Agonist-Induced Receptor Internalization in Chinese Hamster Ovary Cells Stably Co-expressing [beta]1- and [beta]2-Adrenergic Receptors

β1- and β2-Adrenergic receptors (β1-AR and β2-AR) are co-expressed in numerous tissues, for example, heart and bladder. They play a very important role in the responses of a variety of organs to sympathetic nerve stimulation. Recent studies suggest that many G protein-coupled receptors, such as β1-AR, β2-AR, μ opioid receptor and δ opioid receptor, can form homo- and heterooligomers. Previous studies demonstrated that the β1-AR and β2-AR formed dimers in living HEK 293 cells. The aim of the present study is to investigate whether such heterooligomerization affect the agonist-induced receptor internalization in the CHO-K1 cells stably co-expressing β1-AR and β2-AR. Using co-immunoprecipitation, we confirmed that β1-AR and β2-AR formed heterooligomers in the CHO-K1 cells. In cells co-expressing β1-AR and β2-AR, 30% of β1-AR was internalized by isoproterenol, whereas only 20% of β1-AR was internalized in cells expressing the β1-AR alone. Heterooligomerization did not affect the ratio of internalized β2-AR. Salmeterol, a specific β2-AR agonist, broke β1-AR/β2-AR heterooligomers, and induced β2-AR-specific internalization in cells co-expressing β1-AR and β2-AR. The present study demonstrated that heterooligomerization between β1-AR and β2-AR accelerates the isoproterenol-promoted internalization of the β1-AR, and that salmeterol induces β2-AR-specific internalization in Chinese hamster ovary (CHO) cells stably co-expressing β1-AR and β2-AR.