Isolation and Characterization of the Androgen Receptor Mutants with Divergent Transcriptional Activity in Response to Hydroxyflutamide

A yeast genetic screening was developed to isolate androgen receptor (AR) mutants with divergent transactivation characteristics in response to hydroxyflutamide (HF), an active metabolite of flutamide used for prostate cancer treatment. Two mutants carrying the substitution C685Y or E708K were isolated and characterized. Substitution of C685Y for wild-type AR (wtAR) rendered the receptor supersensitive to androgenic activity from HF and female hormones such as 17beta-estradiol (E2) and progesterone (P). Similar effects were observed in the AR mutant, named T876AAR, isolated from LNCaP cells. Surprisingly, we found that C685YAR7, but not T876AAR7, could be activated by casodex (bicalutamide), a nonsteroidal pure antiandrogen, with an induction fold 3- to 5-fold times higher than that for wild type or T876AAR. By contrast, although replacement of E708K for wtAR showed little effect on dihydrotestosterone-mediated transactivation, E708KAR lost its transcriptional response from many other ligands. The effects of ligands on E708KAR could be controlled at the DNA-binding level owing to the finding of a significant decrease in the DNA-binding ability once E708KAR was bound to HF, E2, or P. Together, these results suggest that C685YAR can be a novel tool for assaying the androgenic activity from antiandrogens, and the mechanism revealed from E708KAR could provide a possible explanation for the partial androgen insensitivity syndrome in men with a natural E708KAR mutation.