Signal transduction mechanisms mediated by tyrosine kinase receptors

The receptors for insulin, insulin-like growth factor-I (IGF-I) and epidermal growth factor (EGF) possess tyrosine-specific protein kinase activity which becomes activated upon ligand binding. To detect cellular substrates for these tyrosine-specific protein kinases, KB cells were labeled with [³²P]orthophosphate and immunoprecipitated with phosphotyrosine-specific antibody. We have found that 1) a 185 kDa protein is rapidly (<10 sec) tyrosine phosphorylated by insulin and IGF-I but not EGF; 2) tyrosine phosphorylation of c-erbB-2 gene product is rapidly (<10 sec) induced by EGF; 3) tyrosine phosphorylation of a 240 kDa protein is stimulated within 30 sec by all three growth factors.