Shigella Protein IpaH9.8 Is Secreted from Bacteria within Mammalian Cells and Transported to the Nucleus

Abstract Various pathogenic bacteria such asShigella deliver effector proteins into mammalian cells via the type III secretion system. The delivered Shigellaeffectors have been shown to variously affect host functions required for efficient bacterial internalization into the cells. In the present study, we investigated the IpaH proteins for their ability to be secreted via the type III secretion system and their fate in mammalian cells. Upon incubation in a medium containing Congo red, the bacteria secrete IpaH into the medium, but secretion of IpaH occurs later than that of IpaBCD. Immunofluorescence microscopy indicated that IpaH9.8 is secreted from intracellular bacteria and transported into the nucleus. On microinjection of the protein, intracellular IpaH9.8 is accumulated at one place around the nucleus and transported into the nucleus. This movement seems to be dependent on the microtubule network, since nuclear accumulation of IpaH9.8 is inhibited in cells treated with microtubule-destabilizing agents. In nuclear import assay, IpaH9.8 was efficiently transported into the nucleus, which was completely blocked by treatment with wheat germ agglutinin. The nuclear transport of IpaH9.8 does not depend on host cytosolic factors but is partially dependent on ATP/GTP, suggesting that, like β-catenin, IpaH9.8 secreted from intracellularShigella can be transported into the nucleus.