Actomyosin-dependent assembly of the mechanosensitive machinery from adherens junctions triggers actin polymerization...

Cells rely on cadherin-based adherens junctions (AJs) to form cohesive tissues. To establish contact, cells generate pushing forces through branched actin polymerization mediated by the actin-related protein 2/3 (Arp2/3) complex, followed by the reinforcement of mechanosensitive AJs in response to actomyosin contractility. To investigate how AJ proteins coordinate these events, we combined kinetic assays of actin polymerization, single actin filament observation in total internal reflection fluorescence microscopy, and in vitro reconstitution of AJ mechanosensitivity. Our findings show that actomyosin contractility alone is sufficient to trigger the hierarchical assembly of the AJ mechanosensitive proteins α-catenin, vinculin, and vasodilator-stimulated phosphoprotein (VASP). Once assembled, these proteins act synergistically to promote actin filament nucleation, elongation, and bundling. The α-catenin-vinculin-VASP machinery inhibits Arp2/3-mediated actin branching and instead promotes the myosin-dependent assembly of actin bundles. Together, these results reveal how AJs integrate actin assembly, actomyosin contractility, and mechanosensitivity in a feedback loop.