Received for publication April 20, 2006.
Revised June 2, 2006.
Accepted for publication June 2, 2006.

Alpha-2C-adrenergic receptors exhibit enhanced surface expression and signaling upon association with beta-2-adrenergic receptors

Abstract

The alpha-2C-adrenergic receptor (alpha2C-AR) 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 alpha2C-AR might be enhanced by heterodimerization with other G protein-coupled receptors (GPCRs). Co-transfection of alpha2C-AR with more than twenty-five related GPCRs revealed that only co-expression with the beta-2-adrenergic receptor (beta2-AR) increased the surface localization of alpha2C-AR in HEK-293 cells. Co-immunoprecipitation of alpha2C-AR with beta2-AR confirmed a physical interaction between the two receptors. Confocal microscopy studies demonstrated that alpha2C-AR expressed alone was mainly intracellular, whereas alpha2C-AR co-expressed with beta2-AR was predominantly localized to the plasma membrane. Ligand binding studies revealed a significant increase in alpha2C-AR binding sites upon co-expression with beta2-AR, with no apparent change in affinity for alpha2-AR ligands. Functional assays with the alpha2-AR-specific agonist UK 14,304 revealed that co-expression of beta2-AR with alpha2C-AR enhanced alpha2C-AR-mediated activation of ERK 1/2. Furthermore, analyses of agonist-promoted receptor endocytosis demonstrated enhanced alpha2C-AR internalization in response to alpha2-AR agonists when alpha2C-AR and beta2-AR were co-expressed. Additionally, substantial co-internalization of alpha2C-AR in response to beta-AR agonists was observed when alpha2C-AR was co-expressed with beta2-AR. These data reveal that alpha2C-AR can interact with beta2-AR in cells in a manner that regulates alpha2C-AR surface expression, internalization, and functionality.

Key words: adrenoceptor, dimerization, epinephrine, norepinephrine, oligomerization, trafficking

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