Inhibition of a naturally occurring EGFR oncoprotein by the p185neu ectodomain : implications for subdomain contributions to receptor assembly

Mutant Epidermal Growth Factor Receptor (EGFR) oncoproteins lacking most of subdomains I and II of the extracellular region, a deletion which includes most of the first of two cysteine-rich sequences, have been observed in multiple human epithelial tumors, including malignant gliomas. These EGFR oncoproteins, designated deltaEGFR or EGFRvIII, confer increased tumorigenicity in vivo and are often coexpressed with full-length EGFR in human tumors. We have expressed an ectodomain-derived, carboxyl-terminal deletion mutant of the p185neu oncogene (T691stop) in human glioblastoma cells coexpressing endogenous EGFR and activated deltaEGFR oncoproteins. The p185neu ectodomain-derived mutant forms heterodimers with deltaEGFR proteins and reduces the phosphotyrosine content and kinase activity of deltaEGFR monomers. As a consequence of T691stop neu expression and surface localization, cell proliferation in conditions of full growth and reduced serum and anchorage-independent growth in soft agar was reduced in glioblastoma cells expressing either endogenous EGFR alone or coexpressing EGFR and elevated levels of deltaEGFRs. T691stop neu mutant receptors abrogate the dramatic growth advantage conferred by deltaEGFR in vivo, suggesting that physical associations primarily between subdomains III and IV of the p185neu and EGFR ectodomains are sufficient to modulate signaling from activated EGFR complexes. Receptor-based inhibitory strategies exploit the thermodynamic preference for erbB ectodomains to heterodimerize, thereby creating erbB receptor assemblies which are defective in signaling and do not internalize. Pharmaceuticals which mimic the p185neu ectodomain may therefore have important therapeutic applications in advanced human malignancies expressing erbB receptors.