Heterodimerization of 2 A - and 1 - Adrenergic Receptors

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