Ku counteracts mobilization of PARP1 and MRN in chromatin damaged with DNA double-strand breaks

In mammalian cells, the main pathway for DNA double-strand breaks (DSBs) repair is classical non-homologous end joining (C-NHEJ). An alternative or back-up NHEJ (B-NHEJ) pathway has emerged which operates preferentially under C-NHEJ defective conditions. Although B-NHEJ appears particularly relevant to genomic instability associated with cancer, its components and regulation are still largely unknown. To get insights into this pathway, we have knocked-down Ku, the main contributor to C-NHEJ. Thus, models of human cell lines have been engineered in which the expression of Ku70/80 heterodimer can be significantly lowered by the conditional induction of a shRNA against Ku70. On Ku reduction in cells, resulting NHEJ competent protein extracts showed a shift from C- to B-NHEJ that could be reversed by addition of purified Ku protein. Using a cellular fractionation protocol after treatment with a strong DSBs inducer followed by western blotting or immunostaining, we established that, among C-NHEJ factors, Ku is the main counteracting factor against mobilization of PARP1 and the MRN complex to damaged chromatin. In addition, Ku limits PAR synthesis and single-stranded DNA production in response to DSBs. These data support the involvement of PARP1 and the MRN proteins in the B-NHEJ route for the repair of DNA DSBs

La stabilité télomérique (étude fondamentale et applications thérapeutiques)

TOULOUSE3-BU Sciences (315552104) / SudocSudocFranceF

Schisandra chinensis Protects the Skin from Global Pollution by Inflammatory and Redox Balance Pathway Modulations: An In Vitro Study

Epidemiological results show that airborne particulate matter (PM) induces health alterations in line with pulmonary and cardiovascular pathologies. Deleterious effects of PM on the skin have also been investigated. A possible approach to prevent Reactive Oxygen Species (ROS)-mediated disorders for both preventive and treatment means is based on the use of substances, which can be found in plants. These can act as secondary metabolites, and lignans are a promising candidate. Thus, the objective of this study was firstly to identify reconstructed human epidermis, using a transcriptomic approach, and also to identify the effects of Urban Dust and of Urban Dust and Schisandra chinensis (S.C.) extract on the expression of genes that are involved in the response to cellular protection mechanisms. Secondly, we examined the effect of an active extract from S.C. on the protection of human keratinocytes damages that were caused by pollution, through the evaluation of Nrf2 and AhR pathways, NF-kB, and DJ-1. Urban Dust included the over-expression of metalloproteinases MMP-1 and MMP-9 and an increase in Glutathione peroxidase 2 (GPX2). In the presence of Urban Dust, S.C. extract activated the over-expression of several genes that are involved in the antioxidant response and in the detoxification pathway, including Ferritin light chain (FTL) and GPX2. Exposure to urban dust activated the cytoplasmic expression of NF-kB and AhR, when compared to the control. Co-treatment of Urban Dust and S.C. extract increased DJ-1 protein levels, Nrf2 expression, and decreased AhR and NF-kB in the cytoplasm. At the same time, this co-treatment increased SOD2 expression (50%: p < 0.001) and catalase activity (120%: p < 0.05), when compared to Urban Dust alone. Thus, S.C. might be able to protect the Normal Human Epidermal Keratinocytes (NHEK) from environmental aggression, by fighting the harmful effects of urban pollution

TRF2/RAP1 and DNA–PK mediate a double protection against joining at telomeric ends

DNA-dependent protein kinase (DNA-PK) is a double-strand breaks repair complex, the subunits of which (KU and DNA-PKcs) are paradoxically present at mammalian telomeres. Telomere fusion has been reported in cells lacking these proteins, raising two questions: how is DNA–PK prevented from initiating classical ligase IV (LIG4)-dependent non-homologous end-joining (C-NHEJ) at telomeres and how is the backup end-joining (EJ) activity (B-NHEJ) that operates at telomeres under conditions of C-NHEJ deficiency controlled? To address these questions, we have investigated EJ using plasmid substrates bearing double-stranded telomeric tracks and human cell extracts with variable C-NHEJ or B-NHEJ activity. We found that (1) TRF2/RAP1 prevents C-NHEJ-mediated end fusion at the initial DNA–PK end binding and activation step and (2) DNA–PK counteracts a potent LIG4-independent EJ mechanism. Thus, telomeres are protected against EJ by a lock with two bolts. These results account for observations with mammalian models and underline the importance of alternative non-classical EJ pathways for telomere fusions in cells

Improvement of porphyrins for G-quadruplex DNA targeting

International audienc

Structure-Based Virtual Ligand Screening on the XRCC4/DNA Ligase IV Interface

International audienceDSBs cytotoxicity is largely exploited in anticancer therapy. Thus, NHEJ is an attractive target for strategies aimed at increasing the sensitivity of tumors to clastogenic anticancer treatments. However the high affinity of the XRCC4/Lig4 interaction and the extended protein-protein interface make drug screening on this target particularly challenging. Here, we conducted a pioneering study aimed at interfering with XRCC4/Lig4 assembly. By Molecular Dynamics simulation using the crystal structure of the complex, we first delineated the Lig4 clamp domain as a limited suitable target. Then, we performed in silico screening of ~95,000 filtered molecules on this Lig4 subdomain. Hits were evaluated by Differential Scanning Fluorimetry, Saturation Transfer Difference-NMR spectroscopy and interaction assays with purified recombinant proteins. In this way we identified the first molecule able to prevent Lig4 binding to XRCC4 in vitro. This compound has a unique tripartite interaction with the Lig4 clamp domain that suggests a starting chemotype for rational design of analogous molecules with improved affinity

Are social inequalities in acute myeloid leukemia survival explained by differences in treatment utilization? Results from a French longitudinal observational study among older patients

International audienceBACKGROUND:Evidences support social inequalities in cancer survival. Studies on hematological malignancies, and more specifically Acute Myeloid Leukemia (AML), are sparser. Our study assessed: 1/ the influence of patients' socioeconomic position on survival, 2/ the role of treatment in this relationship, and 3/ the influence of patients' socioeconomic position on treatment utilization.METHODS:This prospective multicenter study includes all patients aged 60 and older, newly diagnosed with AML, excluding promyelocytic subtypes, between 1st January 2009 to 31st December 2014 in the South-West of France. Data came from medical files. Patients' socioeconomic position was measured by an ecological deprivation index, the European Deprivation Index. We studied first, patients' socioeconomic position influence on overall survival (n = 592), second, on the use of intensive chemotherapy (n = 592), and third, on the use of low intensive treatment versus best supportive care among patients judged unfit for intensive chemotherapy (n = 405).RESULTS:We found an influence of patients' socioeconomic position on survival (highest versus lowest position HRQ5: 1.39 [1.05;1.87] that was downsized to become no more significant after adjustment for AML ontogeny (HRQ5: 1.31[0.97;1.76] and cytogenetic prognosis HRQ5: 1.30[0.97;1.75]). The treatment was strongly associated with survival. A lower proportion of intensive chemotherapy was observed among patients with lowest socioeconomic position (ORQ5: 0.41[0.19;0.90]) which did not persist after adjustment for AML ontogeny (ORQ5: 0.59[0.25;1.40]). No such influence of patients' socioeconomic position was found on the treatment allocation among patients judged unfit for intensive chemotherapy.CONCLUSIONS:Finally, these results suggest an indirect influence of patients' socioeconomic position on survival through AML initial presentation