Regulation of human chorionic gonadotropin secretion and messenger ribonucleic acid levels by follistatin in the NUCC-3 choriocarcinoma cell line.

In this study, the NUCC-3 choriocarcinoma cell line was used as an in vitro placental cell model to investigate the effects of follistatin on basal and GnRH-stimulated hCG secretion and/or its subunit mRNA levels. Follistatin (1.5-100 ng/ml; 48 h) alone did not affect basal hCG secretion or its subunit mRNA levels. GnRH increased hCG secretion and hCG beta-subunit mRNA levels in a dose-dependent manner, with maximal effects (2.37- and 2.4-fold increases, respectively) at a dose of 10(-8) M after 24 h of culture (P < 0.001). The time-course study showed that the increase in hCG secretion induced by GnRH occurred between 6-48 h after treatment. Follistatin (6-100 ng/ml; 48 h) significantly suppressed GnRH-stimulated hCG secretion and hCG alpha- and beta-subunit mRNA levels, with maximal suppression of 73.1%, 106.9%, and 129.1%, respectively (P < 0.001). In addition, follistatin (25 ng/ml) inhibited hCG secretion in response to phorbol 12-myristate 13-acetate (100 nM) by 90.3%. However, follistatin had no effect on hCG secretion evoked by forskolin (10 microM), and no change in hCG secretion was observed after treatment with a calcium ionophore (A23187; 10 microM) alone or in combination with follistatin. Furthermore, there was no significant difference in the half-lives of hCG alpha and -beta mRNA induced by GnRH alone compared with those induced by GnRH plus follistatin (P > 0.1), indicating that follistatin did not affect the stability of hCG alpha and -beta mRNA. Our data suggest that follistatin inhibits GnRH-stimulated hCG secretion as well as hCG alpha- and beta-subunit mRNA levels in the NUCC-3 choriocarcinoma cell line by decreasing the rate of transcription through the second messenger transduction system-protein kinase-C, rather than by affecting the stability of mRNA. These findings indicate that follistatin may play an important role in the regulation of hCG production in the placenta during pregnancy.