Control of the human inhibin α chain promoter in cytotrophoblast cells differentiating into syncytium

Inhibins are dimeric proteins consisting of a common alpha subunit linked to one of the beta subunits, betaA or betaB. During pregnancy, the placenta is the main source of inhibin A production and the in-vitro transformation of cytotrophoblast cells into syncytium is associated with an inhibin alpha subunit mRNA up-regulation. In this study, the 5' region of the human inhibin alpha gene was isolated and sequenced. Three transcription initiation sites were identified. When transiently transfected in trophoblast cells with a luciferase reporter vector, the sequence displayed promoter activity. DNase I footprinting and electrophoretic mobility shift assay (EMSA) analysis showed a specific DNA-protein interaction in the promoter when using cytotrophoblast nuclear proteins. This interaction was weaker with syncytiotrophoblast nuclear proteins. Moreover, the deletion of this DNA-protein interaction region suppressed the promoter activity. In an attempt to identify this factor, the potential binding of known factors deltaEFI, AP1 and NFE2 were excluded by competition EMSA experiments. We suggest that it may correspond to an undescribed protein interaction. The identification of the human inhibin alpha promoter could help in understanding the mechanisms modulating inhibin gene transcription. Moreover, the identification of a factor, whose presence is related to the trophoblast cell differentiation state, could help in understanding the transformation of cytotrophoblast cells into syncytium.