E-cadherin-mediated cell-cell attachment activates Cdc42.

E-cadherin is a transmembrane protein that mediates Ca(2+)-dependent cell-cell adhesion. Cdc42, a member of the Rho family of small GTPases, participates in cytoskeletal rearrangement and cell cycle progression. Recent evidence reveals that members of the Rho family modulate E-cadherin function. To further examine the role of Cdc42 in E-cadherin-mediated cell-cell adhesion, we developed an assay for active Cdc42 using the GTPase-binding domain of the Wiskott-Aldrich syndrome protein. Initiation of E-cadherin-mediated cell-cell attachment significantly increased in a time-dependent manner the amount of active Cdc42 in MCF-7 epithelial cell lysates. By contrast, Cdc42 activity was not increased under identical conditions in MCF-7 cells incubated with anti-E-cadherin antibodies nor in MDA-MB-231 (E-cadherin negative) epithelial cells. By fusing the Wiskott-Aldrich syndrome protein/GTPase-binding domain to a green fluorescent protein, activation of endogenous Cdc42 by E-cadherin was demonstrated in live cells. These data indicate that E-cadherin activates Cdc42, demonstrating bi-directional interactions between the Rho- and E-cadherin signaling pathways.