Integrin receptor specificity for human red cell ICAM‐4 ligand

Abstract

The red cell intercellular adhesion molecule‐4 (ICAM‐4) binds to different members of the integrin receptor families. To better define the ICAM‐4 integrin receptor specificity, cell transfectants individually expressing various integrins were used to demonstrate that α L β 2 , α M β 2 , and α IIb β 3 (activated) bind specifically and dose dependently to the recombinant ICAM‐4‐Fc protein. We also show that cell surface ICAM‐4 interacts with the cell surface α V β 3 integrin. In addition, using a α 4 β 1 cell transfectant and β 2 integrin‐deficient LAD cells, we show here that ICAM‐4 failed to interact with α 4 β 1 even after α 4 β 1 activation by phorbol ester or with the monoclonal antibody TS2/16 (+ Mn 2+ ). ICAM‐4 amino acids that are critical for α IIb β 3 and α V β 3 interaction were identified by domain deletion analysis, site‐directed mutagenesis and synthetic peptide inhibition. Our results provide evidence that the β 3 integrin binding sites encompass the first and second Ig‐like domains of ICAM‐4. However, while the α IIb β 3 contact site comprises the ABED face of domain D1 with an extension in the C′‐E loop of domain D2, the α V β 3 contact site comprises residues on both faces of D1 and in the C′‐E loop of D2. These data, together with our previous results, demonstrate that different integrins bind to different but partly overlapping sites on ICAM‐4, and that ICAM‐4 may accommodate multiple integrin receptors present on leukocytes, platelets and endothelial cells.