Androgen Receptor Protein in the Androgen-dependent Dunning R-3327 Prostate Carcinoma¹

The rat prostate carcinoma (Dunning R-3327) contains a relatively high concentration of androgen receptor (80 to 150 fmol/mg cytosol protein). We characterized this receptor for comparison with androgen receptors in normal organs of the rat. Binding of testosterone and dihydrotestosterone was of high affinity (K_a = 2 × 10⁹ m). Rates of dissociation were slow (t_1/2 testosterone = 60 hr; t_1/2 dihydrotestosterone = ∼160 hr). At low ionic strength, the receptor was in an 8S form which dissociated to 4.5 to 5.0S in the presence of 0.4 m KCl. Fractionation of [³H]dihydrotestosterone cytosol by chromatography on phosphocellulose yielded a single peak of radioactivity eluting at 0.2 m Cl^-. Determination of size at high ionic strength by gel filtration chromatography and sucrose gradient centrifugation indicated a Stokes radius of 53 Å and sedimentation coefficient of 5S (M.W. 115,000). Cytosols occasionally yielded a second peak of radioactivity eluting from phosphocellulose at 0.29 m Cl^-. This fraction contained a smaller receptor [36 Å, 3.6S (M.W. 55,000)]. Both receptor forms were observed in cytosols from the normal dorsal prostate. The larger high-salt form of the receptor is identical to native androgen receptor in normal tissues. Smaller receptor forms in the tumor and in normal androgen-responsive tissues have been shown previously to result from proteolytic cleavage of the native receptor during extraction.