Epidermal Growth Factor Receptor Interaction with Clathrin Adaptors Is Mediated by the Tyr⁹⁷⁴-containing Internalization Motif*

Abstract

The carboxyl-terminal regulatory domain of the epidermal growth factor (EGF) receptor is essential for its endocytosis and interaction with the clathrin-associated protein complex AP-2. To identify AP-2 binding motif in the receptor, several single and multiple-point mutations within the region between residues 966 and 977 of the human EGF receptor were made, and the mutant receptors were expressed in NIH3T3 cells. Mutation of tyrosine 974 alone or together with surrounding residues and the deletion of residues 973-975 essentially eliminated AP-2 co-immunoprecipitation with the EGF receptor. Furthermore, a synthetic peptide corresponding to receptor residues 964-978 blocked AP-2 association with the wild-type EGF receptor. These data suggest that AP-2 has only one high-affinity binding site in the EGF receptor composed of Tyr⁹⁷⁴-containing motif. Receptor mutants that did not bind AP-2 displayed a lower rate of internalization, down-regulation, and turnover compared to wild-type receptors when expressed at high levels. However, similar receptor mutants expressed at low levels were internalized and down-regulated as efficiently as wild-type receptors. Internalization of the mutant receptors lacking the high-affinity binding site for AP-2 was inhibited by K⁺-depletion of the cells, indicating that their endocytosis required intact coated pits. We suggest that whereas one mechanism of EGF receptor recruitment into coated pits involves high-affinity binding of AP-2 to Tyr⁹⁷⁴-containing motif, another pathway may be mediated by weak receptor/AP-2 interactions or by proteins other than AP-2.