Pseudomonas aeruginosa prise en flagrant délit de casse ! Pseudomonas aeruginosa caught in the act !

International audienceDes armes qui attaquent le génome eucaryote de façon encore mystérieuse Pseudomonas aeruginosa est une bactérie pathogène opportuniste infectant principalement les individus aux défenses immunitaires affaiblies, les patients ayant une rupture de leurs barrières cutanées (chirurgie, brûlures,...) ou subissant un geste invasif (pose d'une sonde, d'un cathéter) [1]. D'autres sujets sont particulièrement à risque, ainsi 80% des personnes atteintes de mucoviscidose sont chroniquement infectées par cette bactérie. Les infections à P. aeruginosa sont le plus souvent contractées en milieu hospitalier et elles demeurent un défi pour le corps médical en raison de la multi-résistance des souches aux antibiotiques [2]. La pathogénicité liée aux infections aiguës ou chroniques à P. aeruginosa est multifactorielle [3]. L'un des systèmes de virulence majeurs associé aux infections aiguës est le système de sécrétion de type 3 (SST3) [4]. Il est constitué d'une aiguille creuse érigée à la surface de la bactérie qui s'insère dans la membrane plasmique de la cellule hôte et permet l'injection de toxines bactériennes (ExoY, ExoT et ExoS ou ExoU) dans le cytoplasme de la cellule infectée. Nous avons recherché les dommages potentiels causés par P. aeruginosa au patrimoine génétique de la cellule hôte. Pour la première fois, nos travaux montrent que le SST3 est associé à des cassures double-brin de l'ADN, lésions très dangereuses pour le génome, et à une réaction de la cellule hôte qui va tenter de réparer les dégâts [5]

The opportunistic pathogen Pseudomonas aeruginosa activates the DNA double-strand break signaling and repair pathway in infected cells.

International audienceHighly hazardous DNA double-strand breaks can be induced in eukaryotic cells by a number of agents including pathogenic bacterial strains. We have investigated the genotoxic potential of Pseudomonas aeruginosa, an opportunistic pathogen causing devastating nosocomial infections in cystic fibrosis or immunocompromised patients. Our data revealed that infection of immune or epithelial cells by P. aeruginosa triggered DNA strand breaks and phosphorylation of histone H2AX (γH2AX), a marker of DNA double-strand breaks. Moreover, it induced formation of discrete nuclear repair foci similar to gamma-irradiation-induced foci, and containing γH2AX and 53BP1, an adaptor protein mediating the DNA-damage response pathway. Gene deletion, mutagenesis, and complementation in P. aeruginosa identified ExoS bacterial toxin as the major factor involved in γH2AX induction. Chemical inhibition of several kinases known to phosphorylate H2AX demonstrated that Ataxia Telangiectasia Mutated (ATM) was the principal kinase in P. aeruginosa-induced H2AX phosphorylation. Finally, infection led to ATM kinase activation by an auto-phosphorylation mechanism. Together, these data show for the first time that infection by P. aeruginosa activates the DNA double-strand break repair machinery of the host cells. This novel information sheds new light on the consequences of P. aeruginosa infection in mammalian cells. As pathogenic Escherichia coli or carcinogenic Helicobacter pylori can alter genome integrity through DNA double-strand breaks, leading to chromosomal instability and eventually cancer, our findings highlight possible new routes for further investigations of P. aeruginosa in cancer biology and they identify ATM as a potential target molecule for drug design

HOX11L2/TLX3 is transcriptionally activated through T-cell regulatory elements downstream of BCL11B as a result of the t(5;14)(q35;q32).

International audienceThe t(5;14)(q35;q32) chromosomal translocation is specifically observed in up to 20% of childhood T-cell acute lymphoblastic leukemia (T-ALL). It affects the BCL11B/CTIP2 locus on chromosome 14 and the RANBP17-TLX3/HOX11L2 region on chromosome 5. It leads to ectopic activation of TLX3/HOX11L2. To investigate the reasons of the association between t(5;14) and T-ALL, we isolated the translocation breakpoints in 8 t(5;14) patients. Sequence analyses did not involve recombinase activity in the genesis of the translocation. We used DNAse1 hypersensitive experiments to locate transcriptional regulatory elements downstream of BCL11B. By transient transfection experiments, 2 of the 6 regions demonstrated cis-activation properties in T cells and were also effective on the TLX3 promoter. Our data indicate that the basis of the specific association between t(5;14) and T-ALL lies on the juxtaposition of TLX3 to long-range cis-activating regions active during T-cell differentiation

Contribution a l'etude des mecanismes anti-inflammatoires des glucocorticoides. Modulation de la synthese locale des proteines du complement par les cellules monocytaires

SIGLEAvailable from INIST (FR), Document Supply Service, under shelf-number : T 78613 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Les infections bactériennes vues du génome eucaryote

Un nombre croissant d’études indiquent que l’infection par des bactéries pathogènes induit de graves lésions sur le génome de l’hôte, notamment des cassures double-brin. Même après réparation de l’ADN, il reste souvent, au niveau chromosomique, des séquelles qui peuvent générer une instabilité génétique lors d’une division ultérieure. L’inflammation chronique favorise l’expansion des bactéries génotoxiques dans le microbiote intestinal et l’apparition de carcinomes du côlon. Les bactéries manipulent les points de contrôle du cycle cellulaire et les voies de réparation de l’ADN, mais les acteurs moléculaires induisant les lésions sur l’ADN ne sont pas identifiés avec certitude, en dépit de fortes présomptions sur les espèces réactives de l’oxygène

When our genome is targeted by pathogenic bacteria.

International audienceEukaryotic cells repair thousands of lesions arising in the genome at each cell cycle. The most hazardous damage is likely DNA double-strand breaks (DSB) that cleave the double helix backbone. DSBs occur naturally during T-cell receptor and immunoglobulin gene recombination in lymphocytes. DSBs can also arise as a consequence of exogenous stresses (e.g. ionizing irradiation, chemotherapeutic drugs, viruses) or oxidative processes. An increasing number of studies have reported that infection with pathogenic bacteria also alters the host genome, producing DSB and other modifications on DNA. This review focuses on recent data on bacteria-induced DNA damage and the known strategies used by these pathogens to maintain a physiological niche in the host. Even after DNA repair in infected cells, “scars” often remain on chromosomes and might generate genomic instability at the next cell division. Chronic inflammation in tissue, combined with infection and DNA damage, can give rise to genomic instability and eventually cancer. A functional link between the DNA damage response and the innate immune response has been recently established. Pathogenic bacteria also highjack the host cell cycle, often acting on the stability of the master regulator p53, or dampen the DNA damage response to support bacterial replication in an appropriate reservoir. Except in a few cases, the molecular mechanisms responsible for DNA lesions are poorly understood, although ROS release during infection is a serious candidate for generating DNA breaks. Thus, chronic or repetitive infections with genotoxic bacteria represent a common source of DNA lesions that compromise host genome integrity

Les cellules acineuses différenciées se dupliquent pour régénérer les acinus salivaires

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Point mutations in BCL6 DNA-binding domain reveal distinct roles for the six zinc fingers.

International audienceThe B-cell lymphoma 6 (BCL6) gene encodes a transcriptional repressor containing six C-terminal Krüppel-like zinc fingers. The zinc finger (ZF) cluster is necessary and sufficient for interaction with both DNA and several proteins and for nuclear targeting. However, the functional specificity of the six ZFs in these cellular roles is unknown. To characterize this domain, we mutated individually each ZF of BCL6. Our results reveal that mutation of the two N-terminal ZFs does not impair cognate DNA-binding, cellular localization of the protein nor the transcriptional repression capacity of BCL6. By contrast, mutation of any of the remaining ZFs abolishes the binding of BCL6 to DNA in vitro and the transrepressive function of the protein in vivo. Finally, none of the six mutations affect the interaction between BCL6 and class II histone deacetylases. Thus our experiments demonstrate that BCL6 uses each of the four C-terminus ZFs for binding to a target sequence while the two amino terminal fingers are likely engaged in other unknown function(s)