Expression of the genes for 3â-hydroxysteroid dehydrogenase type 1 and cytochrome P450scc during syncytium formation by human placental cytotrophoblast cells in culture and the regulation by progesterone and estradiol

We have investigated the expression of cholesterol side-chain cleavage cytochrome P450 (P450scc) and 3âhydroxysteroid dehydrogenase (3â-HSD) type 1 genes during human trophoblast differentiation in culture and the modulation of their steady-state mRNA levels by steroids. During the first 24 to 48 h after plating, mononucleated cells aggregated, forming colonies. After 60 h in culture, cell diameters were increased and nuclei appeared centrally distributed within large cells, consistent with syncytiotrophoblast formation. During these striking morphological changes in culture the expression and activity levels of 3â-HSD type 1 and P450scc increased significantly as isolated cytotrophoblasts progressed to a differentiated state, with P450scc and 3â-HSD type 1 mRNAs activities being more abundant in cells cultured for 48 to 72 h. In the same culture, however, the amount of 3â-HSD protein decreased during the first 12 to 24 h by 50% compared with freshly isolated trophoblasts but remained at these levels throughout the culture period. The specific activity of the 3â-HSD as determined with pregnenolone or dehydroepiandrosterone was similar but increased with time as syncytiotrophoblast was formed in vitro. These observations provide additional evidence that the expression of these two progesterone-synthesizing enzymes is coincident and that they reach their 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 3â-HSD type 1 mRNAs but had no significant effect on the amount of 3â-HSD protein. These observations of the regulation of 3â-HSD type 1 mRNA levels by steroids suggest a complex relationship of the mechanisms regulating transcription/mRNA processing and transduction of the 3â-HSD type 1 gene. Journal of Endocrinology (1997) 154, 379–387