EXPRESSION OF THE GENES FOR 3-BETA-HYDROXYSTEROID DEHYDROGENASE TYPE-1 AND CYTOCHROME P450SCC DURING SYNCYTIUM FORMATION BY HUMAN PLACENTALCYTOTROPHOBLAST CELLS IN CULTURE AND THE REGULATION BY PROGESTERONE AND ESTRADIOL

We have investigated the expression of cholesterol side-chain cleavage cytochrome P450 (P450scc) and 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD) type 1 genes during human trophoblast differentiation in cul ture and the modulation of their steady-state mRNA levels by steroids. During the first 24 to 48 h after plating, mononucleated cells aggreg ated, forming colonies. After 60 h in culture, cell diameters were inc reased and nuclei appeared centrally distributed within large cells, c onsistent with syncytiotrophoblast formation. During these striking mo rphological changes in culture the expression and activity levels of 3 beta-HSD type 1. and P450scc increased significantly as isolated cyto trophoblasts progressed to a differentiated state, with P450scc and 3 beta-HSD type 1 mRNAs activities being more abundant in cells cultured for 48 to 72 h. In the same culture, however, the amount of 3 beta-HS D protein decreased during the first 12 to 24 h by 50% compared with f reshly isolated trophoblasts but remained at these levels throughout t he culture period. The specific activity of the 3 beta-HSD as determin ed with pregnenolone or dehydroepiandrosterone was similar but increas ed with time as syncytiotrophoblast was formed irt vitro. These observ ations provide additional evidence that the expression of these two pr ogesterone-synthesizing enzymes is coincident and that they reach thei r maximum steady-state mRNA levels at a time when syncytium formation occurs in vitro. Incubation of trophoblast cells with progesterone or estradiol increased the abundance of P450scc and 3 beta-HSD type 1 mRN As but had no significant effect on the amount of 3 beta-HSD protein. These observations of the regulation of 3 beta-HSD type 1 mRNA levels by steroids suggest a complex relationship of the mechanisms regulatin g transcription/mRNA processing and transduction of the 3 beta-HSD typ e 1 gene.