Transformation of the androgen receptor to the deoxyribonucleic acid-binding state: Studies in homogenates and intact cells

Transformation of the [³H]dihydrotestosteronereceptor complex to the DNA-binding state was studied in intact monolayers and in homogenates of cultured human fibroblasts and mouse L-cells. When homogenates of either cell type were prepared in low salt buffer, incubated at 0 C with [³H]dihydrotestosterone, chromatographed on DNA-Sepharose, and eluted with a NaCl gradient, the receptor complex was eluted at 25 mM NaCl (peak A). After incubation of the homogenate at 25 C for 20 min, peak A decreased in amplitude. The major peak of the receptor from human fibroblasts eluted at 100 mM NaCl, while that from L-cells eluted at 170 mM NaCl (peak B). Flow-through fractions contained only minimal amounts of transformable dihydrotestosterone-receptor complex under the same conditions. Furthermore, isolated peak A could be converted to peak B by the same warming process. The appearance of peak B was prevented when 10 mM, but not 1 mM, sodium molybdate was present during the homogenization process. Unoccupied receptor was recovered exclusively in peak A both at 0 C and after incubation at 25 C. When intact fibroblast and L-cell monolayers were incubated with [³H]dihydrotestosterone at 37 C, all receptor in both cytosol and nuclear extract was recovered in peak B. In sucrose density gradient centrifugation, peak A was 6–8S in size, and peak B was 4.6S. These findings suggest that 1) peak A corresponds to the nontransformed and peak B to the transformed states of the androgen receptor; 2) the transformation reaction may be the consequence of a dissociation of a macromolecular complex into subunits; and 3) sodium molybdate acts to stabilize the macromolecular complex.