β(1)-Adrenergic Receptor Recycles Via a Membranous Organelle, Recycling Endosome, by Binding with Sorting Nexin27

In cardiomyocytes, β(1)-adrenergic receptor (β(1)-AR) plays an important role in regulating cardiac functions. Upon continuous ligand stimulation, β(1)-AR is internalized and mostly recycled back to the plasma membrane (PM). The recycling endosome (RE) is one of the membranous organelles involved in the protein recycling pathway. To determine whether RE is involved in the internalization of β(1)-AR upon ligand stimulation, we evaluated the localization of β(1)-AR after stimulation with a β-agonist, isoproterenol (Iso), in β(1)-AR-transfected COS-1 cells. After 30 min of Iso treatment and cell surface labeling with the appropriate antibodies, β(1)-AR was internalized from PM and translocated into the perinuclear region, the same location as the transferrin receptor, an RE marker. We then evaluated whether sorting nexin 27 (SNX27) participated in the β(1)-AR recycling pathway. When β(1)-AR and SNX27 were coexpressed, β(1)-AR coimmunoprecipitated with SNX27. In addition, shRNA-mediated silencing of SNX27 compromised β(1)-AR recycling and enhanced its delivery into lysosome. Overall, β(1)-AR on PM was internalized into RE upon Iso stimulation and recycled by RE through binding with SNX27 in COS-1 cells.