Gonadotrophins inhibit the expression of insulin-like growth factor binding protein-related protein-2 mRNA in cultured human granulosa-luteal cells

Insulin-like growth factors (IGF) and IGF-binding proteins (IGFBP) have been shown to be involved in ovarian follicular growth/development and steroidogenesis. Recently, a number of low-affinity IGFBP-related proteins (IGFBP-rP) have been characterized. In this study, we investigated the expression of the gene for IGFBP-rP2 (also known as connective tissue growth factor, CTGF) in human granulosa cells in vitro and in vivo. Northern blot analysis demonstrated that IGFBP-rP2 mRNA is expressed in cultured human granulosa-luteal cells obtained from women undergoing an IVF programme. Accumulation of IGFBP-rP2 mRNA was dose-dependently down-regulated by FSH and LH after 24 h treatment (both P < 0.05) in cultured granulosa-luteal cells. The inhibitory effects of gonadotrophins were mimicked by treatment with the protein kinase A activator, (Bu)(2)cAMP. Protein kinase C inhibitor staurosporine reduced, whereas protein kinase C activator TPA (12-O-tetradecanoyl phorbol 13-acetate) increased, IGFBP-rP2 mRNA accumulation. These results suggest that the inhibitory effects of gonadotrophins on IGFBP-rP2 gene expression may involve signal transduction via both protein kinase A and C pathways. Immunohistochemical analysis revealed positive staining for IGFBP-rP2 in the granulosa and theca cells of normal human ovarian follicles. Corpus luteum and ovarian surface epithelial cells were also positively stained. Modulation of IGFBP-rP2 expression by gonadotrophic hormones may have a role in ovarian follicular development and in the ovulatory process.