Dataset Information

ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks

ABSTRACT: Mutations in the ATM tumor suppressor gene confer cellular hypersensitivity to various DNA-damaging chemotherapeutic agents. To explore genetic resistance mechanisms towards such drugs, we performed genome-wide CRISPR-Cas9 loss-of-function screens in cells treated with the DNA topoisomerase I poison topotecan. Our ensuing characterizations of hits established that loss of terminal components of the non-homologous end joining (NHEJ) machinery or components of the BRCA1-A complex specifically confer topotecan resistance to ATM-deficient cells. Our findings indicate that hypersensitivity of ATM-mutant cells to topotecan or the poly-(ADP-ribose) polymerase (PARP) inhibitor olaparib is due to delayed engagement of homologous recombination repair (HRR) at a subset of DNA-replication-fork associated single ended double-strand breaks (seDSBs), which allows non-homologous end joining (NHEJ) mediated repair, resulting in toxic chromosome fusions. Thus, restoration of legitimate repair in ATM-deficient cells – either by preventing the DNA ligation step of NHEJ or by enhancing HRR engagement by deregulating the BRCA1-A complex – markedly suppresses this toxicity. We conclude that the crucial role for ATM at seDSBs is to prevent toxic LIG4-mediated NHEJ at damaged replication forks. Furthermore, our observation that suppressor mutations in ATM-mutant backgrounds are fundamentally different to those that operate in BRCA1-mutant scenarios suggests new opportunities for patient stratification in the clinic, as well as additional therapeutic vulnerabilities that might be exploited in drug-resistant cancers.

INSTRUMENT(S): Q Exactive

ORGANISM(S): Homo Sapiens (human)

TISSUE(S): Cell Culture

SUBMITTER: Petra Beli

LAB HEAD: Petra Beli

PROVIDER: PXD011108 | Pride | 2019-11-12

REPOSITORIES: Pride

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ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks.

Balmus Gabriel G Pilger Domenic D Coates Julia J Demir Mukerrem M Sczaniecka-Clift Matylda M Barros Ana C AC Woods Michael M Fu Beiyuan B Yang Fengtang F Chen Elisabeth E Ostermaier Matthias M Stankovic Tatjana T Ponstingl Hannes H Herzog Mareike M Yusa Kosuke K Martinez Francisco Munoz FM Durant Stephen T ST Galanty Yaron Y Beli Petra P Adams David J DJ Bradley Allan A Metzakopian Emmanouil E Forment Josep V JV Jackson Stephen P SP

Nature communications 20190108 1

Mutations in the ATM tumor suppressor gene confer hypersensitivity to DNA-damaging chemotherapeutic agents. To explore genetic resistance mechanisms, we performed genome-wide CRISPR-Cas9 screens in cells treated with the DNA topoisomerase I inhibitor topotecan. Thus, we here establish that inactivating terminal components of the non-homologous end-joining (NHEJ) machinery or of the BRCA1-A complex specifically confer topotecan resistance to ATM-deficient cells. We show that hypersensitivity of A ...[more]

PMID: 30622252

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Project description:Classical non-homologous end-joining (C-NHEJ) is a major mammalian DNA double strand break (DSB) repair pathway. Core C-NHEJ factors, such as XRCC4, are required for joining DSB intermediates of the G1 phase-specific V(D)J recombination reaction in progenitor lymphocytes. Core factors also contribute to joining DSBs in cycling mature B-lineage cells, including DSBs generated during antibody class switch recombination (CSR) and DSBs generated by ionizing radiation (IR). The XLF C-NHEJ factor is dispensable for V(D)J recombination in normal cells, but, due to functional redundancy, is absolutely required for this process in cells deficient for the ATM DSB response factor. The recently identified PAralogue of XRCC4 and XLF (PAXX) factor has homology to these two proteins and variably contributes to IR-induced DSB repair in human and chicken cells. We now report that PAXX is dispensable for joining V(D)J recombination DSBs in G1-arrested mouse pro-B cell lines, dispensable for joining CSR-associated DSBs in a cycling mouse B cell line, and dispensable for normal IR-resistance in both G1-arrested and cycling pro-B lines. However, we find that combined deficiency for PAXX and XLF in G1-arrested pro-B lines abrogates DSB joining during V(D)J recombination and sensitizes the cells to IR exposure. Thus, PAXX provides core C-NHEJ factor-associated functions in the absence of XLF and vice versa in G1-arrested Pro-B cell lines. Finally, we also find that PAXX-deficiency has no impact on V(D)J recombination DSB joining in ATM-deficient pro-B lines. We discuss implications of these findings with respect to potential PAXX and XLF functions in C-NHEJ. Examination of CSR Switch mu-to-alpha junctions from mu bait DSBs using LAM-HTGTS and Illumina Miseq. Two clones of PAXX-/- and XLF-/- and 1 clone of Ligase4-/- were derived from the parental CH12F3 line; the second Ligase4-/- clone was acquired from Keifei Yu. Two clones of XLF-/-PAXX-/-CH12 cells were derived from one of the PAXX-/- clones. Three biological replicates were analyzed for each clone.

Dataset Information

ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks

Publications

ATM orchestrates the DNA-damage response to counter toxic non-homologous end-joining at broken replication forks.

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