Actin Can Reorganize into Podosomes in Aortic Endothelial Cells, a Process Controlled by Cdc42 and RhoA

Abstract

Members of the Rho GTPase family play a central role in the orchestration of cytoskeletal rearrangements, which are of prime importance in endothelial cell physiology. To explore their role in this specialized cell type, we used the bacterial toxin cytotoxic necrotizing factor 1 (CNF1) as a Rho GTPase activator. Punctate filamentous actin structures appeared along the ventral plasma membrane of endothelial cells and were identified as the core of podosomes by the distinctive vinculin ring around the F-actin. Rho, Rac, and Cdc42 were all identified as targets of CNF1, but only a constitutively active mutant of Cdc42 could substitute for CNF1 in podosome induction. Accordingly, organization of F-actin in these structures was highly dependent on the main Cdc42 cytoskeletal effector N-Wiskott-Aldrich syndrome protein. Other components of the actin machinery such as Arp2/3 and for the first time WIP also colocalized at these sites. Like CNF1 treatment, sustained Cdc42 activity induced a time-dependent F-actin-vinculin reorganization, prevented cytokinesis, and downregulated Rho activity. Finally, podosomes were also detected on endothelial cells explanted from patients undergoing cardiac surgery. These data provide the first description of podosomes in endothelial cells. The identification of such specialized structures opens up a new field of investigation in terms of endothelium pathophysiology.

ACKNOWLEDGMENTS

We thank J. Bertoglio, C. Chaponnier, J. Collard (Amsterdam, The Netherlands), P. Fort, J. Saklatvala (London, United Kingdom), D. Cantrell, D. Stewart (Bethesda, Md.), M. Way (London, United Kingdom), and M. Welch (Berkeley, Calif.) for providing toxins, cell lines, constructs, and antibodies. We thank Laura Spinardi (Milan, Italy) for help with gelsolin antibodies and Sandra Sena (U441) for help with manipulating explants. We thank I. Kramer and J. Bertoglio for critical reading of the manuscript.

This work was supported by grants from the Association pour la Recherche contre le Cancer (contract no. 5546) and from La Ligue Nationale contre le Cancer.