Identification of critical amino-acid residues on the erythroid intercellular adhesion molecule-4 (ICAM-4) mediating adhesion to αV integrins

Intercellular adhesion molecule-4 (ICAM-4, syn. LW glycoprotein) interacts with the integrins αLβ2, αMβ2, A4β1, the αV family, and αIIbβ3. Systematic mutagenesis of surface-exposed residues conserved between human and murine ICAM-4 defined 12 single amino-acid changes that affect the interaction of ICAM-4 with αV integrins. Mutation of 10 of these residues, 8 of which are spatially close on the surface of the molecule, led to a reduction in adhesion. Moreover, peptides corresponding to regions of ICAM-4 involved in its interaction with αV integrins inhibited these interactions. The other 2 mutations increased the extent of interaction of ICAM-4 with αV integrins. These mutations appear to prevent glycosylation of N160, suggesting that changes in glycosylation may modulate ICAM-4–αV integrin interactions. The region of ICAM-4 identified as the binding site for αV integrins is adjacent to the binding sites for αLβ2 and αMβ2. Selective binding of ICAM-4 to different integrins may be important for a variety of normal red cell functions and also relevant to the pathology of thrombotic disorders and vasoocclusive events in sickle cell disease. Our findings suggest the feasibility of developing selective inhibitors of ICAM-4–integrin adhesion of therapeutic value in these diseases.