CX3CL1 oligomerization is required for efficient CX3CR1-specific cell adherence

Abstract

During inflammatory response, blood leukocytes adhere to the endothelium. This process involves numerous adhesion molecules, including a transmembrane chemokine, CX3CL1. We previously found that CX3CL1 clusters in oligomers. How this cluster assembles and whether it has a functional role remain unknown. Using various biochemical and biophysical approaches, we show that CX3CL1 clusters are homo-oligomers with 3 to 7 CX3CL1 molecules. We demonstrate that the transmembrane domain peptide self-associates at a similar level in both cellular and acellular lipid environments while its random counterpart (a scrambled peptide) does not. Hence, oligomerization is mainly driven by the transmembrane domain intrinsic properties. Molecular modeling suggests that transmembrane peptide oligomers are mostly made of monomers linearly assembled side by side. Using a new adherence assay, we demonstrate that, functionally, oligomerization is mandatory for the adhesive potency of CX3CL1. Our results indicate that CX3CL1-dependent cellular adherence in key immune processes can be controlled by disrupting clusters using heterotopic peptides, which, in turn, alter the adhesive function of the membrane CX3CL1 without affecting the function of the CX3CL1 soluble form.