Raf‐ERK1/2 signalling pathways mediate steroid hormone synthesis in bovine ovarian granulosa cells

: Steroid hormones are required for normal reproductive function of female. The aim of this study was to investigate the role of Raf-ERK1/2 on steroid hormone synthesis in bovine ovarian granulosa cells. Immunohistochemistry assay showed that both B-Raf and C-Raf were expressed in granulosa cells, theca cells and Sertoli cells. The protein expression of Raf or ERK1/2 was clearly decreased by Raf inhibitor GSK2118436 or ERK1/2 inhibitor SCH772984, respectively (p < 0.05). In addition, western blotting was performed for investigating the crosstalk between Raf and ERK1/2, the data showed that Raf positively regulated ERK1/2, whereas ERK1/2 had a negative feedback effect on Raf. The biosynthesis of oestradiol or testosterone was significantly decreased by treatment with GSK2118436 or SCH772984 (p < 0.05). Conversely, the progesterone biosynthesis was clearly increased by treatment with those inhibitors (p < 0.05). Furthermore, the mRNA expression of STAR, aromatase and CYP17 was blocked by Raf-ERK1/2 signalling inhibition, which oppositely induced the mRNA expression of CYP11. Together, these findings suggested that Raf-ERK1/2 signalling pathways mediate steroid hormone synthesis via affecting the expression of steroidogenic enzymes.