HUMAN PROSTATE-SPECIFIC GLANDULAR KALLIKREIN IS EXPRESSED AS AN ACTIVE AND AN INACTIVE PROTEIN

A polymorphism in the human prostate-specific glandular kallikrein (hK LK2) gene was described by direct sequencing (by PCR) of genomic DNAs isolated from prostatic cancer tissue, benign prostatic hyperplasia ti ssue, and blood leukocyte specimens. Results showed two forms of human prostate-specific glandular kallikrein protein (hK2), a consequence o f a change from C to T at base 792 in the hK2 coding region. Producing the two forms as recombinant proteins in insect cells demonstrated th at Arg(226)-hK2 (CC genotype) is an active protein and Trp(226)-hK2 (T T genotype) is inactive. Polymorphism studies of 36 patients with pros tatic diseases identified only 1 with the TT genotype. The same kind o f polymorphism was not detected in the human prostate-specific antigen (hKLK3) gene. Arg(226)-hK2 possessed only trypsin-like enzyme activit y, whereas recombinant human prostate-specific antigen (hPSA) had only chymotrypsin-like activity. Monoclonal and polyclonal antibodies rais ed against hPSA purified from seminal plasma detected both active and inactive hK2. Thus, because inactive as well as stable hK2 protein may be present, a lack of trypsin-like activity in hPSA standards is not enough to confirm that the materials are free of hK2 contamination.