c-Src-mediated phosphorylation of AP-2 reveals a general mechanism for receptors internalizing through the clathrin pathway.

Clathrin-mediated endocytosis is a complex process regulated at many different levels. We showed previously that activation of the angiotensin type 1 receptor (AT1R), which belongs to the G protein-coupled receptor (GPCR) family, leads to c-Src-dependent tyrosine phosphorylation of beta2-adaptin, a subunit of the clathrin adaptor AP-2. The phosphorylation of beta2-adaptin on tyrosine residue 737 (Y737) negatively regulates its interaction with betaarrestin, another important clathrin adaptor for GPCR internalization. Here we sought to determine whether AP-2 phosphorylation represents a general mechanism for different receptors internalizing through the clathrin pathway. Using a specifically designed antibody against the phosphorylated form of Y737 on beta2-adaptin, we demonstrate that this residue is phosphorylated by AT1R in different cell types like HEK293, COS-7 and vascular smooth muscle cells. Using RNA interference approaches, we reveal that this agonist-mediated event is both betaarrestin- and c-Src-dependent, and that it occurs at the plasma membrane in clathrin-coated vesicles (CCVs). We further show that this is not only a common event employed by other GPCRs like the beta2-adrenergic, vasopressin V2, bradykinin type 2, platelet-activating factor and endothelin A receptors but that the epidermal growth factor receptor is capable of eliciting the phosphorylation of AP-2 in CCVs. Our results imply that tyrosine phosphorylation of Y737 on beta2-adaptin is a common regulatory mechanism employed by different receptors undergoing clathrin-dependent endocytosis, and suggest a wider function for this event than originally anticipated.