Functional analyses of the type III effectors in pathogenic E.coli

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Enteropathogenic Escherichia coli delivers a subset of effectors into host cells via a type III secretion system, and this step is required for the progression of disease. In this study, we demonstrated that the type III effectors, EspG and its homolog EspG2, trigger actin stress fiber formation and the destruction of the microtubule networks beneath adherent bacteria. Both effectors were shown to possess the ability to interact with tubulins, and to stimulate microtubule destabilization in vitro. A recent study showed that microtubule-bound GEF-H1, a RhoA-specific guanine nucleotide exchange factor, was converted to its active form by microtubule destabilization, and this sequence of events resulted in RhoA stimulation. Indeed, EspG- and EspG2-induced stress fiber formation was inhibited by the expression of dominant-negative forms of GEF-H1 and RhoA, but not of Rac1 and Cdc42. These results indicate that the impact of EspG/EspG2 on microtubule networks triggers the activation of the … More RhoA-ROCK signaling pathway via GEF-H1 activity. In addition, we revealed that the EspG/EspG2 alter epithelial paracellular permeability. When MDCK cells were infected with wild-type (WT) EPEC, RhoA was activated, and this event was dependent on the delivery of either EspG or EspG2 into host cells. In contrast, a loss of transepithelial electrical resistance and ZO-1 disruption were induced by infection with an espG/espG2 double-knockout mutant, as was the case with the WT EPEC, indicating that EspG/EspG2 is not involved in the disruption of tight junctions during EPEC infection. Although EspG- and EspG2-expressing MDCK cells exhibited normal overall morphology and maintained fully assembled tight junctions, the paracellular permeability to 4-kDa dextran, but not the paracellular permeability to 500-kDa dextran, was greatly increased. This report reveals for the first time that a pathogen can regulate the size-selective paracellular permeability of epithelial cells in order to elicit a disease process. Less