Functional interplay between two response elements with distinct binding characteristics dictates androgen specificity of the mouse sex-limited protein enhancer.

Abstract

Many of the aspects involved in steroid-specific transcriptional regulation are still unsolved to date. We describe here the detailed characterization of the mouse sex-limited protein enhancer as a paradigm for androgen-specific control of gene expression. By deletion analysis, we delineate the minimal enhancer region displaying androgen sensitivity and specificity. We also show that each of the three hormone response elements (HRE), which constitute this minimal enhancer region, is essential but not sufficient for its functionality. When investigated as isolated elements, HRE1 is inactive and HRE3 is a potent androgen response element as well as GRE. Only the non-canonical HRE2 (5-TGGTCAgccAGTTCT-3') is capable of conferring an androgen-specific transcriptional response to a heterologous promoter. This finding is correlated with the fact that HRE2 is recognized in binding assays in vitro by the DNA-binding domain (DBD) of the androgen but not the glucocorticoid receptor, while HRE3 is recognized by both DBDs. Differential binding of the androgen receptor to HRE2 in the context of the enhancer was analyzed in more detail in footprinting assays in vitro. In transient transfection experiments using chimeric receptors, the inability of the glucocorticoid receptor to transactivate via the slp-ARU as well as the isolated slp-HRE2 was rescued by the replacement of its DNA-binding domain with that of the androgen receptor. Our data suggest that the functional interplay between the weak, but highly androgen-specific HRE2 and the adjacent strong, but non-selective HRE3 is the major determinant in the generation of androgen specificity of transcriptional response via the sex-limited protein enhancer.