Matriptase or MT-SP1 is an epithelial-derived type II transmembrane serine protease that is highly expressd in human cancer-derived cell lines. Matriptase cleaves and activates protease activated receptor-2, pro-urokinase plasminogen activator and pro-hepatocyte growth factor. Matriptase is strongly inhibited by the hepatocyte growth factor activator inhibitor type 1 (HAI-1), which is a reactive site loop of Kunitz domain and also a transmembrane serine protease inhibitor.