Pseudomonas aeruginosa Cytotoxins: Comparison
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Please note this is a comparison between Version 2 by Jason Zhu and Version 1 by Sasha H. Shafikhani.

Pseudomonas aeruginosa is one of the most virulent opportunistic Gram-negative bacterial pathogens in humans. It causes many acute and chronic infections with morbidity and mortality rates as high as 40%. P. aeruginosa owes its pathogenic versatility to a large arsenal of cell-associated and secreted virulence factors which enable this pathogen to colonize various niches within hosts and protect it from host innate immune defenses. Induction of cytotoxicity in target host cells is a major virulence strategy for P. aeruginosa during the course of infection. P. aeruginosa has invested heavily in this strategy, as manifested by a plethora of cytotoxins that can induce various forms of cell death in target host cells.

  • Pseudomonas aeruginosa
  • infection
  • virulence factors
  • cytotoxins

1. Apoptosis-Inducing Cytotoxins in Pseudomonas aeruginosa

1.1. Toxin A (ToxA)

Toxin A (ToxA)–A.K.A., Exotoxin A (ExoA), or Pseudomonas Exotoxin (PE)—is an AB toxin secreted by the T2SS [140,141][1][2]. AB toxins are composed of A and B components where the A component encodes the active enzymatic domain and the B component is responsible for the transport of the A component across the cytoplasmic membrane of target host cells [142][3]. Once internalized in host cells, ToxA ADP-ribosylates eukaryotic elongation factor-2 (eEF-2) resulting in the inhibition of protein synthesis and causing apoptotic cell death [143][4]. ToxA-induced apoptosis exhibits features of both intrinsic and extrinsic apoptosis [144,145][5][6]. In mouse embryonic fibroblasts, ToxA induces intrinsic (mitochondrial) apoptosis manifested by rapid degradation of Mcl-1 pro-survival protein and loss of mitochondrial membrane potential [144][5]. ToxA-induced apoptosis in this cell line was shown to be dependent on BAK (not BAX) oligomerization in the mitochondrial outer membrane, and ToxA-induced apoptosis was completely abolished in cells where Mcl-1 or Bcl-XL were overexpressed [144][5]. In human mast cells, ToxA induces extrinsic apoptosis [145][6]. ToxA-intoxicated mast cells manifest extrinsic apoptosis features including activation of initiator Caspase-8 and down-regulation of FLIPs (FLICE-like inhibitory proteins) [145][6]. Moreover, ToxA-induced apoptosis in this cell line was shown to be dependent on Caspase-8 and Caspase-3 [145][6]. ToxA deficient strains were shown to be significantly less virulent than the wild-type strain in a mouse model of infection [146][7]. Although ToxA-induced apoptosis would be expected to be anti-inflammatory, ToxA impacts on immune responses have not been directly investigated. In one study involving the keratitis model of infection, it was shown that ToxA deficient mutant bacteria were rapidly cleared from the eye, with a reduced sign of inflammation at the site of infection [147][8]. Whether reduced inflammatory responses in the eye were due to reduced bacterial burden or the absence of ToxA remains unknown. Due to its potent cytotoxicity, ToxA has also been extensively evaluated as a potential anti-cancer immunotoxin therapy [148,149][9][10].

1.2. N-3-Oxododecanoyl Homoserine Lactone (C12-HSL)

N-3-oxododecanoyl homoserine lactone (C12-HSL) is a pheromone that functions as the autoinducer for the Las quorum-sensing in P. aeruginosa [150][11]. In addition to its role in the Las quorum-sensing, C12-HSL has been shown to induce various forms of apoptosis, depending on the cell line studied. For example, exposure to C12-HSL has been shown to result in the activation of initiator Caspase-8 and the effector Caspase-3 in macrophages and neutrophils [151][12]. In Jurkat T lymphocytes, C12-HSL causes mitochondrial outer membrane damage leading to intrinsic (mitochondrial) apoptosis, mediated by the initiator Caspase-9 [152][13]. Overexpression of mitochondrial membrane stabilizer Bcl-2 completely abrogated C12-HSL-induced apoptosis in Jurkat T lymphocytes [152][13]. C12-HSL has also been shown to induce intrinsic apoptosis by downregulating the STAT3 survival/proliferation pathway in breast carcinoma cells [153][14]. STAT3 is a known anti-apoptosis transcription factor that protects against intrinsic apoptosis by increasing the expression of anti-apoptotic proteins (i.e., Bcl-2 and Bcl-xL) which stabilize the mitochondrial outer membrane [154][15]. Similarly, C12-HSL causes mitochondrial dysfunction and induces intrinsic apoptosis by attenuating the expression of PGC-1α and its downstream effector BEAS-2B in primary lung epithelial cells [155][16]. PGC-1α is a master regulator of mitochondrial biogenesis and cellular respiration [156][17]. Yet, in airway epithelial cells, exposure to C12-HSL has been shown to lead to both intrinsic apoptosis—manifested by cytochrome c release and Caspase-9 activation—and extrinsic apoptosis, as shown by Caspase-8 activation [157][18]. Interestingly, N-butyryl-L-homoserine lactone (C4-HSL), (a closely related autoinducer that activates the Rhl quorum sensing in P. aeruginosa [150][11]), lacks the ability to induce apoptosis likely because of its relatively shorter fatty acid chain [151,152][12][13]. Interestingly, at sub-lethal doses C12-HSL has been shown to dampen NF-κB activation and suppress TNF-α and IL-12 pro-inflammatory cytokine expression in the RAW264.7 mouse macrophage cell line by triggering the unfolded protein response (UPR) [158][19]. In contrast, C12-HSL has also been shown to induce IL-8 pro-inflammatory cytokine production in human epithelial and fibroblast cells through the activation of NF-κB and AP-2 [159][20]. Moreover, C12-HSL injection into the skin of mice led to the production of inflammatory mediators (IL-1α, IL-6, and MIP-2) in vivo [160][21].

1.3. Azurin

Azurin is a cupredoxin-type electron transfer protein that is involved in electron transfer during denitrification in P. aeruginosa [161][22]. Azurin has also been shown to induce apoptosis in J774 macrophages and many cancer cell lines by stabilizing tumor suppressor p53 and enhancing its activity, which in turn leads to increased levels of ROS and cell demise [162,163,164][23][24][25]. Notably, P53 has been shown to induce intrinsic apoptosis, involving mitochondrial outer membrane damage, cytochrome c release into the cytosol, and activation of Caspase-9 through the Apoptosome [165][26]. It also targets the non-receptor tyrosine kinases (NRTKs) signaling network [166][27]. Azurin expression has been shown to be elevated in P. aeruginosa isolates of the lung in CF patients [167][28]. This finding likely reflects the need for azurin’s redox function in sustaining P. aeruginosa within the anaerobic or microaerobic environment in CF airways [167,168][28][29]. Whether azurin’s function as a cytotoxin plays any physiological role for P. aeruginosa in vivo remains to be determined.

1.4. Pyocyanin

Pyocyanin is another important virulence factor secreted by the T2SS [169,170,171][30][31][32]. Pyocyanin is a water-soluble blue–green, non-fluorescent phenazine-derived pigment metabolite that is capable of oxidizing and reducing molecules and generating reactive oxygen species (ROS) [172,173][33][34]. In the environment, pyocyanin has been shown to have bactericidal activity against many bacteria, particularly Gram-positive bacteria such as Staphylococcus aureus [174][35]. The mechanism underlying pyocyanin-induced cytotoxicity in S. aureus was shown to involve ROS production [175][36]. Pyocyanin has also been shown to induce apoptosis in neutrophils by mitochondrial damage and increased ROS [176,177,178,179][37][38][39][40]. Pyocyanin also impacts immune responses in the host. In mammalian hosts, pyocyanin exposure leads to increased IL-8 via activation of MAPK and NF-kB pathways [180,181][41][42]. Despite this pro-inflammatory effect, which could be counterproductive to pathogenicity, pyocyanin plays an important virulence function for P. aeruginosa in vivo. Pyocyanin has been shown to be crucial for P. aeruginosa in establishing chronic infection and in inducing lung damage in mice [182,183][43][44]. Consistent with these reports, pyocyanin is detected in large quantities in the sputum of cystic fibrosis (CF) patients infected with P. aeruginosa, enough to inhibit ciliary beating and cause toxicity in the respiratory epithelium in vitro [184][45].
There are also other apoptosis-inducing cytotoxins that are discussed below under the categories of membrane-associated cytotoxins and Type III Secretion System (T3SS or TTSS) Exotoxins.

2. Membrane-Associated Cytotoxins

2.1. Lipopolysaccharide (LPS)

Lipopolysaccharide (LPS) is another cell-bound major virulence factor of P. aeruginosa [185,186][46][47]. LPS is found in the outer membrane of the bacterium and is composed of a hydrophobic domain called Lipid A which is anchored onto a core polysaccharide and a hydrophilic tail made of O-specific polysaccharide [185][46]. The O-specific polysaccharide is variable and is useful for serotyping strains of P. aeruginosa [187][48]. LPS is an integral part of the outer membrane of Gram-negative bacteria, providing structural support for the bacteria, serving as an adhesin, and well as protection from the environment [185,188][46][49]. LPS has also been shown to contribute to P. aeruginosa pathogenesis by facilitating host cell adhesion through binding to the ganglioside asialo-GM1 found on epithelial cells [189][50]. LPS recognition by the NLRC4 (a.k.a. IPAF) canonical or Caspase-11 non-canonical inflammasomes has also been shown to result in Caspase-1 or Caspase-11-dependent pyroptotic cell death [190,191][51][52]. In addition, LPS has also been shown to induce apoptosis in A549-transformed lung cells by enhancing ROS production via downregulation of the anti-apoptotic Sirtuin1 (SIRT1) [192][53].
As for its impact on inflammatory responses, LPS is massively immunogenic and can trigger inflammatory responses through TLR4 recognition [193][54]. LPS-triggered TLR4 signaling results in the production of pro-inflammatory cytokines which also contribute to the pathology associated with both sepsis and bacteremia [194,195,196][55][56][57]. In addition, cytoplasmic recognition of LPS can trigger Caspase-11-dependent pyroptotic cell death which is highly pro-inflammatory in nature [197][58]. Given the immunogenicity of LPS, it has been a target for developing anti P. aeruginosa vaccines; however, there has been limited success thus far due to the variability of the O-specific polysaccharide [198][59].

2.2. Flagella

Flagella are membrane associated appendages that perform many virulence functions for P. aeruginosa. Flagella mediate adhesion to biotic and abiotic surfaces [199[60][61],200], mediate swimming motility [201][62] and function in biofilm formation and maturation [202,203][63][64]. Numerous animal models have shown that motility enhances bacterial dissemination and virulence in the host. For example, in neonate mice, flagellation has been demonstrated to enhance virulence in bacteremia and pneumonia models of infection [204][65]. Similarly, flagellated strains have been shown to cause more damage and exacerbate burn wounds than non-flagellated isogenic strains [205,206][66][67]. In addition, P. aeruginosa flagellin recognition by NLRC4/IPAF inflammasome can trigger Caspas-1 dependent pyroptosis [190][51].
Having flagella is beneficial in increasing dissemination and enhancing infection; however, flagella can also be a source of vulnerability for P. aeruginosa, as monomeric flagellin detection by Toll-like receptor 5 (TLR5) has been shown to trigger robust inflammatory responses in various immune leukocytes, resulting in diminished bacterial survival in an acute lung infection model [207,208][68][69]. In addition, cytoplasmic flagellin recognition by Naip5 and Naip6 [209,210][70][71] can also lead to activation of NLRC4 canonical inflammasome which further amplifies inflammatory responses against P. aeruginosa infection [211][72]. As a result, P. aeruginosa strains often downregulate the expression of flagellar components after the establishment of infection and during chronic infection to evade host innate immune responses [212,213,214][73][74][75]. Downregulation of immunogenic virulence factors and/or structures (i.e, flagellum) is a common theme among P. aeruginosa infections, especially in CF patients, where expression of virulence factors could hinder bacterial survival rather than aid in its dissemination [215,216][76][77].

2.3. Porins

P. aeruginosa also possesses over 20 porins in its outer membrane that serve many crucial physiological functions essential for virulence including nutrient uptake, adhesion, decreasing permeability to antibiotics, and signaling ([217,218][78][79]). For example, OprF, one of the major porins in the P. aeruginosa outer membrane, has been shown to be required for full virulence of P. aeruginosa [219][80]. Deletion in the oprF gene impairs many virulence-associated functions including colonization, quorum sensing (QS), and secretion through the T3SS [219][80]. In addition to these virulence functions, purified porins have also been shown to induce intrinsic apoptosis in epithelial target host cells, as manifested by reductions in the bcl-2 gene expression [220][81].
As crucial as they are to the pathophysiology of P. aeruginosa, porin recognition by pattern recognition receptors (PRRs) can also lead to the production of pro-inflammatory cytokines, inflammatory responses, and complement activation, thus interfering with P. aeruginosa’s ability to colonize and cause infection [221,222][82][83]. Interestingly, adoptive transfer of dendritic cells immunized with wild-type or recombinant OprF ex vivo has been shown to be protective against P. aeruginosa lung infection in mice [223][84].

2.4. Rhamnolipids

P. aeruginosa can produce about 30 different congeners of surface-active rhamnolipids, which are glycolipid biosurfactants composed of mono- or di-rhamnose linked to 3-hydroxy-fatty acids of different lengths [224,225,226][85][86][87]. Rhamnolipids have been detected in large quantities (range: 8–65 µg/mL) in the sputum of CF patients, and their presence has been associated with CF lung pathology [227,228][88][89]. Because of their high potential for use in various biotechnological applications P. aeruginosa rhamnolipids have been investigated extensively [226,229,230][87][90][91].
Rhamnolipids play several important virulence functions for P. aeruginosa. First, rhamnolipid-expressing P. aeruginosa strains, as well as purified rhamnolipids, have been shown to compromise the barrier function of human respiratory epithelium by disrupting the tight junctions, thus facilitating the paracellular invasion by P. aeruginosa [231][92]. Second, exposure to rhamnolipids has been shown to interfere with ciliary beating and mucociliary clearance of P. aeruginosa in tracheal rings of guinea pig animal models [227][88]. Third, rhamnolipids have also been shown to aid P. aeruginosa in swarming motility [232][93]; in turn, swarming motility has been demonstrated to regulate the expression of virulence genes and antibiotic resistance in P. aeruginosa [233][94]. Forth, rhamnolipids have also been demonstrated to play a role in structural biofilm development and in maintaining channels between multicellular structures in biofilms [234,235][95][96]. Fifth, rhamnolipids appear to modulate P. aeruginosa membrane composition by reducing LPS and porin membrane proteins [236][97], thus potentially contributing to their well-known intrinsic resistance towards antibiotics [237][98]. Rhamnolipids can also induce cytotoxicity in target epithelial cells. MCF7 breast cancer cells intoxicated with mono- and di-rhamnolipids from P. aeruginosa undergo apoptotic cell death, manifested by nuclear condensation and fragmentation, p53 activation, mitochondrial damage, and appearance of sub-G1 (apoptotic) subpopulations [238,239][99][100]. Rhamnolipids have been shown to cause potent necrotic cell death in human and murine neutrophils and macrophages [240,241][101][102].
As is the case for many virulence factors and virulence structures in P. aeruginosa, rhamnolipids can both trigger and combat host innate immune responses. For instance, rhamnolipids are required for the expression of flagellin-induced psoriasin (S100A7) antimicrobial peptides and chemokines in human skin [242][103]. In this context, the production of rhamnolipids may be detrimental to P. aeruginosa pathogenesis in vivo. In contrast, rhamnolipids have been shown to cause potent necrotic cell death in humans and murine neutrophils and macrophages, therefore protecting P. aeruginosa against clearance in the lungs [240,241][101][102].

3. Type III Secretion System (T3SS or TTSS) Exotoxins

3.1. T3SS Apparatus

A growing body of data has demonstrated that insertion of the T3SS apparatus of Gram-negative pathogens, including P. aeruginosa in the host plasma membrane results in cell death [256,257,258][104][105][106]. It is assumed that the damage caused by the T3SS pore-forming activity is the cause of passive necrotic cell death due to trauma and membrane leakage. However, the T3SS-induced necrosis has been shown to be completely blocked by ExoT [259][107], suggesting that the T3SS-induced cell death is a form of programmed cell death and not accidental necrosis, occurring as a consequence of T3SS-induced massive trauma to the membrane. Similarly, the T3SS in Yersinia has also been shown to cause pore formation and induce cytotoxicity in target host cells and the Yersinia T3SS-induced cytotoxicity was also shown to be blocked by YopE effector toxin [257][105], which is a homolog of the GAP domain of ExoT [260,261][108][109]. Two recent reports have indicated that the cell death induced by the T3SS of P. aeruginosa is pyroptosis [262,263][110][111]. As discussed above, pyroptosis is mediated by Caspases 1 and 11 (in mice) and 4 and 5 (in human), which are inhibited by the pancaspase inhibitor z-VAD. However, the T3SS-induced cytotoxicity was not appreciably affected by z-VAD [259][107], suggesting that T3SS-induced cytotoxicity is not pyroptosis. Given that the T3SS-induced cytotoxicity is completely abrogated by a toxin (ExoT) that induces potent apoptosis (discussed below) suggests that the T3SS-induced cytotoxicity is necroptosis because it is prevented under apoptotic conditions, as discussed above. Whether necroptosis and/or pyroptosis is the underlying mechanism of T3SS-induced cytotoxicity remains to be further investigated.
As for the impact of the T3SS on the host’s innate immune responses, this virulence structure is perhaps the most prominent trigger of inflammatory responses in the host during infection. Various inflammasome subtypes (e.g., NLRP3 and/or NLRC4) have been implicated in the recognition of and in responses to T3SS and P. aeruginosa infection, although NLRC4 canonical inflammasome appears to be the primary mode of T3SS recognition in BMDMs and in host tissues [19,190,264,265,266,267][51][112][113][114][115][116]. There also appears to be some contradictory reports regarding the impact of T3SS-triggered inflammatory responses on the outcome of infection, in that the same inflammasome (NLRC4) has been shown to be either crucial in P. aeruginosa clearance, thus benefiting the host; or paradoxically facilitating bacterial colonization and enhancing P. aeruginosa pathogenesis, thus benefiting the pathogen. For example, Franchi et al. demonstrated that recognition of T3SS-expressing P. aeruginosa by NLRC4 inflammasome triggers the production of IL-1β in intestinal phagocytes that are crucial in limiting P. aeruginosa gastric infections [268][117]. Similarly, NLRC4 was found to contribute to the recognition and clearance of T3SS-expressing P. aeruginosa in a wound model [19][112], and in a cystic fibrosis (CF) lung model of infection [269][118]. In contrast, Faur et al. demonstrated that Nlrc4-deficient mice showed enhanced bacterial clearance and decreased lung injury contributing to increased animal survival following pleural infection with a T3SS-expressing P. aeruginosa strain [270][119]. These reports suggest that specific organs and/or sites within a host may have evolved distinct mechanism(s) to detect and respond to T3SS and its effectors during P. aeruginosa infection.

3.2. ExoS

ExoS is a bifunctional protein consisting of an N-terminal GTPase Activating Protein (GAP) domain and a C-terminal ADP-ribosyltransferase (ADPRT) domain that is directly translocated into host cytoplasm through the T3SS [271][120] using SpcS chaperone protein [272][121]. Upstream of the GAP domain is a membrane localization domain (MLD) which targets the toxin to the mammalian cytoplasmic membrane [273][122]. Deletion of the MLD was found to not affect ExoS translocation; however, ADP-ribosylation of Ras, a known target of ExoS, was lost, thus demonstrating the importance of this sequence in mediating ExoS interaction with some of its targets [274][123].
The GAP domain of ExoS targets RhoA, Rac1, and CDC42 [275,276][124][125]. These small Ras-like GTPases are active when bound to GTP and inactive when bound to GDP [277][126]. ExoS inactivates RhoA, Rac1, and Cdc42 through allosteric interaction of a conserved arginine-finger in its GAP domain with the aforementioned GTPases, stimulating them to hydrolyze their bound GTP to GDP [275,276,277,278][124][125][126][127]. These small GTPases play important roles in coordinating and maintaining the actin cytoskeleton; thus, inactivating their signaling affects processes, such as cell migration and cell division and leads to cell rounding [279,280][128][129].
The ADPRT domain of ExoS has many targets in mammalian cells and requires the host 14-3-3 protein as the cofactor for its activity within host cells [254,281][130][131]. Targets include Ras, Rab and Rho family of proteins, as well as ezrin, radixin, meosin, vimentin, and cychlophilin A [282][132]. ADP ribosylation of these proteins by ExoS/ADPRT can lead to disruption of the cytoskeleton, endocytosis, and cell–cell binding, as well as inhibition of DNA synthesis and ultimately apoptotic cell death [279,282,283,284,285][128][132][133][134][135].
ExoS-intoxicated cells display signs of both Caspase-9 dependent intrinsic apoptosis and death receptor-mediated Caspase-8 dependent extrinsic apoptosis and both domains of ExoS contribute to ExoS-induced apoptosis [285,286,287,288,289][135][136][137][138][139]. Intoxication with ExoS/GAP has been shown to lead to enrichment of Bax and Bim into the mitochondrial outer membrane; disruption of mitochondrial membrane and release of cytochrome c into the cytosol; and activation of initiator Caspase-9 and executioner Caspase-3 caspases, leading to intrinsic/mitochondrial apoptosis in target host cell [285][135]. ExoS/ADPRT intoxication has been shown to result in the activation of initiator Caspase-8 in a manner that is dependent on the FADD adaptor protein, although ExoS-induced apoptosis was independent of Fas death receptor and Caspase-8 activities [290][140].
As for ExoS’s impact on host immune responses, ExoS has been shown to either dampen or trigger immune responses during infection. Intoxication of PBMCs, monocytes, and T cells, with ExoS, or recombinant ExoS (rExoS), strongly induced transcription of pro-inflammatory cytokines and chemokines, namely, IL-1α, IL-1β, IL-6, IL-8, MIP-1α, MIP-1β, MCP-1, RANTES [291,292][141][142]. The same group further showed that the induction of pro-inflammatory cytokines in ExoS-treated monocytes was due to the activation of TLR4 signaling by the ExoS/GAP domain and TLR2 signaling by ExoS/ADPRT domain activities [293][143]. Adding to the confusion in the field, Galle et al. reported that ExoS dampened Caspase-1 mediated IL-1β production in macrophages in a manner that was dependent on its ADPRT domain activity [294][144]. More recently, it was reported that ExoS had no impact on inflammatory responses in a wound model for infection with P. aeruginosa, although ExoS was required for full colonization of bacteria in the wound [19][112]. These discrepancies are likely due to technical differences in these studies.

3.3. ExoT

ExoT is the only T3SS effector that is expressed in all T3SS-expressing P. aeruginosa clinical strains [295][145], indicating a more fundamental role for this virulence factor in P. aeruginosa pathogenesis. The importance of ExoT to P. aeruginosa pathogenesis is further highlighted by the observation that it is actively targeted for degradation by host defenses in epithelial cells. ExoT becomes complexed with Crk and a Crk binding partner Cbl-b, an E3 ubiquitin ligase [296][146]. As a result, ExoT becomes polyubiquitinated and is targeted for proteasomal degradation. In their study, Balachandran et al. showed that mice lacking Cbl-b were significantly more susceptible to infection by strains expressing ExoT.
ExoT shares 76% protein homology with ExoS and possesses an N-terminal GAP domain and a C-terminal ADPRT domain [271,297,298][120][147][148]. ExoT also contains sequence homology with the MLD of ExoS, although this sequence has not been experimentally mapped [282][132]. Nevertheless, support for ExoT MLD is demonstrated by similar intracellular fractionation patterns between ExoS and ExoT [278][127] as well as experiments showing how ADPRT domain switching in ExoS and ExoT maintains their substrate specificities in both chimeras [299][149].
Similar to ExoS/GAP, the ExoT/GAP domain also targets RhoA, Rac1, and CDC42 [279,280][128][129]. In contrast to the ExoS/ADPRT domain, the ADPRT domain of ExoT targets only three non-overlapping substrates; namely, CrkI and CrklI isoforms of Crk adapter protein and phosphoglycerate kinase 1 (PGK1) glycolytic enzyme [300][150]. Similar to ExoS, the ADPRT domain of ExoT also requires the host 14-3-3 protein as the cofactor for its activity [254][130]. ExoT has been shown to inhibit bacterial phagocytosis by macrophages, cell migration, and cause cell rounding in a manner that is primarily dependent on its GAP domain activity, although the ADPRT domain also contributes [21,298,300,301,302][148][150][151][152][153]. ExoT also exerts potent anti-proliferative effects in its target host cells [303][154]. The GAP domain of ExoT has been shown to inhibit cell division in epithelial cells by inhibiting the early stage of cytokinesis at the cleavage furrowing step, likely through its inhibitory effect on RhoA; whereas the ADPRT domain blocks the late stage of cytokinesis at the abscission step by targeting CrkI [303][154]. In addition, both domains of ExoT have been shown to cause cell cycle arrest in G1 interphase in melanoma cells by dampening the expression of G1/S checkpoint proteins ERK1/2, cyclin D1, and cyclin E1 [304][155].
ExoT is also a potent inducer of apoptotic cell death in its target hosts and both domains contribute to this virulence activity [259,305][107][156]. The ExoT/ADPRT was shown to be necessary and sufficient to induce anoikis apoptosis by transforming Crk adaptor protein into a cytotoxin which interfered with the integrin survival signaling by destabilizing the focal adhesion sites through persistent activation of the anoikis mediator, p38β [306][157]. The ExoT/GAP was shown to be necessary and sufficient to induce intrinsic/mitochondrial apoptosis by activating the initiator Caspase-9 and the effector Caspase-3 through upregulation of the expression and subcellular mobilization of Bax, Bid, and Bim—pro-apoptotic Bcl2 family of proteins—into mitochondrial outer membrane [307][158]. Interestingly, the ExoT/ADPRT-induced anoikis apoptosis has faster kinetics occurring within 5.5 ± 1.3 h, whereas the ExoT/GAP-induced mitochondrial apoptosis shows slower kinetics occurring within 16.2 ± 1.3 h in intoxicated cells [306,307][157][158].
It is important to note that while pre-treatment with the pancaspase inhibitor z-VAD effectively protects eukaryotic cells from ExoT-induced apoptosis, it does not protect the host cells from ExoT-induced disruption of actin cytoskeleton [307][158], ExoT-induced focal adhesion site disassembly [306][157], or ExoT-mediated anti-proliferative effects on cytokinesis [303][154], or ExoT-mediated induction of G1 cell cycle arrest in target host cells [304][155], indicating that ExoT-induced apoptosis can be uncoupled from ExoT’s other virulence functions.
As for ExoT’s impact on host immune responses, Mohamed et al. recently demonstrated that ExoT inhibits IL-1β and IL-18 pro-inflammatory cytokines production in primary macrophages by inhibiting the phosphorylation cascade through Abl→PKCδ→NLRC4 by targeting CrkII, which they further showed to be required for Abl transactivation and NLRC4 canonical inflammasome activation in response to T3SS and P. aeruginosa infection [19][112]. They corroborated these in vitro data in an animal model of wound infection, showing that recognition of T3SS leads to the phosphorylation cascade through Abl→PKCδ→NLRC4, culminating in the activation of NLRC4 inflammasome in response to P. aeruginosa infection. Interestingly, they showed that in the wound infection model, ExoT was the primary anti-inflammatory agent for P. aeruginosa, and other T3SS effector proteins (ExoU and ExoS) had no impact on inflammatory responses in wound tissues [19][112].

3.4. ExoU

ExoU is a potent inducer of rapid necrotic cytotoxicity in target eukaryotic host cells [243,255,308,309][159][160][161][162]. ExoU has a patatin-like domain that contains phospholipase A2 activity and can target phospholipids, lysophospholipids, and neutral lipids [255,308,310][160][161][163]. ExoU utilizes the chaperone protein called SpcU for secretion through the T3SS [311][164]. ExoU also requires host DNAJC5 chaperone and ubiquitin as the cofactor for its activity within the target host cell [253,254,255,312,313,314][130][160][165][166][167][168]. The MLD (membrane localization domain) of ExoU has been mapped to residues 550–687 in its C-terminal domain [315][169]. This allows ExoU to target the plasma membrane where it can carry out its phospholipase activity [316][170].
The necrotic nature of ExoU-induced cytotoxicity would suggest a pro-inflammatory consequence for this toxin in the host environment. Consistent with this notion, excessive inflammatory responses due to ExoU-induced endothelial barrier disruption have been shown to culminate in the acute respiratory distress syndrome (ARDs) in a pneumonia animal model of infection [317][171]. Intriguingly, ExoU has also been shown to function as an anti-inflammatory agent for P. aeruginosa. In a pneumonia model of infection, ExoU was shown to create a localized immunosuppressed zone in the vicinity of bacteria by directly killing phagocytic leukocytes (neutrophils and macrophages), albeit there were more inflammatory mediators in the lungs of mice infected with ExoU-expressing P. aeruginosa strain [318,319][172][173]. In another report, ExoU was shown to dampen IL-1β pro-inflammatory cytokine production by inhibiting Caspase-1-dependent NLRC4 (a.k.a., IPAF) activation in macrophages [320][174]. In the same report, ExoU was shown to reduce serum IL-1β and enhance bacterial fitness in a systemic model of infection in mice. To add to the confusion, in a wound model of infection in mice, it was recently demonstrated that ExoU had no impact on pro-inflammatory cytokines production and inflammatory leukocyte responses in a murine wound model of infection [19][112].

3.5. ExoY

ExoY is an adenylyl and guanylyl cyclase that shares sequence homology with Bordetella pertussis CyaA and Bacillus anthracis edema factor [321,322][175][176]. In a recent study, ExoY was detected in 93% of clinical isolates in critically ill pneumonia patients who tested positive for P. aeruginosa, and its presence was associated with end-organ dysfunction in this patient cohort [323][177]. ExoY requires binding to filamentous actin (F-actin) for its activity [324][178]. The primary activity of ExoY on mammalian cells appears to be as an edema factor, increasing vascular permeability [322,325][176][179]. However, ExoY possesses other virulence activities including disruption of actin cytoskeleton [321[175][180],326], inhibition of phagocytic uptake by the host immune system [327][181], and inhibition of endothelial repair after injury [328][182]. ExoY drives vascular permeability through its adenylyl cyclase activity which causes Tau hyperphosphorylation and insolubility [322][176].
In one report, ExoY was also shown to induce cell lysis in Madin–Darby canine kidney (MDCK) epithelial cells, as determined by the release of lactate dehydrogenase (LDH) into the culture supernatant [329][183]. In another report, infection with ExoY-expressing P. aeruginosa was associated with increased apoptosis in the lung of infected mice [330][184]. However, in a recent report, ExoY was found to cause an accumulation of active Caspase-7 without causing cell death in pulmonary microvascular endothelial cells (PMVECs). Whether or not ExoY is a bona fide cytotoxin requires further investigation.
As for ExoY’s impact on host immune responses, Kloth et al. recently reported that infection with ExoY-expressing P. aeruginosa was associated with elevated levels of pro-inflammatory cytokines in the sera and the bronchoalveolar lavage fluids (BALFs) and increased infiltration of neutrophilic granulocytes in the perivascular space in an acute airway infection model in mice [330][184]. Interestingly, these effects were also observed when ExoY was catalytically inactive, suggesting that at least initial inflammatory responses to ExoY are independent of its catalytic activity. Since in these studies, the control infections with the ExoY-deficient and the T3SS mutant strains were not included, it remains unclear whether these pro-inflammatory responses in host tissue were directed at ExoY or whether they were in response to the functional T3SS which itself is a potent inducer of inflammatory responses [19][112].

References

  1. Allured, V.S.; Collier, R.J.; Carroll, S.F.; McKay, D.B. Structure of exotoxin A of Pseudomonas aeruginosa at 3.0-Angstrom resolution. Proc. Natl. Acad. Sci. USA 1986, 83, 1320–1324.
  2. Leppla, S.H. Large-scale purification and characterization of the exotoxin of Pseudomonas aeruginosa. Infect. Immun. 1976, 14, 1077–1086.
  3. Odumosu, O.; Nicholas, D.; Yano, H.; Langridge, W. AB toxins: A paradigm switch from deadly to desirable. Toxins 2010, 2, 1612–1645.
  4. Jørgensen, R.; Wang, Y.; Visschedyk, D.; Merrill, A.R. The nature and character of the transition state for the ADP-ribosyltransferase reaction. EMBO Rep. 2008, 9, 802–809.
  5. Du, X.; Youle, R.J.; FitzGerald, D.J.; Pastan, I. Pseudomonas Exotoxin A-mediated apoptosis is Bak dependent and preceded by the degradation of Mcl-1. Mol. Cell. Biol. 2010, 30, 3444–3452.
  6. Jenkins, C.E.; Swiatoniowski, A.; Issekutz, A.C.; Lin, T.-J. Pseudomonas aeruginosa exotoxin A induces human mast cell apoptosis by a caspase-8 and-3-dependent mechanism. JBC 2004, 279, 37201–37207.
  7. Miyazaki, S.; Matsumoto, T.; Tateda, K.; Ohno, A.; Yamaguchi, K. Role of exotoxin A in inducing severe Pseudomonas aeruginosa infections in mice. J. Med. Microbiol. 1995, 43, 169–175.
  8. Pillar, C.M.; Hobden, J.A. Pseudomonas aeruginosa exotoxin A and keratitis in mice. IOVS 2002, 43, 1437–1444.
  9. Pastan, I.; Beers, R.; Bera, T.K. Recombinant immunotoxins in the treatment of cancer. Methods Mol. Biol. 2004, 248, 503–518.
  10. Du, X.; Ho, M.; Pastan, I. New immunotoxins targeting CD123, a stem cell antigen on acute myeloid leukemia cells. J. Immunother. 2007, 30, 607–613.
  11. Duan, K.; Surette, M.G. Surette, Environmental regulation of Pseudomonas aeruginosa PAO1 Las and Rhl quorum-sensing systems. J. Bacteriol. 2007, 189, 4827–4836.
  12. Tateda, K.; Ishii, Y.; Horikawa, M.; Matsumoto, T.; Miyairi, S.; Pechere, J.C.; Standiford, T.J.; Ishiguro, M.; Yamaguchi, K. The Pseudomonas aeruginosa autoinducer N-3-oxododecanoyl homoserine lactone accelerates apoptosis in macrophages and neutrophils. Infect. Immun. 2003, 71, 5785–5793.
  13. Jacobi, C.A.; Schiffner, F.; Henkel, M.; Waibel, M.; Stork, B.; Daubrawa, M.; Eberl, L.; Gregor, M.; Wesselborg, S. Effects of bacterial N-acyl homoserine lactones on human Jurkat T lymphocytes-OdDHL induces apoptosis via the mitochondrial pathway. Int. J. Med. Microbiol. 2009, 299, 509–519.
  14. Li, L.; Hooi, D.; Chhabra, S.R.; Pritchard, D.; Shaw, P.E. Bacterial N-acylhomoserine lactone-induced apoptosis in breast carcinoma cells correlated with down-modulation of STAT3. Oncogene 2004, 23, 4894–4902.
  15. Bhardwaj, A.; Sethi, G.; Vadhan-Raj, S.; Bueso-Ramos, C.; Takada, Y.; Gaur, U.; Nair, A.S.; Shishodia, S.; Aggarwal, B.B. Resveratrol inhibits proliferation, induces apoptosis, and overcomes chemoresistance through down-regulation of STAT3 and nuclear factor-κB–regulated antiapoptotic and cell survival gene products in human multiple myeloma cells. Blood 2006, 109, 2293–2302.
  16. Maurice, N.M.; Bedi, B.; Yuan, Z.; Goldberg, J.B.; Koval, M.; Hart, C.M.; Sadikot, R.T. Pseudomonas aeruginosa induced host epithelial cell mitochondrial dysfunction. Sci. Rep. 2019, 9, 11929.
  17. Brown, G.C.; Murphy, M.P.; Jornayvaz, F.R.; Shulman, G.I. Regulation of mitochondrial biogenesis. Essays Biochem. 2010, 47, 69–84.
  18. Schwarzer, C.; Fu, Z.; Patanwala, M.; Hum, L.; Lopez-Guzman, M.; Illek, B.; Kong, W.; Lynch, S.V.; Machen, T.E. Pseudomonas aeruginosa biofilm-associated homoserine lactone C12 rapidly activates apoptosis in airway epithelia. Cell Microbiol. 2012, 14, 698–709.
  19. Zhang, J.; Gong, F.; Li, L.; Zhao, M.; Song, J. Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl) homoserine lactone attenuates lipopolysaccharide-induced inflammation by activating the unfolded protein response. Biomed. Rep. 2014, 2, 233–238.
  20. Smith, R.S.; Fedyk, E.R.; Springer, T.A.; Mukaida, N.; Iglewski, B.H.; Phipps, R.P. IL-8 production in human lung fibroblasts and epithelial cells activated by the Pseudomonas autoinducer N-3-oxododecanoyl homoserine lactone is transcriptionally regulated by NF-κB and activator protein-2. J. Immunol. 2001, 167, 366–374.
  21. Smith, R.S.; Harris, S.G.; Phipps, R.; Iglewski, B. The Pseudomonas aeruginosa quorum-sensing molecule N-(3-oxododecanoyl) homoserine lactone contributes to virulence and induces inflammation in vivo. J. Bacteriol. 2002, 184, 1132–1139.
  22. Vijgenboom, E.; Busch, J.E.; Canters, G.W. In vivo studies disprove an obligatory role of azurin in denitrification in Pseudomonas aeruginosa and show that azu expression is under control of RpoS and ANR. Microbiology 1997, 143, 2853–2863.
  23. Yamada, T.; Goto, M.; Punj, V.; Zaborina, O.; Kimbara, K.; Das Gupta, T.K.; Chakrabarty, A.M. The bacterial redox protein azurin induces apoptosis in J774 macrophages through complex formation and stabilization of the tumor suppressor protein p53. Infect. Immun. 2002, 70, 7054–7062.
  24. Punj, V.; Bhattacharyya, S.; Saint-Dic, D.; Vasu, C.; Cunningham, E.A.; Graves, J.; Yamada, T.; Constantinou, A.I.; Christov, K.; White, B.; et al. Bacterial cupredoxin azurin as an inducer of apoptosis and regression in human breast cancer. Oncogene 2004, 23, 2367–2378.
  25. Yang, D.-S.; Miao, X.-D.; Ye, Z.-M.; Feng, J.; Xu, R.-Z.; Huang, X.; Ge, F.-F. Bacterial redox protein azurin induce apoptosis in human osteosarcoma U2OS cells. Pharmacol. Res. 2005, 52, 413–421.
  26. Schuler, M.; Green, D.R. Mechanisms of p53-dependent apoptosis. Biochem. Soc. Trans. 2001, 29, 684–688.
  27. Gao, M.; Zhou, J.; Su, Z.; Huang, Y. Bacterial cupredoxin azurin hijacks cellular signaling networks: Protein–protein interactions and cancer therapy. Protein Sci. 2017, 26, 2334–2341.
  28. Hogardt, M.; Heesemann, J. Adaptation of Pseudomonas aeruginosa during persistence in the cystic fibrosis lung. Int. J. Med. Microbiol. 2010, 300, 557–562.
  29. Yoon, S.S.; Hennigan, R.F.; Hilliard, G.M.; Ochsner, U.A.; Parvatiyar, K.; Kamani, M.C.; Allen, H.L.; DeKievit, T.R.; Gardner, P.R.; Schwab, U.; et al. Pseudomonas aeruginosa anaerobic respiration in biofilms: Relationships to cystic fibrosis pathogenesis. Dev. Cell 2002, 3, 593–603.
  30. Turner, J.M.; Messenger, A. Occurrence, biochemistry and physiology of phenazine pigment production. In Advances in Microbial Physiology; Elsevier: Amsterdam, The Netherlands, 1986; pp. 211–275.
  31. Lau, G.W.; Hassett, D.J.; Ran, H.; Kong, F. The role of pyocyanin in Pseudomonas aeruginosa infection. Trends Mol. Med. 2004, 10, 599–606.
  32. Meyer, J.M.; Neely, A.; Stintzi, A.; Georges, C.; A Holder, I. Pyoverdin is essential for virulence of Pseudomonas aeruginosa. Infect. Immun. 1996, 64, 518–523.
  33. Hall, S.; McDermott, C.; Anoopkumar-Dukie, S.; McFarland, A.J.; Forbes, A.; Perkins, A.V.; Davey, A.K.; Chess-Williams, R.; Kiefel, M.J.; Arora, D.; et al. Cellular effects of pyocyanin, a secreted virulence factor of Pseudomonas aeruginosa. Toxins 2016, 8, 236.
  34. Ran, H.; Hassett, D.J.; Lau, G.W. Human targets of Pseudomonas aeruginosa pyocyanin. Proc. Natl. Acad. Sci. USA 2003, 100, 14315–14320.
  35. Baron, S.S.; Rowe, J.J. Antibiotic action of pyocyanin. Antimicrob. Agents Chemother. 1981, 20, 814–820.
  36. Noto, M.J.; Burns, W.J.; Beavers, W.N.; Skaar, E.P. Mechanisms of pyocyanin toxicity and genetic determinants of resistance in Staphylococcus aureus. J. Bacteriol. 2017, 199, e00221-17.
  37. Usher, L.R.; Lawson, R.A.; Geary, I.; Taylor, C.J.; Bingle, C.D.; Taylor, G.W.; Whyte, M.K.B. Induction of neutrophil apoptosis by the Pseudomonas aeruginosa exotoxin pyocyanin: A potential mechanism of persistent infection. J. Immunol. 2002, 168, 1861–1868.
  38. Leidal, K.G.; Munson, K.L.; Denning, G.M. Small molecular weight secretory factors from Pseudomonas aeruginosa have opposite effects on IL-8 and RANTES expression by human airway epithelial cells. Am. J. Respir. Cell Mol. 2001, 25, 186–195.
  39. Denning, G.M.; A Wollenweber, L.; A Railsback, M.; Cox, C.D.; Stoll, L.L.; Britigan, E.B. Pseudomonas pyocyanin increases interleukin-8 expression by human airway epithelial cells. Infect. Immun. 1998, 66, 5777–5784.
  40. Manago, A.; Becker, K.A.; Carpinteiro, A.; Wilker, B.; Soddemann, M.; Seitz, A.P.; Edwards, M.J.; Grassmé, H.; Szabo, I.; Gulbins, E. Pseudomonas aeruginosa pyocyanin induces neutrophil death via mitochondrial reactive oxygen species and mitochondrial acid sphingomyelinase. Antioxid. Redox Signal 2015, 22, 1097–1110.
  41. Dias, S.; Boyd, R.; Balkwill, F. IL-12 regulates VEGF and MMPs in a murine breast cancer model. Int. J. Cancer 1998, 78, 361–365.
  42. Chai, W.; Zhang, J.; Duan, Y.; Pan, D.; Liu, W.; Li, Y.; Yan, X.; Chen, B. Pseudomonas pyocyanin stimulates IL-8 expression through MAPK and NF-κB pathways in differentiated U937 cells. BMC Microbiol. 2014, 14, 26.
  43. Lau, G.W.; Ran, H.; Kong, F.; Hassett, D.J.; Mavrodi, D. Pseudomonas aeruginosa pyocyanin is critical for lung infection in mice. Infect. Immun. 2004, 72, 4275–4278.
  44. Caldwell, C.C.; Chen, Y.; Goetzmann, H.S.; Hao, Y.; Borchers, M.T.; Hassett, D.J.; Young, L.R.; Mavrodi, D.; Thomashow, L.; Lau, G.W. Pseudomonas aeruginosa exotoxin pyocyanin causes cystic fibrosis airway pathogenesis. AJP 2009, 175, 2473–2488.
  45. Wilson, R.; Sykes, D.A.; Watson, D.; Rutman, A.; Taylor, G.W.; Cole, P. Measurement of Pseudomonas aeruginosa phenazine pigments in sputum and assessment of their contribution to sputum sol toxicity for respiratory epithelium. Infect. Immun. 1988, 56, 2515–2517.
  46. Pier, G.B. Pseudomonas aeruginosa lipopolysaccharide: A major virulence factor, initiator of inflammation and target for effective immunity. Int. J. Med. Microbiol. 2007, 297, 277–295.
  47. Cryz, S.J.; Pitt, T.L.; Fürer, E.; Germanier, R. Role of lipopolysaccharide in virulence of Pseudomonas aeruginosa. Infect. Immun. 1984, 44, 508–513.
  48. Kipnis, E.; Sawa, T.; Wiener-Kronish, J. Targeting mechanisms of Pseudomonas aeruginosa pathogenesis. Med. Mal. Infect. 2006, 36, 78–91.
  49. Ivanov, I.E.; Kintz, E.N.; Porter, L.A.; Goldberg, J.B.; Burnham, N.A.; Camesano, T.A. Relating the physical properties of Pseudomonas aeruginosa lipopolysaccharides to virulence by atomic force microscopy. J. Bacteriol. 2011, 193, 1259–1266.
  50. Gupta, S.K.; Berk, R.S.; Masinick, S.; Hazlett, L.D. Pili and lipopolysaccharide of Pseudomonas aeruginosa bind to the glycolipid asialo GM1. Infect. Immun. 1994, 62, 4572–4579.
  51. Miao, E.A.; Ernst, R.K.; Dors, M.; Mao, D.P.; Aderem, A. Pseudomonas aeruginosa activates caspase 1 through Ipaf. Proc. Natl. Acad. Sci. USA 2008, 105, 2562–2567.
  52. Hagar, J.A.; Powell, D.A.; Aachoui, Y.; Ernst, R.K.; Miao, E.A. Cytoplasmic LPS activates caspase-11: Implications in TLR4-independent endotoxic shock. Science 2013, 341, 1250–1253.
  53. Liu, X.; Shao, K.; Sun, T. SIRT1 regulates the human alveolar epithelial A549 cell apoptosis induced by Pseudomonas aeruginosa lipopolysaccharide. Cell. Physiol. Biochem. 2013, 31, 92–101.
  54. Schoeniger, A.; Fuhrmann, H.; Schumann, J. LPS- or Pseudomonas aeruginosa-mediated activation of the macrophage TLR4 signaling cascade depends on membrane lipid composition. PeerJ 2016, 4, e1663.
  55. Nakamoto, K.; Watanabe, M.; Sada, M.; Inui, T.; Nakamura, M.; Honda, K.; Wada, H.; Ishii, H.; Takizawa, H. Pseudomonas aeruginosa-derived flagellin stimulates IL-6 and IL-8 production in human bronchial epithelial cells: A potential mechanism for progression and exacerbation of COPD. Exp. Lung Res. 2019, 45, 255–266.
  56. Lin, C.K.; Kazmierczak, B.I. Inflammation: A double-edged sword in the response to Pseudomonas aeruginosa infection. J. Innate Immun. 2017, 9, 250–261.
  57. Brandl, K.; Glück, T.; Huber, C.; Salzberger, B.; Falk, W.; Hartmann, P. TLR-4 surface display on human monocytes is increased in septic patients. Eur. J. Med. Res. 2005, 10, 319.
  58. Huang, X.; Feng, Y.; Xiong, G.; Whyte, S.; Duan, J.; Yang, Y.; Wang, K.; Yang, S.; Geng, Y.; Ou, Y.; et al. Caspase-11, a specific sensor for intracellular lipopolysaccharide recognition, mediates the non-canonical inflammatory pathway of pyroptosis. Cell Biosci. 2019, 9, 31.
  59. Pier, G.B. Promises and pitfalls of Pseudomonas aeruginosa lipopolysaccharide as a vaccine antigen. Carbohydr. Res. 2003, 338, 2549–2556.
  60. Lillehoj, E.P.; Kim, B.T.; Kim, K.C. Identification of Pseudomonas aeruginosa flagellin as an adhesin for Muc1 mucin. Am. J. Physiol. 2002, 282, L751–L756.
  61. Lindhout, T.; Lau, P.C.Y.; Brewer, D.; Lam, J.S. Truncation in the core oligosaccharide of lipopolysaccharide affects flagella-mediated motility in Pseudomonas aeruginosa PAO1 via modulation of cell surface attachment. Microbiology 2009, 155, 3449–3460.
  62. Dasgupta, N.; Wolfgang, M.C.; Goodman, A.L.; Arora, S.K.; Jyot, J.; Lory, S.; Ramphal, R. A four-tiered transcriptional regulatory circuit controls flagellar biogenesis in Pseudomonas aeruginosa. Mol. Microbiol. 2003, 50, 809–824.
  63. Rasamiravaka, T.; Labtani, Q.; Duez, P.; El Jaziri, M. The formation of biofilms by Pseudomonas aeruginosa: A review of the natural and synthetic compounds interfering with control mechanisms. Biomed Res. Int. 2015, 2015, 759348.
  64. Baker, A.E.; Webster, S.S.; Diepold, A.; Kuchma, S.L.; Bordeleau, E.; Armitage, J.P.; O’Toole, G.A. Flagellar stators stimulate c-di-GMP production by Pseudomonas aeruginosa. J. Bacteriol. 2019, 201, JB. 00741-18.
  65. Feldman, M.; Bryan, R.; Rajan, S.; Scheffler, L.; Brunnert, S.; Tang, H.; Prince, A. Role of flagella in pathogenesis of Pseudomonas aeruginosa pulmonary infection. Infect. Immun. 1998, 66, 43–51.
  66. Drake, D.; Montie, T.C. Flagella, motility and invasive virulence of Pseudomonas aeruginosa. J. Gen. Microbiol. 1988, 134 Pt 1, 43–52.
  67. Arora, S.K.; Neely, A.N.; Blair, B.; Lory, S.; Ramphal, R. Role of motility and flagellin glycosylation in the pathogenesis of Pseudomonas aeruginosa burn wound infections. Infect. Immun. 2005, 73, 4395–4398.
  68. Feuillet, V.; Medjane, S.; Mondor, I.; Demaria, O.; Pagni, P.P.; Galán, J.E.; Flavell, R.A.; Alexopoulou, L. Involvement of Toll-like receptor 5 in the recognition of flagellated bacteria. Proc. Natl. Acad. Sci. USA 2006, 103, 12487–12492.
  69. Balloy, V.; Verma, A.; Kuravi, S.; Si-Tahar, M.; Chignard, M.; Ramphal, R. The role of flagellin versus motility in acute lung disease caused by Pseudomonas aeruginosa. J. Infect. Dis. 2007, 196, 289–296.
  70. Lightfield, K.L.; Persson, J.J.; Brubaker, S.W.; E Witte, C.; Von Moltke, J.; A Dunipace, E.; Henry, T.; Sun, Y.-H.; Cado, D.; Dietrich, W.F.; et al. Critical function for Naip5 in inflammasome activation by a conserved carboxy-terminal domain of flagellin. Nat. Immunol. 2008, 9, 1171–1178.
  71. Kofoed, E.M.; Vance, R.E. Innate immune recognition of bacterial ligands by NAIPs determines inflammasome specificity. Nature 2011, 477, 592–595.
  72. Zhao, Y.; Shao, F. The NAIP–NLRC 4 inflammasome in innate immune detection of bacterial flagellin and type III secretion apparatus. Immunol. Rev. 2015, 265, 85–102.
  73. Faure, E.; Kwong, K.; Nguyen, D. Pseudomonas aeruginosa in chronic lung infections: How to adapt within the host? Front. Immunol. 2018, 9, 2416.
  74. Evans, T.J. Small colony variants of Pseudomonas aeruginosa in chronic bacterial infection of the lung in cystic fibrosis. Future Microbiol. 2015, 10, 231–239.
  75. Cohen, T.; Parker, D.; Prince, A. Pseudomonas aeruginosa host immune evasion. In Pseudomonas; Springer: Berlin/Heidelberg, Germany, 2015; pp. 3–23.
  76. Pier, G.B.; Meluleni, G.; Neuger, E. A murine model of chronic mucosal colonization by Pseudomonas aeruginosa. Infect. Immun. 1992, 60, 4768–4776.
  77. Mahenthiralingam, E.; E Campbell, M.; Speert, D.P. Nonmotility and phagocytic resistance of Pseudomonas aeruginosa isolates from chronically colonized patients with cystic fibrosis. Infect. Immun. 1994, 62, 596–605.
  78. Beceiro, A.; Tomás, M.; Bou, G. Antimicrobial resistance and virulence: A successful or deleterious association in the bacterial world? CMR 2013, 26, 185–230.
  79. Chevalier, S.; Bouffartigues, E.; Bodilis, J.; Maillot, O.; Lesouhaitier, O.; Feuilloley, M.G.J.; Orange, N.; Dufour, A.; Cornelis, P. Structure, function and regulation of Pseudomonas aeruginosa porins. FEMS Microbiol. Rev. 2017, 41, 698–722.
  80. Fito-Boncompte, L.; Chapalain, A.; Bouffartigues, E.; Chaker, H.; Lesouhaitier, O.; Gicquel, G.; Bazire, A.; Madi, A.; Connil, N.; Véron, W.; et al. Full virulence of Pseudomonas aeruginosa requires OprF. Infect. Immun. 2011, 79, 1176–1186.
  81. Buommino, E.; Morelli, F.; Metafora, S.; Rossano, F.; Perfetto, B.; Baroni, A.; Tufano, M.A. Porin from Pseudomonas aeruginosa induces apoptosis in an epithelial cell line derived from rat seminal vesicles. Infect. Immun. 1999, 67, 4794–4800.
  82. Cusumano, V.; A Tufano, M.; Mancuso, G.; Carbone, M.; Rossano, F.; Fera, M.T.; A Ciliberti, F.; Ruocco, E.; A Merendino, R.; Teti, G. Porins of Pseudomonas aeruginosa induce release of tumor necrosis factor alpha and interleukin-6 by human leukocytes. Infect. Immun. 1997, 65, 1683–1687.
  83. Mishra, M.; Ressler, A.; Schlesinger, L.S.; Wozniak, D.J. Identification of OprF as a complement component C3 binding acceptor molecule on the surface of Pseudomonas aeruginosa. Infect. Immun. 2015, 83, 3006–3014.
  84. Peluso, L.; De Luca, C.; Bozza, S.; Leonardi, A.; Giovannini, G.; Lavorgna, A.; De Rosa, G.; Mascolo, M.; De Luna, L.O.; Catania, M.R.; et al. Protection against Pseudomonas aeruginosa lung infection in mice by recombinant OprF-pulsed dendritic cell immunization. BMC Microbiol. 2010, 10, 9.
  85. Ochsner, U.A.; Fiechter, A.; Reiser, J. Isolation, characterization, and expression in Escherichia coli of the Pseudomonas aeruginosa rhlAB genes encoding a rhamnosyltransferase involved in rhamnolipid biosurfactant synthesis. JBC 1994, 269, 19787–19795.
  86. Cabrera-Valladares, N.; Richardson, A.-P.; Olvera, C.; Treviño, L.G.; Déziel, E.; Lépine, F.; Soberón-Chávez, G. Monorhamnolipids and 3-(3-hydroxyalkanoyloxy)alkanoic acids (HAAs) production using Escherichia coli as a heterologous host. Appl. Microbiol. Biotechnol. 2006, 73, 187–194.
  87. Maier, R.; Soberón-Chávez, G. Pseudomonas aeruginosa rhamnolipids: Biosynthesis and potential applications. Appl. Microbiol. Biotechnol. 2000, 54, 625–633.
  88. Read, R.; Roberts, P.; Munro, N.; Rutman, A.; Hastie, A.; Shryock, T.; Hall, R.; McDonald-Gibson, W.; Lund, V.; Taylor, G.; et al. Effect of Pseudomonas aeruginosa rhamnolipids on mucociliary transport and ciliary beating. J. Appl. Physiol. 1992, 72, 2271–2277.
  89. Kownatzki, R.; Tümmler, B.; Döring, G. Rhamnolipid of Pseudomonas aeruginosa in sputum of cystic fibrosis patients. Lancet 1987, 1, 1026–1027.
  90. Sharma, D.; Kanneganti, T.-D. The cell biology of inflammasomes: Mechanisms of inflammasome activation and regulation. J. Cell Biol. 2016, 213, 617–629.
  91. Varjani, S.J.; Upasani, V.N. Core flood study for enhanced oil recovery through ex-situ bioaugmentation with thermo-and halo-tolerant rhamnolipid produced by Pseudomonas aeruginosa NCIM 5514. Bioresour. Technol. 2016, 220, 175–182.
  92. Zulianello, L.; Canard, C.; Köhler, T.; Caille, D.; Lacroix, J.-S.; Meda, P. Rhamnolipids are virulence factors that promote early infiltration of primary human airway epithelia by Pseudomonas aeruginosa. Infect. Immun. 2006, 74, 3134–3147.
  93. Wang, S.; Yu, S.; Zhang, Z.; Wei, Q.; Yan, L.; Ai, G.; Liu, H.; Ma, L.Z. Coordination of swarming motility, biosurfactant synthesis, and biofilm matrix exopolysaccharide production in Pseudomonas aeruginosa. Appl. Environ. Microbiol. 2014, 80, 6724–6732.
  94. Overhage, J.; Bains, M.; Brazas, M.D.; Hancock, R.E.W. Swarming of Pseudomonas aeruginosa is a complex adaptation leading to increased production of virulence factors and antibiotic resistance. J. Bacteriol. 2008, 190, 2671–2679.
  95. Pamp, S.J.; Tolker-Nielsen, T. Multiple roles of biosurfactants in structural biofilm development by Pseudomonas aeruginosa. J. Bacteriol. 2007, 189, 2531–2539.
  96. Davey, M.E.; Caiazza, N.C.; O’Toole, G.A. Rhamnolipid surfactant production affects biofilm architecture in Pseudomonas aeruginosa PAO1. J. Bacteriol. 2003, 185, 1027–1036.
  97. Sotirova, A.; Spasova, D.; Vasileva-Tonkova, E.; Galabova, D. Effects of rhamnolipid-biosurfactant on cell surface of Pseudomonas aeruginosa. Microbiol. Res. 2009, 164, 297–303.
  98. Okamoto, K.; Gotoh, N.; Nishino, T. Pseudomonas aeruginosa reveals high intrinsic resistance to penem antibiotics: Penem resistance mechanisms and their interplay. Antimicrob. Agents Chemother. 2001, 45, 1964–1971.
  99. Rahimi, K.; Lotfabad, T.B.; Jabeen, F.; Ganji, S.M. Cytotoxic effects of mono-and di-rhamnolipids from Pseudomonas aeruginosa MR01 on MCF-7 human breast cancer cells. Colloids Surf. B 2019, 181, 943–952.
  100. Dwivedi, S.; Saquib, Q.; Al-Khedhairy, A.A.; Ahmad, J.; Siddiqui, M.A.; Musarrat, J. Rhamnolipids functionalized AgNPs-induced oxidative stress and modulation of toxicity pathway genes in cultured MCF-7 cells. Colloids Surf. B 2015, 132, 290–298.
  101. Jensen, P.; Bjarnsholt, T.; Phipps, R.; Rasmussen, T.B.; Calum, H.; Christoffersen, L.; Moser, C.; Williams, P.; Pressler, T.; Givskov, M.; et al. Rapid necrotic killing of polymorphonuclear leukocytes is caused by quorum-sensing-controlled production of rhamnolipid by Pseudomonas aeruginosa. Microbiology 2007, 153, 1329–1338.
  102. Van Gennip, M.; Christensen, L.D.; Alhede, M.; Phipps, R.; Jensen, P.; Christophersen, L.; Pamp, S.J.; Moser, C.; Mikkelsen, P.J.; Koh, A.Y.; et al. Inactivation of the rhlA gene in Pseudomonas aeruginosa prevents rhamnolipid production, disabling the protection against polymorphonuclear leukocytes. APMIS 2009, 117, 537–546.
  103. Meyer-Hoffert, U.; Zimmermann, A.; Czapp, M.; Bartels, J.; Koblyakova, Y.; Gläser, R.; Schröder, J.-M.; Gerstel, U. Flagellin delivery by Pseudomonas aeruginosa rhamnolipids induces the antimicrobial protein psoriasin in human skin. PLoS ONE 2011, 6, e16433.
  104. Stockbauer, K.E.; Foreman-Wykert, A.K.; Miller, J.F. Bordetella type III secretion induces caspase 1-independent necrosis. Cell Microbiol. 2003, 5, 123–132.
  105. Viboud, G.I.; Bliska, J.B. A bacterial type III secretion system inhibits actin polymerization to prevent pore formation in host cell membranes. EMBO J. 2001, 20, 5373–5382.
  106. Lee, V.T.; Smith, R.S.; Tümmler, B.; Lory, S. Activities of Pseudomonas aeruginosa effectors secreted by the Type III secretion system in vitro and during infection. Infect. Immun. 2005, 73, 1695–1705.
  107. Shafikhani, S.H.; Morales, C.; Engel, J. The Pseudomonas aeruginosa type III secreted toxin ExoT is necessary and sufficient to induce apoptosis in epithelial cells. Cell Microbiol. 2008, 10, 994–1007.
  108. Andor, A.; Trulzsch, K.; Essler, M.; Roggenkamp, A.; Wiedemann, A.; Heesemann, J.; Aepfelbacher, M. YopE of Yersinia, a GAP for Rho GTPases, selectively modulates Rac-dependent actin structures in endothelial cells. Cell Microbiol. 2001, 3, 301–310.
  109. Von Pawel-Rammingen, U.; Telepnev, M.V.; Schmidt, G.; Aktories, K.; Wolf-Watz, H.; Rosqvist, R. GAP activity of the Yersinia YopE cytotoxin specifically targets the Rho pathway: A mechanism for disruption of actin microfilament structure. Mol. Microbiol. 2000, 36, 737–748.
  110. Eren, E.; Planès, R.; Buyck, J.; Bordignon, P.J.; Colom, A.; Cunrath, O.; Dreier, R.F.; Santos, J.C.; Duplan-Eche, V.; Näser, E.; et al. Type-3 Secretion System–induced pyroptosis protects Pseudomonas against cell-autonomous immunity. bioRxiv 2019.
  111. Balakrishnan, A.; Karki, R.; Berwin, B.; Yamamoto, M.; Kanneganti, T.-D. Guanylate binding proteins facilitate caspase-11-dependent pyroptosis in response to type 3 secretion system-negative Pseudomonas aeruginosa. Cell Death Discov. 2018, 4, 66.
  112. Mohamed, M.F.; Gupta, K.; Goldufsky, J.W.; Roy, R.; Callaghan, L.T.; Wetzel, D.M.; Kuzel, T.M.; Reiser, J.; Shafikhani, S.H. CrkII/Abl phosphorylation cascade is critical for NLRC4 inflammasome activity and is blocked by Pseudomonas aeruginosa ExoT. Nat. Commun. 2022, 13, 1295.
  113. Franchi, L.; Stoolman, J.; Kanneganti, T.-D.; Verma, A.; Ramphal, R.; Núñez, G. Critical role for Ipaf in Pseudomonas aeruginosa-induced caspase-1 activation. Eur. J. Immunol. 2007, 37, 3030–3039.
  114. Rimessi, A.; Bezzerri, V.; Patergnani, S.; Marchi, S.; Cabrini, G.; Pinton, P. Mitochondrial Ca2+-dependent NLRP3 activation exacerbates the Pseudomonas aeruginosa-driven inflammatory response in cystic fibrosis. Nat. Commun. 2015, 6, 1–16.
  115. Deng, Q.; Wang, Y.; Zhang, Y.; Li, M.; Li, D.; Huang, X.; Wu, Y.; Pu, J.; Wu, M. Pseudomonas aeruginosa triggers macrophage autophagy to escape intracellular killing by activation of the NLRP3 inflammasome. Infect. Immun. 2016, 84, 56–66.
  116. Gugliandolo, E.; Fusco, R.; Ginestra, G.; D’amico, R.; Bisignano, C.; Mandalari, G.; Cuzzocrea, S.; Di Paola, R. Involvement of TLR4 and PPAR-α receptors in host response and NLRP3 inflammasome activation, against pulmonary infection with Pseudomonas aeruginosa. Shock 2019, 51, 221–227.
  117. Franchi, L.; Kamada, N.; Nakamura, Y.; Burberry, A.; Kuffa, P.; Suzuki, S.; Shaw, M.H.; Kim, Y.G.; Núñez, G. NLRC4-driven production of IL-1beta discriminates between pathogenic and commensal bacteria and promotes host intestinal defense. Nat. Immunol. 2012, 13, 449–456.
  118. Iannitti, R.G.; Napolioni, V.; Oikonomou, V.; De Luca, A.; Galosi, C.; Pariano, M.; Massi-Benedetti, C.; Borghi, M.; Puccetti, M.; Lucidi, V.; et al. IL-1 receptor antagonist ameliorates inflammasome-dependent inflammation in murine and human cystic fibrosis. Nat. Commun. 2016, 7, 10791.
  119. Faure, E.; Mear, J.-B.; Faure, K.; Normand, S.; Couturier-Maillard, A.; Grandjean, T.; Balloy, V.; Ryffel, B.; Dessein, R.; Chignard, M.; et al. Pseudomonas aeruginosa type-3 secretion system dampens host defense by exploiting the NLRC4-coupled inflammasome. Am. J. Respir. Crit. Care Med. 2014, 189, 799–811.
  120. Barbieri, J.T. Pseudomonas aeruginosa exoenzyme S, a bifunctional type-III secreted cytotoxin. Int. J. Med. Microbiol. 2000, 290, 381–387.
  121. Da-Kang, S.H.; Quenee, L.; Bonnet, M.; Lauriane, K.U.; Derouazi, M.; Lamotte, D.; Toussaint, B.; Polack, B. Orf1/SpcS chaperones ExoS for type three secretion by Pseudomonas aeruginosa. Biomed. Environ. Sci. 2008, 21, 103–109.
  122. Pederson, K.J.; Krall, R.; Riese, M.J.; Barbieri, J.T. Intracellular localization modulates targeting of ExoS, a type III cytotoxin, to eukaryotic signalling proteins. Mol. Microbiol. 2002, 46, 1381–1390.
  123. Riese, M.J.; Barbieri, J.T. Membrane localization contributes to the in vivo ADP-ribosylation of Ras by Pseudomonas aeruginosa ExoS. Infect. Immun. 2002, 70, 2230–2232.
  124. Henriksson, M.L.; Sundin, C.; Jansson, A.L.; Forsberg, Å.; Palmer, R.H.; Hallberg, B. Exoenzyme S shows selective ADP-ribosylation and GTPase-activating protein (GAP) activities towards small GTPases in vivo. Biochem. J. 2002, 367 Pt 3, 617–628.
  125. Katzmann, D.J.; Odorizzi, G.; Emr, S.D. Receptor downregulation and multivesicular-body sorting. Nat. Rev. Mol. Cell Biol. 2002, 3, 893–905.
  126. Wittinghofer, A.; Würtele, M.; Wolf, E.; Pederson, K.J.; Buchwald, G.; Ahmadian, M.R.; Barbieri, J.T. How the Pseudomonas aeruginosa ExoS toxin downregulates Rac. Nat. Struct. Biol. 2001, 8, 23–26.
  127. Krall, R.; Sun, J.; Pederson, K.J.; Barbieri, J.T. In vivo Rho GTPase-activating protein activity of Pseudomonas aeruginosa cytotoxin ExoS. Infect. Immun. 2002, 70, 360–367.
  128. Krall, R.; Schmidt, G.; Aktories, K.; Barbieri, J.T. Pseudomonas aeruginosa ExoT is a Rho GTPase-activating protein. Infect. Immun. 2000, 68, 6066–6068.
  129. Kazmierczak, B.I.; Engel, J.N. Pseudomonas aeruginosa ExoT acts in vivo as a GTPase-activating protein for RhoA, Rac1, and Cdc42. Infect. Immun. 2002, 70, 2198–2205.
  130. Liu, S.; Yahr, T.; Frank, D.W.; Barbieri, J.T. Biochemical relationships between the 53-kilodalton (Exo53) and 49-kilodalton (ExoS) forms of exoenzyme S of Pseudomonas aeruginosa. J. Bacteriol. 1997, 179, 1609–1613.
  131. Maresso, A.W.; Deng, Q.; Pereckas, M.S.; Wakim, B.T.; Barbieri, J.T. Pseudomonas aeruginosa ExoS ADP-ribosyltransferase inhibits ERM phosphorylation. Cell Microbiol. 2007, 9, 97–105.
  132. Barbieri, J.T.; Sun, J. Pseudomonas aeruginosa ExoS and ExoT. Rev. Physiol. Biochem. Pharmacol. 2004, 152, 79–92.
  133. Jia, J.; Wang, Y.; Zhou, L.; Jin, S. Expression of Pseudomonas aeruginosa Toxin ExoS Effectively Induces Apoptosis in Host Cells. Infect. Immun. 2006, 74, 6557–6570.
  134. Goehring, U.-M.; Schmidt, G.; Pederson, K.J.; Aktories, K.; Barbieri, J.T. The N-terminal domain of Pseudomonas aeruginosa exoenzyme S is a GTPase-activating protein for Rho GTPases. JBC 1999, 274, 36369–36372.
  135. Kaminski, A.; Gupta, K.H.; Goldufsky, J.W.; Lee, H.W.; Gupta, V.; Shafikhani, S.H. Pseudomonas aeruginosa ExoS Induces Intrinsic Apoptosis in Target Host Cells in a Manner That is Dependent on its GAP Domain Activity. Sci. Rep. 2018, 8, 14047.
  136. Fuchs, Y.; Steller, H. Live to die another way: Modes of programmed cell death and the signals emanating from dying cells. Nat. Rev. Mol. Cell Biol. 2015, 16, 329–344.
  137. Jia, J.; Alaoui-El-Azher, M.; Chow, M.; Chambers, T.C.; Baker, H.; Jin, S. c-Jun NH2-terminal kinase-mediated signaling is essential for Pseudomonas aeruginosa ExoS-induced apoptosis. Infect. Immun. 2003, 71, 3361–3370.
  138. Kaufman, M.R.; Jia, J.; Zeng, L.; Ha, U.; Chow, M.; Jin, S. Pseudomonas aeruginosa mediated apoptosis requires the ADP-ribosylating activity of ExoS. Microbiology 2000, 146, 2531–2541.
  139. Peter, M.E. Programmed cell death: Apoptosis meets necrosis. Nature 2011, 471, 310–312.
  140. Alaoui-El-Azher, M.; Jia, J.; Lian, W.; Jin, S. ExoS of Pseudomonas aeruginosa induces apoptosis through a Fas receptor/caspase 8-independent pathway in HeLa cells. Cell. Microbiol. 2006, 8, 326–338.
  141. Epelman, S.; Bruno, T.F.; Neely, G.G.; Woods, D.E.; Mody, C.H. Pseudomonas aeruginosa exoenzyme S induces transcriptional expression of proinflammatory cytokines and chemokines. Infect. Immun. 2000, 68, 4811–4814.
  142. Epelman, S.; Neely, G.G.; Ma, L.L.; Gjomarkaj, M.; Pace, E.; Melis, M.; Woods, D.E.; Mody, C.H. Distinct fates of monocytes and T cells directly activated by Pseudomonas aeruginosa exoenzyme S. J. Leukoc. Biol. 2002, 71, 458–468.
  143. Epelman, S.; Stack, D.; Bell, C.; Wong, E.; Neely, G.G.; Krutzik, S.; Miyake, K.; Kubes, P.; Zbytnuik, L.D.; Ma, L.L.; et al. Different domains of Pseudomonas aeruginosa Exoenzyme S activate distinct TLRs. J. Immunol. 2004, 173, 2031–2040.
  144. Galle, M.; Schotte, P.; Haegman, M.; Wullaert, A.; Yang, H.J.; Jin, S.; Beyaert, R. The Pseudomonas aeruginosa Type III secretion system plays a dual role in the regulation of caspase-1 mediated IL-1beta maturation. J. Cell. Mol. Med. 2008, 12, 1767–1776.
  145. Feltman, H.; Schulert, G.; Khan, S.; Jain, M.; Peterson, L.; Hauser, A.R. Prevalence of type III secretion genes in clinical and environmental isolates of Pseudomonas aeruginosa. Microbiology 2001, 147, 2659–2669.
  146. Balachandran, P.; Dragone, L.; Garrity-Ryan, L.; Lemus, A.; Weiss, A.; Engel, J. The ubiquitin ligase Cbl-b limits Pseudomonas aeruginosa exotoxin T-mediated virulence. J. Clin. Investig. 2007, 117, 419–427.
  147. Yahr, T.; Mende-Mueller, L.M.; Friese, M.; Frank, D.W. Identification of type III secreted products of the Pseudomonas aeruginosa exoenzyme S regulon. J. Bacteriol. 1997, 179, 7165–7168.
  148. Sun, J.; Barbieri, J.T. Pseudomonas aeruginosa ExoT ADP-ribosylates CT10 regulator of kinase (Crk) proteins. JBC 2003, 278, 32794–32800.
  149. Sun, J.; Maresso, A.; Kim, J.J.; Barbieri, J.T. How bacterial ADP-ribosylating toxins recognize substrates. Nat Struct Mol Biol. 2004, 11, 868–876.
  150. Deng, Q.; Sun, J.; Barbieri, J.T. Uncoupling Crk signal transduction by Pseudomonas exoenzyme T. JBC 2005, 280, 35953–35960.
  151. Garrity-Ryan, L.; Shafikhani, S.; Balachandran, P.; Nguyen, L.; Oza, J.; Jakobsen, T.; Sargent, J.; Fang, X.; Cordwell, S.; Matthay, M.A.; et al. The ADP ribosyltransferase domain of Pseudomonas aeruginosa ExoT contributes to its biological activities. Infect. Immun. 2004, 72, 546–558.
  152. Garrity-Ryan, L.; Kazmierczak, B.; Kowal, R.; Comolli, J.; Hauser, A.; Engel, J.N. The arginine finger domain of ExoT is required for actin cytoskeleton disruption and inhibition of internalization of Pseudomonas aeruginosa by epithelial cells and macrophages. Infect. Immun. 2000, 68, 7100–7113.
  153. Cowell, B.A.; Chen, D.Y.; Frank, D.W.; Vallis, A.J.; Fleiszig, S.M.J. ExoT of cytotoxic Pseudomonas aeruginosa prevents uptake by corneal epithelial cells. Infect. Immun. 2000, 68, 403–406.
  154. Shafikhani, S.H.; Engel, J. Pseudomonas aeruginosa type III-secreted toxin ExoT inhibits host-cell division by targeting cytokinesis at multiple steps. Proc. Natl. Acad. Sci. USA 2006, 103, 15605–15610.
  155. Mohamed, M.F.; Wood, S.J.; Roy, R.; Reiser, J.; Kuzel, T.M.; Shafikhani, S.H. Pseudomonas aeruginosa ExoT induces G1 cell cycle arrest in melanoma cells. Cell Microbiol. 2021, 23, e13339.
  156. Goldufsky, J.; Wood, S.; Hajihossainlou, B.; Rehman, T.; Majdobeh, O.; Kaufman, H.L.; Ruby, C.E.; Shafikhani, S.H. Pseudomonas aeruginosa exotoxin T induces potent cytotoxicity against a variety of murine and human cancer cell lines. J. Med. Microbiol. 2015, 64 Pt 2, 164–173.
  157. Wood, S.; Goldufsky, J.; Shafikhani, S.H. Pseudomonas aeruginosa ExoT Induces Atypical Anoikis Apoptosis in Target Host Cells by Transforming Crk Adaptor Protein into a Cytotoxin. PLoS Pathog. 2015, 11, e1004934.
  158. Wood, S.J.; Goldufsky, J.W.; Bello, D.; Masood, S.; Shafikhani, S.H. Pseudomonas aeruginosa ExoT induces mitochondrial apoptosis in target host cells in a manner that depends on its GTPase-activating protein (GAP) domain activity. JBC 2015, 290, 29063–29073.
  159. Hauser, A.R. The type III secretion system of Pseudomonas aeruginosa: Infection by injection. Nat. Rev. Microbiol. 2009, 7, 654–665.
  160. Phillips, R.M.; Six, D.; Dennis, E.A.; Ghosh, P.; Matsumoto, K.; Shionyu, M.; Go, M.; Shimizu, K.; Shinomura, T.; Kimata, K.; et al. In vivo phospholipase activity of the Pseudomonas aeruginosa cytotoxin ExoU and protection of mammalian cells with phospholipase A2 inhibitors. JBC 2003, 278, 41326–41332.
  161. Sato, H.; Frank, D.W. ExoU is a potent intracellular phospholipase. Mol. Microbiol. 2004, 53, 1279–1290.
  162. Finck-Barbançon, V.; Goranson, J.; Zhu, L.; Sawa, T.; Wiener-Kronish, J.P.; Fleiszig, S.M.J.; Wu, C.; Mende-Mueller, L.; Frank, D.W. ExoU expression by Pseudomonas aeruginosa correlates with acute cytotoxicity and epithelial injury. Mol. Microbiol. 1997, 25, 547–557.
  163. Tamura, M.; Ajayi, T.; Allmond, L.R.; Moriyama, K.; Wiener-Kronish, J.P.; Sawa, T. Lysophospholipase A activity of Pseudomonas aeruginosa type III secretory toxin ExoU. Biochem. Biophys Res. Commun. 2004, 316, 323–331.
  164. Finck-Barbançon, V.; Yahr, T.L.; Frank, D.W. Identification and characterization of SpcU, a chaperone required for efficient secretion of the ExoU cytotoxin. J. Bacteriol. 1998, 180, 6224–6231.
  165. Ottmann, C.; Yasmin, L.; Weyand, M.; Veesenmeyer, J.L.; Diaz, M.H.; Palmer, R.H.; Francis, M.; Hauser, A.R.; Wittinghofer, A.; Hallberg, B. Phosphorylation-independent interaction between 14-3-3 and exoenzyme S: From structure to pathogenesis. EMBO J. 2007, 26, 902–913.
  166. Deruelle, V.; Bouillot, S.; Job, V.; Taillebourg, E.; Fauvarque, M.-O.; Attrée, I.; Huber, P. The bacterial toxin ExoU requires a host trafficking chaperone for transportation and to induce necrosis. Nat. Commun. 2021, 12, 1–14.
  167. Anderson, D.M.; Schmalzer, K.M.; Sato, H.; Casey, M.; Terhune, S.S.; Haas, A.L.; Feix, J.B.; Frank, D.W. Ubiquitin and ubiquitin-modified proteins activate the Pseudomonas aeruginosa T3SS cytotoxin, ExoU. Mol. Microbiol. 2011, 82, 1454–1467.
  168. Anderson, D.M.; Feix, J.B.; Monroe, A.L.; Peterson, F.C.; Volkman, B.F.; Haas, A.L.; Frank, D.W. Identification of the major ubiquitin-binding domain of the Pseudomonas aeruginosa ExoU A2 phospholipase. JBC 2013, 288, 26741–26752.
  169. Rabin, S.D.P.; Veesenmeyer, J.L.; Bieging, K.T.; Hauser, A.R. A C-terminal domain targets the Pseudomonas aeruginosa cytotoxin ExoU to the plasma membrane of host cells. Infect. Immun. 2006, 74, 2552–2561.
  170. Gendrin, C.; Contreras-Martel, C.; Bouillot, S.; Elsen, S.; Lemaire, D.; Skoufias, D.; Huber, P.; Attree, I.; Dessen, A. Structural basis of cytotoxicity mediated by the type III secretion toxin ExoU from Pseudomonas aeruginosa. PLoS Pathog. 2012, 8, e1002637.
  171. Lindsey, A.S.; Sullivan, L.M.; Housley, N.A.; Koloteva, A.; King, J.A.; Audia, J.P.; Alvarez, D.F. Analysis of pulmonary vascular injury and repair during Pseudomonas aeruginosa infection-induced pneumonia and acute respiratory distress syndrome. Pulm. Circ. 2019, 9, 2045894019826941.
  172. Diaz, M.H.; Shaver, C.M.; King, J.D.; Musunuri, S.; Kazzaz, J.A.; Hauser, A.R. Pseudomonas aeruginosa induces localized immunosuppression during pneumonia. Infect. Immun. 2008, 76, 4414–4421.
  173. Diaz, M.H.; Hauser, A.R. Pseudomonas aeruginosa cytotoxin ExoU is injected into phagocytic cells during acute pneumonia. Infect. Immun. 2010, 78, 1447–1456.
  174. Sutterwala, F.S.; Mijares, L.A.; Li, L.; Ogura, Y.; Kazmierczak, B.I.; Flavell, R.A. Immune recognition of Pseudomonas aeruginosa mediated by the IPAF/NLRC4 inflammasome. JEM 2007, 204, 3235–3245.
  175. Yahr, T.L.; Vallis, A.J.; Hancock, M.K.; Barbieri, J.T.; Frank, D.W. ExoY, an adenylate cyclase secreted by the Pseudomonas aeruginosa type III system. Proc. Natl. Acad. Sci. USA 1998, 95, 13899–13904.
  176. Ochoa, C.D.; Alexeyev, M.; Pastukh, V.; Balczon, R.; Stevens, T. Pseudomonas aeruginosa exotoxin Y is a promiscuous cyclase that increases endothelial tau phosphorylation and permeability. JBC 2012, 287, 25407–25418.
  177. Wagener, B.M.; Anjum, N.; Christiaans, S.C.; Banks, M.E.; Parker, J.C.; Threet, A.T.; Walker, R.R.; Isbell, K.D.; Moser, S.A.; Stevens, T.; et al. Exoenzyme Y contributes to end-organ dysfunction caused by Pseudomonas aeruginosa pneumonia in critically ill patients: An exploratory study. Toxins 2020, 12, 369.
  178. Belyy, A.; Raoux-Barbot, D.; Saveanu, C.; Namane, A.; Ogryzko, V.; Worpenberg, L.; David, V.; Henriot, V.; Fellous, S.; Merrifield, C.; et al. Actin activates Pseudomonas aeruginosa ExoY nucleotidyl cyclase toxin and ExoY-like effector domains from MARTX toxins. Nat. Commun. 2016, 7, 1–14.
  179. Sayner, S.L.; Frank, D.W.; King, J.; Chen, H.; VandeWaa, J.; Stevens, T. Paradoxical cAMP-induced lung endothelial hyperpermeability revealed by Pseudomonas aeruginosa ExoY. Circ Res. 2004, 95, 196–203.
  180. Sayner, S.L.; Frank, D.W.; King, J.; Chen, H.; VandeWaa, J.; Stevens, T. The amino-terminal domain of Pseudomonas aeruginosa ExoS disrupts actin filaments via small-molecular-weight GTP-binding proteins. Mol. Microbiol. 1999, 32, 393–401.
  181. Cowell, B.A.; Evans, D.J.; Fleiszig, S.M. Actin cytoskeleton disruption by ExoY and its effects on Pseudomonas aeruginosa invasion. FEMS Microbiol. Lett. 2005, 250, 71–76.
  182. Stevens, T.C.; Ochoa, C.D.; Morrow, K.A.; Robson, M.J.; Prasain, N.; Zhou, C.; Alvarez, D.F.; Frank, D.W.; Balczon, R.; Stevens, T. The Pseudomonas aeruginosa exoenzyme Y impairs endothelial cell proliferation and vascular repair following lung injury. Am. J. Physiol. Lung Cell Mol. Physiol. 2014, 306, L915–L924.
  183. Lin, H.-H.; Huang, S.-P.; Teng, H.-C.; Ji, D.-D.; Chen, Y.-S.; Chen, Y.-L. Presence of the exoU gene of Pseudomonas aeruginosa is correlated with cytotoxicity in MDCK cells but not with colonization in BALB/c mice. JCM 2006, 44, 4596–4597.
  184. Kloth, C.; Schirmer, B.; Munder, A.; Stelzer, T.; Rothschuh, J.; Seifert, R. The role of Pseudomonas aeruginosa ExoY in an acute mouse lung infection model. Toxins 2018, 10, 185.
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