Biased agonists of the chemokine receptor CXCR3 differentially drive formation of G αi :β-arrestin complexes

Abstract G-protein-coupled receptors (GPCRs), the largest family of cell surface receptors, signal through the proximal effectors G proteins and β-arrestins to influence nearly every biological process. Classically, the G protein and β-arrestin signaling pathways have largely been considered separable. Recently, direct interactions between Gα protein and β-arrestin have been described and suggest a distinct GPCR signaling pathway. Within these newly described Gα:β-arrestin complexes, Gαi/o, but not other Gα protein subtypes, have been appreciated to directly interact with β-arrestin, regardless of canonical GPCR Gα protein subtype coupling. However it is unclear how biased agonists differentially regulate this newly described Gαi:β-arrestin interaction, if at all. Here we report that endogenous ligands (chemokines) of the GPCR CXCR3, CXCL9, CXCL10, and CXCL11, along with two small molecule biased CXCR3 agonists, differentially promote the formation of Gαi:β-arrestin complexes. The ability of CXCR3 agonists to form Gαi:β-arrestin complexes does not correlate well with either G protein signaling or β-arrestin recruitment. Conformational biosensors demonstrate that ligands that promoted Gαi:β-arrestin complex formation generated similar β-arrestin conformations. We find these Gαi:β-arrestin complexes can associate with CXCR3, but not with ERK. These findings further support that Gαi:β-arrestin complex formation is a distinct GPCR signaling pathway and enhance our understanding of biased agonism.