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)

Serum stimulation of quiescent fibroblasts leads to a dramatic depolarization of the plasma membrane; however, the identity of the active serum factor(s) and the underlying mechanism are unknown. We find that this serum activity is attributable to albumin-bound lysophosphatidic acid (LPA) acting on its own G protein-coupled receptor, and that membrane depolarization is due to activation of an anion conductance mediating Cl- efflux. This depolarizing Cl- current can also be activated by thrombin and neuropeptide receptors; it is distinct from volume-regulated Cl- currents. Activation of the Cl- current consistently follows stimulation of phospholipase C and coincides with remodelling of the actin cytoskeleton, which is regulated by the Ras-related GTPase Rho. However, the response is not due to Ca2+/protein kinase C signalling and requires neither Rho nor Ras activation. The results indicate that in quiescent fibroblasts, LPA and other G protein-coupled receptor agonists evoke membrane depolarization by activating a new type of Cl- channel through a signalling pathway that is closely associated with phosphoinositide hydrolysis, yet independent of known second messengers.
 ...
PMID:Serum-induced membrane depolarization in quiescent fibroblasts: activation of a chloride conductance through the G protein-coupled LPA receptor. 859 7

The glucagon receptor is a member of the G protein-coupled receptor superfamily. Since several G protein-coupled receptors undergo phosphorylation in response to agonist, we investigated the phosphorylation of the glucagon receptor following the addition of glucagon to a Chinese hamster ovary cell line expressing the human glucagon receptor (CHO/hGR). Glucagon induced a rapid, time and concentration-dependent phosphorylation of its receptor on serine residues. Neither forskolin nor phorbol ester increased receptor phosphorylation, suggesting that cAMP-dependent protein kinase and protein kinase C do not catalyze this phosphorylation event. Furthermore, two mutant cell lines expressing glucagon receptors with successively truncated receptor cytoplasmic tails were tested. A strong correlation between the number of potential phosphorylation sites, receptor phosphorylation and receptor internalization was observed, suggesting that phosphorylation of the glucagon receptor in CHO/hGR cells is functionally linked to its internalization.
 ...
PMID:Glucagon induces a rapid and sustained phosphorylation of the human glucagon receptor in Chinese hamster ovary cells. 860 65

We have characterized the mechanism whereby a G protein-coupled receptor, the alpha 1-adrenergic receptor, promotes cellular AA release via the activation of phospholipase A2 (PLA2) in Madin-Darby canine kidney (MDCK-D1) cells. Stimulation of cells with the receptor agonist epinephrine or with the protein kinase C (PKC) activator PMA increased AA release in intact cells and the activity of PLA2 in subsequently prepared cell lysates. The effects of epinephrine were mediated by alpha 1-adrenergic receptors since they were blocked by the alpha 1-adrenergic antagonist prazosin. Epinephrine- and PMA-promoted AA release and activation of the PLA2 were inhibited by AACOCF3, an inhibitor of the 85-kD cPLA2. The 85-kD cPLA2 could be immunoprecipitated from the cell lysate using a specific anti-cPLA2 serum. Enhanced cPLA2 activity in cells treated with epinephrine or PMA could be recovered in such immunoprecipitates, thus directly demonstrating that alpha 1-adrenergic receptors activate the 85-kD cPLA2. Activation of cPLA2 in cell lysates by PMA or epinephrine could be reversed by treatment of lysates with exogenous phosphatase. In addition, both PMA and epinephrine induced a molecular weight shift, consistent with phosphorylation, as well as an increase in activity of mitogen-activated protein (MAP) kinase. The time course of epinephrine-promoted activation of MAP kinase preceded that of the accumulation of released AA and correlated with the time course of cPLA2 activation. Down-regulation of PKC by overnight incubation of cells with PMA or inhibition of PKC with the PKC inhibitor sphingosine blocked the stimulation of MAP kinase by epinephrine and, correspondingly, epinephrine-promoted AA release was inhibited under these conditions. Similarly, blockade of MAP kinase stimulation by the MAP kinase cascade inhibitor PD098059 inhibited epinephrine-promoted AA release. The sensitivity to Ca2+ was similar, although the maximal activity of cPLA2 was enhanced by treatment of cells with epinephrine or PMA. The data thus demonstrate that in MDCK-D1 cells alpha 1-adrenergic receptors regulate AA release through phosphorylation-dependent activation of the 85-kD cPLA2 by MAP kinase subsequent to activation of PKC. This may represent a general mechanism by which G protein-coupled receptors stimulate AA release and formation of products of AA metabolism.
 ...
PMID:Protein kinase C-dependent activation of cytosolic phospholipase A2 and mitogen-activated protein kinase by alpha 1-adrenergic receptors in Madin-Darby canine kidney cells. 863 43

The type 1A angiotensin II receptor (AT1A-R), which mediates cardiovascular effects of angiotensin II, has been shown to undergo rapid agonist-induced desensitization. We investigated the potential role of second messenger-activated kinases and G protein-coupled receptor kinases (GRKs) in the regulation of this receptor. In 293 cells transfected with the AT1A-R, a 3-min challenge with angiotensin II engendered a 46% decrease in subsequent angiotensin II-stimulated phosphoinositide hydrolysis in intact cells. This agonist-induced desensitization correlated temporally and dose-dependently with the phosphorylation of the receptor to a stoichiometry of 1 mol of phosphate/mol of receptor, as assessed by immunoprecipitation of receptors from cells metabolically labeled with 32Pi. Agonist-induced receptor phosphorylation was reduced by 40-50% by either overexpression of a dominant negative K220R mutant GRK2 or treatment of the cells with the protein kinase C (PKC) inhibitor staurosporine, in a virtually additive fashion. Cellular overexpression of GRK2K220R not only inhibited agonist-induced AT1A-R phosphorylation, but also prevented receptor desensitization, as assessed by angiotensin II-stimulated GTPase activity in membranes prepared from agonist-treated and control cells. In contrast, PKC inhibition by staurosporine did not affect homologous desensitization of the AT1A-R. Overexpression of GRKs 2, 3, or 5 significantly augmented the agonist-induced AT1A-R phosphorylation 1.5- to 1.7-fold (p < 0.001). These findings suggest a role for receptor phosphorylation by one or several GRKs in the rapid agonist-induced desensitization of the AT1A-R.
 ...
PMID:Phosphorylation of the type 1A angiotensin II receptor by G protein-coupled receptor kinases and protein kinase C. 866 16

Glucagon-like peptide-1 stimulates glucose-induced insulin secretion by binding to a specific G protein-coupled receptor that activates the adenylyl cyclase pathway. We previously demonstrated that heterologous desensitization of the receptor by protein kinase C correlated with phosphorylation in a 33-amino acid-long segment of the receptor carboxyl-terminal cytoplasmic tail. Here, we determined that the in vivo sites of phosphorylation are four serine doublets present at positions 431/432, 441/442, 444/445, and 451/452. In vitro phosphorylation of fusion proteins containing mutant receptor C-tails, however, indicated that whereas serines at position 431/432 were good substrates for protein kinase C (PKC), serines 444/445 and 451/452 were poor substrates, and serines 441/442 were not substrates. In addition, serine 416 was phosphorylated on fusion protein but not in intact cells. This indicated that in vivo a different PKC isoform or a PKC-activated kinase may phosphorylate the receptor. The role of phosphorylation on receptor desensitization was assessed using receptor mutants expressed in COS cells or Chinese hamster lung fibroblasts. Mutation of any single serine doublet to alanines reduced the extent of phorbol 12-myristate 13-acetate-induced desensitization, whereas substitution of any combination of two serine doublets suppressed it. Our data thus show that the glucagon-like peptide-1 receptor can be phosphorylated in response to phorbol 12-myristate 13-acetate on four different sites within the cytoplasmic tail. Furthermore, phosphorylation of at least three sites was required for desensitization, although maximal desensitization was only achieved when all four sites were phosphorylated.
 ...
PMID:Heterologous desensitization of the glucagon-like peptide-1 receptor by phorbol esters requires phosphorylation of the cytoplasmic tail at four different sites. 870 11

Glucagon-like peptide-1 (GLP-1) stimulates glucose-induced insulin secretion by binding to a specific G protein-coupled receptor linked to activation of the adenylyl cyclase pathway. Here, using insulinoma cell lines, we studied homologous and heterologous desensitization of GLP-1-induced cAMP production. Preexposure of the cells to GLP-1 induced a decrease in GLP-1-mediated cAMP production, as assessed by a 3- to 5-fold rightward shift of the dose-response curve and an approximately 20 percent decrease in the maximal production of cAMP. Activation of protein kinase C by the phorbol ester phorbol 12-myristate 13-acetate (PMA) also induced desensitization of the GLP-1-mediated response, leading to a 6- to 9-fold shift in the EC50 and a 30% decrease in the maximal production of cAMP. Both forms of desensitization were additive, and the protein kinase C inhibitor RO-318220 inhibited PMA-induced desensitization, but not agonist-induced desensitization. GLP-1- and PMA-dependent desensitization correlated with receptor phosphorylation, and the levels of phosphorylation induced by the two agents were additive. Furthermore, PMA-induced, but not GLP-1-induced, phosphorylation was totally inhibited by RO-318220. Internalization of the GLP-1 receptor did not participate in the desensitization induced by PMA, as a mutant GLP-1 receptor lacking the last 20 amino acids of the cytoplasmic tail was found to be totally resistant to the internalization process, but was still desensitized after PMA preexposure. PMA and GLP-1 were not able to induce the phosphorylation of a receptor deletion mutant lacking the last 33 amino acids of the cytoplasmic tail, indicating that the phosphorylation sites were located within the deleted region. The cAMP production mediated by this deletion mutant was not desensitized by PMA and was only poorly desensitized by GLP-1. Together, our results indicate that the production of cAMP and, hence, the stimulation of insulin secretion induced by GLP-1 can be negatively modulated by homologous and heterologous desensitization, mechanisms that involve receptor phosphorylation.
 ...
PMID:Desensitization and phosphorylation of the glucagon-like peptide-1 (GLP-1) receptor by GLP-1 and 4-phorbol 12-myristate 13-acetate. 883 46

The effect of aluminum (AI) on inorganic phosphate (P(i)) transport stimulation induced by fluoride (F) was investigated in MC3T3-E1 osteoblast-like cells. Al potentiated the increase in P(i) transport activity induced by F in a dose- and time-dependent manner. Results obtained with deferoxamine mesylate, an Al chelator, suggest that a fluoroalumino complex is probably the active F molecule responsible for the change in P(i) transport observed in this study. The signaling pathway responsible for the stimulation of P(i) transport by F+Al likely involves a tyrosine phosphorylation process but neither a protein kinase C nor a mitogen-activated protein kinase pathway. As previously found in UMR-106 cells for F alone, F+Al potentiated the change in P(i) transport induced by fetal calf serum. A similar interaction was found between F+Al and thrombin acting through a G protein-coupled receptor. These observations are compatible with the hypothesis that F+Al could interact with G protein-coupled receptors associated with a signaling tyrosine phosphorylation process involved in the regulation of P(i), transport in osteoblast-like cells.
 ...
PMID:Aluminum potentiates P(i) transport stimulation induced by fluoride in osteoblast-like cells. 889 57

In 1321N1 astrocytoma cells, thrombin, but not carbachol, induces AP-1-mediated gene expression and DNA synthesis. To understand the divergent effects of these G protein-coupled receptor agonists on cellular responses, we examined Gq-dependent signaling events induced by thrombin receptor and muscarinic acetylcholine receptor stimulation. Thrombin and carbachol induce comparable changes in phosphoinositide and phosphatidylcholine hydrolysis, mobilization of intracellular Ca2+, diglyceride generation, and redistribution of protein kinase C; thus, activation of these Gq-signaling pathways appears to be insufficient for gene expression and mitogenesis. Thrombin increases Ras and mitogen-activated protein kinase activation to a greater extent than carbachol in 1321N1 cells. The effects of thrombin are not mediated through Gi, since ribosylation of Gi/Go proteins by pertussis toxin does not prevent thrombin-induced gene expression or thrombin-stimulated DNA synthesis. We recently reported that the pertussis toxin-insensitive G12 protein is required for thrombin-induced DNA synthesis. We demonstrate here, using transfection of receptors and G proteins in COS-7 cells, that G alpha 12 selectively couples the thrombin receptor to AP-1-mediated gene expression. This does not appear to result from increased mitogen-activated protein kinase activity but may reflect activation of a tyrosine kinase pathway. We suggest that preferential coupling of the thrombin receptor to G12 accounts for the selective ability of thrombin to stimulate Ras, mitogen-activated protein kinase, gene expression, and mitogenesis in 1321N1 cells.
 ...
PMID:Coupling of the thrombin receptor to G12 may account for selective effects of thrombin on gene expression and DNA synthesis in 1321N1 astrocytoma cells. 893 Aug 92

Two patterns of rapid desensitization have been characterized for G protein-coupled receptors: homologous desensitization, which mainly involves G protein-coupled receptor kinases and arrestins, and heterologous desensitization, which mainly involves protein kinases A (PKA) and C (PKC). In this review, Tsu Tshen Chuang and colleagues discuss evidence to show that PKA and PKC can modify the functional state of the G protein-coupled receptor kinases/arrestin homologous desensitization machinery, providing a novel level of cross-talk in signal transduction. Studies on regulation of G protein-coupled receptor kinases and arrestins confirm that the functional state of this machinery may have important consequences for cellular responsiveness and may represent new targets for therapeutic strategies.
 ...
PMID:G protein-coupled receptors: heterologous regulation of homologous desensitization and its implications. 899 Sep 58

G protein-coupled receptor kinases (GRKs) specifically recognize and phosphorylate the hormone-occupied form of numerous G protein-coupled receptors, ultimately resulting in termination of receptor signaling. While little is presently known about the regulation of GRK function, recent studies suggest a role for protein kinase C (PKC) phosphorylation of the beta-adrenergic receptor kinase in membrane association and activation of the kinase. To assess a potential general role for PKC in regulating GRK function, we characterized the ability of PKC to phosphorylate GRK5, a recently identified member of the GRK family. We demonstrate that GRK5 can be rapidly and stoichiometrically phosphorylated by PKC in vitro. Intact cell studies reveal that GRK5 is also phosphorylated when transiently expressed in COS-1 cells following treatment with the PKC activator, phorbol 12-myristate 13-acetate. In vitro analysis reveals two major sites of PKC phosphorylation within the C-terminal 26 amino acids of GRK5. GRK5 phosphorylation by PKC dramatically reduces its ability to phosphorylate both receptor (light-activated rhodopsin) and non-receptor (casein and phosvitin) substrates. Kinetic analysis reveals an approximately 5-fold increased Km and approximately 3-fold decreased Vmax for rhodopsin, with no change in the Km for ATP. The reduced affinity of PKC-phosphorylated GRK5 for rhodopsin was also evident in a decreased ability to bind to rhodopsin-containing membranes, while direct binding of GRK5 to phospholipids appeared unaltered. These results suggest that PKC might play an important role in modulating the ability of GRK5 to regulate receptor signaling and that GRK phosphorylation by PKC may serve as a disparate mechanism for regulating GRK activity.
 ...
PMID:Regulation of the G protein-coupled receptor kinase GRK5 by protein kinase C. 901 39


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