Structural recognition of a novel fibrinogen γ chain sequence (117-133) by intercellular adhesion molecule-1 mediates leukocyte-endothelium interaction

Abstract

In addition to its role in hemostasis, fibrinogen is obligatorily required to mount competent inflammatory responses in vivo. A molecular prerequisite of fibrinogen-dependent inflammation may reside in its ability to associate with intercellular adhesion molecule-1 (ICAM-1), and enhance monocyte adhesion to endothelium by bridging the two cell types. Structure-function characterization of the novel ICAM-1 recognition of fibrinogen was carried out by synthetic peptidyl mimicry of the fibrinogen γ chain. A novel peptide sequence, N117NQKIVNLKEKVAQLEA133, designated γ3, dose-dependently inhibited (IC50 ~ 20-40 μg/ml) binding of 125I-fibrinogen to endothelial cells or ICAM-1-expressing B lymphoblastoid Daudi cells. In contrast, none of the previously identified vascular cell fibrinogen interacting sequences was effective. Increasing concentrations of γ3 completely inhibited fibrinogen-mediated adhesion of peripheral blood mononuclear cells or vitamin D3-differentiated monocytic HL-60 cells to endothelium, but did not affect leukocyte-endothelium interaction in the absence of fibrinogen. 125I-Labeled γ3 bound specifically and saturably to genetically engineered ICAM-1 transfectants, but not to control non- transfected cells, and associated with ICAM-1 on cytokine-activated endothelium with a K(d) of 34 μM. Consistent with functional recognition of ICAM-1, immobilized γ3 supported adhesion of JY lymphoblasts in a dose- dependent reaction inhibited by monoclonal antibodies to ICAM-1. We conclude that a novel fibrinogen γ3 sequence N117NQKIVNLKEKVAQLEA133 binds to ICAM-1 and modulates ICAM-1-dependent adhesion. These findings define the structural basis of fibrinogen:ICAM-1 recognition and provide a potential selective target for inhibiting fibrinogen-dependent inflammatory responses.