Cellular responses to mechanical perturbation are vital to cell physiology. In particular, migrating cells have been shown to sense substrate stiffness and alter cell morphology and speed. Zyxin is a focal adhesion protein that responds to external mechanical forces; however, the mechanisms of zyxin recruitment at force-bearing sites are unknown. Using force-sensing microfabricated substrates, we simultaneously measured traction force and zyxin recruitment at force-bearing sites. GFP-tagged zyxin accumulates at force-bearing sites at the leading edge, but not at the trailing edge, of migrating epithelial cells. Zyxin recruitment at force-bearing sites depends on Rho-kinase and myosin II activation, suggesting that zyxin responds not only to the externally applied force, as previously shown, but also to the internally generated actin-myosin force. Zyxin in turn recruits vasodilator-stimulated phosphoprotein, a regulator of actin assembly, to force-bearing sites. To dissect the domains of zyxin that are essential for this unique force-dependent accumulation, we generated two zyxin truncation mutants: one lacking the LIM domain (ΔLIM) and one containing only the LIM domain with all three LIM motifs (LIM). GFP-tagged ΔLIM does not localize to the force-bearing sites, but GFP-tagged zyxin LIM-domain is sufficient for the recruitment to and dynamics at force-bearing focal adhesions. Furthermore, one or two LIM motifs are not sufficient for force-dependent accumulation, suggesting that all three LIM motifs are required. Therefore, the LIM domain of zyxin recruits zyxin to force-bearing sites at the leading edge of migrating cells.
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