Characterization of androgen receptors in human prostatic glands

The experiments performed in this research were designed to characterize androgen receptors in different subcellular fractions of normal human prostatic glands and to study possible relationships between these receptors. Two androgen-binding components with sedimentation coefficients of 5S and 9.5S, respectively, were observed in the cytosol fraction of normal human prostate. The 5S component had similar steroid-binding specificity and sedimentation coefficient as the testosterone-estradiol-binding globulin (TeBG) of human plasma. In addition, both cytosol 5S and TeBG were eluted out with 0.04M phosphate buffer solution, pH 6.0, in DEAE-cellulose column chromatography. The quantitative immunodiffusion assay showed that plasma contamination in the prostatic cytosol was about 9%. The cytosol 9.5S component, on the other hand, had a very specific binding affinity toward 5alph-dihydrotestosterone, but not toward testosterone, estradiol-17beta, progesterone or hydrocortisone. The 9.5S androgen-binding component was never found in human sera at various protein concentrations and was very likely the androgen receptor of human prostate glands. The formation of the 9.5S DHT-receptor complex was a slow process. Preheating the mixture of tritium labeled DHT and cytosol at 37°C for 30 minutes enhanced the rate of complex formation. A 7.5S androgen-binding component with high specific binding affinity toward 5alph-DHT was observed in microsomal fraction after solubilization with a 2M urea buffer solution. This 7.5S DHT-binding component became 9.5S form in the medium without 2M urea, a similar characteristic as that of cytosol 9.5S component. The translocational studies of androgen receptors in both minced tissue and cell-free systems showed that the 7.5S androgen-binding component was translocated from the microsomal fraction to the cytoplasmic fraction. This process was facilitated by both prostatic cytosol and 5alph-DHT. In the nuclear fraction, a 5.5S androgen-binding component was found in the extract of a 2M urea solution. This 5.5S component was more heat-labile than either the cytoplasmic or microsomal receptors. In addition, it showed equally high binding affinities toward progesterone, testosterone and estrodiol-7beta. From the results presented above, it can be concluded that the cytosol 9.5S DHT-binding protein is probably and androgen receptor of human prostatic glands. The microsomal 7.5S component and cytosol 9.5S component seem to be the same protein which exhibits different sedimentation coefficient upon exposure to 2M urea. The translocational process of androgen-binding receptor from microsome to cytosol indicates that the DHT may play some physiological role in the overall enhancement of protein synthesis.