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)

The exposure of ligand-binding sites for adhesive proteins on platelet integrin alpha IIB/beta 3 (glycoprotein IIB/IIIA) by platelet-activating (PAF) is transient, whereas sites exposed by alpha-thrombin remain accessible. The same difference is seen in the phosphorylation of the beta 3 subunit. Inhibition of protein kinases (1 microM staurosporine) and protein kinase C (10 microM bisindolylmaleimide) closes binding sites exposed by both agonists and induces dephosphorylation of beta 3. Inhibition of Tyr-kinases (20 microM Herbimycin A) has only a slight effect. Inhibition of Ser/Thr-phosphatases (1 microM okadaic acid, 30 s preincubation) changes the transient exposure and beta phosphorylation by PAF into the 'permanent' patterns induced by alpha-thrombin. Inhibition of Tyr-phosphatases (100 microM vanadate) has little effect. Preincubation with okadaic acid makes exposed binding sites and phosphorylated beta 3 insensitive to staurosporine, resulting in exposed alpha IIB/beta 3 independent of concurrent phosphorylation/dephosphorylation. The stoichiometry of beta 3 phosphorylation by alpha-thrombin is 0.80+/-0.10. Thus, one of the mechanisms that regulates exposure and closure of ligand-binding sites on the alpha IIb/beta 3 is phosphorylation/dephosphorylation of a Ser/Thr-residue in the beta 3 subunit.
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PMID:Exposure of ligand-binding sites on platelet integrin alpha IIB/beta 3 by phosphorylation of the beta 3 subunit. 861 68

Taking into account their stereochemical similarity with 1-O-alkyl-2-acetyl-sn-glycerol-3-phosphorylcholine (PAF), which is known to exhibit a diverse spectrum of biological actions, including platelet aggregating and glycogenolytic activity, the acetylated derivatives of sphingosylphosphorylcholine and sphingomyelin were synthesized and tested for their ability to promote washed rabbit platelet aggregation and glycogenolysis in Tetrahymena pyriformis cells. Sphingomyelin (SPM) and sphingosylphosphorylcholine (SPC) were subjected to acetylation, following chromatographic purification and physicochemical characterization. The synthesized compounds N-acetyl, O-acetyl SPC (NAc, OAc SPC), N-acetyl SPC (NAc SPC) and O-acetyl SPM (OAc, SPM) were tested for their biological activity in the washed rabbit platelets and washed Tetrahymena pyriformis cell systems. These derivatives induced [3H]serotonin and ATP release and a monophasic aggregation of washed rabbit platelets in the concentration range 10(-8)-10(-6) M. However, authentic PAF-induced washed rabbit platelet aggregation was inhibited at higher concentrations of the acetylated sphingophospholipid compounds ( > 10(-6) M) and by the PAF-specific receptor(s) antagonists kadsurenone and triazolam. Platelet desensitization and crossed desensitization experiments with authentic PAF and the acetylated sphingophospholipids, suggested interaction with the same receptor(s) as PAF and different from the ADP or thrombin receptor. The involvement of calmodulin and protein kinase C in the biological activity of the prepared analogues was also demonstrated. Besides their action on rabbit platelets, the PAF-like activity of the acetylated sphingophospholipids was also demonstrated in a platelet-independent system, by showing that they stimulate glycogenolysis in washed Tetrahymena pyriformis cells. These observations indicate that a new class of compounds with PAF-like activity were synthesized but their role in the cellular metabolism remains to be shown. The existence of acetylated sphingophospholipids with PAF-like activity has so far been reported only in Urtica dioica.
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PMID:The biological activity of acetylated sphingosylphosphorylcholine derivatives. 862 45

We investigated the effects of proximal modulators of cytokines, tyrosine kinase (TK), and protein kinase C (PKC) on reactive oxygen species (ROS) generation and the induction of scavenging enzymes, superoxide dismutase (SOD), catalase, and glutathione peroxidase (GSH-Px) of human neutrophils and lymphocytes, by using IL1-alpha, TNF-alpha, and IFN-gamma and neutralizing antibodies to these cytokines. Inhibitors of TK (ST638 and herbimycin) or PKC (H-7, calphostin, and staurosporine) were also used. The results revealed that both (O2)- generation stimulated by five different agents (opsonized zymosan, A23187, PAF, PMA, and fMLP) and the inductions of all three scavenging enzymes were potentiated by priming with TNF-alpha. In contrast, both (O2)- generation and enzyme induction were attenuated by priming with IL1-alpha, with the exception of PMA-stimulated (O2)- generation. IFN-gamma decreased (O2)- generation but increased scavenging enzyme induction. Antibodies to all three cytokines and all the TK and PKC inhibitors decreased (O2)- stimulated by most agents, but markedly enhanced (O2)- levels stimulated by PAF. Induction of all three enzymes was enhanced equally by low concentrations of each of the three anticytokine antibodies, while each of the TK or PKC inhibitors decreased induction of SOD and GSH-Px and increased catalase induction. These results suggest that both ROS generation and scavenging enzyme induction are controlled in complex ways by the actions of these three proximal mediators. This supports our hypothesis that disturbances in the regulation of early events of cell activation can lead to oxidative tissue injury.
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PMID:Role of cytokines, tyrosine kinase, and protein kinase C on production of superoxide and induction of scavenging enzymes in human leukocytes. 863 90

The role of protein kinase C (PKC) using its selective inhibitor, chelerythrine, in agonist mediated platelet aggregation was studied. Chelerythrine had no effect on the aggregation induced by adrenaline, PAF, collagen and ADP at the maximum doses of these agonists. However, it potentiated the aggregatory response of low doses of adrenaline (0.4-1 microM). Such an effect was blocked by Ca(++)-channel blockers, verapamil and diltiazem indicating the likely involvement of Ca++ influx in the platelet aggregation during the cascade.
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PMID:Protein kinase C inhibitor, chelerythrine, potentiates the adrenaline-mediated aggregation of human platelets through calcium influx. 873 35

Human erythroid progenitor cells grown in a suspension culture system were used to study possible interactions between different guanine nucleotide-binding protein (G-protein)-coupled receptor-effector systems during normal cell differentiation. Agonist-stimulated adenylyl cyclase was not inhibited by any one of a panel of ligands (ADP, UTP, platelet-activating factor, thrombin, alpha2-adrenoceptor agonists, interleukin 8, lysophosphatidic acid) most of which are known, in other cells, to reduce cAMP formation by a Gi-mediated, pertussis toxin-sensitive mechanism. The first four of these ligands are also known to cause transient changes in intracellular [Ca2+] in erythroid cells. Rather than inhibiting, thrombin (but not ADP, UTP or PAF) specifically caused a fivefold increase in the maximum adenosine- or prostaglandin E1-stimulated cAMP formation, without any shift of the concentration/response curves. Thrombin did not enhance forskolin- and AlF4-stimulated cyclase activity and had only a marginal effect on isoprenaline-dependent stimulation. The effect of thrombin seemed to be unrelated to intracellular Ca2+ release but could be partially mimicked by phorbol ester (PMA)-induced stimulation of protein kinase C (PKC) and was inhibited by staurosporin or by inactivation of PKC after long-term incubation with PMA. The activity of thrombin was restricted to proliferating, colony-forming progenitor cells while proerythroblasts were completely unresponsive. Our results suggest that the interaction of thrombin with Gs-linked receptors requires phosphorylation of a target protein that is different from adenylyl cyclase, Gs or Gi but may be involved in the regulation of receptor desensitization.
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PMID:Crosstalk between thrombin and adenylyl cyclase-stimulating agonists in proliferating human erythroid progenitor cells. 875 Sep 12

Membrane phospholipids not only constitute structural membrane components, they also contain a wealth of biochemical information. They are the source of numerous lipid mediators (prostaglandins, leukotrienes, thromboxane, paf, lysophosphatidic acid and free fatty acids). These lipids act as second messengers inside the cell to modulate enzyme (e.g. PKC and GAP), ion channels (e.g. Ca2+ and K+) or the activity of factors regulating gene expression either at the transcriptional level (e.g. on the TNF alpha gene) or at the post-transcriptional level (e.g. on the GLUT4 transporter). The synthesis of lipid mediators results from the stimulation of phospholipase A2 (PLA2) activities. PLA2 cleaves membrane phospholipids to give rise to lysophospholipids and to free fatty acids from which second messengers are generated. More specifically, PLA2 provides the precursor for the eicosanoids, when the cleaved fatty acid is arachidonic acid, or for PAF, when the sn-1 position of the phospholipid is an alkyl ether linkage. Therefore, PLA2 is a key enzyme in the regulation of lipid mediators of inflammatory process. The purification and cloning of several PLA2s have demonstrated clear differences between secreted and intracellular PLA2. The secreted PLA2s are closely related proteins of low molecular weight (14 kDa) with calcium requirement in the mM range. They contain numerous bonds and retain the same amino-acids at the active site. In mammals, two types of secreted PLA2 have been identified: type I pancreatic PLA2 and type II inflammatory PLA2 which show 70% sequence homology. Recently, two others 14 kDa sPLA2 have been cloned which share also high homologies with type I and type II but contain respectively 6 and 8 disulpide bonds. In contrast, cellular PLA2s have higher molecular weights (40-110 kDa) and are either calcium independent or require microM amounts for activity. Cellular PLA2s preferentially act on sn-2-arachidonoyl phospholipids in vitro whereas sPLA2 do not display such selectivity in vitro. Both cellular and secreted PLA2s are involved in lipid mediator production. Cellular PLA2 can be activated by membrane receptors coupled to G proteins or by tyrosine kinase receptor, through the ras-raf1-MAP kinases network. Cellular PLA2s are thought to be involved in the initial production of lipid mediators after cell activation. Several lines of evidence suggest that secreted PLA2 is involved in the sustained production of lipid mediators in several cell types. These lines of evidence include the decrease in eicosanoid production by antibodies RNA of sPLA2. Furthermore, secreted PLA2s might trigger autocrine loops and proliferation responses through interaction with a specific receptor.
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PMID:[Diversity of phospholipases A2 and their functions]. 895 91

Sphingosine induces many protein kinase C-dependent and -independent effects on biological systems. In parallel, C2-ceramide used by investigators as an unnatural, cell permeable analog of long-chain acyl-ceramides, possesses biological activities similar with natural ceramides. We have recently characterized a membrane-associated. CoA-independent transacetylase that can transfer the acetate group from PAF to sphingosine and form C2-ceramide. This enzyme has a strict stereochemical configuration requirement for sphingosine; only the naturally-occurring D-erythro-isomers of sphingosine accepts the acetate from PAF. Also, it has a rigid substrate specificity for sphingolipid-related analogues. Dipalmitoyl-glycerophosphocholine (-GPC) or hexadecylarachidonoyl-GPC can not transfer their long-chain acyl groups directly to sphingosine and sphingosine can not be acetylated by acetyl-CoA:lyso-PAF acetyltransferase. Results obtained from studies on pH optima, subcellular distribution, temperature sensitivities, inhibitors, tissue distributions, and expression of enzyme activities in Xenopus oocytes suggest that PAF:sphingosine transacetylase is similar, but not identical to the PAF:lysophospholipid transacetylase we have previously identified. The transacetylases function to diversify the biological responses of PAF.
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PMID:Acetylation of sphingosine by PAF-dependent transacetylase. 913 Nov 36

Lipid bodies, inducible lipid-rich cytoplasmic inclusions, are characteristically abundant in cells associated with inflammation, including eosinophils. Here we reviewed the formation and function of lipid bodies in human eosinophils. We now have evidence that the formation of lipid bodies is not attributable to adverse mechanisms, but is centrally mediated by specific signal transduction pathways. Arachidonic acid and other cis fatty acids by an NSAID-inhibitable process, diglycerides, and PAF by a 5-lipoxygenase dependent pathway are potent stimulators of lipid body induction. Lipid body formation develops rapidly by processes that involve PKC, PLC, and de novo mRNA and protein synthesis. These structures clearly serve as repositories of arachidonyl-phospholipids and are more than inert depots. Specific enzymes, including cytosolic phospholipase A2, MAP kinases, lipoxygenases and cyclooxygenases, associate with lipid bodies. Lipid bodies appear to be dynamic, organelle-like structures involved in intracellular pathways of lipid mobilization and metabolism. Indeed, increases in lipid body numbers correlated with enhanced production of both lipoxygenase- and cyclooxygenase-derived eicosanoids. We hypothesize that lipid bodies are distinct inducible sites for generating eicosanoids as paracrine mediators with varied activities in inflammation. The capacity of lipid body formation to be specifically and rapidly induced in leukocytes enhances eicosanoid mediator formation, and conversely pharmacologic inhibition of lipid body induction represents a potential novel and specific target for anti-inflammatory therapy.
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PMID:Mechanisms of formation and function of eosinophil lipid bodies: inducible intracellular sites involved in arachidonic acid metabolism. 969 25

The Cinchona bark contains alkaloids like quinine, quinidine, cinchonine and cinchonidine. These agents are effective antimalarial drugs and have been used clinically in malaria caused by Plasmodium falciparum. Previous studies show that quinine and quinidine exert effects on cardiovascular system. This study was conducted to examine the effect of cinchonine on human platelet aggregation. The results show that cinchonine inhibited platelet aggregation mediated by platelet agonists, epinephrine (200 microM), ADP (4.3 microM), platelet activating factor (PAF; 800 nM) and collagen (638 nM) but had no effect on arachidonic acid (AA; 0.75 mM). Cinchonine was most effective in inhibiting aggregation induced by platelet activating factor and epinephrine with IC50 values of 125 and 180 microM respectively, however, higher concentrations of cinchonine were required to inhibit aggregation mediated by ADP or collagen (IC50; 300 microM). Pretreatment of platelets with cinchonine inhibited aggregation caused by Ca2+ ionophore, A-23187 (6 microM), in a dose-dependent manner (IC50; 300 microM) indicating an inhibitory effect on Ca2+-signaling cascade. This was supported by measuring [Ca2+]i in platelets loaded with Fura-2AM where cinchonine inhibited the rise in cytosolic Ca2+ mediated by A-23187 (6 microM) or collagen (638 nM). Results show that cinchonine (20 microM) also inhibited aggregation when platelets were pretreated with protein kinase C (PKC) activator, phorbol myristate acetate (PMA; 0.1 microM) in combination with low doses of platelet activating factor (80 nM). Cinchonine, however, had no effect on AA-induced platelet aggregation and thromboxane A2 (TXA2) synthesis in platelets. These results suggest that antiplatelet effects of cinchonine are mediated mainly through inhibition of Ca2+-influx and protein kinase C pathways in platelets.
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PMID:The inhibitory effect of cinchonine on human platelet aggregation due to blockade of calcium influx. 977 5

We have shown previously that both 1,2-diacylglycerol (AAG) and 1-O-alkyl-2-acylglycerol (EAG) prime neutrophil release of arachidonic acid via uncharacterized phospholipases A2. Therefore, we investigated the actions of EAG and AAG specifically on neutrophil cytosolic (cPLA2) and secretory (sPLA2) phospholipase A2s. We hypothesized that AAG as a protein kinase activator would activate cPLA2 via phosphorylation events. EAG is antagonistic to the AAG activation of PKC, thus it was not expected to act via phosphorylation of cPLA2. Neutrophils were primed with either AAG or EAG and then stimulated with fMLP. When neutrophils were primed with 5-20 microM 1,2-diacylglycerol, a shift was observed in cPLA2 migration on SDS-PAGE gels, consistent with phosphorylation of the protein. This gel shift was not seen after exposure to EAG. AAG also caused a parallel increase in enzymatic activity of cPLA2 that was not seen with EAG. We also investigated whether either diglyceride would cause similar priming or direct secretion of sPLA2. Both AAG and EAG directly caused significant secretion of neutrophil sPLA2. EAG also increased the release of sPLA2 in cells subsequently stimulated with fMLP. Thus, AAG activated cPLA2 and stimulated secretion of sPLA2. In contrast, EAG did not activate cPLA2, but directly activated secretion of sPLA2. We also demonstrated that human synovial fluid sPLA2 increased AA release from resting and fMLP-stimulated neutrophils. Given that diglycerides prime for release of AA, PAF, and LTB4, these current data support the hypothesis that such priming may be mediated by phosphorylation dependent (cPLA2) or phosphorylation independent (e.g. secretion of sPLA2) events.
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PMID:Differential activation of human neutrophil cytosolic phospholipase A2 and secretory phospholipase A2 during priming by 1,2-diacyl- and 1-O-alkyl-2-acylglycerols. 979 28


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