Expression of the Prostate-specific Membrane Antigen1

We have recently cloned a 2.65-kilobase complementary DNA (cI)NA) encoding the prostate-specific membrane antigen i I'SM i recognized by the 7E11-C5.3 anti-prostate monoclonal antibody. Immunohistochemical analysis of the LNCaP, 1)1-1-15, and PC-3 prostate cancer cell lines for I'SM expression using the 71,11-< 5J antibody reveals intense staining in the LNCaP cells with no detectable expression in both the 1)1-145 and PC-3 cells. Coupled in vitro transcription/translation of the 2.65-kilobase full-length I'SM cDNA yields an U, 84,000 protein corresponding to the predicted polypeptide molecular weight of I'SM. Posttranslational modi fication of this protein with pancreatic canine microsomes yields the expected W, 100,000 I'SM antigen. Following transfection of PC-3 cells with the full-length I'SM cDNA in a eukaryotic expression vector, we detect expression of the I'SM glycoprotein by Western analysis using the 7E11-C5.3 monoclonal antibody. Ribonuclease protection analysis dem onstrates that the expression of I'SM inUNA 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-dihydrotestosterone down-regulating PSM expression in the human prostate 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, expression of PSM in benign prostatic hyperplasia. LNCaP tumors im planted and grown both orthotopically and s.c. in nude mice abundantly express PSM, providing an excellent in vivo model system to study the regulation and modulation of PSM expression.