EAST, AN EPIDERMAL GROWTH-FACTOR RECEPTOR-ASSOCIATED AND EPS15-ASSOCIATED PROTEIN WITH SRC HOMOLOGY 3 AND TYROSINE-BASED ACTIVATION MOTIF DOMAINS

We describe the cloning and characterization of a new cytoplasmic prot ein designated epidermal growth factor receptor-associated protein wit h SH3- and TAM domains (EAST). It contains an Src homology 3 domain in its midregion and a tyrosine-based activation motif in its COOH termi nus. Antibodies to EAST recognize a 68-kDa protein that is present in most chicken tissues. An epidermal growth factor (EGF) dependent assoc iation between the EGF receptor (EGFR) and EAST was shown by reciproca l immunoprecipitation/immunoblotting studies with specific antibodies. Activated EGFR catalyzed the tyrosine phosphorylation of EAST, as jud ged by an in vitro kinase assay with both immunoprecipitated and purif ied EGFR Immunoprecipitation/immunoblotting experiments also demonstra ted an association between EAST and eps15, an EGFR substrate associate d with clathrin-coated pits and vesicles, which is essential in the en docytotic pathway. The association between EAST and eps15 was not affe cted by EGF treatment. In immunofluorescence microscopy, EAST was show n to partially colocalize with clathrin. The sequence of the NH2-termi nal portion of EAST shows a high degree of similarity with a group of proteins involved in endocytosis or vesicle trafficking. Thus, EAST is a novel signal transduction component probably involved in EGF signal ing and in the endocytotic machinery.