Agonist-induced phosphorylation of the luteinizing hormone/chorionic gonadotropin receptor expressed in a stably transfected cell line.
Much of the definitive work on G-protein-coupled receptor phosphorylation and its impact on receptor function has been performed with the catecholamine receptors. Evidence for receptor phosphorylation is lacking, however, for G-protein-coupled receptors that bind larger ligands, such as LH/CG. Using immunoprecipitation techniques and a clonal cell line stably transfected with the LH/CG receptor, we show here for the first time that exposure of cells to hCG induces phosphorylation of its cognate receptor. The hCG-induced increase in receptor phosphorylation requires receptor activation because it cannot be elicited with a hCG antagonist and is mediated at least in part by the cAMP second messenger system. This hypothesis is supported by the finding that the hCG-induced receptor phosphorylation is greatly reduced (but not abolished) in a cell line that overexpresses cAMP phosphodiesterase and that receptor phosphorylation can be induced by activation of endogenous cAMP synthesis with prostaglandin E2 or by addition of 8-bromo-cAMP. Last, we show that LH/CG receptor phosphorylation can be induced with a phorbol ester, but not with a calcium ionophore. We also examined a potential correlation between LH/CG receptor phosphorylation and uncoupling of the receptor from its effector. Although the phorbol ester-induced phosphorylation of the LH/CG receptor can be correlated with uncoupling, other experiments indicate that hCG-induced uncoupling of the LH/CG receptor can occur under conditions where the cAMP-mediated receptor phosphorylation is greatly reduced (or abolished).
Hipkin
R W
RW
Department of Pharmacology, University of Iowa College of Medicine, Iowa City 52242-1109.
Sánchez-Yagüe
J
J
Ascoli
M
M
D000001:Calcimycin / Q000494:pharmacology; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D000242:Cyclic AMP / Q000494:pharmacology; D004075:Diglycerides / Q000502:physiology; D006031:Glycosylation; D006801:Humans; D007295:Inositol Phosphates / Q000502:physiology; D007668:Kidney / Q000166:cytology; D010703:Phorbol Esters / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D011233:Precipitin Tests; D011967:Receptors, Gonadotropin / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D011974:Receptors, LH / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D015290:Second Messenger Systems / Q000502:physiology; D014162:Transfection
D006063:Chorionic Gonadotropin; D004075:Diglycerides; D007295:Inositol Phosphates; D010703:Phorbol Esters; D011967:Receptors, Gonadotropin; D011974:Receptors, LH; D000001:Calcimycin; D000242:Cyclic AMP