Functional characterization of a novel tyrosine phosphorylated protein in signal transduction of hepatocyte growth factor

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Hepatocyte growth factor (HGF) functions as a growth factor during tissue formation in embryogenesis and during tissue regeneration after tissue injury. We found a 115kDa protein which is tyrosine-phoshorylated in cells stimulated by HGF and designated it Hrs. The nucleotide sequence of its cDNA revealed that Hrs is a novel protein with a zinc-finger domain. In this study, we analyzed the function of the protein and obtained the following results.1. Analysis of intracellular localization of Hrs by subcellular fractionation and immunofluorescence staining revealed that Hrs is localized to early endosomes. Several proteins with the conserved zinc-finger domain that are localized to endosomes are involved in vesicular transport. Thus, Hrs may be involved in vesicular transport such as internalization of growth factor-receptor complexes.2. Tyrosine phosphorylation of Hrs was induced in cells treated by EGF or PDGF.These results suggest that Hrs plays a unique and important role in ths signaling pathway of growth factors.3. By screening a mouse liver cDNA library using yeast two-hybrid system, we isolated a cDNA of a Hrs binding protein. The nucleotide sequence of the cDNA revealed that the binding protein is a novel protein with a SH3 domain. Using the antibodies against Hrs and the binding protein, we showed that both proteins are strongly associated in various cells. These results suggest that Hrs plays an important role in HGF signaling by interaction with the binding protein.