Characterization of factors regulating the activity of hepatocyte growth factor which is being developed for a medicine

点击翻译按钮获取中文摘要

Hepatocyte growth factor (HGF) is a potent factor responsible for liver regeneration, and is being developed for a medicine of liver disease. The activity of HGF is regulated by extracellular and intracellular factors. In this study, we analyzed the function of these factors in regulating the activity of HGF and obtained the following results.(1) HGF activator (HGFA) was identified as a serine protease responsible for activation of HGF after liver injury. Analysis of HGFA after liver injury revealed that amount of HGFA mRNA increased, and HGFA was activated following liver injury.(2) Two types of HGFA inhibitors (HAIs) were identified as potent inhibitors of HGFA.cDNA cloning revealed that both HAIs are serine protease inhibitors with Kunitz domains. Introduction of mutations in the Kunitz domains markedly reduced the activity of HAIs, indicating that the domains are essential for the activity. Immunoblotting analysis demonstrated that HAIs are initially produced in transmembrane forms, and then secreted by the producing cells by proteolytic processing.(3) Hrs and its binding protein (Hbp) were identified as intracellular molecules regulating the activity of HGF.Functional characterization of Hrs/Hbp complexes revealed that the complexes are localized to early endosomes and play an important role in regulating the degradation of HGF and its receptor after internalization. Further, deubiquitinating enzyme UBPY was isolated as a binding partner of the SH3 domain of Hbp, suggesting that UBPY regulates the function of the Hrs/Hbp complexes.