12-O-Tetradecanoyl Phorbol-13-Acetate Potentiates Adenosine 3′,5′-Monophosphate-Mediated Chorionic Gonadotropin Secretion by Cultured Human Choriocarcinoma Cells*

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Abstract
The activation of protein kinase C and adenylate cyclase in the regulation of human CG (hCG) synthesis by cultured BeWo choriocarcinoma cells was studied. Both cholera toxin (CT), which activates adenylate cyclase, and 12-0-tetradecanoylphorbol-13-acetate (TPA), a protein kinase C activator, stimulated the secretion of hCG in dose-dependent manner. During a 72-h culture, stimulation with the maximal effective concentration of CT (1.0 ng/ml) exerted a more pronounced increase (16-fold) in hCG synthesis than TPA (10 ng/ml) (2.8-fold), whereas the inactive phorbol ester 4.alpha.-phorbol 12,13-didecanoate (100 ng/ml) was ineffective. When added together, TPA potentiated the effect of CT on hCG secretion (from 16-to 27-fold) and cAMP accumulation (from 36- to 54-fold) in the medium. TPA (1.0 ng/ml) also caused a 2.0-fold increase in basal cAMP production after 72 h. Time-course studies indicated that the effect of TPA on CT-induced cAMP and hCG productions became significant at 45 min and 6 h, respectively, form the beginning of stimulation. Proliferation of cells was not responsible for the responses, since the treatments only slightly increased the total protein content and did not alter the rate of incorporation of C3H3-methylated thymidine of the cells. Our results demonstrate that TPA potentiates CT-induced cAMP and hCG production in cultured human choriocarcinoma cells.