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First published online 5 August 2008
doi: 10.1242/jcs.030320

Journal of Cell Science 121, 2795-2804 (2008)
Published by The Company of Biologists 2008
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Research Article

Mechanical forces facilitate actin polymerization at focal adhesions in a zyxin-dependent manner

Hiroaki Hirata1,2, Hitoshi Tatsumi3 and Masahiro Sokabe1,2,3,*

1 Cell Mechanosensing Project, ICORP/SORST, Japan Science and Technology Agency, 65 Tsurumai, Showa-ku, Nagoya, Aichi 466-8550, Japan
2 Department of Molecular Physiology, National Institute for Physiological Sciences, National Institutes of Natural Sciences, 38 Nishigonaka, Myodaiji-cho, Okazaki, Aichi 444-8585, Japan
3 Department of Physiology, Nagoya University Graduate School of Medicine, 65 Tsurumai, Showa-ku, Nagoya, Aichi 466-8550, Japan

* Author for correspondence (e-mail: msokabe{at}med.nagoya-u.ac.jp)

Accepted 29 May 2008

We examined the effects of mechanical forces on actin polymerization at focal adhesions (FAs). Actin polymerization at FAs was assessed by introducing fluorescence-labeled actin molecules into permeabilized fibroblasts cultured on fibronectin. When cell contractility was inhibited by the myosin-II inhibitor blebbistatin, actin polymerization at FAs was diminished, whereas {alpha}5β1 integrin remained accumulated at FAs. This suggests that actin polymerization at FAs depends on mechanical forces. To examine the action of mechanical forces more directly, the blebbistatin-treated cells were subjected to a sustained uniaxial stretch, which induced actin polymerization at FAs. These results demonstrate the novel role of mechanical forces in inducing actin polymerization at FAs. To reveal the molecular mechanism underlying the force-induced actin polymerization at FAs, we examined the distribution of zyxin, a postulated actin-regulatory protein. Actin-polymerizing activity was strong at zyxin-rich FAs. Accumulation of zyxin at FAs was diminished by blebbistatin, whereas uniaxial stretching of the cells induced zyxin accumulation. Displacing endogenous zyxin from FAs by expressing the FA-targeting region of zyxin decreased the force-induced actin polymerization at FAs. These results suggest that zyxin is involved in mechanical-force-dependent facilitation of actin polymerization at FAs.

Key words: Focal adhesion, Mechanical force, Actin polymerization, Zyxin, Integrin


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