Functional Characterization of the Obesity-Linked Variant of the β3-Adrenergic Receptor

Adrenergic receptor beta(3) (ADR beta(3)) is a member of the rhodopsin-like G protein-coupled receptor family. The binding of the ligand to ADR beta(3) activates adenylate cyclase and increases cAMP in the cells. ADR beta(3) is highly expressed in white and brown adipocytes and controls key regulatory pathways of lipid metabolism. Trp64Arg (W64R) polymorphism in the ADR beta(3) is associated with the early development of type 2 diabetes mellitus, lower resting metabolic rate, abdominal obesity, and insulin resistance. It is unclear how the substitution of W64R affects the functioning of ADR beta(3). This study was initiated to functionally characterize this obesity-linked variant of ADR beta(3). We evaluated in detail the expression, subcellular distribution, and post-activation behavior of the WT and W64R ADR beta(3) using single cell quantitative fluorescence microscopy. When expressed in HEK 293 cells, ADR beta(3) shows a typical distribution displayed by other GPCRs with a predominant localization at the cell surface. Unlike adrenergic receptor beta(2) (ADR beta(2)), agonist-induced desensitization of ADR beta(3) does not involve loss of cell surface expression. WT and W64R variant of ADR beta(3) displayed comparable biochemical properties, and there was no significant impact of the substitution of tryptophan with arginine on the expression, cellular distribution, signaling, and post-activation behavior of ADR beta(3). The obesity-linked W64R variant of ADR beta(3) is indistinguishable from the WT ADR beta(3) in terms of expression, cellular distribution, signaling, and post-activation behavior.