title: Modulation of Gs activity by phorbol myristate acetate in rat hepatocytes.
abstract: Activation of protein kinase C promotes heterologous desensitization of hepatic adenylate cyclase. The basis for this desensitization was explored by use of a strategy with several independent approaches. Although not influencing the amount of forskolin-stimulated adenylate cyclase activity (catalyst), treatment with phorbol 12-myristate 13-acetate (PMA) decreased adenylate cyclase activation in response to either sodium fluoride or guanylyl imidodiphosphate [Gpp(NH)p]. Adenosine 3',5'-cyclic monophosphate (cAMP) accumulation in cholera toxin-treated hepatocytes and both the basal and GTP-stimulated adenylate cyclase activity of membranes from toxin-treated cells displayed a marked reduction in response to PMA. The ability of cholate extracts of hepatocyte membranes to reconstitute beta-adrenergic-stimulated adenylate cyclase activity of membrane of S49 mouse lymphoma cyc- cells was reduced by treatment with PMA. Cholera toxin-catalyzed labeling of Gs alpha-subunits was likewise diminished by phorbol ester treatment. Immunoblots of membranes from control or PMA-treated hepatocytes showed no difference in the amount of Gs alpha. Immunoprecipitation studies failed to detect phosphorylation of this G protein alpha-subunit. The data demonstrate that PMA induces an alteration in the functional status of Gs without altering the amount of this transmembrane signaling element. The alteration in Gs function may play a significant role in heterologous desensitization.
authors.affiliation: Instituto de Fisiología Celular, Universidad Nacional Autónoma de México, Mexico D.F.
authors.forename: S M
authors.initials: SM
authors.lastname: Hernández-Sotomayor
authors.forename: M
authors.initials: M
authors.lastname: Macías-Silva
authors.forename: C C
authors.initials: CC
authors.lastname: Malbon
authors.forename: J A
authors.initials: JA
authors.lastname: García-Sáinz
mesh_terms: D015056:1-Methyl-3-isobutylxanthine / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000187:drug effects / Q000201:enzymology; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D005260:Female; D019204:GTP-Binding Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006165:Guanylyl Imidodiphosphate / Q000494:pharmacology; D007700:Kinetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D006165:Guanylyl Imidodiphosphate; D002772:Cholera Toxin; D000242:Cyclic AMP; D011493:Protein Kinase C; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D013755:Tetradecanoylphorbol Acetate; D015056:1-Methyl-3-isobutylxanthine