Mechanism of antiandrogen action: key role of hsp90 in conformational change and transcriptional activity of the androgen receptor.

Activation of the androgen receptor (AR) is induced by ligand binding through conformational changes leading to control of gene expression. Antiandrogens compete with androgens for AR occupancy and subsequently block at least one step in AR action. Analysis of nuclear transfer kinetics using the GFP-AR fusion protein and partial proteolysis analysis provided evidence that the ligand-bound receptor was in equilibrium between at least two distinct conformations, leading to the production of 35 and 29 kDa trypsin-resistant fragments. It also indicated that this equilibrium may regulate the rate of nuclear transfer. The slowing of nuclear transfer by antiandrogens was correlated with the amount of receptor in conformation leading to the 35 kDa trypsin-resistant fragment. To establish the role of heat shock protein (hsp) 90 activity in antiandrogenic action, the effect of geldanamycin (GA) was evaluated in both in vitro assays and live cells. We demonstrated that in vitro hsp90s are required to stabilize the r...