Contextual dependence of steroid receptor function on an androgen-responsive enhancer.

摘要

The enhancer of the mouse sex-limited protein (Slp) gene includes a consensus hormone response element (HRE) that interacts with several auxiliary elements for steroid induction. The 160-bp fragment. C' delta 2, confers response to androgen or glucocorticoid in transfection, while a 120-bp subfragment, C' delta 9, is activated only by androgen in some cells. Site-directed mutants were tested to identify elements affecting differential response of androgen or glucocorticoid receptors (AR, GR). While most mutations of C' delta 2 affected induction by either steroid similarly, disruptions of the consensus HRE or an octamer-like sequence were more severe for GR than AR activity. An HRE half-site was critical to androgen-specific induction of C' delta 9 but had little impact in the nonspecific C' delta 2 context. In DNase I footprinting, full-length AR and GR bound similarly to the consensus HRE but dissimilarly to nonconsensus sites. Intriguingly, NF-kappa B bound the region of C' delta 2 absent from C' delta 9. Expression of I kappa B decreased response of C' delta 2, but not C' delta 9, confirming a permissive role of NF-kappa B in steroid activation. In this case, different factors may associate with receptors in the presence of NF-kappa B than those that confer androgen specificity in NF-kappa B's absence, suggesting that exclusion of some factors from a specific transcription complex is as crucial as inclusion of others. This dissection of C' delta 2 and C' delta 9 in vitro reveals subtle distinctions in AR and GR interactions that may underlie specific hormonal response in vivo.