α-catenin phosphorylation is actomyosin-sensitive and required for epithelial barrier functions through Afadin

Zonula adherens junctions (zAJ) are spatially proximal to tight junctions (TJ), in a superstructure known as the apical junctional complex (AJC). A key component of the AJC is a circumferential ring of filamentous (F)-actin, but how actomyosin contractility drives AJC structure and epithelial barrier function is incompletely understood. Here, we show that a central mechanosensitive component of zAJ, -catenin (-cat), undergoes force-dependent phosphorylation in an unstructured linker region. This modification in turn primes the -cat mechanosensitive Middle-region for effector-binding. We credential Afadin, a multi-domain TJ/AJ scaffold protein, as mechano-chemical binding partner of -cat, identifying residues in -cat required for this interaction. -cat phosphorylation and Afadin-binding are required for their co-enrichment at zAJ and epithelial barrier function. A mouse model that prevents -cat phosphorylation is particularly detrimental to post-natal brain development. These data support a stepwise model where -cat integrates mechanical and chemical signals to progressively promote zAJ enrichment, effector recruitment and epithelial barrier function.