An amphipathic helix of vinexin α is necessary for a substrate stiffness-dependent conformational change in vinculin.

Extracellular matrix (ECM) stiffness regulates various cell behaviors, including cell differentiation, proliferation and migration. Vinculin and vinexin α (an isoform encoded by the SORBS3 gene), both of which localize to focal adhesions, cooperatively function as mechanosensors of ECM stiffness. On a rigid ECM, vinexin α interacts with vinculin and induces a conformational change in vinculin to give an 'open' form, which promotes nuclear localization of Yes-associated protein (YAP, also known as YAP1) and transcriptional coactivator with a PDZ-binding motif (TAZ, also known as WWTR1) (hereafter YAP/TAZ). However, the detailed mechanism by which vinexin α induces the conformational change in vinculin has not been revealed. Here, we identify an amphipathic helix named H2 as a novel vinculin-binding site in vinexin α. The H2 helix interacts with the vinculin D1b subdomain and promotes the formation of a talin-vinculin-vinexin α ternary complex. Mutations in the H2 region not only impair the ability of vinexin α to induce the ECM stiffness-dependent conformational change in vinculin but also to promote nuclear localization of YAP/TAZ on rigid ECM. Taken together, these results demonstrate that the H2 helix in vinexin α plays a critical role in ECM stiffness-dependent regulation of vinculin and cell behaviors.