Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: EC:3.1.4.3 (phospholipase C)
 18,461 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Thrombin is believed to activate platelets via cell surface receptors coupled to G proteins. In order to better understand this process, we have examined the interaction of thrombin with HEL cells, a leukemic cell line that has served as a useful model for studies of platelet structure and function. In HEL cells, as in platelets, thrombin stimulated inositol trisphosphate (IP3) formation and suppressed cAMP synthesis. Both events were inhibited by pertussis toxin with 50% inhibition occurring at a toxin concentration that ADP-ribosylated 50% of the Gi alpha subunits present in HEL cells. IP3 formation was also stimulated by a second serine protease, trypsin. The trypsin response was identical to the thrombin response in time course, magnitude, and pertussis toxin sensitivity, suggesting that a similar mechanism is involved. Agonist-induced changes in the cytosolic-free Ca2+ concentration were used to test this hypothesis. Both proteases caused a transient increase in intracellular calcium [Ca2+]i that could be inhibited with D-phenylalanyl-L-prolyl-L-arginine chloromethyl ketone thrombin. Exposure to either protease desensitized HEL cells against subsequent increases in [Ca2+]i and IP3 caused by the other, although responses to other agonists were retained. This loss of responsiveness persisted despite repeated washing of the cells and the addition of hirudin. Complete recovery occurred after 20 h and could be prevented with cycloheximide. These observations suggest that 1) HEL cell thrombin receptors, like those on platelets, are coupled to phospholipase C and adenylylcyclase by pertussis toxin-sensitive G proteins, 2) the G proteins involved are equally accessible to pertussis toxin in situ, 3) when access is limited to the outside of the cell the response mechanisms for thrombin and trypsin are similar, if not identical, despite the broader substrate specificity of trypsin, 4) both proteases cause persistent changes that may involve proteolysis of their receptors or associated proteins, and 5) desensitization of the thrombin response occurs at a step no later than the activation of phospholipase C and requires protein synthesis for recovery.
 ...
PMID:Receptor and G protein-mediated responses to thrombin in HEL cells. 184 99

Cotton bract tannin is a potent stimulus for platelet aggregation and secretion. Tannin has been shown to stimulate the phosphorylation of two 19-kD and 47-kD cytosolic proteins in platelets, but earlier steps in signal transducing mechanisms of platelet activation are unknown. In this study, measurements of 32P-labeled phospholipids, 14C-labeled arachidonic acid, and levels of intracellular free calcium (Ca2+) were performed before and after the addition of thrombin (1 U/ml) or various concentrations of tannin to human platelets. The results showed that tannin induced a dose-dependent synthesis of phosphatidic acid, an early and transient hydrolysis of phosphatidylinositol monophosphate and bisphosphate, a transient synthesis of diacylglycerol, and a release of arachidonic acid metabolites. The kinetics of phosphatidic acid, diacylglycerol, and arachidonic acid metabolite synthesis were similar after platelet stimulation by tannin (75 micrograms/ml) or thrombin. Tannin also induced a reversible rise of intracellular Ca2+ due to a mobilization of the internal stores and an influx of extracellular Ca2+. These results suggest that cotton bract tannin, as thrombin, activates human platelets by phospholipase C and A2 activations, release of diacylglycerol, and mobilization of intracellular free Ca2+.
 ...
PMID:Signal transducing mechanisms in human platelets stimulated by cotton bract tannin. 184 78

Endothelin (ET)-1 is a powerful vasoconstrictor known to be produced and secreted by endothelial cells lining large vessels. Because ET-1 stimulates glomerular mesangial cell contraction, glomerular capillary endothelial cells (GEN), normally situated in close apposition to mesangial cells, were examined for potential ET expression and secretion. Cultured bovine GEN released ET in a time-dependent fashion. ET secretion was significantly stimulated by bradykinin, an agonist known to activate phospholipase C in these cells. Preproendothelin 1 (preproET-1) mRNA levels in GEN rose in a biphasic manner on stimulation with bradykinin. The early increments (at 30 min) were not dependent on new protein synthesis, whereas the late rise (6 h after addition of bradykinin) appeared to be protein synthesis dependent. Neither early or late bradykinin-stimulated preproET-1 mRNA expression in glomerular endothelial cells was due to inhibition of mRNA breakdown. Both phases of preproET-1 mRNA expression were observed with other glomerular endothelial cell calcium-mobilizing agonists, namely thrombin, and were mimicked by the calcium ionophore ionomycin. By contrast, the protein kinase C activator phorbol myristate acetate only enhanced preproET-1 mRNA expression at 30 min and suppressed expression thereafter. It is concluded that GEN have the potential to express and secrete ET-1 in a phospholipase C-regulated fashion. Furthermore, because glomerular mesangial cells respond to this peptide, the findings raise the possibility of paracrine regulation of mesangial cell tone by glomerular endothelial cell-derived ET-1.
 ...
PMID:Regulated expression of endothelin 1 in glomerular capillary endothelial cells. 185 92

The phenolic antioxidant 2,6-bis(1,1-dimethyl ethyl)-4-methylphenol (BHT) evokes a transient phosphorylation of two platelet proteins of Mr 20,000 and 47,000 that are well-known substrates of protein kinase C (PKC) and, similarly to phorbol esters, a slight but persistent phosphorylation of a protein of Mr 26,000. These effects are observed both in the presence and in the absence of extracellular calcium, but are abolished in the presence of the protein kinase C inhibitor staurosporine. The phosphorylation of the 47 kDa protein takes place mostly at the serine and, to a lesser extent, at threonine residues. BHT induces an increased binding of tritiated phorbol dibutyrate to platelets indicating a PKC translocation from cytosol to plasma membrane. Addition of BHT (20 microM) a few min prior to thrombin causes inhibition of both agonist-evoked protein phosphorylation and increase in the Ca2+ concentration, the latter inhibition being counteracted by staurosporine. The inhibitory effect lasts for several minutes even after removal of BHT from the cellular suspending medium. Similar results are obtained with nordihydroguaiaretic acid, whereas 2- and 3-tert-butyl-4-methoxyphenol (BHA) produce only slight effects. BHT activates the protein kinase C purified from pig brain in a concentration-dependent manner (up to 200 microM), whereas it does not affect the activity of other purified protein kinases such as type 1 and 2 casein kinases, type II A, II B and III tyrosine protein kinases from rat spleen and the catalytic subunit of cyclic AMP-dependent protein kinase. It is concluded that, similarly to diacylglycerols and phorbol esters, these phenolic antioxidants activate the protein kinase C, which in turn desensitizes platelets towards subsequent phospholipase C activation.
 ...
PMID:The antioxidant butylated hydroxytoluene stimulates platelet protein kinase C and inhibits subsequent protein phosphorylation induced by thrombin. 188 50

Platelet aggregation to incremental doses of eight different platelet agonists (collagen, thrombin, platelet-activating factor [PAF], arachidonic acid [AA] plus epinephrine, the calcium ionophore A23187, ADP, phospholipase C [PLC], and 12-O-tetradecanoyl phorbol-13-acetate [TPA]) was compared in normal (N) and cyclic hematopoietic (CH) dogs. Platelet aggregation was defective with collagen, PAF, TPA, and possibly thrombin as agonists but normal when ADP, PLC, arachidonic acid plus epinephrine, and A23187 were used as agonists with CH platelets. In heterozygous CH dogs, platelet aggregation was intermediately defective when tested with collagen and PAF as agonists. Thromboxane B2 (TXB2) concentrations (mean +/- SD; pg/10(6) platelets), as measured by RIA, were similar in CH and normal dogs both prior to (CH: 7.6 +/- 7.0; N: 5.5 +/- 3.9) and after collagen stimulation (collagen: 141.3 +/- 42.5; 123.1 +/- 38.4). Granule storage pools of serotonin and platelet adenine nucleotides were markedly decreased in homozygous CH but not heterozygous CH dogs. Thrombin stimulated phosphorylation of 40- and 20-kd proteins in platelets from CH and normal dogs to an equal extent. However, collagen-stimulated phosphorylation of the 40- but not the 20-kd protein was significantly decreased in platelets from CH dogs. These data suggest that there is a biochemical defect in platelets from CH dogs that results in storage pool disease and decreased phosphorylation of a 40-kd protein.
 ...
PMID:Characterization of platelet function in cyclic hematopoietic dogs. 189 69

Diets containing high levels of monounsaturated, n-6 polyunsaturated and n-3 polyunsaturated fatty acids were fed to Wistar rats. This resulted in decreases in the arachidonate content in platelet phospholipids to 91%, 79% and 51% respectively of the level found after feeding a diet rich in saturated fatty acids. In the presence of CaCl2, collagen- and thrombin-induced aggregation of washed platelets from the saturated-fat dietary group (with highest level of arachidonate) was low compared with that of platelets from the other dietary groups, despite a relatively high production of thromboxane B2. On the other hand, n-3 polyunsaturated fatty acids in the diet resulted in platelets aggregating actively, but producing low levels of levels of thromboxane B2. When indomethacin-treated rat platelets were activated with the thromboxane A2 analogue U46619, the presence of a second agonist such as collagen. ADP or thrombin was necessary for aggregate formation. U46619-induced aggregation in combination with either co-activator was relatively low in arachidonate-rich platelets, and was higher in platelets with a low arachidonate content. Similarly, phospholipase C-catalysed formation of L-myo-inositol phosphates was higher in platelets with a low arachidonate content. We conclude that the ability of platelets to react with thromboxane A2 is modified by diet in such a way that a decreased substrate-limited generation of thromboxane A2 is compensated for by an increased response to thromboxane, and vice versa. No significant differences were detected in the binding of U46619 or SQ29548 to platelets from the various dietary groups. Therefore the changed response seems not to be caused by modified properties of the thromboxane A2/prostaglandin H2 receptors, but by altered transduction of the thromboxane signal.
 ...
PMID:Dietary fat modifies thromboxane A2-induced stimulation of rat platelets. 189 33

Thrombin stimulation of human platelets is known to result in phosphatidylinositol turnover (PI response), the activation of protein kinase C (C-kinase), and the release of arachidonic acid (AA). The authors studied the effects of chlorpromazine (CPZ) on these responses. At a concentration of 100 microM, CPZ inhibited the phosphorylation of 40,000-dalton protein through C-kinase activation. CPZ failed to inhibit initial transient synthesis of 1,2-diacylglycerol (1,2-DAG) through the PI response, although it slowed the concurrent decreasing process. CPZ inhibited promotion of compensatory synthesis of phosphatidylinositol 4,5-bisphosphate (PIP2), and also inhibited the synthesis of phosphatidic acid (PA). These results suggest that phosphatidylinositol 4-monophosphate kinase and diacylglycerol kinase (DAG-kinase) may be inhibited by CPZ. CPZ also intensified the accumulation of inositol phosphates caused by the PI response, indicating possible inhibition of the phosphatases that metabolize these phosphates. Thus, CPZ partially inhibited the PI response. However, it appears likely that the inhibition of C-kinase activity by CPZ was not due to inhibition of 1,2-DAG production nor to direct inhibition of phospholipase C. CPZ also inhibited AA release. This action might be partially a result of the inhibitory effect of CPZ on PA production.
 ...
PMID:Effects of chlorpromazine on phosphatidylinositol turnover following thrombin stimulation of human platelets. 190 65

To gain insight into the mechanisms that could account for the augmentation of cellular reactivity in primary hypertension, we have examined some of the biochemical events which are implicated in the transmission of mitogenic signal as well as in cell reactivity. This study focussed on phospholipase C, protein kinase C and GTP-binding proteins (G-proteins), in response to thrombin or arginin-vasopressin (AVP). Cultured fibroblasts prepared from the adventitia of thoracic aorta of spontaneously hypertensive rat (SHR) were used as cell models and were compared with fibroblasts prepared from controls Wistar-Kyoto (WKY) rats. The mitogenicity of each agonist was estimated by measuring the incorporation of 3H-thymidine into the newly synthesized DNA. The agonist-induced phospholipase C activity was evaluated by measuring the production of 3H-inositol phosphates in cells prelabeled with 3H-inositol. The influence of protein kinase C and that of G proteins on the mitogenesis in cells stimulated by thrombin or AVP was determined by pretreating cells with phorbol 12-myristate, 13-acetate (TPA) and pertussis toxin, respectively. Kinetics and dose response studies have demonstrated that in response to thrombin and AVP, the phospholipase C activity and the incorporation of 3H-thymidine were significantly higher in the fibroblasts derived from SHR.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:[Activation mechanisms by thrombin and vasopressin of fibroblasts in spontaneously hypertensive rats]. 195 75

Electropermeabilized human platelets containing 5-hydroxy[14C]tryptamine ([14C]5-HT) were suspended in a glutamate medium containing ATP and incubated for 10 min with (in various combinations) Ca2+ buffers, phorbol 12-myristate 13-acetate (PMA), guanine nucleotides, and thrombin. Release of [14C]5-HT and beta-thromboglobulin (beta TG) were used to measure secretion from dense and alpha-granules, respectively. Ca2+ alone induced secretion from both granule types; half-maximal effects were seen at a -log [Ca2+ free] (pCa) of 5.5 and maximal secretion at a pCa of 4.5, when approximately 80% of 5-HT and approximately 50% of beta TG were released. Addition of PMA, guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S), GTP, or thrombin shifted the Ca2+ dose-response curves for secretion of both 5-HT and beta TG to the left and caused small increases in the maximum secretion observed. These results suggested that secretion from alpha-granules, like that from dense granules, is a Ca(2+)-dependent process stimulated by the sequential activation of a G-protein, phospholipase C, and protein kinase C (PKC). However, high concentrations of PMA and GTP gamma S had distinct effects in the absence of Ca2+ (pCa greater than 9); 100 nM PMA released approximately 20% of platelet 5-HT but little beta TG, whereas 100 microM GTP gamma S stimulated secretion of approximately 25% of each. Simultaneous addition of PMA greatly enhanced these effects of GTP gamma S. Phosphorylation of pleckstrin in permeabilized platelets incubated with [gamma-32P]ATP was used as an index of the activation of PKC during secretion. In the absence of Ca2+, 100 nM PMA caused maximal phosphorylation of pleckstrin and 100 microM GTP gamma S was approximately 50% as effective as PMA; neither GTP gamma S nor Ca2+ enhanced the phosphorylation of pleckstrin caused by 100 nM PMA. These results indicate that, although activation of PKC promoted secretion, GTP gamma S exerted additional stimulatory effects on secretion from both dense and alpha-granules that were not mediated by PKC. Measurement of [3H]inositol phosphate formation in permeabilized platelets containing [3H]phosphoinositides showed that GTP gamma S did not stimulate phosphoinositide-specific phospholipase C in the absence of Ca2+. It follows that in permeabilized platelets, GTP gamma S can both stimulate PKC and enhance secretion via G-protein-linked effectors other than this phospholipase.
 ...
PMID:Factors affecting dense and alpha-granule secretion from electropermeabilized human platelets: Ca(2+)-independent actions of phorbol ester and GTP gamma S. 196 91

Vascular permeability factor (VPF), a tumor-secreted heparin-binding protein (Mr approximately 38,000), is responsible for increased vessel permeability and fluid accumulation associated with tumor growth. Vascular permeability factor also promotes the growth of human umbilical vein endothelial cells (EC) and bovine pulmonary ECs in vitro. It is shown for the first time that guinea pig VPF (half-maximal and maximal dose approximately 0.4 and 22 pmol/l (picomolar), respectively), as well as human VPF, are potent stimuli for human ECs resulting in [Ca2+]i increases (maximal three- to fourfold) and inositol triphosphate (IP3) formation. Unlike the maximal responses to thrombin and histamine, the [Ca2+]i response to a maximal VPF dose was preceded by a characteristic 10- to 15-second delay. Guinea pig VPF also selectively increased [Ca2+]i in cultured aortic and pulmonary artery ECs, but not aortic smooth muscle cells, human fibroblasts, or neutrophils. Affinity-purified rabbit antibody (raised to a synthetic peptide representing VPF N-terminal amino acids 1 to 24) adsorbed all vessel permeability-increasing activity, EC growth-promoting activity, and specifically all activity responsible for increasing EC [Ca2+]i. Similar to other mediators that increase [Ca2+]i in cultured ECs, VPF also induced a 200% increase in von Willebrand factor release. Together these data indicate that VPF acts directly on ECs and that rapid cellular events in its in vivo/in vitro actions are likely to involve phospholipase C activation, [Ca2+]i increase, and von Willebrand factor release.
 ...
PMID:Tumor-secreted vascular permeability factor increases cytosolic Ca2+ and von Willebrand factor release in human endothelial cells. 198 67


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>