Directed Actin Polymerization is the Driving Force for Epithelial Cell-cell Adhesion

We have found that epithelial cells engage in a process of cadherin-mediated intercellular adhesion that utilizes calcium and actin polymerization in unexpected ways. Calcium stimulates filopodia, which penetrate and embed into neighboring cells. E-cadherin complexes cluster at filopodia tips, generating a two-rowed zipper of embedded puncta. Opposing cell surfaces are clamped by desmosomes, while vinculin, zyxin, VASP, and Mena are recruited to adhesion zippers by a mechanism that requires alpha-catenin. Actin reorganizes and polymerizes to merge puncta into a single row and seal cell borders. In keratinocytes either null for alpha-catenin or blocked in VASP/Mena function, filopodia embed, but actin reorganization/polymerization is prevented, and membranes cannot seal. Taken together, a dynamic mechanism for intercellular adhesion is unveiled involving calcium-activated filopodia penetration and VASP/Mena-dependent actin reorganization/polymerization.