Molecular cloning and expression of a variant form of hippostasin/KLKII in prostate

BACKGROUND. Hippostasin is a kallikrein-like serine protease, which has two alternatively spliced isoforms, brain-type and prostate-type. We previously reported alternative expression of hippostasin in prostate cancer cell lines. METHODS. We studied the expression of a variant-form hippostasin (isoform 3) mRNA by RT-PCR. Localization of the isoform 3 protein was examined by immunohistochemistry. The enzymatic activity of the recombinant protein was measured with synthetic substrates. RESULTS. A novel isoform of hippostasin contains 25 additional amino acids in the catalytic triad of brain-type hippostasin. Its mRNA was expressed in normal prostate tissue, BPH, and prostate cancer cell lines. The protein was localized in the prostate secretory epithelium. The enzyme activity was similar to that of brain-type hippostasin, which has kallikrein-like activity. CONCLUSIONS. In this study, we have identified a third isoform of hippostasin, which was designated variant-form (isoform 3). Hippostasin isoform 3 may play a role in the prostate, including reproductive and/or turnorigenic functions. Prostate 54: 299-305, 2003. (C) 2003 Wiley-Liss, Inc.