Vinculin regulates cell-surface E-cadherin expression by binding to beta-catenin

Vinculin was identified as a component of adherens junctions 30 years ago, yet its function there remains elusive. Deletion studies are consistent with the idea that vinculin is important for the organization of cell-cell junctions. However, this approach removes vinculin from both cell-matrix and cell-cell adhesions, making it impossible to distinguish its contribution at each site. To define the role of vinculin in cell-cell junctions, we established a powerful short hairpin-RNA-based knockdown/substitution model system that perturbs vinculin preferentially at sites of cell-cell adhesion. When this system was applied to epithelial cells, cell morphology was altered, and cadherin-dependent adhesion was reduced. These defects resulted from impaired E-cadherin cell-surface expression. We have investigated the mechanism for the effects of vinculin and found that the reduced surface E-cadherin expression could be rescued by introduction of vinculin, but not of a vinculin A50I substitution mutant that is defective for beta-catenin binding. These findings suggest that an interaction between beta-catenin and vinculin is crucial for stabilizing E-cadherin at the cell surface. This was confirmed by analyzing a beta-catenin mutant that fails to bind vinculin. Thus, our study identifies vinculin as a novel regulator of E-cadherin function and provides important new insight into the dynamic regulation of adherens junctions.