title: Acetylcholine muscarinic m1 receptor regulation of cyclic AMP synthesis controls growth factor stimulation of Raf activity.
abstract: Acetylcholine muscarinic m2 receptors (m2R) couple to heterotrimeric Gi proteins and activate the Ras/Raf/mitogen-activated protein kinase pathway and phosphatidylinositol 3-kinase in Rat 1a cells. In contrast to the m2R, stimulation of the acetylcholine muscarinic m1 receptor (m1R) does not activate the Ras/Raf/mitogen-activated protein kinase regulatory pathway in Rat 1a cells but rather causes a pronounced inhibition of epidermal growth factor and platelet-derived growth factor receptor activation of Raf. In Rat 1a cells, m1R stimulation of phospholipase C beta and the marked rise in intracellular calcium stimulated cyclic AMP (cAMP) synthesis, resulting in the activation of protein kinase A. Stimulation of protein kinase A inhibited Raf activation in response to growth factors. Platelet-derived growth factor receptor stimulation of phosphatidylinositol 3-kinase activity was not affected by either m1R stimulation or protein kinase A activation in response to forskolin-stimulated cAMP synthesis. GTP loading of Ras in response to growth factors was unaffected by protein kinase A activation but was partially inhibited by carbachol stimulation of the m1R. Therefore, protein kinase A action at the Ras/Raf activation interface selectively inhibited only one branch of the signal transduction network initiated by tyrosine kinases. Specific adenylyl cyclases responding to different signals, including calcium, with enhanced cAMP synthesis will regulate Raf activation in response to Ras.GTP. Taken together, the data indicate that G protein-coupled receptors can positively and negatively regulate the responsiveness of tyrosine kinase-stimulated mitogenic response pathways.
authors.affiliation: Division of Basic Sciences, National Jewish Center for Immunology and Respiratory Medicine, Denver, Colorado 80206.
authors.forename: M
authors.initials: M
authors.lastname: Russell
authors.forename: S
authors.initials: S
authors.lastname: Winitz
authors.forename: G L
authors.initials: GL
authors.lastname: Johnson
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D001285:Atropine / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002217:Carbachol / Q000494:pharmacology*; D002460:Cell Line; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004789:Enzyme Activation; D004815:Epidermal Growth Factor / Q000494:pharmacology*; D066246:ErbB Receptors / Q000187:drug effects / Q000502:physiology; D019204:GTP-Binding Proteins / Q000378:metabolism; D015870:Gene Expression; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007700:Kinetics; D008954:Models, Biological; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins / Q000187:drug effects / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000378:metabolism; D011976:Receptors, Muscarinic / Q000096:biosynthesis / Q000502:physiology*; D017479:Receptors, Platelet-Derived Growth Factor / Q000187:drug effects / Q000502:physiology; D014162:Transfection
chemical_list: D000262:Adenylyl Cyclases; D001285:Atropine; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D002217:Carbachol; D005576:Colforsin; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D004815:Epidermal Growth Factor; D066246:ErbB Receptors; D019204:GTP-Binding Proteins; D006160:Guanosine Triphosphate; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D010982:Platelet-Derived Growth Factor; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D019908:Proto-Oncogene Proteins c-raf; D020794:Receptor Protein-Tyrosine Kinases; D011976:Receptors, Muscarinic; D017479:Receptors, Platelet-Derived Growth Factor