The β 2 -adrenergic receptor/βarrestin complex recruits the clathrin adaptor AP-2 during endocytosis

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Abstract
βarrestins mediate the desensitization of the β 2 -adrenergic receptor (β 2 AR) and many other G protein-coupled receptors (GPCRs). Additionally, βarrestins initiate the endocytosis of these receptors via clathrin coated-pits and interact directly with clathrin. Consequently, it has been proposed that βarrestins serve as clathrin adaptors for the GPCR family by linking these receptors to clathrin lattices. AP-2, the heterotetrameric clathrin adaptor protein, has been demonstrated to mediate the internalization of many types of plasma membrane proteins other than GPCRs. AP-2 interacts with the clathrin heavy chain and cytoplasmic domains of receptors such as those for epidermal growth factor and transferrin. In the present study we demonstrate the formation of an agonist-induced multimeric complex containing a GPCR, βarrestin 2, and the β2-adaptin subunit of AP-2. β2-Adaptin binds βarrestin 2 in a yeast two-hybrid assay and coimmunoprecipitates with βarrestins and β 2 AR in an agonist-dependent manner in HEK-293 cells. Moreover, β2-adaptin translocates from the cytosol to the plasma membrane in response to the β 2 AR agonist isoproterenol and colocalizes with β 2 AR in clathrin-coated pits. Finally, expression of βarrestin 2 minigene constructs containing the β2-adaptin interacting region inhibits β 2 AR endocytosis. These findings point to a role for AP-2 in GPCR endocytosis, and they suggest that AP-2 functions as a clathrin adaptor for the endocytosis of diverse classes of membrane receptors.