FIBRINOGEN BINDING TO ICAM-1 ON EA.HY-926 ENDOTHELIAL-CELLS IS DEPENDENT ON AN INTACT CYTOSKELETON

Fibrinogen is a ligand for Intercellular Adhesion Molecule-1 (ICAM-1), and enhances monocyte-endothelial cell interaction by coupling Mac-1 on monocytes to ICAM-1 on endothelial cells. We investigated the role of the cytoskeleton in fibrinogen binding to the human endothelial cel l line EA.hy 926 using immunofluorescence techniques. In this cell lin e TNF alpha induced the simultaneous appearance of stress fibers and o f ICAM-1, which was clustered predominantly on endothelial cell projec tions. Incubation of TNF alpha-stimulated endothelial cells with fibri nogen resulted in binding of fibringen to ICAM-1 on these cell project ions. Disruption of the cytoskeleton by cytocholasin B abolished fibri nogen binding. Activation of protein kinase C with 12-O-tetradecanoyl phorbol-13-acetate resulted in simultaneous loss of both stress fibers and Fibrinogen binding. These results suggest that a connection betwe en ICAM-1 and the cytoskeleton results in clustering of ICAM-1 on cell projections, which is required for fibrinogen binding.