| 1. |
- Guerra, Lina, et al.
(författare)
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The biology of the cytolethal distending toxins
- 2011
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Ingår i: Toxins. - : MDPI. - 2072-6651 .- 2072-6651. ; 3:3, s. 172-190
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Forskningsöversikt (refereegranskat)abstract
- The cytolethal distending toxins (CDTs), produced by a variety of Gram-negative pathogenic bacteria, are the first bacterial genotoxins described, since they cause DNA damage in the target cells. CDT is an A-B(2) toxin, where the CdtA and CdtC subunits are required to mediate the binding on the surface of the target cells, allowing internalization of the active CdtB subunit, which is functionally homologous to the mammalian deoxyribonuclease I. The nature of the surface receptor is still poorly characterized, however binding of CDT requires intact lipid rafts, and its internalization occurs via dynamin-dependent endocytosis. The toxin is retrograde transported through the Golgi complex and the endoplasmic reticulum, and subsequently translocated into the nuclear compartment, where it exerts the toxic activity. Cellular intoxication induces DNA damage and activation of the DNA damage responses, which results in arrest of the target cells in the G1 and/or G2 phases of the cell cycle and activation of DNA repair mechanisms. Cells that fail to repair the damage will senesce or undergo apoptosis. This review will focus on the well-characterized aspects of the CDT biology and discuss the questions that still remain unanswered.
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| 2. |
- Guidi, Riccardo, et al.
(författare)
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Chronic exposure to the cytolethal distending toxins of Gram-negative bacteria promotes genomic instability and altered DNA damage response
- 2013
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Ingår i: Cellular Microbiology. - : John Wiley & Sons. - 1462-5814 .- 1462-5822. ; 15:1, s. 98-113
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Tidskriftsartikel (refereegranskat)abstract
- Epidemiological evidence links chronic bacterial infections to the increased incidence of certain types of cancer but the molecular mechanisms by which bacteria contribute to tumour initiation and progression are still poorly characterized. Here we show that chronic exposure to the genotoxin cytolethal distending toxin (CDT) of Gram-negative bacteria promotes genomic instability and acquisition of phenotypic properties of malignancy in fibroblasts and colon epithelial cells. Cells grown for more than 30 weeks in the presence of sublethal doses of CDT showed increased mutation frequency, and accumulation of chromatin and chromosomal aberrations in the absence of significant alterations of cell cycle distribution, decreased viability or senescence. Cell survival was dependent on sustained activity of the p38 MAP kinase. The ongoing genomic instability was associated with impaired activation of the DNA damage response and failure to efficiently activate cell cycle checkpoints upon exposure to genotoxic stress. Independently selected sublines showed enhanced anchorage-independent growth as assessed by the formation of colonies in semisolid agarose. These findings support the notion that chronic infection by CDT-producing bacteria may promote malignant transformation, and point to the impairment of cellular control mechanisms associated with the detection and repair of DNA damage as critical events in the process.
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| 3. |
- Bassères, Eugénie, et al.
(författare)
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The ubiquitin C-terminal hydrolase UCH-L1 promotes bacterial invasion by altering the dynamics of the actin cytoskeleton
- 2010
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Ingår i: Cellular Microbiology. - : Wiley-Blackwell. - 1462-5814 .- 1462-5822. ; 12:11, s. 1622-1633
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Tidskriftsartikel (refereegranskat)abstract
- Invasion of eukaryotic target cells by pathogenic bacteria requires extensive remodelling of the membrane and actin cytoskeleton. Here we show that the remodelling process is regulated by the ubiquitin C-terminal hydrolase UCH-L1 that promotes the invasion of epithelial cells by Listeria monocytogenes and Salmonella enterica. Knockdown of UCH-L1 reduced the uptake of both bacteria, while expression of the catalytically active enzyme promoted efficient internalization in the UCH-L1-negative HeLa cell line. The entry of L. monocytogenes involves binding to the receptor tyrosine kinase Met, which leads to receptor phosphorylation and ubiquitination. UCH-L1 controls the early membrane-associated events of this triggering cascade since knockdown was associated with altered phosphorylation of the c-cbl docking site on Tyr1003, reduced ubiquitination of the receptor and altered activation of downstream ERK1/2- and AKT-dependent signalling in response to the natural ligand Hepatocyte Growth Factor (HGF). The regulation of cytoskeleton dynamics was further confirmed by the induction of actin stress fibres in HeLa expressing the active enzyme but not the catalytic mutant UCH-L1(C90S). These findings highlight a previously unrecognized involvement of the ubiquitin cycle in bacterial entry. UCH-L1 is highly expressed in malignant cells that may therefore be particularly susceptible to invasion by bacteria-based drug delivery systems.
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| 4. |
- Fahrer, Jörg, et al.
(författare)
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Cytolethal distending toxin (CDT) is a radiomimetic agent and induces persistent levels of DNA double-strand breaks in human fibroblasts
- 2014
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Ingår i: DNA Repair. - : Elsevier. - 1568-7864 .- 1568-7856. ; 18, s. 31-43
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Tidskriftsartikel (refereegranskat)abstract
- Cytolethal distending toxin (CDT) is a unique genotoxin produced by several pathogenic bacteria. The tripartite protein toxin is internalized into mammalian cells via endocytosis followed by retrograde transport to the ER. Upon translocation into the nucleus, CDT catalyzes the formation of DNA double-strand breaks (DSBs) due to its intrinsic endonuclease activity. In the present study, we compared the DNA damage response (DDR) in human fibroblasts triggered by recombinant CDT to that of ionizing radiation (IR), a well-known DSB inducer. Furthermore, we dissected the pathways involved in the detection and repair of CDT-induced DNA lesions. qRT-PCR array-based mRNA and western blot analyses showed a partial overlap in the DDR pattern elicited by CDT and IR, with strong activation of both the ATM-Chk2 and the ATR-Chk1 axis. In line with its in vitro DNase I-like activity on plasmid DNA, neutral and alkaline Comet assay revealed predominant induction of DSBs in CDT-treated fibroblasts, whereas irradiation of cells generated higher amounts of SSBs and alkali-labile sites. Using confocal microscopy, the dynamics of the DSB surrogate marker γ-H2AX was monitored after pulse treatment with CDT or IR. In contrast to the fast induction and disappearance of γ-H2AX-foci observed in irradiated cells, the number of γ-H2AX-foci induced by CDT were formed with a delay and persisted. 53BP1 foci were also generated following CDT treatment and co-localized with γ-H2AX foci. We further demonstrated that ATM-deficient cells are very sensitive to CDT-induced DNA damage as reflected by increased cell death rates with concomitant cleavage of caspase-3 and PARP-1. Finally, we provided novel evidence that both homologous recombination (HR) and non-homologous end joining (NHEJ) protect against CDT-elicited DSBs. In conclusion, the findings suggest that CDT functions as a radiomimetic agent and, therefore, is an attractive tool for selectively inducing persistent levels of DSBs and unveiling the associated cellular responses.
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| 5. |
- Guerra, Lina, et al.
(författare)
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Bacterial genotoxin triggers FEN1-dependent RhoA activation, cytoskeleton remodeling and cell survival
- 2011
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Ingår i: Journal of Cell Science. - : The Company of Biologists. - 0021-9533 .- 1477-9137. ; 124:16, s. 2735-2742
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Tidskriftsartikel (refereegranskat)abstract
- The DNA damage response triggered by bacterial cytolethal distending toxins (CDTs) is associated with activation of the actin-regulating protein RhoA and phosphorylation of the downstream-regulated mitogen-activated protein kinase (MAPK) p38, which promotes the survival of intoxicated (i.e. cells exposed to a bacterial toxin) cells. To identify the effectors of this CDT-induced survival response, we screened a library of 4492 Saccharomyces cerevisiae mutants that carry deletions in nonessential genes for reduced growth following inducible expression of CdtB. We identified 78 genes whose deletion confers hypersensitivity to toxin. Bioinformatics analysis revealed that DNA repair and endocytosis were the two most overrepresented signaling pathways. Among the human orthologs present in our data set, FEN1 and TSG101 regulate DNA repair and endocytosis, respectively, and also share common interacting partners with RhoA. We further demonstrate that FEN1, but not TSG101, regulates cell survival, MAPK p38 phosphorylation, RhoA activation and actin cytoskeleton reorganization in response to DNA damage. Our data reveal a previously unrecognized crosstalk between DNA damage and cytoskeleton dynamics in the regulation of cell survival, and might provide new insights on the role of chronic bacteria infection in carcinogenesis.
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| 6. |
- Guerra, Lina, et al.
(författare)
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Do bacterial genotoxins contribute to chronic inflammation, genomic instability and tumor progression?
- 2011
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Ingår i: The FEBS Journal. - : John Wiley & Sons. - 1742-464X .- 1742-4658. ; 278:23, s. 4577-4588
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Forskningsöversikt (refereegranskat)abstract
- Cytolethal distending toxin, produced by several Gram-negative bacteria, and colibactin, secreted by several commensal and extraintestinal pathogenic Escherichia coli strains, are the first bacterial genotoxins to be described to date. Exposure to cytolethal distending toxin and colibactin induces DNA damage, and consequently activates the DNA damage response, resulting in cell cycle arrest of the intoxicated cells and DNA repair. Irreversible DNA damage will lead to cell death by apoptosis or to senescence. It is well established that chronic exposure to DNA damaging agents, either endogenous (reactive oxygen species) or exogenous (ionizing radiation), may cause genomic instability as a result of the alteration of genes coordinating the DNA damage response, thus favoring tumor initiation and progression. In this review, we summarize the state of the art of the biology of cytolethal distending toxin and colibactin, focusing on the activation of the DNA damage response and repair pathways, and discuss the cellular responses induced in intoxicated cells, as well as how prolonged intoxication may lead to chronic inflammation, the accumulation of genomic instability, and tumor progression in both in vitro and in vivo models.
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| 7. |
- Guerra, Lina, et al.
(författare)
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Myc is required for activation of the ATM-dependent checkpoints in response to DNA damage
- 2010
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Ingår i: PLOS ONE. - : Public Library Science. - 1932-6203. ; 5:1
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: The MYC protein controls cellular functions such as differentiation, proliferation, and apoptosis. In response to genotoxic agents, cells overexpressing MYC undergo apoptosis. However, the MYC-regulated effectors acting upstream of the mitochondrial apoptotic pathway are still unknown.PRINCIPAL FINDINGS: In this study, we demonstrate that expression of Myc is required to activate the Ataxia telangiectasia mutated (ATM)-dependent DNA damage checkpoint responses in rat cell lines exposed to ionizing radiation (IR) or the bacterial cytolethal distending toxin (CDT). Phosphorylation of the ATM kinase and its downstream effectors, such as histone H2AX, were impaired in the myc null cell line HO15.19, compared to the myc positive TGR-1 and HOmyc3 cells. Nuclear foci formation of the Nijmegen Breakage Syndrome (Nbs) 1 protein, essential for efficient ATM activation, was also reduced in absence of myc. Knock down of the endogenous levels of MYC by siRNA in the human cell line HCT116 resulted in decreased ATM and CHK2 phosphorylation in response to irradiation. Conversely, cell death induced by UV irradiation, known to activate the ATR-dependent checkpoint, was similar in all the cell lines, independently of the myc status.CONCLUSION: These data demonstrate that MYC contributes to the activation of the ATM-dependent checkpoint responses, leading to cell death in response to specific genotoxic stimuli.
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| 8. |
- Guidi, Riccardo, et al.
(författare)
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Salmonella enterica delivers its genotoxin through outer membrane vesicles secreted from infected cells
- 2013
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Ingår i: Cellular Microbiology. - : Wiley-Blackwell. - 1462-5814 .- 1462-5822. ; 15:12, s. 2034-2050
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Tidskriftsartikel (refereegranskat)abstract
- Cytolethal-distending toxins (CDTs) belong to a family of DNA damage inducing exotoxins that are produced by several Gram-negative bacteria. Salmonella enterica serovar Typhi expresses its CDT (named as Typhoid toxin) only in the Salmonella-containing vacuole (SCV) of infected cells, which requires its export for cell intoxication. The mechanisms of secretion, release in the extracellular space and uptake by bystander cells are poorly understood. We have addressed these issues using a recombinant S. Typhimurium strain, MC71-CDT, where the genes encoding for the PltA, PltB and CdtB subunits of the Typhoid toxin are expressed under control of the endogenous promoters. MC71-CDT grown under conditions that mimic the SCV secreted the holotoxin in outer membrane vesicles (OMVs). Epithelial cells infected with MC71-CDT also secreted OMVs-like vesicles. The release of these extracellular vesicles required an intact SCV and relied on anterograde transport towards the cellular cortex on microtubule and actin tracks. Paracrine internalization of Typhoid toxin-loaded OMVs by bystander cells was dependent on dynamin-1, indicating active endocytosis. The subsequent induction of DNA damage required retrograde transport of the toxin through the Golgi complex. These data provide new insights on the mode of secretion of exotoxins by cells infected with intracellular bacteria.
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| 9. |
- Levi, Laura, et al.
(författare)
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Bacterial genotoxins promote inside-out integrin β1 activation, formation of focal adhesion complexes and cell spreading
- 2015
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Ingår i: PLOS ONE. - : Public Library Science. - 1932-6203. ; 10:4
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Tidskriftsartikel (refereegranskat)abstract
- Integrins are membrane bound receptors that regulate several cellular processes, such as cell adhesion, migration, survival and proliferation, and may contribute to tumor initiation/progression in cells exposed to genotoxic stress. The extent of integrin activation and its role in cell survival upon intoxication with bacterial genotoxins are still poorly characterized. These toxins induce DNA strand breaks in the target cells and activate the DNA damage response (DDR), coordinated by the Ataxia Telangectasia Mutated (ATM) kinase. In the present study, we demonstrate that induction of DNA damage by two bacterial genotoxins promotes activation of integrin β1, leading to enhanced assembly of focal adhesions and cell spreading on fibronectin, but not on vitronectin. This phenotype is mediated by an ATM-dependent inside-out integrin signaling, and requires the actin cytoskeleton remodeler NET1. The toxin-mediated cell spreading and anchorage-independent survival further relies on ALIX and TSG101, two components of the endosomal sorting complex required for transport (ESCRT), known to regulate integrin intracellular trafficking. These data reveal a novel aspect of the cellular response to bacterial genotoxins, and provide new tools to understand the carcinogenic potential of these effectors in the context of chronic intoxication and infection.
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| 10. |
- Seiwert, Nina, et al.
(författare)
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AKT2 suppresses pro-survival autophagy triggered by DNA double-strand breaks in colorectal cancer cells
- 2017
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Ingår i: Cell Death and Disease. - : Nature Publishing Group. - 2041-4889 .- 2041-4889. ; 8:8
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Tidskriftsartikel (refereegranskat)abstract
- DNA double-strand breaks (DSBs) are critical DNA lesions, which threaten genome stability and cell survival. DSBs are directly induced by ionizing radiation (IR) and radiomimetic agents, including the cytolethal distending toxin (CDT). This bacterial genotoxin harbors a unique DNase-I-like endonuclease activity. Here we studied the role of DSBs induced by CDT and IR as a trigger of autophagy, which is a cellular degradation process involved in cell homeostasis, genome protection and cancer. The regulatory mechanisms of DSB-induced autophagy were analyzed, focusing on the ATM-p53-mediated DNA damage response and AKT signaling in colorectal cancer cells. We show that treatment of cells with CDT or IR increased the levels of the autophagy marker LC3B-II. Consistently, an enhanced formation of autophagosomes and a decrease of the autophagy substrate p62 were observed. Both CDT and IR concomitantly suppressed mTOR signaling and stimulated the autophagic flux. DSBs were demonstrated as the primary trigger of autophagy using a DNase I-defective CDT mutant, which neither induced DSBs nor autophagy. Genetic abrogation of p53 and inhibition of ATM signaling impaired the autophagic flux as revealed by LC3B-II accumulation and reduced formation of autophagic vesicles. Blocking of DSB-induced apoptotic cell death by the pan-caspase inhibitor Z-VAD stimulated autophagy. In line with this, pharmacological inhibition of autophagy increased cell death, while ATG5 knockdown did not affect cell death after DSB induction. Interestingly, both IR and CDT caused AKT activation, which repressed DSB-triggered autophagy independent of the cellular DNA-PK status. Further knockdown and pharmacological inhibitor experiments provided evidence that the negative autophagy regulation was largely attributable to AKT2. Finally, we show that upregulation of CDT-induced autophagy upon AKT inhibition resulted in lower apoptosis and increased cell viability. Collectively, the findings demonstrate that DSBs trigger pro-survival autophagy in an ATM- and p53-dependent manner, which is curtailed by AKT2 signaling.
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