BETA-ARRESTIN ACTS AS A CLATHRIN ADAPTER IN ENDOCYTOSIS OF THE BETA(2)-ADRENERGIC RECEPTOR

THE ability of a system to regulate its responsiveness in the presence of a continuous stimulus, often termed desensitization, has been exte nsively characterized for the beta(2)-adrenergic receptor (beta(2)AR). beta(2)AR signalling is rapidly attenuated through receptor phosphory lation and subsequent binding of the protein beta-arrestin(1,2). Ultim ately the receptor undergoes internalization(3,4), and although the mo lecular mechanism is unclear, receptor phosphorylation and beta-arrest in binding have been implicated in this process(5,6). Here we report t hat beta-arrestin and arrestin-3, but not visual arrestin, promote bet a(2)AR internalization and bind with high affinity directly and stoich iometrically to clathrin, the major structural protein of coated pits, Moreover, beta-arrestin/arrestin chimaeras that are defective in eith er beta(2)AR or clathrin binding show a reduced ability to promote bet a(2)AR endocytosis. Immunofluorescence microscopy of intact cells indi cates an agonist-dependent colocalization of the beta(2)AR and beta-ar restin with clathrin, These results show that beta-arrestin functions as an adaptor in the receptor-mediated endocytosis pathway, and sugges t a general mechanism for regulating the trafficking of G-protein-coup led receptors.