Extended repertoire of CXC chemokines acting as agonists and antagonists of the human and murine atypical chemokine receptor ACKR2

Atypical chemokine receptors are a subfamily of important regulators of chemokine functions. Among them, ACKR2 has long been considered a scavenger of multiple inflammatory chemokines exclusively from the CC family. Recently, we demonstrated the ability of ACKR2 to scavenge the CXC chemokine CXCL10, previously reported to bind solely the classical receptor CXCR3. This discovery emphasized the need for systematic reassessments of chemokine-receptor pairings. In this work, we established a highly sensitive NanoBRET-based competition binding assay using a novel proprietary ACKR2 modulator (LIH222) and applied it in a comprehensive reassessment of the pairings between human and murine chemokines and their respective ACKR2 orthologs. We confirmed CXCL10 as a ligand for the human but also the mouse ACKR2. We also identified CXCL5, CXCL11, and CXCL12 as new CXC chemokines for both ACKR2 orthologs. Furthermore, we showed that CXCL2 is a ligand for the human but not the mouse ACKR2, whereas CXCL1 binds the mouse but not the human receptor. Finally, we found that N-terminally truncated CXCL5 (CXCL58-78) loses its capacity to bind ACKR2, whereas the removal of the first 2 residues of CXCL11 (CXCL113-73) enhances its antagonist potency, showing a tendency toward a reduction of the receptor basal interactions with β-arrestins. Altogether, this study demonstrates that ACKR2 is not exclusive to CC chemokines, and although with a weaker affinity, it can also bind and scavenge a subset of inflammatory and homeostatic CXC chemokines important for the regulation of the immune system.