EXPRESSION OF THE PROSTATE-SPECIFIC MEMBRANE ANTIGEN

We have recently cloned a 2.65-kilobase complementary DNA (cDNA) encod ing the prostate-specific membrane antigen (PSM) recognized by the 7E1 1-C5.3 anti-prostate monoclonal antibody. Immunohistochemical analysis of the LNCaP, DU-145, and PC-3 prostate cancer cell lines for PSM exp ression using the 7E11-C5.3 antibody reveals intense staining in the L NCaP cells with no detectable expression in both the DU-145 and PC-3 c ells. Coupled in vitro transcription/translation of the 2.65-kilobase full-length PSM cDNA yields an M(r) 84,000 protein corresponding to th e predicted polypeptide molecular weight of PSM. Posttranslational mod ification of this protein with pancreatic canine microsomes yields the expected M(r) 100,000 PSM antigen. Following transfection of PC-3 cel ls with the full-length PSM cDNA in a eukaryotic expression vector, we detect expression of the PSM glycoprotein by Western analysis using t he 7E11-C5.3 monoclonal antibody. Ribonuclease protection analysis dem onstrates that the expression of PSM mRNA is almost entirely prostate specific in human tissues. PSM expression appears to be highest in hor mone-deprived states and is hormonally modulated by steroids, with 5-a lpha-dihydrotestosterone down-regulating PSM expression in the human p rostate cancer cell line LNCaP by 8-10-fold, testosterone down-regulat ing PSM by 3-4-fold, and corticosteroids showing no significant effect . Normal and malignant prostatic tissues consistently show high PSM ex pression, whereas we have noted heterogeneous, and at times absent, ex pression of PSM in benign prostatic hyperplasia. LNCaP tumors implante d and grown both orthotopically and s.c. in nude mice abundantly expre ss PSM, providing an excellent in vivo model system to study the regul ation and modulation of PSM expression.