Rab11 regulates the recycling and lysosome targeting of β2-adrenergic receptors

Abstract

The pericentriolar recycling endosome (RE) may be an alternative compartment through which some β₂-adrenergic receptors (β₂ARs) recycle from early endosomes to the cell surface during prolonged exposure to agonist. For the transferrin receptor, CXCR2, and the M₄-muscarinic acetylcholine receptor, trafficking through the RE and receptor recycling is regulated by the small GTPase rab11. The precise role of the RE and rab11 in regulating the cellular trafficking of the β₂AR is not understood. We therefore monitored trafficking of β₂ARs in HEK293 cells following the modulation of rab11 activity. Expression of a rab11 mutant deficient in GTP binding (as a fusion between enhanced green fluorescent protein (EGFP) and the rab11S25N mutant) significantly slowed receptor recycling to the cell surface from dispersed transferrin-positive peripheral vesicles following a brief exposure to agonist. The agonist was applied at a time when receptors have undergone only one or two rounds of endocytosis and recycling. In cells overexpressing wild-type rab11, β₂ARs localized to a rab11-positive compartment and the rate of β₂AR recycling to the cell surface was reduced, but only after prolonged exposure to agonist and multiple rounds of receptor endocytosis and recycling. This effect was associated with impaired β₂AR trafficking to lysosomes and receptor proteolysis, whereas the sorting of low-density lipoprotein from transferrin-positive vesicles to late endosomes and lysosomes was not affected. These data highlight a pivotal role for rab11 in regulating the traffic of a G protein-coupled receptor at the level of the RE, where modulation of rab11 activity dictates the balance between receptor recycling and downregulation during prolonged exposure to agonist.