QUANTITATIVE DIFFERENCES IN ANDROGEN AND GLUCOCORTICOID RECEPTOR DNA-BINDING PROPERTIES CONTRIBUTE TO RECEPTOR-SELECTIVE TRANSCRIPTIONAL REGULATION

Androgen receptor (AR) and glucocorticoid receptor (GR) belong to the same subfamily of steroid/nuclear receptors and have been shown to bin d qualitatively to the same hormone response element (HRE) DNA sequenc es. Despite this similarity in target gene recognition, AR and GR have differential affects on the transcriptional regulation of genes conta ining both simple and complex HRE control regions. Using HREs from the mouse mammary tumor virus (MMTV), tyrosine aminotransferase (TAT), pr ostatein (C3) or sex-limited protein (SLP) genes, linked to the thymid ine kinase promoter, we found receptor-selective differences in the ab ility of rat AR and rat GR to induce transcription of these various re porter genes. Since AR and CR have a 20% amino acid sequence differenc e in their DNA binding domains (DBDs), which could result in altered D NA binding affinities, we measured the ability of purified AR and GR D BDs to bind selectively and with high affinity to these HRE sequences in vitro. Gel shift mobility assays showed that the GR DBD had a highe r affinity for a consensus HRE than did the AR DBD, and quantitative D Nase I footprinting revealed that AR and GR DBDs bound to the MMTV, TA T, C3 and SLP HREs with different affinities. It was found that AR had a dissociation constant (K-d) that was 2-3 times higher than GR on th e TAT, C3 and SLP HREs and that the K-d of AR for the C3 and SLP HREs differed by an order of magnitude (43 nM and 460 nM, respectively). Ta ken together, these data suggest that amino acid differences in the AR and GR DBDs contribute to altered receptor-DNA interactions, however it is likely that non-receptor factors are involved in further modulat ing receptor-selective DNA binding and transactivation functions.