LIGAND-INDUCED ENDOCYTOSIS OF EPIDERMAL GROWTH-FACTOR RECEPTORS THAT ARE DEFECTIVE IN BINDING ADAPTER PROTEINS

Ligand-activated epidermal growth factor receptors (EGFRs) associate w ith coated pit adaptor proteins (AP2) in vivo, implying a mechanism fo r receptor retention in coated pits during internalization. Using an i n vitro binding assay, we localized the adaptor binding determinant to residues 970-991 of EGFRs and confirmed specificity by competition wi th a synthetic peptide corresponding to this sequence. A mutant EGFR l acking this AP2 binding determinant did not associate with AP2 in vivo but demonstrated internalization and down-regulation kinetics indisti nguishable from its wildtype counterpart. Immunocytochemistry confirme d ligand-induced internalization of the mutant EGFR. These data sugges t that endocytic determinants are distinct from AP2 binding determinan ts and that processes other than association with AP2 regulate endocyt osis of EGFRs.