A steroidogenic factor-1 binding element is essential for basal human ACTH receptor gene transcription

We have previously shown that the promoter of the human ACTH receptor (ACTH-R) contains, at -35 bp, a binding site for the steroidogenic factor 1 (SF-1), an orphan nuclear receptor which could be responsible for the transcriptional activity of this promoter. In the presence study, electrophoretic mobility shift assays demonstrated that the sequence -43/-19 bound the SF-1 protein present in the nuclear extracts of adrenocortical cells. Mutation of the SF-I binding site markedly reduced (40%) the basal transcription of the reporter gene in Y-1 cells transfected with the mutated p(-56/+22)GN construct compared to the wild-type construct. These results demonstrate that the SF-I binding element present in this fragment is required for the basal promoter activity of the human ACTH-R gene, In addition, other binding elements located upstream from this characterized SF-l binding site are involved ire the full basal promoter activity of the human ACTH-R since transfection studies with a longer p(-1017/+22)GH construct resulted in a higher GN release than with the p(-56/+22)GIP construct. (C) 1998 Academic Press.