Binding Sites of Leukocyte β2 Integrins (LFA-1, Mac-1) on the Human ICAM-4/LW Blood Group Protein

Abstract

The red cell ICAM-4/LW blood group glycoprotein, which belongs to the family of intercellular adhesion molecules (ICAMs), has been reported to interact with CD11a/CD18 (LFA-1) and CD11b/CD18 (Mac-1) ␤ 2 integrins. To better define the basis of the ICAM-4/␤ 2 integrin interaction, we have generated wild-type, domain-

Red Cell ICAM-4 Is a Novel Ligand for Platelet-activated αIIbβ3 Integrin

“…Interestingly, the data suggested that adhesion of RBCs to neutrophils might be mediated through Mac-1 (CD11b/CD18) and ICAM-4, supporting recent findings indicating that ␤ 2 integrins and ICAM-4 interact with each other (26). Additionally, RBC-platelet interaction was strongly reduced by soluble fibrinogen and EDTA and was partially inhibited by antibodies to CD36 and GPIb, but no inhibition was noted with a single antibody against the ␣ IIb chain (CD41) of the ␣ IIb ␤ 3 integrin (62).…”

“…5, A and B). A similar effect has been observed when ICAM-4 mutant proteins interact with the leukocyte ␣ M ␤ 2 (Mac-1) integrin, whereas interaction with the ␣ L ␤ 2 (LFA-1) integrin requires predominantly the first Ig domain D1 (26). The binding of adhesive proteins to ␣ IIb ␤ 3 integrin is predominantly mediated by the RGD peptide motif present on the respective adhesive ligands (45), but this peptide, which is absent from ICAM-4, blocks the ICAM-4/␣ IIb ␤ 3 interaction.…”

“…The platelet ␣ IIb ␤ 3 integrin also binds to the carboxyl-terminal end of the Fg ␥-chain via a dodecapeptide sequence (peptide FBI, residues 400 -411) containing the motif QAGDV (46). Interestingly, ICAM-4 contains a similar motif at position 70 -74 (QLLDV) located in the first ICAM-4 Ig-like domain (26) and the ICAM-4 peptide Gly-Val (residues 65-74), including this motif, is a potent inhibitor of the ICAM-4/␣ IIb ␤ 3 interaction. Moreover, the peptide FBI also inhibited platelet binding to ICAM-4-Fc.…”

“…These findings suggest that the platelet ␣ IIb ␤ 3 integrin might interact with the Gly-65-Val-74 sequence of ICAM-4 that includes a QXXDV motif known to be involved in the fibrinogen/␣ IIb ␤ 3 integrin interaction. The Gly-65-Val-74 sequence motif which forms the tip of the E strand of domain D1 and is in contact with the loop CЈ-E of domain D2 (26), most probably constitutes a major part of the ␣ IIb ␤ 3 integrin binding site on ICAM-4. Therefore, binding inhibition by RGD and FBI peptides, which bind to the ␤ 3 chain (GPIIIa) and ␣ IIb chain (GPIIb), respectively (47), suggest that ICAM-4 binds to the same or overlapping site(s) on the ␣ IIb ␤ 3 complex.…”

“…ImmunoPure mouse IgG from Pierce was used as negative control IgG. Chimeric ICAM-pIgI constructs derived from intact ICAM-4 (LW a allele) carrying the two Ig-like domains D1 and D2 (residues 1-208), or deletion mutants D1-ICAM-4 (residues 1-101) or D2-ICAM-4/(residues 102-208) were used to produce soluble Fc-fusion proteins as described (26). ICAM-1-and ICAM-2-pIgI constructs (kindly provided by Dr. D. Simmons and E. Ferguson, Oxford, UK) were used to produce ICAM-Fc soluble fusion proteins as above.…”