Contribution of AD4BP, a steroidogenic cell-specific transcription factor, to regulation of the human CYP11A and bovine cyp11b genes through their distal promoters

We analyzed the upstream regions of the human CYP11A and bovine CYP11B genes, and identified a distal promoter in each gene. The distal promoters are located at -1.8 to -1.5 kb in the upstream region of the CYP11A gene and -1.5 to -1.1 kb in the upstream region of the CYP11B gene. Transient transfection of CAT plasmid carrying each of the two distal promoters indicated that the regions had a transcriptional activating function and that the function was stimulated by cAMP. The basal and cAMP-stimulated transcriptional activities were detected only in steroidogenic cells. On structural analyses of the regions, we identified two Ad4 sites and a cAMP responsive element in the distal promoter of CYP11A, and two Ad4 sites and one NF-IL6 binding site in the distal promoter of CYP11B. The presence of an Ad4 site in common suggests its major contribution to the transcriptional activation. We also investigated the functional interactions between the distal promoters and basal promoters of both genes. Interestingly, the two distal promoters showed different requirements as to the basal promoter.