The Small GTPases Rho and Rac Are Required for the Establishment of Cadherin-dependent Cell–Cell Contacts

Abstract

Cadherins are calcium-dependent cell–cell adhesion molecules that require the interaction of the cytoplasmic tail with the actin cytoskeleton for adhesive activity. Because of the functional relationship between cadherin receptors and actin filament organization, we investigated whether members of the Rho family of small GTPases are necessary for cadherin adhesion. In fibroblasts, the Rho family members Rho and Rac regulate actin polymerization to produce stress fibers and lamellipodia, respectively. In epithelial cells, we demonstrate that Rho and Rac are required for the establishment of cadherin-mediated cell–cell adhesion and the actin reorganization necessary to stabilize the receptors at sites of intercellular junctions. Blocking endogenous Rho or Rac selectively removed cadherin complexes from junctions induced for up to 3 h, while desmosomes were not perturbed. In addition, withdrawal of cadherins from intercellular junctions temporally precedes the removal of CD44 and integrins, other microfilament-associated receptors. Our data showed that the concerted action of Rho and Rac modulate the establishment of cadherin adhesion: a constitutively active form of Rac was not sufficient to stabilize cadherindependent cell–cell contacts when endogenous Rho was inhibited. Upon induction of calcium-dependent intercellular adhesion, there was a rapid accumulation of actin at sites of cell–cell contacts, which was prevented by blocking cadherin function, Rho or Rac activity. However, if cadherin complexes are clustered by specific antibodies attached to beads, actin recruitment to the receptors was perturbed by inhibiting Rac but not Rho. Our results provide new insights into the role of the small GTPases in the cadherin-dependent cell– cell contact formation and the remodelling of actin filaments in epithelial cells.

Turn‐off, drop‐out: Functional state switching of cadherins

“…p120 ctn also alters the relative activities of the small G-proteins Rho A, Rac, and Cdc42 Grosheva et al, 2000;Noren et al, 2000). This may well be related to changes in the activities of these proteins initiated by adhesion Noren et al, 2001) and involved in actin-driven cadherin clustering (Braga et al, 1997(Braga et al, , 1999Jou and Nelson, 1998;Takaishi et al, 1997).…”

Isolation and characterization of mammalian homologues of Caenorhabditis elegans lin-7: localization at cell-cell junctions

“…Recent studies have revealed that the cadherin-based cell-cell adhesions are regulated by Rac1 small GTPbinding protein (Rac1) (Braga et al, 1997;Takaishi et al, 1997). We checked the localization of mlin-7 in MDCK cell lines stably expressing a dominant active (V12Rac1) or negative (N17Rac1) mutant of Rac1.…”

Involvement of Cdc42 small G protein in cell-cell adhesion, migration and morphology of MDCK cells

“…Rac regulates formation of lamellipodia and membrane ru ing in various types of cultured cells (for reviews, see Hall, 1994Hall, , 1998. Rac regulates actin assembly at the adherens junction of the wing disc epithelium in Drosophila (Luo et al, 1994;Eaton et al, 1995), the formation of cadherin-dependent cell-cell adhesion in MDCK cells and human keratinocytes (Braga et al, 1997;Hordijk et al, 1997;Takaishi et al, 1997;, and tight junction in MDCK cells . Cdc42 regulates the formation of ®lopodia in various types of cells (for review, see Hall, 1998).…”