Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:2.7.11.13 (protein kinase C)
 49,245 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Serotonin 5-HT1A receptors have been reported to be negatively coupled to muscarinic receptor-stimulated phosphoinositide turnover in the rat hippocampus. In the present study, we have investigated further the pharmacological specificity of this negative control and attempted to elucidate the mechanism whereby 5-HT1A receptor activation inhibits the carbachol-stimulated phosphoinositide response in immature or adult rat hippocampal slices. Various 5-HT1A receptor agonists were found to inhibit carbachol (10 microM)-stimulated formation of total inositol phosphates in immature rat hippocampal slices with the following rank order of potency (IC50 values in nM): 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (11) greater than ipsapirone (20) greater than gepirone (120) greater than RU 24969 (140) greater than buspirone (560) greater than 1-(m-trifluoromethylphenyl)piperazine (1,500) greater than methysergide (5,644); selective 5-HT1B, 5-HT2, and 5-HT3 receptor agonists were inactive. The potency of the 5-HT1A receptor agonists investigated as inhibitors of the carbachol response was well correlated (r = 0.92) with their potency as inhibitors of the forskolin-stimulated adenylate cyclase in guinea pig hippocampal membranes. 8-OH-DPAT (10 microM) fully inhibited the carbachol-stimulated formation of inositol di-, tris-, and tetrakisphosphate but only partially antagonized (-40%) inositol monophosphate production. The effect of 8-OH-DPAT on carbachol-stimulated phosphoinositide turnover was not prevented by addition of tetrodotoxin (1 microM), by prior destruction of serotonergic afferents, by experimental manipulations causing an increase in cyclic AMP levels (addition of 10 microM forskolin), or by changes in membrane potential (increase in K+ concentration or addition of tetraethylammonium). Prior intrahippocampal injection of pertussis toxin also failed to alter the ability of 8-OH-DPAT to inhibit the carbachol response. Carbachol-stimulated phosphoinositide turnover in immature rat hippocampal slices was inhibited by the protein kinase C activators phorbol 12-myristate 13-acetate (10 microM) and arachidonic acid (100 microM). Moreover, the inhibitory effect of 8-OH-DPAT on the carbachol response was blocked by 10 microM quinacrine (a phospholipase A2 inhibitor) but not by BW 755C (100 microM), a cyclooxygenase and lipoxygenase inhibitor. These results collectively suggest that 5-HT1A receptor activation inhibits carbachol-stimulated phosphoinositide turnover by stimulating a phospholipase A2 coupled to 5-HT1A receptors, leading to arachidonic acid release. Arachidonic acid could in turn activate a gamma-protein kinase C with as a consequence an inhibition of carbachol-stimulated phosphoinositide turnover. This inhibition may be the consequence of a phospholipase C phosphorylation and/or a direct effect on the muscarinic receptor.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Potential mechanisms involved in the negative coupling between serotonin 5-HT1A receptors and carbachol-stimulated phosphoinositide turnover in the rat hippocampus. 184 78

There is substantial evidence that the tumor promoter 4 beta-12-O-tetradecanoylphorbol-13-acetate (TPA) elicits enhanced arachidonic acid release and its metabolism to prostaglandins and lipoxygenase products in many cell types. The goal of this study was to determine whether 4 alpha-12-O-tetradecanoylphorbol-13-acetate (4 alpha TPA), a stereoisomer of TPA, can induce arachidonic acid release and whether it is by the same mechanism as release induced by TPA. The finding that 10 micrograms/ml 4 alpha TPA produces a response comparable with 1 microgram/ml TPA and with similar kinetics was unexpected. The mechanism mediating the TPA response appears to be the activation of protein kinase C (PKC), which subsequently results in phospholipase A2 activation. This is suggested by the observation that TPA-induced arachidonate release is inhibited 65% by 1-(5-isoquinolinesulfonyl)-2-methylpiperazine dihydrochloride (H-7), an inhibitor of PKC and that TPA completely down-regulates PKC. In addition, down-regulation or depletion of PKC by prior treatment with TPA results in a 75% loss of response to a second TPA treatment. In vitro activation of partially purified PKC could be demonstrated for TPA but not 4 alpha TPA. 4 alpha TPA thus appears to induce the release of arachidonate by a different but unknown mechanism. The 4 alpha TPA effect is not significantly reduced by the PKC inhibitor H-7, and no evidence of PKC activation or down-regulation was observed. Additionally, 4 alpha TPA is unable to "down-regulate" arachidonate release when the two-treatment protocol is used and the down-regulation of PKC by TPA has little effect on 4 alpha TPA-induced arachidonate release. Cycloheximide inhibited TPA-induced arachidonate release by 80% and 4 alpha TPA-induced release by 50%, indicating a partial requirement for protein synthesis for both phorbol esters. Actinomycin D, on the other hand, inhibited the TPA response by 70%, but enhanced the 4 alpha TPA response by 169%. When used at 10- or 100-micrograms doses, 4 alpha TPA was found to lack activity with respect to ornithine decarboxylase induction, oxidant production, hyperplasia, inflammation, and tumor promotion, suggesting that arachidonate release is not sufficient to induce these events. This may be related to the observation that with TPA the extent of arachidonate metabolism to prostaglandin E2 is four- to fivefold greater than occurred with 4 alpha TPA, even under conditions of equivalent arachidonate release.
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PMID:4 Beta- and 4 alpha-12-O-tetradecanoylphorbol-13-acetate elicit arachidonate release from epidermal cells through different mechanisms. 189 47

The effect of the carcinogen diethylnitrosamine (DEN) on prostaglandins (PGs), leukotrienes (LTs) and reactive oxygen intermediates production by murine peritoneal macrophages was assessed. In vitro exposure to DEN (0.8, 1.6 and 8 mM) resulted in a dose-dependent stimulation of the PGs and LTs generation by macrophages. DEN-exposed peritoneal macrophages demonstrated enhanced production of arachidonic acid (AA) metabolites following stimulation with 12-O-tetradecanoylphorbol 13-acetate (TPA) as compared to macrophages stimulated with TPA alone. Studies of [3H]AA release from glycerolipids of prelabelled macrophages and of the distribution of AA metabolites between intra and extracellular compartments indicated that DEN induced de novo synthesis of AA metabolites. The stimulation of AA metabolism by DEN was decreased by H-7 and staurosporine, protein kinase C (PKC) inhibitors, and so could be dependent on PKC activation. The generation of PGs by macrophages after DEN exposure was also inhibited by indomethacin (cyclo-oxygenase inhibitor). DEN at high concentrations (1.6-16 mM) inhibited chemiluminescence production by peritoneal macrophages in a dose-dependent manner, triggered by tumour promoter TPA; lower concentrations (0.8 and 1.2 mM) increased this reactive oxygen intermediates dependent chemiluminescence production induced by TPA. The role of AA metabolism in the alteration of chemiluminescence production by murine peritoneal macrophages treated in vitro with DEN and triggered by TPA has been evaluated by using AA metabolism inhibitors. The stimulation of chemiluminescence by TPA was inhibited by the addition of phospholipase A2 (PLA2) inhibitor, 4-p-BPB; this metabolic inhibitor did not affect the decrease of chemiluminescence production induced by DEN. The cyclo-oxygenase (CO) inhibitor, indomethacin, reversed the inhibition of TPA-induced chemiluminescence caused by DEN. These results suggest that AA and/or a lipoxygenase product can potentiate the reactive oxygen intermediates production by macrophages stimulated by TPA. The CO pathway could be involved in the inhibition by DEN of the reactive oxygen intermediates generating enzyme system. It is suggested that this inhibition could be related to AA metabolites issued from the CO pathway or to DEN oxygenated metabolites issued from the co-oxidation of the DEN by the PGs endoperoxide synthase. These results also raise the problem of macrophage dysfunction by chemical carcinogens and the implication of the CO pathway in this process.
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PMID:Possible implication of arachidonic acid metabolism in the decrease of chemiluminescence production after exposure of murine peritoneal macrophages to diethylnitrosamine and tumour promoter, 12-O-tetradecanoylphorbol-13-acetate. 190 Dec 51

To investigate a possible regulatory role of protein kinase C (PKC) on collagen-induced phospholipase activity, human platelets were prelabelled with either [3H] arachidonic acid or [14C]stearic acid and stimulated with collagen (2 micrograms/ml) in the presence or absence of the protein kinase inhibitor, staurosporine (1 microM). The collagen-induced release of [3H]arachidonic acid and formation of [14C]stearoyl-labelled lysophospholipids was inhibited by prior incubation with staurosporine, as was the formation of 3H-labelled thromboxane B2, thereby suggesting inhibition of the collagen-induced phospholipase A2 activity. The degradation of phosphatidylinositol (PI) and elevation of phosphatidic acid (PA) in platelets prelabelled with either radiotracer were also completely blocked by staurosporine pretreatment, indicating a suppression of collagen-stimulated phospholipase C activity. Suppressed phospholipase C activity may have been due to diminished thromboxane A2 formation since treatment with the dual cyclo-oxygenase/lipoxygenase inhibitor, BW755C, also resulted in an inhibition of the collagen-stimulated loss of 14C-labelled PI and rise in PA by 75-80%. Our results suggest that protein kinase, possible PKC, may be involved in the regulation of these phospholipases in collagen-stimulated human platelets.
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PMID:Inhibition of phosphatidic acid production and lysophospholipid formation in collagen-stimulated human platelets by staurosporine, a protein kinase inhibitor. 190 94

Histologically distinct lung tumor and normal cell lines were treated with a variety of potential inhibitors of cell growth such as inducers of cell differentiation, inhibitors of protein kinase C and inhibitors of tumor promotion. The response was assessed by 3H thymidine incorporation and cloning efficiency. Both phorbol retinoate acetate and mezerein stimulated growth in lung normal cell lines (human fibroblastic PEH cells and rat epithelial TP9 cells) while inhibiting growth in lung tumor cell lines (human small-cell cancer-derived cell line IRSC-10M and adenocarcinoma-derived cell line A549). Likewise, the hydrophobic peptide melittin did not inhibit growth and cloning efficiency of normal cells at 1 microM, a concentration which prevented proliferation in tumor cells. Protein kinase C inhibitors, chlorpromazine, trifluoperazine and 1-(5 isoquinolinylsulfonyl) 2-methylpiperazine, were much more effective on proliferation of IRSC-1OM than of A549 cells. In contrast, the latter cells were more susceptible to anti-promoters such as glycyrrhetic acid, an anti-inflammatory agent, and 3,4',2', 4'-tetrahydroxychalcone or 2,3,5-trimethyl-6 (12-hydroxy-5,10-dodecadiynyl)-1,4-benzoquinone, two inhibitors of lipoxygenase, a key enzyme in arachidonate metabolism. Our results provide evidence that small-cell carcinoma-derived cells, in contrast with adenocarcinoma-derived cells, are growth-inhibited by protein kinase C inhibitors and poorly dependent on the arachidonate metabolism. This difference in responsiveness suggests that different growth signalling pathways are preferentially triggered in these histologically distinct lung tumor cell lines. As a consequence, the proper susceptibility of tumor cells to phenotype modifiers has to be taken into account in cancer therapy.
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PMID:Different susceptibility of lung cell lines to inhibitors of tumor promotion and inducers of differentiation. 191 Feb 48

Neutrophils produce reactive oxygen species (superoxide anion [O2-]) via activation of reduced nicotinamide dinucleotide phosphate oxidase. In the intact neutrophil, this enzyme can be activated by increases in cytosolic calcium, protein kinase C, and unsaturated fatty acids such as arachidonic acid, all of which are produced on stimulation by chemotactic peptides like N-formyl-methionyl-leucyl-phenylalanine. Cytokines such as granulocyte-macrophage colony-stimulating factor (GM-CSF) do not stimulate the respiratory burst but instead prime the cell for an enhanced response by an appropriate stimulus. We examined the role and potential mechanisms of free fatty acids in stimulating or priming neutrophil O2- production. Except for arachidonic acid, the ability of an unsaturated fatty acid to stimulate O2- production was not correlated with its critical micellar concentration, suggesting that detergent action was not the primary mechanism. Eicosatetraynoic acid, which blocks further arachidonate metabolism by the 5- and 15-lipoxygenases, inhibited O2- production by arachidonic acid. However, eicosatetraenoic acid did not inhibit other unsaturated fatty acid or phorbol ester-induced O2- production, suggesting that the effects of arachidonic acid were mediated at least in part by a metabolite. The same negatively charged, unsaturated fatty acids that directly stimulated O2- production when used in micromolar concentrations also primed neutrophils when added in nanomolar concentrations. The amount of a priming response was independent of chain length or number of double bonds. The magnitude of priming observed in GM-CSF-treated cells could be reconstituted with combinations of arachidonic acid and its lipoxygenase products.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Unsaturated fatty acids and lipoxygenase products regulate phagocytic NADPH oxidase activity by a nondetergent mechanism. 194 May 76

Release of eicosanoids is an important response of macrophages to inflammation and bacterial infection. At low concentrations, bacterial lipopolysaccharide (1-2 micrograms/ml) fails to stimulate eicosanoid release in resident peritoneal macrophages but primes the macrophages for a greatly enhanced release of eicosanoids on stimulation with the calcium ionophore A23187 (0.1 microM) or with phorbol 12-myristate 13-acetate (50 nM), an activator of protein kinase C. Incubation of macrophages with Bordetella pertussis toxin, prior to priming with lipopolysaccharide, inhibited the release of both cyclooxygenase and lipoxygenase products upon A23187 stimulation. Pertussis toxin treatment of macrophages had no effect on eicosanoid release when the stimulus was phorbol 12-myristate 13-acetate. The presence of 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine (H-7), an effective inhibitor of protein kinase C, during lipopolysaccharide priming and subsequent stimulation significantly inhibited eicosanoid release when phorbol 12-myristate 13-acetate was the stimulus, but did not affect eicosanoid release stimulated by A23187. Based on these results, at least two mechanisms, distinguished by apparent differences in sensitivity to pertussis-toxin-sensitive, guanine-nucleotide-binding proteins and protein kinase C, are involved in eicosanoid secretion by lipopolysaccharide-activated macrophages in response to A23187 and phorbol 12-myristate 13-acetate.
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PMID:Pertussis toxin and H-7 distinguish mechanisms involved in eicosanoid release from lipopolysaccharide-primed macrophages. Eicosanoid release from lipopolysaccharide-primed macrophages. 210 89

The induction of eicosanoid synthesis in various cell types by different physiological stimuli is dependent on an increase in the intracellular calcium level and stimulation of the protein kinase C (PKC). In a model system this can be mimicked by using calcium ionophores and direct PKC activators. In mouse peritoneal macrophages calcium ionophores induced the formation of prostaglandin E2 (PGE2) and leukotriene C4 (LTC4). A synergistic enhancement of both eicosanoids could be achieved by simultaneous addition of the calcium ionophore A23187 together with a suboptimal dose of the direct protein kinase C activator 12-O-tetradecanoylphorbol 13-acetate (TPA). Low concentrations of the ionophore, resulting in only marginally increased intracellular calcium levels, led to a more than additive prostaglandin E2 production in combination with TPA. Higher concentrations of A23187 together with TPA favoured LTC4 synthesis, whereas PGE2 levels at the same time were even diminished. This observed shift from prostaglandin to leukotriene formation was amplified by simultaneous addition of indomethacin. Manganese as inhibitor of the A23187-induced calcium influx decreased PGE2 synthesis. On the other hand, in the presence of manganese LTC4 production was also inhibited at high concentrations of A23187 but elevated in the absence or at low doses of A23187. Our data provide evidence that in macrophages the ratio of cyclooxygenase and lipoxygenase products caused by mediators, acting via the phospholipase C or D/PKC signal transduction pathway, is regulated by the extent of the intracellular calcium increase.
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PMID:The ratio of macrophage prostaglandin and leukotriene synthesis is determined by the intracellular free calcium level. 210 88

Unlike unsaturated fatty acids, which almost fully activated purified brain protein kinase C in a phosphatidylserine- and Ca2(+)-free reaction, related methyl esters were poorly active in vitro. In contrast, methyl arachidonate was revealed to be as potent as arachidonic acid in activating protein kinase C in intact platelets. Arachidonic acid-mediated activation peaked at 20 s while methyl arachidonate-mediated activation plateaued at 2 min when both lipids were added at 50 microM. At concentrations higher than 0.3 mM, all tested unsaturated fatty acids and related methyl esters were weak activators of the enzyme, with the exception of linolenic acid and methyl linolenate which evoked strong enzyme activation. However, inhibitors of arachidonate metabolism blocked both arachidonic-acid and methyl-arachidonate-induced responses. At 5 microM arachidonic acid and methyl arachidonate, protein kinase C activation was due to a cyclooxygenase product(s) whereas at 50 microM the lipoxygenase pathway was mostly involved in the reaction. Therefore, arachidonic acid and its methyl ester activate protein kinase C in platelets mainly through action of their metabolites and eicosanoid synthesis. It is suggested that such indirect protein kinase C activation may account for the tumor-promoting activity of unsaturated fatty acids and related methyl esters.
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PMID:Arachidonic acid and related methyl ester mediate protein kinase C activation in intact platelets through the arachidonate metabolism pathways. 211 10

Ebselen is a new anti-inflammatory drug with a wide spectrum of pharmacological activities. Since this compound might be useful in diseases related to airway inflammation we evaluated the effects of ebselen on the contractile responses of guinea-pig parenchymal lung strip. Ebselen and its sulfur analogue RP 62373 depressed both histamine H1-receptor-mediated and KCl-induced (50 mM) contractions of guinea-pig lung strips equipotently. The responses to histamine were only affected via depression of the maximal response; treatment with 3 microM ebselen for 30 min resulted in depression to 77 +/- 5% of the control value, whereas 10 and 30 microM inhibited the contractions to 53 +/- 4 and 52 +/- 4% of the control value respectively. The responses after membrane depolarisation (50 mM KCl) were less sensitive to ebselen pretreatment; 10 microM ebselen inhibited contractions by only 20%, whereas 30 and 100 microM depressed the response by approximately 50%. These observations were evaluated in the context of the activities of ebselen already described. The effects of lipoxygenase, cyclooxygenase, protein kinase C inhibition and thiol alkylation were studied, using established agents. However, although interaction with critical thiol groups might explain our data, the mode of action of ebselen is yet not fully elucidated.
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PMID:Ebselen inhibits contractile responses of guinea-pig parenchymal lung strips. 211 94


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