The action of phorbol ester on steroidogenesis in cultured human fetal adrenal cells

The potent mitogen and tumor promoter, phorbol 12-myristate 13-acetate (PMA), has a primary action via activation of calciumdependent protein kinase C. The treatment of monolayer cultures of human fetal adrenal neocortex (HFA) cells with PMA (50-250 nM) stimulated basal dehydroepiandrosterone sulfate (DS) secretion 2-3 fold. ACTH-treated HFA cells secreted amounts of DS and cortisol (F) 10-50 fold greater than basal secretions. PMA (250 nM) addition with ACTH to HFA cells decreased DS and F secretions at least 75% on days 2 and 3 of treatment. Treatment of HFA cells with 4αphorbol, which does not activate calcium-dependent protein kinase C, did not inhibit steroidogenesis. The attenuated rates of steroidogenesis after PMA treatment correlated with the decreased amounts of steroid 11β 17α and 21-hydroxylase cholesterol side-chain cleavage steroid dehydrogenase and sulfotransferase activities. The decrease of steroid 17αhydroxylase activity correlated with the decreased amount of cytochrome P-450_17α as determined after protein immunoblotting of NaDodSO₄ cell lysates. After PMA treatment the ACTH-promoted increases of hydroxysteroid sulfotransferase and dehydrogenase activities of HFA cells were suppressed. PMA (50 nM) inhibited cAMP accumulation in ACTH-treated HFA cells, while 4αphorbol had no effect. Importantly, dibutyryl cAMP (0.2 mM) treatment of HFA cells did not reverse phorbol ester-promoted attenuation of steroidogenesis. We conclude that, in the presence of ACTH, phorbol ester chronically inhibits both cAMP synthesis and cAMP-dependent protein kinase action with resultant decreased steroidogenic enzyme synthesis and steroid production. This may be a consequence of activation, migration and a slow degradation of protein kinase C activity. These multifaceted actions of phorbol ester and associated protein kinase C activation may have critical effects on the ontogeny of fetal adrenal function.