Cadherin Regulation of Endoplasmic Reticulum-Plasma Membrane Contact Sites.

The spatial organization and dynamics of the endoplasmic reticulum (ER) govern when and where ER tubules engage with other organelles and the plasma membrane. We previously found that ER tubules are closely associated with desmosomes, but the mechanisms of ER recruitment to these adhesive intercellular junctions were unclear. Here, we demonstrate that adherens junctions recruit ER tubules to intercellular junctions in a manner dependent upon E-cadherin association with α-catenin and vinculin. During cell-cell junction assembly, adherens junctions and ER appear nearly simultaneously at nascent cell-cell contacts, followed by desmosome formation. ER recruitment to cell-cell contacts allows the formation of ER-plasma membrane contact sites (ER-PMCS) and the assembly of a complex comprising adherens junctions, ER-PMCS, and desmosomes. Ablating adherens junctions disrupts this tripartite complex and perturbs global cellular lipid levels. Collectively, our findings identify cadherins as key organizers of ER-PMCS positioning and suggest that this complex integrates cellular mechanical elements with plasma membrane homeostasis.