Mechanisms of Biased Signaling at the Chemokine Receptor CXCR3

Abstract

G protein-coupled receptors (GPCRs) are the most common transmembrane receptors in the human genome and the target of approximately one-third of all approved drugs. GPCRs interact with many transducers like G proteins and β-arrestins. Some GPCRs preferentially activate specific signaling transducers over others, leading to unique signaling profiles – a phenomenon called biased signaling. The chemokine system, a subfamily of GPCRs, serves as an endogenous example of biased signaling where over 50 different chemokines and 20 receptors interact promiscuously. While previous research has shown that chemokines which activate the same receptor can produce different physiologic responses, the mechanisms underlying these findings remain unclear. Using the three endogenous chemokines of the chemokine receptor CXCR3, we investigated two mechanisms underlying biased signaling at GPCRs. First, using mass spectrometry and cell-based assays, we determined that the chemokines induce different amounts and patterns of GPCR phosphorylation which direct CXCR3 engagement with different transducers. Second, we determined that biased signaling is dependent on the specific location of CXCR3, and subcellular signaling regulates inflammation in a mouse model of contact hypersensitivity. Together, we conclude that differential receptor phosphorylation and subcellular signaling are two mechanisms underlying the biased signaling observed at GPCRs.