Biased agonists of the chemokine receptor CXCR3 differentially drive formation of Gαi:β-arrestin complexes
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 G α protein and β-arrestin have been described and suggest a distinct GPCR signaling pathway. Within these newly described G α β-arrestin complexes, G αi/o , but not other G α protein subtypes, have been appreciated to directly interact with β-arrestin, regardless of canonical GPCR G α protein subtype coupling. However it is unclear how biased agonists differentially regulate this newly described G αi 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 G αi β-arrestin complexes. The ability of CXCR3 agonists to form G αi β-arrestin complexes does not correlate well with either G protein signaling or β-arrestin recruitment. Conformational biosensors demonstrate that ligands that promoted G αi β-arrestin complex formation generated similar β-arrestin conformations. We find these G αi β-arrestin complexes can associate with CXCR3, but not with ERK. These findings further support that G αi β-arrestin complex formation is a distinct GPCR signaling pathway and enhance our understanding of biased agonism.
