Estrogen receptor-mediated repression of gonadotropin-releasing hormone (gnRH) promoter activity in transfected CHO-K1 cells.

To examine the transcriptional regulation of gonadotropin-releasing hormone (GnRH) gene in reproductive tissues, the expression of human GnRH gene promoter in cultured human granulosa cells and a Chinese hamster ovary-derived CHO-K1 tumor cells was studied. Transfection of luciferase reporter gene construct containing either upstream (hU) or downstream (hD) human GnRH gene promoter into both human granulosa and CHO-K1 cells showed that the upstream promoter, hU, was more active than hD in directing luciferase expression in these ovarian tissues. CHO-K1 cells transfected with either hU or hD construct showed insignificant changes in luciferase activity in response to 17beta-estradiol and GnRH. However, cotransfection of hU construct with a vector expressing a human estrogen receptor-alpha (ER-alpha) cDNA results in dose-dependent decreases in luciferase activity in response to both 17beta-estradiol and a GnRH agonist. By functional analysis of a series of deletion constructs, the ER-mediated suppression of GnRH promoter activity by 17beta-estradiol was localized to a region between -169 and -548 bp 5' of the upstream transcription start site of the human GnRH gene. Results of this study demonstrated that estrogen receptor can mediate the negative feedback regulation of human GnRH upstream promoter activity by both estrogen and GnRH in the ovary.