A cAMP-regulatory sequence (CRS1) of CYP17 is a cellular target for the homeodomain protein Pbx1.

Cytochrome P450c17 encoded by CYP17, whose expression is regulated by peptide hormones via cAMP, is required for cortisol and sex hormone biosynthesis thereby playing a key role in biological processes including sexual differentiation. Utilizing the cAMP-regulatory sequence CRS1 of the bovine CYP17 gene as an affinity ligand, four CRS1-binding proteins have been purified from nuclear extracts of mouse adrenocortical Y1 cells and shown to enhance the in vitro transcription of a reporter gene promoted by CRS1. Microsequencing of these four proteins established two of them to be the homeodomain proteins Pbx1a and Pbx1b, originally discovered by their involvement in the t(1;19) chromosomal translocation in pre-B-cell acute lymphoblastic leukemias. Overexpression of Pbx1 in Y1 cells enhances cAMP-dependent transcription of the CRS1-dependent reporter gene. These results identify the CRS1 of bovine CYP17 as a cellular target for Pbx1 and suggest that one role of this homeodomain protein is in the regulation of steroidogenesis and subsequently sexual development.