Epidermal growth factor-induced heterologous desensitization of the luteinizing hormone choriogonadotopin receptor in a cell-free membrane preparation is associated with the tyrosine phosphorylation of the epidermal growth factor receptor

Epidermal growth factor (EGF) attenuated hCG-stimulated adenylyl cyclase ac tivity in rat luteal and follicular membranes. H7, an equipotent serine/thr eonine protein kinase inhibitor of cAMP-dependent protein kinases, cGMP-dep endent protein kinases, and lipid-dependent protein kinase C, did not effec t the ability of EGF to decrease hCG-responsive adenylyl cyclase activity, suggesting that a serine/threonine phosphorylation event catalyzed by these kinases was not critically involved in EGF-induced desensitization. Likewi se, pertussis toxin-catalyzed ADP-ribosylation of a 40-kDa luteal membrane protein, which exhibited immunoreactivity with an antibody against G(i)alph a did not hinder the ability of EGF to attenuate hCG-stimulated adenylyl cy clase activity, indicating that Gi did not mediate EGF-induced desensitizat ion. Rather, EGF-induced heterologous desensitization of LH/CG receptor in ovarian membranes was closely associated with the specific and prominent ty rosine phosphorylation of the 170-kDa EGF receptor. Both EGF-stimulated aut ophosphorylation of EGF receptor and EGF-induced LH/CG receptor desensitiza tion were attenuated by genistein, a tyrosine kinase inhibitor. These resul ts suggest that tyrosine phosphorylation of the 170-kDa EGF receptor is a n ecessary component of the signaling pathway in EGF-induced heterologous des ensitization of the LH/CG receptor.