Label-free impedance responses of endogenous and synthetic chemokine receptor CXCR3 agonists correlate with Gi-protein pathway activation.

The chemokine receptor CXCR3 is a G-protein-coupled receptor that signals through the Gα(i) class of heterotrimeric G-proteins. CXCR3 is highly expressed on activated T cells and has been proposed to be a therapeutic target in autoimmune disease. CXCR3 is activated by the chemokines CXCL9, CXCL10 and CXCL11. CXCR3 signaling properties in response to CXCL10, CXCL11 and the synthetic agonist VUF10661 have previously been evaluated using conventional endpoint assays. In the present study, label-free impedance measurements were used to characterize holistic responses of CXCR3-expressing cells to stimulation with chemokines and VUF10661 in real time and to compare these responses with both G-protein and non-G-protein (β-arrestin2) mediated responses. Differences in response kinetics were apparent between the chemokines and VUF10661. Moreover, CXCR3-independent effects could be distinguished from CXCR3-specific responses with the use of the selective CXCR3 antagonist NBI-74330 and the Gα(i) inhibitor pertussis toxin. By comparing the various responses, we observed that CXCL9 is a biased CXCR3 agonist, stimulating solely G-protein-dependent pathways. Moreover, CXCR3-mediated changes in cellular impedance correlated with G-protein signaling, but not β-arrestin2 recruitment.