Summary
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 cell line EA.hy 926 using immunofluorescence techniques.
In this cell line TNFα induced the simultaneous appearance of stress fibers and of
ICAM-1, which was clustered predominantly on endothelial cell projections. Incubation
of TNFα-stimulated endothelial cells with fibrinogen resulted in binding of fibrinogen
to ICAM-1 on these cell projections. Disruption of the cytoskeleton by cytocholasin
B abolished fibrinogen 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 between ICAM-1 and the cytoskeleton
results in clustering of ICAM-1 on cell projections, which is required for fibrinogen
binding.