A novel isoform of a kallikrein-like protease, TLSP/hippostasin, (PRSS20),is expressed in the human brain and prostate

cDNAs encoding two splicing variants of a serine protease, termed hippostas in, were isolated by a PCR-based cloning strategy. The difference of 5' nuc leotide sequence resulted in the variation in the amino terminal ends of th e two, brain and prostate, types of human hippostasin. The longest ORF of t he brain-type was 250 amino acids with a putative signal peptide, while tha t of the prostate-type was 282 amino acids. Homology search using the amino acid sequence revealed that prostate-type hippostasin was identical to TLS P (PRSS20), which is expressed in human primary keratinocytes (1). Transien t expression analysis showed that both brain- and prostate-type TLSP/hippos tasin were secreted into the conditioned medium as about 40 kDa proteins. H uman TLSP/hippostasin showed 47% and 45% identity to trypsinogen II and kal likrein, respectively. In fact, the recombinant human TLSP/ hippostasin eff iciently cleaved Bz-Phe-Arg-4-methylcoumaryl-7-amide, a kallikrein substrat e, and weakly cleaved other substrates for kallikrein and trypsin. Northern blot analysis detected a 1.3 kb band in the whole brain and a 1.4 kb band in the prostate and the lung. In situ hybridization revealed that it was ex pressed preferentially by the pyramidal neurons in the human hippocampus an d secretory epithelial cells in the prostate. These results indicated that TLSP/hippostasin is involved in the functions of the human central nervous system and prostate and that it is a multifunctional protease present in va rious organs. (C) 2000 Academic Press.