Placental corticotropin-releasing hormone (CRH) plays an important role in the mechanisms controlling human pregnancy and parturition, and several endogenous factors are known to regulate placental CRH gene expression. In this article, the authors investigate the regulation of the CRH gene's promoter activity by a protein kinase C (PKC) activator, phorbol-12-myristate-13-acetate (PMA), in primary cultures of placental cells. The PMA stimulation of the CRH gene promoter activity was dose dependent, and further studies, including progressive deletion and mutation analysis of the CRH promoter, localized the region essential for PMA responsiveness to a consensus cyclic adenosine monophosphate regulatory element (CRE). Furthermore, estradiol treatment resulted in decreases of both basal and PMA-stimulated promoter activity when the CRE element was present but had no effect when the CRE element was absent. Thus, PMA stimulates CRH gene transcriptional activity through the CRE, suggesting that cross-talk between PKC and protein kinase A signaling pathways targets this regulatory element in placental cells.