Cooperative interaction between α- and β-chains of hepatocyte growth factor on c-Met receptor confers ligand-induced receptor tyrosine phosphorylation and multiple biological responses

Abstract

Hepatocyte growth factor (HGF) is a heterodimeric molecule composed of the α-chain containing the N-terminal hairpin domain, four kringle domains, and the serine protease-like β-chain. We prepared HGF/NK4 and HGF/β from the entire HGF after single-cut digestion with elastase. HGF/NK4 contains the N-terminal hairpin and four kringle domains, while HGF/β is composed of the C-terminal 16 amino acids of the α-chain and the entire β-chain, linked by a disulfide bridge. HGF/NK4 competitively inhibited the binding of 125I- HGF to the receptor, and affinity cross-linking analysis indicated that HGF/NK4 alone can bind to the c-Met receptor. In contrast, HGF/β alone did not competitively inhibit the binding of 125I-HGF to the receptor and did not bind to the c-Met/HGF receptor. Scatchard analysis and affinity cross- linking experiments indicated that HGF/β specifically binds to c-Met in the presence of HGF/NK4 but not HGF/NK2. Neither HGF/NK4 nor HGF/β alone induced mitogenic, motogenic (cell scattering), and morphogenic (induction of branching tubulogenesis) responses; however, HGF/β did induce these biological responses in the presence of HGF/NK4. Consistent with these results, although neither HGF/NK4 alone nor HGF/β alone induced tyrosine phosphorylation of the c-Met/HGF receptor, HGF/β induced tyrosine phosphorylation of the receptor when c-Met/HGF receptor was occupied by HGF/NK4. These results indicate that HGF/β binds to the c-Met/HGF receptor that is occupied by HGF/NK4 and induces receptor tyrosine phosphorylation and the subsequent biological activities of HGF. We propose that there exists a unique cooperative interaction between α- and β-chains, this interaction leading to β-chain-dependent receptor tyrosine phosphorylation and subsequent biological responses.