Establishment of a mammalian expression system for recombinant [-2]proPSA and a specific antibody against the truncated leader peptide.

A truncated precursor form of prostate-specific antigen (PSA), [-2]proPSA, is a well-known biomarker for prostate cancer. To develop a biomarker assay, highly purified [-2]proPSA is required as a standard reference and for generation of a specific antibody. In this study, we generated an efficient mammalian expression system for producing a recombinant [-2]proPSA-human kappa constant domain (C ) fusion protein. N-terminal amino acid sequencing using Edman degradation demonstrated that over 95% of the recombinant protein produced is [-2]proPSA, thereby showing for the first time that recombinant [-2]proPSA can be produced as a major fraction. We also generated a recombinant chicken antibody specific to [-2]proPSA but not cross-reactive to recombinant [-7]proPSA-C , [-5]proPSA-C , and PSA purified from human seminal fluid in enzyme-linked immunosorbent assay (ELISA) and immunoblot analysis. Also, the recombinant chicken antibody reacted to recombinant [-2]proPSA protein bound to an anti-PSA antibody coated on the micrometer plate in a sandwich ELISA. All of these results suggest that the N-terminus of the [-2]proPSA-C fusion protein resides on the exterior of the protein, thus allowing exposure to the antibody.