Interferon alpha inhibits a Src-mediated pathway necessary for Shigella-induced cytoskeletal rearrangements in epithelial cells.
Bottom Line: Shigella flexneri, the causative agent of bacillary dysentery, has the ability to enter nonphagocytic cells.The interferon (IFN) family of cytokines was found to inhibit Shigella invasion of cultured epithelial cells.Immunofluorescence studies showed that IFN-alpha inhibits Shigella-induced actin polymerization required for bacterial entry into cells.
Affiliation: Unité de Génétique Humaine, INSERM U276.
Shigella flexneri, the causative agent of bacillary dysentery, has the ability to enter nonphagocytic cells. The interferon (IFN) family of cytokines was found to inhibit Shigella invasion of cultured epithelial cells. We show here that IFN-alpha inhibits a Src-dependent signaling cascade triggered by Shigella that leads to the reorganization of the host cell cytoskeleton. Immunofluorescence studies showed that IFN-alpha inhibits Shigella-induced actin polymerization required for bacterial entry into cells. Phosphorylation of cortactin, a Src-substrate specifically tyrosyl-phosphorylated during Shigella entry, was inhibited by IFN-alpha. Overexpression of a dominant interfering form of pp60c-src led to inhibition of Shigella-induced cytoskeletal rearrangements and decreased cortactin phosphorylation indicating a role for Src in Shigella entry. Also, Shigella uptake in cells that expressed constitutively active Src was unaffected by IFN-alpha treatment. We conclude that Src kinase activity is necessary for Shigella invasion of epithelial cells and that IFN-alpha inhibits this Src-dependent signaling pathway.
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Mentions: Confocal microscopy analysis was used to determine if, in addition to the reduction in number of foci, actin polymerization at the site of Shigella entry was qualitatively affected. 10 foci were chosen randomly from IFN-α–treated (Fig. 3, bottom) and untreated cells (top) and analyzed using the same parameters. Despite some variations in the level of F-actin labeling among the different foci, a weaker signal was generally observed when cells were pretreated with IFN-α. Confocal analysis indicated that recruitment of other cytoskeletal proteins such as ezrin and α−actinin at the entry foci was also affected by IFN-α treatment (not shown). These data further support the notion that IFN-α interferes with early events during Shigella entry, by impairing ability of the bacterium to reorganize the actin-cytoskeleton into entry structures.