Oral Presentation 2014 International Biophysics Congress

Actin filaments work as a mechanosensor by transducing tension into their structural dynamics (#65)

Masahiro Sokabe 1 , Kimihide Hayakawa 1 , Hitoshi Tatsumi 1
  1. Nagoya University Graduate School of Medicine, Nagoya, Japan
Mechanical forces play crucial roles in a variety of cell behaviors, including morphogenesis, proliferation and migration. A remarkable force dependent event across these cell responses is orchestrated dynamics (scrap and built) of actin cytoskeletons, though the underlying mechanisms are largely unknown. Actin filaments (AFs) are typically associated with myosin to form a contractile machinery like stress fibers (SFs). SFs are strengthened with tension while disrupted with tension release, suggesting that SFs sense tension and transduce it into their dynamics. We hypothesized that, when SF tension is released, the major SF component AFs would be disrupted by an actin depolymerizing factor (ADF). ADF/cofilin is an actin-modulating protein ubiquitously distributed in eukaryotes and one of the likely candidates to drive SF disruption in response to tension-release. To test this hypothesis, we placed single AFs under tension using optical tweezers. When AFs were tensed, cofilin severing of AFs was largely inhibited in comparison with relaxed AFs. Single molecular imaging revealed that the cofilin binding rate was decreased when AFs were tensed, indicating that tension in an AF retards cofilin binding. An AF has a double helix structure and cofilin binding makes it more twisted, implying that cofilin binding rate increases when the AF helix is in a more twisted structure. As we found that torsional fluctuations of single AFs were decreased with tension, it was suggested that AFs convert tension negatively into their torsional fluctuations to retard cofilin activity, thus working as a negative tension sensor to disrupt AFs with cofilin.