Modulation of steroidogenesis in choriocarcinoma cells by cholera toxin, phorbol ester, epidermal growth factor and insulin-like growth factor I

Abstract

The effects of cholera toxin (CT), which stimulates adenylate cyclase, 12-0-tetradecanoylphorbol 13-acetate (TPA), a protein kinase C activator, epidermal growth factor (EGF) and insulin-like growth factor I (IGF-I) on progesterone (P) and estradiol (E2) secretion by human choriocarcinoma JEG-3 cells were studied. During a 48 h incubation, CT, TPA and EGF stimulated P production in a concentration-dependent manner, whereas IGF-I was without effect. CT (1.0 ng/ml), TPA (10 ng/ml) and EGF (10 ng/ml) stimulated P production maximally 4.3-, 3.3- and 2.3-fold over basal, respectively. When added together with CT, TPA and EGF stimulated P production 10.0- and 5.0-fold over basal production showing that the effects of CT plus TPA were more than additive but those of CT plus EGF less than additive. Time-course studies indicated that the effects were detectable at 12 h, and continued to increase up to 48 h. The conversion of added dehydroepiandrosterone sulfate (DHEAS) to E 2 was stimulated by CT and TPA and inhibited by IGF-I in a concentration-dependent manner. By contrast, EGF had no effect. The maximal responses in E 2 production were 3.2- and 2.0-fold over unstimulated cells by CT (1.0 ng/ml) and TPA (10 ng/ml), respectively. When both agents were added together, their effects on E 2 production were additive with 5.5-fold increase over unstimulated cells. IGF-I (30 ng/ml) inhibited maximally basal and CT-stimulated E2 production by 33% and 42%, respectively. Time-course studies indicated that the stimulatory effects obtained with CT and TPA were detectable at 12 h and increased up to 72 h, whereas the inhibitory effects of IGF-I on basal and CT-stimulated E2 production were seen after 24 h and they continued up to 72 h. The results suggest that the secretion of P and E 2 in JEG-3 cells is similarly stimulated by CT and TPA. By contrast, polypeptide growth factors EGF and IGF-I have differential effects on steroidogenesis in these cells. EGF stimulated P production without affecting E 2, whereas IGF-I inhibited E 2 but had no effect on P production.