title: Syk is required for monocyte/macrophage chemotaxis to CX3CL1 (Fractalkine).
abstract: CX3CL1 (fractalkine), the only member of the delta subclass of chemokines, is a known chemotactic factor for monocytes/macrophages as well as NK cells and T lymphocytes. In several pathologies, excessive production of CX3CL1 at specific sites leads primarily to monocyte/macrophage recruitment, which causes tissue and vascular damage. Despite their clinical relevance, the mechanisms underlying monocyte/macrophage chemotaxis to CX3CL1 remain poorly documented. The present report addresses this issue and identifies cell signaling crucial for this process. Using the murine monocyte/macrophage RAW cell line, we show that CX3CL1 treatment elicits a rapid and transient increase in F-actin and the formation of F-actin-enriched cell protrusions. CX3CL1 also triggers tyrosine phosphorylation of proteins localized in those protrusions. The protein tyrosine kinase Syk is activated upon CX3CL1 treatment, and reduction of Syk expression using RNA-mediated interference results in a specific and massive impairment of RAW cell migration to CX3CL1. Similar results are obtained using the Syk inhibitor, piceatannol. Cells with reduced Syk expression also exhibit a major defect in CX3CL1-induced cytoskeletal remodeling. These data suggest that in monocytes/macrophages, Syk is essential for proper reorganization of the actin cytoskeleton in response to CX3CL1 and is therefore required for cell chemotaxis to CX3CL1.
authors.affiliation: Department of Anatomy and Structural Biology, Albert Einstein College of Medicine, Bronx, NY 10461, USA.
authors.forename: Jean-Claude
authors.initials: JC
authors.lastname: Gevrey
authors.forename: Beth M
authors.initials: BM
authors.lastname: Isaac
authors.forename: Dianne
authors.initials: D
authors.lastname: Cox
mesh_terms: D000199:Actins / Q000187:drug effects; D000818:Animals; D002460:Cell Line; D022081:Cell Surface Extensions / Q000187:drug effects; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C / Q000494:pharmacology*; D002633:Chemotaxis; D003599:Cytoskeleton / Q000187:drug effects; D047908:Intracellular Signaling Peptides and Proteins; D008264:Macrophages / Q000502:physiology*; D008565:Membrane Proteins / Q000494:pharmacology*; D051379:Mice; D009000:Monocytes / Q000502:physiology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000502:physiology*; D000072377:Syk Kinase
chemical_list: D000199:Actins; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; C515539:Cx3cl1 protein, mouse; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D047428:Protein Kinase Inhibitors; D011505:Protein-Tyrosine Kinases; D000072377:Syk Kinase; C000606897:Syk protein, mouse