Dynamin and beta-arrestin reveal distinct mechanisms for G protein-coupled receptor internalization

The process of agonist-promoted internalization (sequestration) of G protein-coupled receptors (GPCRs) is intimately linked to the regulation of GPCR responsiveness, Following agonist-mediated desensitization, sequestration of GPCR is presumably associated with the dephosphorylation and recycling of functional receptors, However, the exact mechanisms responsible for GPCR sequestration, even for the prototypic beta(2)-adrenergic receptor (beta(2)AR), have remained controversial, We demonstrate here that dynamin, a GTPase that regulates the formation and internalization of clathrin-coated vesicles, is essential for the agonist-promoted sequestration of the beta(2)AR, suggesting that the beta(2)AR internalizes via the clathrin-coated vesicle-mediated endocytic pathway, In contrast, internalization of the angiotensin II type 1A receptor (AT(1A)R), another typical GPCR, does not require dynamin, In addition, the AT(1A)R internalizes independent of the function of beta-arrestin, a critical component for beta(2)AR cellular trafficking, but additional AT(1A)Rs are mobilized to the dynamin-dependent pathway upon overexpression of beta- arrestin. These findings demonstrate that GPCRs can utilize distinct endocytic pathways, distinguishable by dynamin and beta-arrestin, and that beta-arrestins function as adaptor proteins specifically targeting GPCRs for dynamin-dependent endocytosis via clathrin-coated vesicles.