Cell Surface Expression of 1 D - Adrenergic Receptors Is Controlled by Heterodimerization with 1 B - Adrenergic Receptors

1-Adrenergic receptors (ARs) belong to the large Class I G protein-coupled receptor superfamily and comprise three subtypes ( 1A, 1B, and 1D). Previous work with heterologously expressed C-terminal green fluorescent protein (GFP)-tagged 1-ARs showed that 1Aand 1B-ARs localize to the plasma membrane, whereas 1D-ARs accumulate intracellularly. We recently showed that 1Dand 1B-ARs form heterodimers, whereas 1Dand 1A-ARs do not. Here, we examined the role of heterodimerization in regulating 1D-AR localization using both confocal imaging of GFPor CFPtagged 1-ARs and a luminometer-based surface expression assay in HEK293 cells. Co-expression with 1B-ARs caused 1D-ARs to quantitatively translocate to the cell surface, but co-expression with 1A-ARs did not. Truncation of the 1B-AR extracellular N terminus or intracellular C terminus had no effect on surface expression of 1D-ARs, suggesting primary involvement of the hydrophobic core. Co-transfection with an uncoupled mutant 1B-AR ( 12 1B) increased both 1D-AR surface expression and coupling to norepinephrine-stimulated Ca mobilization. Finally, GFP-tagged 1D-ARs were not detected on the cell surface when expressed in rat aortic smooth muscle cells that express no endogenous ARs, but were almost exclusively localized on the surface when expressed in DDT1MF-2 cells, which express endogenous 1B-ARs. These studies demonstrate that 1B/ 1D-AR heterodimerization controls surface expression and functional coupling of 1D-ARs, the Nand Cterminal domains are not involved in this interaction, and that 1B-AR G protein coupling is not required. These observations may be relevant to many other Class I G protein-coupled receptors, where the functional consequences of heterodimerization are still poorly understood.