title: Hormonal control of epidermal growth factor receptors by gonadotropins during granulosa cell differentiation.
abstract: The hormonal induction of epidermal growth factor (EGF) receptor formation was analyzed during the maturation of granulosa cells obtained from diethylstilbestrol-implanted immature rats. In the absence of FSH, EGF receptors (as measured by the binding of [125I]iodo-EGF to the intact cells) rose by 50% at 6 h of culture, but then declined to about 25-40% of their initial levels at 24-96 h of culture. Scatchard analyses demonstrated the presence of high affinity EGF-binding sites in both freshly prepared cells and after FSH treatment. FSH stimulated a dose-dependent increase in the EGF receptor content of granulosa cells during a 96-h culture period. Concentrations of FSH as low as 2.5-5 ng/ml elevated EGF receptor levels 2- to 3-fold compared to those in untreated control cells, and 30 ng/ml FSH caused a maximal 15-fold rise. FSH increased EGF receptor levels approximately 2-fold in the first 6 h of culture and by up to 7-fold at 96 h compared to levels in freshly prepared cells. FSH treatment did not change the binding affinity (Kd = 5-6 X 10(-11) M) of the EGF receptor, but increased the total number of EGF-binding sites. The stimulatory effects of FSH on EGF receptor expression were mimicked by other cAMP-inducing ligands, including 8-bromo-cAMP, forskolin, and choleragen. Ligands known to inhibit granulosa cell function, including GnRH agonists and the phorbol ester 12-O-tetradecanoyl-phorbol 13-acetate, reduced the stimulation of EGF receptors by FSH. However, only 12-O-tetradecanoyl-phorbol 13-acetate suppressed the induction of EGF receptors by 8-bromo-cAMP. In granulosa cells cultured for 48 h with FSH, subsequent treatment with hCG for 24 h reduced EGF receptor content by 25%. Autoradiographic studies with [125I]iodo-EGF in ovarian thin sections demonstrated that EGF-binding sites were uniformly dispersed throughout the ovaries of diethylstilbestrol-implanted rats. Treatment with PMSG markedly increased EGF receptors in the outer walls of the growing follicles, while hCG treatment after PMSG caused a general decline in ovarian labeling. These results indicate that FSH maintains and increases the number of EGF receptors during granulosa cell differentiation, while LH/hCG reduces EGF-binding sites. Such changes in EGF receptors in the presence of endogenous growth factors may influence the number and selection of follicles destined for ovulation.
mesh_terms: D015124:8-Bromo Cyclic Adenosine Monophosphate / Q000494:pharmacology; D000818:Animals; D002454:Cell Differentiation; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D004054:Diethylstilbestrol / Q000494:pharmacology; D066246:ErbB Receptors / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism; D007700:Kinetics; D010053:Ovary / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D006063:Chorionic Gonadotropin; D015124:8-Bromo Cyclic Adenosine Monophosphate; D004054:Diethylstilbestrol; D005640:Follicle Stimulating Hormone; D066246:ErbB Receptors; D013755:Tetradecanoylphorbol Acetate