Mechanical force mobilizes zyxin from focal adhesions to actin filaments and regulates cytoskeletal reinforcement

Abstract

Organs and tissues adapt to acute or chronic mechanical stress by remodeling their actin cytoskeletons. Cells that are stimulated by cyclic stretch or shear stress in vitro undergo bimodal cytoskeletal responses that include rapid reinforcement and gradual reorientation of actin stress fibers; however, the mechanism by which cells respond to mechanical cues has been obscure. We report that the application of either unidirectional cyclic stretch or shear stress to cells results in robust mobilization of zyxin from focal adhesions to actin filaments, whereas many other focal adhesion proteins and zyxin family members remain at focal adhesions. Mechanical stress also induces the rapid zyxin-dependent mobilization of vasodilator-stimulated phosphoprotein from focal adhesions to actin filaments. Thickening of actin stress fibers reflects a cellular adaptation to mechanical stress; this cytoskeletal reinforcement coincides with zyxin mobilization and is abrogated in zyxin-null cells. Our findings identify zyxin as a mechanosensitive protein and provide mechanistic insight into how cells respond to mechanical cues.

Zyxin Mediates Actin Fiber Reorganization in Epithelial–Mesenchymal Transition and Contributes to Endocardial Morphogenesis

“…Previous reports confirmed the localization of EGFP-tagged zyxin corresponded to the endogenous zyxin (Nix et al, 2001;Hotulainen and Lappalainen, 2006). Without stimulation, consistent with a previous report (Yoshigi et al, 2005), zyxin localized to focal adhesions and focal complexes in the lamellipodia ( Figure 1G, ϪTGF-␤1). Of note, upon TGF-␤1 stimulation, zyxin mobilized from focal adhesions to actin fibers ( Figure 1G, ϩTGF-␤1).…”

“…Although our findings are based on EGFP-fusion protein study, EGFP-tagged zyxin was reported to display a distribution pattern that is indistinguishable from that of the endogenous zyxin (Nix et al, 2001;Hotulainen and Lappalainen, 2006). Mechanostressinduced relocation of zyxin has been reported (Yoshigi et al, 2005). Yoshigi et al showed that cyclic stretch or sheer stress to cells in vitro resulted in mobilization of zyxin from focal adhesions to actin filaments.…”

“…Similarly, sheer stress induced by blood flow or mechanostress altered through cardiac morphogenesis might induce the relocation of proteins that sense mechanical forces, thereby contributing to endocardial morphogenesis. The significance of relocation requires further analysis, although it is speculated that zyxin interacts with a set of proteins such as VASP (Yoshigi et al, 2005) as an adaptor protein on the actin stress fibers. The cells transfected with zyxin siRNA failed to show TGF-␤1-enhanced cell motility and fiber formation, indicating that zyxin is essential for motility acquisition and actin fiber reorganization induced by TGF-␤1 in NMuMG cells.…”

Retrograde Fluxes of Focal Adhesion Proteins in Response to Cell Migration and Mechanical Signals

“…An alternative function of the focal adhesion flux is to facilitate the transport of signals from focal adhesions in response to mechanical cues, as suggested by impaired responses of zyxin Ϫ/Ϫ cells to ECM anchorage and mechanical stimulations (Yoshigi et al, 2005;Hoffman et al, 2006). Although focal adhesions have been recognized as an important source of signals with multiple downstream effects such as activation of the mitogen-activated protein kinase pathway and eventually gene expression (Giancotti and Ruoslahti, 1999), how these signals propagate is unclear.…”

“…Several proteins, including zyxin and vasodilator-stimulated phosphoprotein (VASP), are known to localize to a variable extent at focal adhesions (Crawford et al, 1992;Rottner et al, 2001), or to shuttle between focal adhesions and the nucleus (Nix and Beckerle, 1997;Aplin and Juliano, 2001). Recent studies further indicated that mechanical stimulation can induce the change in distribution of zyxin from focal adhesions to either actin stress fibers in cultured fibroblasts (Yoshigi et al, 2005), or the nucleus of vascular smooth muscle cells (Cattaruzza et al, 2004). The latter may be related to the suspected ability of zyxin to regulate gene expression (Degenhardt and Silverstein, 2001).…”