Integrins αvβ3 and α4β1 act as coreceptors for fractalkine, and the integrin-binding defective mutant of fractalkine is an antagonist of CX3CR1.

Abstract

The membrane-bound chemokine fractalkine (FKN, CX3CL1) on endothelial cells plays a role in leukocyte trafficking. The chemokine domain (FKN-CD) is sufficient for inducing FKN signaling (e.g., integrin activation), and FKN-CD binds to its receptor CX3CR1 on leukocytes. Whereas previous studies suggest that FKN-CD does not directly bind to integrins, our docking simulation studies predicted that FKN-CD directly interacts with integrin α(v)β(3). Consistent with this prediction, we demonstrated that FKN-CD directly bound to α(v)β(3) and α(4)β(1) at a very high affinity (K(D) of 3.0 × 10(-10) M to α(v)β(3) in 1 mM Mn(2+)). Also, membrane-bound FKN bound to integrins α(v)β(3) and α(4)β(1), suggesting that the FKN-CD/integrin interaction is biologically relevant. The binding site for FKN-CD in α(v)β(3) was similar to those for other known α(v)β(3) ligands. Wild-type FKN-CD induced coprecipitation of integrins and CX3CR1 in U937 cells, suggesting that FKN-CD induces ternary complex formation (CX3CR1, FKN-CD, and integrin). Based on the docking model, we generated an integrin-binding defective FKN-CD mutant (the K36E/R37E mutant). K36E/R37E was defective in ternary complex formation and integrin activation, whereas K36E/R37E still bound to CX3CR1. These results suggest that FKN-CD binding to CX3CR1 is not sufficient for FKN signaling, and that FKN-CD binding to integrins as coreceptors and the resulting ternary complex formation are required for FKN signaling. Notably, excess K36E/R37E suppressed integrin activation induced by wild-type FKN-CD and effectively suppressed leukocyte infiltration in thioglycollate-induced peritonitis. These findings suggest that K36E/R37E acts as a dominant-negative CX3CR1 antagonist and that FKN-CD/integrin interaction is a novel therapeutic target in inflammatory diseases.

• Authors: Masaaki Fujita, Yoko K Takada, Yoshikazu Takada
• Journal: Journal of immunology (Baltimore, Md. : 1950) (J Immunol) Vol. 189 Issue 12 Pg. 5809-19 (Dec 15 2012) ISSN: 1550-6606 [Electronic] United States
• PMID: 23125415 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't, Research Support, U.S. Gov't, Non-P.H.S.)

Chemical References

• CX3C Chemokine Receptor 1
• Chemokine CX3CL1
• Chemokines
• Integrin alpha4beta1
• Integrin alphaVbeta3
• Receptors, Cytokine
• Receptors, HIV

Topics

• Animals
• CHO Cells
• CX3C Chemokine Receptor 1
• Chemokine CX3CL1 (genetics, metabolism)
• Chemokines (metabolism)
• Computer Simulation
• Cricetinae
• Cricetulus
• Humans
• Integrin alpha4beta1 (metabolism)
• Integrin alphaVbeta3 (metabolism)
• K562 Cells
• Mutation (genetics)
• Protein Binding (genetics, immunology)
• Protein Structure, Tertiary (genetics)
• Receptors, Cytokine (antagonists & inhibitors, metabolism)
• Receptors, HIV (antagonists & inhibitors, metabolism)
• Signal Transduction (genetics, immunology)
• U937 Cells