|Ono, S. & Ono, K.
(2002) Tropomyosin inhibits ADF/cofilin-dependent actin filament
dynamics. J.Cell Biol. 156, 1065-1076.
|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.