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Published 18 March 2002. doi:10.1083/jcb.200110013
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© The Rockefeller University Press, 0021-9525/2002/3/1065 $5.00
The Journal of Cell Biology, Volume 156, Number 6, March 18, 2002 1065-1076


Article

Tropomyosin inhibits ADF/cofilin-dependent actin filament dynamics

Shoichiro Ono and Kanako Ono

Department of Pathology, Emory University, Atlanta, Georgia 30322

Address correspondence to Shoichiro Ono, Dept. of Pathology, Emory University, 615 Michael St., Whitehead Research Bldg., Rm. 105N, Atlanta, GA 30322. Tel.: (404) 727-3916. Fax: (404) 727-8538. E-mail: sono{at}emory.edu

Tropomyosin binds to actin filaments and is implicated in stabilization of actin cytoskeleton. We examined biochemical and cell biological properties of Caenorhabditis elegans tropomyosin (CeTM) and obtained evidence that CeTM is antagonistic to ADF/cofilin-dependent actin filament dynamics. We purified CeTM, actin, and UNC-60B (a muscle-specific ADF/cofilin isoform), all of which are derived from C. elegans, and showed that CeTM and UNC-60B bound to F-actin in a mutually exclusive manner. CeTM inhibited UNC-60B–induced actin depolymerization and enhancement of actin polymerization. Within isolated native thin filaments, actin and CeTM were detected as major components, whereas UNC-60B was present at a trace amount. Purified UNC-60B was unable to interact with the native thin filaments unless CeTM and other associated proteins were removed by high-salt extraction. Purified CeTM was sufficient to restore the resistance of the salt-extracted filaments from UNC-60B. In muscle cells, CeTM and UNC-60B were localized in different patterns. Suppression of CeTM by RNA interference resulted in disorganized actin filaments and paralyzed worms in wild-type background. However, in an ADF/cofilin mutant background, suppression of CeTM did not worsen actin organization and worm motility. These results suggest that tropomyosin is a physiological inhibitor of ADF/cofilin-dependent actin dynamics.

Key Words: myofibrils; thin filaments; actin; ADF/cofilin; tropomyosin


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