title: Phosphorylation-independent desensitization of the luteinizing hormone/chorionic gonadotropin receptor in porcine follicular membranes.
abstract: Phosphorylation of several G protein-coupled receptors mediates desensitization. This study determined whether LH/CG receptor was phosphorylated under conditions that promoted human CG (hCG)-induced desensitization. Cell-free desensitization of LH/CG receptor-mediated adenylylcyclase activity in porcine follicular membranes occurred in the presence of GTP and was time- and hCG dose-dependent, reaching 36-52% upon preincubation at 30 C for 40 min with 1.0 micrograms/ml hCG. However, under conditions that promoted GTP-dependent desensitization, there was no apparent phosphorylation of LH/CG receptor (obtained via immunoprecipitation) by endogenous membrane-associated protein kinases using [gamma-32P]GTP or [gamma-32P]ATP as phosphate donor. On the other hand, LH/CG receptor (88-90 kilodaltons) from both control and hCG-incubated membranes was phosphorylated in vitro by the catalytic subunit of cAMP-dependent protein kinase (protein kinase A). However, protein kinase A (in the absence of exogenous GTP) did not promote LH/CG receptor desensitization. These data demonstrate that, unlike with other G protein-linked receptors, LH/CG receptor phosphorylation by endogenous follicular membrane-associated protein kinase(s) does not mediate desensitization.
authors.affiliation: Department of Cell and Molecular Biology, Northwestern University Medical School, Chicago, Illinois 60611.
authors.forename: M L
authors.initials: ML
authors.lastname: Lamm
authors.forename: M
authors.initials: M
authors.lastname: Hunzicker-Dunn
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D002462:Cell Membrane / Q000378:metabolism; D002474:Cell-Free System / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D005260:Female; D019204:GTP-Binding Proteins / Q000378:metabolism; D006160:Guanosine Triphosphate / Q000378:metabolism / Q000494:pharmacology; D007986:Luteinizing Hormone / Q000378:metabolism / Q000494:pharmacology; D008565:Membrane Proteins / Q000378:metabolism; D006080:Ovarian Follicle / Q000378:metabolism*; D010766:Phosphorylation; D011974:Receptors, LH / Q000276:immunology / Q000378:metabolism*; D015398:Signal Transduction; D013552:Swine
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D008565:Membrane Proteins; D011974:Receptors, LH; D006160:Guanosine Triphosphate; D000255:Adenosine Triphosphate; D007986:Luteinizing Hormone; D017868:Cyclic AMP-Dependent Protein Kinases; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases