OBJECTIVE:
Prostate-specific antigen measurement, widely used for early detection of
prostate cancer (CaP),
suffers from low specificity. Additional
tumor markers are needed for the early detection of clinically relevant CaP. Our objective was to perform a qualitative
proteomic analysis of conditioned medium (CM) from the CaP
cell line PC3(AR)(6). METHODS: We used a roller bottle culture system to culture the
PC3(AR)(6)
cell line in chemically defined serum-free medium for 14 days. By using strong anion-exchange
chromatography, we
fractionated the CM and trypsinized the fractions. The
tryptic peptides were further
fractionated by reversed-phase C-18
chromatography before being subjected to electrospray
ionization tandem
mass spectrometry. We used MASCOT software to search the
mass spectra generated and organized identified proteins based on their genome ontology classification of cellular location. We used an
immunoassay to measure a newly identified
secreted protein, Mac-2BP, and
kallikreins 5, 6, and 11 in serum samples from CaP patients and healthy men. RESULTS: We classified 262 proteins according to cellular location; the sample was found to contain a significant proportion of
secreted (23%) and membrane (16%) proteins. In a proportion of
cancer patients compared with healthy men, we determined by
ELISA that serum concentrations of a novel candidate biomarker Mac-2BP were increased. CONCLUSIONS: These identified proteins, and possibly many others found in the CM, may have
utility as novel CaP biomarkers.
