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Shigella deliver an effector protein to trigger host microtubule destabilization, which promotes Rac1 activity and efficient bacterial internalization

Sei Yoshida, Eisaku Katayama, Asaomi Kuwae, Hitomi Mimuro, Toshihiko Suzuki, Chihiro Sasakawa

Author Affiliations

  1. Sei Yoshida1,2,
  2. Eisaku Katayama3,
  3. Asaomi Kuwae1,
  4. Hitomi Mimuro1,
  5. Toshihiko Suzuki1,2 and
  6. Chihiro Sasakawa*,1
  1. 1 Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, 4‐6‐1, Shirokanedai, Minato‐Ku, Tokyo, 108‐8639, Japan
  2. 2 PRESTO, Japan Science and Technology Corporation (JST), Japan
  3. 3 Department of Basic Medical Sciences, Institute of Medical Science, University of Tokyo, 4‐6‐1, Shirokanedai, Minato‐Ku, Tokyo, 108‐8639, Japan
  1. *Corresponding author. E‐mail: sasakawa{at}ims.u-tokyo.ac.jp
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Abstract

Shigella deliver a subset of effectors into the host cell via the type III secretion system, that stimulate host cell signal pathways to modulate the actin dynamics required for invasion of epithelial cells. Here we show that one of the Shigella effectors, called VirA, can interact with tubulin to promote microtubule (MT) destabilization, and elicit protrusions of membrane ruffling. Under in vitro conditions, VirA inhibited polymerization of tubulin and stimulated MT destabilization. Upon microinjection of VirA into HeLa cells, a localized membrane ruffling was induced rapidly. Overexpression of VirA in host cells caused MT destruction and protruding membrane ruffles which were absent when VirA was co‐expressed with a dominant‐negative Rac1 mutant. Indeed, Shigella but not the virA mutant stimulated Rac1, including the formation of membrane ruffles in infected cells. Importantly, the MT structure beneath the protruding ruffling was destroyed. Furthermore, drug‐induced MT growth in HeLa cells greatly enhanced the Shigella entry. These results indicate that VirA is a novel type of bacterial effector capable of inducing membrane ruffling through the stimulation of MT destabilization.

  • Received October 1, 2001.
  • Revision received April 4, 2002.
  • Accepted April 30, 2002.
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