Characterization and partial purification of androgen binding proteins from human prostate

Abstract

The prostate is one of the target organs of androgen. This fact is the foundation of the anti-androgen therapy for the treatment of prostatic of cancer as there are many prostatic cancers which show no response to hormone therapy. Since androgen acts via an androgen-androgen receptor complex in cytosol, trials to predict the effectiveness of the anti-androgen therapy for the treatment of prostatic cancers by means of the measurement of androgen receptor (AR) have been done. However some investigators emphasize that the response to hormone therapy and the contents of AR are not necessarily parallel. This discrepancy is probably due to the inaccurate measurement of AR. AR is measured by a radio-receptor-assay method, but it is possible that androgen binding proteins other than AR are also measured by the radioreceptor-assay method. In the human prostatic tissues, there are several androgen binding proteins other than AR. These are mainly testosterone-binding globulin (TeBG) and progesterone-binding protein (PBP). In this study, I attempted to separate and characterize androgen-binding proteins in human prostates. 500 g of benign prostatic hyperplasia (BPH) tissues obtained from patients undergoing retropublic or suprapubic prostatectomy were used. In order to separate these androgen-binding proteins, DEAE-cellulose ion exchange chromatography was used. Prostatic cytosol was applied on the DEAE-cellulose column. Two 3H-R1881 binding peaks were eluted: one was a flow-through fraction (peak I), and the other was an 0.1M KCl eluted fraction (peak II). When human serum was applied to the column, one 3H-DHT binding peak flowed through the column (peak III). It was thought that peak III contained TeBG. In order to ascertain whether AR was composed in peak I or peak II, an inhibition test by various non-radioactive steroids, R1881, DHT, testosterone, progesterone and estradiol was performed. 3H-R1881 binding of peak I was not inhibited by DHT or testosterone, while 3H-R1881 binding of peak II was inhibited by DHT and testosterone. The androgen-binding affinity of the peak I and peak II fraction was also measured using Scatchard's analysis. The dissociation constant of peak I was 6.25 nM, and that of peak II was 0.76 nM. Judging from these measurements the androgen-binding protein of peak II contained a specificity and high affinity to androgen. Consequently it was thought that AR was composed in peak II. Peak II fraction was applied on a Sephadex G200 gel chromatography column. A single androgen binding peak eluted in the void fraction.(ABSTRACT TRUNCATED AT 400 WORDS)