Somatomedin-C enhances induction of luteinizing hormone receptors by follicle-stimulating hormone in cultured rat granulosa cells.
Recent studies have documented the ability of somatomedin-C (Sm-C) to synergize with FSH in the induction of rat granulosa cell progesterone biosynthesis. This direct cytodifferentiative action of Sm-C proved distinct from its established mitogenic property. To determine whether Sm-C partakes in the differentiation of granulosa cell functions other than progesterone biosynthesis, the role of Sm-C in the acquisition of LH receptors was investigated in vitro. Granulosa cells were obtained from immature, hypophysectomized diethylstilbestrol-treated rats and cultured under serum-free conditions for up to 72 h. Specific granulosa cell LH/hCG binding under basal conditions was relatively low and was not significantly affected by treatment with highly purified Sm-C (50 ng/ml). In contrast, treatment with FSH (oFSH; NIH FSH S14; 20 ng/ml) produced a 3.8-fold increase in LH/hCG binding to 3167 +/- 660 (+/- SE) cpm/10(6) cells. However, concurrent treatment with Sm-C (50 ng/ml) resulted in a 6.1-fold enhancement of the FSH effect. The ability of Sm-C to synergize with FSH in the induction of LH receptors was dose and time dependent, with an apparent median effective dose (ED50) of 6.2 +/- 0.6 (+/-SE) ng/ml, and a minimal time requirement of 24 h or less. Examination of the binding parameters of the LH/hCG receptor revealed that the Sm-C-mediated increase in LH/hCG binding was due to enhanced binding capacity, but not affinity (Kd = 4.4 X 10(-11) M). Decreasing dilutions (1:128,000-1:8,000) of a monoclonal antibody raised against Sm-C (sm 1.2), produced progressive and virtually complete immunoneutralization of the synergistic interaction between Sm-C and FSH, suggesting specificity of action. The ability of Sm-C to enhance LH receptor induction was associated with increased hCG-stimulated progesterone biosynthesis, suggesting that the newly acquired receptors are functional in nature. Our present findings indicate that nanomolar concentrations of Sm-C are capable of enhancing FSH-stimulated LH/hCG-binding capacity, but not affinity, in a time- and dose-dependent fashion. These observations suggest that the direct cytodifferentiative effect of Sm-C is not limited to the induction of progesterone biosynthesis, but other key granulosa cell functions may also be subject to modulation by this regulatory peptide.
Adashi
E Y
EY
Resnick
C E
CE
Svoboda
M E
ME
Van Wyk
J J
JJ
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D002478:Cells, Cultured; D006063:Chorionic Gonadotropin / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D005260:Female; D005640:Follicle Stimulating Hormone / Q000494:pharmacology*; D006107:Granulosa Cells / Q000187:drug effects*; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D011956:Receptors, Cell Surface / Q000187:drug effects*; D011974:Receptors, LH; D013002:Somatomedins / Q000096:biosynthesis / Q000276:immunology / Q000494:pharmacology*; D013997:Time Factors
D000911:Antibodies, Monoclonal; D006063:Chorionic Gonadotropin; D011956:Receptors, Cell Surface; D011974:Receptors, LH; D013002:Somatomedins; D007334:Insulin-Like Growth Factor I; D007986:Luteinizing Hormone; D005640:Follicle Stimulating Hormone