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.