Isolation and characterization of androgen receptor mutant, AR(M749L), with hypersensitivity to 17-β estradiol treatment

Estrogens, primarily 17beta-estradiol (E-2), may play important roles in male physiology via the androgen receptor (AR). It has already been shown that E-2 modulates AR function in LNCaP prostate cancer cells and xenograft CWR22 prostate cancer tissues. Using a molecular model of E-2 bound-AR-ligand binding domain (LBD) and employing site-directed mutagenesis strategies, we screened several AR mutants that were mutated at E-2-AR contact sites. We found a mutation at amino acid 749, AR(M749L), which confers AR hypersensitivity to E-2. The reporter assays demonstrate that E-2 can function, like androgen, to induce AR(M749L) transactivation. This E-2-induced AR mutant transactivation is a direct effect of the AR(M749L), because the transactivation was blocked by antiandrogens. The hypersensitivity of AR(M749L) to E-2 is not due to increased affinity of AR(M749L) for E-2, rather it may be due to the existence of the proper conformation necessary to maintain E-2 binding to the AR-LBD long enough to result in E-2-induced transactivation. AR(M749L) transactivation can be further enhanced in the presence of AR coregulators, such as ARA70 and SRC-1. Therefore, amino acid 749 may represent an important site within the AR-LBD that is involved in interaction with E-2 that, when mutated, allows E-2 induction of AR transactivation.