Shigella interactions with the actin cytoskeleton in the absence of Ena/VASP family proteins

Shigella move through the cytosol of infected cells by assembly of a propulsive actin tail at one end of the bacterium. Vasodilator-stimulated phosphoprotein (VASP), a member of the Ena/VASP family of proteins, is important in cellular actin dynamics and is present on intracellular Shigella . VASP binds both profilin, an actin monomer-binding protein, and vinculin, a component of intercellular contacts that also binds the Shigella actin assembly protein IcsA. It has been postulated that VASP might serve as a linker between vinculin and profilin on intracellular Shigella , thereby delivering profilin to the Shigella actin assembly machinery. We show that Shigella actin-based motility is unaltered in cells that are deficient for the Ena/ VASP family of proteins. In these cells, Shigella form normal-appearing actin tails and move at rates that are comparable to the rates of bacterial movement in Ena/VASP-deficient cells complemented with the Ena/ VASP family member Mena. Finally, whereas vinculin can bind the Arp2/3 complex, we show that Arp2/3 recruitment to Shigella is not correlated with vinculin recruitment, indicating that the role of vinculin in Shigella motility is not recruitment of Arp2/3. Thus, although VASP is recruited to the surface of intracellular Shigella , it is not essential for Shigella actinbased motility. not required to reconstitute IcsA-mediated motility using purified cytoskeletal proteins Actin-based motility of Shigella in F9 5.51 cells, which are deficient in vinculin, is no different from that in the vinculin-expressing parent cell line (Goldberg, 1997). However, small amounts of truncated vinculin can be detected in F9 5.51 cells, leading other investigators to suggest that the small amount of truncated protein is