The integrin α4β7 is the cell adhesion receptor for the mucosal vascular addressin MAdCAM-1, and this interaction is dominant in lymphocyte homing to Peyer's patch high endothelial venules, and plays key roles in lymphocyte recruitment at sites of inflammation. To identify α4 subunit amino acids important for α4β7/MAdCAM-1 interaction, we expressed mutant α4 and wild type β7 chains in K562 cells and analyzed the effect of the mutations on cell adhesion to a soluble MAdCAM-1 (sMAdCAM-1-Ig). Transfectants expressing mutated α4 at Tyr187 displayed a substantial decrease in adhesion to this ligand, which was associated with a reduced α4β7/sMAdCAM-1-Ig interaction, as determined by soluble binding assays. Addition of Mn2+ to the adhesion assays did not restore the impaired adhesion. Mutations at α4 Gln152Asp153 also affected transfectant adhesion to sMAdCAM-1-Ig, but did not involve an alteration of α4β7/MAdCAM-1 binding, and adhesion was restored by Mn2+. Instead, mutations at α4 Asn123Glu124 did not affect this adhesion. Mutation of α4 Tyr187abolished α4β7-mediated cell adhesion to CS-1/fibronectin, an additional ligand for α4β7, while α4Gln152Asp153 transfectant mutants showed a reduced adhesion. These results identify α4Tyr187 as a key residue during receptor α4β7/ligand interactions, indicating that it plays important roles in α4β7-mediated leukocyte adhesion, and provide a potential target for therapeutic intervention in several inflammatory pathologies.
This work was supported by Grants PM95-0017 and SAF99-0057 from the plan General del Conocimiento-Ministerio de Educaciòn y Ciencia (Spain).The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
