Androgen-binding proteins in human benign prostatic hypertrophy.

Abstract

Prostatic samples were surgically removed from 7 patients suffering from benign prostatic hypertrophy. High-speed supernatants (cytosol) containing 20-25 mg of protein/ml were prepared. Glycerol gradient ultracentrifugations were performed, using cytosol labeled at 0 C with 2-5 nM 3H-17beta-hydroxy-androstan-3-one (androstanolone or dihydrotestosterone) alone, or in the presence of 50-250-fold excess of androstanolone, estradiol, or androstane-3alpha, 17beta-diol (androstanediol). Two high-affinity saturable binding components were observed. One binding component was the androgen receptor. Its sedimentation coefficient was 8 S in low-salt medium. It had a high affinity for androstanolone. The binding of 3H-androstanolone was strongly completed by androstanolone itself, less by estradiol, and not by androstanediol. In one case, endogenous androstanolone found in the 8 S region of glycerol gradients was measured by radioimmunoassay, and it was calculated that more than 90% of the cytosol receptor binding sites might be occupied by this steroid while the total binding capacity of the 8 S receptor was estimated to approximate 2.6 pmol of androstanolone/g of prostate. No testosterone was found in the receptor fraction. The second binding component was attributable, at least in part, to the sex steroid-binding plasma protein (SBP), as indicated by its sedimentation coefficient (congruent to 4 S in low salt medium), its high affinity for androstanolone and androstanediol and its lower affinity for estradiol, and finally, its migration on polyacrylamide gel electrophoresis. In one instance, the concentration of the SBP-like protein in prostate cytosol was measured by equilibrium dialysis, and it was calculated that the binding capacity of the prostate SBP-like component corresponded to 4 pmol of androstanolone/g of prostate, a small (less than 5%) value with regard to SBP concentration in the plasma of the same patient. The blood contamination of the cytosol, as obtained from the measurement of hemoglobin, did not account for the amount of SBP found in the prostate sample. Since SBP-like protein is probably of plasma origin, to determine whether SBP was located in the extracellular space or inside the prostate cells, BPH slices from another patient were incubated in the presence of 3H-testosterone, the cytosol was prepared, and was fractionated by Sephadex G-150 column chromatography. The androstanolone/testosterone ratio in the receptor-containing peak was high (1.7), whereas in the incubation medium it was very low (0.08). In the peak containing the SBP-like protein, the ratio was 0.74, which may suggest that all or part had been exposed to the predominant androstanolone environment inside the prostatic cell.