β-Arrestin- but Not G Protein-Mediated Signaling by the "Decoy" Receptor CXCR7

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 107; no. 2; pp. 628 - 632
• Main Authors: Rajagopal, Sudarshan, Kim, Jihee, Ahn, Seungkirl, Craig, Stewart, Lam, Christopher M., Gerard, Norma P., Gerard, Craig, Lefkowitz, Robert J.
• Format: Journal Article
• Language: English
• Published: United States National Academy of Sciences 12.01.2010; National Acad Sciences
• Subjects: Agonists; Animals; Antibodies; Arrestins - physiology; beta-Arrestins; Biological Sciences; Calcium; Cell Line; Chemokine receptors; Chemokines; Enzyme Activation; Extracellular Signal-Regulated MAP Kinases - metabolism; GTP-Binding Proteins - genetics; GTP-Binding Proteins - physiology; HEK293 cells; Humans; Ligands; Mice; Muscle, Smooth, Vascular - physiology; Phosphorylation; Rats; Receptors; Receptors, Chemokine - genetics; Receptors, CXCR - genetics; Receptors, CXCR - physiology; RNA, Messenger - genetics; Signal Transduction - physiology; Small interfering RNA; T-Lymphocytes - cytology; T-Lymphocytes - physiology; Transfection
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.0912852107

Ubiquitously expressed seven-transmembrane receptors (7TMRs) classically signal through heterotrimeric G proteins and are commonly referred to as G protein-coupled receptors. It is now recognized that 7TMRs also signal through β-arrestins, which act as versatile adapters controlling receptor signaling, desensitization, and trafficking. Most endogenous receptors appear to signal in a balanced fashion using both β-arrestin and G protein-mediated pathways. Some 7TMRs are thought to be nonsignaling "decoys" because of their inability to activate typical G protein signaling pathways; it has been proposed that these receptors act to scavenge ligands or function as coreceptors. Here we demonstrate that ligand binding to the decoy receptor CXCR7 does not result in activation of signaling pathways typical of G proteins but does activate MAP kinases through β-arrestins in transiently transfected cells. Furthermore, we observe that vascular smooth muscle cells that endogenously express CXCR7 migrate to its ligand interferoninducible T-cell alpha chemoattractant (ITAC), an effect that is significantly attenuated by treatment with either a CXCR7 antagonist or β-arrestin depletion by siRNA. This example of an endogenous "β-arrestin-biased" 7TMR that signals through β-arrestin in the absence of G protein activation demonstrates that some 7TMRs encoded in the genome have evolved to signal through β-arrestin exclusively and suggests that other receptors that are currently thought to be orphans or decoys may also signal through such nonclassical pathways.