The amino‐terminal domain of <i>Pseudomonas aeruginosa</i> ExoS disrupts actin filaments via small‐molecular‐weight GTP‐binding proteins

Pederson, Kristin J.; Vallis, Amy J.; Aktories, Klaus; Frank, Dara W.; Barbieri, Joseph T.

doi:10.1046/j.1365-2958.1999.01359.x

Cited by 136 publications

(131 citation statements)

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“…The absence of significant synergistic interactions between ExoS, ExoT and ExoU indicates that the pathogenic effects of these proteins can be adequately characterized by using a reductionist approach of studying each when expressed individually. Thus, these findings validate the results of earlier reports looking at effector proteins expressed alone (Finck-Barbançon & Frank, 2001;Henriksson et al, 2002;Pederson & Barbieri, 1998;Pederson et al, 1999;Phillips et al, 2003;Sato & Frank, 2004).…”

Section: Discussionsupporting

confidence: 90%

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: Discussionsupporting

confidence: 90%

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 homology is limited to the GTPase-activating-protein (GAP) binding domain, which mediates actin disruption, and is not found in the ADP-ribosylating domain (Frithz-Lindsten et al, 1997 ;Pederson et al, 1999). In addition, SptP has a tyrosine phosphatase domain at the C terminus while YopE has none.…”

Section: Discussionmentioning

confidence: 99%

“…Similar to these examples, our data suggest P. aeruginosa also induces apoptosis by one of its type III secreted proteins. ExoS possesses two functional domains with its N-terminal 234 amino acids capable of causing cell rounding and actin rearrangement in a Rhodependent manner whereas the C-terminal 221 residues have a FAS-dependent ADP-ribosyltransferase activity (Pederson et al, 1999). In addition, it has been demonstrated that exposure to ExoS-producing bacteria, but not non-producing mutants, caused cultured mammalian cells to round up and prevented entry into S phase (McGuffie et al, 1998).…”

Section: Discussionmentioning

confidence: 99%

“…The N-terminal domain is capable of disrupting the actin cytoskeleton and causing cell rounding through interaction with the host Rho factor, while its C-terminal domain has an ADP-ribosylating activity that is capable of modifying the eukaryotic Ras protein (Pederson et al, 1999). A mutant form of ExoS, ExoSE381A, has a glutamic acid residue changed into alanine at position 381, eliminating the ADP-ribosylase activity (Liu et al, 1996).…”

Section: Adp-ribosylating Activity Of Exos Is Essential For Apoptosismentioning

confidence: 99%

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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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“…Similarly, plant pathogens utilize TTSS to cause disease in susceptible plants and to trigger a hypersensitive response in resistant plants (Hueck, 1998;Muller et al, 2001 (Yahr et al, 1995;Frank, 1997). Upon activation, the type III secretion apparatus translocates effector molecules into the cytoplasm of host cells, resulting in cell rounding and lifting and cell death by necrosis or apoptosis (Finck-Barbancon et al, 1997;Pederson et al, 1999;Kaufman et al, 2000). There are four known effector molecules, including ExoS and ExoT, two homologous toxins with both ADP-ribosyltransferase and GTPaseactivating protein activities, an acute cytotoxin, ExoU, with lipase activity, and an adenylate cyclase, ExoY (Yahr et al, 1996(Yahr et al, , 1998Finck-Barbancon et al, 1997;Hauser et al, 1998;Sato et al, 2005).…”

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confidence: 99%

Factors triggering type III secretion in Pseudomonas aeruginosa

et al. 2005

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The type III secretion system of Pseudomonas aeruginosa is tightly regulated by various environmental signals, such as low calcium and contact with the host cell. However, the exact signals triggering type III secretion are unknown. The present study describes the finding that secretion of P. aeruginosa type III effector molecules requires protein factors from serum and L broth, designated type III secretion factors (TSFs), in addition to the low-calcium environment. In the absence of TSF or calcium chelator EGTA, basal levels of type III effector molecules are accumulated intracellularly. Addition of TSF and EGTA together effectively triggers the secretion of pre-existing effector molecules in a short time, even before the active expression of type III genes; thus, active type III gene expression does not seem to be a prerequisite for type III secretion. A search for TSF molecules in serum and L broth resulted in the identification of albumin and casein as the functional TSF molecules. Although there is no clear sequence similarity between albumin and casein, both proteins are known to have a low-affinity, high-capacity calcium-binding property. Tests of well-studied calcium-binding proteins seemed to indicate that low-affinity calcium-binding proteins have TSF activity, although the requirement of low-affinity calcium-binding ability for the TSF activity is not clear. P. aeruginosa seems to have evolved a sensing mechanism to detect target cells for type III injection through host-derived proteins in combination with a low-calcium signal. Disruption of the bacterial ability to sense low calcium or TSF might be a valid avenue to the effective control of this bacterial pathogen. INTRODUCTIONThe remarkable ability of Pseudomonas aeruginosa to adapt to and thrive in a wide variety of environments contributes significantly to the ability of this bacterium to cause various human infections (Bodey et al., 1983;Holder, 1993;Pier, 2002). Unlike most human pathogens possessing highly restricted host ranges, P. aeruginosa is pathogenic not only to humans, but also to Caenorhabditis elegans, Drosophila and Arabidopsis thaliana (Rahme et al., 1995;D'Argenio et al., 2001;Aballay & Ausubel, 2002). This broad host range is contributed in part by the numerous virulence factors encoded by P. aeruginosa, including exotoxin A, phospholipase C, alkaline protease, elastase, alginate, pyocyanin, pili and non-pilus adhesins (Ramphal et al., 1991;Deretic et al., 1995;Lory & Strom, 1997;Vasil & Ochsner, 1999). P. aeruginosa, like many other Gram-negative animal and plant pathogens, also encodes a type III secretion machinery, where over 30 proteins assemble into a complex designed to deliver effector molecules directly into the cytoplasmic compartment of eukaryotic cells (Yahr et al., 1995;Frank, 1997). Injection of the bacterial effector molecules into the host cells results in various physiological changes, all of which seem to confer a survival advantage on the bacterial pathogen within the host environment (Hueck, 1998;Muller et al...

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The amino‐terminal domain of Pseudomonas aeruginosa ExoS disrupts actin filaments via small‐molecular‐weight GTP‐binding proteins

Abstract: Summary Pseudomonas aeruginosa delivers exoenzyme S (ExoS

Cited by 136 publications

References 30 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

Factors triggering type III secretion in Pseudomonas aeruginosa

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