title: Coupling of the thrombin receptor to G12 may account for selective effects of thrombin on gene expression and DNA synthesis in 1321N1 astrocytoma cells.
abstract: 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.
authors.affiliation: Department of Pharmacology, University of California, San Diego, La Jolla 92093-0636, USA.
authors.forename: G R
authors.initials: GR
authors.lastname: Post
authors.forename: L R
authors.initials: LR
authors.lastname: Collins
authors.forename: E D
authors.initials: ED
authors.lastname: Kennedy
authors.forename: S A
authors.initials: SA
authors.lastname: Moskowitz
authors.forename: A M
authors.initials: AM
authors.lastname: Aragay
authors.forename: D
authors.initials: D
authors.lastname: Goldstein
authors.forename: J H
authors.initials: JH
authors.lastname: Brown
mesh_terms: D000818:Animals; D001253:Astrocytes / Q000187:drug effects / Q000378:metabolism*; D001254:Astrocytoma; D019556:COS Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology; D004247:DNA / Q000096:biosynthesis*; D019204:GTP-Binding Proteins / Q000378:metabolism*; D005786:Gene Expression Regulation / Q000187:drug effects*; D006160:Guanosine Triphosphate / Q000378:metabolism; D006801:Humans; D018721:Muscarinic Agonists / Q000494:pharmacology; D037342:Pertussis Toxin; D011493:Protein Kinase C / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000378:metabolism; D018179:Receptors, Thrombin / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D013917:Thrombin / Q000494:pharmacology*; D018808:Transcription Factor AP-1 / Q000378:metabolism; D014162:Transfection; D014407:Tumor Cells, Cultured; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D018631:ras Proteins / Q000378:metabolism
chemical_list: D018721:Muscarinic Agonists; D011976:Receptors, Muscarinic; D018179:Receptors, Thrombin; D018808:Transcription Factor AP-1; D010566:Virulence Factors, Bordetella; D006160:Guanosine Triphosphate; D002217:Carbachol; D004247:DNA; D037342:Pertussis Toxin; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D013917:Thrombin; D019204:GTP-Binding Proteins; D018631:ras Proteins