cAMP and beta gamma subunits of heterotrimeric G proteins stimulate the mitogen-activated protein kinase pathway in COS-7 cells.
Mitogen-activated protein kinases (MAPKs) are activated by a variety of extracellular stimuli, including agonists for G protein-coupled receptors. Using transient transfection of COS-7 cells, we have studied the stimulation of a hemagglutinin-tagged p44mapk (p44HA-mapk) by receptors coupled to Gs, Gq, and Gi. Agonists that act via all three G proteins stimulated p44HA-mapk activity. A constitutively activated alpha s mutant, forskolin, and a cAMP analog also increased p44HA-mapk activity, indicating that cAMP in COS-7 cells, in contrast to other cell types, activates the MAPK pathway. Similarly, a constitutively activated alpha q mutant, overexpression of phospholipase C-beta 2, and a phorbol ester also stimulated p44HA-mapk, suggesting that Gq-coupled receptors stimulate the MAPK pathway by increasing phosphatidylinositol turnover and probably stimulating protein kinase C. In COS-7 cells, in contrast to Rat-1 cells, mutationally activated alpha i did not stimulate the MAPK pathway. G protein beta and gamma subunits, overexpressed together, did activate p44HA-mapk; this finding suggests that in COS-7 cells Gi-coupled receptors may stimulate the MAPK pathway through beta gamma. These unexpected results in COS-7 cells show that G proteins and second messengers regulate the MAPK pathway differently in different cell types.
Faure
M
M
Department of Pharmacology, University of California, San Francisco 94143.
Voyno-Yasenetskaya
T A
TA
Bourne
H R
HR
D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000096:biosynthesis / Q000378:metabolism*; D002217:Carbachol / Q000494:pharmacology; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D006224:Cricetinae; D003412:Cricetulus; D000242:Cyclic AMP / Q000378:metabolism*; D018076:DNA, Complementary / Q000378:metabolism; D004815:Epidermal Growth Factor / Q000494:pharmacology; D004873:Ergolines / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism*; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D016296:Mutagenesis; D010660:Phenylisopropyladenosine / Q000494:pharmacology; D010716:Phosphatidylinositols / Q000378:metabolism*; D011493:Protein Kinase C / Q000096:biosynthesis / Q000378:metabolism; D019257:Quinpirole; D051381:Rats; D018004:Receptors, Bombesin / Q000187:drug effects / Q000502:physiology; D017448:Receptors, Dopamine D2 / Q000187:drug effects / Q000502:physiology; D011974:Receptors, LH / Q000187:drug effects / Q000502:physiology; D011976:Receptors, Muscarinic / Q000187:drug effects / Q000502:physiology; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology; D014162:Transfection
D006063:Chorionic Gonadotropin; D018076:DNA, Complementary; D004873:Ergolines; D046911:Macromolecular Substances; D010716:Phosphatidylinositols; D018004:Receptors, Bombesin; D017448:Receptors, Dopamine D2; D011974:Receptors, LH; D011976:Receptors, Muscarinic; D018047:Receptors, Purinergic P1; D019257:Quinpirole; D010660:Phenylisopropyladenosine; D004815:Epidermal Growth Factor; D002217:Carbachol; D000242:Cyclic AMP; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D001839:Bombesin