Analysis of glucocorticoid and androgen receptor gene fusions delineates domains required for transcriptional specificity

Androgen receptor (AR) and glucocorticoid receptor (GR) influence distinct physiologic responses in steroid-responsive cells despite their shared abil ity to selectively bind in vitro to the same canonical DNA sequence (TGTTCT ). While the DNA-binding domains (DBDs) of these receptors are highly conse rved, the amino N-terminal domain (NTD) and hormone-binding domain (HBD) ar e evolutionarily divergent. To determine the relative contribution of these functional domains to steroid-specific effects in vivo, we constructed a p anel of AR/GR gene fusions by interchanging the NTD, DBD, and HRD regions o f each receptor and measured transcriptional regulatory activities in trans fected kidney and prostate cell lines. We found that GR was approximately 1 0-fold more active than AR when tested with the mouse mammary tumor virus p romoter, and that this difference in activity was primarily owing to sequen ce divergence in the NTDs. We also tested transcriptional activation of the androgen-dependent rat probasin promoter, and in this case, AR was at leas t twofold more active than GR. Analysis of the chimeric receptors revealed that this difference mapped to the DBD region of the two receptors. Transcr iptional repression functions of the wild-type and chimeric receptors were measured using an activator protein 1 (AP-1) transrepression assay and iden tified the GR HBD as a more potent transrepressor of AP-1 transcriptional a ctivation than the AR HBD. Taken together, our analyses reveal that evoluti onary sequence divergence between AR and GR functional domains results in u nique promoter-specific activities within biologic systems in which both AR and GR are normally expressed.