IDENTIFICATION OF C-ERBB-3 BINDING-SITES FOR PHOSPHATIDYLINOSITOL 3'-KINASE AND SHC USING AN EGF RECEPTOR C-ERBB-3 CHIMERA

c-erbB-3 is a member of the type I (EGF receptor-related) family of gr owth factor receptors for which no ligand has been identified. To faci litate ligand stimulation we have constructed a chimeric receptor whic h possesses an activatable kinase and promotes the growth of NIH 3T3 f ibroblasts. In this study we have shown that SHC and phosphatidylinosi tol 3 '-kinase bind to the activated EGF receptor/c-erbB-3 chimera. Wh ereas p85 is not phosphorylated to a significant extent, SHC appears t o be a major substrate for phosphorylation on tyrosine. In contrast to EGF receptor and c-erbB-2, we were unable to detect binding of activa ted c-erbB-3 to GRB2. Using synthetic peptides corresponding to each o f 13 potential phosphorylation sites on c-erbB-3, we have shown that t yrosine 1309 is responsible for SHC binding. Peptides containing the m otif YXXRM inhibit p85 association. By comparison with recently report ed SHC binding sites on Middle T antigen and Trk we have identified a SHC binding motif, NPXY.