Myosin light chain kinase plays an essential role in S-flexneri dissemination

Shigella flexneri, the causitive agent of bacillary dysentery, has been sho wn to disseminate in colonic epithelial cells via protrusions that extend f rom infected cells and are endocytosed by adjacent cells. This phenomenon o ccurs in the region of the eukaryotic cell's adherens junctions and is inhi bited by pharmacological reagents or host cell mutations that completely di srupt the junctional complex. In this study, inhibitors of the myosin light chain kinase (MLCK) were shown to dramatically decrease intercellular spre ad of S. flexneri but to have no inhibitory effect on bacterial entry, mult iplication or actin-based motility within the host cell. Furthermore, cell- to-cell spread of Listeria monocytogenes, another bacterial pathogen that u ses an actin-based mechanism to move within the eukaryotic cytoplasm and to spread from cell to cell, was not affected by the MLCK inhibitors, indicat ing that (1) the inhibition of S, flexneri cell-to-cell spread in treated c ells is not due to a complete break down of cell-cell contacts, which was s ubsequently confirmed by confocal microscopy, and (2) MLCK plays a role in a S, flexneri-specific mechanism of dissemination. Myosin has been shown to play a role in a variety of membrane-based phenomena. The work presented h ere suggests that activation of this molecule via phosphorylation by MLCK, at the very least participates in the formation of the bacteria-containing protrusion, and could also contribute to the endocytosis of this structure by neighboring cells.