Modulation of the protein tyrosine kinase activity and autophosphorylation of the epidermal growth factor receptor by its juxtamembrane region

Using peptides epidermal growth factor receptor (EGFR)-13 and EGFR-14, which correspond to residues 645-657 and 679-692, respectively, in the juxtamembrane, cytosolic region of the epidermal growth factor receptor (EGFR) we have investigated the role of specific regions of the receptor in regulating its autophosphorylation and protein tyrosine kinase activity. EGFR-13, but not EGFR-14, increased autophosphorylation (by twofold) of the full-length and two truncated forms (Delta1022-1186 and a constitutively active receptor kinase domain) of the EGFR. EGFR-13 increased the stoichiometry of tyrosine phosphorylation of the full-length receptor from 4.2 to 10.1 mol Pi/mol EGFR and that of EGFRDelta1022-1186 from 1.0 to 2 mol Pi/mol receptor. Increased receptor autophosphorylation in the presence of EGFR-13 cannot solely be attributed to an increase in tyrosine kinase activity because EGFR-14 and polylysine increased tyrosine kinase activity of EGFRDelta1022-1186 and full-length EGFR, respectively, to the same extent as EGFR-13 without any effects on receptor autophosphorylation. Phosphorylation of EGFR-13 (P-EGFR-13) on the threonine residue corresponding to Thr654 in EGFR obliterated the ability of the peptide to increase autophosphorylation and markedly diminished its capacity to increase receptor tyrosine kinase activity. Additionally, EGFR-13, but not EGFR-14 or P-EGFR-13, decreased the migration of the receptor on nondenaturing gels, indicating that EGFR-13 induces some conformational change. Phosphopeptide maps of the EGFR phosphorylated in the presence of EGFR-13 or pp60(c-src) demonstrated that the additional sites phosphorylated in the presence of EGFR-13 were the same as those phosphorylated by pp60(c-src) (i.e., Y803, Y845, Y891, Y920, and Y1101). Thus, we conclude that EGFR-13, but not EGFR-14 or P-EGFR-13, competes to disrupt interactions between amino acids 645-657 and some other region(s) on the EGFR to either alleviate a conformational constraint or alter dimer conformation. This change increases the protein tyrosine kinase activity of the EGFR and provides access to additional tyrosine autophosphorylation sites in the receptor.