Heterodimerization of α2A- and β1-Adrenergic Receptors

Jianguo Xu,Junqi He,Amanda M Castleberry,Srividya Balasubramanian,Anthony G Lau,Randy A Hall

doi:10.1074/jbc.m207968200

Abstract

beta- and alpha(2)-adrenergic receptors are known to exhibit substantial cross-talk and mutual regulation in tissues where they are expressed together. We have found that the beta(1)-adrenergic receptor (beta(1)AR) and alpha(2A)-adrenergic receptor (alpha(2A)AR) heterodimerize when coexpressed in cells. Immunoprecipitation studies with differentially tagged beta(1)AR and alpha(2A)AR expressed in HEK-293 cells revealed robust co-immunoprecipitation of the two receptors. Moreover, agonist stimulation of alpha(2A)AR was found to induce substantial internalization of coexpressed beta(1)AR, providing further evidence for a physical association between the two receptors in a cellular environment. Ligand binding assays examining displacement of [(3)H]dihydroalprenolol binding to the beta(1)AR by various ligands revealed that beta(1)AR pharmacological properties were significantly altered when the receptor was coexpressed with alpha(2A)AR. Finally, beta(1)AR/alpha(2A)AR heterodimerization was found to be markedly enhanced by a beta(1)AR point mutation (N15A) that blocks N-linked glycosylation of the beta(1)AR as well as by point mutations (N10A/N14A) that block N-linked glycosylation of the alpha(2A)AR. These data reveal an interaction between beta(1)AR and alpha(2A)AR that is regulated by glycosylation and that may play a key role in cross-talk and mutual regulation between these receptors.

Highlights

The physiological actions of epinephrine and norepinephrine are mediated via the activation of the following three distinct classes of G protein-coupled receptors (GPCR)1: ␣1, ␣2, and ␤-adrenergic receptors
A key question in this field is: how widespread is the phenomenon of receptor heterodimerization? The most clearcut case of the importance of GPCR heterodimerization comes from the GABAB receptor, a pharmacologically defined entity that is known to be comprised of two distinct GPCRs, GABABR1 and GABABR2 [10]
␣2ARs and ␤adrenergic receptor (AR) couple primarily to G proteins with opposing cellular effects on cAMP production, it is known that agonist activation of ␣2ARs can in some cases paradoxically sensitize ␤AR signaling in brain tissue [2,3,4]

Summary

Introduction

The physiological actions of epinephrine and norepinephrine are mediated via the activation of the following three distinct classes of G protein-coupled receptors (GPCR)1: ␣1-, ␣2-, and ␤-adrenergic receptors. The pharmacological properties of ␤ARs in brain tissue are known to be regulated by ␣2ARs [5, 6], and reciprocally the pharmacological properties of ␣2ARs in brain tissue are known to regulated by ␤ARs [7, 8] These examples of cross-talk and mutual regulation between ␤- and ␣2-adrenergic receptors have been well known for more than 20 years, but the underlying molecular mechanisms remain unclear. We have found recently [14] that the ␤1AR exhibits robust homodimerization in cells It has been shown recently [15] that ␤1AR and ␤2AR can heterodimerize in a functionally important manner. Based on the previously reported functional interactions between ␣2ARs and ␤ARs, as well as the overlapping distribution patterns of ␣2AAR and ␤1AR, we examined the possibility that ␤1AR might be able to heterodimerize with

Methods

Results

Conclusion