Transcriptional Regulation of the Epiregulin Gene in the Rat Ovary

Abstract

Ovarian follicular development is initiated by FSH secreted from the pituitary gland. The FSH-induced follicular development involves granulosa cell proliferation and differentiation. We demonstrated that a growth factor of epidermal growth factor (EGF) family epiregulin was rapidly induced in the primary culture of rat ovarian granulosa cells by FSH within 1 h. Epiregulin gene expression was also observed in granulosa cells of antral ovarian follicles from pregnant mare's serum gonadotropin-primed rats in vivo. To analyze the regulation of gene expression of epiregulin, we isolated and characterized the rat epiregulin gene of 22.1 kb, including 3.8 kb of 5'-upstream region as well as all five exons and four introns. We determined the transcriptional start site of rat epiregulin gene by primer extension analysis and then characterized the upstream promoter region of the gene. By using a luciferase reporter system, deletion and mutation analyses of rat epiregulin gene promoter region revealed that 125 bp upstream of transcriptional start site was essential, and that two CT boxes and one GT box within this region were important for the gene expression. We also demonstrated by EMSAs that Sp1/Sp3 proteins were involved in the epiregulin gene expression via the upstream sequence. Involvement of Sp1/Sp3 was also demonstrated that transfection of Sp1 or Sp3 expression plasmids dramatically increased the epiregulin gene promoter activities about 90- or 7.9-fold, respectively, in Drosophila SL2 cells that lack endogenous Sp family proteins. Such an increase in the promoter activity was also observed in mammalian cells when NIH-3T3 cells were used. In conclusion, we demonstrated here for the first time that EGF-type growth factor epiregulin is rapidly and strongly induced in the ovarian granulosa cells by FSH stimulation, and that two CT boxes and one GT box present in the upstream region are essential for the promoter activity of rat epiregulin. We also demonstrated that Sp family members play crucial roles in the epiregulin promoter activity through the CT boxes. The restricted and hormonally regulated expression of epiregulin in the rat ovarian granulosa cells may correspond to the physiological relevance of this peptide growth factor to the FSH-induced ovarian follicular growth and maturation.