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

Stimulation of phospholipase C-gamma (PLC-gamma) is a critical event in angiotensin II (Ang II) signal transduction. We have previously shown that in rat aortic smooth muscle (RASM) cells Ang II stimulates tyrosine phosphorylation of PLC-gamma via activation of c-Src. Because we failed to demonstrate a direct association between c-Src and PLC-gamma, we hypothesized that a linker protein mediates the interaction between these molecules. To identify PLC-gamma-associated proteins, RASM cells were labeled with [32P]orthophosphate and stimulated with 100 nmol/L Ang II for 5 minutes. PLC-gamma was immunoprecipitated, and associated proteins were characterized by autoradiography and Western blotting with anti-phosphotyrosine antibodies. Ang II stimulated the phosphorylation of 47-, 60-, 84-, and 97-kD PLC-gamma-associated proteins. Because Ang II increased tyrosine phosphorylation of only the 97-kD protein, we characterized p97 further. An important role for Src in tyrosine phosphorylation of p97 was suggested by findings that p97 phosphorylation was inhibited by the selective Src-family kinase inhibitor CP-118,556, diminished in mouse aortic smooth muscle (MASM) cells from c-Src knockout mice compared with wild-type MASM cells, and increased in v-Src-transformed NIH-3T3 cells compared with wild-type NIH-3T3 cells. These studies are the first to define a PLC-gamma-associated protein that may be required for Ang II-mediated signal transduction.
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PMID:Angiotensin II stimulates tyrosine phosphorylation of phospholipase C-gamma-associated proteins. Characterization of a c-Src-dependent 97-kD protein in vascular smooth muscle cells. 931 36

In the present study, we have examined the effect of increased cyclic AMP (cAMP) levels on the stimulatory action of angiotensin II (Ang II) on protein synthesis. Treatment with cAMP-elevating agents potently inhibited Ang II-induced protein synthesis in rat aortic smooth muscle cells and in rat fibroblasts expressing the human AT1 receptor. The inhibition was dose-dependent and was observed at all concentrations of the peptide. To explore the mechanism of cAMP action, we have analyzed the effects of forskolin and 3-isobutyl-1-methylxanthine on various receptor-mediated responses. Elevation of cAMP did not alter the binding properties of the AT1 receptor and did not interfere with the activation of phospholipase C or the induction of early growth response genes by Ang II. Likewise, Ang II-dependent activation of the mitogen-activated protein kinases ERK1/ERK2 and p70 S6 kinase was unaffected by cAMP. In contrast, we found that increased concentration of cAMP strongly inhibited the stimulatory effect of Ang II on protein tyrosine phosphorylation. Specifically, cAMP abolished Ang II-induced tyrosine phosphorylation of the focal adhesion-associated protein paxillin and of the tyrosine kinase Tyk2. These results identify a novel mechanism by which the cAMP signaling system may exert growth-inhibitory effects in specific cell types.
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PMID:Cyclic AMP-mediated inhibition of angiotensin II-induced protein synthesis is associated with suppression of tyrosine phosphorylation signaling in vascular smooth muscle cells. 934 Nov 20

1. Angiotensin II (Ang II), the main effector of the renin-angiotensin system, exerts its vasoconstrictory and trophic actions on smooth muscle cells via AT1 receptors. However, Ang II does not act only on smooth muscle cells, as Ang II receptors are also present in endothelial cells. 2. The receptor type on these cells differs depending on the origin of the endothelium and the species. The rat endothelial receptors are mostly of the AT1 type, but AT2 receptors have also been found. The pharmacological characteristics of the AT1 receptors on endothelial cells are similar to those of other cell types. 3. Ang II stimulates phospholipase C and phospholipase A2 activation via the AT1 receptor in endothelial cells. Ang II also stimulates the tyrosine phosphorylation of several proteins in these cells. 4. Some studies suggest that the AT1 receptor mediates the release of vasodilator molecules by endothelial cells and could modulate Ang II effect on smooth muscle cells. Ang II may also inhibit endothelial cell growth via the AT2 receptor. Finally, endothelial Ang II receptors may be implicated in the regulation of fibrinolysis.
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PMID:Angiotensin II receptors in endothelial cells. 934 11

Stretch of neonatal cardiomyocytes activates phospholipase C with production of inositol trisphosphate and diacylglycerol in part by formation of angiotensin II (Ang II). However, the response of this pathway to physical stimuli in the adult heart is poorly understood. Thus, in isovolumic perfused guinea pig hearts, we characterized stretch-mediated phosphatidylinositol (PI) hydrolysis and protein kinase C (PKC) isoform translocation using elevated diastolic pressure. Balloon dilatation (minimum diastolic pressure, 25 mm Hg) of the left ventricle (LV) stimulated PI hydrolysis. Pretreatment of stretched hearts with the specific angiotensin (AT1) receptor antagonist losartan abolished stretch-mediated accumulation of inositol phosphates. To examine PKC isoform expression and activation under these conditions, whole-heart extracts were examined by immunoblot analysis. Ang II translocated PKC epsilon to the particulate fraction. 4 beta-Phorbol 12-myristate 13-acetate but not an inactive congener translocated PKC epsilon to the particulate fraction and produced a decrease in myocardial contractile function. Mechanical stretch also translocated PKC epsilon to the particulate fraction; however, this was attenuated but not abolished by losartan. We conclude that in the adult heart, LV dilation produced stretch-mediated activation of phospholipase C, which resulted in PI hydrolysis and PKC epsilon activation in part by stimulation of the local renin angiotensin system. In contrast to stretch-mediated inositol phosphate accumulation, PKC epsilon translocation is not prevented by AT1 receptor blockade, indicating that this PKC isoform can be activated in response to mechanical deformation by an Ang II-independent mechanism in the adult myocardium.
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PMID:Left ventricular stretch stimulates angiotensin II--mediated phosphatidylinositol hydrolysis and protein kinase C epsilon isoform translocation in adult guinea pig hearts. 935 35

We recently reported that replacement of Tyr302 for Ala in the human angiotensin II type 1 receptor (hAT1) severely impaired its ability to activate phospholipase C (PLC). Another study demonstrated that the same mutation in the rat AT1 receptor only slightly impaired its ability to activate PLC. The most striking difference between the two studies was the use of LiCl in the experimental conditions. Thus, in the present report we evaluated the effect of LiCl on the rate of accumulation of inositol trisphosphate (IP3) in transfected cells stimulated with angiotension II (Ang II). In the presence of LiCl, Ang II caused a significant accumulation of IP3 in COS-7 cells transfected with the hAT1Y302A mutant receptor. In stably expressing CHO cells, stimulation of hAT1Y302A did not induce any IP3 elevation even in the presence of LiCl whereas the hAT1 wild-type receptor increased the production of IP3 exclusively in the presence of LiCl. These results show that LiCl is a convenient tool to enhance the sensitivity of PLC assays. However, in structure-activity relationship studies, it may underestimate or mask the debilitating effect of some mutations.
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PMID:Use of LiCl in phospholipase C assays masks the impaired functionality of a mutant angiotensin II receptor. 937 18

GRK5, a recently cloned member of the G protein-coupled receptor kinase family, has been shown to phosphorylate and participate in the desensitization of angiotensin II (Ang II) type 1A (AT1A) receptors. In this study, the effect of angiotensin II on GRK5 expression was examined in cultured vascular smooth muscle cells and aortas of Ang II-infused hypertensive rats. In vascular smooth muscle cells, Ang II (100 nM) up-regulated GRK5 mRNA as early as 1 h, with a peak at 16 h. This up-regulation was dose- and calcium-dependent. The increase in GRK5 mRNA was reflected in a smaller increase in protein expression, which nonetheless had functional significance since AT1 receptor phosphorylation was increased and phospholipase C activation was decreased following prolonged incubation with Ang II. In aortas of Ang II-infused hypertensive rats, both GRK5 mRNA and protein levels increased approximately 3-fold compared with sham-operated rats at 5 and 7 days, respectively. This up-regulation was blocked either by losartan or by the nonspecific vasodilator hydralazine. Since a subpressor dose of Ang II did not increase GRK5 mRNA levels and norepinephrine infusion also increased GRK5 mRNA expression, we conclude that Ang II-induced GRK5 up-regulation in rat aortas may be due to hypertension per se. Hormone- and hemodynamic stress-induced GRK5 regulation may provide a novel molecular basis for long-term regulation of agonist sensitivity of vascular cells.
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PMID:G protein-coupled receptor kinase 5 in cultured vascular smooth muscle cells and rat aorta. Regulation by angiotensin II and hypertension. 940 59

AT1 receptor is responsible for most of the physiological effects of Angiotensin II (Ang II). AT1 receptor belongs to the G-protein-coupled receptor (GPCR) family, and it mediates its actions through the coupling of the Gq/11 protein with phospholipase C beta. Classical pharmacology has used the sensitivity of GPCR ligands to uncoupling agents as a criteria to discriminate agonists (which are sensitive) from antagonists (which are insensitive). In this study, the uncoupling agents GTP gamma S and pentosan sulfate (PS) (a low molecular weight polyanion) were used to further characterize the molecular interactions between Ang II analogs and the AT1 receptor. We show that some Ang II antagonists are sensitive to the conformational change of the AT1 receptor induced by uncoupling agents. These results demonstrate that there is no direct relationship between the intrinsic activity of a ligand and its affinity for different conformations of the AT1 receptor and that the sensitivity of GPCR ligands to uncoupling agents can not be used as a criteria to discriminate agonists from antagonists.
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PMID:Effect of uncoupling agents on AT1 receptor affinity for antagonist analogs of angiotensin II. 966 23

Activation of phospholipase C (PLC) is one of the earliest events in angiotensin II (Ang II) type 1 (AT1) receptor (R)-mediated signal transduction in vascular smooth muscle cells (VSMCs). The coupling mechanisms of AT1 Rs to PLC, however, are controversial, because both tyrosine phosphorylation of PLC-gamma and G protein-dependent PLC-beta activation pathways have been reported. The expression of PLC-beta1, furthermore, has not been consistently demonstrated in VSMCs. Here we identified the PLC subtypes and subunits of heterotrimeric G proteins involved in AT1 R-PLC coupling using cultured rat VSMCs. Western analysis revealed the expression of PLC-beta1, -gamma1, and -delta1 in VSMCs. Ang II-stimulated inositol trisphosphate (IP3) formation measured at 15 s, which corresponds to the peak response, was significantly inhibited by electroporation of antibodies against PLC-beta1, but not by anti-PLC-gamma and -delta antibodies. Electroporation of anti-Galphaq/11 and -Galpha12 antibodies also showed significant inhibition of the Ang II-induced IP3 generation at 15 s, while anti-Galphai and Galpha13 antibodies were ineffective. Furthermore, in VSMCs electroporated with anti-Gbeta antibody and cells stably transfected with the plasmid encoding the Gbetagamma-binding region of the carboxyl terminus of beta-adrenergic receptor kinase1, the peak Ang II-stimulated PLC activity (at 15 s) was significantly inhibited. The tyrosine kinase inhibitor, genistein, had no effect on the peak response to Ang II stimulation, but significantly inhibited IP3 production after 30 s, a time period which temporally correlated with PLC-gamma tyrosine phosphorylation in response to Ang II. Moreover, electropor-ation of anti-PLC-gamma antibody markedly inhibited the IP3 production measured at 30 s, indicating that tyrosine phosphorylation of PLC-gamma contributes mainly to the later phase of PLC activation. Thus, these results suggest that: 1) AT1 receptors sequentially couple to PLC-beta1 via a heterotrimeric G protein and to PLC-gamma via a downstream tyrosine kinase; 2) the initial AT1 receptor-PLC-beta1 coupling is mediated by Galphaq/11beta gamma and Galpha12 beta gamma; 3) Gbeta gamma acts as a signal transducer for activation of PLC in VSMCs. The sequential coupling of AT1 receptors to PLC-beta1 and PLC-gamma, as well as dual coupling of AT1 receptors to distinct Galpha proteins, suggests a novel mechanism for a temporally controlled, highly organized and convergent Ang II-signaling network in VSMCs.
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PMID:Temporal dispersion of activation of phospholipase C-beta1 and -gamma isoforms by angiotensin II in vascular smooth muscle cells. Role of alphaq/11, alpha12, and beta gamma G protein subunits. 967 8

This study was performed to investigate a mechanism of angiotensin II (Ang II)-mediated activation of the fibronectin (FN) gene in rat vascular smooth muscle cells. Actinomycin D and CV11974 completely inhibited Ang II-mediated increase in FN mRNA levels. Inhibitors of protein kinase C (PKC), protein-tyrosine kinase (PTK), phosphatidylinositol-specific phospholipase C, Ras, phosphatidylinositol 3-kinase, p70 S6 kinase, and Ca2+/calmodulin kinase also decreased Ang II-induced activation of FN mRNA. In contrast, cycloheximide; PD123319; or inhibitors of Gi, protein kinase A, or mitogen-activated protein kinase kinase did not affect the induction. FN promoter contained a putative AP-1 binding site (rFN/AP-1; -463 to -437), and the results of a transient transfection and electrophoretic mobility shift assay showed that Ang II enhanced rFN/AP-1 activity. CV11974 and inhibitors of PKC or PTK suppressed Ang II-mediated increases in rFN/AP-1 activity, although neither PD123319 nor a protein kinase A inhibitor affected the induction. Furthermore, mutation of rFN/AP-1 that disrupted nuclear binding suppressed Ang II-induced transcription in the native FN promoter (-1908 to +136) context. Thus, Ang II activates transcription of the FN gene through the Ang II type 1 receptor in vascular smooth muscle cells, at least in part, via the activation of AP-1 by a signaling mechanism dependent on PKC and PTK.
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PMID:Mechanism of angiotensin II-mediated regulation of fibronectin gene in rat vascular smooth muscle cells. 975 84

In cardiac fibroblasts, angiotensin II (Ang II) induced a rapid increase in extracellular signal regulated kinase (ERK) activity in a pertussis toxin insensitive manner. This ERK activation was abolished by the Gq-associated phospholipase C inhibitor U73122 but was insensitive to protein kinase C (PKC) inhibitors or PKC downregulation by phorbol ester. Intracellular Ca2+ chelation by BAPTA-AM or TMB-8 abolished Ang II induced ERK activation, whereas treatment with EGTA or nifedipine did not affect it. Ca2+ ionophore A23187 also induced a rapid increase in ERK activity to an extent similar to that of Ang II stimulation. Calmodulin inhibitors (W7 and calmidazolium) and tyrosine kinase inhibitors (genistein and ST638) completely blocked ERK activation by Ang II and A23187. Both Ang II and A23187 caused a rapid increase in the binding of GTP to p21(Ras), which was nearly abolished by genistein and calmidazolium. Transfection with the dominant negative mutant of Ras and the Ras inhibitor manumycin completely inhibited Ang II induced ERK activation. It was also found for the first time that cardiac fibroblasts abundantly expressed Ca2+-sensitive tyrosine kinase Pyk2/CAKbeta/RAFTK and that Ang II markedly induced its activation in a Ca2+/calmodulin-sensitive manner. Overexpression of the dominant negative mutant of Pyk2 significantly attenuated Ang II or A23187-induced ERK activities (36% and 38% inhibition compared with that in mock-transfected cells, respectively) and ERK tyrosine phosphorylation levels, as well as an increase in the binding of GTP to p21(Ras). These findings demonstrate that in cardiac fibroblasts, Ang II induced Ras/ERK activation is dominantly regulated by Gq-coupled Ca2+/calmodulin signaling and that Pyk2 plays an important role in the signal transmission for efficient activation of the Ang II induced Ras/ERK pathway.
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PMID:Role of calcium-sensitive tyrosine kinase Pyk2/CAKbeta/RAFTK in angiotensin II induced Ras/ERK signaling. 977 61


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