The Homeodomain Protein Pbx1 Is Involved in cAMP-Dependent Transcription of Human CYP17

Pbx1 is a homeodomain transcription factor involved in cAMP-dependent transcriptional regulation of the bovine CYP17 gene. In this study, we have investigated the involvement of Pbx1 in the transcriptional regulation of the human CYP17 gene. Although a sequence identical to previously determined Pbx-binding sites is not present in the promoter region of the human CYP17 gene, three putative Pbx-binding sites are identified by sequence similarity analysis. Coexpression of Pbx1 and a catalytic subunit of protein kinase A (PKA) greatly enhances reporter gene transcription via the 5′-flanking region of the human CYP17 gene. Upon gel shift analysis utilizing nuclear extracts from human adrenal H295R cells, one of the three putative Pbx1-binding sites, −250/−241 bp, shows the typical intense doublet observed with other Pbx-binding sites. 5′-Deletion analyses of the reporter construct containing this Pbx-binding site showed approximately sixfold induction by coexpression of Pbx1 and PKA compared to the basal transcription, suggesting that Pbx1 binds the −250/−241 bp sequence and participates in cAMP-dependent regulation of the human CYP17 gene.