Profilin is required for sustaining efficient intra- and intercellular spreading of Shigella flexneri

The ability of Shigella to mediate actin-based motility within the host cell is a prominent pathogenic feature of bacillary dysentery. The ability is dependent on the interaction of VirG with neural Wiskott-Aldrich syndrome protein (N-WASP), which in turn mediates recruitment of Arp2/3 complex and several actin-related proteins. In the present study, we show that profilin I is essential to the rapid movement of Shigella in epithelial cells, for which the capacity of profilin to interact with G-actin and N-WASP is critical. In COS-7 cells overexpressing either mutated profilin H119E, which failed to bind G-actin, or H133S, which is unable to interact with poly-l-proline, Shigella motility was significantly inhibited. Similarly, depletion of profilin from Xenopus egg extracts resulted in a decrease in bacterial motility that was completely rescued by adding back profilin I but not H119E or H133S. In COS-7 cells overexpressing a N-WASP mutant lacking the proline-rich domain (Deltap) unable to interact with profilin, the actin tail formation of intracellular Shigella was inhibited. In N-WASP-depleted extracts, addition of Deltap but not full-length N-WASP was unable to restore the bacterial motility. Furthermore, in a plaque formation assay with Madin-Darby canine kidney cell monolayers infected by Shigella, Madin-Darby canine kidney cells stably expressing H119E, H133S, or Deltap reduced the bacterial cell-to-cell spreading. These results indicate that profilin I associated with N-WASP is an essential host factor for sustaining efficient intra- and intercellular spreading of Shigella.