title: Phorbol ester causes desensitization of gonadotropin-responsive adenylate cyclase in a murine Leydig tumor cell line.
abstract: The murine Leydig tumor cell line, MLTC-1, contains gonadotropin receptors and a gonadotropin-responsive adenylate cyclase system that became refractory (desensitized) when exposed to human chorionic gonadotropin (hCG). MLTC-1 cells also contain phorbol ester receptors with a Kd of 53 nM for [3H]phorbol dibutyrate. Exposing cells to 12-O-tetradecanoyl phorbol 13-acetate (TPA) also causes desensitization of the hCG response. TPA-induced desensitization was similar to hCG-induced desensitization by every criteria tested. Both TPA- and hCG-induced desensitization caused approximately 50% loss of the hormone response within 30 min. Neither TPA or hCG altered receptor affinity for hCG. The dose response of adenylate cyclase to hCG or GTP in isolated membranes was not affected by either hCG- or TPA-induced desensitization. Similarly the dose response to hCG of cAMP accumulation in intact cells was not altered by desensitization with hCG or TPA. It was determined that MLTC-1 cells have Ca2+/phospholipid-dependent protein kinase activity that displayed a dose-dependent response to TPA. The concentration of TPA required to activate the protein kinase was similar to that required for desensitization. Phorbol esters that were unable to activate protein kinase C were also unable to desensitize MLTC-1 cells. The protein kinase from MLTC-1 cells was also activated by diacylglycerol. In addition, diacylglycerols caused desensitization of the hCG response. TPA- and diacylglycerol-induced desensitization is probably mediated by protein kinase C, and the similarities between hCG- and TPA-induced refractoriness suggests a convergence of mechanisms at some point of MLTC-1 cell desensitization.
authors.forename: R V
authors.initials: RV
authors.lastname: Rebois
authors.forename: J
authors.initials: J
authors.lastname: Patel
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000494:pharmacology*; D004075:Diglycerides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D007700:Kinetics; D007984:Leydig Cell Tumor / Q000201:enzymology*; D008297:Male; D051379:Mice; D015240:Phorbol 12,13-Dibutyrate; D010703:Phorbol Esters / Q000494:pharmacology*; D010704:Phorbols / Q000494:pharmacology*; D011493:Protein Kinase C; D011956:Receptors, Cell Surface / Q000378:metabolism; D011955:Receptors, Drug; D011971:Receptors, Immunologic / Q000378:metabolism; D011974:Receptors, LH; D013736:Testicular Neoplasms / Q000201:enzymology*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D029742:Caenorhabditis elegans Proteins; D002352:Carrier Proteins; D006063:Chorionic Gonadotropin; D004075:Diglycerides; D010703:Phorbol Esters; D010704:Phorbols; D011956:Receptors, Cell Surface; D011955:Receptors, Drug; D011971:Receptors, Immunologic; D011974:Receptors, LH; C083141:phorbol ester binding protein; C027776:phorbol ester receptor; D015240:Phorbol 12,13-Dibutyrate; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D013755:Tetradecanoylphorbol Acetate