Takeshi Matsuzawa

Enteropathogenic Escherichia coli activates the RhoA signaling pathway via the stimulation of GEF-H1.

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. Here, we show that the type III effectors, EspG and its homolog Orf3, 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 Orf3‐induced stress fiber formation was inhibited by the expression of dominant‐negative forms of GEF‐H1 and RhoA, but not of Rac1 and Cdc42, and by treatment with a ROCK inhibitor. These results indicate that the impact of EspG/Orf3 on microtubule networks triggers the activation of the RhoA–ROCK signaling pathway via GEF‐H1 activity. This report reveals for the first time that a pathogen can exploit the host factor GEF‐H1.

Enteropathogenic Escherichia coli Type III Effectors EspG and EspG2 Alter Epithelial Paracellular Permeability

ABSTRACT Enteropathogenic Escherichia coli (EPEC) delivers a subset of effectors into host cells via a type III secretion system. Here we show that the type III effector EspG and its homologue 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.

Assembly of the Type III Secretion Apparatus of Enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC) secretes many Esps (E. coli-secreted proteins) and effectors via the type III secretion (TTS) system. We previously identified a novel needle complex (NC) composed of a basal body and a needle structure containing an expandable EspA sheath-like structure as a central part of the EPEC TTS apparatus. To further investigate the structure and protein components of the EPEC NC, we purified it in successive centrifugal steps. Finally, NCs with long EspA sheath-like structures could be separated from those with short needle structures on the basis of their densities. Although the highly purified NC appeared to lack an inner ring in the basal body, its core structure, composed of an outer ring and a central rod, was observed by transmission electron microscopy. Matrix-assisted laser desorption ionization-time-of-flight mass spectrometry, Western blot, and immunoelectron microscopic analyses revealed that EscC was a major protein component of the outer ring in the core basal body. To investigate the mechanisms of assembly of the basal body, interactions between the presumed components of the EPEC TTS apparatus were analyzed by a glutathione S-transferase pulldown assay. The EscC outer ring protein was associated with both the EscF needle protein and EscD, a presumed inner membrane protein. EscF was also associated with EscJ, a presumed inner ring protein. Furthermore, escC, escD, and escJ mutant strains were unable to produce the TTS apparatus, and thereby the secretion of the Esp proteins and Tir effector was abolished. These results indicate that EscC, EscD, and EscJ are required for the formation of the TTS apparatus.

BopC Is a Novel Type III Effector Secreted by Bordetella bronchiseptica and Has a Critical Role in Type III-dependent Necrotic Cell Death

In Bordetella bronchiseptica, the functional type III secretion system (TTSS) is required for the induction of necrotic cell death in infected mammalian cells. To identify the factor(s) involved in necrotic cell death, type III-secreted proteins from B. bronchiseptica were analyzed using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and electrospray ionization tandem mass spectrometry. We identified a 69-kDa secreted protein designated BopC. The gene encoding BopC is located outside of the TTSS locus and is also highly conserved in both Bordetella parapertussis and Bordetella pertussis. The results of a lactate dehydrogenase release assay and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end-labeling assay demonstrated that BopC is required for necrotic cell death. It has been reported that tyrosine-phosphorylated proteins (PY) of host cells are dephosphorylated during B. bronchiseptica infection in a TTSS-dependent manner. We found that BopC is also involved in PY dephosphorylation in infected host cells. It appears that the necrotic cell death triggered by BopC occurs prior to the PY reduction in host cells, because Bordetella-induced cell death was not affected even in the presence of a dephosphorylation inhibitor. Furthermore, a translocation assay showed that the signal sequence for both secretion into culture supernatant and translocation into the host cell is located in 48 amino acid residues of the BopC N terminus. This report reveals for the first time that a novel type III effector, BopC, is required for the induction of necrotic cell death during Bordetella infection.

Enteropathogenic Escherichia coli, Shigella flexneri, and Listeria monocytogenes Recruit a Junctional Protein, Zonula Occludens-1, to Actin Tails and Pedestals

ABSTRACT Enteropathogenic Escherichia coli, Shigella flexneri, and Listeria monocytogenes induce localized actin polymerization at the cytoplasmic face of the plasma membrane or within the host cytoplasm, creating unique actin-rich structures termed pedestals or actin tails. The process is known to be mediated by the actin-related protein 2 and 3 (Arp2/3) complex, which in these cases acts downstream of neural Wiskott-Aldrich syndrome protein (N-WASP) or of a listerial functional homolog of WASP family proteins. Here, we show that zonula occludens-1 (ZO-1), a protein in the tight junctions of polarized epithelial cells, is recruited to actin tails and pedestals. Immunocytochemical analysis revealed that ZO-1 was stained most in the distal part of the actin-rich structures, and the incorporation was mediated by the proline-rich region of the ZO-1 molecule. The direct clustering of membrane-targeted Nck, which is known to activate the N-WASP-Arp2/3 pathway, triggered the formation of the ZO-1-associated actin tails. The results suggest that the activation of the Arp2/3 complex downstream of N-WASP or a WASP-related molecule is a key to the formation of the particular actin-rich structures that bind with ZO-1. We propose that an analysis of the recruitment on a molecular basis will lead to an understanding of how ZO-1 recognizes a distinctive actin-rich structure under pathophysiological conditions.

The Type III Secreted Protein BopD in Bordetella bronchiseptica Is Complexed with BopB for Pore Formation on the Host Plasma Membrane

The cytotoxicity of Bordetella bronchiseptica to infected cells is known to be dependent on a B. bronchiseptica type III secretion system. Although BopB, BopN, BopD, and Bsp22 have been identified as type III secreted proteins, these proteins remain to be characterized. In this study, in order to clarify the function of BopD during Bordetella infection, a BopD mutant was generated. Although secretion of BopD into the culture supernatant was completely abolished by the bopD mutation, the secretion of other type III secreted proteins was not affected by this mutation. It has been reported that severe cytotoxicity, including cell detachment from the substrata, and release of lactate dehydrogenase (LDH) into the supernatant are induced in L2 cells by wild-type B. bronchiseptica infection, and these phenotypes are dependent on the type III secretion system. In contrast, neither cell detachment nor LDH release was induced in L2 cells infected with the BopD mutant. Furthermore, the hemolytic activity of the BopD mutant was greatly impaired compared with that of the wild-type strain. On the basis of the results of coimmunoprecipitation assays with anti-BopB antibodies, we conclude that BopD has the ability to associate with BopB. Finally, we show that the BopD-BopB complex is responsible for the pore formation in the host plasma membrane that functions as the conduit for the transition of effector proteins into host cells.

In vivo modifications of small GTPase Rac and Cdc42 by Bordetella dermonecrotic toxin.

ABSTRACT Bordetella dermonecrotic toxin (DNT) is known to activate the small GTPase Rho through deamidation or polyamination. In this study, we examined whether Rac and Cdc42, the two other members of the Rho family, serve as intracellular targets for the toxin. Immunoprecipitation and immunoblot assays revealed that DNT deamidated or polyaminated intracellular Rac and Cdc42. After the modifications, both Rac and Cdc42 lost their GTP-hydrolyzing, but not GTP-binding, activities. The interactions of the modified Rac and Cdc42 with their respective effectors were strictly dependent on GTP. MC3T3-E1 cells treated with DNT at high concentrations demonstrated extensive formations of lamellipodia and filopodia, which indicate the intracellular activation of Rac and Cdc42, respectively.

Identification of a Receptor-Binding Domain of Bordetella Dermonecrotic Toxin

ABSTRACT Bordetella dermonecrotic toxin (DNT) stimulates the assembly of actin stress fibers and focal adhesions by deamidating or polyaminating Gln63 of the small GTPase Rho. DNT is an A-B toxin which is composed of an N-terminal receptor-binding (B) domain and a C-terminal enzymatically active (A) domain. In this study, to analyze the functional and structural organization of DNT, we prepared 10 clones of hybridoma producing anti-DNT monoclonal antibodies. One of these antibodies, 2B3, neutralized the effects of DNT on target cells when mixed with the toxin. When microinjected into cells, however, 2B3 did not inhibit the intoxication by DNT. Western blot analysis revealed that 2B3 recognized the N-terminal region of DNT. To delineate the DNT-binding domain, we examined a series of truncated DNT mutants for the ability to competitively inhibit the intoxication of cells by the full-length DNT and found that a fragment consisting of the N-terminal 54 amino acids (DNT1-54) was the smallest inhibitory fragment. The radioiodinated DNT1-54 actually bound to target cells, which was inhibited by 2B3. These results suggest that the N-terminal 54 amino acids of DNT are responsible for the binding to target cells. DNT1-54 bound to none of the DNT-resistant cells, implying the presence of a cell surface receptor specific to DNT-sensitive cells.

Cloning of the gene coding for Staphylococcus hyicus exfoliative toxin B and its expression in Escherichia coli.

The Staphylococcus hyicus exfoliative toxin B (SHETB) gene was cloned into pUC118 and expressed in Escherichia coli. The nucleotide sequence of the SHETB gene consists of a coding region of 804 bp specifying a polypeptide of 268 amino acid residues, which included a putative 20-residue signal sequence.