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Department of Biomolecular Sciences, Graduate School of Life Sciences, Tohoku University, Sendai, Miyagi 980-8578, Japan

Slingshot-1 (SSH1) is known to regulate actin filament dynamics by dephosphorylating and activating cofilin, an actin-depolymerizing factor. SSH1 binds to filamentous (F-) actin through its multiple F-actin-binding sites and its cofilin-phosphatase activity is enhanced by binding to F-actin. In this study, we demonstrate that SSH1 has F-actin-stabilizing and -bundling activities. In vitro actin depolymerization assays revealed that SSH1 suppressed spontaneous and cofilin-induced actin depolymerization in a dose-dependent manner. SSH1 inhibited F-actin binding and severing activities of cofilin. Low-speed centrifugation assays combined with fluorescence and electron microscopic analysis revealed that SSH1 has F-actin-bundling activity, independently of its cofilin-phosphatase activity. Deletion of N- or C-terminal regions of SSH1 significantly reduced its F-actin-stabilizing and -bundling activities, indicating that both regions are critical for these functions. As SSH1 does not form a homodimer, it probably bundles F-actin through its multiple F-actin-binding sites. Knockdown of SSH1 expression by RNA interference significantly suppressed stress fiber formation in C2C12 myoblast cells, indicating a role for SSH1 in stress fiber formation or stabilization in cells. SSH1 thus has the potential to regulate actin filament dynamics and organization in cells via F-actin-stabilizing and -bundling activities, in addition to its ability to dephosphorylate cofilin.

^* Correspondence: E-mail: kmizuno{at}biology.tohoku.ac.jp

This article has been cited by other articles:

				S. Kurita, Y. Watanabe, E. Gunji, K. Ohashi, and K. Mizuno Molecular Dissection of the Mechanisms of Substrate Recognition and F-actin-mediated Activation of Cofilin-phosphatase Slingshot-1 J. Biol. Chem., November 21, 2008; 283(47): 32542 - 32552. [Abstract] [Full Text] [PDF]