REGULATION OF 3-BETA-HYDROXYSTEROID DEHYDROGENASE AND 17-BETA-HYDROXYSTEROID DEHYDROGENASE MESSENGER-RIBONUCLEIC-ACID LEVELS BY CYCLIC ADENOSINE-3',5'-MONOPHOSPHATE AND PHORBOL-MYRISTATE ACETATE IN HUMAN CHORIOCARCINOMA CELLS

3beta-Hydroxysteroid dehydrogenase (3betaHSD) in human placenta converts 3beta-hydroxy-5-ene steroids producing progesterone, whereas 17beta-hydroxysteroid dehydrogenase (17betaHSD) mediates the interconversion of estrone and estradiol. We first showed that the expression of type I 17betaHSD (17betaHSD-I) gene was undetectable in human JEG-3 cells. We then studied the effects of cAMP- and protein kinase-C-dependent pathways on the expression of 3betaHSD-I and l7betaHSD-II genes using an analog of cAMP [8-(4-chlorophenylthio)cAMP (8CPTcAMP)] and a protein kinase-C (PKC) activator, phorbol 12-myristate 13-acetate (PMA), in JEG-3 cells. Novel inhibitors of protein kinase-A (PKA) and PKC were also used. The 3betaHSD cDNA probe hybridized to a single 1.7-kilobase (kb) 3betaHSD mRNA species corresponding to the transcript of the 3betaHSD-I gene. The 17betaHSD cDNA probe hybridized to two l7betaHSD transcripts of 1.3 and 2.2 kb. The 1.3-kb l7betaHSD mRNA species was regulated, whereas the 2.2-kb species was constitutively expressed in JEG-3 cells. When JEG-3 cells were exposed to 8CPTcAMP or PMA, 3betaHSD-I and l7betaHSD-II gene transcriptions were increased in a dose- and time-dependent manner. Moreover, the combined effects of PMA and 8CPTcAMP on 3betaHSD-I mRNA levels was additive and synergistic on 17betaHSD-II mRNA levels. The mechanism by which cAMP activated accumulation of 3betaHSD-I and l7betaHSD-II mRNAs involved an activation of the cyclase. The effects of a cAMP-dependent kinase inhibitor and a diacylglycerol-dependent kinase inhibitor in JEG-3 cells indicated that cAMP acts on 3betaHSD-1 mRNA via a PKA-dependent mechanism, but on l7betaHSD-II mRNA via another nonclassical cAMP-dependent mechanism. Finally, the effect of activation of both signaling pathways on expression of the l7betaHSD-II gene as well as the effect of PMA on the 3betaHSD-I gene did not require protein synthesis. These data provide strong evidence for the regulation of the 3betaHSD-II and l7betaHSD-II genes by cAMP and PKC and, thus, indicate an important endocrine and/or paracrine regulation of steroid hormone production in human placenta.