LNCAP PRODUCES BOTH PUTATIVE ZYMOGEN AND INACTIVE, FREE-FORM OF PROSTATE-SPECIFIC ANTIGEN

BACKGROUND. Our objective was to investigate the presence of prostate specific antigen (PSA) and alpha-1-antichymotrypsin (ACT) mRNA and pro tein in prostate cancer cell lines, and the complexing characteristics of expressed PSA. METHODS. RT-PCR, immunohistochemistry, and Western blots were employed. Trypsin treatment of PSA was performed to establi sh the possible presence of all activatable form of PSA. RESULTS. ACT mRNA and protein were detected in LNCaP, PC-3, and DU 145 by RT-PCR an d by immunohistochemistry, respectively. Only LNCaP cells were positiv e for PSA mRNA and protein. LNCaP expressed similar to 30% active PSA, similar to 40% putative zymogen form of PSA, and similar to 30% stabl y inactive PSA. CONCLUSIONS. We have shown that the majority of PSA ex pressed by LNCaP cells is present in free, noncomplexed forms in the c onditioned media. A portion (40%) can be activated by trypsin, while t he rest is stably inactive PSA. LNCaP cells may serve as a source of t he ''unreactive'' PSA present in prostate cancer patients' serum. (C) 1998 Wiley-Liss, Inc.