HGF and melanoma: Among the receptor tyrosine kinase substrates, the hepatocyte growth factor (HGF)—regulated tyrosine kinase substrate, abbreviated HRS, was first identified as a phosphotyrosine-containing protein, whose phosphorylation was rapidly induced in HGF-treated mouse melanoma cells.1 Cloning and sequencing analysis has revealed that HRS contains a zinc-finger domain, a proline-rich region, and a proline-and glutamine-rich region.