Specificity of ligand-dependent androgen receptor stabilization: receptor domain interactions influence ligand dissociation and receptor stability.

The molecular basis for the different physiological effects of testosterone (T) and dihydrotestosterone (DHT) was investigated using recombinantly expressed wild-type and mutant androgen receptor (AR). Rates of androgen dissociation from nuclear and cytoplasmic AR were compared with hormone- and concentration-dependent receptor degradation rates. T dissociates from AR 3 times faster than DHT or methyltrienolone (R1881) and is less effective in stabilizing the receptor. Analysis of AR deletion mutants and AR/glucocorticoid receptor chimeras indicates that the AR NH2-terminal domain has a specific role in stabilizing the receptor by slowing the rate of ligand dissociation and AR degradation. Amino acid mutations that abolish receptor dimerization, nuclear localization, or DNA-binding activity have no significant effect on androgen dissociation or AR degradation. A naturally occurring steroid-binding domain mutation (Val889 to Met) that causes androgen insensitivity, but does not alter equilibrium androgen binding affinity, lowered the androgen-binding capacity as a result of increased rates of androgen dissociation and AR degradation. Thus, AR stabilization and function require prolonged receptor occupancy with androgen, with a similar extent of stabilization observed at higher concentrations of faster dissociating androgens and lower concentrations of slower dissociating androgens. Retention of receptor-bound androgen is enhanced by an interaction between the AR NH2-terminal and steroid-binding domains. The ligand specificity and concentration dependence of receptor stabilization provide an explanation for physiological differences in the actions of T and DHT.