Uncoupling of hormone-dependence from chaperone-dependence in the L701H mutation of the androgen receptor

The mechanisms underlying androgen receptor (AR)-mediated progression of prostate cancer following androgen ablation have yet to be fully determined. On this basis we screened naturally occurring mutants of human AR for hormone-independent activity using a yeast model system. An initial screen of 43 different mutants revealed that ARs having a Leu701His mutation (ARL701H) exhibited hormone-independent activation of a lacZ reporter gene. The ARL701H mutant bound dihydrotestosterone to a similar extent as did wild type AR, although its ability to be induced by hormone for transactivation was reduced substantially. Subsequent studies focused on the dependence of ARL701H on molecular chaperones for folding to the active state. We found that ARL701H was highly dependent on Hsp90 for its hormone-independent activation, suggesting that this chaperone functions in ARL701H folding. However, the mutant did not respond specifically to increased levels of FKBP52, suggesting that this chaperone functions at the hormone-dependent activation stage in the folding process. Further studies of ARL701H in PC3 cells suggested that this mutant is prohibited from hormone-independent transactivation in mammalian cells. However, basal expression of a reporter gene by ARL701H was not impaired by the presence of 17-allylamino-17-demethoxygeldanamycin as was wild type AR, suggesting differential interactions of these receptors with molecular chaperones in animal cells.