206. Differential regulation of activin and inhibin production by interleukin 1 (IL1), transforming growth factor β1 (TGFβ1) and protein kinase C (PKC) in the Sertoli cell and granulosa cell

Abstract

Activin and inhibin are gonadal regulatory proteins comprising an α-subunit and either a βA-subunit or βB-subunit (inhibin A or B), or two βA-subunits (activin A). Synthesis of the α-subunit, and the inhibins, is regulated by FSH via cAMP/protein kinase A. Regulation of the β-subunits in the gonads is less well defined, but the IL1/MAP kinase, TGFβ /Smad and PKC pathways have been implicated. Sertoli cells and granulosa cells were isolated from 18–22 day-old Sprague-Dawley rats under standard conditions and cultured with IL1, TGFβ1 and the PKC agonists, gonadotrophin releasing hormone (GnRH) or phorbol myristate acetate (PMA). Activin A, inhibin A and inhibin B were measured in culture medium (at 48h) by ELISA. Subunit mRNA expression was measured in cell extracts (at 4 h and 8h) using quantitative RT–PCR. IL1 stimulated βA-subunit and activin A production and inhibited α-subunit and βB-subunit expression and inhibin B production in Sertoli cells, but had no effect in granulosa cells. TGFβ1 stimulated activin A in both cell types, as well as the inhibins in granulosa cells. Surprisingly, TGFβ1 had no effect on Sertoli cell α-subunit or βA-subunit mRNA expression, but did cause a slight reduction of βB-subunit expression. GnRH increased activin A and inhibin A, but not inhibin B, production by granulosa cells and had no effect on Sertoli cells, which lack the GnRH receptor. However, direct activation of PKC by PMA stimulated βA-subunit mRNA expression and activin A production and decreased βB-subunit and inhibin B production by Sertoli cells, with marginal effects on inhibin A. These results indicate that activation of the TGFβ or PKC signalling pathways preferentially stimulates βA-subunit expression and/or translation, leading to increased activin A secretion by Sertoli cells and both activin A and inhibin A secretion by granulosa cells. The ability of IL1 to stimulate activin A is confined to the Sertoli cell.