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MBC in Press, published online ahead of print December 20, 2006
Mol. Biol. Cell 10.1091/mbc.E06-05-0423

A more recent version of this article appeared on March 1, 2007
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Submitted on May 17, 2006
Revised on December 4, 2006
Accepted on December 7, 2006

Villin Severing Activity Enhances Actin-based Motility In Vivo

Céline Revenu,* Matthieu Courtois,{dagger} Alphée Michelot,{ddagger} Cécile Sykes,{dagger} Daniel Louvard,* and Sylvie Robine*

*Laboratoire de Morphogenèse et Signalisation Cellulaire, Unité Mixte de Recherche 144/ Institut Curie, 75248 Paris Cedex 05, France; {dagger}Laboratoire Physico-Chimie Curie, Unité Mixte de Recherche 168, Institut Curie/Centre National de la Recherche Scientifique/Universités Paris 6 and 7, 75231 Paris Cedex 05, France; {ddagger}Laboratoire de Physiologie Cellulaire Végétale (PCV), Unité Mixte de Recherche 5168, DRDC, CEA/Centre National de la Recherche Scientifique/Institut National de la Recherche Agronomique/UJF, CEA, 38054 Grenoble Cedex 9, France

Monitoring Editor: Yu-li Wang

Villin, an actin-binding protein associated with the actin bundles that support microvilli, bundles, caps, nucleates and severs actin in a calcium-dependant manner in vitro. We hypothesized that the severing activity of villin is responsible for its reported role in enhancing cell plasticity and motility. To test this hypothesis, we chose a loss of function strategy and introduced mutations in villin based on sequence comparison with CapG. By pyrene-actin assays, we demonstrate that this mutant has a strongly reduced severing activity whereas nucleation and capping remain unaffected. The bundling activity and the morphogenic effects of villin in cells are also preserved in this mutant. We thus succeeded in dissociating the severing from the three other activities of villin. The contribution of villin severing to actin dynamics is analyzed in vivo through the actin-based movement of the intracellular bacteria Shigella flexneri in cells expressing villin and its severing variant. The severing mutations abolish the gain of velocity induced by villin. To further analyze this effect, we reconstituted an in vitro actin-based bead movement in which the usual capping protein is replaced by either the WT or the severing mutant of villin. Confirming the in vivo results, villin severing activity enhances the velocity of beads by more than two folds and reduces the density of actin in the comets. We propose a model in which, by severing actin filaments and capping their barbed-ends, villin increases the concentration of actin monomers available for polymerization, a mechanism that might be paralleled in vivo when an enterocyte undergoes an epithelio-mesenchymal transition.

Address correspondence to: Sylvie Robine (sylvie.robine{at}curie.fr)




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