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 α‐1‐antichymotrypsin (ACT) mRNA and protein 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 establish the possible presence of an activatable form of PSA. RESULTS ACT mRNA and protein were detected in LNCaP, PC‐3, and DU 145 by RT‐PCR and by immunohistochemistry, respectively. Only LNCaP cells were positive for PSA mRNA and protein. LNCaP expressed ∼30% active PSA, ∼40% putative zymogen form of PSA, and ∼30% stably inactive PSA. CONCLUSIONS We have shown that the majority of PSA expressed by LNCaP cells is present in free, noncomplexed forms in the conditioned media. A portion (40%) can be activated by trypsin, while the rest is stably inactive PSA. LNCaP cells may serve as a source of the “unreactive” PSA present in prostate cancer patients' serum. Prostate 35:135–143, 1998. © 1998 Wiley‐Liss, Inc.