1
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Lee JJ, Kim H, Park H, Lee U, Kim C, Lee M, Shin Y, Jung JJ, Lee HB, Han W, Lee H. Disruption of G-quadruplex dynamicity by BRCA2 abrogation instigates phase separation and break-induced replication at telomeres. Nucleic Acids Res 2024:gkae251. [PMID: 38587189 DOI: 10.1093/nar/gkae251] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2023] [Revised: 03/08/2024] [Accepted: 04/03/2024] [Indexed: 04/09/2024] Open
Abstract
Dynamic interaction between BRCA2 and telomeric G-quadruplexes (G4) is crucial for maintaining telomere replication homeostasis. Cells lacking BRCA2 display telomeric damage with a subset of these cells bypassing senescence to initiate break-induced replication (BIR) for telomere synthesis. Here we show that the abnormal stabilization of telomeric G4 following BRCA2 depletion leads to telomeric repeat-containing RNA (TERRA)-R-loop accumulation, triggering liquid-liquid phase separation (LLPS) and the assembly of Alternative Lengthening of Telomeres (ALT)-associated promyelocytic leukemia (PML) bodies (APBs). Disruption of R-loops abolishes LLPS and impairs telomere synthesis. Artificial engineering of telomeric LLPS restores telomere synthesis, underscoring the critical role of LLPS in ALT. TERRA-R-loops also recruit Polycomb Repressive Complex 2 (PRC2), leading to tri-methylation of Lys27 on histone H3 (H3K27me3) at telomeres. Half of paraffin-embedded tissue sections from human breast cancers exhibit APBs and telomere length heterogeneity, suggesting that BRCA2 mutations can predispose individuals to ALT-type tumorigenesis. Overall, BRCA2 abrogation disrupts the dynamicity of telomeric G4, producing TERRA-R-loops, finally leading to the assembly of telomeric liquid condensates crucial for ALT. We propose that modulating the dynamicity of telomeric G4 and targeting TERRA-R-loops in telomeric LLPS maintenance may represent effective therapeutic strategies for treating ALT-like cancers with APBs, including those with BRCA2 disruptions.
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Affiliation(s)
- Jennifer J Lee
- Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - Hyungmin Kim
- Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - Haemin Park
- Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - UkJin Lee
- Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
| | - Chaelim Kim
- Interdisciplinary Program in Bioengineering, Seoul National University, Seoul 08826, Korea
| | - Min Lee
- Interdisciplinary Program in Bioengineering, Seoul National University, Seoul 08826, Korea
| | - Yongdae Shin
- Department of Mechanical Engineering, Seoul National University, Seoul 08826, Korea
- Interdisciplinary Program in Bioengineering, Seoul National University, Seoul 08826, Korea
| | - Ji-Jung Jung
- Department of Surgery, Seoul National University College of Medicine, Seoul 03080, Korea
| | - Han-Byoel Lee
- Department of Surgery, Seoul National University College of Medicine, Seoul 03080, Korea
- Biomedical Research Institute, Seoul National University Hospital, Seoul 03080, Korea
- Cancer Research Institute, Seoul National University, Seoul 03080, Korea
| | - Wonshik Han
- Department of Surgery, Seoul National University College of Medicine, Seoul 03080, Korea
- Biomedical Research Institute, Seoul National University Hospital, Seoul 03080, Korea
- Cancer Research Institute, Seoul National University, Seoul 03080, Korea
| | - Hyunsook Lee
- Department of Biological Sciences & Institute of Molecular Biology and Genetics (IMBG), Seoul National University, 1 Gwanak-Ro, Gwanak-Gu, Seoul 08826, Korea
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2
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Udroiu I, Marinaccio J, Sgura A. Inhibition of p53 and ATRX increases telomeric recombination in primary fibroblasts. FEBS Open Bio 2023; 13:1683-1698. [PMID: 37499040 PMCID: PMC10476563 DOI: 10.1002/2211-5463.13680] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2023] [Revised: 07/11/2023] [Accepted: 07/25/2023] [Indexed: 07/29/2023] Open
Abstract
Telomere length can be maintained either by the telomerase enzyme or by alternative lengthening of telomeres (ALT), which is based on telomeric recombination. However, both mechanisms are inactive in most human somatic cells. ATRX has been previously identified as an ALT repressor gene. Nonetheless, TP53 is also deficient in most ALT cell lines, and previous works showed that it is an inhibitor of homologous recombination (HR). Despite this, the role of p53 as an ALT repressor has not been previously examined. Therefore, we investigated the effects of p53 and ATRX inhibition on normal human fibroblasts (devoid of any mutation), in the presence or absence of X-ray-induced telomeric damage. Performing immunofluorescence with antibodies for RAD51, H2AX, and TRF1 (for studying HR-mediated DNA damage repair) and CO-FISH (for telomeric sister chromatid exchanges), we observed that HR is a normal mechanism for the repair of telomeric damage, present also in noncancer cells. Moreover, we discovered that telomeric HR, as for HR in general, is significantly inhibited by p53. Indeed, we observed that inhibition of p53 drastically increases telomeric sister chromatid exchanges. We also confirmed that ATRX inhibition increases telomeric recombination. In particular, we observed an increase in crossover products, but a much higher increase in noncrossover products.
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Affiliation(s)
- Ion Udroiu
- Dipartimento di Scienze, Università "Roma Tre", Italy
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3
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Barnes RP, Thosar SA, Opresko PL. Telomere Fragility and MiDAS: Managing the Gaps at the End of the Road. Genes (Basel) 2023; 14:genes14020348. [PMID: 36833275 PMCID: PMC9956152 DOI: 10.3390/genes14020348] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/28/2022] [Revised: 01/20/2023] [Accepted: 01/24/2023] [Indexed: 01/31/2023] Open
Abstract
Telomeres present inherent difficulties to the DNA replication machinery due to their repetitive sequence content, formation of non-B DNA secondary structures, and the presence of the nucleo-protein t-loop. Especially in cancer cells, telomeres are hot spots for replication stress, which can result in a visible phenotype in metaphase cells termed "telomere fragility". A mechanism cells employ to mitigate replication stress, including at telomeres, is DNA synthesis in mitosis (MiDAS). While these phenomena are both observed in mitotic cells, the relationship between them is poorly understood; however, a common link is DNA replication stress. In this review, we will summarize what is known to regulate telomere fragility and telomere MiDAS, paying special attention to the proteins which play a role in these telomere phenotypes.
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Affiliation(s)
- Ryan P. Barnes
- Department of Environmental and Occupational Health, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, University of Pittsburgh, 5117 Centre Avenue, Pittsburgh, PA 15213, USA
- Correspondence: (R.P.B.); (P.L.O.)
| | - Sanjana A. Thosar
- Department of Environmental and Occupational Health, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, University of Pittsburgh, 5117 Centre Avenue, Pittsburgh, PA 15213, USA
| | - Patricia L. Opresko
- Department of Environmental and Occupational Health, School of Public Health, University of Pittsburgh, Pittsburgh, PA 15261, USA
- UPMC Hillman Cancer Center, University of Pittsburgh, 5117 Centre Avenue, Pittsburgh, PA 15213, USA
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh, Pittsburgh, PA 15213, USA
- Correspondence: (R.P.B.); (P.L.O.)
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4
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Ragupathi A, Singh M, Perez AM, Zhang D. Targeting the BRCA1/ 2 deficient cancer with PARP inhibitors: Clinical outcomes and mechanistic insights. Front Cell Dev Biol 2023; 11:1133472. [PMID: 37035242 PMCID: PMC10073599 DOI: 10.3389/fcell.2023.1133472] [Citation(s) in RCA: 16] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2022] [Accepted: 03/14/2023] [Indexed: 04/11/2023] Open
Abstract
BRCA1 and BRCA2 play a critical role in a variety of molecular processes related to DNA metabolism, including homologous recombination and mediating the replication stress response. Individuals with mutations in the BRCA1 and BRCA2 (BRCA1/2) genes have a significantly higher risk of developing various types of cancers, especially cancers of the breast, ovary, pancreas, and prostate. Currently, the Food and Drug Administration (FDA) has approved four PARP inhibitors (PARPi) to treat cancers with BRCA1/2 mutations. In this review, we will first summarize the clinical outcomes of the four FDA-approved PARPi in treating BRCA1/2 deficient cancers. We will then discuss evidence supporting the hypothesis that the cytotoxic effect of PARPi is likely due to inducing excessive replication stress at the difficult-to-replicate (DTR) genomic regions in BRCA1/2 mutated tumors. Finally, we will discuss the ongoing preclinical and clinical studies on how to combine the PARPi with immuno-oncology drugs to further improve clinical outcomes.
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5
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Lee J, Sung K, Joo SY, Jeong JH, Kim SK, Lee H. Dynamic interaction of BRCA2 with telomeric G-quadruplexes underlies telomere replication homeostasis. Nat Commun 2022; 13:3396. [PMID: 35697743 PMCID: PMC9192595 DOI: 10.1038/s41467-022-31156-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 05/31/2022] [Indexed: 12/02/2022] Open
Abstract
BRCA2-deficient cells precipitate telomere shortening upon collapse of stalled replication forks. Here, we report that the dynamic interaction between BRCA2 and telomeric G-quadruplex (G4), the non-canonical four-stranded secondary structure, underlies telomere replication homeostasis. We find that the OB-folds of BRCA2 binds to telomeric G4, which can be an obstacle during replication. We further demonstrate that BRCA2 associates with G-triplex (G3)-derived intermediates, which are likely to form during direct interconversion between parallel and non-parallel G4. Intriguingly, BRCA2 binding to G3 intermediates promoted RAD51 recruitment to the telomere G4. Furthermore, MRE11 resected G4-telomere, which was inhibited by BRCA2. Pathogenic mutations at the OB-folds abrogated the binding with telomere G4, indicating that the way BRCA2 associates with telomere is innate to its tumor suppressor activity. Collectively, we propose that BRCA2 binding to telomeric G4 remodels it and allows RAD51-mediated restart of the G4-driven replication fork stalling, simultaneously preventing MRE11-mediated breakdown of telomere. G-quadruplex (G4) can be formed in telomeric DNA. Here the authors show that BRCA2 interacts with telomere G4 structure generated during telomere replication, protecting telomere from nuclease attack.
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Affiliation(s)
- Junyeop Lee
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Keewon Sung
- Department of Chemistry, Seoul National University, Seoul, 08826, South Korea
| | - So Young Joo
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Jun-Hyeon Jeong
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Seong Keun Kim
- Department of Chemistry, Seoul National University, Seoul, 08826, South Korea.
| | - Hyunsook Lee
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea.
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6
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Li D, Hou K, Zhang K, Jia S. Regulation of Replication Stress in Alternative Lengthening of Telomeres by Fanconi Anaemia Protein. Genes (Basel) 2022; 13:genes13020180. [PMID: 35205225 PMCID: PMC8872277 DOI: 10.3390/genes13020180] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2021] [Revised: 01/17/2022] [Accepted: 01/19/2022] [Indexed: 02/04/2023] Open
Abstract
Fanconi anaemia (FA)-related proteins function in interstrand crosslink (ICL) repair pathways and multiple damage repair pathways. Recent studies have found that FA proteins are involved in the regulation of replication stress (RS) in alternative lengthening of telomeres (ALT). Since ALT cells often exhibit high-frequency ATRX mutations and high levels of telomeric secondary structure, high levels of DNA damage and replicative stress exist in ALT cells. Persistent replication stress is required to maintain the activity of ALT mechanistically, while excessive replication stress causes ALT cell death. FA proteins such as FANCD2 and FANCM are involved in the regulation of this balance by resolving or inhibiting the formation of telomere secondary structures to stabilize stalled replication forks and promote break-induced repair (BIR) to maintain the survival of ALT tumour cells. Therefore, we review the role of FA proteins in replication stress in ALT cells, providing a rationale and direction for the targeted treatment of ALT tumours.
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7
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BRCA2 Haploinsufficiency in Telomere Maintenance. Genes (Basel) 2021; 13:genes13010083. [PMID: 35052422 PMCID: PMC8775325 DOI: 10.3390/genes13010083] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2021] [Revised: 12/13/2021] [Accepted: 12/23/2021] [Indexed: 11/17/2022] Open
Abstract
Our previous studies showed an association between monoallelic BRCA2 germline mutations and dysfunctional telomeres in epithelial mammary cell lines and increased risk of breast cancer diagnosis for women with BRCA2 999del5 germline mutation and short telomeres in blood cells. In the current study, we analyzed telomere dysfunction in lymphoid cell lines from five BRCA2 999del5 mutation carriers and three Fanconi Anemia D1 patients by fluorescence in situ hybridization (FISH). Metaphase chromosomes were harvested from ten lymphoid cell lines of different BRCA2 genotype origin and analyzed for telomere loss (TL), multitelomeric signals (MTS), interstitial telomere signals (ITS) and extra chromosomal telomere signals (ECTS). TL, ITS and ECTS were separately found to be significantly increased gradually between the BRCA2+/+, BRCA2+/- and BRCA2-/- lymphoid cell lines. MTS were found to be significantly increased between the BRCA2+/+ and the BRCA2+/- heterozygous (p < 0.0001) and the BRCA2-/- lymphoid cell lines (p < 0.0001) but not between the BRCA2 mutated genotypes. Dysfunctional telomeres were found to be significantly increased in a stepwise manner between the BRCA2 genotypes indicating an effect of BRCA2 haploinsufficiency on telomere maintenance.
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8
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ATRX proximal protein associations boast roles beyond histone deposition. PLoS Genet 2021; 17:e1009909. [PMID: 34780483 PMCID: PMC8629390 DOI: 10.1371/journal.pgen.1009909] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2021] [Revised: 11/29/2021] [Accepted: 10/23/2021] [Indexed: 12/31/2022] Open
Abstract
The ATRX ATP-dependent chromatin remodelling/helicase protein associates with the DAXX histone chaperone to deposit histone H3.3 over repetitive DNA regions. Because ATRX-protein interactions impart functions, such as histone deposition, we used proximity-dependent biotinylation (BioID) to identify proximal associations for ATRX. The proteomic screen captured known interactors, such as DAXX, NBS1, and PML, but also identified a range of new associating proteins. To gauge the scope of their roles, we examined three novel ATRX-associating proteins that likely differed in function, and for which little data were available. We found CCDC71 to associate with ATRX, but also HP1 and NAP1, suggesting a role in chromatin maintenance. Contrastingly, FAM207A associated with proteins involved in ribosome biosynthesis and localized to the nucleolus. ATRX proximal associations with the SLF2 DNA damage response factor help inhibit telomere exchanges. We further screened for the proteomic changes at telomeres when ATRX, SLF2, or both proteins were deleted. The loss caused important changes in the abundance of chromatin remodelling, DNA replication, and DNA repair factors at telomeres. Interestingly, several of these have previously been implicated in alternative lengthening of telomeres. Altogether, this study expands the repertoire of ATRX-associating proteins and functions. ATRX is a protein that is needed to keep repetitive DNA regions organized. It does so in part by binding the DAXX histone chaperone to deposit histone proteins on DNA and assemble structures known as nucleosomes. While important, ATRX has additional functions that remain understudied. To better understand its various biological roles, we first identified the other proteins that are found in its proximity. ATRX-associating proteins were implicated in a range of functions, in addition to histone deposition. Our results suggest that ATRX-associating proteins likely help compact DNA after it is assembled into nucleosomes, and also promote its stability. We then examined the effect of ATRX on telomeres (repetitive DNA regions at the end of chromosomes). ATRX and at least one of its associating proteins suppressed spurious DNA exchanges at telomeres. To understand why, we then identified proteomic changes that occur at telomeres when ATRX was deleted. Loss of ATRX altered the enrichment of a surprising number of proteins at telomeres, including several DNA damage response and chromatin remodelling proteins.
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9
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Breuer M. The FEBS Journal: hidden gems. FEBS J 2021; 289:858-860. [PMID: 34689410 DOI: 10.1111/febs.16223] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Every quarter, The FEBS Journal presents some of its 'hidden gems'-original research and review-type articles that provide a significant advance or discuss recent developments in the molecular or cellular life sciences. These articles are of high value to the scientific community, and we like to take the opportunity to promote these contributions from previous issues of the journal, as we feel their scientific content merits a boost in exposure.
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Affiliation(s)
- Manuel Breuer
- The FEBS Journal Editorial Office Suite B1, Cambridge, UK
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10
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Sharma AB, Erasimus H, Pinto L, Caron MC, Gopaul D, Peterlini T, Neumann K, Nazarov PV, Fritah S, Klink B, Herold-Mende CC, Niclou SP, Pasero P, Calsou P, Masson JY, Britton S, Van Dyck E. XAB2 promotes Ku eviction from single-ended DNA double-strand breaks independently of the ATM kinase. Nucleic Acids Res 2021; 49:9906-9925. [PMID: 34500463 PMCID: PMC8464071 DOI: 10.1093/nar/gkab785] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2021] [Revised: 08/16/2021] [Accepted: 09/01/2021] [Indexed: 12/18/2022] Open
Abstract
Replication-associated single-ended DNA double-strand breaks (seDSBs) are repaired predominantly through RAD51-mediated homologous recombination (HR). Removal of the non-homologous end-joining (NHEJ) factor Ku from resected seDSB ends is crucial for HR. The coordinated actions of MRE11-CtIP nuclease activities orchestrated by ATM define one pathway for Ku eviction. Here, we identify the pre-mRNA splicing protein XAB2 as a factor required for resistance to seDSBs induced by the chemotherapeutic alkylator temozolomide. Moreover, we show that XAB2 prevents Ku retention and abortive HR at seDSBs induced by temozolomide and camptothecin, via a pathway that operates in parallel to the ATM-CtIP-MRE11 axis. Although XAB2 depletion preserved RAD51 focus formation, the resulting RAD51-ssDNA associations were unproductive, leading to increased NHEJ engagement in S/G2 and genetic instability. Overexpression of RAD51 or RAD52 rescued the XAB2 defects and XAB2 loss was synthetically lethal with RAD52 inhibition, providing potential perspectives in cancer therapy.
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Affiliation(s)
- Abhishek Bharadwaj Sharma
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
| | - Hélène Erasimus
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg.,Faculty of Science, Technology and Communication, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Lia Pinto
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg.,Faculty of Science, Technology and Communication, University of Luxembourg, Esch-sur-Alzette, Luxembourg
| | - Marie-Christine Caron
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Diyavarshini Gopaul
- Institut de Génétique Humaine, CNRS et Université de Montpellier, Equipe Labellisée Ligue Contre le Cancer, Montpellier, France
| | - Thibaut Peterlini
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Katrin Neumann
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
| | - Petr V Nazarov
- Quantitative Biology Unit, Multiomics Data Science Group, LIH, Luxembourg
| | - Sabrina Fritah
- NorLux Neuro-Oncology Laboratory, Department of Oncology, LIH, Luxembourg
| | - Barbara Klink
- National Center of Genetics, Laboratoire National de Santé, Dudelange, Luxembourg.,Functional Tumour Genetics Group, Department of Oncology, LIH, Luxembourg
| | | | - Simone P Niclou
- NorLux Neuro-Oncology Laboratory, Department of Oncology, LIH, Luxembourg.,Department of Biomedicine, University of Bergen, Norway
| | - Philippe Pasero
- Institut de Génétique Humaine, CNRS et Université de Montpellier, Equipe Labellisée Ligue Contre le Cancer, Montpellier, France
| | - Patrick Calsou
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France, Equipe Labellisée Ligue Nationale Contre le Cancer 2018
| | - Jean-Yves Masson
- CHU de Québec Research Center, Oncology Division, Québec City, Canada.,Department of Molecular Biology, Medical Biochemistry and Pathology, Laval University Cancer Research Center, Québec City, Canada
| | - Sébastien Britton
- Institut de Pharmacologie et de Biologie Structurale, Université de Toulouse, CNRS, UPS, Toulouse, France, Equipe Labellisée Ligue Nationale Contre le Cancer 2018
| | - Eric Van Dyck
- DNA Repair and Chemoresistance Group, Department of Oncology, Luxembourg Institute of Health (LIH), Luxembourg, Luxembourg
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11
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Alternative paths to telomere elongation. Semin Cell Dev Biol 2020; 113:88-96. [PMID: 33293233 DOI: 10.1016/j.semcdb.2020.11.003] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/11/2020] [Revised: 10/31/2020] [Accepted: 11/09/2020] [Indexed: 11/24/2022]
Abstract
Overcoming cellular senescence that is induced by telomere shortening is critical in tumorigenesis. A majority of cancers achieve telomere maintenance through telomerase expression. However, a subset of cancers takes an alternate route for elongating telomeres: recombination-based alternative lengthening of telomeres (ALT). Current evidence suggests that break-induced replication (BIR), independent of RAD51, underlies ALT telomere synthesis. However, RAD51-dependent homologous recombination is required for homology search and inter-chromosomal telomere recombination in human ALT cancer cell maintenance. Accumulating evidence suggests that the breakdown of stalled replication forks, the replication stress, induces BIR at telomeres. Nevertheless, ALT research is still in its early stage and a comprehensive view is still unclear. Here, we review the current findings regarding the genesis of ALT, how this recombinant pathway is chosen, the epigenetic regulation of telomeres in ALT, and perspectives for clinical applications with the hope that this overview will generate new questions.
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12
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Eckelmann BJ, Bacolla A, Wang H, Ye Z, Guerrero EN, Jiang W, El-Zein R, Hegde ML, Tomkinson AE, Tainer JA, Mitra S. XRCC1 promotes replication restart, nascent fork degradation and mutagenic DNA repair in BRCA2-deficient cells. NAR Cancer 2020; 2:zcaa013. [PMID: 32776008 PMCID: PMC7397735 DOI: 10.1093/narcan/zcaa013] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2020] [Revised: 06/30/2020] [Accepted: 07/30/2020] [Indexed: 12/20/2022] Open
Abstract
Homologous recombination/end joining (HR/HEJ)-deficient cancers with BRCA mutations utilize alternative DNA double-strand break repair pathways, particularly alternative non-homologous end joining or microhomology-mediated end joining (alt-EJ/MMEJ) during S and G2 cell cycle phases. Depletion of alt-EJ factors, including XRCC1, PARP1 and POLQ, is synthetically lethal with BRCA2 deficiency; yet, XRCC1 roles in HR-deficient cancers and replication stress are enigmatic. Here, we show that after replication stress, XRCC1 forms an active repair complex with POLQ and MRE11 that supports alt-EJ activity in vitro. BRCA2 limits XRCC1 recruitment and repair complex formation to suppress alt-EJ at stalled forks. Without BRCA2 fork protection, XRCC1 enables cells to complete DNA replication at the expense of increased genome instability by promoting MRE11-dependent fork resection and restart. High XRCC1 and MRE11 gene expression negatively impacts Kaplan–Meier survival curves and hazard ratios for HR-deficient breast cancer patients in The Cancer Genome Atlas. The additive effects of depleting both BRCA2 and XRCC1 indicate distinct pathways for replication restart. Our collective data show that XRCC1-mediated processing contributes to replication fork degradation, replication restart and chromosome aberrations in BRCA2-deficient cells, uncovering new roles of XRCC1 and microhomology-mediated repair mechanisms in HR-deficient cancers, with implications for chemotherapeutic strategies targeting POLQ and PARP activities.
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Affiliation(s)
- Bradley J Eckelmann
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston, TX 77030, USA
| | - Albino Bacolla
- Departments of Cancer Biology and Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Haibo Wang
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston, TX 77030, USA
| | - Zu Ye
- Departments of Cancer Biology and Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Erika N Guerrero
- Gorgas Memorial Institute for Health Studies, Panama City, Panama
| | - Wei Jiang
- National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital & Shenzhen Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Shenzhen, 518036, China
| | - Randa El-Zein
- Department of Radiology, Houston Methodist Research Institute, Houston, TX 77030, USA
| | - Muralidhar L Hegde
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston, TX 77030, USA
| | - Alan E Tomkinson
- Departments of Internal Medicine and Molecular Genetics & Microbiology, and the University of New Mexico Cancer Center, University of New Mexico, Albuquerque, NM 87131, USA
| | - John A Tainer
- Departments of Cancer Biology and Molecular and Cellular Oncology, University of Texas MD Anderson Cancer Center, Houston, TX 77030, USA
| | - Sankar Mitra
- Department of Radiation Oncology, Houston Methodist Research Institute, Houston, TX 77030, USA
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13
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Telomere replication-When the going gets tough. DNA Repair (Amst) 2020; 94:102875. [PMID: 32650286 DOI: 10.1016/j.dnarep.2020.102875] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2020] [Revised: 05/23/2020] [Accepted: 05/26/2020] [Indexed: 12/28/2022]
Abstract
Telomeres consist of repetitive tracts of DNA that shield a chromosome's contents from erosion and replicative attrition. However, telomeres are also late-replicating regions of the genome in which a myriad of replicative obstructions reside. The obstacles contained within telomeres, as well as their genomic location, drive replicative stalling and subsequent fork collapse in these regions. Consequently, large scale deletions, under-replicated DNA, translocations, and fusion events arise following telomere replication failure. Further, under-replicated DNA and telomere fusions that are permitted to enter mitosis will produce mitotic DNA bridges - known drivers of genetic loss and chromothripsis. Thus, aberrant telomere replication promotes genomic instability, which, in turn leads either to cellular death, senescence or oncogenic transformation. The importance of these issues for organismal well-being necessitates a need for resolute telomere maintenance. Here, we describe recent advances in identifying and understanding the molecular mechanisms that are in place in human cells to escort the replisome through the telomere's unwieldy structures and repetitive sequences. Finally, we review the pathways that combat the deleterious outcomes that occur when telomeric replication forks do collapse.
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Peker Eyüboğlu İ, Yenmiş G, Bingöl EN, Yüksel Ş, Tokat F, Özbek P, Güllü Amuran G, Yakıcıer C, Akkiprik M. Next-Generation Sequencing Identifies BRCA1 and/or BRCA2 Mutations in Women at High Hereditary Risk for Breast Cancer with Shorter Telomere Length. OMICS-A JOURNAL OF INTEGRATIVE BIOLOGY 2019; 24:5-15. [PMID: 31851867 DOI: 10.1089/omi.2019.0103] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
Telomeres, and telomere length in particular, have broad significance for genome biology and thus are prime research targets for complex diseases such as cancers. In this context, BRCA1 and BRCA2 gene mutations have been implicated in relationship to telomere length, and breast cancer susceptibility. Yet, the linkages among human genetic variation and telomere length in persons with high hereditary cancer risk are inadequately mapped. We report here original findings in 113 unrelated women at high hereditary risk for breast cancer, who were characterized for the BRCA1 and BRCA2 mutations using next-generation sequencing. Thirty-one BRCA2 and 21 BRCA1 mutations were identified in 47 subjects (41.6%). The women with a mutation in BRCA1 and/or BRCA2 genes had, on average, 12% shorter telomere compared to women with no BRCA1 or BRCA2 mutation (p = 0.0139). Moreover, the association between telomere length and BRCA mutation status held up upon stratified analysis in those with or without a breast cancer diagnosis. We also indentified two rare mutations, c.536_537insT and c.10078A>G, and a novel mutation c.8680C>G in BRCA2 that was studied further by homology modeling of the DNA binding tower domain of BRCA2 and the structure of the protein. These data collectively lend evidence to the idea that BRCA1 and BRCA2 mutations play a role in telomere length in women at high hereditary risk for breast cancer. Further clinical and diagnostics discovery research on BRCA1 and BRCA2 variation, telomere length, and breast cancer mechanistic linkages are called for in larger study samples.
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Affiliation(s)
- İrem Peker Eyüboğlu
- Department of Medical Biology, School of Medicine, Marmara University, Istanbul, Turkey
| | - Güven Yenmiş
- Biruni University Medical School, Department of Medical Biology and Genetics, Istanbul, Turkey
| | - Elif Naz Bingöl
- Department of Bioengineering, Institute of Pure and Applied Sciences, Marmara University, Kadikoy, Istanbul, Turkey
| | - Şirin Yüksel
- Department of Molecular Biology and Genetics, Acıbadem Mehmet Ali Aydınlar University, Istanbul, Turkey
| | - Fatma Tokat
- Department of Pathology, Subdivision of Cytopathology, Acibadem University, Istanbul, Turkey.,Acibadem Research Institute of Senology, Acıbadem Mehmet Ali Aydınlar University, Istanbul, Turkey
| | - Pemra Özbek
- Department of Bioengineering, Faculty of Engineering, Marmara University, Kadikoy, Istanbul, Turkey
| | - Gökçe Güllü Amuran
- Department of Medical Biology, School of Medicine, Marmara University, Istanbul, Turkey
| | - Cengiz Yakıcıer
- Department of Molecular Biology and Genetics, Acıbadem Mehmet Ali Aydınlar University, Istanbul, Turkey.,Acibadem Research Institute of Senology, Acıbadem Mehmet Ali Aydınlar University, Istanbul, Turkey
| | - Mustafa Akkiprik
- Department of Medical Biology, School of Medicine, Marmara University, Istanbul, Turkey
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Pompili L, Maresca C, Dello Stritto A, Biroccio A, Salvati E. BRCA2 Deletion Induces Alternative Lengthening of Telomeres in Telomerase Positive Colon Cancer Cells. Genes (Basel) 2019; 10:genes10090697. [PMID: 31510074 PMCID: PMC6771010 DOI: 10.3390/genes10090697] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Revised: 08/16/2019] [Accepted: 09/03/2019] [Indexed: 11/25/2022] Open
Abstract
BRCA1/2 are tumor suppressor genes controlling genomic stability also at telomeric and subtelomeric loci. Their mutation confers a predisposition to different human cancers but also sensitivity to antitumor drugs including poly(ADP-ribose) polymerase (PARP) inhibitors and G-quadruplex stabilizers. Here we demonstrate that BRCA2 deletion triggers TERRA hyperexpression and alternative lengthening mechanisms (ALT) in colon cancer cells in presence of telomerase activity. This finding opens the question if cancer patients bearing BRCA2 germline or sporadic mutation are suitable for anti-telomerase therapies, or how ALT activation could influence the short or long-term response to anti-PARP inhibitors or anti-G-quadruplex therapies.
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Affiliation(s)
- Luca Pompili
- Oncogenomic and Epigenetic Unit, IRCSS Regina Elena National Cancer Institute, Via Elio Chianesi, 53-00144 Rome, Italy.
| | - Carmen Maresca
- Oncogenomic and Epigenetic Unit, IRCSS Regina Elena National Cancer Institute, Via Elio Chianesi, 53-00144 Rome, Italy.
| | - Angela Dello Stritto
- Biology and Biotechnology Department "Charles Darwin", Sapienza University of Rome, Piazzale Aldo Moro, 5-00185 Rome, Italy.
| | - Annamaria Biroccio
- Oncogenomic and Epigenetic Unit, IRCSS Regina Elena National Cancer Institute, Via Elio Chianesi, 53-00144 Rome, Italy.
| | - Erica Salvati
- Oncogenomic and Epigenetic Unit, IRCSS Regina Elena National Cancer Institute, Via Elio Chianesi, 53-00144 Rome, Italy.
- Institute of Molecular Biology and Pathology, CNR, Via degli Apuli, 4-00185 Rome, Italy.
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