UMR3348 – Intégrité du génome, ARN et cancer

Publications de l’unité

Année de publication : 2012

Ismail Iraqui, Yasmina Chekkal, Nada Jmari, Violena Pietrobon, Karine Fréon, Audrey Costes, Sarah A E Lambert (2012 Oct 18)

Recovery of arrested replication forks by homologous recombination is error-prone.

PLoS genetics : e1002976 : DOI : 10.1371/journal.pgen.1002976 En savoir plus
Résumé

Homologous recombination is a universal mechanism that allows repair of DNA and provides support for DNA replication. Homologous recombination is therefore a major pathway that suppresses non-homology-mediated genome instability. Here, we report that recovery of impeded replication forks by homologous recombination is error-prone. Using a fork-arrest-based assay in fission yeast, we demonstrate that a single collapsed fork can cause mutations and large-scale genomic changes, including deletions and translocations. Fork-arrest-induced gross chromosomal rearrangements are mediated by inappropriate ectopic recombination events at the site of collapsed forks. Inverted repeats near the site of fork collapse stimulate large-scale genomic changes up to 1,500 times over spontaneous events. We also show that the high accuracy of DNA replication during S-phase is impaired by impediments to fork progression, since fork-arrest-induced mutation is due to erroneous DNA synthesis during recovery of replication forks. The mutations caused are small insertions/duplications between short tandem repeats (micro-homology) indicative of replication slippage. Our data establish that collapsed forks, but not stalled forks, recovered by homologous recombination are prone to replication slippage. The inaccuracy of DNA synthesis does not rely on PCNA ubiquitination or trans-lesion-synthesis DNA polymerases, and it is not counteracted by mismatch repair. We propose that deletions/insertions, mediated by micro-homology, leading to copy number variations during replication stress may arise by progression of error-prone replication forks restarted by homologous recombination.

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Adrien Decorsière, Christine Toulas, Françoise Fouque, Anne-Françoise Tilkin-Mariamé, Janick Selves, Rosine Guimbaud, Edith Chipoulet, Caroline Delmas, Jean-Marc Rey, Pascal Pujol, Gilles Favre, Stefania Millevoi, Stéphan Vagner (2012 Jul 1)

Decreased efficiency of MSH6 mRNA polyadenylation linked to a 20-base-pair duplication in Lynch syndrome families.

Cell cycle (Georgetown, Tex.) : 2578-80 : DOI : 10.4161/cc.20625 En savoir plus
Résumé

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Stefania Millevoi, Hervé Moine, Stéphan Vagner (2012 Jul 1)

G-quadruplexes in RNA biology.

Wiley interdisciplinary reviews. RNA : 495-507 : DOI : 10.1002/wrna.1113 En savoir plus
Résumé

G-quadruplexes are noncanonical structures formed by G-rich DNA and RNA sequences that fold into a four-stranded conformation. Experimental studies and computational predictions show that RNA G-quadruplexes are present in transcripts associated with telomeres, in noncoding sequences of primary transcripts and within mature transcripts. RNA G-quadruplexes at these specific locations play important roles in key cellular functions, including telomere homeostasis and gene expression. Indeed, RNA G-quadruplexes appear as important regulators of pre-mRNA processing (splicing and polyadenylation), RNA turnover, mRNA targeting and translation. The regulatory mechanisms controlled by RNA G-quadruplexes involve the binding of protein factors that modulate G-quadruplex conformation and/or serve as a bridge to recruit additional protein regulators. In this review, we summarize the current knowledge on the role of G-quadruplexes in RNA biology with particular emphasis on the molecular mechanisms underlying their specific function in RNA metabolism occurring in physiological or pathological conditions.

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Sébastien Rouzeau, Fabrice P Cordelières, Géraldine Buhagiar-Labarchède, Ilse Hurbain, Rosine Onclercq-Delic, Simon Gemble, Laura Magnaghi-Jaulin, Christian Jaulin, Mounira Amor-Guéret (2012 Apr 26)

Bloom’s syndrome and PICH helicases cooperate with topoisomerase IIα in centromere disjunction before anaphase.

PloS one : e33905 : DOI : 10.1371/journal.pone.0033905 En savoir plus
Résumé

Centromeres are specialized chromosome domains that control chromosome segregation during mitosis, but little is known about the mechanisms underlying the maintenance of their integrity. Centromeric ultrafine anaphase bridges are physiological DNA structures thought to contain unresolved DNA catenations between the centromeres separating during anaphase. BLM and PICH helicases colocalize at these ultrafine anaphase bridges and promote their resolution. As PICH is detectable at centromeres from prometaphase onwards, we hypothesized that BLM might also be located at centromeres and that the two proteins might cooperate to resolve DNA catenations before the onset of anaphase. Using immunofluorescence analyses, we demonstrated the recruitment of BLM to centromeres from G2 phase to mitosis. With a combination of fluorescence in situ hybridization, electron microscopy, RNA interference, chromosome spreads and chromatin immunoprecipitation, we showed that both BLM-deficient and PICH-deficient prometaphase cells displayed changes in centromere structure. These cells also had a higher frequency of centromeric non disjunction in the absence of cohesin, suggesting the persistence of catenations. Both proteins were required for the correct recruitment to the centromere of active topoisomerase IIα, an enzyme specialized in the catenation/decatenation process. These observations reveal the existence of a functional relationship between BLM, PICH and topoisomerase IIα in the centromere decatenation process. They indicate that the higher frequency of centromeric ultrafine anaphase bridges in BLM-deficient cells and in cells treated with topoisomerase IIα inhibitors is probably due not only to unresolved physiological ultrafine anaphase bridges, but also to newly formed ultrafine anaphase bridges. We suggest that BLM and PICH cooperate in rendering centromeric catenates accessible to topoisomerase IIα, thereby facilitating correct centromere disjunction and preventing the formation of supernumerary centromeric ultrafine anaphase bridges.

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Jean Philippe Arnault, Christine Mateus, Bernard Escudier, Gorana Tomasic, Janine Wechsler, Emilie Hollville, Jean-Charles Soria, David Malka, Alain Sarasin, Magalie Larcher, Jocelyne André, Nyam Kamsu-Kom, Lise Boussemart, Ludovic Lacroix, Alain Spatz, Alexander M Eggermont, Sabine Druillennec, Stephan Vagner, Alain Eychène, Nicolas Dumaz, Caroline Robert (2012 Jan 1)

Skin tumors induced by sorafenib; paradoxic RAS-RAF pathway activation and oncogenic mutations of HRAS, TP53, and TGFBR1.

Clinical cancer research : an official journal of the American Association for Cancer Research : 263-72 : DOI : 10.1158/1078-0432.CCR-11-1344 En savoir plus
Résumé

The emergence of skin tumors in patients treated with sorafenib or with more recent BRAF inhibitors is an intriguing and potentially serious event. We carried out a clinical, pathologic, and molecular study of skin lesions occurring in patients receiving sorafenib.

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Année de publication : 2011

Carsten Janke, Jeannette Chloë Bulinski (2011 Nov 16)

Post-translational regulation of the microtubule cytoskeleton: mechanisms and functions.

Nature reviews. Molecular cell biology : 773-86 : DOI : 10.1038/nrm3227 En savoir plus
Résumé

Half a century of biochemical and biophysical experiments has provided attractive models that may explain the diverse functions of microtubules within cells and organisms. However, the notion of functionally distinct microtubule types has not been explored with similar intensity, mostly because mechanisms for generating divergent microtubule species were not yet known. Cells generate distinct microtubule subtypes through expression of different tubulin isotypes and through post-translational modifications, such as detyrosination and further cleavage to Δ2-tubulin, acetylation, polyglutamylation and polyglycylation. The recent discovery of enzymes responsible for many tubulin post-translational modifications has enabled functional studies demonstrating that these post-translational modifications may regulate microtubule functions through an amazing range of mechanisms.

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Ana Leticia Maragno, Martine Pironin, Hélène Alcalde, Xiuli Cong, Klaus-Peter Knobeloch, Frederic Tangy, Dong-Er Zhang, Jacques Ghysdael, Christine Tran Quang (2011 Oct 12)

ISG15 modulates development of the erythroid lineage.

PloS one : e26068 : DOI : 10.1371/journal.pone.0026068 En savoir plus
Résumé

Activation of erythropoietin receptor allows erythroblasts to generate erythrocytes. In a search for genes that are up-regulated during this differentiation process, we have identified ISG15 as being induced during late erythroid differentiation. ISG15 belongs to the ubiquitin-like protein family and is covalently linked to target proteins by the enzymes of the ISGylation machinery. Using both in vivo and in vitro differentiating erythroblasts, we show that expression of ISG15 as well as the ISGylation process related enzymes Ube1L, UbcM8 and Herc6 are induced during erythroid differentiation. Loss of ISG15 in mice results in decreased number of BFU-E/CFU-E in bone marrow, concomitant with an increased number of these cells in the spleen of these animals. ISG15(-/-) bone marrow and spleen-derived erythroblasts show a less differentiated phenotype both in vivo and in vitro, and over-expression of ISG15 in erythroblasts is found to facilitate erythroid differentiation. Furthermore, we have shown that important players of erythroid development, such as STAT5, Globin, PLC γ and ERK2 are ISGylated in erythroid cells. This establishes a new role for ISG15, besides its well-characterized anti-viral functions, during erythroid differentiation.

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Luc Friboulet, Daniel Barrios-Gonzales, Frédéric Commo, Ken André Olaussen, Stephan Vagner, Julien Adam, Aïcha Goubar, Nicolas Dorvault, Vladimir Lazar, Bastien Job, Benjamin Besse, Pierre Validire, Philippe Girard, Ludovic Lacroix, Johanna Hasmats, Fabienne Dufour, Fabrice André, Jean-Charles Soria (2011 Sep 1)

Molecular Characteristics of ERCC1-Negative versus ERCC1-Positive Tumors in Resected NSCLC.

Clinical cancer research : an official journal of the American Association for Cancer Research : 5562-72 : DOI : 10.1158/1078-0432.CCR-11-0790 En savoir plus
Résumé

Excision repair cross-complementation group 1 (ERCC1) is a protein involved in repair of DNA platinum adducts and stalled DNA replication forks. We and others have previously shown the influence of ERCC1 expression upon survival rates and benefit of cisplatin-based chemotherapy in patients with resected non-small-cell lung cancer (NSCLC). However, little is known about the molecular characteristics of ERCC1-positive and ERCC1-negative tumors.

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Aura Carreira, Stephen C Kowalczykowski (2011 Jun 28)

Two classes of BRC repeats in BRCA2 promote RAD51 nucleoprotein filament function by distinct mechanisms.

Proceedings of the National Academy of Sciences of the United States of America : 10448-53 : DOI : 10.1073/pnas.1106971108 En savoir plus
Résumé

The human tumor suppressor protein BRCA2 plays a key role in recombinational DNA repair. BRCA2 recruits RAD51 to sites of DNA damage through interaction with eight conserved motifs of approximately 35 amino acids, the BRC repeats; however, the specific function of each repeat remains unclear. Here, we investigated the function of the individual BRC repeats by systematically analyzing their effects on RAD51 activities. Our results reveal the existence of two categories of BRC repeats that display unique functional characteristics. One group, comprising BRC1, -2, -3, and -4, binds to free RAD51 with high affinity. The second group, comprising BRC5, -6, -7, and -8, binds to free RAD51 with low affinity but binds to the RAD51-ssDNA filament with high affinity. Each member of the first group reduces the ATPase activity of RAD51, whereas none of the BRC repeats of the second group affects this activity. Thus, through different mechanisms, both types of BRC repeats bind to and stabilize the RAD51 nucleoprotein filament on ssDNA. In addition, members of the first group limit binding of RAD51 to duplex DNA, where members of the second group do not. Only the first group enhances DNA strand exchange by RAD51. Our results suggest that the two groups of BRC repeats have differentially evolved to ensure efficient formation of a nascent RAD51 filament on ssDNA by promoting its nucleation and growth, respectively. We propose that the BRC repeats cooperate in a partially redundant but reinforcing manner to ensure a high probability of RAD51 filament formation.

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Pauline Chabosseau, Géraldine Buhagiar-Labarchède, Rosine Onclercq-Delic, Sarah Lambert, Michelle Debatisse, Olivier Brison, Mounira Amor-Guéret (2011 Jun 28)

Pyrimidine pool imbalance induced by BLM helicase deficiency contributes to genetic instability in Bloom syndrome.

Nature communications : 368 : DOI : 10.1038/ncomms1363 En savoir plus
Résumé

Defects in DNA replication are associated with genetic instability and cancer development, as illustrated in Bloom syndrome. Features of this syndrome include a slowdown in replication speed, defective fork reactivation and high rates of sister chromatid exchange, with a general predisposition to cancer. Bloom syndrome is caused by mutations in the BLM gene encoding a RecQ helicase. Here we report that BLM deficiency is associated with a strong cytidine deaminase defect, leading to pyrimidine pool disequilibrium. In BLM-deficient cells, pyrimidine pool normalization leads to reduction of sister chromatid exchange frequency and is sufficient for full restoration of replication fork velocity but not the fork restart defect, thus identifying the part of the Bloom syndrome phenotype because of pyrimidine pool imbalance. This study provides new insights into the molecular basis of control of replication speed and the genetic instability associated with Bloom syndrome. Nucleotide pool disequilibrium could be a general phenomenon in a large spectrum of precancerous and cancer cells.

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Benjamin Lacroix, Carsten Janke (2011 Jun 25)

Generation of differentially polyglutamylated microtubules.

Methods in molecular biology (Clifton, N.J.) : 57-69 : DOI : 10.1007/978-1-61779-252-6_4 En savoir plus
Résumé

Microtubules are cytoskeletal structures built of alpha- and beta-tubulins. Although tubulins are highly conserved throughout evolution, microtubules can be adapted to a range of different functions. A powerful mechanism that could regulate the functional specialization of microtubules is the posttranslational modification of tubulin molecules. Two tubulin modifications, polyglutamylation and polyglycylation, generate amino acid side chains of different length on tubulin. These modifications are thought to regulate interactions between microtubules and their associated proteins; however, detailed studies of this potential mechanism have not been performed. The investigation of the potential regulatory role of polyglutamylation requires in vitro tools to visualize the molecular events that could be affected by this modification. Classically, in vitro work with microtubules is performed with tubulin from brain tissue; however, this tubulin is highly posttranslationally modified. Here, we describe a method for the purification of tubulin carrying controlled levels of polyglutamylation, which can be used in basic in vitro assays.

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Pierre Zindy, Yann Bergé, Ben Allal, Thomas Filleron, Sandra Pierredon, Anne Cammas, Samantha Beck, Loubna Mhamdi, Li Fan, Gilles Favre, Jean-Pierre Delord, Henri Roché, Florence Dalenc, Magali Lacroix-Triki, Stéphan Vagner (2011 Jun 15)

Formation of the eIF4F translation-initiation complex determines sensitivity to anticancer drugs targeting the EGFR and HER2 receptors.

Cancer research : 4068-73 : DOI : 10.1158/0008-5472.CAN-11-0420 En savoir plus
Résumé

Elucidating how cancer cells respond to antagonists of HER receptor family members is critical to understanding mechanisms of therapeutic resistance that arise in patients. In large part, resistance to such agents appears to arise from deregulation of the phosphatidylinositol-3-kinase (PI3K)/Akt/mTOR pathway. mTOR-dependent phosphorylation of the translation repressor 4E-BP1 leads to its dissociation from eIF4E, thereby causing an increase in the formation of the eIF4F complex, which also comprises eIF4G and eIF4A. In this study, we show that trastuzumab, cetuximab, and erlotinib all decrease the formation of the eIF4F complex in breast, colon, and head and neck cancer cells, respectively. Ectopic expression of eIF4E restores the trastuzumab-dependent defect in eIF4F formation, renders cells resistant to the trastuzumab-mediated decrease in cell proliferation, and rescues breast cancer xenografts from inhibition by trastuzumab. In breast tumor specimens, the level of eIF4E expression is associated with the therapeutic response to a trastuzumab-based regimen. Together, our findings suggest that formation of the eIF4F complex may be a critical determinant of the response to anticancer drugs that target HER2 and epidermal growth factor receptor.

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Marie-Jo Moutin, Annie Andrieux, Carsten Janke (2011 May 25)

[Microtubule polyglutamylation and neurodegeneration].

Médecine sciences : M/S : 464-7 : DOI : 10.1051/medsci/2011275006 En savoir plus
Résumé

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Adrien Decorsière, Anne Cayrel, Stéphan Vagner, Stefania Millevoi (2011 Feb 1)

Essential role for the interaction between hnRNP H/F and a G quadruplex in maintaining p53 pre-mRNA 3′-end processing and function during DNA damage.

Genes & development : 220-5 : DOI : 10.1101/gad.607011 En savoir plus
Résumé

Following DNA damage, mRNA 3′-end formation is inhibited, contributing to repression of mRNA synthesis. Here we investigated how DNA-damaged cells accomplish p53 mRNA 3′-end formation when normal mechanisms of pre-mRNA 3′-end processing regulation are inhibited. The underlying mechanism involves the interaction between a G-quadruplex structure located downstream from the p53 cleavage site and hnRNP H/F. Importantly, this interaction is critical for p53 expression and contributes to p53-mediated apoptosis. Our results uncover the existence of a specific rescue mechanism of 3′-end processing regulation allowing stress-induced p53 accumulation and function in apoptosis.

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Année de publication : 2010

Robin Jeannet, Jérôme Mastio, Alejandra Macias-Garcia, Attila Oravecz, Todd Ashworth, Anne-Solen Geimer Le Lay, Bernard Jost, Stéphanie Le Gras, Jacques Ghysdael, Thomas Gridley, Tasuku Honjo, Freddy Radtke, Jon C Aster, Susan Chan, Philippe Kastner (2010 Dec 16)

Oncogenic activation of the Notch1 gene by deletion of its promoter in Ikaros-deficient T-ALL.

Blood : 5443-54 : DOI : 10.1182/blood-2010-05-286658 En savoir plus
Résumé

The Notch pathway is frequently activated in T-cell acute lymphoblastic leukemias (T-ALLs). Of the Notch receptors, Notch1 is a recurrent target of gain-of-function mutations and Notch3 is expressed in all T-ALLs, but it is currently unclear how these receptors contribute to T-cell transformation in vivo. We investigated the role of Notch1 and Notch3 in T-ALL progression by a genetic approach, in mice bearing a knockdown mutation in the Ikaros gene that spontaneously develop Notch-dependent T-ALL. While deletion of Notch3 has little effect, T cell-specific deletion of floxed Notch1 promoter/exon 1 sequences significantly accelerates leukemogenesis. Notch1-deleted tumors lack surface Notch1 but express γ-secretase-cleaved intracellular Notch1 proteins. In addition, these tumors accumulate high levels of truncated Notch1 transcripts that are caused by aberrant transcription from cryptic initiation sites in the 3′ part of the gene. Deletion of the floxed sequences directly reprograms the Notch1 locus to begin transcription from these 3′ promoters and is accompanied by an epigenetic reorganization of the Notch1 locus that is consistent with transcriptional activation. Further, spontaneous deletion of 5′ Notch1 sequences occurs in approximately 75% of Ikaros-deficient T-ALLs. These results reveal a novel mechanism for the oncogenic activation of the Notch1 gene after deletion of its main promoter.

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