Receptor Proteins for Androgens ON THE ROLE OF SPECIFIC PROTEINS IN SELECTIVE RETENTION OF 17β-HYDROXY-5α-ANDROSTAN-3-ONE BY RAT VENTRAL PROSTATE IN VIVO AND IN VITRO

Abstract 3H-Testosterone injected into castrated rats was rapidly reduced to 3H-5α-dihydrotestosterone (3H-5α-androstan-17β-ol-3-one) in the ventral prostate. 3H-5α-Dihydrotestosterone was then retained by the ventral prostate for at least 6 hours, although virtually all radioactive steroids had disappeared from blood and some other rat tissues that are relatively insensitive to androgens. This selective retention was caused by a firm retention of 5α-dihydrotestosterone by a protein in prostate cell nuclei. The dihydrotestosterone-bound protein extracted from the labeled nuclei by a buffered salt solution migrated in a sucrose gradient centrifugation with a sedimentation constant of 3.0 ± 0.3 s20,w. The cytosol fraction of rat ventral prostate homogenates also contained a specific 5α-dihydrotestosterone-binding protein which has a sedimentation constant of 3.5 ± 0.3 s20,w. The selective retention of 5α-dihydrotestosterone by cell nuclei of ventral prostate could be shown by incubating minced prostate with 3H-testosterone, 3H-dihydrotestosterone, or 3H-Δ4-androstene-3,17-dione in vitro. If prostate cell nuclei were first isolated from castrated rats and then incubated with 3H-testosterone or 3H-5α-dihydrotestosterone, there was no retention of 5α-dihydrotestosterone in a protein-bound form; but upon addition of a cytosol fraction the nuclear fraction reisolated was found to retain 3H-5α-dihydrotestosterone as a complex with a 3 S protein. Available evidence suggests that prostate cell nuclei have specific sites that can retain a specific 5α-dihydrotestosterone-protein complex but not the protein moiety alone. The cytosol 3.5 S protein binds dihydrotestosterone spontaneously at 0°. At 37°, the 5α-dihydrotestosterone-protein complex extracted from prostate cell nuclei gradually releases the bound dihydrotestosterone. On the other hand, incubation of the cytosol protein at temperatures between 15–50° enhanced the 5α-dihydrotestosterone-binding capacity. Heating of the cytosol protein at temperature above 50° for 10 min destroyed such binding ability. Testosterone and cortisol bound to the 3.5 S prostate cytosol protein poorly, whereas binding of progesterone and 17β-estradiol was significant. Cyproterone (1,2α-methylene-6-chloro-Δ4, 6-pregnadien-17α-ol-3,20-dione) 17α-acetate, a potent antiandrogen, suppressed the uptake of radioactive androgens by rat ventral prostate in vivo. This was accompanied by a decrease in the retention of 5α-dihydrotestosterone by prostate cell nuclei. Cyproterone and its 17α-acetate (less than 1 µm) also inhibited the formation of a specific dihydrotestosterone-protein complex in prostate cell nuclei when minced prostate tissue was incubated with radioactive testosterone or 5α-dihydrotestosterone. 17β-Estradiol, diethylstilbestrol, and progesterone, but not cortisol, also suppressed the retention of 5α-dihydrotestosterone by prostatic cell nuclei in vitro, but to a much lesser extent than cyproterone acetate. The antagonistic action of antiandrogens strongly supports the contention that the binding of 5α-dihydrotestosterone by proteins described in this paper is germane to the stimulation of prostate growth and function by androgens.