Roles of integral-membrane serine proteinase inhibitors in proliferation, migration and invasion of epithelial cells

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Cell surface proteolysis is an important mechanism for the generation of biologically active proteins that mediates a diverse range of cellular functions. Therefore the interactions between proteinases and cellular surface inhibitors must have important regulatory roles in cellular functions. There is a unique class of SPIs that is synthesized as a transmembrane glycoprotein. These SPIs have one or two extracellular Kunitz-type serine proteinase inhibitor domains, a presumed transmembrane domain near the carboxyl-terminus and a short intracytoplasmic domain. This unique group of SPIs consists of 4 distinct proteins at present. These are APP, APP-like protein 2 (APLP2), HAI-1 and HAI-2. In this project, the functions of these membrane-type inhibitors were extensively analyzed. Following are the results of the project (April, 2000 - March, 2002).(1) Roles of HAI-1 in the regulation of pericellular activation of HGFActivation of hepatocyte growth factor/scatter factor (HGF/SF) is a critic … More al limiting step in the HGF/SF-induced signaling pathway mediated by MET receptor tyrosine kinase. Although HGF/SF-MET signaling could have potentially important roles in the tissue regeneration and tumor progression, little is known about the regulation of HGF/SF activation. In this project, we have shown that HGF activator (HGFA) a recently identified factor XII-like serine proteinase, is critically involved in this process. Furthermore, we also showed that HGF activator inhibitor type 1 (HAI-1) should have an important regulatory role in the pericellular activation of HGF/SF having diverse roles acting as a cell surface specific inhibitor of active HGFA and a reservoir of this enzyme on the cell surface. The latter property might paradoxically ensure the concentrated pericellular HGFA activity in certain cellular conditions in which shedding of HAI-1/HGFA complex from the plasma membrane is upregulated.(2) APP is involved in the growth of colon carcinoma cells in vitro and in vivoIn a panel of human colon carcinoma cell lines, sAPP/PN-II was a major SPI secreted by all the cell lines examined. In this project we found that the downregulation of APP mRNA by an antisense mRNA strategy resulted in significantly reduced cellular proliferation of a colon carcinoma cell line in vitro, indicating that APP is somehow involved in the regulation of cellular proliferation. Of importance was the observation that reduced cellular growth was observed not only in vitro but also in vivo when the antisense colon carcinoma clones were transplanted into nude mice.(3) Generation of HGFA knock-out mouse and HAI-1 knock-out mouse.(4) Identification of a novel nuclear localization signal protein namely HAI-2-related small peptide (H2RSP). Less