EVIDENCE FOR AN ANTI-PARALLEL ORIENTATION OF THE LIGAND-ACTIVATED HUMAN ANDROGEN RECEPTOR DIMER

Domain interactions of the human androgen receptor (AR) dimer were inv estigated using a protein-protein interaction assay in which the NH2- and carboxyl-terminal regions of human AR mere fused to the Saccharomy ces cerevisiae GAL4 DNA-binding domain and herpes simplex virus VP16 t ransactivation domain to produce chimeric proteins. Transcriptional ac tivation of a GAIA luciferase reporter vector up to 100-fold was great er than Fos/Jun leucine zipper binding, indicating stable AR interacti on between AR NH2-terminal residues 1-503 and steroid-binding domain r esidues 624-919 that was specific for and dependent on androgen bindin g to the steroid-binding domain and was inhibited by anti-androgen bin ding, Deletion mutagenesis within the NH2-terminal region indicated tr ansactivation domain residues 142-337 were not required for dimerizati on, whereas deletions near the NH2 terminus (Delta 14-150) or NH2-term inal to the DNA-binding domain (Delta 339-499) reduced or eliminated t he AR interaction, respectively, An NH2-/NH2-terminal interaction was also observed, but no interaction was detected between ligand-free or bound steroid-binding domains. The results indicate that high affinity androgen binding promotes interactions between the NH2-terminal and s teroid-binding domains of human AR, raising the possibility of an andr ogen-induced anti-parallel AR dimer.