CX3CL1, a chemokine finely tuned to adhesion: critical roles of the stalk glycosylation and the membrane domain

Abstract

The multi-domain CX3CL1 transmembrane chemokine triggers leukocyte adherence without rolling and migration by presenting its chemokine domain (CD) to its receptor CX3CR1. Through the combination of functional adhesion assays with structural analysis using FRAP, we investigated the functional role of the other domains of CX3CL1, i.e., its mucin stalk, transmembrane domain, and cytosolic domain. Our results indicate that the CX3CL1 molecular structure is finely adapted to capture CX3CR1 in circulating cells and that each domain has a specific purpose: the mucin stalk is stiffened by its high glycosylation to present the CD away from the membrane, the transmembrane domain generates the permanent aggregation of an adequate amount of monomers to guarantee adhesion and prevent rolling, and the cytosolic domain ensures adhesive robustness by interacting with the cytoskeleton. We propose a model in which quasi-immobile CX3CL1 bundles are organized to quickly generate adhesive patches with sufficiently high strength to capture CX3CR1+ leukocytes but with sufficiently low strength to allow their patrolling behavior.

The Fractalkine-Receptor Axis Improves Human Colorectal Cancer Prognosis by Limiting Tumor Metastatic Dissemination

“…By protruding out of the membrane and the glycocalix, the mucin stalk facilitates the availability and presentation of CX 3 CL1 to the receptor; furthermore, the transmembrane domain generates a permanent aggregation of chemokine monomers, and the cytosolic domain ensures adhesive robustness by interacting with the cytoskeleton (41).…”

CX3CR1 expression and megakaryocytic series assessment on bone marrow biopsies in acquired aplastic anemia. Correlations with hematological parameters.

“…CX3CL1 (fractalkine) shows an isoform bound to the cell membrane and a soluble isoform (16). Previous studies show that the expression of membrane-bound fractalkine is decreased by endothelial cells, which release soluble fractalkine as a response to Th1 cytokines, such as TNFα, IFNγ (17,18).…”

Allergenic proteases cleave the chemokine CX3CL1 directly from the surface of airway epithelium and augment the effect of rhinovirus

“…The 90 kDa band is most likely fully glycosylated CX3CL1, similar to the 85-90 kDa full-length CX3CL1 observed by others. [46][47][48] We postulate that the 40 kDa product might result from cleavage of CX3CL1 by the HDM cysteine protease at F162, resulting in a CKD-bearing peptide chain of 17.3 kDa with 11 O-glycosylation sites. Taking into account that there are 26 such sites in full-length CX3CL1, 8 and that complete de-glycosylation results in a loss of B50-55 kDa, 8,46 it could be calculated that each glycosylation adds B2 kDa to the mass of the protein, and so if fully glycosylated, this fragment would have a mass of 39.3 kDa, corresponding to that observed on the blot.…”