosporine, norathyriol did not affect porcine heart protein kinase A activity. On the immunoblot analysis of protein kinase C subcellular distribution, the PMA-induced translocation of protein kinase C-beta from the cytosol to the membrane was not affected by norathyriol. These results show that the inhibition by a plant product, norathyriol, of PMA-induced respiratory burst and aggregation is, at least partly, attributed to the direct suppression of protein kinase C activity through blockade of the catalytic region, but is not due to interference with the membrane translocation of protein kinase C during PMA-induced cell activation.

Cytosolic phospholipase A2 and its mode of activation in human neutrophils by opsonized zymosan. Correlation between 42/44 kDa mitogen-activated protein kinase, cytosolic phospholipase A2 and NADPH oxidase

The role of cytosolic phospholipase A2 (cPLA2) and its mode of activation by opsonized zymosan (OZ) was studied in human neutrophils in comparison with activation by PMA. The activation of cPLA2 by 1 mg/ml OZ or 50 ng/ml PMA is evidenced by its translocation to the membrane fractions on stimulation. This translocation is consistent with dithiothreitol (DTT)-resistant phospholipase A2 (PLA2) activity detected in the membranes of activated cells. Neutrophils stimulated by either OZ or PMA exhibited an immediate stimulation of extracellular-signal-regulated kinases (ERKs). The inhibition of ERKs, DTT-resistant PLA2 and NADPH oxidase activities by the MAP kinase kinase inhibitor PD-98059 indicates that ERKs mediate the activation of cPLA2 and NADPH oxidase stimulated by either OZ or PMA. The protein kinase C (PKC) inhibitor GF-109203X inhibited epidermal growth factor receptor peptide kinase activity, the release of [3H]arachidonic acid, DTT-resistant PLA2 activity and superoxide generation induced by PMA, but did not inhibit any of these activities induced by OZ. PKC activity was similarly inhibited by GF-109203X in membrane fractions separated from neutrophils stimulated by either PMA or OZ. In the presence of the tyrosine kinase inhibit orgenistein, ERKs, PLA2 and NADPH oxidase activities were inhibited in cells stimulated by OZ, whereas they were hardly affected in cells stimulated by PMA. The results suggest that the activation of cPLA2 by PMA or OZ is mediated by ERKs. Whereas PMA stimulates ERKs activity through a PKC-dependent pathway, signal transduction stimulated by OZ involves tyrosine kinase activity leading to activation of ERKs via a PKC-independent pathway.

Phosphatidic acid-mediated phosphorylation of the NADPH oxidase component p47-phox. Evidence that phosphatidic acid may activate a novel protein kinase

Phosphatidic acid (PA), generated by phospholipase D activation, has been linked to the activation of the neutrophil respiratory burst enzyme, NADPH oxidase; however, the intracellular enzyme targets for PA remain unclear. We have recently shown (McPhail, L. C., Qualliotine-Mann, D., and Waite, K. A. (1995) Proc. Natl. Acad. Sci. U. S. A. 92, 7931-7935) that a PA-activated protein kinase is involved in the activation of NADPH oxidase in a cell-free system. This protein kinase phosphorylates numerous endogenous proteins, including p47-phox, a component of the NADPH oxidase complex. Phospholipids other than PA were less effective at inducing endogenous protein phosphorylation. Several of these endogenous substrates were also phosphorylated during stimulation of intact cells by opsonized zymosan, an agonist that induces phospholipase D activation. We sought to identify the PA-activated protein kinase that phosphorylates p47-phox. The PA-dependent protein kinase was shown to be cytosolic. cis-Unsaturated fatty acids were poor inducers of protein kinase activity, suggesting that the PA-activated protein kinase is not a fatty acid-regulated protein kinase (e.g. protein kinase N). Chromatographic techniques separated the PA-activated protein kinase from a number of other protein kinases known to be activated by PA or to phosphorylate p47-phox. These included isoforms of protein kinase C, p21 (Cdc42/Rac)-activated protein kinase, and mitogen-activated protein kinase. Gel filtration chromatography indicated that the protein kinase has an apparent molecular size of 125 kDa. Screening of cytosolic fractions from several cell types and rat brain suggested the enzyme has widespread cell and tissue distribution. The partially purified protein kinase was sensitive to the same protein kinase inhibitors that diminished NADPH oxidase activation and was independent of guanosine 5'-3-O-(thio)triphosphate and Ca2+. Phosphoamino acid analysis showed that serine and tyrosine residues were phosphorylated on p47-phox by this kinase(s). These data indicate that one or more potentially novel protein kinases are targets for PA in neutrophils and other cell types. Furthermore, a PA-activated protein kinase is likely to be an important regulator of the neutrophil respiratory burst by phosphorylation of the NADPH oxidase component p47-phox.

Translocation of protein kinase C isoforms in rat neutrophils

In this study, we examined the protein kinase C (PKC) isoforms present in cytosol and membrane fractions of rat neutrophils by Western blotting analysis with monoclonal antibodies against PKC isoforms and demonstrated that rat neutrophils express at least three conventional PKCs (cPKC), alpha, beta and gamma, four novel PKCs (nPKC), delta, epsilon, theta and mu, and three atypical PKCs (aPKC), iota, lambda and zeta, although PKC lambda and zeta were barely detected. Cells stimulated with phorbol 12-myristate 13-acetate (PMA) induce a sustained and marked translocation of cPKC and nPKC from the cytosol to particulate fraction. A concentration-dependence of PMA on the membrane translocation of PKC isoforms was observed. Treatment with formyl-Met-Leu-Phe (fMLP), in contrast with PMA, caused a transient and less prominent association of cPKC and nPKC with particulate fraction. However, the distribution of PKC iota isoform was affected neither by fMLP nor by PMA. These data indicate that the rat neutrophils contain PKCs of three isoform families and the membrane translocation of cPKC and nPKC was observed in cells in response to PMA as well as to fMLP.

Chemotactic peptide N-formyl-met-leu-phe activation of p38 mitogen-activated protein kinase (MAPK) and MAPK-activated protein kinase-2 in human neutrophils

Activation of polymorphonuclear leukocytes (PMN) by chemotactic peptides initiates a series of functional responses that serve to eliminate pathogens. The intermediate steps that link engagement of the chemoattractant receptor to the microbicidal responses involve protein kinases that have yet to be identified. In this study we detected in human PMN the presence of p38 mitogen-activated protein kinase (MAPK), which became rapidly tyrosine phosphorylated and activated in response to the chemotactic peptide N-formyl-methionyl-leucyl-phenylalanine (fMLP). Pretreatment of PMN with wortmannin, a phosphatidylinositol 3-kinase inhibitor, or bis-indolylmaleimide, a protein kinase C antagonist, resulted in partial inhibition of p38 phosphorylation upon fMLP stimulation. Similarly, phosphorylation of p38 was only partially inhibited when the fMLP-induced cytosolic calcium transient was prevented. Stimulation of PMN by the chemoattractant also resulted in the rapid phosphorylation and activation of MAPK-activated protein kinase-2 (MAPKAPK-2), which was completely inhibited by the specific p38 inhibitor, SB203580. The physical interaction of p38 with MAPKAPK-2 was studied by coimmunoprecipitation. These two kinases were found to be associated in unstimulated PMN but dissociated upon activation of the cells by fMLP. Together these findings demonstrate the activation of p38 by chemotactic peptides in human PMN by a process involving phosphatidylinositol 3-kinase, protein kinase C, and calcium. p38, in turn, is an upstream activator of MAPKAPK-2.

Stimulation of protein kinase C redistribution and inhibition of leukotriene B4-induced inositol 1,4,5-trisphosphate generation in human neutrophils by lipoxin A4

1. To test the hypothesis that protein kinase C (PKC) is involved in the inhibitory actions of lipoxin A4 (LXA4) on second messenger generation, we studied the effects of LXA4 on PKC in human neutrophils and on leukotriene B4 (LTB4)-stimulated inositol-1,4,5-trisphosphate (Ins(1,4,5)P3) generation. 2. LXA4, 1 microM, caused a fall in cytosolic PKC-dependent histone phosphorylating activity to 23.5% of basal levels. 3. LXA4, caused an increase in particulate PKC-dependent histone phosphorylating activity with a bell-shaped dose-response fashion; maximal stimulation was observed at 10 nM LXA4. 4. Western blot analysis with affinity-purified antibodies to alpha- and beta-PKC showed that only the beta-PKC isotype was translocated by LXA4. 5. LXA4 inhibited LTB4-stimulated Ins(1,4,5)P3 generation in a bell-shaped fashion with maximal inhibition at 1 nM LXA4. The observed inhibition was dose-dependently removed by pre-incubation with a PKC inhibitor (Ro-31-8220). 6. These results show that LXA4 activates PKC in whole cells and supports a role for PKC activation in the inhibitory action of LXA4 on LTB4-induced Ins(1,4,5)P3 generation. 7. LXA4 (1-1000 nM) pre-incubation did not affect specific binding of [3H]-LTB4 to neutrophils. Thus, the inhibitory effect of LXA4 on LTB4-stimulated Ins(1,4,5)P3 generation could not be attributed to an effect on LTB4 receptors.

Interferon-gamma affects protein kinase C activity in human neutrophils

Interferon-gamma (IFN-gamma) is a priming agent of polymorphonuclear neutrophilic granulocyte (PMN) oxygen metabolism, and protein kinase C (PKC) is traditionally believed to play a central role in activation of this oxygen metabolism. In the present study, we have shown that the PKC activity in PMN is affected by IFN-gamma. After only 2 minutes exposure to IFN-gamma (100 U/ml), PKC activity was significantly increased in the noncytosolic fraction of the cells. This increase was transient, but toward the end of the priming period of 2 h, the membrane-associated PKC activity increased again to about 152% of control. In the cytosolic fraction, a small and hardly detectable decrease in PKC activity was observed. Treatment of PMN with granulocyte-macrophage colony-stimulating factor (GM-CSF), another PMN priming agent, showed no significant effects on the PKC activity. When the cells were stimulated with the bacterial peptide fMLP after a priming period with IFN-gamma or GM-CSF for 2 h, no significant difference between treated and control cells could be observed. PMN oxygen metabolism, measured by flow cytometry as an accumulation of the fluorescent compound dichlorofluorescein, was in these experiments significantly primed by IFN-gamma, both at baseline and when stimulated with fMLP. The protein kinase C inhibitors H7 and Ro31-8220 blocked the fMLP responses to some extent, but not completely. However, no significant difference between fMLP responses in control and IFN-gamma-treated cells could be detected after administration of inhibitors.(ABSTRACT TRUNCATED AT 250 WORDS)

Protein kinase C isoforms in muscle cells and their regulation by phorbol ester and calpain

Objectives were to identify the PKC isoforms in cultured muscle cells, to examine roles of Ca(2+)-dependent proteinases (calpains) in processing of various muscle PKC isozymes and to obtain a mechanistic description of the processing of PKCs by examining the temporal relationships between phorbol ester-dependent translocation of muscle PKCs and calpains between cytosolic and membrane compartments. Using six isoform (alpha, beta, gamma, delta, epsilon, zeta)-specific polyclonal antibodies, PKC alpha, delta and zeta were detected in rat skeletal muscle and in L8 myoblasts and myotubes. PKC alpha and zeta were primarily localized in the cytosolic fraction of L8 myotubes whereas PKC delta was more abundant in the membrane fraction. Phorbol ester (TPA) caused rapid depletion of myotube PKC alpha and PKC alpha and PKC delta isoforms from the cytosolic compartment and rapid appearance of these isoforms in the membrane fraction. However, long-term exposure of myotubes to TPA eventually caused down-regulation of PKCs in the membrane compartment. Down-regulation of PKCs in the membrane fraction was partially blocked by calpain inhibitor II. However, the rapid TPA-dependent cytosolic depletion of PKCs was unaffected by calpain inhibitor. This suggests that calpains may be responsible for membrane-associated down-regulation of PKCs but not for cytosolic depletion. In the final study we assessed the effects of phorbol ester on compartmentation of m-calpain with PKCs in muscle cells. Like the PKCs, TPA caused rapid association of m-calpain with the membrane fraction followed by down-regulation. This demonstrates that phorbol esters cause translocation of both PKCs and calpains to membranes where processing of PKCs may occur via the limited proteolysis exerted by calpains.

Immunochemical identification and translocation of protein kinase C zeta in human neutrophils

Western blots of human polymorphonuclear leukocyte (PMN) extracts were immunostained with antibodies specific for various protein kinase C (PKC) isoforms. Two bands corresponding to PKC type zeta with apparent molecular masses of 81 kDa and 76 kDa were identified in the cytosolic fraction of resting cells, in addition to PKC types alpha and beta. PKC zeta was apparently abundant, like PKC beta, whereas PKC delta, -epsilon, and -gamma were not detectable. Following short stimulation (5 min) of PMN with phorbol-12-myristate-13-acetate (1 microgram/ml), physical translocation of PKC zeta from the cytosol to the plasma membrane fraction occurred, although this isoform does not bind phorbol esters. These data show that, in addition to the two calcium-dependent isoenzymes alpha and beta, human PMN express a calcium-independent isoenzyme zeta which translocates in stimulated cells, suggesting a role in the regulation of antibacterial activities.

The requirement of p47 phosphorylation for activation of NADPH oxidase by opsonized zymosan in human neutrophils

Protein kinase C (PKC) inhibitors, staurosporine or 1,5-isoquinolinesulfonyl)-2-methylpiperazine (H7), inhibited NADPH oxidase activity and phosphorylation of 47 kDa protein (p47) in PMA-stimulated neutrophils in a dose-dependent manner. These PKC inhibitors, at the same doses, did not affect oxidase activity and caused only partial inhibition of p47 phosphorylation in OZ-stimulated neutrophils. There was residual (20%) phosphorylated p47 in the membranes of OZ-stimulated cells in the presence of PKC inhibitors, at concentrations which caused total inhibition of oxidase activity and p47 phosphorylation in PMA-stimulated neutrophils. In the presence of ionomycin, which increased intracellular calcium ion concentrations, staurosporine was less effective in inhibiting both superoxide generation and p47 phosphorylation stimulated by PMA, similar to its effect in OZ-stimulated cells. The results indicate that some phosphorylation of p47 always accompanied oxidase activation induced by PMA or OZ, though the degree of phosphorylation of membrane-bound p47 does not directly correlate with rates of superoxide production.

Neutrophil chemotaxis induced by the diacylglycerol kinase inhibitor R59022

The diacylglycerol kinase inhibitor R59022 induced chemotaxis in neutrophils. The response to R59022 was primarily chemotactic and only very little chemokinetic. Pretreatment with the protein kinase C inhibitors staurosporine and AMG-C16 inhibited chemotaxis induced by R59022 indicating the involvement of protein kinase C. In contrast, chemotaxis induced by fMet-Leu-Phe was only slightly inhibited by staurosporine and AMG16. The effects of R59022 were comparable to the effects of the protein kinase C activators DiC8 and PMA and suggest an involvement of protein kinase C. Pretreatment with pertussis toxin inhibited R59022-induced migration, fMet-Leu-Phe-induced migration, and random migration. GTP gamma S, which stimulates migration of electropermeabilized neutrophils by itself, causes an additive increase of migration in electropermeabilized neutrophils stimulated with a suboptimal concentration R59022, but causes a synergistic increase of migration in cells stimulated with a suboptimal concentration fMet-Leu-Phe. The effects of GTP gamma S on migration are completely inhibited by AMG-C16. This suggests that the GTP-binding protein involved in R59022-activated migration is the G protein that is associated with random migration.