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)

Treatment of intact human umbilical vein endothelial cells with NaF results in a dose-dependent biphasic response in both prostacyclin and inositol phosphate production: the stimulation observed with 10-20 mM NaF decreases with higher concentrations. High concentrations of NaF furthermore reduce thrombin- or A23187-stimulated prostacyclin production. Direct assay of phospholipase C activity in cell homogenates shows a similar biphasic response to NaF, also after chelation of Ca2+; addition of AlCl3 shifts the inhibition toward lower NaF concentrations. Guanosine 5'-O-(3-thiotriphosphate) (GTP gamma S) also causes a dose-dependent biphasic response in inositol phosphate formation in permeabilized cells and homogenates; a higher inhibitory concentration of GTP gamma S abolishes the stimulation of inositol phosphate production by low NaF concentrations. A high concentration of NaF furthermore inhibits the non-G-protein-dependent activation of phospholipase C by deoxycholate. NaF also induces a dose-dependent biphasic response in cyclic AMP formation in intact cells, indicating that the inhibition of phospholipase C at higher NaF concentrations does not result from a rise in cyclic AMP. The data are compatible with the existence of a guanine nucleotide-dependent, cyclic AMP-independent, phospholipase C-inhibitory pathway in endothelial cells.
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PMID:Guanine nucleotide-dependent inhibition of phospholipase C in human endothelial cells. 169 18

Human erythroleukemia (HEL) cells phosphorylate [3H]inositol 1,4,5-trisphosphate to inositol 1,3,4,5-tetrakisphosphate; they also contain all the enzymes to sequentially dephosphorylate [3H]inositol 1,4,5-trisphosphate and [3H]inositol 1,3,4,5-tetrakisphosphate to inositol. alpha-Thrombin, 1-O-alkyl-2-acetyl-sn-glycero-3-phosphocholine, and sodium fluoride caused the formation of [3H]inositol phosphates in HEL cells that were previously labeled with [3H]inositol. This indicates agonist-induced activation of phospholipase C and hydrolysis of the inositol phospholipids. Pretreatment of the HEL cells with iloprost, a prostacyclin analog that increases cellular cyclic AMP levels, dramatically reduced the formation of inositol phosphates and the increase of [3H]phosphatidylinositol 4,5-bisphosphate. The inhibitory effects of iloprost were associated with the phosphorylation of a 24-kDa protein, which was detected with an antiserum obtained against the rap 1 protein. The catalytic subunit of protein kinase A inhibited formation of polyphosphoinositides during phosphorylation of the rap 1 protein in membranes. This rap 1 protein might have functional relevance in the inhibition of agonist-induced inositide metabolism.
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PMID:Effect of protein kinase A on inositide metabolism and rap 1 G-protein in human erythroleukemia cells. 169 2

Thrombin induced an increase in [Ca2+]i in mouse mastocytoma P-815 cells. This increase was markedly reduced by prior exposure to pertussis toxin (PT) but not by removal of extracellular Ca2+, suggesting that thrombin stimulates phospholipase C via a PT-sensitive GTP-binding protein. ATP also induced an increase in [Ca2+]i. This increase was insensitive to PT but completely suppressed on removal of extracellular Ca2+, suggesting that ATP stimulates Ca2+ influx in a PT-insensitive manner. Iloprost, a stable prostacyclin analogue, increased the cellular cAMP level and dose-dependently inhibited the thrombin-induced increase in [Ca2+]i, whereas the ATP-induced increase in [Ca2+]i was markedly enhanced by iloprost. Cyclic AMP analogues, dibutyryl cAMP and 8-bromo cAMP, also inhibited the increase in [Ca2+]i induced by thrombin and promoted that by ATP, indicating that the inhibitory and stimulatory effects of iloprost are mediated by cAMP. These results suggest that the prostacyclin receptor differentially regulates two distinct Ca2+ mobilizing systems via cAMP in mastocytoma cells.
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PMID:Differential regulation of thrombin- or ATP-induced mobilization of intracellular Ca2+ by prostacyclin receptor in mouse mastocytoma cells. 170 39

Changes in the intracellular free calcium ([Ca2+]i) of cultured normal human epidermal keratinocytes (NHEK) were investigated in order to determine whether the adenylate cyclase cAMP (AC) system and phospholipase C activating system are involved in increasing [Ca2+]i. NHEK were obtained from neonatal foreskin and grown in serum-free medium (K-GM) supplemented with 2% bovine pituitary extract. [Ca2+]i was measured by fluorescence ratio imaging microscopy using Fura-2 as the indicator. In the case of the AC system, transient increases in [Ca2+]i were observed in response to stimulation with epinephrine, norepinephrine, isoproterenol and salbutamol. Methoxamine, clonidine and dobutamine did not induce any [Ca2+]i increase. The [Ca2+]i increase evoked by epinephrine was inhibited by pretreatment with propranolol, but not by prazosin or yohimbine, indicating that epinephrine-induced [Ca2+]i elevation via beta 2-adrenergic stimulation. Similar changes were observed when NHEK were stimulated with histamine, adenosine, GTP gamma S, forskolin and dibutyryl cAMP respectively. The absence of extracellular Ca2+ had no effect on the epinephrine-induced [Ca2+]i increase. It appears that activated protein kinase A, based on cAMP accumulation via stimulatory GTP binding protein, elicited the release of Ca2+ from intracellular stores. On the other hand, when drugs known to activate phospholipase C in a wide variety of cell types were tested, a transient increase in [Ca2+]i was demonstrated in response to the addition of thrombin, bradykinin and substance P. This reaction was not affected by the presence of EGTA, suggesting that these drugs raise [Ca2+]i via phosphatidylinositol breakdown. Vasopressin, angiotensin II, serotonin and acetylcholine did not induce any increase in [Ca2+]i. On the basis of these studies, it was concluded that NHEK possess the mechanism which increase [Ca2+]i via AC system and phospholipase C activating system. It seems probable that this rise in [Ca2+]i initiates a calcium-dependent cellular response, such as activation of calcium/calmodulin dependent kinase, and subsequently regulates the proliferation and differentiation of human epidermal keratinocytes.
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PMID:[Changes in the intracellular free calcium of cultured human epidermal keratinocytes]. 171 97

Phosphatidylinositol (PtdIns)-4- and -3-kinases, PtdIns(4)P-5-kinase, diacylglycerol (DAG) kinase, and PtdIns-phospholipase C were all detected in cytoskeletons of resting human platelets. The total cytoskeletal enzyme activities were greatly increased upon thrombin stimulation of the intact cells. Those reached a maximum after a 60-s stimulation for PtdIns(4)P-5-kinase and phospholipase C, while the other kinases appeared to be slightly delayed. Specific activities were stimulated from about 4-fold (PtdIns-3-kinase) to about 6-fold (PtdIns-4-kinase). Thrombin treatment also promoted a co-extraction of pp60c-src with the cytoskeletons and its disappearance from the Triton X-100 soluble fraction. These results suggest that stimulation of platelets by thrombin causes the association of enzymes responsible for lipid phosphorylation and hydrolysis with the cytoskeletons. This could occur at cytoskeleton anchoring points to the membranes.
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PMID:Interaction of pp60c-src, phospholipase C, inositol-lipid, and diacyglycerol kinases with the cytoskeletons of thrombin-stimulated platelets. 171 96

We have shown that platelets stimulated with thrombin or guanosine 5'-[gamma-thio]triphosphate (GTP[S]), both of which activate phospholipase C and protein kinase C (PKC), show enhancement of 3-phosphorylated phosphoinositide accumulation (3-PPI). We now report the following. (1) Inhibition of thrombin- or GTP[S]-stimulated PKC by pseudo-substrate peptide (RFARK) added to permeabilized platelets markedly inhibits 3-PPI, whereas the serine/threonine phosphatase inhibitor, okadaic acid, promotes 3-PPI. PKC activity, insufficient in itself for fully activating 3-PPI, appears crucial to receptor and post-receptor stimulation of 3-PPI, even when tyrosine phosphorylation is unimpaired. (2) Alteration of Gi by ADP-ribosylation only slightly affects the stimulation of 3-PPI by thrombin, and activation of the G-protein Gi by adrenaline has no effect on 3-PPI. (3) Inhibition of PKC blocks activated secretion of platelet-derived growth factor (PDGF). However, PDGF cannot promote platelet 3-PPI, and thus cannot account for the inhibitory effects of RFARK on 3-PPI.
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PMID:Protein kinase C regulates the stimulated accumulation of 3-phosphorylated phosphoinositides in platelets. 171 81

Endothelial cells can produce contracting factors; endothelin, a 21-amino acid peptide that can control local vascular tone, is the most potent of these factors. Of the three isoforms of endothelin, endothelial cells appear to release primarily endothelin-1. The peptide is formed from its precursor big endothelin via the activity of the endothelin converting enzyme. The basal production of the peptide is stimulated by epinephrine, angiotensin II, arginine vasopressin, transforming growth factor beta, thrombin, interleukin-1, and the calcium ionophore A23187. In vascular smooth muscle cells, endothelin binds to a specific receptor that activates phospholipase C and leads to the formation of inositol trisphosphate, diacylglycerol, and increased intracellular calcium levels. In certain blood vessels, the endothelin receptor is linked to a voltage-operated calcium channel via a Gi protein. This may explain why calcium antagonists inhibit endothelin-induced contractions only in certain blood vessels. In the human forearm circulation, calcium antagonists of different classes prevent endothelin-induced contractions. In hypertension, the circulating endothelin levels appear to be normal, whereas the vascular sensitivity to the peptide is reduced in most vascular tissues, but normal and enhanced responses have also been reported. In atherosclerosis and other forms of vascular disease, circulating endothelin levels are augmented, a phenomenon that may be related to an increased formation of the peptide induced by modified forms of low-density lipoproteins.
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PMID:Endothelin. 172 99

To examine the mechanism of action of antidepressant drugs, we studied the effect of desipramine (DMI) in vitro on agonist-stimulated inositol phosphate formation and inositol phospholipids in rat brain and human platelets. We observed that DMI inhibited thrombin-stimulated 3H-inositol bisphosphate (IP2) and 3H-inositol trisphosphate (IP3) but not 3H-inositol monophosphate (IP1) formation in human platelets. DMI also inhibited norepinephrine (NE) and serotonin (5-HT) stimulated 3H-IP1 formation in rat cerebral cortex. DMI increased levels of all three 3H-inositol phospholipids, 3H-phosphatidyl inositol (PI), 3H-PI-4-phosphate (PIP), and 3H-PI 4,5-bisphosphate (PIP2), in both platelets and rat cortex. The decreased formation of inositol phosphates and increased levels of [3H]-PI, [3H]-PIP, and [3H]-PIP2 by DMI appears to be due to the inhibition of the enzyme phospholipase C rather than its effects on receptors. It is thus possible that interaction of tricyclic antidepressant drugs with the PI-signaling system may be related to their mechanism of action.
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PMID:Effect of desipramine on inositol phosphate formation and inositol phospholipids in rat brain and human platelets. 177 95

The blood coagulation factor, human thrombin has been shown to have chemotactic and mitogenic effects on mononuclear phagocytic inflammatory cells. In the present study, we have used the U937 human monocytic cell line to explore the signal transduction mechanisms utilised by thrombin in these cells. In U937 cells differentiated into a macrophage-like phenotype, thrombin stimulated the formation of inositol trisphosphate (IP3) and the mobilisation of intracellular Ca2+ [( Ca2+]i) via a mechanism which was partially sensitive to pertussis toxin. Thrombin failed, however, to evoke thromboxane (Tx) B2 synthesis in the differentiated cells. In contrast, the chemotactic peptide N-formyl-L-methionylleucyl-L-phenylalanine (FMLP) stimulated TxB2 synthesis under conditions where it evoked increases in IP3 formation and [Ca2+]i mobilisation, via a pertussis toxin-sensitive mechanism, comparable in extent to those mediated by thrombin. Thrombin also failed to cause inhibitory guanine nucleotide binding protein (Gi)-mediated inhibition of adenylate cyclase activity in U937 cell membranes. These results indicate that U937 cells express receptors for thrombin which are in part coupled via a pertussis toxin-sensitive guanine nucleotide binding protein to phospholipase C activation, the formation of IP3 and the mobilisation of [Ca2+]i. However, the failure of thrombin to stimulate TxB2 synthesis or cause Gi-mediated inhibition of adenylate cyclase in U937 cells contrasts with its effects in human platelets and other thrombin-responsive cells. These results suggest that the thrombin receptor or receptor-effector coupling mechanism(s) in mononuclear cells is functionally distinct from the thrombin receptor or receptor-effector coupling mechanism(s) present in other thrombin-responsive cells.
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PMID:Thrombin signalling in U937 human monocytic cells is coupled to inositol phosphate formation but not to thromboxane B2 synthesis nor to inhibition of adenylate cyclase: distinct differences in thrombin signalling between U937 cells and platelets. 180 Jan 26

Platelet-activating factor (PAF) activates human platelets by binding to a putative PAF receptor which evokes the rapid formation of inositol-1,4,5-trisphosphate (IP3) by phospholipase C mediated phosphatidylinositol-4,5-bisphosphate (PIP2) hydrolysis. Stimulation of [3H]inositol-labeled human platelets by PAF (1 nM-1 microM) resulted in a concentration-dependent increase of intracellular IP3, IP2 and inositolmonophosphate (IP1). IP1 levels increased up to three-fold upon maximum stimulation by 100 nM PAF. The EC50 concentration for PAF was 1.2 +/- 0.3 nM. Addition of the hetrazepinoic PAF antagonist, WEB 2086, inhibited PAF stimulated hydrolysis of PIP2 in a dose-dependent manner. WEB 2086 (100 microM) blocked inositol-1,4,5-trisphosphate formation down to baseline levels (IC50 = 33 +/- 12 microM WEB 2086). In thrombin and ADP stimulated platelets, inositol phosphate (IP) generation was not influenced by WEB 2086. It is concluded that WEB 2086 selectively antagonizes PAF-induced increases in IP and does not interfere directly with intracellular signal transduction. Instead, WEB 2086, which has been shown to bind specifically and with high affinity (Ki 15 nM) to human platelets, acts as a competitive antagonist at the PAF receptor level.
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PMID:Inhibition by the PAF antagonist WEB 2086 of PAF induced inositol-1,4,5-trisphosphate production in human platelets. 181 88


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