Rab11 regulates the recycling of the β2-adrenergic receptor through a direct interaction

Abstract

The β2ARs (β2-adrenergic receptors) undergo ligand-induced internalization into early endosomes, but then are rapidly and efficiently recycled back to the plasma membrane, restoring the numbers of functional cell-surface receptors. Gathering evidence suggests that, during prolonged exposure to agonist, some β2ARs also utilize a slow recycling pathway through the perinuclear recycling endosomal compartment regulated by the small GTPase Rab11. In the present study, we demonstrate by co-immunoprecipitation studies that there is a β2AR–Rab11 association in HEK-293 cells (human embryonic kidney cells). We show using purified His6-tagged Rab11 protein and β2AR intracellular domains fused to GST (glutathione transferase) that Rab11 interacts directly with the C-terminal tail of β2AR, but not with the other intracellular domains of the receptor. Pull-down and immunoprecipitation assays revealed that the β2AR interacts preferentially with the GDP-bound form of Rab11. Arg333 and Lys348 in the C-terminal tail of the β2AR were identified as crucial determinants for Rab11 binding. A β2AR construct with these two residues mutated to alanine, β2AR RK/AA (R333A/K348A), was generated. Analysis of cell-surface receptors by ELISA revealed that the recycling of β2AR RK/AA was drastically reduced when compared with wild-type β2AR after agonist washout, following prolonged receptor stimulation. Confocal microscopy demonstrated that the β2AR RK/AA mutant failed to co-localize with Rab11 and recycle to the plasma membrane, in contrast with the wild-type receptor. To our knowledge, the present study is the first report of a direct interaction between the β2AR and a Rab GTPase, which is required for the accurate intracellular trafficking of the receptor.