Article

Identification of the Salmonella enterica serotype typhimurium SipA domain responsible for inducing neutrophil recruitment across the intestinal epithelium.

Mucosal Immunology Laboratory, Department of Pediatric Gastroenterology and Nutrition, Massachusetts General Hospital, Charlestown, MA 02129, USA.
Cellular Microbiology (Impact Factor: 4.82). 10/2007; 9(9):2299-313. DOI: 10.1111/j.1462-5822.2007.00960.x
Source: PubMed

ABSTRACT 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.

0 Bookmarks
 · 
63 Views
  • [Show abstract] [Hide abstract]
    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.
    Frontiers in Immunology 07/2014; 5:311. DOI:10.3389/fimmu.2014.00311
    This article is viewable in ResearchGate's enriched format
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Neutrophil (polymorphonuclear leukocytes; PMN) transmigration across mucosal surfaces contributes to dysfunction of epithelial barrier properties, a characteristic underlying many mucosal inflammatory diseases. Using Salmonella enterica serovar Typhimurium (S. Typhimurium) as a prototypic proinflammatory insult, we have previously reported that the eicosanoid hepoxilin A3 (HXA3 ), an endogenous product of 12-lipoxygenase (12-LOX) activity, is secreted from the apical surface of the intestinal epithelium to establish a chemotactic gradient that guides PMN across the epithelial surface. Since little is known regarding the molecular mechanisms that regulate 12-LOX during S. Typhimurium infection, we investigated this pathway. We found that expression of phospholipid glutathione peroxidase (GPX4), which is known to have an inhibitory effect on 12-LOX activity, is significantly decreased at both the mRNA and protein level during infection with S. Typhimurium. Moreover, employing intestinal epithelial cell monolayers expressing siRNA against GPX4 mRNA, S. Typhimurium-induced PMN migration was significantly increased compared to the nonspecific siRNA control cells. Conversely, in cells engineered to overexpress GPX4, S. Typhimurium-induced PMN migration was significantly decreased, which is consistent with the finding that partial depletion of GPX4 by RNAi resulted in a significant increase in HXA3 secretion during S. Typhimurium infection. Mechanistically, although we found Salmonella entry not to be required for the induced decrease in GPX4, the secreted effector, SipA, which is known to induce epithelial responses leading to stimulation of HXA3 , governed the decrease in GPX4 in a process that does not lead to an overall increase in the levels of ROS. Taken together, these results suggest that S. Typhimurium induces apical secretion of HXA3 by decreasing the expression of phospholipid GPX, which in turn leads to an increase in 12-LOX activity, and hence HXA3 synthesis.
    Cellular Microbiology 03/2014; 16(9). DOI:10.1111/cmi.12290 · 4.82 Impact Factor
  • [Show abstract] [Hide abstract]
    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.
    Cellular Microbiology 09/2014; DOI:10.1111/cmi.12368 · 4.82 Impact Factor

Full-text (2 Sources)

Download
6 Downloads
Available from
Oct 8, 2014