Seven transmembrane receptor core signaling complexes are assembled prior to plasma membrane trafficking

Abstract

Much is known about β2-adrenergic receptor trafficking and internalization following prolonged agonist stimulation. However, less is known about outward trafficking of the β2-adrenergic receptor to the plasma membrane or the role that trafficking might play in the assembly of receptor signaling complexes, important for targeting, specificity, and rapidity of subsequent signaling events. Here, by using a combination of bioluminescence resonance energy transfer, bimolecular fluorescence complementation, and confocal microscopy, we evaluated the steps in the formation of the core receptor-G protein heterotrimer complex. By using dominant negative Rab and Sar GTPase constructs, we demonstrate that receptor dimers and receptor- Gβγ complexes initially associate in the endoplasmic reticulum, whereas Gα subunits are added to the complex during endoplasmic reticulum-Golgi transit. We also observed that G protein heterotrimers adopt different trafficking itineraries when expressed alone or with stoichiometric co-expression with receptor. Furthermore, deliberate mistargeting of specific components of these complexes leads to diversion of other members from their normal subcellular localization, confirming the role of these early interactions in targeting and formation of specific signaling complexes. © 2006 by The American Society for Biochemistry and Molecular Biology, Inc.