Rho family GTPases control entry of Shigella flexneri into epithelial cells but not intracellular motility

Shigella flexneri, an invasive bacterial pathogen, promotes formation of tw o cytoskeletal structures: the entry focus that mediates bacterial uptake i nto epithelial cells and the actin-comet tail that enables the bacteria to spread intracellularly, During the entry step, secretion of bacterial invas ins causes a massive burst of subcortical actin polymerization leading the formation of localised membrane projections. Fusion of these membrane ruffl es leads to bacterial internalization. Inside the cytoplasm, polar expressi on of the IcsA protein on the bacterial surface allows polymerization of ac tin filaments and their organization into an actin-comet tail leading to ba cterial spread. The Rho family of small GTPases plays an essential role in the organization and regulation of cellular cytoskeletal structures (i.e. f ilopodia, lamellipodia, adherence plaques and intercellular junctions). We show here that induction of Shigella entry foci is controlled by the Cdc42, Rac and Rho GTPases, but not by RhoG, In contrast, actin-driven intracellu lar motility of Shigella does not require Rho GTPases, Therefore, Shigella appears to manipulate the epithelial cell cytoskeleton both by Rho GTPase-d ependent and -independent processes.