title: In vivo structure/function and expression analysis of the CX3C chemokine fractalkine.
abstract: The CX3C chemokine family is composed of only one member, CX3CL1, also known as fractalkine, which in mice is the sole ligand of the G protein-coupled, 7-transmembrane receptor CX3CR1. Unlike classic small peptide chemokines, CX3CL1 is synthesized as a membrane-anchored protein that can promote integrin-independent adhesion. Subsequent cleavage by metalloproteases, either constitutive or induced, can generate shed CX3CL1 entities that potentially have chemoattractive activity. To study the CX3C interface in tissues of live animals, we generated transgenic mice (CX3CL1cherry:CX3CR1gfp), which express red and green fluorescent reporter genes under the respective control of the CX3CL1 and CX3CR1 promoters. Furthermore, we performed a structure/function analysis to differentiate the in vivo functions of membrane-tethered versus shed CX3CL1 moieties by comparing their respective ability to correct established defects in macrophage function and leukocyte survival in CX3CL1-deficient mice. Specifically, expression of CX3CL1(105Δ), an obligatory soluble CX3CL1 isoform, reconstituted the formation of transepithelial dendrites by intestinal macrophages but did not rescue circulating Ly6Clo CX3CR1hi blood monocytes in CX3CR1gfp/gfp mice. Instead, monocyte survival required the full-length membrane-anchored CX3CL1, suggesting differential activities of tethered and shed CX3CL1 entities.
authors.affiliation: Department of Immunology, Weizmann Institute of Science, Rehovot, Israel.
authors.forename: Ki-Wook
authors.initials: KW
authors.lastname: Kim
authors.forename: Alexandra
authors.initials: A
authors.lastname: Vallon-Eberhard
authors.forename: Ehud
authors.initials: E
authors.lastname: Zigmond
authors.forename: Julia
authors.initials: J
authors.lastname: Farache
authors.forename: Elias
authors.initials: E
authors.lastname: Shezen
authors.forename: Guy
authors.initials: G
authors.lastname: Shakhar
authors.forename: Andreas
authors.initials: A
authors.lastname: Ludwig
authors.forename: Sergio A
authors.initials: SA
authors.lastname: Lira
authors.forename: Steffen
authors.initials: S
authors.lastname: Jung
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D054428:Chemokine CX3CL1 / Q000737:chemistry* / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D020523:Chemokines, CX3C / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D005260:Female; D020869:Gene Expression Profiling; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008954:Models, Biological; D050505:Mutant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D020033:Protein Isoforms / Q000737:chemistry / Q000235:genetics / Q000378:metabolism / Q000502:physiology; D013329:Structure-Activity Relationship
chemical_list: D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D050505:Mutant Proteins; D020033:Protein Isoforms; D049452:Green Fluorescent Proteins