Force-dependent vinculin binding to talin in live cells: a crucial step in anchoring the actin cytoskeleton to focal adhesions

Abstract

(FAs) where the actin cytoskeleton is anchored to the extracellular matrix through integrin and a variety of linker proteins including talin and vinculin. The localization of vinculin at FAs depends on mechanical forces. While in vitro studies have demonstrated the force-induced increase in vinculin binding to talin, it remains unclear whether such a mechanism exists at FAs in vivo. In this study, using fibroblasts cultured on elastic silicone substrata, we have examined the role of forces in modulating talin-vinculin binding at FAs. Stretching the substrata caused vinculin accumulation at talin-containing FAs, and this accumulation was abrogated by expressing the talin-binding domain of vinculin (domain D1, which inhibits endogenous vinculin from binding to talin). These results indicate that mechanical forces loaded to FAs facilitate vinculin binding to talin at FAs. In cellprotruding regions, the actin network moved backward over talincontaining FAs in domain D1-expressing cells while it was anchored to FAs in control cells, suggesting that the force-dependent vinculin binding to talin is crucial for anchoring the actin cytoskeleton to FAs in living cells. talin; vinculin; focal adhesion; mechanotransduction; molecular clutch CELL ADHESION TO EXTRACELLULAR matrices (ECMs) is crucial for cellular morphogenesis, migration, proliferation, and differentiation. Cell-to-ECM adhesion is primarily mediated by the transmembrane ECM receptors integrins. Integrin molecules are clustered at focal adhesions (FAs), where the actin cytoskeleton is anchored to the ECM through integrin clusters and plaques of a variety of linker proteins (16). There is bidirectional transmission of forces at FAs between ECM and the actin cytoskeleton (30). Thus FAs sustain tensile stress generated in the actin cytoskeleton. When integrin-actin cytoskeleton linkage is dissected, actin stress fibers are retracted and FAs are disassembled (37,43,53,54), indicating that the linkage is crucial for maintaining the integrity of FAs.Molecular processes of formation of integrin-cytoskeleton linkages have been extensively studied. Talin has both ␤-integrin-and actin-binding sites (9) and initially forms a molecular bond between ECM-bound integrin and the actin cytoskeleton in fibroblasts (17,34,65). The talin-mediated link between the actin cytoskeleton and clustered integrin is broken repeatedly by a small force of ϳ2 pN generated by the retrograde flow of actin filaments (34). On the other hand, the integrin-actin cytoskeleton linkage is strengthened when a mechanical force is loaded to it (7, 61). The strengthened linkage can sustain much larger forces (ϳ20 pN), which prevents the slippage between the actin cytoskeleton and integrin clusters (7).Vinculin also plays an important role in mediating the integrin-actin linkage because vinculin-deficient cells exhibit weaker linkage (1, 11). Vinculin binds to talin via its NH 2 -terminal domain D1, while its COOH-terminal tail domain has an actin-binding site (19,32,66). Talin has up to 11 vinculinbind...

Vinculin promotes nuclear localization of TAZ to inhibit ECM stiffness-dependent differentiation into adipocytes

“…Grashoff et al reported the requirement of tension to activate vinculin (Grashoff et al, 2010). Vinculin binding to talin at FAs occurs under forcegenerating conditions (Hirata et al, 2014). Taken together, these observations suggest that vinculin is used as a 'mechanosensor' for various physical cues.…”

Distinct focal adhesion protein modules control different aspects of mechanotransduction

“…Mechanical forces are thought to contribute to the activation of both talin and vinculin (del Rio et al, 2009;Hirata et al, 2014b;Yao et al, 2014). Previously, we have shown that the turnover of talin and vinculin reflects their activation state (Atherton et al, 2015;Carisey et al, 2013).…”

A helping hand: How vinculin contributes to cell-matrix and cell-cell force transfer

“…13,14 The application of stretching forces to vinculin's binding partners, thereby exposing cryptic vinculin binding sites (VBS), has also been implicated in vinculin activation. 15,16 Once activated, V H binds to integrin-talin complexes and drives FA growth, whereas V T binds to F-actin thereby enhancing the connectivity between FAs and the actin CSK. 17 To what extent activated vinculin mediates force transfer across FAs is largely unknown.…”

“…46 Recent studies have implicated a-catenin as a key regulatory of vinculin recruitment to FAJs through forceinduced exposure of VBS-a process analogous to stretch-induced exposure of VBS on talin in the context of FAs. 16,[47][48][49] 52 The interaction of vinculin with cadherins can have a significant impact on the molecular composition and function of each cell-cell junction. New evidence supports a role for vinculin in stabilizing vascular endothelial cadherin (VE-cadherin) complexes that undergo remodeling in response to inflammatory cytokines and angiogenic growth factors.…”