REGULATION OF FOLLISTATIN MESSENGER-RIBONUCLEIC-ACID IN PORCINE GRANULOSA-CELLS BY EPIDERMAL GROWTH-FACTOR AND THE PROTEIN-KINASE-C PATHWAY

Follistatin is a 35-kilodalton monomer isolated from follicular fluid by virtue of its ability to suppress FSH secretion from cultured pituitary cells. Experiments were designed to test the hypothesis that the accumulation of follistatin RNA in the ovary is regulated by epidermal growth factor (EGF) and activation of the protein kinase-C (PKC) pathway. Follistatin mRNA was quantitated by slot blot hybridization of total RNA from primary cultures of porcine granulosa cells treated with the phorbol ester phorbol 12-myristate 13-acetate (PMA), an activator of PKC. PMA (0.1, 1.0, 10, and 100 nm) induced a dose-dependent increase in follistatin mRNA accumulation after 2 h, with a maximal increase of 40-fold over that in untreated control cultures at a dose of 10 nm. PMA (10 nm) induced a time-dependent increase in follistatin mRNA levels, with a maximal response at 2 h. Follistatin gene expression was induced by a 2-h incubation with EGF (3 nm), but not by LH (100 ng/ml), GnRH (10 nm) or prostaglandin F2alpha (80 mug/ml). EGF (0.01, 0.1, 1, and 10 nm) induced a dose-dependent induction of follistatin gene expression in granulosa cells after 2-h incubation, with maximal stimulation of 33-fold at a dose of 1 nm. The time course of induction of follistatin mRNA by EGF was very similar to that induced by PMA, with maximal stimulation occurring at 2 h and declining thereafter. Pretreatment of granulosa cells for 24 h with PMA abrogated the EGF-induced stimulation of follistatin mRNA accumulation. However, cotreatment of granulosa cells with EGF and PMA for 2 h resulted in additive stimulation of follistatin mRNA. These results demonstrate that 1) follistatin gene expression in cultured porcine granulosa cells is acutely stimulated by PMA and EGF in a time- and dose-dependent manner; 2) follistatin gene expression may be regulated by the PKC pathway; and 3) the stimulatory effect of EGF on follistatin gene expression may require PKC.