Detection and cloning of a protein recognized by anti-human prostate-specific antigen (PSA) antibody in the rat ventral prostate

Prostate-specific antigen (PSA), a 33 kDa glycoprotein produced in the epit helium of the human prostate, has become established as a useful tumor mark er for prostate cancer in man. Since reports of homologous proteins in anim als other than primates have been lacking, the present investigation was ca rried out to identify any PSA-like protein in rats. Immunoblot analysis usi ng a specific monoclonal anti-human PSA antibody detected a 32 kDa immunore active protein in the ventral lobe of the rat prostate, but not in other lo bes or in other tissues. Positive immunostaining was observed only for the luminal surface of the glandular epithelium and the intraductal fluid in th e ventral prostate. Sequence analysis of a cDNA for the rat PSA-like protei n, cloned by immunoscreening of an expression cDNA library prepared from th e ventral lobe, revealed identity to the rat submaxillary gland S3 kallikre in. Human PSA also belongs to the kallikrein family. Thus, this protein pro duced in the rat ventral prostate was suggested to be a possible counterpar t of human PSA.