Molecular uncoupling of fractalkine-mediated cell adhesion and signal transduction. Rapid flow arrest of CX3CR1-expressing cells is independent of G-protein activation.
Fractalkine is a novel multidomain protein expressed on the surface of activated endothelial cells. Cells expressing the chemokine receptor CX3CR1 adhere to fractalkine with high affinity, but it is not known if adherence requires G-protein activation and signal transduction. To investigate the cell adhesion properties of fractalkine, we created mutated forms of CX3CR1 that have little or no ability to transduce intracellular signals. Cells expressing signaling-incompetent forms of CX3CR1 bound rapidly and with high affinity to immobilized fractalkine in both static and flow assays. Video microscopy revealed that CX3CR1-expressing cells bound more rapidly to fractalkine than to VCAM-1 (60 versus 190 ms). Unlike VCAM-1, fractalkine did not mediate cell rolling, and after capture on fractalkine, cells did not dislodge. Finally, soluble fractalkine induced intracellular calcium fluxes and chemotaxis, but it did not activate integrins. Taken together these data provide strong evidence that CX3CR1, a seven-transmembrane domain receptor, mediates robust cell adhesion to fractalkine in the absence of G-protein activation and suggest a novel role for this receptor as an adhesion molecule.
Haskell
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CA
Gladstone Institute of Cardiovascular Disease, San Francisco, CA 94141-9100, USA.
Cleary
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MD
Charo
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IF
D000818:Animals; D000073883:CX3C Chemokine Receptor 1; D002448:Cell Adhesion; D002460:Cell Line; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D019743:Chemokines, CXC / Q000378:metabolism*; D006801:Humans; D008565:Membrane Proteins / Q000378:metabolism*; D051379:Mice; D016297:Mutagenesis, Site-Directed; D018121:Receptors, Cytokine / Q000235:genetics / Q000378:metabolism*; D015728:Receptors, HIV / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D012995:Solubility; D014162:Transfection; D019010:Vascular Cell Adhesion Molecule-1 / Q000378:metabolism
D000073883:CX3C Chemokine Receptor 1; C515538:CX3CL1 protein, human; D054428:Chemokine CX3CL1; D020523:Chemokines, CX3C; D019743:Chemokines, CXC; C515539:Cx3cl1 protein, mouse; D008565:Membrane Proteins; D018121:Receptors, Cytokine; D015728:Receptors, HIV; D019010:Vascular Cell Adhesion Molecule-1