Biochemical and biophysical demonstration of GPCR oligomerization in mammalian cells

In contrast to other families of cell surface receptors, like tyrosine kina se receptors, for which dimerization is an integral part of the activation process, G-protein-coupled receptors (GPCRs) were thought, until recently, to function as monomeric units. However, a growing body of evidence indicat es that GPCRs could exist and be active as oligomeric complexes. Because th ey are major pharmacological targets, their existence as homo- or hetero- o ligomers could have important implications for the development and screenin g of new drugs. The major evidences supporting the idea of GPCR oligomeriza tion come from indirect biochemical or pharmacological experiments. Here we report, using traditional co-immunoprecipitation methods, the existence of differentially epitope-tagged beta2-adrenergic receptor (beta 2AR) oligome rs in mammalian HEK-293 cells. Moreover, we validate the existence of recep tor oligomers in living cells by a new Bioluminescence Resonance Energy Tra nsfer (BRET) technique. Our results clearly demonstrate the presence of con stitutive beta 2AR oligomers in living cells that can be modulated by the s elective adrenergic agonist isoproterenol, suggesting a pertinent physiolog ical role for GPCR oligomerization. (C) 2001 Elsevier Science Inc. All righ ts reserved.