Shigella flexneri is the causative agent of shigellosis (bacillary dysentery). After invading the cells of the host colonic epithelium and escaping in the cytosol, the bacterial IcsA protein interacts with the host N-WASP (neural Wiskott-Aldrich syndrome protein) which recruits the Arp2/3 complex to initiate F-actin polymerisation. The F-actin tail generates a propulsive force that allows the bacterium to spread within the cell and into the neighbouring cells. Protrusion formation during cell to cell spreading also requires host proteins associated with the enterocyte tight junctions. It is reasoned that by targeting host factors important in Shigella cell spreading, the progression of the infection can be limited, thus providing an alternative target for novel Shigella treatment strategies.
Dynamin II (DynII) is a large GTPase that plays an essential role in clathrin mediated endocytosis. The effect of dynasore, an inhibitor of dynamin II and siRNA knockdown of DynII on HeLa cell plaque formation by S. flexneri 2457T was investigated. A dose dependent inhibition of plaque formation with dynasore was observed. siRNA knockdown of DynII also reduced plaque formation. Immunofluorescence labelling showed DynII colocalised at the tip of the bacteria where the F-actin tail has formed irrespective of the addition of dynasore, indicating that DynII recruitment to the F-actin tail was not affected by dynasore. A murine Sereny test was used to compare the effect of dynasore with the carrier, NMP/PEG. Although there was no difference in the Sereny scores, dynasore significantly protected the mice from weight loss at 24 and 48 hours post infection. These data support our in vitro findings, and suggest DynII inhibition may alleviate symptoms associated with Shigella infection.