Abstract

The α_2C-adrenergic receptor (α_2CAR) is known to be poorly trafficked to the cell surface when expressed in a variety of cell types. We tested the hypothesis that the surface expression and signaling of α_2CAR might be enhanced by heterodimerization with other G protein-coupled receptors (GPCRs). Cotransfection of α_2CAR with more than 25 related GPCRs revealed that only coexpression with the β₂-adrenergic receptor (β₂AR) increased the surface localization of α_2CAR in human embryonic kidney-293 cells. Coimmunoprecipitation of α_2CAR with β₂AR confirmed a physical interaction between the two receptors. Confocal microscopy studies demonstrated that α_2CAR expressed alone was mainly intracellular, whereas α_2CAR coexpressed with β₂AR was predominantly localized to the plasma membrane. Ligand binding studies revealed a significant increase in α_2CAR binding sites upon coexpression with β₂AR, with no apparent change in affinity for α₂AR ligands. Functional assays with the α₂AR-specific agonist brimonidine (UK 14,304) revealed that coexpression of β₂AR with α_2CAR enhanced α_2CAR-mediated activation of extracellular signal-regulated kinase 1/2. Furthermore, analyses of agonist-promoted receptor endocytosis demonstrated enhanced α_2CAR internalization in response to α₂AR agonists when α_2CAR and β₂AR were coexpressed. In addition, substantial cointernalization of α_2CAR in response to βAR agonists was observed when α_2CAR was coexpressed with β₂AR. These data reveal that α_2CAR can interact with β₂AR in cells in a manner that regulates α_2CAR surface expression, internalization, and functionality.