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J. Cell Biol.,
Volume 145, Number 6, June 14, 1999 1293-1307
* Ludwig Institute for Cancer Research, London W1P 8BT, United Kingdom; and The GTPase Rho is known to mediate the assembly of integrin-containing focal adhesions and actin
stress fibers. Here, we investigate the role of Rho in regulating the distribution of the monocyte-binding receptors E-selectin, ICAM-1, and VCAM-1 in human endothelial cells. Inhibition of Rho activity with C3
transferase or N19RhoA, a dominant negative RhoA
mutant, reduced the adhesion of monocytes to activated endothelial cells and inhibited their spreading. Similar effects were observed after pretreatment of endothelial cells with cytochalasin D. In contrast, dominant negative Rac and Cdc42 proteins did not affect
monocyte adhesion or spreading. C3 transferase and cytochalasin D did not alter the expression levels of
monocyte-binding receptors on endothelial cells, but did inhibit clustering of E-selectin, ICAM-1, and
VCAM-1 on the cell surface induced by monocyte adhesion or cross-linking antibodies. Similarly, N19RhoA
inhibited receptor clustering. Monocyte adhesion and
receptor cross-linking induced stress fiber assembly,
and inhibitors of myosin light chain kinase prevented
this response but did not affect receptor clustering. Finally, receptor clusters colocalized with ezrin/moesin/
radixin proteins. These results suggest that Rho is required in endothelial cells for the assembly of stable adhesions with monocytes via the clustering of monocyte-binding receptors and their association with the actin
cytoskeleton, independent of stress fiber formation.
Department of Biochemistry and
Molecular Biology, University College London, London WC1E 6BT, United Kingdom
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