Regulation of growth factor activity by Kunitz-type serine proteinase inhibitors

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Hepatocyte growth factor (HGF) is a multifunctinal growth factor that acts as mitogen, morphogen, and motogen. HGF is secreted by stromal cells as an inactive precursor form and is specifically activated by HGF activator (HGFA) to the active form. Activity of HGFA is regulated by two recently identified specific inhibitors, namely HGF activator inhibitor type 1 (HAI-I) and type 2 (HAI-2), both of which have two Kunitz-type serine proteinase inhibitor domains. Although the activation of HGF/SF is a critical limiting step in HGF/SF-induced signaling pathway mediated by Met receptor tyrosine kinase, little is known concerning the regulation of HGF activation in various tissues. In this study, we generated the knock-out mice of these HGF regulatory molecules and examine their function in vivo. First, we cloned characterized the genes coding for mouse counter parts of HGFA, HAI-1 and HAI-2 from mouse BAC library, and then made the targeting vectors by insertion of positive/negative selectio … More n markers. Targeting vecters were transfected into ES cells by electroporation and positive clones were selected and injected into blastcysts from C57BL/6 female mice. Some chimeric mice were obtained and mated for generating heterozygous mutant mice. Now, we have some heterozygous mice and they are mating to obtain homo zygous mutant mice. We also reported some other results of relevant studies as follows ; 1) Upregulation of HAI-1 but not HAI-2 along with regeneration of intestinal mucosa, 2) HAI-2 taking the first Kunitz domain is a major product in mouse but not in human, 3) upregulation of HAI-1 and HGFA in colorectal carcinomas, 4) HAI-1 but not HAI-2 is not only an inhibitor but also a specific cell surface binding protein of active HGFA acting a reservoir of this enzyme on the cell surface. These results suggest that HAI-1 is a cell surface acceptor of activated HGFA in regenerative epithelial cells, functioning on the cellular surface to localize the active HGFA on the cells which are going to enter the repair process. The concentrated HGFA activity would ensure the efficient pericellular activation of HGF/SF in the damaged gastrointestinal mucosa and promote proliferation and migration of gastrointestinal epithelial cells. Less