Domain-specific Interactions between the p185 neu and Epidermal Growth Factor Receptor Kinases Determine Differential Signaling Outcomes

We expressed the epidermal growth factor receptor (EGFR) along with mutant p185 neu proteins containing the rat transmembrane point mutation. The work concerned the study of the contributions made by various p185 neu subdomains to signaling induced by a heterodimeric ErbB complex. Co-expression of full-length EGFR and oncogenic p185 neu receptors resulted in an increased EGF-induced phosphotyrosine content of p185 neu , increased cell proliferation to limiting concentrations of EGF, and increases in both EGF-induced MAPK and phosphatidylinositol 3-kinase (PI 3-kinase) activation. Intracellular domain-deleted p185 neu receptors (T691stop neu) were able to associate with full-length EGFR, but induced antagonistic effects on EGF-dependent EGF receptor down-regulation, cell proliferation, and activation of MAPK and PI 3-kinase pathways. Ectodomain-deleted p185 neu proteins (TΔ5) were unable to physically associate with EGFR, and extracellular domain-deleted p185 neu forms failed to augment activation of MAPK and PI 3-kinase in response to EGF. Association of EGFR with a carboxyl-terminally truncated p185 neu mutant (TAPstop) form did not increase transforming efficiency and phosphotyrosine content of the TAPstop species, and proliferation of EGFR·TAPstop-co-expressing cells in response to EGF was similar to cells containing EGFR only. Thus, neither cooperative nor inhibitory effects were observed in cell lines co-expressing either TΔ5 or TAPstop mutant proteins. Unlike the formation of potent homodimer assemblies composed of oncogenic p185 neu , the induction of signaling from p185 neu ·EGFR heteroreceptor assemblies requires the ectodomain for ligand-dependent physical association and intracellular domain contacts for efficient intermolecular kinase activation.