Identification of the Salmonella enterica serotype typhimurium SipA domain responsible for inducing neutrophil recruitment across the intestinal epithelium. Cell Microbiol 9(9):2299-2313 Epub 2007 May 18

Mucosal Immunology Laboratory, Department of Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital, Charlestown, MA 02129, USA.
Cellular Microbiology (Impact Factor: 4.92). 10/2007; 9(9):2299-313. DOI: 10.1111/j.1462-5822.2007.00960.x
Source: PubMed


In human intestinal disease induced by Salmonella enterica serotype Typhimurium (S. typhimurium) transepithelial migration of polymorphonuclear leukocytes (PMNs) rapidly follows attachment of the bacteria to the epithelial apical membrane. Previously, we have shown that the S. typhimurium effector protein, SipA, plays a pivotal role in signalling epithelial cell responses that lead to the transepithelial migration of PMNs. Thus, the objective of this study was to determine the functional domain of SipA that regulates this signalling event. SipA was divided into two fragments: the SipAb C-terminal fragment(426-684) (259 AA), which binds actin, and the SipAa fragment(2-425) (424 AA), which a role has yet to be described. In both in vitro and in vivo models of S. typhimurium-induced intestinal inflammation the SipAa fragment exhibited a profound ability to induce PMN transmigration, whereas the SipAb actin-binding domain failed to induce PMN transmigration. Subsequent mapping of the SipAa domain identified a 131-amino-acid region (SipAa3(294-424)) responsible for modulating PMN transepithelial migration. Interestingly, neither intracellular translocation nor actin association of SipA was necessary for its ability to induce PMN transepithelial migration. As these results indicate SipA has at least two separate functional domains, we speculate that during infection S. typhimurium requires delivery of SipA to both extracellular and intracellular spaces to maximize pro-inflammatory responses and mechanisms of bacterial invasion.

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    • "Moreover, we have previously reported on the secretion profile of SipA from the ΔsipB non-polar deletion strain, confirming that this strain secretes identical amounts of SipA compared with the parent wild-type S. Typhimurium strain (SL1344). As shown in Fig. 5C and consistent with our prior studies (Lee et al., 2000; Wall et al., 2007; Srikanth et al., 2010) infection with the ΔsipB non-polar deletion mutant failed to disrupt PERP accumulation at the apical surface. Thus, these observations provide important geneticbased evidence to further substantiate our contention that SipA does not need to be translocated into the epithelial cell cytosol but rather acts extracellularly to elicit PERP accumulation. "
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    ABSTRACT: Salmonella enterica Typhimurium induces intestinal inflammation through the activity of type III secreted effector (T3SE) proteins. Our prior results indicate that the secretion of the T3SE SipA and the ability of SipA to induce epithelial cell responses that lead to induction of PMN transepithelial migration are not coupled to its direct delivery into epithelial cells from Salmonella. We therefore tested the hypothesis that SipA interacts with a membrane protein located at the apical surface of intestinal epithelial cells. Employing a split ubiquitin yeast-two-hybrid screen, we identified the tetraspanning membrane protein, PERP (p53-effector related to PMP-22), as a SipA binding partner. SipA and PERP appear to have intersecting activities as we found PERP to be involved in proinflammatory pathways shown to be regulated by SipA. In sum, our studies reveal a critical role for PERP in the pathogenesis of S. Typhimurium, and for the first time demonstrate that SipA, a T3SE protein, can engage a host protein at the epithelial surface. This article is protected by copyright. All rights reserved.
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    • "In keeping with this premise, we discovered that many T3SEs from S. Typhimurium harbour a functional caspase-3 cleavage site uniquely positioned at the junction separating their distinct functional domains, thereby producing two independently functional proteins (Srikanth et al., 2010). Salmonella invasion protein A (SipA), is a bifunctional molecule with an actin-binding function of SipA is localized to a C-terminal fragment (Lilic et al., 2003) while the N-terminal fragment triggers signal transduction cascades that promote polymorphonuclear leukocyte migration (Lee et al., 2000; Wall et al., 2007). SipA also harbours a functionally active caspase-3 motif that is precisely located at the junction separating the two functional domains of this protein (Srikanth et al., 2010). "
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    ABSTRACT: Apoptosis is a critical process that intrinsically links organism survival to its ability to induce controlled death. Thus, functional apoptosis allows organisms to remove perceived threats to their survival by targeting those cells that it determines pose a direct risk. Central to this process are apoptotic caspases, enzymes that form a signaling cascade, converting danger signals via initiator caspases into activation of the executioner caspase, caspase-3. This enzyme begins disassembly of the cell by activating DNA degrading enzymes and degrading the cellular architecture. Interaction of pathogenic bacteria with caspases, and in particular caspase-3, can therefore impact both host cell and bacterial survival. With roles outside cell death such as cell differentiation, control of signaling pathways and immunomodulation also being described for caspase-3, bacterial interactions with caspase-3 may be of far more significance in infection than previously recognized. In this review, we highlight the ways in which bacterial pathogens have evolved to subvert caspase-3 both through effector proteins that directly interact with the enzyme or by modulating pathways that influence its activation and activity.
    Full-text · Article · Sep 2014 · Cellular Microbiology
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    • "Phosphatidic acid is then converted to diacylglycerol (DAG), which recruits protein kinase C-α (PKC-α) to the apical membrane (Figure 2). PKC-α, in addition to an ERM protein ezrin, modulate the localization of MRP2 to the apical membrane of epithelial cells, thereby allowing the secretion of HXA3 into the lumen and production of the chemattractant gradient that induces neutrophil transmigration (Figure 2) (72, 74, 75). "
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    ABSTRACT: The human intestinal epithelium consists of a single layer of epithelial cells that forms a barrier against food antigens and the resident microbiota within the lumen. This delicately balanced organ functions in a highly sophisticated manner to uphold the fidelity of the intestinal epithelium and to eliminate pathogenic microorganisms. On the luminal side, this barrier is fortified by a thick mucus layer, and on the serosal side exists the lamina propria containing a resident population of immune cells. Pathogens that are able to breach this barrier disrupt the healthy epithelial lining by interfering with the regulatory mechanisms that govern the normal balance of intestinal architecture and function. This disruption results in a coordinated innate immune response deployed to eliminate the intruder that includes the release of antimicrobial peptides, activation of pattern-recognition receptors, and recruitment of a variety of immune cells. In the case of Salmonella enterica serovar typhimurium (S. typhimurium) infection, induction of an inflammatory response has been linked to its virulence mechanism, the type III secretion system (T3SS). The T3SS secretes protein effectors that exploit the host's cell biology to facilitate bacterial entry and intracellular survival, and to modulate the host immune response. As the role of the intestinal epithelium in initiating an immune response has been increasingly realized, this review will highlight recent research that details progress made in understanding mechanisms underlying the mucosal inflammatory response to Salmonella infection, and how such inflammatory responses impact pathogenic fitness of this organism.
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