Activation of protein kinase C potentiates cyclic AMP production and stimulates steroidogenesis in differentiated ovarian granulosa cells.
Gonadotropin-stimulated steroidogenesis in the differentiating ovarian granulosa cell is mediated through the activation of cAMP-dependent protein kinase, and is also modulated by calcium-dependent mechanisms. Granulosa cells contain calcium-activated, phospholipid-dependent protein kinase (C kinase), and show an increase in phosphatidylinositol turnover in response to GnRH agonist analogs. To evaluate the role of C kinase in ovarian steroidogenesis, the potent phorbol ester, TPA, and the permeant diacylglycerol, OAG, were used to activate C kinase in granulosa cells from PMSG-treated immature rats. Both TPA and OAG caused dose-dependent stimulation of progesterone production without affecting intra- or extracellular cAMP levels. However, the maximum steroid responses to these compounds were less than those stimulated by cAMP. The ED50 for TPA-stimulated progesterone production was 3 nM, which is close to the known Km for activation of C kinase. Stimulation of steroidogenesis was only observed with biologically-active phorbol esters and permeant diacylglycerols such as OAG and DOG. Exposure of granulosa cells to phospholipase C also increased progesterone production in a dose-dependent manner without changing the cAMP content. Although TPA and OAG did not increase basal cAMP production, both agents enhanced the cAMP responses stimulated by hCG and forskolin; likewise, phospholipase C alone did not change cAMP production but caused a dose-dependent increase in the cAMP responses to hCG and forskolin. These results demonstrate that activation of C kinase promotes steroidogenesis in ovarian granulosa cells, and potentiates the activation of adenylate cyclase by hCG and forskolin. Such findings support the possibility that the calcium, phospholipid-dependent enzyme could be involved in the regulation of progesterone production by hormonal ligands such as gonadotropins and GnRH.
D000818:Animals; D002454:Cell Differentiation; D006063:Chorionic Gonadotropin / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000096:biosynthesis*; D004075:Diglycerides / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005260:Female; D006107:Granulosa Cells / Q000187:drug effects / Q000378:metabolism*; D010906:Pituitary Hormone-Releasing Hormones / Q000494:pharmacology; D011374:Progesterone / Q000096:biosynthesis*; D011493:Protein Kinase C / Q000032:analysis*; D051381:Rats; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D010738:Type C Phospholipases / Q000494:pharmacology
D006063:Chorionic Gonadotropin; D004075:Diglycerides; D010906:Pituitary Hormone-Releasing Hormones; D005576:Colforsin; D011374:Progesterone; C038237:1-oleoyl-2-acetylglycerol; D000242:Cyclic AMP; D011493:Protein Kinase C; D010738:Type C Phospholipases; D013755:Tetradecanoylphorbol Acetate