Villin Function in the Organization of the Actin Cytoskeleton

Abstract

Villin is an actin-binding protein of the intestinal brush border that bundles, nucleates, caps, and severs actin in a Ca 2؉ -dependent manner in vitro. Villin induces the growth of microvilli in transfected cells, an activity that requires a carboxyl-terminally located KKEK motif. By combining cell transfection and biochemical assays, we show that the capacity of villin to induce growth of microvilli in cells correlates with its ability to bundle F-actin in vitro but not with its nucleating activity. In agreement with its importance for microfilament bundling in cells, the KKEK motif of the carboxyl-terminal F-actin-binding site is crucial for bundling in vitro. In addition, substitutions of basic residues in a second site, located in the amino-terminal portion of villin, impaired its activity in cells and reduced its binding to F-actin in the absence of Ca 2؉ as well as its bundling and severing activities in vitro. Altogether, these findings suggest that villin participates in the organization and stabilization of the brush border core bundle but does not initiate its assembly by nucleation of actin filaments.

Interaction of Phospholipase C-γ1with Villin Regulates Epithelial Cell Migration

“…It has been reported previously that actin nucleation by 44T is significantly less than full-length villin protein (37,38). A similar observation was made using a villin variant (V1-3 ϩ HP) that lacks domains S4 -S6 (39). Consistent with this observation, actin nucleation by gelsolin requires the domains S4 -S6 (or G4 -G6) (40,41).…”

Association of Villin with Phosphatidylinositol 4,5-Bisphosphate Regulates the Actin Cytoskeleton

“…Thus there is a structure-function relationship between the PIP 2 -binding sites as well as the actin-modifying functions of these proteins. PB2 and PB5 overlap with previously described actin-binding sites in villin (54,66). Similar overlapping PIP 2 and actin-binding sites have been described for other actin-binding proteins including actophorin (67), profilin (9), and gelsolin (55).…”

Tyrosine Phosphorylation of Villin Regulates the Organization of the Actin Cytoskeleton

“…Negative charges exposed on the surface of the actin filaments favor their alignment into bundles, and polyanions can disintegrate actin bundles into single filaments (14). Basic amino acids in villin have been shown to promote villin binding to actin (15). This may explain why introduction of negative charges by phosphorylation weakens villin-actin interactions, and the phosphorylated villin shows poor bundling activity.…”