Differential mechanisms of translocation of protein kinase C to plasma membranes in activated human neutrophils

Protein Kinase C-α Is a Gatekeeper of Cryptosporidium Sporozoite Adherence and Invasion

Cryptosporidium infection is a leading cause of diarrhea-associated morbidity and mortality in young children globally. Single nucleotide polymorphisms (SNPs) in the human protein kinase C-α (PRKCA) gene region have been associated with susceptibility to cryptosporidiosis. Here, we examined the role of protein kinase C-α (PKCα) activity in human HCT-8 intestinal epithelial cells during infection with Cryptosporidium parvum sporozoites. To delineate the role of PKCα in infection, we developed a fluorescence-based imaging assay to differentiate adherent from intracellular parasites. We tested pharmacological agonists and antagonists of PKCα and measured the effect on C. parvum sporozoite adherence to and invasion of HCT-8 cells. We demonstrate that both PKCα agonists and antagonists significantly alter parasite adherence and invasion in vitro. We found that HCT-8 cell PKCα is activated by C. parvum infection. Our findings suggest intestinal epithelial cell PKCα as a potential host-directed therapeutic target for cryptosporidiosis and implicate PKCα activity as a mediator of parasite adherence and invasion.

Formylpeptides trigger selective molecular pathways that are required in the physiological functions of human neutrophils

For-Met-Delta(z)Leu-Phe-OMe ([Delta(z)Leu(2)]) is a conformationally restricted for-Met-Leu-Phe-OMe (fMLP-OMe) analogue able to discriminate between different responses of human neutrophils. In contrast, [Delta(z)Leu(2)] significantly activates the transduction pathways-involving Ca(2+), inositol phosphate, and cyclic AMP (cAMP) enhancement, as is the case with the full agonist fMLP-OMe. Here, we have studied the specific involvement of protein kinase C (PKC) isoforms and mitogen activated protein kinases (MAPKs) in the presence or absence of extracellular Ca(2+), being the cation clearly involved in the activation of neutrophils by fMLP. A strong correlation has been found between PKC isoforms, MAPKs and the selective physiological functions by [Delta(z)Leu(2)]-activated neutrophils. In a calcium-free condition, our data suggest that the failure of PKC beta1 translocation and of p38 MAPK phosphorylation by the analogue refers to its inability to induce chemotaxis, and that the failure by both fMLP-OMe and [Delta(z)Leu(2)] to evoke extracellular response kinase 1 and 2 (ERK1/2) phosphorylation would suggest a reduction in superoxide anion production.

The fatty acid bimodal action on superoxide anion production by human adherent monocytes under phorbol 12-myristate 13-acetate or diacylglycerol activation can be explained by the modulation of protein kinase C and p47phox translocation

We studied the translocation of protein kinase C (PKC), the endogenous phosphorylation and presence in the membrane fraction of p47phox (the 47-kDa cytosolic component of the phagocyte NADPH oxidase), and the O-.2 production in human adherent monocytes (HAMs). This was performed under phorbol myristate acetate (PMA) or diacylglycerol stimulation after cell preincubation in the presence of either 13-methyltetradecanoate or arachidonate. At 3 nM and 30 microM, both fatty acids had enhancing and depressing effects, respectively, on PKC translocation and O-.2 production strictly depending on the PMA- or diacylglycerol-stimulated state of the cell. Endogenous phosphorylation and membrane presence of p47phox were markedly reinforced in PMA-stimulated HAMs in the presence as compared to the absence of 13-methyltetradecanoate. These results emphasize the fact that in intact cells the capacity of both FAs to potentiate or depress the HAM O-.2 production is mediated by a direct action on the PKC membrane translocation leading to a simultaneous endogenous phosphorylation and membrane translocation of p47phox. They confirm the recent findings (Kadri-Hassani, N., Léger, C. L., and Descomps, B. (1995) J. Lipid Med. Cell Signal. 11, 159-173) on the PKC-mediated, adherent monocyte-specific capacity of these fatty acids and others (with the exception of linear saturated fatty acids) to enhance the PMA-stimulated O-.2 production at nanomolar concentrations and to depress it at micromolar concentrations.

Inhibition of protein kinase C of human neutrophils by phosphatidylcholines

Pulmonary surfactant phospholipids, particularly phosphatidylcholines (PCs), inhibit superoxide generation in neutrophils. The activation of neutrophils is in part dependent on protein kinase C (PKC). To investigate the mechanism of action of PCs in inhibition of neutrophil activation, we studied the effect of PCs, commonly found in pulmonary surfactant, on the distribution of PKC in intact resting and stimulated neutrophils as well as on their kinase activity in vitro. In general, in contrast to PCs with saturated fatty acyl moieties, PCs with unsaturated fatty acyl moieties inhibited PKC activity in vitro. To determine the effect of PCs on the activation of PKC in intact neutrophils, neutrophils preincubated with PCs for 2 hours were stimulated by 1,2-sn-dioctanoylglycerol (diC8) or 4-beta-phorbol 12-beta-myristate 13-alpha-acetate (PMA). The cytosolic PKC activity did not change in cells preincubated with PCs after stimulation with diC8 (3.76 +/- 0.83 units vs 3.90 +/- 1.48 units), as would be expected in control cells (3.06 +/- 0.41 units to 1.01 +/- 0.29 units). In contrast to diC8, PMA-induced translocation of PKC to the membrane was unaffected by PCs. These data suggest that specific PCs not only inhibit neutrophil PKC in vitro but can also affect its translocation in response to stimulation by diacylglycerol in intact neutrophils.

Airway eosinophils from actively sensitized guinea pigs exhibit enhanced superoxide anion release in response to antigen challenge

Antigen challenge of actively sensitized guinea pigs produces airway eosinophilia, airway hyperreactivity, and late-phase bronchoconstriction. The recruited eosinophils are thought to be important cells in the development of the airway hyperreactivity and the late-phase bronchoconstriction. However, the functional abilities of these eosinophils have not been determined in response to antigen challenge. The purpose of this study was to describe the characteristics of superoxide anion release from airway eosinophils obtained 24 h after ovalbumin challenge of actively sensitized guinea pigs. Eosinophils were collected by bronchoalveolar lavage. The total bronchoalveolar lavage eosinophil count was 17- to 27-fold greater in sensitized, ovalbumin-challenged guinea pigs (9.30 +/- 0.11 x 10(6)/guinea pig) than in unsensitized guinea pigs (0.35 +/- 0.07 x 10(6)/guinea pig) or sensitized, saline-challenged guinea pigs (0.56 x 10(6)/guinea pig; n = 2). The increase in eosinophils was due to increased lavage leukocyte count and increased eosinophil differential. Eosinophils were isolated on a Percoll-plasma discontinuous gradient. Two populations of eosinophils were collected, one at the 1.093 g/ml gradient step and one at the 1.107 g/ml gradient step. Unstimulated or phorbol myristate acetate (PMA)-stimulated superoxide anion release was measured by the reduction of ferricytochrome c. Unstimulated superoxide anion release from both eosinophil populations of challenged guinea pigs (4.50 +/- 2.37 and 4.07 +/- 1.48 nmol from 1.093 and 1.107 g/ml eosinophils, respectively) was 6- to 7-fold greater than superoxide anion release from eosinophils of control guinea pigs (0.74 +/- 0.43 and 0.56 +/- 025 nmol from 1.093 and 1.107 g/ml eosinophils, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

A comparison of the priming effect of phorbol myristate acetate and phorbol dibutyrate on fMet-Leu-Phe-induced oxidative burst in human neutrophils

Phorbol esters such as phorbol myristate acetate (PMA) and phorbol dibutyrate (PDBU) are generally considered to have similar effects through a similar mechanism, i.e. protein kinase C (PKC) activation. We recently suggested that this was not the case in human neutrophils. To identify further differences between the two phorbol esters, we compared their priming effects on fMet-Leu-Phe-induced superoxide anion (O2-) production, cytosolic PKC activity and binding of fMet-Leu-Phe. Priming could be initiated with a low (0.2 nM) concentration of both PDBU and PMA. Their effects on the pattern of fMet-Leu-Phe-induced superoxide production were similar in both Ca2(+)-containing and Ca2(+)-free medium. PDBU, like PMA, abolished the Ca2+ dependency of fMet-Leu-Phe-induced O2- production in a dose-dependent manner. In cytochalasin B-treated cells and in the presence of Ca2+, priming with PDBU or PMA did not alter the enhancing effect of cytochalasin B on fMet-Leu-Phe-induced O2- production. In Ca2(+)-free medium, priming abolished the Ca2+ dependency of fMet-Leu-Phe stimulation in cytochalasin B-treated cells. Cytochalasin B, however, enhanced the effect of PMA but not that of PDBU. Priming with PDBU was not associated under any experimental conditions with a decrease in cytosolic PKC activity, or an increase in PKM activity before or after fMet-Leu-Phe stimulation. Furthermore, priming effects were abolished by cell washing but not by H-7 or staurosporine, which are potent PKC inhibitors. PDBU, in contrast to PMA, increased fMet-Leu-Phe binding to PMNs through a decrease in the dissociation constant and induced degranulation of specific granules as measured by the release of vitamin B12 binding protein. These findings show that the priming effects of PDBU differ in certain respects from those of PMA, namely with regard to its synergism with cytochalasin B and the expression of fMet-Leu-Phe receptors. In addition, priming concentrations of PDBU, like PMA, did not alter cytosolic PKC activity in fMet-Leu-Phe-stimulated neutrophils.

Inhibition of NADPH oxidase by aminoacyl chloromethane protease inhibitors in phorbol-ester-stimulated human neutrophils: a reinvestigation. Are proteases really involved in the activation process?

Superoxide anion production by polymorphonuclear leukocytes stimulated with phorbol 12-myristate 13-acetate is known to be inhibited by a number of inhibitors and substrates of serine proteases, in particular by tosylphenylalanylchloromethane (TosPheCH2Cl) and to a lesser extent by tosyllysylchloromethane (TosLysCH2Cl). We have reinvestigated the characteristics of this inhibition, in view of the fact that other serine protease inhibitors with similar specificities, phenylmethanesulfonyl fluoride and leupeptin, were without effect. We found that the inhibition of phorbol-ester-induced superoxide production after cell preincubation with the chloromethanes followed saturation kinetics, with Kinact and kinact values of 100 microM and 31 min-1 for TosPheCH2Cl and 2 mM and 18 min-1 for TosLysCh2Cl. We also showed that the two compounds, which can inhibit protein kinase C in vitro, inhibited neither its activity in vivo, nor its translocation induced by phorbol myristate acetate. Furthermore the intracellular non-protein sulfhydryl group content was not affected by the treatment with the chloromethanes. Finally, addition of the inhibitors to stimulated cells also led to a time-dependent, concentration-dependent inhibition of superoxide production. Altogether, our results suggest that the chloromethane target is neither a protease nor protein kinase C and is not involved in NADPH oxidase activation, but rather in maintenance of its activity. The possible identity of this protein is discussed.

Translocation of protein kinase C to subcellular fractions of human neutrophils

The subcellular localization of protein kinase C in unstimulated human neutrophils and neutrophils stimulated by phorbol-myristate-acetate (PMA), 1-oleoyl-2-acetyl-rac-glycerol (OAG), and ionomycin was investigated in subcellular fractions obtained by nitrogen cavitation and Percoll density gradient centrifugation. Protein kinase C was found to be localized mainly in the cytosol in unstimulated cells, whereas significant translocation to fractions containing the plasma membrane was observed after stimulation by PMA, OAG, and ionomycin. At the same time, phospholipid-insensitive protein kinase activity appeared in the cytosol and the plasma membrane fractions. To determine whether binding of protein kinase C occurred to the plasma membrane or to intracellular membranes that had translocated to the plasma membrane, we investigated the ability of isolated azurophil, specific and secretory granules, and plasma membrane vesicles to bind protein kinase C in response to addition of PMA and OAG. Only fractions containing plasma membranes and secretory granules were able to bind protein kinase C. The observation explains the selective activation of plasma membrane structures by protein kinase C.

Diacylglycerol generation and phosphoinositide turnover in human neutrophils: effects of particulate versus soluble stimuli

Serum-treated, or "opsonized" zymosan (OZ), a particulate material which can be phagocytized by polymorphonuclear leukocytes, activates the superoxide-generating respiratory burst in these cells. The use of dual wavelength spectroscopy in the present studies has allowed accurate continuous monitoring of superoxide generation (cytochrome c reduction) upon cellular activation by this turbid material; activation occurs after a short lag period (about 20 s) which is similar to the lag seen after activation with the chemoattractant formyl-methionyl-leucyl-phenylalanine (fMLP). Unlike the fMLP response which terminates after about 90 s, superoxide generation in response to OZ continues beyond 10 min, and is similar in this regard to the response seen with the protein kinase C activator phorbol myristate acetate (PMA). OZ and fMLP, but not PMA, also activate receptor-linked phospholipase C mechanisms as judged by the appearance of inositol trisphosphate (IP3) (as well as other inositol phosphates) and diacylglycerol (DAG), with the latter measured by a mass assay. The appearance of these potential mediators corresponded to the loss of phosphoinositides, in particular phosphatidylinositol 4,5-bisphosphate (PIP2). The magnitude of DAG and inositol sugar generation as well as the breakdown of PIP2 was considerably greater using OZ than with fMLP. In addition, while fMLP resulted in a transient increase in IP3 and DAG, OZ resulted in a sustained elevation of these molecules. With both agonists, the onset and duration of generation of putative mediators corresponded to the period of generation of O2-, consistent with a role for DAG and/or IP3 in the activation of the respiratory burst.

Activation of the respiratory burst oxidase in neutrophils: on the role of membrane-derived second messengers, Ca++, and protein kinase C

A major bactericidal mechanism of neutrophils involves activation of the respiratory burst oxidase to generate superoxide (O2-). The oxidase is activated rapidly, often within a minute, in response to extracellular signals such as chemoattractants, inflammatory mediators, and invading microorganisms. Increasing evidence indicates that lipases also respond rapidly, releasing potent regulatory molecules from progenitor lipids. Released molecules include potential regulators of protein kinase C--diacylglycerol (DAG), arachidonate, and sphingosine--and levels of one of these, DAG, frequently correlate with O2- production. In this author's view, the available data implicate DAG and protein kinase C as key factors in the regulation of the respiratory burst. Herein, the array of activating agonists, the generation and function of some lipid-derived mediators, and evidence pertaining to the participation of protein kinase C are reviewed.

Temperature-dependent inhibition of fmet-leu-phe-stimulated superoxide generation by C-I and H-7 in human neutrophils

Contrary to previous reports by other investigators, protein kinase inhibitors C-I and H-7 (at 10(-6)M) caused a significant inhibition of fmet-leu-phe-stimulated superoxide (O2-) generation in human neutrophils. The observed inhibition of O2- production was a highly temperature-sensitive event and occurred only when C-I or H-7 was added to neutrophils at 37 degrees C. When the temperature at which C-I or H-7 added to neutrophils was varied between 16 degrees C to 37 degrees C, no significant inhibition of fmet-leu-phe-stimulated O2- production by C-I or H-7 was observed even at 35 degrees C. However, when added at 37 degrees C, both the maximal rate and the final extent of fmet-leu-phe induced O2- production were significantly inhibited (greater than 50%) by 10(-6)M C-I or H-7. A relatively weaker protein kinase C antagonist, HA1004, was not inhibitory under identical experimental conditions. In contrast, inhibition of the PMA-induced O2- generation by C-I or H-7 was not found to be similarly temperature-dependent. These results indicate that some temperature-dependent cellular event(s) is critically involved in the observed inhibition of fmet-leu-phe-induced O2- generation by C-I or H-7, and suggest a role for protein kinase C in the signal transduction process.

Human peripheral blood and pleural fluid eosinophils can be induced by immune complexes to release IgG immune complexes and aggregated IgE

The ability of IgG and IgE immune complexes and of phorbol myristate acetate (PMA), a soluble membrane activator, to stimulate hydrogen peroxide (H2O2) release and to induce oxygen radical-mediated cytotoxic activity by human peripheral blood (PBL) eosinophils and by PBL neutrophils was evaluated in normal volunteers and patients with hypereosinophilic malignant pleural effusions due to lung cancer. PMA stimulated a significant respiratory burst. Similar results were obtained with IgG IC stimulation, although the levels of H2O2 were lower. Agg IgE induced H2O2 release only by PBL and PE eosinophils and not by neutrophils. PMA stimulation resulted in detectable cytotoxic activity. IgG IC generated both PBL and PE eosinophil and PBL neutrophil cytotoxicity. Agg IgE induced significant cellular cytotoxicity in both PBL and PE eosinophils. This study suggests that eosinophil oxidative metabolic burst and cytotoxic activity stimulated by IgG and IgE immune complexes could represent a possible mechanism of parenchymal injury in eosinophilic disorders.

Charge-dependent regulation of NADPH oxidase activities in intact and subcellular systems of polymorphonuclear leukocytes

It has been reported that respiratory bursts with N-formylmethionylleucylphenylalanine, A23187, phorbol ester and fatty acids are switched off and on by modulating the net charges of plasma membranes in guinea-pig neutrophils (Miyahara, M. et al. (1987), Biochim. Biophys. Acta, 929, 253-262). In the present study, this was further extended in cells treated with protein kinase C inhibitors which completely suppressed the phorbol ester-dependent respiratory burst. This suggested that the initiation of the respiratory burst, which is generally accepted as linked to protein kinase C activation, might also be implicated in the net charge changes of plasma membranes. The above results were also supported by data obtained with a cell-free system reconstituted with plasma membranes and cytosolic fractions from unstimulated neutrophils, guanosine 5'-[gamma-thio]triphosphate and NADPH. Arachidonate stimulated NADPH oxidase activity accompanied by a marked phosphorylation of membrane proteins. The phosphorylation was sensitive to H-7, but it did not appear to be essential for the respiratory burst, because the oxidase activation was insensitive to H-7. Pretreating the plasma membranes with positively charged cetylamine inhibited the oxidase activation by arachidonate. These results suggest that a charge-dependent process, which does not use protein kinase C, may play an important role in the reaction leading to NADPH oxidase activation, and this may be related to the interaction of plasma membranes with the cytosolic activation factor.

Schistosoma mansoni: evidence for protein kinase-C-like modulation of muscle activity

The phorbol esters, phorbol-12,13-dibutyrate, phorbol-12-myristate-13-acetate, phorbol-12,13-didecanoate, and phorbol-12,13-diacetate, as well as mezerin at concentrations as low as 10 nM produce a spastic paralysis of the schistosome musculature. The action of these protein kinase-C activators is dependent on the sites of esterification and is stereo-specific since phorbol-13,20-diacetate, phorbol-12,13,20-triacetate, 20-oxo, 20-deoxy-beta-phorbol-12,13-dibutyrate, alpha-phorbol-12,13-didecanoate, and alpha-phorbol are inactive. A phospholipid and phorbol ester-dependent protein kinase is identified. This kinase is stimulated by all of the phorbol esters that increase muscle tone but is not stimulated by phorbol esters that do not affect muscle tone. A high affinity, stereo-specific phorbol ester receptor is identified. Dose-response curves of phorbol-12,13-dibutyrate-induced muscle tension and -stimulated kinase activity and receptor binding indicate that these responses are mediated by the same system. These results indicate that protein kinase-C-like enzyme may play an important role in modulating activity of the schistosome musculature.

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.

Human neutrophil protein kinase C: calcium-induced changes in the solubility of the enzyme do not always correlate with enzymatic activity

We hypothesized that calcium and 1,2-diacylglycerols stimulated human neutrophil (PMN) protein kinase C (EC 2.7.1.37) in a two-step mechanism. The proposed mechanism entails (1) increased insoluble protein kinase C activity and (2) endogenous protein phosphorylation, events which have not been biochemically dissociated. PMN which were treated with 100 nM ionomycin shifted protein kinase C activity from being mostly soluble to insoluble. Concentrations of ionomycin greater than 300 nM stimulated a doubling of total cellular (soluble + insoluble) protein kinase activity and stimulated increased endogenous phosphorylation of PMN proteins. Intracellular calcium (measured with fura-2) increased from 65 nM (basal) to 680 nM using 500 nM ionomycin; calcium increases were dose-dependent. The anti-inflammatory agents acetylsalicylic acid and sodium salicylate (but not ibuprophen, indomethacin or acetaminophen) inhibited ionomycin-induced protein kinase C activation and protein phosphorylation in a dose-dependent manner by inhibiting the production of diacylglycerols. 1-Oleoyl-2-acetylglycerol reversed the inhibitory effect of salicylates. In contrast to the effect of acetylsalicylates on protein kinase C functional activity the distribution of phorbol receptors was unaffected in acetylsalicylate-treated, ionomycin-stimulated PMN using a phorbol-binding assay. Our results show that ionomycin increased intracellular diacylglycerol levels 3.5-fold over those present in control PMN, while acetylsalicylate decreased diacylglycerol production in ionomycin-stimulated PMN below baseline values. These results support the hypothesis that increased intracellular calcium activated protein kinase C leading to protein phosphorylation in two distinct dissociable events: (1) increased intracellular calcium; and (2) increased 1,2-diacylglycerol levels.

Phorbol ester prevents the thyroid-stimulating-hormone-induced but not the forskolin-induced decrease of cAMP-dependent protein kinase activity in thyroid cell cultures

The potent tumor promoter 12-O-tetradecanoyl-phorbol 13-acetate (TPA) affects several thyroid cell functions and interacts with thyroid-stimulating hormone (TSH) either by inhibiting or potentiating its action on different cellular parameters. Since phorbol ester acts mainly through the activation of protein kinase C, which is its receptor, we studied this activation and its interaction with TSH and forskolin in suspension cultures of porcine thyroid cells. In thyroid cell cultures, TPA has a dual effect on protein kinase C activity: immediately (2-5 min) after exposure of cells to TPA, it began to be translocated from the cytosol to the particulate fraction. The transfer of the cytosolic enzyme was total and could occur with or without a loss of activity. The translocated enzyme still needed Ca2+ and phospholipids for its activation. The basal activity increased transiently (2-4 h) in both the cytosol and particulate fractions during translocation. The peak activity in the particulate fraction was reached 10-30 min after exposure of cells to TPA, and was followed by down-regulation of protein kinase C and almost complete disappearance of its activity. The residual activity was about 13% of control after a 2-day exposure to TPA. It was unequally distributed between cytosol (4%) and particulate fraction (9%). Prolonged exposure of cells to TPA did not affect either the activity or the subcellular distribution of the cAMP-dependent protein kinase activity. TPA interacted with TSH and prevented the decrease of this activity induced by prolonged exposure of cells to the hormone not only when it was introduced simultaneously with TSH, but also when it was added 24 h after TSH. However, the forskolin-induced decrease in cAMP-dependent protein kinase activity was not prevented by the presence of TPA. TPA also affected the increases in cAMP accumulation mediated by TSH and forskolin. The TSH-induced increase was significantly stimulated by TPA after short contacts (5-15 min), while longer preincubations of cells with TPA provoked a very strong inhibition of the TSH action. However, the forskolin-induced stimulation of the cAMP accumulation was maintained and even further increased in the presence of TPA. Consequently, the actions of TSH and TPA are apparently interdependent, while those of forskolin and TPA seem to be parallel and independent. Neither TSH nor forskolin prevented the TPA-induced down regulation of protein kinase C. The biologically inactive phorbol ester analogue 4 alpha-phorbol 12,13-didecanoate had no effect on protein kinase C activity, and did not interact with either TSH or forskolin.(ABSTRACT TRUNCATED AT 400 WORDS)

Phosphorylation of the neuronal protein kinase C substrate B-50: in vitro assay conditions alter sensitivity to ACTH

We have explored the hypothesis that changes in the in vitro assay conditions alter both the extent of endogenous phosphorylation of B-50 protein in synaptosomal plasma membrane (SPM) and also the ability of the neuropeptide, ACTH-(1-24) to inhibit the phosphorylation of this protein. B-50 phosphorylation is influenced by preincubation, pH and ionic strength. ACTH-(1-24)-induced inhibition of B-50 phosphorylation varies with ionic strength and SPM protein concentration. Reduction of the buffer ionic strength and the SPM protein concentration enhances the ability of ACTH-(1-24) to inhibit B-50 phosphorylation. Furthermore, loss of ACTH-(1-24) by adsorption to plastic pipettes and test tubes reduces the peptide concentration in the assay. Addition of a low concentration of bovine serum albumin (BSA) essentially eliminates this loss without affecting the extent of phosphate incorporation into B-50. These data provide an explanation for the relatively high (and variable) IC50 values for ACTH-(1-24)-induced inhibition of B-50 phosphorylation reported in the literature. Further, these data suggest that in vitro assay conditions must be carefully investigated before modulation of protein phosphorylation can adequately be studied.

5-Hydroxyeicosatetraenoate promotes Ca2+ and protein kinase C mobilization in neutrophils

5-Hydroxyeicosatetraenoate (5-HETE) stimulated human neutrophils to elevate their cytosolic Ca2+. It also enhanced the actions of phorbol myristate acetate and a diacylglycerol in stimulating these cells to: a) translocate protein kinase C from cytosol to membranes; b) generate superoxide anion; and c) release granule-bound enzymes. 5,20-DiHETE and 15-HETE possessed little or none of these bioactions. 5-HETE may influence neutrophil function by elevating cytosolic Ca2+ and thereby promoting the mobilization of protein kinase C.

Immunocytochemical localization of protein kinase C in resting and activated human neutrophils

An immunocytochemical method was used to determine possible changes in the subcellular distribution of protein kinase C (PKC) in human neutrophils in response to opsonized latex beads and zymosan. While in resting cells most of the PKC immunoreactivity was localized in the cytoplasm, a redistribution of PKC to the plasma and phagosomal membranes was observed in cells treated with latex beads or zymosan for 5-20 min, suggesting a participation of PKC in endocytosis.

Charge-dependent regulation of NADPH oxidase activity in guinea-pig polymorphonuclear leukocytes

The mechanism of respiratory burst was studied by modulating membrane surfaces with lipophilic ions in guinea-pig polymorphonuclear leukocytes and their subcellular membranes. Positively charged alkylamines in concentration ranges of 0.5 to 15 microM (ED50 values) inhibited the O2- generation with phorbol 12-myristate 13-acetate, N-formylmethionylleucylphenylalanine, A23187, myristate and arachidonate in intact cells, and the inhibition was relieved by negatively charged agents. A similar molecular size of alkylalcohols had no effects. A similar charge-dependent O2- generation was also observed with fatty acids in subcellular membrane fractions prepared from unstimulated control cells, and this was insensitive to H-7 and W-7. These results suggest that triggering of NADPH oxidase activation involves a reaction(s) that is regulated by membrane charges.

Insulin but not phorbol ester treatment increases phosphorylation of vinculin by protein kinase C in BC3H-1 myocytes

Insulin was found to increase protein kinase C activity in BC3H-1 myocytes as determined by in vitro phosphorylation of both a lysine-rich histone fraction (histone III-S) and vinculin. TPA treatment for 20 min or 18 h provoked an apparent loss of histone-directed but not vinculin-directed phosphorylation by cytosolic C-kinase. Thus, chronic TPA-induced 'desensitization' or 'depletion' of cellular protein kinase C is more apparent than real, and is not a valid means for evaluating the role of C-kinase in hormone action.

Rapid microassay for protein kinase C translocation in Swiss 3T3 cells

The Ca2+/phosphatidylserine-stimulated protein kinase C (PKC) appears to exist as interconvertible inactive, soluble and active, membrane-bound forms. Changes in the bimodal distribution of PKC induced by diacylglycerol or tumor-promoting phorbol esters have been proposed to regulate the activity of this kinase [Nishizuka, Y. (1984) Nature (London) 308, 693-698]. A rapid microassay for assessment of protein kinase C translocation between cytosol and membranes was developed. This procedure, which relied on the selective digitonin-mediated release of cytoplasmic proteins, eliminated potential homogenization and fractionation artifacts. PKC activity toward histone H1 was determined after limited trypsinolysis, which abolished the Ca2+/phospholipid requirement of the enzyme and prevented interference by inhibitory proteins. Complete translocation of PKC to the membrane fraction and subsequent down-regulation of the kinase in response to 12-O-tetradecanoylphorbol-13-acetate treatment of Swiss 3T3 cells could be demonstrated by this method. Platelet-derived growth factor, insulin-like growth factor 1, vasopressin, and prostaglandin F2 alpha facilitated partial conversions of PKC to the membrane-bound form in quiescent 3T3 cells.

Activation of NADPH oxidase and phosphorylation of membrane proteins in human neutrophils: coordinate inhibition by a surface antigen-directed monoclonal antibody

Exposure of human neutrophils to low concentrations of phorbol myristate acetate (PMA) results, after a brief lag, in the production of superoxide anion and the phosphorylation of membrane proteins. Evidence that these responses are linked has now been obtained using a monoclonal antibody directed against an undefined macrophage surface antigen. The addition of this antibody, which recognizes a 90 kDa neutrophil membrane protein, caused dose-dependent delays in the onset of both phosphorylation of neutrophil membrane proteins and in the appearance of superoxide anion, following addition of PMA to the cell suspensions. For each response the lag period increased with increasing concentrations of antibody, but the onset of phosphorylation always preceded by a few minutes the initial appearance of superoxide anion.

Phosphorylation of proteins in human neutrophils activated with phorbol myristate acetate or with chemotactic factor

In human neutrophils stimulated with phorbol myristate acetate (PMA) or with the chemotactic factor N-formyl-methionyl-leucyl-phenylalanine (fMLF) a number of proteins are phosphorylated, including proteins recovered in the membrane fraction corresponding to molecular masses of 130, 78, 46, 40, and 34 kDa and proteins recovered in the cytosol fraction corresponding to molecular masses of 65, 55, 48, 38, 36, 30, and 22 kDa. Phosphorylation of the membrane proteins was fourfold greater in cells stimulated with PMA, as compared to cells stimulated with fMLF, whereas both activators induced similar phosphorylation of proteins recovered in the cytosol fraction. Phosphorylation of membrane proteins appeared to be mediated by native protein kinase C (PKC) translocated from the cytosol to the plasma membrane. Thus phosphate incorporation was inhibited by retinal and a similar pattern of incorporation was reproduced in a reconstituted system composed of isolated cell membranes and purified PKC. Phosphorylation of cytosol proteins, on the other hand, appeared to be mediated by the proteolytically modified form of PKC. In this case, phosphate incorporation was inhibited by leupeptin, which prevents the conversion of native PKC to the proteolytically modified form, The phosphorylation pattern was reproduced when isolated cytosol fractions were incubated with the proteolytically modified form of the enzyme but not with the native PKC. These results demonstrate that responses to stimuli such as PMA or fMLF are mediated by different forms of PKC and that the proteolytically modified form is responsible for the major responses elicited by fMLF.

Features of the translocation of protein kinase C in neutrophils stimulated with the chemotactic peptide f-Met-Leu-Phe

The effects of f-Met-Leu-Phe (fMLP) on neutrophils, i.e. elevation of the levels of cytoplasmic Ca2+ and intramembranous diacylglycerol, would be expected to be accompanied by translocation of protein kinase C (PKC) to the plasmalemma. However, fMLP-induced PKC translocation could hitherto be demonstrated only when cells were additionally treated with cytochalasin B. We show here that treatment of guinea pig neutrophils with fMLP alone does lead to a significant PKC translocation which can be inhibited by pertussis toxin. The translocation can be detected only if the incubation is terminated within 30 sec after addition of fMLP, the termination is rapid, e.g. by application of a freeze clamp-technique, and the concentration of Ca2+ chelators in the buffer used for lysing the cells is low.

Phorbol ester-induced alteration of protein kinase C catalytic properties occurs at the membrane level and is not reproduced by physiological stimuli

Potent tumor promoter TPA (1-100 nM) has previously been shown to induce a striking alteration of protein kinase C catalytic properties in target cells (C. Cochet et al., 1986, Biochem. Biophys. Res. Comm. 134, 1031-1037). This alteration contributes to the apparent loss of cellular protein kinase C, secondary to TPA treatment, when the enzyme is probed by its phospholipid-dependent histone kinase activity. This effect was observed as well when rat-1 cells were treated by other tumor promoters such as mezerein, teleocidin, aplysiatoxin and palytoxin, whereas inactive phorbol ester structures were ineffective. On the other hand, 1,2-dioctanoyl glycerol did not induce that effect. This protein kinase C alteration was shown to occur at the cellular membrane level. It is suggested that membrane translocation and activation of protein kinase C induced by potent tumor promoter structures are not functionally equivalent to that secondary to physiological stimuli. Although the mechanisms underlying this phenomenon remains to be understood at the molecular level, it may be of significance in the process of tumor promotion.