Serum bound forms of PSP94 (prostate secretory protein of 94 amino acids) in prostate cancer patients

PSP94 (prostate secretory protein of 94 amino acids) was regarded as a poss ible prostate cancer marker, however, it has been controversial. All prior studies were designed to test the free form in serum using antibodies to PS P94. Results presented here demonstrate that PSP94 exists in prostate cance r patients in two forms, free and bound, and that the majority is present a s serum bound complexes. This result was demonstrated by using both native and SDS-PAGE analyses of serum protei ns from prostate cancer patients. Chr omatograph ic separation of serum total protei ns by a molecular sieve colu mn generated two peaks (peak I and II), which were reactive with rabbit ant iserum to human PSP94 in Western blot experiments. Peak I was eluted before the IgG Fraction at a molecular weight larger than 150 kDa, and peak II ap peared after serum albumin (similar to 67 kDa) was eluted. By using a bioti nylated PSP94 as an indicator of the free form of PSP94, we demonstrate tha t peak I contains serum PSP94-bound complexes and peak II is likely the fre e form of serum PSP94. Since the molecular weight of serum PSP94-bound comp lexes is close to IgG during molecular sieve separation, serum PSP94 comple xes were further purified through two rounds of protein A column separation , followed by DEAE-ion exchange column chromatography. In vitro dissociatio n tests of the purified PSP94-bound complexes showed that the binding of se rum PSP94-complexes is probably via disulfide bonds and is chemically stabl e. The results presented here indicate that serum PSP94-bound complexes mus t be considered in evaluating the clinical utility of PSP94 as a prostate c ancer marker. J. Cell. Biochem. 76:71-83, 1999. (C) 1999 Wiley-Liss, Inc.