BAP60 plays an opposite role to the MRT-NURF complex in regulating lipid droplet size

Steroidogenesis from cholesterol in placental trophoblasts is fundamentally involved in the establishment and maintenance of pregnancy. The transcription factor gene heart and neural crest derivatives expressed 1 (Hand1) promotes differentiation of mouse trophoblast giant cells. However, the role of HAND1 in human trophoblasts remains unknown. Here, we report that HAND1 inhibits human trophoblastic progesterone (P4) and estradiol (E2) from cholesterol through downregulation of the expression of steroidogenic enzymes, including aromatase, P450 cholesterol side-chain cleavage enzyme (P450scc), and 3β-hydroxysteroid dehydrogenase type 1 (3β-HSD1). Mechanically, although HAND1 inhibits transcription of aromatase by directly binding to aromatase gene promoter, it restrains transcription of P450scc by upregulation of the methylation status of P450scc gene promoter through its binding to ALKBH1, a demethylase. Unlike aromatase and P450scc, HAND1 decreases 3β-HSD1 mRNA levels by the reduction of its RNA stability through binding to and subsequent destabilizing protein HuR. Finally, HAND1 suppresses circulating P4 and E2 levels derived from JEG-3 xenograft and attenuates uterine response to P4 and E2. Thus, our results uncover a hitherto uncharacterized role of HAND1 in the regulation of cholesterol metabolism in human trophoblasts, which may help pinpoint the underlying mechanisms involved in supporting the development and physiological function of the human placenta.