ExoT of Cytotoxic
            <i>Pseudomonas aeruginosa</i>
            Prevents Uptake by Corneal Epithelial Cells

Cowell, Brigitte A.; Chen, David Y.; Frank, Dara W.; Vallis, Amy J.; Fleiszig, Suzanne M. J.

doi:10.1128/iai.68.1.403-406.2000

Cited by 97 publications

(88 citation statements)

References 19 publications

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“…PA99S and PA99T each were internalized to a lesser degree, with PA99T exhibiting the smallest amount of bacterial uptake. (Cowell et al, 2000;Ha & Jin, 2001). These variable results may be due to differences in the cell types or bacterial strains tested.…”

Section: Cytotoxicitymentioning

confidence: 99%

“…The amino-terminal GAP activity acts on Rho family GTPases while the carboxylterminal ADPRT activity is directed towards Ras and other host-cell proteins (Fraylick et al, 2001;Goehring et al, 1999;Henriksson et al, 2000Henriksson et al, , 2002Krall et al, 2002;Olson et al, 1999;Rocha et al, 2003;Vincent et al, 1999). As a result of these enzymic activities, intoxication with ExoS is associated with several observable phenotypes, including cytotoxicity and inhibition of bacterial internalization by both phagocytic and non-phagocytic mammalian cells (Cowell et al, 2000;Fleiszig et al, 1997;Frithz-Lindsten et al, 1997;Henriksson et al, 2000;Kaufman et al, 2000;Olson et al, 1997Olson et al, , 1999Pederson & Barbieri, 1998;Vincent et al, 1999). (Throughout this discussion, the term 'cytotoxicity' will be used to refer to cytolytic cell death.)…”

Section: Introductionmentioning

confidence: 99%

“…The ADPRT activity of ExoT, however, targets the cellular Crk-I and Crk-II kinases rather than Ras (Sun & Barbieri, 2003). As a result, ExoT intoxication is associated with inhibition of bacterial internalization but not cytotoxicity (Cowell et al, 2000;Garrity-Ryan et al, 2000;Krall et al, 2000). ExoU possesses phospholipase A 2 and lysophospholipase activities (Phillips et al, 2003;Rabin & Hauser, 2005;Sato et al, 2003;Tamura et al, 2004) that lead to rapid lysis of mammalian cells (Coburn & Frank, 1999; Finck-Barbançon et al, 1997;Fleiszig et al, 1997;Hauser et al, 1998a;Vallis et al, 1999).…”

Section: Introductionmentioning

confidence: 99%

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Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Shaver

Hauser

2006

Microbiology

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The effector proteins of the type III secretion systems of many bacterial pathogens act in a coordinated manner to subvert host cells and facilitate the development and progression of disease. It is unclear whether interactions between the type-III-secreted proteins of Pseudomonas aeruginosa result in similar effects on the disease process. We have previously characterized the contributions to pathogenesis of the type-III-secreted proteins ExoS, ExoT and ExoU when secreted individually. In this study, we extend our prior work to determine whether these proteins have greater than expected effects on virulence when secreted in combination. In vitro cytotoxicity and anti-internalization activities were not enhanced when effector proteins were secreted in combinations rather than alone. Likewise in a mouse model of pneumonia, bacterial burden in the lungs, dissemination and mortality attributable to ExoS, ExoT and ExoU were not synergistically increased when combinations of these effector proteins were secreted. Because of the absence of an appreciable synergistic increase in virulence when multiple effector proteins were secreted in combination, we conclude that any cooperation between ExoS, ExoT and ExoU does not translate into a synergistically significant enhancement of disease severity as measured by these assays. INTRODUCTIONAn emerging theme in bacterial type III secretion is that the multiple effector proteins transported by these systems cooperate to subvert specific host-cell processes, resulting in enhanced virulence. Each factor alone has a minor effect on the overall virulence process, but together they cooperate to dramatically enhance virulence. Often, individual effector proteins target different points within a single host-cell pathway to facilitate an essential step in pathogenesis. For example YopE, YopH, YopT and YopO, four type III effector proteins of Yersinia, impede neutrophil and macrophage phagocytosis by targeting the actin cytoskeleton of these cells in a coordinated manner (Cornelis, 2002). The net result is that Yersinia bacteria are able to persist in the presence of a robust host immune response. Similar cooperation occurs between Salmonella type III effector proteins to orchestrate bacterial entry into intestinal epithelial cells, an essential step in the development of enteritis. A large number of type III effector proteins working in concert are required to achieve maximal levels of Salmonella bacterial uptake (Raffatellu et al., 2005). These proteins cause a complex series of actin cytoskeletal changes, which result in the transient formation of localized host-cell surface membrane ruffles that engulf the invading bacteria. SopB, SopE and SopE2 activate the Rho family GTPases Cdc42 and Rac1, thereby facilitating actin recruitment and polymerization at the site of bacterial entry (Hardt et al., 1998;Zhou et al., 2001). Two other effector proteins, SipA and SipC, further enhance actin nucleation, polymerization and cross-linking by directly binding to actin (Zhou et al., 1999a,b). O...

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Section: Cytotoxicitymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Shaver

Hauser

2006

Microbiology

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“…The cytolytic phenotype associated with noninvasive strains results mainly from the action of the exoU gene product (Finck-Barbancon et al, 1997 ;Hauser et al, 1998). Although the factor(s) for the invasive phenotype is not clearly understood, Cowell et al (2000) have recently shown that both ExoS and ExoT have an invasioninhibitory effect on cytolytic P. aeruginosa strains. Despite extensive characterization of these factors including their abilities to cause morphological changes on various tissue culture cells (Finck-Barbancon et al, Hanahan (1983) …”

Section: Introductionmentioning

confidence: 99%

Pseudomonas aeruginosa mediated apoptosis requires the ADP-ribosylating activity of ExoS

et al. 2000

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Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Using a tissue culture system, invasive strains of P. aeruginosa were discovered to induce apoptosis at high frequency in HeLa and other epithelial and fibroblast cell lines. This apoptotic phenotype in the infected cells was determined by several criteria including (i) visual changes in cell morphology, (ii) induction of chromatin condensation and nuclear marginalization, (iii) the presence of a high percentage of cells with subG1 DNA content, and (iv) activation of caspase-3 activity. Induction of the type III secretion machinery, but not invasion of P. aeruginosa is required for induction of apoptosis. The apoptosis phenotype is independent of the cytoskeletal rearrangements that occur in the host cell early after infection. Mutants in P. aeruginosa exoS fail to induce apoptosis and complementation with wild-type exoS restored the apoptosis-inducing capacity, demonstrating that ExoS is the effector molecule. Analysis of exoS activity mutants shows that the ADP-ribosylating capacity of ExoS is essential for inducing the apoptotic pathway.

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“…Although the precise role of ExoS in P. aeruginosa virulence is not fully understood, the exoS gene is found in the majority of clinical isolates (Feltman et al, 2001) and there is a sixfold greater risk of mortality associated with the expression of type III effectors, including ExoS, in P. aeruginosa lower respiratory and systemic infections (Roy-Burman et al, 2001). In cell culture models of infection, ExoS has been implicated as an antiphagocytic or anti-invasive factor (Frithz-Lindsten et al, 1997;Cowell et al, 2000). In analyses of epithelial cells, bacterial translocation of ExoS has been associated with a general inactivation of cell function, including inhibition of DNA synthesis, loss of re-adherence and cytoskeletal alterations .…”

Section: Introductionmentioning

confidence: 99%

Cell line differences in bacterially translocated ExoS ADP-ribosyltransferase substrate specificity

et al. 2003

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Exoenzyme S (ExoS) is an ADP-ribosyltransferase (ADPRT) directly translocated into eukaryotic cells by the type III secretory (TTS) process of Pseudomonas aeruginosa. Comparisons of the functional effects of ExoS on human epithelial and murine fibroblastic cells showed that human epithelial cells exhibited an overall increased sensitivity to the effects of bacterially translocated ExoS on cell proliferation, morphology and re-adherence. ExoS was also found to ADP-ribosylate a greater number of low-molecular-mass G (LMMG) proteins in human epithelial cells, as compared to murine fibroblasts. Examination of the cellular mechanism for differences in ExoS ADPRT substrate modification found that the more restricted pattern of substrate modification in murine fibroblasts was not linked to the efficiency of bacterial adherence nor to the efficiency of ExoS internalization by the TTS process. In exploring the cellular nature of patterns of substrate modification, more extensive substrate modification was detected in human and simian cell lines, while rodent cell lines, including rat, mouse and hamster lines, consistently exhibited the more limited pattern of LMMG protein ADP-ribosylation. Patterns of substrate modification were not altered by cellular transformation and occurred independently of cell type. These studies suggest that eukaryotic cell properties, as recognized through studies of cells of different animal origins, affect the substrate targeting of ExoS ADPRT activity, and that this in turn can influence the severity of effects of ExoS on host-cell function.

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ExoT of Cytotoxic Pseudomonas aeruginosa Prevents Uptake by Corneal Epithelial Cells

Cited by 97 publications

References 19 publications

Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Interactions between effector proteins of the Pseudomonas aeruginosa type III secretion system do not significantly affect several measures of disease severity in mammals

Pseudomonas aeruginosa mediated apoptosis requires the ADP-ribosylating activity of ExoS

Cell line differences in bacterially translocated ExoS ADP-ribosyltransferase substrate specificity

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