Receptor Nucleation and Clustering in Cellular Adhesion and Mechanical Signal Transduction

E-cadherin-based cell-cell adhesions are key to development and maintenance of the epithelial tissue, and a loss of these adhesions may contribute to cancer development. These are mechanosensitive structures in that they are strengthened under tension. Mechanotransduction in these adhesions has been postulated to be mediated, in part, by a force-dependent conformational activation of α-catenin, which allows it to interact with vinculin, in addition to F-actin, resulting in strengthening of junctions. Here, using E-cadherin adhesions reconstituted on synthetic, nanopatterned membranes, we show that activation of α-catenin is dependent on E-cadherin clustering, and is sustained in the absence of mechanical force or association with F-actin or vinculin. Adhesions are formed by filopodia-mediated nucleation and micron-scale assembly of E-cadherin clusters, which could be distinguished as either peripheral or central depending on their relative location at the cell-bilayer adhesion. While F-actin, vinculin and phosphorylated myosin light chain associate only with the peripheral assemblies, activated α-catenin is present in both peripheral and central assemblies, and persisted in the central assemblies in the absence of actomyosin tension. Impeding filopodia-mediated nucleation and micron-scale assembly of E-cadherin adhesion complexes, by confining bilayer bound E-cadherin extracellular domain movement on nanopatterned substrates, reduced levels of activated α-catenin. Taken together, although the initial activation of α-catenin requires micron-scale clustering that may allow development of mechanical forces, sustained force is not required for maintaining α-catenin in the active state.