DIFFERENTIAL REGULATION OF INHIBIN ACTIVIN ALPHA-SUBUNIT AND BETA(A)-SUBUNIT AND FOLLISTATIN MESSENGER-RNAS BY CYCLIC-AMP AND PHORBOL ESTERIN CULTURED HUMAN GRANULOSA-LUTEAL CELLS/

Granulosa cell-derived inhibin A (a dimer of alpha- and beta(A)-subuni ts), activin A (a homodimer of beta(A)-subunits) and the activin-bindi ng protein follistatin are important regulators of human ovarian stero idogenesis. We here studied how 8-bromo-cAMP (8br-cAMP), a protein kin ase A activator, and 12-O-tetradecanoylphorbol 13-acetate (TPA), a pro tein kinase C activator, affect the steady-state levels of alpha- and beta(A)-subunit and follistatin mRNAs in cultured human granulosa-lute al cells. 8br-cAMP induced alpha- and beta(A)-subunit and follistatin steady-state mRNA levels in a time- and concentration-dependent manner . The levels of alpha-subunit mRNAs were stimulated by 8br-cAMP in a s ustained manner with a maximal induction seen at the time points 24 an d 48 h. By contrast, beta(A)- subunit and follistatin mRNA levels were rapidly and transiently induced by 8br-cAMP with maximal effects obse rved at 3 h and 8 h, respectively. TPA did not affect basal alpha-subu nit mRNA levels but it rapidly induced beta(A)-subunit mRNAs at 3 h an d the stimulation was still evident at 48 h. TPA induced follistatin m RNA levels with kinetics similar to 8br-cAMP but to a lesser extent. M oreover, 8br-cAMP and TPA stimulated beta(A)-subunit and follistatin m RNA levels synergistically at 3 h. By contrast, TPA had a potent inhib itory effect on 8br-cAMP- and hCG-induced alpha-subunit levels. Neithe r 8br-cAMP nor TPA regulated inhibin/activin beta(B)-subunit mRNA leve ls. Taken together, the activation of protein kinase-A and -C by 8br-c AMP and TPA, respectively, lead to clearly differential responses in t he steady-state levels of inhibin/activin alpha- and beta(A)-subunit a nd follistatin mRNAs. These results suggest that the inhibin A vs. act ivin A ratio as well as follistatin levels are regulated by multiple s econd-messenger pathways in the human ovary.