OspF and OspC1 Are Shigella flexneri Type III Secretion System Effectors That Are Required for Postinvasion Aspects of Virulence

Department of Microbiology and Immunology, 4301 Jones Bridge Rd., Bethesda, MD 20814-4799, USA.
Infection and Immunity (Impact Factor: 3.73). 11/2006; 74(10):5964-76. DOI: 10.1128/IAI.00594-06
Source: PubMed


Shigella flexneri is the causative agent of dysentery, and its pathogenesis is mediated by a type III secretion system (T3SS). S. flexneri secretes effector proteins into the eukaryotic cell via the T3SS, and these proteins usurp host cellular functions to the
benefit of the bacteria. OspF and OspC1 are known to be secreted by S. flexneri, but their functions are unknown. We transformed S. flexneri with a plasmid that expresses a two-hemagglutinin tag (2HA) in frame with OspF or OspC1 and verified that these proteins
are secreted in a T3SS-dependent manner. Immunofluorescence of HeLa cells infected with S. flexneri expressing OspF-2HA or OspC1-2HA revealed that both proteins localize in the nucleus and cytoplasm of host cells. To elucidate
the function of these T3SS effectors, we constructed ΔospF and ΔospC1 deletion mutants by allelic exchange. We found that ΔospF and ΔospC1 mutants invade host cells and form plaques in confluent monolayers similar to wild-type S. flexneri. However, in the polymorphonuclear (PMN) cell migration assay, a decrease in neutrophil migration was observed for both mutants
in comparison to the migration of wild-type bacteria. Moreover, infection of polarized T84 intestinal cells infected with
ΔospF and ΔospC1 mutants resulted in decreased phosphorylation of extracellular signal-regulated kinase 1/2 in comparison to that of T84 cells
infected with wild-type S. flexneri. To date, these are the first examples of T3SS effectors implicated in mitogen-activated protein kinase kinase/extracellular
signal-regulated kinase pathway activation. Ultimately, OspF and OspC1 are essential for PMN transepithelial migration, a
phenotype associated with increased inflammation and bacterial access to the submucosa, which are fundamental aspects of S. flexneri pathogenesis.

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Available from: Daniel Vincent Zurawski
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    • "It has been shown that the capacity of S. flexneri to divert host immune response for its growth and deeper dissemination success relies mainly on the control of mitogen-activated protein kinase (MAPK) signaling pathways (Ashida et al., 2011; Sperandio and Sansonetti, 2014). Consequently, the activity of key factors involved in all the three well-defined MAPK pathways, the extracellular signal-regulated protein kinases (ERK1/2), the p38 kinases, and the c-Jun NH 2 -terminal kinases (JNK1/2), is subjected to attack by multiple bacterial effectors (Zurawski et al., 2006; Arbibe et al., 2007; Li et al., 2007; Zurawski et al., 2009). Although much progress has been made recently in the molecular and biochemical characterization of these T3SS effectors (Marteyn et al., 2012; Carayol and Tran Van Nhieu, 2013), a defined role for the OspB effector in S. flexneri pathogenesis has not been elucidated yet. "
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    ABSTRACT: Through the action of the type three secretion system (T3SS) Shigella flexneri delivers several effectors into host cells to promote cellular invasion, multiplication and to exploit host-cell signaling pathways to modulate the host innate immune response. Although much progress has been made in the understanding of many type III effectors, the molecular and cellular mechanism of the OspB effector is still poorly characterized. In this study we present new evidence that better elucidates the role of OspB as pro-inflammatory factor at very early stages of infection. Indeed, we demonstrate that, during the first hour of infection, OspB is required for full activation of ERK1/2 and p38 MAPKs and the cytosolic phospholipase A2 (cPLA2). Activation of cPLA2 ultimately leads to the production and secretion of PMN chemoattractant metabolite(s) uncoupled with release of IL-8. Moreover, we also present evidence that OspB is required for the development of the full and promptly inflammatory reaction characteristic of S. flexneri wild-type infection in vivo. Based on OspB and OspF similarity (both effectors share similar transcription regulation, temporal secretion into host cells and nuclear localization) we hypothesized that OspB and OspF effectors may form a pair aimed at modulating the host cell response throughout the infection process, with opposite effects. A model is presented to illustrate how OspB activity would promote S. flexneri invasion and bacterial dissemination at early critical phases of infection.
    Full-text · Article · Nov 2014 · International Journal of Medical Microbiology
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    • "Specifically, OspF inhibits expression of a small set of immune genes including immediate early genes and a subset of NF-κB-responsive genes including IL-8, which is responsible for recruiting neutrophils (Fig. 3) [53, 54]. This corroborates the finding that OspF inhibits neutrophil recruitment [52]. "
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    ABSTRACT: Bacterial pathogens can alter global host gene expression via histone modifications and chromatin remodeling in order to subvert host responses, including those involved with innate immunity, allowing for bacterial survival. Shigella flexneri, Listeria monocytogenes, Chlamydia trachomatis, and Anaplasma phagocytophilum express effector proteins that modify host histones and chromatin structure. A. phagocytophilum modulates granulocyte respiratory burst in part by dampening transcription of several key phagocyte oxidase genes. The A. phagocytophilum protein AnkA localizes to the myeloid cell nucleus where it binds AT-rich regions in the CYBB promoterand decreases its transcription. AT-rich regions of DNA are characteristic of matrix attachment regions (MARs) which are critical for chromatin structure and transcription. MAR-binding proteins, such as SATB1, interact with histone modifying enzymes resulting in altered gene expression. With A. phagocytophilum infection, histone deacetylase 1 (HDAC1) expression is increased and histone H3 acetylation is decreased at the CYBB promoter, suggesting a role for AnkA in altering host epigenetics and modulating gene transcription, at this, and perhaps other loci. This review will focus on how bacterial pathogens alter host epigenetics, by specifically examining A. phagocytophilum AnkA cis-regulation of CYBB transcription and epigenetic changes associated with infection.
    Full-text · Article · Oct 2012
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    • "Distinguishing it from S. Typhimurium , PMN transmigration across epithelial monolayers induced by EAEC 042 does not involve PKC-a, nor does it appear to rely on MAPK pathways as is the case for S. flexneri and DAEC. Moreover, EAEC 042 does not possess any of the T3SS-secreted effector proteins SipA or OspF/OspC1 demonstrated to play key roles in initiating inflammatory responses by S. Typhimurium or S. flexneri respectively (Lee et al., 2000; Zurawski et al., 2006). The AAF/II organelle expressed by EAEC 042 has been shown to be required for basolateral IL-8 secretion as well as for intestinal epithelial barrier disruption induced by this strain (Harrington et al., 2005; Strauman et al., 2010). "
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    ABSTRACT: Enteroaggregative Escherichia coli (EAEC) induces release of pro-inflammatory markers and disruption of intestinal epithelial barriers in vitro, suggesting an inflammatory aspect to EAEC infection. However, the mechanisms underlying EAEC-induced mucosal inflammatory responses and the extent to which these events contribute to pathogenesis is not well characterized. Employing an established in vitro model we demonstrated that EAEC prototype strain 042 induces migration of polymorphonuclear neutrophils (PMNs) across polarized T84 cell monolayers. This event was mediated through a conserved host cell signalling cascade involving the 12/15-LOX pathway and led to apical secretion of an arachidonic acid-derived lipid PMN chemoattractant, guiding PMNs across the epithelia to the site of infection. Moreover, supporting the hypothesis that inflammatory responses may contribute to EAEC pathogenesis, we found that PMN transepithelial migration promoted enhanced attachment of EAEC 042 to T84 cells. These findings suggest that EAEC-induced PMN infiltration may favour colonization and thus pathogenesis of EAEC.
    Full-text · Article · Sep 2011 · Cellular Microbiology
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