Isolation of a Prostate Carcinoma Cell Proliferation-inhibiting Factor from Human Seminal Plasma and Its Similarity to Transforming Growth Factor β

Human seminal plasma (SP) has been known to contain both growth-inhibitory and -stimulatory factors. We attempted to identify a factor that inhibited DNA synthesis in some metastatic prostate cancer cell lines. The SP factor was sensitive to digestion by trypsin, but its activity increased after boiling or dialysis against 1 M acetic acid, by 3- to 4-fold. The SP factor was partially purified using a cation-exchange resin. Apparent molecular mass determination by sodium dodecyl sulfate-polyacrylamide gel electrophoresis revealed it to be a Mr 25,000 protein, and Mr 13,000 after reduction. This protein strongly inhibited DNA synthesis in two metastatic androgen-independent human prostatic carcinoma cell lines (PC3 and DU145) and the Dunning R3327G rat prostatic adenocarcinoma. It was ineffective on androgen-dependent LNCaP cells. The proliferation-inhibiting activity of this SP protein was specifically and completely abolished by a neutralizing anti-trans-forming growth factor 0 (TGF-0) antiserum. Furthermore, immunoblot analysis using the anti-TGF-0 antiserum showed the similarity of this protein to TGF-0. The maximum concentration of this protein in SP was 165 ±11.7 ng/ml (mean ± SD), of which only one-fourth may be present in active form under normal conditions. Identification of a TGF-0-like protein in SP might also explain the variety of growth and immune modulation properties of human SP.