AN INITIATOR ELEMENT IS REQUIRED FOR MAXIMAL HUMAN CHORIONIC SOMATOMAMMOTROPIN GENE PROMOTER AND ENHANCER FUNCTION

Previous studies have indicated that cell-specific expression of the h uman chorionic somatomammotropin (hCS) gene may be mediated by a place ntal-specific enhancer (CSEn). In the current studies, we have analyze d the promoter elements that are required for enhancer and promoter fu nction in choriocarcinoma cells (BeWo). Mutation of both hCS GHF1 site s had no effect on promoter or enhancer activity. In contrast, mutatio n of the Spl site diminished basal and CSEn-stimulated transcription b y approximate to 75% and approximate to 56%, respectively, indicating that Spl was necessary but not sufficient for maximal basal and enhanc er-mediated transcription. Deletion and site-specific mutation of the proximal promoter region indicated that the TATA box and an initiator site (InrE) located between nucleotides -15/+1 of the hCS promoter wer e required for maximal promoter and enhancer function. Mutations of th e InrE were associated with reduced basal and enhancer-stimulated acti vities and altered transcription initiation sites. A protein of 70-kDa mass, that was preferentially expressed in human choriocarcinoma cell s (BeWo and JEG-3), bound specifically to the InrE. The data suggest t hat an initiator present in high concentrations in placental cells con tributes to the control of cell-specific hCS gene expression at the pr omoter level and is required for maximal enhancer function.