p120 catenin regulates the actin cytoskeleton via Rho family GTPases

Cadherins are calcium-dependent adhesion molecules responsible for the esta blishment of tight cell-cell contacts, p120 catenin (p120ctn) binds to the cytoplasmic domain of cadherins in the juxtamembrane region, which has been implicated in regulating cell motility. It has previously been shown that overexpression of p120ctn induces a dendritic morphology in fibroblasts (Re ynolds,A.B., J. Daniel,Y. Mo, J. Wu, and Z. Zhang. 1996. Exp. Cell Res. 225 :328-337.),We show here that this phenotype is suppressed by coexpression o f cadherin constructs that contain the juxtamembrane region, but not by con structs lacking this domain. Overexpression of p120ctn disrupts stress fibe rs and focal adhesions and results in a decrease in RhoA activity. The p120 ctn-induced phenotype is blocked by dominant negative Cdc42 and Rad and by constitutively active Rho-kinase, but is enhanced by dominant negative RhoA . p120ctn overexpression increased the activity of endogenous Cdc42 and Rad . Exploring how p120ctn may regulate Rho family GTPases, we find that p120c tn binds the Rho family exchange factor Vav2, The behavior of p120ctn sugge sts that it is a vehicle for cross-talk between cell-cell junctions and the motile machinery of cells. We propose a model in which p120ctn can shuttle between a cadherin-bound state and a cytoplasmic pool in which it can inte ract with regulators of Rho family GTPases. Factors that perturb cell-cell junctions, such that the cytoplasmic pool of p120ctn is increased, are pred icted to decrease RhoA activity but to elevate active Rad and Cdc42, thereb y promoting cell migration.