Neural Wiskott-Aldrich syndrome protein is implicated in the actin-based motility of Shigella flexneri

Shigella, the causative agent of bacillary dysentery, is capable of directing its own movement in the cytoplasm of infected epithelial cells. The bacterial surface protein VirG recruits host components mediating actin polymerization, which is thought to serve as the propulsive force. Here, we show that neural Wiskott-Aldrich syndrome protein (N-WASP), which is a critical target for filopodium formation downstream of Cdc42, is required for assembly of the actin tail generated by intracellular S. flexneri. N-WASP accumulates at the front of the actin tail and is capable of interacting with VirG in vitro and in vivo, a phenomenon that is not observed in intracellular Listeria monocytogenes, The verprolin-homology region in N-WASP was required for binding to the glycine-rich repeats domain of VirG, an essential domain for recruitment of F-actin on intracellular S. flexneri. Overexpression of a dominant-negative N-WASP mutant greatly inhibited formation of the actin tail by intracellular S. flexneri, Furthermore, depletion of N-WASP from Xenopus egg extracts shut off Shigella actin tail assembly, and this was restored upon addition of N-WASP protein, suggesting that N-WASP is a critical host factor for the assembly of the actin tail by intracellular Shigella.