Effects of estradiol and progesterone on gonadotropin LHβ- and FSHβ-subunit promoter activities in gonadotroph LβT2 cells.
OBJECTIVES: Sex steroid hormones play roles in the regulation of pituitary hormone synthesis and secretion. Here we investigated the role of estradiol (E2) and progesterone (P4) on pituitary gonadotropin luteinizing hormone (LH)β- and follicle stimulating hormone (FSH)β-transcriptional activity in a single colony of gonadotroph LβT2 cells.
METHODS: Pituitary gonadotroph cell line, LβT2 cells were used in this study. Cells were transfected with LHβ- or FSHβ-subunit promoter region-linked luciferase vector, and stimulated with gonadotropin-releasing hormone (GnRH) in the presence or absence of sex steroids. Transcriptional activity for LHβ- and FSHβ-subunit were determined by luciferase assay. Effects of sex steroids on cell proliferation was also determined by measurement of 5-bromoe-2'-deoxyuridine (BrdU) incorporation.
RESULTS: The basal promoter activity of the LHβ subunit was not modulated by 10 nM E2, but gonadotropin releasing hormone (GnRH)-induced LHβ promoter activity was significantly increased by the same concentration of E2. Similarly, although the basal FSHβ promoter was not modulated by 10 nM E2, GnRH-induced FSHβ promoters were significantly potentiated in the presence of E2. One micromole E2 modulated neither basal nor GnRH-induced LHβ and FSHβ promoters. On the other hand, basal LHβ promoter activity was enhanced by 1 µM P4, but the stimulatory response of GnRH on LHβ promoters was significantly inhibited in the presence of 1 µM P4. Similar to LHβ promoters, the basal activity of the FSHβ promoter was increased by 1 µM P4; however, the response to GnRH was not modulated in the presence of P4. Ten micromoles P4 modified neither basal nor GnRH-induced promoter activity for LHβ and FSHβ. E2 had no antagonistic effect on P4-induced basal promoter activities of LHβ or FSHβ. A cell proliferation assay showed that neither E2 nor P4 modulated the growth of LβT2 cells, even in the presence or absence of GnRH.
CONCLUSION: These observations suggest that both E2 and P4 uniquely modulate basal and GnRH-stimulated gonadotropin promoters without affecting cell growth....