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 thromboxane A(2) receptor (TP), which mediates vasoconstriction, mitogenesis, and platelet aggregation, has been shown to undergo rapid agonist-induced desensitization. Two isoforms (alpha and beta) of TP have been recognized. The potential role of the G protein-coupled receptor kinases (GRKs) in the phosphorylation and desensitization of TP alpha was investigated. Human embryonic kidney (HEK) 293 cells stably transfected with the His-tagged TP alpha was used to study the phosphorylation and desensitization of the receptor. Rapid isolation of the (32)P-labeled receptor was achieved by Ni(2+)-nitrilotriacetic acid agarose after agonist stimulation of HEK293 cells prelabeled with (32)P(i). [1S-[1 alpha,2 alpha(Z),3 beta(1E,3S*),4 alpha]]-7-[3-[3-Hydroxy-4-(4-iodophenoxy)-1-butenyl]-7-oxabicyclo[2,2,1]hept-2-yl]-5-heptenoic acid (I-BOP) induced receptor phosphorylation and Ca(2+) release in a time- and dose-dependent manner. Pretreatment of cells with I-BOP abolished subsequent induction of Ca(2+) release through a second dose of I-BOP. Transfection with expression plasmids encoding the cDNA of GRK5 or GRK6 augmented I-BOP-induced phosphorylation and inhibited I-BOP-stimulated Ca(2+) release. Both I-BOP-induced and GRK-mediated phosphorylation and phorbol ester-induced phosphorylation were blocked by the addition of 2-[1-(3-dimethylaminopropyl)-1H-indol-3-yl]-3-(1H-indol-3-yl)-maleimide) (GF 109203X). This indicates that GF 109203X, a known protein kinase C (PKC) inhibitor, also inhibits GRKs. This finding was further supported by in vitro studies in which preparations of GRK5 and GRK6 were found to be inhibited by GF 109203X. These results suggest that GRK5 and GRK6 may phosphorylate the TP alpha in an agonist-dependent manner. Furthermore, the results obtained with PKC inhibitors in assessing the role of PKC in agonist-induced receptor phosphorylation should be interpreted with caution.
 ...
PMID:Phosphorylation and desensitization of the human thromboxane receptor-alpha by G protein-coupled receptor kinases. 1150 27

We examined whether protein kinase D (PKD) overexpression in Swiss 3T3 cells potentiates the proliferative response to either the G protein-coupled receptor agonists bombesin and vasopressin or the biologically active phorbol ester phorbol 12,13-dibutyrate (PDBu). In order to generate Swiss 3T3 cells stably overexpressing PKD, cultures of these cells were infected with retrovirus encoding murine PKD and green fluorescent protein (GFP) expressed as two separate proteins translated from the same mRNA. GFP was used as a marker for selection of PKD-positive cells. PKD overexpressed in Swiss 3T3 cells was dramatically activated by cell treatment with bombesin or PDBu as judged by in vitro kinase autophosphorylation assays and exogenous substrate phosphorylation. Concomitantly, these stimuli induced PKD phosphorylation at Ser(744), Ser(748), and Ser(916). PKD activation and phosphorylation were prevented by exposure of the cells to protein kinase C-specific inhibitors. Addition of bombesin, vasopressin, or PDBu to cultures of Swiss 3T3 cells overexpressing PKD induced a striking increase in DNA synthesis and cell number compared with cultures of Swiss 3T3-GFP cells. In contrast, stimulation of DNA synthesis in response to epidermal growth factor, which acts via protein kinase C/PKD-independent pathways, was not enhanced. Our results demonstrate that overexpression of PKD selectively potentiates mitogenesis induced by bombesin, vasopressin, or PDBu in Swiss 3T3 cells.
 ...
PMID:Protein kinase D potentiates DNA synthesis and cell proliferation induced by bombesin, vasopressin, or phorbol esters in Swiss 3T3 cells. 1151 71

Reversible phosphorylation plays important roles in G protein-coupled receptor signaling, desensitization, and endocytosis, yet the precise location and role of in vivo phosphorylation sites is unknown for most receptors. Using metabolic 32P labeling and phosphopeptide sequencing we provide a complete phosphorylation map of the human bradykinin B2 receptor in its native cellular environment. We identified three serine residues, Ser(339), Ser(346), and Ser(348), at the C-terminal tail as principal phosphorylation sites. Constitutive phosphorylation occurs at Ser(348), while ligand-induced phosphorylation is found at Ser(339) and Ser(346)/Ser(348) that could be executed by several G protein-coupled receptor kinases. In addition, we found a protein kinase C-dependent phosphorylation of Ser(346) that was mutually exclusive with the basal phosphorylation at Ser(348) and therefore may be implicated in differential regulation of B2 receptor activation. Functional analysis of receptor mutants revealed that a low phosphorylation stoichiometry is sufficient to initiate receptor sequestration while a clustered phosphorylation around Ser(346) is necessary for desensitization of the B2 receptor-induced phospholipase C activation. This was further supported by the specifically reduced Ser(346)/Ser(348) phosphorylation observed upon stimulation with a nondesensitizing B2 receptor agonist. The differential usage of clustered phosphoacceptor sites points to distinct roles of multiple kinases in controlling G protein-coupled receptor function.
 ...
PMID:Determination of bradykinin B2 receptor in vivo phosphorylation sites and their role in receptor function. 1151 30

Protein kinase D (PKD)/protein kinase C mu is a serine/threonine protein kinase activated by growth factors, antigen-receptor engagement, and G protein-coupled receptor (GPCR) agonists via a phosphorylation-dependent mechanism that requires protein kinase C (PKC) activity. In order to investigate the dynamic mechanisms associated with GPCR signaling, the intracellular distribution of PKD was analyzed in live cells by imaging fluorescent protein-tagged PKD and in fixed cells by immunocytochemistry. We found that PKD shuttled between the cytoplasm and the nucleus in both fibroblasts and epithelial cells. Cell stimulation with mitogenic GPCR agonists that activate PKD induced a transient nuclear accumulation of PKD that was prevented by inhibiting PKC activity. The nuclear import of PKD requires its cys2 domain in conjunction with a nuclear import receptor, while its nuclear export requires its pleckstrin homology domain and a competent Crm1-dependent nuclear export pathway. This study thus characterizes the regulated nuclear transport of a signaling molecule in response to mitogenic GPCR agonists and positions PKD as a serine kinase whose kinase activity and intracellular localization is coordinated by PKC.
 ...
PMID:Regulated nucleocytoplasmic transport of protein kinase D in response to G protein-coupled receptor activation. 1164 11

PDZ domain proteins use the PDZ domain binding motif to bind to the C-terminal sequence of membrane proteins to help scaffold them and spatially organize the components of the intracellular signaling machinery. We have identified a sequence at the C terminus of a G protein-coupled receptor, the PrRP receptor, that shares similarities with the C-terminal sequence of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor (AMPA-R) subunits that interact with PDZ domain proteins. When coexpressed in human embryonic kidney 293 cells, PrRP receptor was able to coimmunoprecipitate the three PDZ domain proteins known to interact with AMPA receptors: glutamate receptor interacting protein (GRIP), AMPA binding protein (ABP), and protein that interacts with C-kinase (PICK1), but not the PDZ domain protein PSD-95, which does not interact with AMPA receptors. These interactions are sequence-selective as determined by mutagenesis. Furthermore, we show that PrRP receptor forms intracellular clusters when coexpressed with PICK1, and that this clustering effect is dependent on the interaction between the PICK1 PDZ domain and the last four amino acids of PrRP receptor. We found that PrRP receptor interaction with GRIP is not protein kinase C-regulated but may be regulated by other unidentified kinase because okadaic acid dramatically reduced GRIP interaction. By in situ hybridization, we show that the PrRP receptor is expressed in neurons that also express these PDZ domain proteins. We thus demonstrate that PrRP receptor interacts with the same PDZ domain proteins as the AMPA-Rs, raising the possibility that these two proteins could be scaffolded together at the synapse. These results may help to gain important insights into PrRP functions within the central nervous system.
 ...
PMID:The carboxyl terminus of the prolactin-releasing peptide receptor interacts with PDZ domain proteins involved in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid receptor clustering. 1164 19

The histamine H2 receptor (H2r) belongs to the heptahelical receptor family; upon agonist binding, members of this family activate a G protein and the downstream effector adenylyl cyclase. Like other G protein-coupled receptors, exposure of H2r to agonists produces a desensitization of the response. The present study focused on the desensitization mechanism of this receptor. Using transiently transfected COS-7 cells expressing tagged-H2r, the desensitization induced by amthamine, characterized by decreased cAMP production, was studied. Results show that the receptor was rapidly desensitized with a t(1/2) = 0.49 +/- 0.01 min. Because of the rapid nature of H2r desensitization, receptor phosphorylation was examined as a likely mechanism for signal attenuation. H2r desensitization was not affected by protein kinases A and C (PKA and PKC) inhibitors but was remarkably reduced by Zn(2+), an inhibitor of G protein-coupled receptor kinases (GRKs). Cotransfection experiments using tagged H2r and different GRKs (2, 3, 5, or 6), demonstrated that GRK2 and GRK3 were the most potent in augmenting desensitization, causing a reduction in the maximal response to amthamine and a decrease of the t(1/2) for desensitization, whereas GRK5 and GRK6 did not affect the signaling. Receptor phosphorylation correlates with desensitization for each GRK studied, whereas phosphorylation that is dependent on protein kinases A and C seemed irrelevant in receptor signal termination. These results indicate that in H2r-transfected COS-7 cells, exposure to an agonist caused desensitization controlled by H2r phosphorylation via GRK2 and GRK3.
 ...
PMID:Histamine H2 receptor desensitization: involvement of a select array of G protein-coupled receptor kinases. 1164 33

Bradykinin (BK) and vascular endothelial growth factor (VEGF)-165 stimulate vasodilatation, microvascular permeability, and angiogenesis via the activation of the B2-type and KDR/Flk-1 receptors. To delineate the signal transduction pathways distal to the receptor activation in microvascular permeability, we compared their effects on two downstream targets, i.e. endothelial nitric-oxide (NO) synthase (eNOS) and F-actin, in primary cultures of cardiac capillary endothelial cells. The two mediators induced a similar cytoskeletal reorganization and both the translocation and activation of eNOS, leading to NO release within the first minutes of cell exposure. At the same time, BK produced the tyrosine phosphorylation and internalization of KDR/Flk-1 as did VEGF itself. This transactivation was blocked by the selective inhibitor of VEGF receptor tyrosine kinase activity but not by inhibitors of epidermal growth factor receptor or protein kinase C activity. The selective inhibitor of VEGF receptor tyrosine kinase activity totally prevented the effects of VEGF but only partially inhibited NO release induced by BK without affecting the concomitant cytoskeletal reorganization. Thus, BK transactivated KDR/Flk-1 through an intrinsic kinase activity of KDR/Flk-1, resulting in a further eNOS activation in endothelial cells. This represents a novel mechanism whereby a G protein-coupled receptor activates a receptor tyrosine kinase to generate biological response.
 ...
PMID:Rapid transactivation of the vascular endothelial growth factor receptor KDR/Flk-1 by the bradykinin B2 receptor contributes to endothelial nitric-oxide synthase activation in cardiac capillary endothelial cells. 1171 43

Prolonged opioid exposure occurs frequently as a result of clinical use or drug abuse. Research using different ligands, cell lines, and animal models in the past three decades has elucidated some correlation between the biochemical events and behavioral changes resulting from opioid tolerance, dependence and addiction. For the most part, opioid tolerance and dependence are associated with up-regulation of the cAMP pathway, mediated by the supersensitization of adenylyl cyclase and by the altered coupling of opioid receptors to stimulatory G proteins. Neuroadaptive changes in signal transduction following prolonged opioid exposure are mediated by protein kinase systems, such as protein kinase C (PKC), cyclic AMP-dependent protein kinase (PKA), Ca2+/camodulin-dependent protein kinase II (CaMKII), G protein-coupled receptor kinases (GRKs) and mitogen-activated protein kinases (MAPKs). Intermediate steps between opioid receptor activation and the second- or third-messenger cascades include GRK-mediated receptor endocytosis and intracellular trafficking, as well as interactions with excitatory amino acid receptors and regulation of nitric oxide synthesis. Thus, prolonged occupancy by opioid receptor agonists can have differential effects on opioid receptor internalization, down-regulation and desensitization, and in the supersensitization of adenylyl cyclase, which contribute to the development of opioid tolerance and dependence. We discuss the role of various protein kinases in the signaling mechanisms underlying these differences. Clearer understanding of the molecular mechanisms of opioid tolerance and dependence will help in the treatment of patients suffering from acute and chronic pain, or drug dependence and addiction.
 ...
PMID:Protein kinases modulate the cellular adaptations associated with opioid tolerance and dependence. 1175 Sep 24

The G protein-coupled receptor encoded by Kaposi's sarcoma-associated herpesvirus, also referred to as ORF74, has been shown to stimulate oncogenic and angiogenic signaling pathways in a constitutively active manner. The biochemical routes linking ORF74 to these signaling pathways are poorly defined. In this study, we show that ORF74 constitutively activates p44/p42 mitogen-activated protein kinase (MAPK) and Akt via G(i)- and phospholipase C (PLC)-mediated signaling pathways. Activation of Akt by ORF74 appears to be phosphatidylinositol 3-kinase (PI3-K) dependent but, interestingly, is also mediated by activation of protein kinase C (PKC) and p44/p42 MAPK. ORF74 may signal to Akt via p44/p42 MAPK, which can be activated by G(i), through activation of PI3-K or through PKC via the PLC pathway. Signaling of ORF74 to these proliferative and antiapoptotic signaling pathways can be further modulated positively by growth-related oncogene (GROalpha/CXCL1) and negatively by human gamma interferon-inducible protein 10 (IP-10/CXCL10), thus acting as an agonist and an inverse agonist, respectively. Despite the ability of the cytomegalovirus-encoded chemokine receptor US28 to constitutively activate PLC, this receptor does not increase phosphorylation of p44/p42 MAPK or Akt in COS-7 cells. Hence, ORF74 appears to signal through a larger diversity of G proteins than US28, allowing it to couple to proliferative and antiapoptotic signaling pathways. ORF74 can therefore be envisioned as an attractive target for novel treatment of Kaposi's sarcoma.
 ...
PMID:Kaposi's sarcoma-associated herpesvirus-encoded G protein-coupled receptor ORF74 constitutively activates p44/p42 MAPK and Akt via G(i) and phospholipase C-dependent signaling pathways. 1179 69

G protein-coupled receptor (GPCR)-evoked signal transduction pathways leading to the activation of extracellular signal-regulated kinases (ERK) are quite different among cell types. In cardiomyocytes, much attention has been focused on the activation of protein kinase C (PKC) or mobilization of intracellular Ca(2+) ([Ca(2+)](i)), however, the contributions of tyrosine kinases are controversial. In the present study, we characterized the signaling pathways involving tyrosine kinases, Pyk2 and epidermal growth factor receptor (EGFR), and their contribution to ERK activation in cultured cardiomyocytes. We initially investigated the potential involvement of [Ca(2+)](i) and PKC on the activation of these kinases in endothelin-stimulated cardiomyocytes. Interestingly, activation of Pyk2 was abrogated by chelating [Ca(2+)](i) or by downregulation of PKC, whereas transactivation of EGFR was solely dependent on PKC. By using a compound that selectively interferes with EGFR (AG1478), c-Src (PP1), or disrupts actin cytoskeleton (cytochalasin D), we demonstrated that cytochalasin D completely inhibited the activation of Pyk2, but not that of EGFR, whereas AG1478 did not inhibit the activation of Pyk2, indicating that transactivation of EGFR and signaling pathways involving Pyk2 were distinct pathways. Furthermore, activation of ERK and Shc, and c- fos gene expression were significantly inhibited by AG1478 but not by cytochalasin D or PP1. Overexpression of deletion mutant of EGFR attenuated the activation of ERK. These facts demonstrated the existence of two distinct tyrosine kinase pathways requiring Pyk2 or EGFR downstream from GPCR in cardiomyocytes. EGFR was Ca(2+)-independently activated and predominantly contributed to Shc/ERK/c- fos activation, while Pyk2 or c-Src contributed less to it.
 ...
PMID:Role of EGF Receptor and Pyk2 in endothelin-1-induced ERK activation in rat cardiomyocytes. 1185 54


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