title: IpgB1 is a novel Shigella effector protein involved in bacterial invasion of host cells. Its activity to promote membrane ruffling via Rac1 and Cdc42 activation.
abstract: Shigella, the causative agent of bacillary dysentery, is capable of inducing the large scale membrane ruffling required for the bacterial invasion of host cells. Shigella secrete a subset of effectors via the type III secretion system (TTSS) into the host cells to induce membrane ruffling. Here, we show that IpgB1 is secreted via the TTSS into epithelial cells and plays a major role in producing membrane ruffles via stimulation of Rac1 and Cdc42 activities, thus promoting bacterial invasion of epithelial cells. The invasiveness of the ipgB1 mutant was decreased to less than 50% of the wild-type level (100%) in a gentamicin protection or plaque forming assay. HeLa cells infected with the wild-type or a IpgB1-hyperproducing strain developed membrane ruffles, with the invasiveness and the scale of membrane ruffles being comparable with the level of IpgB1 production in bacteria. Upon expression of EGFP-IpgB1 in HeLa cells, large membrane ruffles are extended, where the EGFP-IpgB1 was predominantly associated with the cytoplasmic membrane. The IpgB1-mediated formation of ruffles was significantly diminished by expressing Rac1 small interfering RNA and Cdc42 small interfering RNA or by treatment with GGTI-298, an inhibitor of the geranylgeranylation of Rho GTPases. When IpgB1 was expressed in host cells or wild-type Shigella-infected host cells, Rac1 and Cdc42 were activated. The results thus indicate that IpgB1 is a novel Shigella effector involved in bacterial invasion of epithelial cells via the activation of Rho GTPases.
authors.affiliation: Department of Microbiology and Immunology, Institute of Medical Science, University of Tokyo, 4-6-1 Shirokanedai, Minato-ku, Tokyo 108-8639, Japan.
authors.forename: Kenji
authors.initials: K
authors.lastname: Ohya
authors.forename: Yutaka
authors.initials: Y
authors.lastname: Handa
authors.forename: Michinaga
authors.initials: M
authors.lastname: Ogawa
authors.forename: Masato
authors.initials: M
authors.lastname: Suzuki
authors.forename: Chihiro
authors.initials: C
authors.lastname: Sasakawa
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000037:antagonists & inhibitors; D000595:Amino Acid Sequence; D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000502:physiology*; D001483:Base Sequence; D002462:Cell Membrane / Q000378:metabolism; D017931:DNA Primers; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D012760:Shigella / Q000502:physiology*; D020764:cdc42 GTP-Binding Protein / Q000502:physiology*; D020830:rac1 GTP-Binding Protein / Q000502:physiology*
chemical_list: D001426:Bacterial Proteins; D017931:DNA Primers; D004791:Enzyme Inhibitors; C107953:RAC1 protein, human; D019883:Alkyl and Aryl Transferases; C083291:geranylgeranyltransferase type-I; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein