UMR3348 – Intégrité du génome, ARN et cancer

Publications de l’unité

Année de publication : 2014

Carsten Janke (2014 Aug 18)

The tubulin code: molecular components, readout mechanisms, and functions.

The Journal of cell biology : 461-72 : DOI : 10.1083/jcb.201406055 En savoir plus
Résumé

Microtubules are cytoskeletal filaments that are dynamically assembled from α/β-tubulin heterodimers. The primary sequence and structure of the tubulin proteins and, consequently, the properties and architecture of microtubules are highly conserved in eukaryotes. Despite this conservation, tubulin is subject to heterogeneity that is generated in two ways: by the expression of different tubulin isotypes and by posttranslational modifications (PTMs). Identifying the mechanisms that generate and control tubulin heterogeneity and how this heterogeneity affects microtubule function are long-standing goals in the field. Recent work on tubulin PTMs has shed light on how these modifications could contribute to a « tubulin code » that coordinates the complex functions of microtubules in cells.

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Ellen Tsang, Izumi Miyabe, Ismail Iraqui, Jiping Zheng, Sarah A E Lambert, Antony M Carr (2014 Jul 1)

The extent of error-prone replication restart by homologous recombination is controlled by Exo1 and checkpoint proteins.

Journal of cell science : 2983-94 : DOI : 10.1242/jcs.152678 En savoir plus
Résumé

Genetic instability, a hallmark of cancer, can occur when the replication machinery encounters a barrier. The intra-S-phase checkpoint maintains stalled replication forks in a replication-competent configuration by phosphorylating replisome components and DNA repair proteins to prevent forks from catastrophically collapsing. Here, we report a novel function of the core Schizosaccharomyces pombe checkpoint sensor kinase, Rad3 (an ATR orthologue), that is independent of Chk1 and Cds1 (a CHK2 orthologue); Rad3(ATR) regulates the association of recombination factors with collapsed forks, thus limiting their genetic instability. We further reveal antagonistic roles for Rad3(ATR) and the 9-1-1 clamp – Rad3(ATR) restrains MRN- and Exo1-dependent resection, whereas the 9-1-1 complex promotes Exo1 activity. Interestingly, the MRN complex, but not its nuclease activity, promotes resection and the subsequent association of recombination factors at collapsed forks. The biological significance of this regulation is revealed by the observation that Rad3(ATR) prevents Exo1-dependent genome instability upstream of a collapsed fork without affecting the efficiency of recombination-mediated replication restart. We propose that the interplay between Rad3(ATR) and the 9-1-1 clamp functions to fine-tune the balance between the need for the recovery of replication through recombination and the risk of increased genome instability.

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Josée Guirouilh-Barbat, Sarah Lambert, Pascale Bertrand, Bernard S Lopez (2014 Jun 11)

Is homologous recombination really an error-free process?

Frontiers in genetics : 175 : DOI : 10.3389/fgene.2014.00175 En savoir plus
Résumé

Homologous recombination (HR) is an evolutionarily conserved process that plays a pivotal role in the equilibrium between genetic stability and diversity. HR is commonly considered to be error-free, but several studies have shown that HR can be error-prone. Here, we discuss the actual accuracy of HR. First, we present the product of genetic exchanges (gene conversion, GC, and crossing over, CO) and the mechanisms of HR during double strand break repair and replication restart. We discuss the intrinsic capacities of HR to generate genome rearrangements by GC or CO, either during DSB repair or replication restart. During this process, abortive HR intermediates generate genetic instability and cell toxicity. In addition to genome rearrangements, HR also primes error-prone DNA synthesis and favors mutagenesis on single stranded DNA, a key DNA intermediate during the HR process. The fact that cells have developed several mechanisms protecting against HR excess emphasize its potential risks. Consistent with this duality, several pro-oncogenic situations have been consistently associated with either decreased or increased HR levels. Nevertheless, this versatility also has advantages that we outline here. We conclude that HR is a double-edged sword, which on one hand controls the equilibrium between genome stability and diversity but, on the other hand, can jeopardize the maintenance of genomic integrity. Therefore, whether non-homologous end joining (which, in contrast with HR, is not intrinsically mutagenic) or HR is the more mutagenic process is a question that should be re-evaluated. Both processes can be « Dr. Jekyll » in maintaining genome stability/variability and « Mr. Hyde » in jeopardizing genome integrity.

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Benjamin Uzan, Sandrine Poglio, Bastien Gerby, Ching-Lien Wu, Julia Gross, Florence Armstrong, Julien Calvo, Xavier Cahu, Caroline Deswarte, Florent Dumont, Diana Passaro, Corinne Besnard-Guérin, Thierry Leblanc, André Baruchel, Judith Landman-Parker, Paola Ballerini, Véronique Baud, Jacques Ghysdael, Frédéric Baleydier, Francoise Porteu, Francoise Pflumio (2014 Jun 1)

Interleukin-18 produced by bone marrow-derived stromal cells supports T-cell acute leukaemia progression.

EMBO molecular medicine : 821-34 : DOI : 10.1002/emmm.201303286 En savoir plus
Résumé

Development of novel therapies is critical for T-cell acute leukaemia (T-ALL). Here, we investigated the effect of inhibiting the MAPK/MEK/ERK pathway on T-ALL cell growth. Unexpectedly, MEK inhibitors (MEKi) enhanced growth of 70% of human T-ALL cell samples cultured on stromal cells independently of NOTCH activation and maintained their ability to propagate in vivo. Similar results were obtained when T-ALL cells were cultured with ERK1/2-knockdown stromal cells or with conditioned medium from MEKi-treated stromal cells. Microarray analysis identified interleukin 18 (IL-18) as transcriptionally up-regulated in MEKi-treated MS5 cells. Recombinant IL-18 promoted T-ALL growth in vitro, whereas the loss of function of IL-18 receptor in T-ALL blast cells decreased blast proliferation in vitro and in NSG mice. The NFKB pathway that is downstream to IL-18R was activated by IL-18 in blast cells. IL-18 circulating levels were increased in T-ALL-xenografted mice and also in T-ALL patients in comparison with controls. This study uncovers a novel role of the pro-inflammatory cytokine IL-18 and outlines the microenvironment involvement in human T-ALL development.

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Mery Pina, Tamara Basta, Tessa E F Quax, Alexandra Joubert, Sonia Baconnais, Diego Cortez, Sarah Lambert, Eric Le Cam, Stephen D Bell, Patrick Forterre, David Prangishvili (2014 Jun 1)

Unique genome replication mechanism of the archaeal virus AFV1.

Molecular microbiology : 1313-25 : DOI : 10.1111/mmi.12630 En savoir plus
Résumé

The exceptional genomic content and genome organization of the Acidianus filamentous virus 1 (AFV1) that infects the hyperthermophilic archaeon Acidianus hospitalis suggest that this virus might exploit an unusual mechanism of genome replication. An analysis of replicative intermediates of the viral genome by two-dimensional (2D) agarose gel electrophoresis revealed that viral genome replication starts by the formation of a D-loop and proceeds via strand displacement replication. Characterization of replicative intermediates using dark-field electron microscopy, in combination with the 2D agarose gel electrophoresis data, suggests that recombination plays a key role in the termination of AFV1 genome replication through the formation of terminal loops. A terminal protein was found to be attached to the ends of the viral genome. The results allow us to postulate a model of genome replication that relies on recombination events for initiation and termination.

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Indiana Magdalou, Bernard S Lopez, Philippe Pasero, Sarah A E Lambert (2014 Jun 1)

The causes of replication stress and their consequences on genome stability and cell fate.

Seminars in cell & developmental biology : 154-64 : DOI : 10.1016/j.semcdb.2014.04.035 En savoir plus
Résumé

Alterations of the dynamics of DNA replication cause genome instability. These alterations known as « replication stress » have emerged as a major source of genomic instability in pre-neoplasic lesions, contributing to cancer development. The concept of replication stress covers a wide variety of events that distort the temporal and spatial DNA replication program. These events have endogenous or exogenous origins and impact globally or locally on the dynamics of DNA replication. They may arise within a short window of time (acute stress) or during each S phase (chronic stress). Here, we review the known situations in which the dynamics of DNA replication is distorted. We have united them in four main categories: (i) inadequate firing of replication origins (deficiency or excess), (ii) obstacles to fork progression, (iii) conflicts between replication and transcription and (iv) DNA replication under inappropriate metabolic conditions (unbalanced DNA replication). Because the DNA replication program is a process tightly regulated by many factors, replication stress often appears as a cascade of events. A local stress may prevent the completion of DNA replication at a single locus and subsequently compromise chromosome segregation in mitosis and therefore have a global effect on genome integrity. Finally, we discuss how replication stress drives genome instability and to what extent it is relevant to cancer biology.

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Maria M Magiera, Carsten Janke (2014 May 5)

Post-translational modifications of tubulin.

Current biology : CB : R351-4 : DOI : 10.1016/j.cub.2014.03.032 En savoir plus
Résumé

Microtubules are the largest filamentous components of the eukaryotic cytoskeleton. In spite of their extraordinary level of structural conservation, microtubules fulfill a vast range of different functions in cells. How this functional diversity is achieved remains an open question; however, recent advances point towards post-translational modifications (PTMs) of tubulin as a potent mechanism to generate microtubule identities. As many microtubule functions have direct implications for development and homeostasis of organisms, understanding the molecular functions of tubulin PTMs could provide a more differentiated view on the role of microtubules in both normal and pathological aspects of organism development.

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Florence Nguyen-Khac, Véronique Della Valle, Rodolphe G Lopez, Jacques Ghysdael, Olivier A Bernard (2014 May 1)

Deregulation of AhR function by the human acute leukemia TEL-ARNT fusion protein.

American journal of hematology : 566-7 : DOI : 10.1002/ajh.23680 En savoir plus
Résumé

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Matthew Holderfield, Edward Lorenzana, Ben Weisburd, Lisa Lomovasky, Lise Boussemart, Ludovic Lacroix, Gorana Tomasic, Michel Favre, Stephan Vagner, Caroline Robert, Majid Ghoddusi, Dylan Daniel, Nancy Pryer, Frank McCormick, Darrin Stuart (2014 Apr 15)

Vemurafenib cooperates with HPV to promote initiation of cutaneous tumors.

Cancer research : 2238-45 : DOI : 10.1158/0008-5472.CAN-13-1065-T En savoir plus
Résumé

Treatment with RAF inhibitors such as vemurafenib causes the development of cutaneous squamous cell carcinomas (cSCC) or keratoacanthomas as a side effect in 18% to 30% of patients. It is known that RAF inhibitors activate the mitogen-activated protein kinase (MAPK) pathway and stimulate growth of RAS-mutated cells, possibly accounting for up to 60% of cSCC or keratoacanthoma lesions with RAS mutations, but other contributing events are obscure. To identify such events, we evaluated tumors from patients treated with vemurafenib for the presence of human papilloma virus (HPV) DNA and identified 13% to be positive. Using a transgenic murine model of HPV-driven cSCC (K14-HPV16 mice), we conducted a functional test to determine whether administration of RAF inhibitors could promote cSCC in HPV-infected tissues. Vemurafenib treatment elevated MAPK markers and increased cSCC incidence from 22% to 70% in this model. Furthermore, 55% of the cSCCs arising in vemurafenib-treated mice exhibited a wild-type Ras genotype, consistent with the frequency observed in human patients. Our results argue that HPV cooperates with vemurafenib to promote tumorigenesis, in either the presence or absence of RAS mutations.

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Chong Sun, Liqin Wang, Sidong Huang, Guus J J E Heynen, Anirudh Prahallad, Caroline Robert, John Haanen, Christian Blank, Jelle Wesseling, Stefan M Willems, Davide Zecchin, Sebastijan Hobor, Prashanth K Bajpe, Cor Lieftink, Christina Mateus, Stephan Vagner, Wipawadee Grernrum, Ingrid Hofland, Andreas Schlicker, Lodewyk F A Wessels, Roderick L Beijersbergen, Alberto Bardelli, Federica Di Nicolantonio, Alexander M M Eggermont, Rene Bernards (2014 Apr 3)

Reversible and adaptive resistance to BRAF(V600E) inhibition in melanoma.

Nature : 118-22 : DOI : 10.1038/nature13121 En savoir plus
Résumé

Treatment of BRAF(V600E) mutant melanoma by small molecule drugs that target the BRAF or MEK kinases can be effective, but resistance develops invariably. In contrast, colon cancers that harbour the same BRAF(V600E) mutation are intrinsically resistant to BRAF inhibitors, due to feedback activation of the epidermal growth factor receptor (EGFR). Here we show that 6 out of 16 melanoma tumours analysed acquired EGFR expression after the development of resistance to BRAF or MEK inhibitors. Using a chromatin-regulator-focused short hairpin RNA (shRNA) library, we find that suppression of sex determining region Y-box 10 (SOX10) in melanoma causes activation of TGF-β signalling, thus leading to upregulation of EGFR and platelet-derived growth factor receptor-β (PDGFRB), which confer resistance to BRAF and MEK inhibitors. Expression of EGFR in melanoma or treatment with TGF-β results in a slow-growth phenotype with cells displaying hallmarks of oncogene-induced senescence. However, EGFR expression or exposure to TGF-β becomes beneficial for proliferation in the presence of BRAF or MEK inhibitors. In a heterogeneous population of melanoma cells having varying levels of SOX10 suppression, cells with low SOX10 and consequently high EGFR expression are rapidly enriched in the presence of drug, but this is reversed when the drug treatment is discontinued. We find evidence for SOX10 loss and/or activation of TGF-β signalling in 4 of the 6 EGFR-positive drug-resistant melanoma patient samples. Our findings provide a rationale for why some BRAF or MEK inhibitor-resistant melanoma patients may regain sensitivity to these drugs after a ‘drug holiday’ and identify patients with EGFR-positive melanoma as a group that may benefit from re-treatment after a drug holiday.

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Annemarie Wehenkel, Carsten Janke (2014 Apr 1)

Towards elucidating the tubulin code.

Nature cell biology : 303-5 : DOI : 10.1038/ncb2938 En savoir plus
Résumé

Genetically encoded and post-translationally generated variations of tubulin C-terminal tails give rise to extensive heterogeneity of the microtubule cytoskeleton. The generation of different tubulin variants in yeast now demonstrates how single amino-acid differences or post-translational modifications can modulate the behaviour of selected molecular motors.

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Charlotte Sagne, Virginie Marcel, Maria Bota, Ghyslaine Martel-Planche, Amanda Nobrega, Edenir Inêz Palmero, Laury Perriaud, Mathieu Boniol, Stephan Vagner, David G Cox, Chang S Chan, Jean-Louis Mergny, Magali Olivier, Patricia Ashton-Prolla, Janet Hall, Pierre Hainaut, Maria Isabel Achatz (2014 Apr 1)

Age at cancer onset in germline TP53 mutation carriers: association with polymorphisms in predicted G-quadruplex structures.

Carcinogenesis : 807-15 : DOI : 10.1093/carcin/bgt381 En savoir plus
Résumé

Germline TP53 mutations predispose to multiple cancers defining Li-Fraumeni/Li-Fraumeni-like syndrome (LFS/LFL), a disease with large individual disparities in cancer profiles and age of onset. G-quadruplexes (G4s) are secondary structural motifs occurring in guanine tracks, with regulatory effects on DNA and RNA. We analyzed 85 polymorphisms within or near five predicted G4s in TP53 in search of modifiers of penetrance of LFS/LFL in Brazilian cancer families with (n = 35) or without (n = 110) TP53 mutations. Statistical analyses stratified on family structure showed that cancer tended to occur ~15 years later in mutation carriers who also carried the variant alleles of two polymorphisms within predicted G4-forming regions, rs17878362 (TP53 PIN3, 16 bp duplication in intron 3; P = 0.082) and rs17880560 (6 bp duplication in 3′ flanking region; P = 0.067). Haplotype analysis showed that this inverse association was driven by the polymorphic status of the remaining wild-type (WT) haplotype in mutation carriers: in carriers with a WT haplotype containing at least one variant allele of rs17878362 or rs17880560, cancer occurred ~15 years later than in carriers with other WT haplotypes (P = 0.019). No effect on age of cancer onset was observed in subjects without a TP53 mutation. The G4 in intron 3 has been shown to regulate alternative p53 messenger RNA splicing, whereas the biological roles of predicted G4s in the 3′ flanking region remain to be elucidated. In conclusion, this study demonstrates that G4 polymorphisms in haplotypes of the WT TP53 allele have an impact on LFS/LFL penetrance in germline TP53 mutation carriers.

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Barouyr Baroudjian, Lise Boussemart, Emilie Routier, Brigitte Dreno, Yungan Tao, Eric Deutsch, Pierre Blanchard, Frédéric Dhermain, Laurence Vilcot, Stephan Vagner, Alexander Eggermont, Christine Mateus, Caroline Robert (2014 Mar 1)

Dramatic response to radiotherapy combined with vemurafenib. Is vemurafenib a radiosensitizer?

European journal of dermatology : EJD : 265-7 : DOI : 10.1684/ejd.2014.2300 En savoir plus
Résumé

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Martin Dutertre, Sarah Lambert, Aura Carreira, Mounira Amor-Guéret, Stéphan Vagner (2014 Mar 1)

DNA damage: RNA-binding proteins protect from near and far.

Trends in biochemical sciences : 141-9 : DOI : 10.1016/j.tibs.2014.01.003 En savoir plus
Résumé

Recent work, including large-scale genetic and molecular analyses, identified RNA-binding proteins (RBPs) as major players in the prevention of genome instability. These studies show that RBPs prevent harmful RNA/DNA hybrids and are involved in the DNA damage response (DDR), from DNA repair to cell survival decisions. Indeed, specific RBPs allow the selective regulation of DDR genes at multiple post-transcriptional levels (from pre-mRNA splicing/polyadenylation to mRNA stability/translation) and are directly involved in DNA repair. These multiple activities are mediated by RBP binding to mRNAs, nascent transcripts, noncoding RNAs, and damaged DNA. Finally, because DNA damage modifies RBP localization and binding to different RNA/DNA molecules, we propose that upon DNA damage, RBPs coordinately regulate various aspects of both RNA and DNA metabolism.

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Martin Dutertre, Fatima Zahra Chakrama, Emmanuel Combe, François-Olivier Desmet, Hussein Mortada, Micaela Polay Espinoza, Lise Gratadou, Didier Auboeuf (2014 Feb 28)

A recently evolved class of alternative 3′-terminal exons involved in cell cycle regulation by topoisomerase inhibitors.

Nature communications : 3395 : DOI : 10.1038/ncomms4395 En savoir plus
Résumé

Alternative 3′-terminal exons, which use intronic polyadenylation sites, are generally less conserved and expressed at lower levels than the last exon of genes. Here we discover a class of human genes, in which the last exon appeared recently during evolution, and the major gene product uses an alternative 3′-terminal exon corresponding to the ancestral last exon of the gene. This novel class of alternative 3′-terminal exons are downregulated on a large scale by doxorubicin, a cytostatic drug targeting topoisomerase II, and play a role in cell cycle regulation, including centromere-kinetochore assembly. The RNA-binding protein HuR/ELAVL1 is a major regulator of this specific set of alternative 3′-terminal exons. HuR binding to the alternative 3′-terminal exon in the pre-messenger RNA promotes its splicing, and is reduced by topoisomerase inhibitors. These findings provide new insights into the evolution, function and molecular regulation of alternative 3′-terminal exons.

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