title: Homologous desensitization of the murine luteinizing hormone receptor expressed in L cells.
abstract: Using a clonal cell line that stably expresses the murine luteinizing hormone receptor (LHR 11/6 cells), we studied the molecular mechanisms of agonist-induced desensitization of the luteinizing hormone/chorionic gonadotropin-responsive adenylyl cyclase. Exposure of transfected cells to human chorionic gonadotropin (hCG) resulted in a dose-dependent loss of maximal hCG-stimulable adenylyl cyclase activity without a significant shift to the right of the dose-response curve to hCG. This rapid uncoupling of the LH receptor from the cellular adenylyl cyclase system was not accompanied by internalization of receptor sites. A 6-h exposure to hCG led only to minor (ca. 25%) loss of membrane binding sites. The dose-response curve to hCG was not altered by pretreating cells with 8-Br-cAMP or prostaglandin E1. These findings, and the observation that hCG-induced desensitization can still be monitored at Mg2+ concentrations in the assay as high as 10 mM, preclude a significant contribution of protein kinase A to LH receptor uncoupling. The murine LH receptor not only stimulates adenylyl cyclase but also phospholipase C and probably protein kinase C (PKC) via diacylglycerol. Activation of PKC by 4 beta-phorbol 12-myristate 13-acetate failed to desensitize. When PKC was down-regulated hCG could still exert a maximal desensitizing effect. It is concluded that in LHR 11/6 cells there is no evidence for a major role of PKC in homologous desensitization. Thus, it is likely that a second messenger-independent kinase, such as beta-adrenergic receptor kinase, or a different, as yet unknown mechanism is involved in the agonist-induced desensitization of the LH receptor.
authors.affiliation: Institut für Pharmakologie, Freie Universität Berlin, Germany.
authors.forename: T
authors.initials: T
authors.lastname: Gudermann
authors.forename: M
authors.initials: M
authors.lastname: Birnbaumer
authors.forename: L
authors.initials: L
authors.lastname: Birnbaumer
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000262:Adenylyl Cyclases / Q000378:metabolism; D000527:Alprostadil / Q000494:pharmacology; D000818:Animals; D002460:Cell Line; D006063:Chorionic Gonadotropin / Q000008:administration & dosage / Q000494:pharmacology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D004361:Drug Tolerance; D015870:Gene Expression; D007739:L Cells / Q000378:metabolism; D008274:Magnesium / Q000494:pharmacology; D051379:Mice; D011493:Protein Kinase C / Q000378:metabolism; D011974:Receptors, LH / Q000187:drug effects* / Q000235:genetics*; D012969:Sodium Fluoride / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014162:Transfection
chemical_list: D006063:Chorionic Gonadotropin; D011974:Receptors, LH; D015124:8-Bromo Cyclic Adenosine Monophosphate; D012969:Sodium Fluoride; D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D000527:Alprostadil; D008274:Magnesium; D013755:Tetradecanoylphorbol Acetate