Change of specificity mutations in androgen-selective enhancers - Evidencefor a role of differential DNA binding by the androgen receptor

The androgen and glucocorticoid receptors recognize identical DNA motifs, l eaving unanswered the question of how steroid specificity of transcriptiona l regulation is established in cells containing both receptors, Here, we pr otide evidence that subtle differences in low affinity DNA recognition migh t be a crucial element in the generation of steroid-specific responses. Her e we identify simple hormone response elements in the mouse sex-limited pro tein enhancer and the human secretory component androgen response unit to b e essential for the androgen specificity of both enhancers. We describe spe cific in vitro binding to these motifs by the DNA-binding domain of the and rogen but not the glucocorticoid receptor. Both elements can be considered partial direct repeats of the 5'-TGTTCT-3' core binding motif. In addition, we show that specific point mutations in their left half-sites, essentiall y changing the nature of the repeats, strongly enhance the glucocorticoid s ensitivity of the respective enhancers, whereas they have no effect on thei r androgen responsiveness. Accordingly, these mutations allow specific bind ing of the glucocorticoid receptor DNA-binding domain to both elements in, vitro. With these experiments, we demonstrate that differential recognition by the androgen receptor of nonconventional steroid response elements is, at least in some cases, an important mechanism in androgen-specific transcr iptional regulation.