Evidence that lack of ligand-binding domain correlates with nuclear distribution of unliganded human androgen receptor and loss of transactivation activity.

Androgen receptor (AR) is one of the large superfamily of nuclear hormone receptors. AR consists of distinct domains including an N-terminal DNA-binding domain and a C-terminal ligand-binding domain (LBD). Regulation of AR nuclear import and subsequent transactivation activity represent essential steps in androgen action. Mutations in the AR gene are known to cause different degrees of androgen insensitivity syndrome (AIS). This study aimed to identify the possible contribution of LBD of AR to cellular distribution, ligand binding, and transactivation activities using mutant AR clone lacking the entire LBD that we previously observed in an AIS patient. Subcellular distribution was assessed by green fluorescence protein-tagged vector and transcriptional activity was analyzed by luciferase assay. Wild-type AR had ligand-dependent transcriptional activation and nuclear import activities. On the other hand, mutant AR had no transcriptional activity regardless of the presence of ligand, 5-α-dihydroxytestosterone (DHT). These mutants were presented predominantly in the nucleus even without DHT. The observation of no transactivation in the mutant receptor must be due to the loss of complex formation between androgen and AR protein. The C-terminal domain has the critical role in the cellular localization and transactivation as well as on the ligand binding.