Identification of an 8S androgen receptor-promoting factor that converts the 4.5S form of the androgen receptor to 8S.

A protein has been identified that reconstitutes the 4.5S androgen receptor to the classical 8S form on sucrose gradients of low ionic strength (25 mM KCl and 50 mM Tris). Rat prostate Dunning tumor (R3327) cytosol labeled with [3H]dihydrotestosterone was chromatographed on phosphocellulose to separate the 4.5S receptor from this protein, which we refer to as 8S androgen receptor-promoting factor. The 8S promoting factor has the following physiocochemical properties: heat labile (60 C; 30 min), Stokes radius of 58 degrees A, molecular weight of 170,000 or more, precipitates in 40% saturated (NH4)2SO4, elutes from DEAE-Sepharose in 0.1 M KCl, and elutes from phosphocellulose in 0.1 M KCl. The reconstituted 8S receptor complex is similar to the native 8S receptor in that it is labile to heat and physiological salt concentrations, has a Stokes radius of 91 degrees A, and has a molecular weight of approximately 326,000. The 8S promoting factor is present in mature male rat serum, but is undetectable in sera of male rats 16 days of age or younger. The factor appears to be produced by androgen-responsive cells, since it was found in all tissues of the 15-day-old male rat known to contain androgen receptor. Spleen was found to lack both the 8S promoting factor and the androgen receptor. The 8S promoting factor was detected in serum of female rats and in hypophysectomized (44 days) or castrated (2 or 4 weeks) mature male rats. Salt extracts of purified nuclei from the androgen-dependent Dunning tumor also contain the factor. It is suggested that a specific interaction between the two intracellular proteins, 8S androgen receptor-promoting factor and the androgen receptor, may modulate the androgen responsiveness of target cells.