LES PROTEINES KIN17, XPC, DNA-PKCS ET XRCC4 DANS LA REPONSE CELLULAIRE AUX DOMMAGES DE L'ADN. ETUDE DES RELATIONS ENTRE LA REPARATION PAR EXCISION DE NUCLEOTIDES ET LA RECOMBINAISON NON HOMOLOGUE DANS UN MODELE SYNGENIQUE HUMAIN

The response to genotoxic stress involves many cellular factors in a complex network of mechanisms that aim to preserve the genetic integrity of the organism. These mechanisms enclose the detection and repair of DNA lesions, the regulation of transcription and replication and, eventually, the setting of cell death. Among the nuclear proteins involved in this response, kin17 proteins are zinc-finger proteins conserved through evolution and activated by ultraviolet (UV) or ionizing radiations (IR). We showed that human kin17 protein (HSAkin17) is found in the cell under a soluble form and a form tightly anchored to nuclear structures. A fraction of HSAkin17 protein is directly associated with chromatin. HSAkin17 protein is recruited to nuclear structures 24 hours after treatment with various agents inducing DNA double-strand breaks (DSB) and/or replication forks blocage. Moreover, the reduction of total HSAkin17 protein level sensitizises RKO cells to IR. We also present evidence for the involvement of HSAkin17 protein in DNA replication. This hypothesis was further confirmed by the biochemical demonstration of its belonging to the replication complex. HSAkin17 protein could link DNA replication and DNA repair, a defect in the HSAkin17 pathway leading to an increased radiosensitivity. In a second part, we studied the interactions between two DNA repair mechanisms: nucleotide excision repair (NER) and non-homologous end joining (NHEJ). NER repairs a wide variety of lesions inducing a distortion of the DNA double helix including UV-induced pyrimidine dimers. NHEJ allows the repair of DSB by direct joining of DNA ends. We used a syngenic model for DNA repair defects based on RNA interference developed in the laboratory. Epstein-Barr virus-derived vectors (pEBV) allow long-term expression of siRNA and specific exctinction of the targeted gene. The reduction of the expression of genes involved in NER (XPA and XPC) or NHEJ (DNA-PKcs and XRCC4) leads to the expected phenotypes. We showed that a reduced level of XPC protein sensitizes HeLa cells to etoposide, a topoisomerase II inhibitor that induced DSB, and affects their in vitro NHEJ activity. These results suggest that XPC protein could be required for the repair of certain types of breaks or could participate in a global regulation mechanism of the cellular response to DNA lesions. Our model offers interesting opportunities for studying the relations between the different DNA repair pathways in human cells.La réponse au stress génotoxique met en jeu de nombreux facteurs cellulaires impliqués dans un réseau complexe de mécanismes visant à assurer le maintien de l'intégrité génétique de l'organisme. Ces mécanismes incluent la détection et la réparation des lésions de l'ADN, la régulation de la transcription et de la réplication et le déclenchement éventuel de la mort cellulaire. Parmi les protéines nucléaires participant à cette réponse, les protéines kin17 sont des protéines à doigt de zinc conservées au cours de l'évolution et activées par les ultraviolets (UV) et les radiations ionisantes (RI). Nous avons montré que la protéine kin17 humaine (HSAkin17) est présente dans la cellule sous une forme soluble et sous une forme ancrée aux structures nucléaires. Une fraction de la protéine HSAkin17 est directement associée à la chromatine. La protéine HSAkin17 est recrutée sur les structures nucléaires 24 heures après traitement par différents agents induisant des cassures double-brin de l'ADN (DSB) et/ou un blocage des fourches de réplication. Par ailleurs, la réduction du niveau total de protéine HSAkin17 sensibilise les cellules RKO aux RI. Nous présentons également des résultats impliquant la protéine HSAkin17 dans la réplication de l'ADN. Cette hypothèse a été confirmée par la démonstration biochimique de son appartenance au complexe de réplication. La protéine HSAkin17 pourrait donc assurer le lien entre réplication et réparation de l'ADN, un défaut de la voie HSAkin17 entraînant une augmentation de la radiosensibilité. Dans un deuxième temps, nous avons étudié les interactions entre deux mécanismes de réparation de l'ADN : la réparation par excision de nucléotides (NER) et la recombinaison non homologue (NHEJ). Le NER prend en charge une grande variété de lésions provoquant une distortion de la double hélice d'ADN dont les dimères de pyrimidines induits par les UV. Le NHEJ assure la réparation des DSB par jonction directe des extrémités d'ADN. Nous avons utilisé un modèle syngénique de défaut de la réparation basé sur l'interférence ARN développé au laboratoire. En effet, les vecteurs dérivés du virus d'Epstein-Barr (pEBV) permettent l'expression à long terme de siRNA et l'extinction spécifique du gène cible. La réduction de l'expression de gènes impliqués dans le NER (XPA et XPC) ou le NHEJ (DNA-PKcs et XRCC4) entraîne les phénotypes attendus. Nous avons montré que la réduction du niveau de protéine XPC sensibilise les cellules HeLa à l'étoposide, un inhibiteur de la topoisomérase II qui induit des DBS, et affecte leur activité NHEJ in vitro. Ces résultats suggèrent que la protéine XPC pourrait être requise pour la réparation de certains types de cassures ou participer à un système global de régulation de la réponse cellulaire aux lésions de l'ADN. Notre modèle ouvre donc des perspectives intéressantes pour l'étude des relations entre les différentes voies de réparation de l'ADN dans des cellules humaines

Les protéines KIN17, XPC, DNA-PKCS et XRCC4 dans la réponse cellulaire aux dommages de l'ADN. Etude des relations entre la réparation par excision de nucléotides et la recombinaison non homologué dans un modèle syngénique humain

Au cours de la vie cellulaire, l ADN, support de l information génétique, est soumis à des atteintes d origine endogène ou exogène qui entraînent une grande variété de modifications. Si elles ne sont pas réparées correctement, les lésions de l ADN peuvent causer l apparition de mutations et entraîner instabilité génétique et cancer (pour revue voir Hoeijmakers, 2001).Les liaisons chimiques au sein de la double hélice d ADN peuvent s altérer spontanément : perte du groupement amino-exocyclique (déamination) ou hydrolyse de la liaison des bases au désoxyribose (dépurination ou dépyrimidination). Malgré une fidélité importante, il arrive également que la machinerie de réplication de l ADN commette des erreurs ...PARIS5-BU-Necker : Fermée (751152101) / SudocSudocFranceF

Replication intermediate architecture reveals the chronology of DNA damage tolerance pathways at UV-stalled replication forks in human cells

Abstract DNA lesions in S phase threaten genome stability. The DNA damage tolerance (DDT) pathways overcome these obstacles and allow completion of DNA synthesis by the use of specialised translesion (TLS) DNA polymerases or through recombination-related processes. However, how these mechanisms coordinate with each other and with bulk replication remain elusive. To address these issues, we monitored the variation of replication intermediate architecture in response to ultraviolet irradiation using transmission electron microscopy. We show that the TLS polymerase η , able to accurately bypass the major UV lesion and mutated in the skin cancer-prone xeroderma pigmentosum variant (XPV) syndrome, acts at the replication fork to resolve uncoupling and prevent post-replicative gap accumulation. Repriming occurs as a compensatory mechanism when this on-the-fly mechanism cannot operate, and is therefore predominant in XPV cells. Interestingly, our data support a recombination-independent function of RAD51 at the replication fork to sustain repriming. Finally, we provide evidence for the post-replicative commitment of recombination in gap repair and for pioneering observations of in vivo recombination intermediates. Altogether, we propose a chronology of UV damage tolerance in human cells that highlights the key role of pol η in shaping this response and ensuring the continuity of DNA synthesis

The Spi1/PU.1 transcription factor accelerates replication fork progression by increasing PP1 phosphatase in leukemia

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FF483–484 motif of human Polη mediates its interaction with the POLD2 subunit of Polδ and contributes to DNA damage tolerance

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The SLX4 Complex Is a SUMO E3 Ligase that Impacts on Replication Stress Outcome and Genome Stability

International audienceThe SLX4 Fanconi anemia protein is a tumor suppres- sor that may act as a key regulator that engages the cell into specific genome maintenance pathways. Here, we show that the SLX4 complex is a SUMO E3 ligase that SUMOylates SLX4 itself and the XPF sub- unit of the DNA repair/recombination XPF-ERCC1 endonuclease. This SLX4-dependent activity is medi- ated by a remarkably specific interaction between SLX4 and the SUMO-charged E2 conjugating enzyme UBC9 and relies not only on newly identified SUMO- interacting motifs (SIMs) in SLX4 but also on its BTB domain. In contrast to its ubiquitin-binding UBZ4 motifs, SLX4 SIMs are dispensable for its DNA inter- strand crosslink repair functions. Instead, while detri- mental in response to global replication stress, the SUMO E3 ligase activity of the SLX4 complex is crit- ical to prevent mitotic catastrophe following common fragile site expression

In vivo inactivation of RAD51-mediated homologous recombination leads to premature aging, but not to tumorigenesis

Abstract Genetic instability is a hallmark of both cancer and aging. Homologous recombination (HR) is a prominent DNA repair pathway maintaining genomic integrity. Mutations in many HR genes lead to cancer predisposition. Paradoxically, the consequences of mutations in the pivotal HR player, RAD51 , on cancer development remain puzzling. Moreover, in contrast with other HR genes, RAD51 mouse models are not available to experimentally address the role of RAD51 on aging and carcinogenesis, in vivo . Here, we engineered a mouse model with an inducible dominant negative form of RAD51 ( SMRad51 ) that suppresses RAD51-mediated HR without stimulating alternative non-conservative repair pathways. We found that, in vivo expression of SMRad51 did not trigger tumorigenesis, but instead induced premature aging. We propose that these in vivo phenotypes result from the exhaustion of proliferating progenitors submitted to chronic endogenous replication stress resulting from RAD51-mediated HR suppression. Our data underline the importance of the RAD51 activity for progenitors homeostasis, preventing aging, and more generally for the balance between cancer and aging

In vivo reduction of RAD51 ‐mediated homologous recombination triggers aging but impairs oncogenesis

Abstract Homologous recombination (HR) is a prominent DNA repair pathway maintaining genome integrity. Mutations in many HR genes lead to cancer predisposition. Paradoxically, the implication of the pivotal HR factor RAD51 on cancer development remains puzzling. Particularly, no RAD51 mouse models are available to address the role of RAD51 in aging and carcinogenesis in vivo . We engineered a mouse model with an inducible dominant‐negative form of RAD51 ( SMRad51 ) that suppresses RAD51‐mediated HR without stimulating alternative mutagenic repair pathways. We found that in vivo expression of SMRad51 led to replicative stress, systemic inflammation, progenitor exhaustion, premature aging and reduced lifespan, but did not trigger tumorigenesis. Expressing SMRAD51 in a breast cancer predisposition mouse model (PyMT) decreased the number and the size of tumors, revealing an anti‐tumor activity of SMRAD51. We propose that these in vivo phenotypes result from chronic endogenous replication stress caused by HR decrease, which preferentially targets progenitors and tumor cells. Our work underlines the importance of RAD51 activity for progenitor cell homeostasis, preventing aging and more generally for the balance between cancer and aging