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Waitkus MS, Erman EN, Reitman ZJ, Ashley DM. Mechanisms of telomere maintenance and associated therapeutic vulnerabilities in malignant gliomas. Neuro Oncol 2024; 26:1012-1024. [PMID: 38285162 PMCID: PMC11145458 DOI: 10.1093/neuonc/noae016] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/2023] [Indexed: 01/30/2024] Open
Abstract
A majority of cancers (~85%) activate the enzyme telomerase to maintain telomere length over multiple rounds of cellular division. Telomerase-negative cancers activate a distinct, telomerase-independent mechanism of telomere maintenance termed alternative lengthening of telomeres (ALT). ALT uses homologous recombination to maintain telomere length and exhibits features of break-induced DNA replication. In malignant gliomas, the activation of either telomerase or ALT is nearly ubiquitous in pediatric and adult tumors, and the frequency with which these distinct telomere maintenance mechanisms (TMMs) is activated varies according to genetically defined glioma subtypes. In this review, we summarize the current state of the field of TMMs and their relevance to glioma biology and therapy. We review the genetic alterations and molecular mechanisms leading to telomerase activation or ALT induction in pediatric and adult gliomas. With this background, we review emerging evidence on strategies for targeting TMMs for glioma therapy. Finally, we comment on critical gaps and issues for moving the field forward to translate our improved understanding of glioma telomere maintenance into better therapeutic strategies for patients.
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Affiliation(s)
- Matthew S Waitkus
- The Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, North Carolina, USA
- Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina, USA
| | - Elise N Erman
- The Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, North Carolina, USA
- Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina, USA
| | - Zachary J Reitman
- The Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, North Carolina, USA
- Department of Radiation Oncology, Duke University Medical Center, Durham, North Carolina, USA
| | - David M Ashley
- The Preston Robert Tisch Brain Tumor Center, Duke University Medical Center, Durham, North Carolina, USA
- Department of Neurosurgery, Duke University Medical Center, Durham, North Carolina, USA
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2
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Lee J, Lee J, Sohn EJ, Taglialatela A, O’Sullivan RJ, Ciccia A, Min J. Extrachromosomal telomere DNA derived from excessive strand displacements. Proc Natl Acad Sci U S A 2024; 121:e2318438121. [PMID: 38696464 PMCID: PMC11087782 DOI: 10.1073/pnas.2318438121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2023] [Accepted: 04/03/2024] [Indexed: 05/04/2024] Open
Abstract
Alternative lengthening of telomeres (ALT) is a telomere maintenance mechanism mediated by break-induced replication, evident in approximately 15% of human cancers. A characteristic feature of ALT cancers is the presence of C-circles, circular single-stranded telomeric DNAs composed of C-rich sequences. Despite the fact that extrachromosomal C-rich single-stranded DNAs (ssDNAs), including C-circles, are unique to ALT cells, their generation process remains undefined. Here, we introduce a method to detect single-stranded telomeric DNA, called 4SET (Strand-Specific Southern-blot for Single-stranded Extrachromosomal Telomeres) assay. Utilizing 4SET, we are able to capture C-rich single-stranded DNAs that are near 200 to 1500 nucleotides in size. Both linear C-rich ssDNAs and C-circles are abundant in the fractions of cytoplasm and nucleoplasm, which supports the idea that linear and circular C-rich ssDNAs are generated concurrently. We also found that C-rich ssDNAs originate during Okazaki fragment processing during lagging strand DNA synthesis. The generation of C-rich ssDNA requires CST-PP (CTC1/STN1/TEN1-PRIMASE-Polymerase alpha) complex-mediated priming of the C-strand DNA synthesis and subsequent excessive strand displacement of the C-rich strand mediated by the DNA Polymerase delta and the BLM helicase. Our work proposes a model for the generation of C-rich ssDNAs and C-circles during ALT-mediated telomere elongation.
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Affiliation(s)
- Junyeop Lee
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
| | - Jina Lee
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
- Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
| | - Eric J. Sohn
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
| | - Angelo Taglialatela
- Department of Genetics and Development, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
| | - Roderick J. O’Sullivan
- Department of Pharmacology and Chemical Biology, Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA15213
| | - Alberto Ciccia
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
- Department of Genetics and Development, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
- Herbert Irving Comprehensive Cancer Center, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
| | - Jaewon Min
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
- Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
- Herbert Irving Comprehensive Cancer Center, Columbia University Vagelos College of Physicians and Surgeons, New York, NY10032
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3
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Chen S, Pan C, Huang J, Liu T. ATR limits Rad18-mediated PCNA monoubiquitination to preserve replication fork and telomerase-independent telomere stability. EMBO J 2024; 43:1301-1324. [PMID: 38467834 PMCID: PMC10987609 DOI: 10.1038/s44318-024-00066-9] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2023] [Revised: 02/15/2024] [Accepted: 02/26/2024] [Indexed: 03/13/2024] Open
Abstract
Upon replication fork stalling, the RPA-coated single-stranded DNA (ssDNA) formed behind the fork activates the ataxia telangiectasia-mutated and Rad3-related (ATR) kinase, concomitantly initiating Rad18-dependent monoubiquitination of PCNA. However, whether crosstalk exists between these two events and the underlying physiological implications of this interplay remain elusive. In this study, we demonstrate that during replication stress, ATR phosphorylates human Rad18 at Ser403, an adjacent residue to a previously unidentified PIP motif (PCNA-interacting peptide) within Rad18. This phosphorylation event disrupts the interaction between Rad18 and PCNA, thereby restricting the extent of Rad18-mediated PCNA monoubiquitination. Consequently, excessive accumulation of the tumor suppressor protein SLX4, now characterized as a novel reader of ubiquitinated PCNA, at stalled forks is prevented, contributing to the prevention of stalled fork collapse. We further establish that ATR preserves telomere stability in alternative lengthening of telomere (ALT) cells by restricting Rad18-mediated PCNA monoubiquitination and excessive SLX4 accumulation at telomeres. These findings shed light on the complex interplay between ATR activation, Rad18-dependent PCNA monoubiquitination, and SLX4-associated stalled fork processing, emphasizing the critical role of ATR in preserving replication fork stability and facilitating telomerase-independent telomere maintenance.
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Affiliation(s)
- Siyuan Chen
- Zhejiang Provincial Key Laboratory of Geriatrics and Geriatrics Institute of Zhejiang Province, Affiliated Zhejiang Hospital, Zhejiang University School of Medicine, 310058, Hangzhou, China
- The MOE Key Laboratory of Biosystems Homeostasis & Protection and Zhejiang Provincial Key Laboratory of Cancer Molecular Cell Biology, Life Sciences Institute, Zhejiang University, 310058, Hangzhou, China
| | - Chen Pan
- The MOE Key Laboratory of Biosystems Homeostasis & Protection and Zhejiang Provincial Key Laboratory of Cancer Molecular Cell Biology, Life Sciences Institute, Zhejiang University, 310058, Hangzhou, China
| | - Jun Huang
- Zhejiang Provincial Key Laboratory of Geriatrics and Geriatrics Institute of Zhejiang Province, Affiliated Zhejiang Hospital, Zhejiang University School of Medicine, 310058, Hangzhou, China.
- The MOE Key Laboratory of Biosystems Homeostasis & Protection and Zhejiang Provincial Key Laboratory of Cancer Molecular Cell Biology, Life Sciences Institute, Zhejiang University, 310058, Hangzhou, China.
- Center for Life Sciences, Shaoxing Institute, Zhejiang University, 321000, Shaoxing, China.
| | - Ting Liu
- Zhejiang Provincial Key Laboratory of Geriatrics and Geriatrics Institute of Zhejiang Province, Affiliated Zhejiang Hospital, Zhejiang University School of Medicine, 310058, Hangzhou, China.
- Department of Cell Biology, and Department of General Surgery of Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 310058, Hangzhou, China.
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4
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Yin L, Jiang N, Li T, Zhang Y, Yuan S. Telomeric function and regulation during male meiosis in mice and humans. Andrology 2024. [PMID: 38511802 DOI: 10.1111/andr.13631] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2023] [Revised: 02/26/2024] [Accepted: 03/03/2024] [Indexed: 03/22/2024]
Abstract
BACKGROUND Telomeres are unique structures situated at the ends of chromosomes. Preserving the structure and function of telomeres is essential for maintaining genomic stability and promoting genetic diversity during male meiosis in mammals. MATERIAL-METHODS This review compiled recent literature on the function and regulation of telomeres during male meiosis in both mice and humans, and also highlighted the critical roles of telomeres in reproductive biology and medicine. RESULTS-DISCUSSION Various structures, consisting of the LINC complex (SUN-KASH), SPDYA-CDK2, TTM trimer (TERB1-TERB2-MAJIN), and shelterin, are critical in controlling telomeric activities, such as nuclear envelope attachment and bouquet formation. Other than telomere-related proteins, cohesins and genes responsible for regulating telomere function are also highlighted, though the exact mechanism remains unclear. The gene-mutant mouse models with meiotic defects directly reveal the essential roles of telomeres in male meiosis. Recently reported mutant genes associated with telomere activity in clinical practice have also been illustrated in detail. CONCLUSIONS Proper regulation of telomere activities is essential for male meiosis progression in mice and humans.
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Affiliation(s)
- Lisha Yin
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Nan Jiang
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Tao Li
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
| | - Youzhi Zhang
- School of Pharmacy, Xianning Medical College, Hubei University of Science and Technology; Hubei Engineering Research Center of Traditional Chinese Medicine of South Hubei Province, Xianning, China
| | - Shuiqiao Yuan
- Institute of Reproductive Health, Tongji Medical College, Huazhong University of Science and Technology, Wuhan, China
- Laboratory of Animal Center, Huazhong University of Science and Technology, Wuhan, China
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5
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Azzalin CM. TERRA and the alternative lengthening of telomeres: a dangerous affair. FEBS Lett 2024. [PMID: 38445359 DOI: 10.1002/1873-3468.14844] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2024] [Revised: 02/14/2024] [Accepted: 02/20/2024] [Indexed: 03/07/2024]
Abstract
Eukaryotic telomeres are transcribed into the long noncoding RNA TERRA. A fraction of TERRA remains associated with telomeres by forming RNA:DNA hybrids dubbed telR-loops. TERRA and telR-loops are essential to promote telomere elongation in human cancer cells that maintain telomeres through a homology-directed repair pathway known as alternative lengthening of telomeres or ALT. However, TERRA and telR-loops compromise telomere integrity and cell viability if their levels are not finely tuned. The study of telomere transcription in ALT cells will enormously expand our understanding of the ALT mechanism and of how genome integrity is maintained. Moreover, telomere transcription, TERRA and telR-loops are likely to become exceptionally suited targets for the development of novel anti-cancer therapies.
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Affiliation(s)
- Claus M Azzalin
- Instituto de Medicina Molecular João Lobo Antunes (iMM), Faculdade de Medicina da Universidade de Lisboa, Portugal
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Zhao R, Xu M, Wondisford AR, Lackner RM, Salsman J, Dellaire G, Chenoweth DM, O’Sullivan RJ, Zhao X, Zhang H. SUMO Promotes DNA Repair Protein Collaboration to Support Alterative Telomere Lengthening in the Absence of PML. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.29.582813. [PMID: 38463993 PMCID: PMC10925274 DOI: 10.1101/2024.02.29.582813] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 03/12/2024]
Abstract
Alternative lengthening of telomeres (ALT) pathway maintains telomeres in a significant fraction of cancers associated with poor clinical outcomes. A better understanding of ALT mechanisms can provide a basis for developing new treatment strategies for ALT cancers. SUMO modification of telomere proteins plays a critical role in the formation of ALT telomere-associated PML bodies (APBs), where telomeres are clustered and DNA repair proteins are enriched to promote homology-directed telomere DNA synthesis in ALT. However, whether and how SUMO contributes to ALT beyond APB formation remains elusive. Here, we report that SUMO promotes collaboration among DNA repair proteins to achieve APB-independent telomere maintenance. By using ALT cancer cells with PML protein knocked out and thus devoid of APBs, we show that sumoylation is required for manifesting ALT features, including telomere clustering and telomeric DNA synthesis, independent of PML and APBs. Further, small molecule-induced telomere targeting of SUMO produces signatures of phase separation and ALT features in PML null cells in a manner depending on both sumoylation and SUMO interaction with SUMO interaction motifs (SIMs). Mechanistically, SUMO-induced effects are linked to the enrichment of DNA repair proteins, including Rad52, Rad51AP1, and BLM, to the SUMO-containing telomere foci. Finally, we find that Rad52 can undergo phase separation, enrich SUMO on telomeres, and promote telomere DNA synthesis in collaboration with the BLM helicase in a SUMO-dependent manner. Collectively, our findings suggest that, in addition to forming APBs, SUMO also promotes collaboration among DNA repair proteins to support telomere maintenance in ALT cells. Given the promising effects of sumoylation inhibitors in cancer treatment, our findings suggest their potential use in perturbing telomere maintenance in ALT cancer cells.
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Affiliation(s)
- Rongwei Zhao
- Department of Biology, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Meng Xu
- Department of Biology, Carnegie Mellon University, Pittsburgh, PA 15213, USA
| | - Anne R. Wondisford
- Department of Pharmacology and Chemical Biology, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Rachel M. Lackner
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19014 , USA
| | - Jayme Salsman
- Department of Pathology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - Graham Dellaire
- Department of Pathology, Dalhousie University, Halifax, Nova Scotia, B3H 4R2, Canada
| | - David M. Chenoweth
- Department of Chemistry, University of Pennsylvania, Philadelphia, PA 19014 , USA
| | - Roderick J. O’Sullivan
- Department of Pharmacology and Chemical Biology, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA 15213, USA
| | - Xiaolan Zhao
- Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065
| | - Huaiying Zhang
- Department of Biology, Carnegie Mellon University, Pittsburgh, PA 15213, USA
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7
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Mori JO, Keegan J, Flynn RL, Heaphy CM. Alternative lengthening of telomeres: mechanism and the pathogenesis of cancer. J Clin Pathol 2024; 77:82-86. [PMID: 37890990 DOI: 10.1136/jcp-2023-209005] [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: 08/21/2023] [Accepted: 10/12/2023] [Indexed: 10/29/2023]
Abstract
Telomere maintenance and elongation allows cells to gain replicative immortality and evade cellular senescence during cancer development. While most cancers use telomerase to maintain telomere lengths, a subset of cancers engage the alternative lengthening of telomeres (ALT) pathway for telomere maintenance. ALT is present in 5%-10% of all cancers, although the prevalence is dramatically higher in certain cancer types, including complex karyotype sarcomas, isocitrate dehydrogenase-mutant astrocytoma (WHO grade II-IV), pancreatic neuroendocrine tumours, neuroblastoma and chromophobe hepatocellular carcinomas. ALT is maintained through a homology-directed DNA repair mechanism. Resembling break-induced replication, this aberrant process results in dramatic cell-to-cell telomere length heterogeneity, widespread chromosomal instability and chronic replication stress. Additionally, ALT-positive cancers frequently harbour inactivating mutations in either chromatin remodelling proteins (ATRX, DAXX and H3F3A) or DNA damage repair factors (SMARCAL1 and SLX4IP). ALT can readily be detected in tissue by assessing the presence of unique molecular characteristics, such as large ultrabright nuclear telomeric foci or partially single-stranded telomeric DNA circles (C-circles). Importantly, ALT has been validated as a robust diagnostic and prognostic biomarker for certain cancer types and may even be exploited as a therapeutic target via small molecular inhibitors and/or synthetic lethality approaches.
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Affiliation(s)
- Joakin O Mori
- Medicine, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA
| | - Joshua Keegan
- Pharmacology, Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA
| | - Rachel L Flynn
- Medicine, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA
- Pharmacology, Physiology & Biophysics, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA
| | - Christopher M Heaphy
- Medicine, Boston University Chobanian & Avedisian School of Medicine, Boston, Massachusetts, USA
- Pathology and Laboratory Medicine, Boston Medical Center, Boston, Massachusetts, USA
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8
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Lim J, Kim W, Kim J, Lee J. Telomeric repeat evolution in the phylum Nematoda revealed by high-quality genome assemblies and subtelomere structures. Genome Res 2023; 33:gr.278124.123. [PMID: 37918961 PMCID: PMC10760449 DOI: 10.1101/gr.278124.123] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2023] [Accepted: 10/16/2023] [Indexed: 11/04/2023]
Abstract
Telomeres are composed of tandem arrays of telomeric-repeat motifs (TRMs) and telomere-binding proteins (TBPs), which are responsible for ensuring end-protection and end-replication of chromosomes. TRMs are highly conserved owing to the sequence specificity of TBPs, although significant alterations in TRM have been observed in several taxa, except Nematoda. We used public whole-genome sequencing data sets to analyze putative TRMs of 100 nematode species and determined that three distinct branches included specific novel TRMs, suggesting that evolutionary alterations in TRMs occurred in Nematoda. We focused on one of the three branches, the Panagrolaimidae family, and performed a de novo assembly of four high-quality draft genomes of the canonical (TTAGGC) and novel TRM (TTAGAC) isolates; the latter genomes revealed densely clustered arrays of the novel TRM. We then comprehensively analyzed the subtelomeric regions of the genomes to infer how the novel TRM evolved. We identified DNA damage-repair signatures in subtelomeric sequences that were representative of consequences of telomere maintenance mechanisms by alternative lengthening of telomeres. We propose a hypothetical scenario in which TTAGAC-containing units are clustered in subtelomeric regions and pre-existing TBPs capable of binding both canonical and novel TRMs aided the evolution of the novel TRM in the Panagrolaimidae family.
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Affiliation(s)
- Jiseon Lim
- Department of Biological Sciences, Seoul National University, Gwanak-gu, Seoul 08826, South Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Seoul 08826, South Korea
| | - Wonjoo Kim
- Department of Biological Sciences, Seoul National University, Gwanak-gu, Seoul 08826, South Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Seoul 08826, South Korea
| | - Jun Kim
- Department of Biological Sciences, Seoul National University, Gwanak-gu, Seoul 08826, South Korea;
- Research Institute of Basic Sciences, Seoul National University, Seoul 08826, South Korea
- Department of Convergent Bioscience and Informatics, College of Bioscience and Biotechnology, Chungnam National University, Daejeon 34134, South Korea
| | - Junho Lee
- Department of Biological Sciences, Seoul National University, Gwanak-gu, Seoul 08826, South Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Seoul 08826, South Korea
- Research Institute of Basic Sciences, Seoul National University, Seoul 08826, South Korea
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9
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Loe TK, Lazzerini Denchi E, Tricola GM, Azeroglu B. ALTercations at telomeres: stress, recombination and extrachromosomal affairs. Biochem Soc Trans 2023; 51:1935-1946. [PMID: 37767563 DOI: 10.1042/bst20230265] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2023] [Revised: 09/21/2023] [Accepted: 09/22/2023] [Indexed: 09/29/2023]
Abstract
Approximately 15% of human cancers depend on the alternative lengthening of telomeres (ALT) pathway to maintain telomeres and proliferate. Telomeres that are elongated using ALT display unique features raising the exciting prospect of tailored cancer therapies. ALT-mediated telomere elongation shares several features with recombination-based DNA repair. Strikingly, cells that use the ALT pathway display abnormal levels of replication stress at telomeres and accumulate abundant extrachromosomal telomeric DNA. In this review, we examine recent findings that shed light on the ALT mechanisms and the strategies currently available to suppress this telomere elongation mechanism.
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Affiliation(s)
- Taylor K Loe
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, U.S.A
| | - Eros Lazzerini Denchi
- Laboratory of Genome Integrity, National Cancer Institute, NIH, Bethesda, MD 20892, U.S.A
| | - Gianna M Tricola
- Laboratory of Genome Integrity, National Cancer Institute, NIH, Bethesda, MD 20892, U.S.A
| | - Benura Azeroglu
- Laboratory of Genome Integrity, National Cancer Institute, NIH, Bethesda, MD 20892, U.S.A
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10
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Lee J, Lee J, Sohn EJ, Taglialatela A, O’Sullivan RJ, Ciccia A, Min J. Extrachromosomal Telomeres Derived from Excessive Strand Displacements. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.07.31.551186. [PMID: 37577643 PMCID: PMC10418088 DOI: 10.1101/2023.07.31.551186] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/15/2023]
Abstract
Alternative Lengthening of Telomeres (ALT) is a telomere maintenance mechanism mediated by break-induced replication (BIR), evident in approximately 15% of human cancers. A characteristic feature of ALT cancers is the presence of C-circles, circular single-stranded telomeric DNAs composed of C-rich sequences. Despite the fact that extrachromosomal C-rich single-stranded DNAs (ssDNAs), unique to ALT cells, are considered potential precursors of C-circles, their generation process remains undefined. Here, we introduce a highly sensitive method to detect single stranded telomeric DNA, called 4SET (Strand-Specific Southern-blot for Single-stranded Extrachromosomal Telomeres) assay. Utilizing 4SET, we are able to capture C-rich single stranded DNAs that are near 200 to 1500 nucleotides in size. Both linear C-rich ssDNAs and C-circles are abundant in the fractions of cytoplasm and nucleoplasm, which supports the idea that linear C-rich ssDNA accumulation may indeed precede C-circle formation. We also found that C-rich ssDNAs originate during Okazaki fragment processing during lagging strand DNA synthesis. The generation of C-rich ssDNA requires CST-PP (CTC1/STN1/TEN1-PRIMASE-Polymerase alpha) complex-mediated priming of the C-strand DNA synthesis and subsequent excessive strand displacement of the C-rich strand mediated by the DNA Polymerase delta and the BLM helicase. Our work proposes a new model for the generation of C-rich ssDNAs and C-circles during ALT-mediated telomere elongation.
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Affiliation(s)
- Junyeop Lee
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
| | - Jina Lee
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
- Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
| | - Eric J. Sohn
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
| | - Angelo Taglialatela
- Department of Genetics and Development, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
| | - Roderick J. O’Sullivan
- Department of Pharmacology and Chemical Biology, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA, USA
| | - Alberto Ciccia
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
- Department of Genetics and Development, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
- Herbert Irving Comprehensive Cancer Center, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
| | - Jaewon Min
- Institute for Cancer Genetics, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
- Department of Pathology and Cell Biology, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
- Herbert Irving Comprehensive Cancer Center, Columbia University Vagelos College of Physicians and Surgeons, New York, NY, USA
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11
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Sung S, Kim E, Niida H, Kim C, Lee J. Distinct characteristics of two types of alternative lengthening of telomeres in mouse embryonic stem cells. Nucleic Acids Res 2023; 51:9122-9143. [PMID: 37496110 PMCID: PMC10516625 DOI: 10.1093/nar/gkad617] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2022] [Revised: 06/27/2023] [Accepted: 07/13/2023] [Indexed: 07/28/2023] Open
Abstract
Telomere length must be maintained in actively dividing cells to avoid cellular arrest or death. In the absence of telomerase activity, activation of alternative lengthening of telomeres (ALT) allows the maintenance of telomeric length and prolongs the cellular lifespan. Our previous studies have established two types of ALT survivors from mouse embryonic stem cells. The key differences between these ALT survivors are telomere-constituting sequences: non-telomeric sequences and canonical telomeric repeats, with each type of ALT survivors being referred to as type I and type II, respectively. We explored how the characteristics of the two types of ALT lines reflect their fates using multi-omics approaches. The most notable gene expression signatures of type I and type II ALT cell lines were chromatin remodelling and DNA repair, respectively. Compared with type II cells, type I ALT cells accumulated more mutations and demonstrated persistent telomere instability. These findings indicate that cells of the same origin have separate routes for survival, thus providing insights into the plasticity of crisis-suffering cells and cancers.
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Affiliation(s)
- Sanghyun Sung
- Department of Biological Sciences, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
| | - Eunkyeong Kim
- Department of Biological Sciences, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
| | - Hiroyuki Niida
- Department of Molecular Biology, Hamamatsu University School of Medicine, Hamamatsu, Shizuoka 431-3192, Japan
| | - Chuna Kim
- Aging Convergence Research Center, Korea Research Institute of Bioscience and Biotechnology, Gwahak-ro 125, Daejeon 34141, Korea
- Department of Bioinformatics, KRIBB School of Bioscience, Korea University of Science and Technology (UST), Daejeon 34113, Korea
| | - Junho Lee
- Department of Biological Sciences, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
- Institute of Molecular Biology and Genetics, Seoul National University, Gwanak-ro 1, Seoul 08826, Korea
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12
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Rose AM, Goncalves T, Cunniffe S, Geiller HEB, Kent T, Shepherd S, Ratnaweera M, O’Sullivan R, Gibbons R, Clynes D. Induction of the alternative lengthening of telomeres pathway by trapping of proteins on DNA. Nucleic Acids Res 2023; 51:6509-6527. [PMID: 36940725 PMCID: PMC10359465 DOI: 10.1093/nar/gkad150] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 02/06/2023] [Accepted: 02/21/2023] [Indexed: 03/23/2023] Open
Abstract
Telomere maintenance is a hallmark of malignant cells and allows cancers to divide indefinitely. In some cancers, this is achieved through the alternative lengthening of telomeres (ALT) pathway. Whilst loss of ATRX is a near universal feature of ALT-cancers, it is insufficient in isolation. As such, other cellular events must be necessary - but the exact nature of the secondary events has remained elusive. Here, we report that trapping of proteins (such as TOP1, TOP2A and PARP1) on DNA leads to ALT induction in cells lacking ATRX. We demonstrate that protein-trapping chemotherapeutic agents, such as etoposide, camptothecin and talazoparib, induce ALT markers specifically in ATRX-null cells. Further, we show that treatment with G4-stabilising drugs cause an increase in trapped TOP2A levels which leads to ALT induction in ATRX-null cells. This process is MUS81-endonuclease and break-induced replication dependent, suggesting that protein trapping leads to replication fork stalling, with these forks being aberrantly processed in the absence of ATRX. Finally, we show ALT-positive cells harbour a higher load of genome-wide trapped proteins, such as TOP1, and knockdown of TOP1 reduced ALT activity. Taken together, these findings suggest that protein trapping is a fundamental driving force behind ALT-biology in ATRX-deficient malignancies.
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Affiliation(s)
- Anna M Rose
- MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
- Department of Paediatrics, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Tomas Goncalves
- MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Siobhan Cunniffe
- Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | | | - Thomas Kent
- MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - Sam Shepherd
- Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
| | | | - Roderick J O’Sullivan
- Department of Pharmacology and Chemical Biology, UPMC Hillman Cancer Center, University of Pittsburgh, Pittsburgh, PA, USA
| | - Richard J Gibbons
- MRC Molecular Haematology Unit, Weatherall Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, Oxford OX3 9DS, UK
| | - David Clynes
- Department of Oncology, University of Oxford, Oxford OX3 7DQ, UK
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13
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Reiss M, Keegan J, Aldrich A, Lyons SM, Flynn RL. The exoribonuclease XRN2 mediates degradation of the long non-coding telomeric RNA TERRA. FEBS Lett 2023; 597:1818-1836. [PMID: 37191774 PMCID: PMC10524182 DOI: 10.1002/1873-3468.14639] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2023] [Revised: 05/01/2023] [Accepted: 05/05/2023] [Indexed: 05/17/2023]
Abstract
The telomeric repeat-containing RNA, TERRA, associates with both telomeric DNA and telomeric proteins, often forming RNA:DNA hybrids (R-loops). TERRA is most abundant in cancer cells utilizing the alternative lengthening of telomeres (ALT) pathway for telomere maintenance, suggesting that persistent TERRA R-loops may contribute to activation of the ALT mechanism. Therefore, we sought to identify the enzyme(s) that regulate TERRA metabolism in mammalian cells. Here, we identify that the 5'-3' exoribonuclease XRN2 regulates the stability of TERRA RNA. Moreover, while stabilization of TERRA alone was insufficient to drive ALT, depletion of XRN2 in ALT-positive cells led to a significant increase in TERRA R-loops and exacerbated ALT activity. Together, our findings highlight XRN2 as a key determinant of TERRA metabolism and telomere stability in cancer cells that rely on the ALT pathway.
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Affiliation(s)
- Matthew Reiss
- Departments of Pharmacology and Experimental Therapeutics, and Medicine, Cancer Center, Boston University Chobanian & Avedisian School of Medicine, Boston, MA 02118, USA
| | - Joshua Keegan
- Departments of Pharmacology and Experimental Therapeutics, and Medicine, Cancer Center, Boston University Chobanian & Avedisian School of Medicine, Boston, MA 02118, USA
| | - Anne Aldrich
- Departments of Biochemistry and Cell Biology, Boston University Chobanian & Avedisian School of Medicine, Boston, MA 02118, USA
| | - Shawn M. Lyons
- Departments of Biochemistry and Cell Biology, Boston University Chobanian & Avedisian School of Medicine, Boston, MA 02118, USA
| | - Rachel Litman Flynn
- Departments of Pharmacology and Experimental Therapeutics, and Medicine, Cancer Center, Boston University Chobanian & Avedisian School of Medicine, Boston, MA 02118, USA
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14
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Zhang T, Rawal Y, Jiang H, Kwon Y, Sung P, Greenberg RA. Break-induced replication orchestrates resection-dependent template switching. Nature 2023; 619:201-208. [PMID: 37316655 PMCID: PMC10937050 DOI: 10.1038/s41586-023-06177-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2022] [Accepted: 05/05/2023] [Indexed: 06/16/2023]
Abstract
Break-induced telomere synthesis (BITS) is a RAD51-independent form of break-induced replication that contributes to alternative lengthening of telomeres1,2. This homology-directed repair mechanism utilizes a minimal replisome comprising proliferating cell nuclear antigen (PCNA) and DNA polymerase-δ to execute conservative DNA repair synthesis over many kilobases. How this long-tract homologous recombination repair synthesis responds to complex secondary DNA structures that elicit replication stress remains unclear3-5. Moreover, whether the break-induced replisome orchestrates additional DNA repair events to ensure processivity is also unclear. Here we combine synchronous double-strand break induction with proteomics of isolated chromatin segments (PICh) to capture the telomeric DNA damage response proteome during BITS1,6. This approach revealed a replication stress-dominated response, highlighted by repair synthesis-driven DNA damage tolerance signalling through RAD18-dependent PCNA ubiquitination. Furthermore, the SNM1A nuclease was identified as the major effector of ubiquitinated PCNA-dependent DNA damage tolerance. SNM1A recognizes the ubiquitin-modified break-induced replisome at damaged telomeres, and this directs its nuclease activity to promote resection. These findings show that break-induced replication orchestrates resection-dependent lesion bypass, with SNM1A nuclease activity serving as a critical effector of ubiquitinated PCNA-directed recombination in mammalian cells.
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Affiliation(s)
- Tianpeng Zhang
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Yashpal Rawal
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Haoyang Jiang
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Youngho Kwon
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Patrick Sung
- Department of Biochemistry and Structural Biology and Greehey Children's Cancer Research Institute, University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
| | - Roger A Greenberg
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA.
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15
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Jones CY, Williams CL, Moreno SP, Morris DK, Mondello C, Karlseder J, Bertuch AA. Hyperextended telomeres promote formation of C-circle DNA in telomerase positive human cells. J Biol Chem 2023; 299:104665. [PMID: 37003504 PMCID: PMC10235436 DOI: 10.1016/j.jbc.2023.104665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2023] [Revised: 03/17/2023] [Accepted: 03/18/2023] [Indexed: 04/01/2023] Open
Abstract
Telomere length maintenance is crucial to cancer cell immortality. Up to 15% of cancers utilize a telomerase-independent, recombination-based mechanism termed alternative lengthening of telomeres (ALT). Currently, the primary ALT biomarker is the C-circle, a type of circular DNA with extrachromosomal telomere repeats (cECTRs). How C-circles form is not well characterized. We investigated C-circle formation in the human cen3tel cell line, a long-telomere, telomerase+ (LTT+) cell line with progressively hyper-elongated telomeres (up to ∼100 kb). cECTR signal was observed in 2D gels and C-circle assays but not t-circle assays, which also detect circular DNA with extrachromosomal telomere repeats. Telomerase activity and C-circle signal were not separable in the analysis of clonal populations, consistent with C-circle production occurring within telomerase+ cells. We observed similar cECTR results in two other LTT+ cell lines, HeLa1.3 (∼23 kb telomeres) and HeLaE1 (∼50 kb telomeres). In LTT+ cells, telomerase activity did not directly impact C-circle signal; instead, C-circle signal correlated with telomere length. LTT+ cell lines were less sensitive to hydroxyurea than ALT+ cell lines, suggesting that ALT status is a stronger contributor to replication stress levels than telomere length. Additionally, the DNA repair-associated protein FANCM did not suppress C-circles in LTT+ cells as it does in ALT+ cells. Thus, C-circle formation may be driven by telomere length, independently of telomerase and replication stress, highlighting limitations of C-circles as a stand-alone ALT biomarker.
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Affiliation(s)
- Celina Y Jones
- Division of Hematology/Oncology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA; Texas Children's Cancer Center, Texas Children's Hospital, Houston, Texas, USA
| | - Christopher L Williams
- Division of Hematology/Oncology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA; Texas Children's Cancer Center, Texas Children's Hospital, Houston, Texas, USA
| | - Sara Priego Moreno
- Molecular and Cell Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California, USA
| | - Danna K Morris
- Division of Hematology/Oncology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA; Texas Children's Cancer Center, Texas Children's Hospital, Houston, Texas, USA
| | - Chiara Mondello
- Institute of Molecular Genetics, Luigi Luca Cavalli-Sforza, National Research Council, Pavia, Italy
| | - Jan Karlseder
- Molecular and Cell Biology Laboratory, The Salk Institute for Biological Studies, La Jolla, California, USA
| | - Alison A Bertuch
- Division of Hematology/Oncology, Department of Pediatrics, Baylor College of Medicine, Houston, Texas, USA; Texas Children's Cancer Center, Texas Children's Hospital, Houston, Texas, USA.
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16
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Broderick R, Cherdyntseva V, Nieminuszczy J, Dragona E, Kyriakaki M, Evmorfopoulou T, Gagos S, Niedzwiedz W. Pathway choice in the alternative telomere lengthening in neoplasia is dictated by replication fork processing mediated by EXD2's nuclease activity. Nat Commun 2023; 14:2428. [PMID: 37105990 PMCID: PMC10140042 DOI: 10.1038/s41467-023-38029-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2022] [Accepted: 04/12/2023] [Indexed: 04/29/2023] Open
Abstract
Telomerase-independent cancer proliferation via the alternative lengthening of telomeres (ALT) relies upon two distinct, largely uncharacterized, break-induced-replication (BIR) processes. How cancer cells initiate and regulate these terminal repair mechanisms is unknown. Here, we establish that the EXD2 nuclease is recruited to ALT telomeres to direct their maintenance. We demonstrate that EXD2 loss leads to telomere shortening, elevated telomeric sister chromatid exchanges, C-circle formation as well as BIR-mediated telomeric replication. We discover that EXD2 fork-processing activity triggers a switch between RAD52-dependent and -independent ALT-associated BIR. The latter is suppressed by EXD2 but depends specifically on the fork remodeler SMARCAL1 and the MUS81 nuclease. Thus, our findings suggest that processing of stalled replication forks orchestrates elongation pathway choice at ALT telomeres. Finally, we show that co-depletion of EXD2 with BLM, DNA2 or POLD3 confers synthetic lethality in ALT cells, identifying EXD2 as a potential druggable target for ALT-reliant cancers.
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Affiliation(s)
| | - Veronica Cherdyntseva
- Laboratory of Genetics, Center of Clinical Research, Experimental Surgery and Translational Research Biomedical Research Foundation Academy of Athens (BRFAA), Athens, Greece
| | | | - Eleni Dragona
- Laboratory of Genetics, Center of Clinical Research, Experimental Surgery and Translational Research Biomedical Research Foundation Academy of Athens (BRFAA), Athens, Greece
| | - Maria Kyriakaki
- Laboratory of Genetics, Center of Clinical Research, Experimental Surgery and Translational Research Biomedical Research Foundation Academy of Athens (BRFAA), Athens, Greece
| | - Theodora Evmorfopoulou
- Laboratory of Genetics, Center of Clinical Research, Experimental Surgery and Translational Research Biomedical Research Foundation Academy of Athens (BRFAA), Athens, Greece
| | - Sarantis Gagos
- Laboratory of Genetics, Center of Clinical Research, Experimental Surgery and Translational Research Biomedical Research Foundation Academy of Athens (BRFAA), Athens, Greece.
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17
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Moreno SP, Fusté JM, Kaiser M, Li JSZ, Nassour J, Haggblom C, Denchi EL, Karlseder J. TZAP overexpression induces telomere dysfunction and ALT-like activity in ATRX/DAXX-deficient cells. iScience 2023; 26:106405. [PMID: 37013192 PMCID: PMC10066556 DOI: 10.1016/j.isci.2023.106405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 11/13/2022] [Accepted: 03/10/2023] [Indexed: 03/14/2023] Open
Abstract
The appropriate regulation of telomere length homeostasis is crucial for the maintenance of genome integrity. The telomere-binding protein TZAP has been suggested to regulate telomere length by promoting t-circle and c-circle excisions through telomere trimming, yet the molecular mechanisms by which TZAP functions at telomeres are not understood. Using a system based on TZAP overexpression, we show that efficient TZAP recruitment to telomeres occurs in the context of open telomeric chromatin caused by loss of ATRX/DAXX independently of H3.3 deposition. Moreover, our data indicate that TZAP binding to telomeres induces telomere dysfunction and ALT-like activity, resulting in the generation of t-circles and c-circles in a Bloom-Topoisomerase IIIα-RMI1-RMI2 (BTR)-dependent manner.
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Affiliation(s)
- Sara Priego Moreno
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Javier Miralles Fusté
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Melanie Kaiser
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Julia Su Zhou Li
- The Ludwig Institute for Cancer Research, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Joe Nassour
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Candy Haggblom
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Eros Lazzerini Denchi
- Laboratory for Genome Integrity, National Cancer Institute, Building 37, Room 2144B, Bethesda, MD 20892, USA
| | - Jan Karlseder
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
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18
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Li F, Wang Y, Hwang I, Jang JY, Xu L, Deng Z, Yu EY, Cai Y, Wu C, Han Z, Huang YH, Huang X, Zhang L, Yao J, Lue NF, Lieberman PM, Ying H, Paik J, Zheng H. Histone demethylase KDM2A is a selective vulnerability of cancers relying on alternative telomere maintenance. Nat Commun 2023; 14:1756. [PMID: 36991019 PMCID: PMC10060224 DOI: 10.1038/s41467-023-37480-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2022] [Accepted: 03/17/2023] [Indexed: 03/31/2023] Open
Abstract
Telomere length maintenance is essential for cellular immortalization and tumorigenesis. 5% - 10% of human cancers rely on a recombination-based mechanism termed alternative lengthening of telomeres (ALT) to sustain their replicative immortality, yet there are currently no targeted therapies. Through CRISPR/Cas9-based genetic screens in an ALT-immortalized isogenic cellular model, here we identify histone lysine demethylase KDM2A as a molecular vulnerability selectively for cells contingent on ALT-dependent telomere maintenance. Mechanistically, we demonstrate that KDM2A is required for dissolution of the ALT-specific telomere clusters following recombination-directed telomere DNA synthesis. We show that KDM2A promotes de-clustering of ALT multitelomeres through facilitating isopeptidase SENP6-mediated SUMO deconjugation at telomeres. Inactivation of KDM2A or SENP6 impairs post-recombination telomere de-SUMOylation and thus dissolution of ALT telomere clusters, leading to gross chromosome missegregation and mitotic cell death. These findings together establish KDM2A as a selective molecular vulnerability and a promising drug target for ALT-dependent cancers.
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Affiliation(s)
- Fei Li
- Department of Neurosurgery, Southwest Hospital, Chongqing, 400038, China
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 11724, USA
| | - Yizhe Wang
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Inah Hwang
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
- Graduate School of Pharmaceutical Sciences, College of Pharmacy, Ewha Womans University, Seoul, 03760, Republic of Korea
| | - Ja-Young Jang
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Libo Xu
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 11724, USA
- Key Laboratory of Pathobiology, Ministry of Education, and Department of Pathophysiology, College of Basic Medical Sciences, Jilin University, Changchun, Jilin, China
| | - Zhong Deng
- The Wistar Institute, Philadelphia, PA, 19104, USA
| | - Eun Young Yu
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Yiming Cai
- Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Caizhi Wu
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 11724, USA
| | - Zhenbo Han
- Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Yu-Han Huang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 11724, USA
| | - Xiangao Huang
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA
| | - Ling Zhang
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY, 11724, USA
- Key Laboratory of Pathobiology, Ministry of Education, and Department of Pathophysiology, College of Basic Medical Sciences, Jilin University, Changchun, Jilin, China
| | - Jun Yao
- Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Neal F Lue
- Department of Microbiology and Immunology, W. R. Hearst Microbiology Research Center, Weill Cornell Medicine, New York, NY, 10065, USA
| | | | - Haoqiang Ying
- Department of Molecular and Cellular Oncology, The University of Texas M. D. Anderson Cancer Center, Houston, TX, 77030, USA
| | - Jihye Paik
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA.
| | - Hongwu Zheng
- Department of Pathology and Laboratory Medicine, Weill Cornell Medicine, New York, NY, 10065, USA.
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19
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Sohn EJ, Goralsky JA, Shay JW, Min J. The Molecular Mechanisms and Therapeutic Prospects of Alternative Lengthening of Telomeres (ALT). Cancers (Basel) 2023; 15:cancers15071945. [PMID: 37046606 PMCID: PMC10093677 DOI: 10.3390/cancers15071945] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 04/14/2023] Open
Abstract
As detailed by the end replication problem, the linear ends of a cell's chromosomes, known as telomeres, shorten with each successive round of replication until a cell enters into a state of growth arrest referred to as senescence. To maintain their immortal proliferation capacity, cancer cells must employ a telomere maintenance mechanism, such as telomerase activation or the Alternative Lengthening of Telomeres pathway (ALT). With only 10-15% of cancers utilizing the ALT mechanism, progress towards understanding its molecular components and associated hallmarks has only recently been made. This review analyzes the advances towards understanding the ALT pathway by: (1) detailing the mechanisms associated with engaging the ALT pathway as well as (2) identifying potential therapeutic targets of ALT that may lead to novel cancer therapeutic treatments. Collectively, these studies indicate that the ALT molecular mechanisms involve at least two distinct pathways induced by replication stress and damage at telomeres. We suggest exploiting tumor dependency on ALT is a promising field of study because it suggests new approaches to ALT-specific therapies for cancers with poorer prognosis. While substantial progress has been made in the ALT research field, additional progress will be required to realize these advances into clinical practices to treat ALT cancers and improve patient prognoses.
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Affiliation(s)
- Eric J Sohn
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Julia A Goralsky
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Jerry W Shay
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA
| | - Jaewon Min
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY 10032, USA
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20
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Robinson NJ, Schiemann WP. Amplification and Quantitation of Telomeric Extrachromosomal Circles. Bio Protoc 2023; 13:e4627. [PMID: 36908640 PMCID: PMC9993076 DOI: 10.21769/bioprotoc.4627] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2022] [Revised: 12/14/2022] [Accepted: 02/07/2023] [Indexed: 03/07/2023] Open
Abstract
Telomeres are structures that cap the ends of linear chromosomes and play critical roles in maintaining genome integrity and establishing the replicative lifespan of cells. In stem and cancer cells, telomeres are actively elongated by either telomerase or the alternative lengthening of telomeres (ALT) pathway. This pathway is characterized by several hallmark features, including extrachromosomal C-rich circular DNAs that can be probed to assess ALT activity. These so-called C-circles are the product of ALT-associated DNA damage repair processes and simultaneously serve as potential templates for iterative telomere extension. This bifunctional nature makes C-circles highly sensitive and specific markers of ALT. Here, we describe a C-circle assay, adapted from previous reports, that enables the quantitation of C-circle abundance in mammalian cells subjected to a wide range of experimental perturbations. This protocol combines the Quick C-circle Preparation (QCP) method for DNA isolation with fluorometry-based DNA quantification, rolling circle amplification (RCA), and detection of C-circles using quantitative PCR. Moreover, the inclusion of internal standards with well-characterized telomere maintenance mechanisms (TMMs) allows for the reliable benchmarking of cells with unknown TMM status. Overall, our work builds upon existing protocols to create a generalizable workflow for in vitro C-circle quantitation and ascertainment of TMM identity.
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Affiliation(s)
- Nathaniel J Robinson
- Department of Neurobiology, University of Alabama at Birmingham, Birmingham, AL 35233, USA
| | - William P Schiemann
- Department of Biochemistry, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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21
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Histone demethylase KDM2A is a selective vulnerability of cancers relying on alternative telomere maintenance. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.02.10.528023. [PMID: 36798426 PMCID: PMC9934630 DOI: 10.1101/2023.02.10.528023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/16/2023]
Abstract
Telomere length maintenance is essential for cellular immortalization and tumorigenesis. 5% - 10% of human cancers rely on a recombination-based mechanism termed alternative lengthening of telomeres (ALT) to sustain their replicative immortality, yet there are currently no targeted therapies. Through CRISPR/Cas9-based genetic screens in an ALT-immortalized isogenic cellular model, here we identify histone lysine demethylase KDM2A as a molecular vulnerability selectively for cells contingent on ALT-dependent telomere maintenance. Mechanistically, we demonstrate that KDM2A is required for dissolution of the ALT-specific telomere clusters following homology-directed telomere DNA synthesis. We show that KDM2A promotes de-clustering of ALT multitelomeres through facilitating isopeptidase SENP6-mediated SUMO deconjugation at telomeres. Inactivation of KDM2A or SENP6 impairs post-recombination telomere de-SUMOylation and thus dissolution of ALT telomere clusters, leading to gross chromosome missegregation and mitotic cell death. These findings together establish KDM2A as a selective molecular vulnerability and a promising drug target for ALT-dependent cancers.
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22
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de Bardet JC, Cardentey CR, González BL, Patrone D, Mulet IL, Siniscalco D, Robinson-Agramonte MDLA. Cell Immortalization: In Vivo Molecular Bases and In Vitro Techniques for Obtention. BIOTECH 2023; 12:biotech12010014. [PMID: 36810441 PMCID: PMC9944833 DOI: 10.3390/biotech12010014] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/20/2022] [Revised: 01/25/2023] [Accepted: 01/26/2023] [Indexed: 01/31/2023] Open
Abstract
Somatic human cells can divide a finite number of times, a phenomenon known as the Hayflick limit. It is based on the progressive erosion of the telomeric ends each time the cell completes a replicative cycle. Given this problem, researchers need cell lines that do not enter the senescence phase after a certain number of divisions. In this way, more lasting studies can be carried out over time and avoid the tedious work involved in performing cell passes to fresh media. However, some cells have a high replicative potential, such as embryonic stem cells and cancer cells. To accomplish this, these cells express the enzyme telomerase or activate the mechanisms of alternative telomere elongation, which favors the maintenance of the length of their stable telomeres. Researchers have been able to develop cell immortalization technology by studying the cellular and molecular bases of both mechanisms and the genes involved in the control of the cell cycle. Through it, cells with infinite replicative capacity are obtained. To obtain them, viral oncogenes/oncoproteins, myc genes, ectopic expression of telomerase, and the manipulation of genes that regulate the cell cycle, such as p53 and Rb, have been used.
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Affiliation(s)
- Javier Curi de Bardet
- Department of Neurobiology, International Center for Neurological Restoration, Havana 11300, Cuba
| | | | - Belkis López González
- Department of Allergy, Calixto Garcia General University Hospital, Havana 10400, Cuba
| | - Deanira Patrone
- Department of Experimental Medicine, Division of Molecular Biology, Biotechnology and Histology, University of Campania, 80138 Naples, Italy
| | | | - Dario Siniscalco
- Department of Experimental Medicine, Division of Molecular Biology, Biotechnology and Histology, University of Campania, 80138 Naples, Italy
- Correspondence:
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23
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Jones CY, Williams CL, Moreno SP, Morris DK, Mondello C, Karlseder J, Bertuch AA. Hyperextended telomeres promote C-circle formation in telomerase positive human cells. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023. [PMID: 36747763 PMCID: PMC9900909 DOI: 10.1101/2023.01.26.525615] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Telomere length maintenance is crucial to cancer cell immortality. Up to 15% of cancers utilize a telomerase-independent, recombination-based mechanism termed alternative lengthening of telomeres (ALT). The primary ALT biomarker is the C-circle, a type of circular DNA with extrachromosomal telomere repeats (cECTRs). How C-circles form is not well characterized. To investigate C-circle formation in telomerase+ cells, we studied the human cen3tel cell line, in which telomeres progressively hyper-elongated post TERT -immortalization. cECTR signal was observed in 2D gels and C-circle assays but not t-circle assays, which also detect cECTRs. Telomerase activity and C-circle signal were not separable in the analysis of clonal populations, consistent with C-circle production occurring within telomerase+ cells. Two other long telomere, telomerase+ (LTT+) cell lines, HeLa1.3 (~23 kb telomeres) and HeLaE1 (~50 kb telomeres), had similar cECTR properties. Telomerase activity did not directly impact C-circle signal in LTT+ cells; instead, C-circle signal correlated with telomere length. LTT+ lines were less sensitive to hydroxyurea than an ALT+ cell line, suggesting that ALT status is a stronger contributor to replication stress levels than telomere length. Additionally, FANCM did not suppress C-circles in LTT+ cells as it does in ALT+ cells. Thus, C-circle formation may be driven by telomere length, independently of telomerase and replication stress, highlighting limitations of C-circles as a stand-alone ALT biomarker.
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Yadav T, Zhang JM, Ouyang J, Leung W, Simoneau A, Zou L. TERRA and RAD51AP1 promote alternative lengthening of telomeres through an R- to D-loop switch. Mol Cell 2022; 82:3985-4000.e4. [PMID: 36265486 PMCID: PMC9637728 DOI: 10.1016/j.molcel.2022.09.026] [Citation(s) in RCA: 28] [Impact Index Per Article: 14.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 08/08/2022] [Accepted: 09/23/2022] [Indexed: 11/05/2022]
Abstract
Alternative lengthening of telomeres (ALT), a telomerase-independent process maintaining telomeres, is mediated by break-induced replication (BIR). RAD52 promotes ALT by facilitating D-loop formation, but ALT also occurs through a RAD52-independent BIR pathway. Here, we show that the telomere non-coding RNA TERRA forms dynamic telomeric R-loops and contributes to ALT activity in RAD52 knockout cells. TERRA forms R-loops in vitro and at telomeres in a RAD51AP1-dependent manner. The formation of R-loops by TERRA increases G-quadruplexes (G4s) at telomeres. G4 stabilization enhances ALT even when TERRA is depleted, suggesting that G4s act downstream of R-loops to promote BIR. In vitro, the telomeric R-loops assembled by TERRA and RAD51AP1 generate G4s, which persist after R-loop resolution and allow formation of telomeric D-loops without RAD52. Thus, the dynamic telomeric R-loops formed by TERRA and RAD51AP1 enable the RAD52-independent ALT pathway, and G4s orchestrate an R- to D-loop switch at telomeres to stimulate BIR.
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Affiliation(s)
- Tribhuwan Yadav
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Jia-Min Zhang
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Jian Ouyang
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Wendy Leung
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Antoine Simoneau
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Lee Zou
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA; Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA.
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25
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Gu X, Dai Q, Du P, Li N, Li J, Zeng S, Peng S, Tang S, Wang L, Zhou Z. Pold4 is dispensable for mouse development, DNA replication and DNA repair. Gene X 2022; 851:147029. [DOI: 10.1016/j.gene.2022.147029] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2022] [Revised: 10/09/2022] [Accepted: 10/31/2022] [Indexed: 11/09/2022] Open
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26
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Choi J, Kong M, Gallagher DN, Li K, Bronk G, Cao Y, Greene EC, Haber JE. Repair of mismatched templates during Rad51-dependent Break-Induced Replication. PLoS Genet 2022; 18:e1010056. [PMID: 36054210 PMCID: PMC9477423 DOI: 10.1371/journal.pgen.1010056] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2022] [Revised: 09/15/2022] [Accepted: 08/10/2022] [Indexed: 12/02/2022] Open
Abstract
Using budding yeast, we have studied Rad51-dependent break-induced replication (BIR), where the invading 3’ end of a site-specific double-strand break (DSB) and a donor template share 108 bp of homology that can be easily altered. BIR still occurs about 10% as often when every 6th base is mismatched as with a perfectly matched donor. Here we explore the tolerance of mismatches in more detail, by examining donor templates that each carry 10 mismatches, each with different spatial arrangements. Although 2 of the 6 arrangements we tested were nearly as efficient as the evenly-spaced reference, 4 were significantly less efficient. A donor with all 10 mismatches clustered at the 3’ invading end of the DSB was not impaired compared to arrangements where mismatches were clustered at the 5’ end. Our data suggest that the efficiency of strand invasion is principally dictated by thermodynamic considerations, i.e., by the total number of base pairs that can be formed; but mismatch position-specific effects are also important. We also addressed an apparent difference between in vitro and in vivo strand exchange assays, where in vitro studies had suggested that at a single contiguous stretch of 8 consecutive bases was needed to be paired for stable strand pairing, while in vivo assays using 108-bp substrates found significant recombination even when every 6th base was mismatched. Now, using substrates of either 90 or 108 nt–the latter being the size of the in vivo templates–we find that in vitro D-loop results are very similar to the in vivo results. However, there are still notable differences between in vivo and in vitro assays that are especially evident with unevenly-distributed mismatches. Mismatches in the donor template are incorporated into the BIR product in a strongly polar fashion up to ~40 nucleotides from the 3’ end. Mismatch incorporation depends on the 3’→ 5’ proofreading exonuclease activity of DNA polymerase δ, with little contribution from Msh2/Mlh1 mismatch repair proteins, or from Rad1-Rad10 flap nuclease or the Mph1 helicase. Surprisingly, the probability of a mismatch 27 nt from the 3’ end being replaced by donor sequence was the same whether the preceding 26 nucleotides were mismatched every 6th base or fully homologous. These data suggest that DNA polymerase δ “chews back” the 3’ end of the invading strand without any mismatch-dependent cues from the strand invasion structure. However, there appears to be an alternative way to incorporate a mismatch at the first base at the 3’ end of the donor. DNA double-strand breaks (DSBs) are the most lethal forms of DNA damage and inaccurate repair of these breaks presents a serious threat to genomic integrity and cell viability. Break-induced replication (BIR) is a homologous recombination pathway that results in a nonreciprocal translocation of chromosome ends. We used budding yeast Saccharomyces cerevisiae to investigate Rad51-mediated BIR, where the invading 3’ end of the DSB and a donor template share 108 bp of homology. We examined the tolerance of differently distributed mismatches on a homologous donor template. A donor with all 10 mismatches clustered every 6th base at the 3’ invading end of the DSB was not impaired compared to arrangements where mismatches were clustered at the 5’ end. We also compared the efficiency of in vivo BIR with in vitro D-loop formation and find that for substrates of the same length, the tolerance for mismatches is comparable. However, there are still notable differences between in vivo and in vitro assays that are especially evident in substrates with unevenly-distributed mismatches. Mismatches are incorporated into the BIR product in a strongly polar fashion as far as about 40 nucleotides from the 3’ end, dependent on the 5’ to 3’ proofreading activity of DNA polymerase δ. Pol δ can “chew back” the 3’ end of the invading strand even when the sequences removed have no mismatches for the first 26 nucleotides. However, a mismatch at the first base can be removed from the 3’ end by another, unidentified mechanism.
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Affiliation(s)
- Jihyun Choi
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, United States of America
| | - Muwen Kong
- Department of Biochemistry & Molecular Biophysics, Columbia University, New York, New York, United States of America
| | - Danielle N. Gallagher
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, United States of America
| | - Kevin Li
- Department of Physics, Brandeis University, Waltham, Massachusetts, United States of America
| | - Gabriel Bronk
- Department of Physics, Brandeis University, Waltham, Massachusetts, United States of America
| | - Yiting Cao
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, United States of America
| | - Eric C. Greene
- Department of Biochemistry & Molecular Biophysics, Columbia University, New York, New York, United States of America
| | - James E. Haber
- Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, Massachusetts, United States of America
- * E-mail:
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Brenner KA, Nandakumar J. Consequences of telomere replication failure: the other end-replication problem. Trends Biochem Sci 2022; 47:506-517. [PMID: 35440402 PMCID: PMC9106919 DOI: 10.1016/j.tibs.2022.03.013] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2021] [Revised: 02/28/2022] [Accepted: 03/17/2022] [Indexed: 01/14/2023]
Abstract
Telomeres are chromosome-capping structures that protect ends of the linear genome from DNA damage sensors. However, these structures present obstacles during DNA replication. Incomplete telomere replication accelerates telomere shortening and limits replicative lifespan. Therefore, continued proliferation under conditions of replication stress requires a means of telomere repair, particularly in the absence of telomerase. It was recently revealed that replication stress triggers break-induced replication (BIR) and mitotic DNA synthesis (MiDAS) at mammalian telomeres; however, these mechanisms are error prone and primarily utilized in tumorigenic contexts. In this review article, we discuss the consequences of replication stress at telomeres and how use of available repair pathways contributes to genomic instability. Current research suggests that fragile telomeres are ultimately tumor-suppressive and thus may be better left unrepaired.
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Affiliation(s)
- Kirsten A Brenner
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
| | - Jayakrishnan Nandakumar
- Department of Molecular, Cellular, and Developmental Biology, University of Michigan, Ann Arbor, MI 48109, USA.
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28
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Bhargava R, Lynskey ML, O’Sullivan RJ. New twists to the ALTernative endings at telomeres. DNA Repair (Amst) 2022; 115:103342. [DOI: 10.1016/j.dnarep.2022.103342] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2022] [Revised: 05/02/2022] [Accepted: 05/05/2022] [Indexed: 11/30/2022]
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29
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Buemi V, Schillaci O, Santorsola M, Bonazza D, Broccia PV, Zappone A, Bottin C, Dell'Omo G, Kengne S, Cacchione S, Raffa GD, Piazza S, di Fagagna FD, Benetti R, Cortale M, Zanconati F, Del Sal G, Schoeftner S. TGS1 mediates 2,2,7-trimethyl guanosine capping of the human telomerase RNA to direct telomerase dependent telomere maintenance. Nat Commun 2022; 13:2302. [PMID: 35484160 PMCID: PMC9050681 DOI: 10.1038/s41467-022-29907-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2020] [Accepted: 03/25/2022] [Indexed: 11/21/2022] Open
Abstract
Pathways that direct the selection of the telomerase-dependent or recombination-based, alternative lengthening of telomere (ALT) maintenance pathway in cancer cells are poorly understood. Using human lung cancer cells and tumor organoids we show that formation of the 2,2,7-trimethylguanosine (TMG) cap structure at the human telomerase RNA 5′ end by the Trimethylguanosine Synthase 1 (TGS1) is central for recruiting telomerase to telomeres and engaging Cajal bodies in telomere maintenance. TGS1 depletion or inhibition by the natural nucleoside sinefungin impairs telomerase recruitment to telomeres leading to Exonuclease 1 mediated generation of telomere 3′ end protrusions that engage in RAD51-dependent, homology directed recombination and the activation of key features of the ALT pathway. This indicates a critical role for 2,2,7-TMG capping of the RNA component of human telomerase (hTR) in enforcing telomerase-dependent telomere maintenance to restrict the formation of telomeric substrates conductive to ALT. Our work introduces a targetable pathway of telomere maintenance that holds relevance for telomere-related diseases such as cancer and aging. Telomerase protects chromosome ends in stem cells and cancer cells. Here the authors show that Trimethylguaonsine Synthase 1 (TGS-1) – dependent trimethylguanosine capping of the RNA component of the human telomerase complex has an important role in directing telomere dependent telomere maintenance and suppressing the ALT pathway in cancer cells.
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Affiliation(s)
- Valentina Buemi
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy.,Cancer Research UK Cancer Therapeutics Unit, The Institute of Cancer Research, London, SM2 5NG, United Kingdom
| | - Odessa Schillaci
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy
| | - Mariangela Santorsola
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy
| | - Deborah Bonazza
- Struttura Complessa di Anatomia ed Istologia Patologica, Azienda Sanitaria Universitaria Giuliano Isontina (ASUGI) Trieste, Strada di Fiume 447, 34149, Trieste, Italy
| | - Pamela Veneziano Broccia
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy
| | - Annie Zappone
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy
| | - Cristina Bottin
- Dipartimento Universitario Clinico di Scienze Mediche Chirurgiche e della Salute, Università degli Studi di Trieste, Ospedale di Cattinara - Strada di Fiume 447, 34149, Trieste, Italy
| | - Giulia Dell'Omo
- IFOM Foundation-FIRC Institute of Molecular Oncology Foundation, Milan, 20139, Italy
| | - Sylvie Kengne
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy
| | - Stefano Cacchione
- Dipartimento di Biologia e Biotecnologie, Sapienza Università di Roma, Roma, Italy
| | - Grazia Daniela Raffa
- Dipartimento di Biologia e Biotecnologie, Sapienza Università di Roma, Roma, Italy
| | - Silvano Piazza
- International Centre for Genetic Engineering and Biotechnology (ICGEB), Area Science Park - Padriciano, 34149, Trieste, Italy
| | - Fabrizio d'Adda di Fagagna
- IFOM Foundation-FIRC Institute of Molecular Oncology Foundation, Milan, 20139, Italy.,Istituto di Genetica Molecolare, Consiglio Nazionale delle Ricerche (IGM-CNR), Pavia, 27100, Italy
| | - Roberta Benetti
- Dipartimento di Area Medica (Dame), Università degli Studi di Udine, p.le Kolbe 4, 33100, Udine, Italy
| | - Maurizio Cortale
- Struttura Complessa di Chirurgia Toracica, Azienda Sanitaria Universitaria Giuliano Isontina (ASUGI) Trieste, Strada di Fiume 447, 34149, Trieste, Italy
| | - Fabrizio Zanconati
- Struttura Complessa di Anatomia ed Istologia Patologica, Azienda Sanitaria Universitaria Giuliano Isontina (ASUGI) Trieste, Strada di Fiume 447, 34149, Trieste, Italy.,Dipartimento Universitario Clinico di Scienze Mediche Chirurgiche e della Salute, Università degli Studi di Trieste, Ospedale di Cattinara - Strada di Fiume 447, 34149, Trieste, Italy
| | - Giannino Del Sal
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy.,IFOM Foundation-FIRC Institute of Molecular Oncology Foundation, Milan, 20139, Italy.,International Centre for Genetic Engineering and Biotechnology (ICGEB), Area Science Park - Padriciano, 34149, Trieste, Italy
| | - Stefan Schoeftner
- Dipartimento di Scienze della Vita, Università degli Studi di Trieste, Via E. Weiss 2, 34127, Trieste, Italy.
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30
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Hou K, Yu Y, Li D, Zhang Y, Zhang K, Tong J, Yang K, Jia S. Alternative Lengthening of Telomeres and Mediated Telomere Synthesis. Cancers (Basel) 2022; 14:cancers14092194. [PMID: 35565323 PMCID: PMC9105334 DOI: 10.3390/cancers14092194] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2022] [Revised: 04/24/2022] [Accepted: 04/25/2022] [Indexed: 12/01/2022] Open
Abstract
Simple Summary Alternative lengthing of telomere (ALT) is an important mechanism for maintaining telomere length and cell proliferation in telomerase-negative tumor cells. However, the molecular mechanism of ALT is still poorly understood. ALT occurs in a wide range of tumor types and usually associated with a worse clinical consequence. Here, we review the recent findings of ALT mechanisms, which promise ALT could be a valuable drug target for clinical telomerase-negative tumor treatment. Abstract Telomeres are DNA–protein complexes that protect eukaryotic chromosome ends from being erroneously repaired by the DNA damage repair system, and the length of telomeres indicates the replicative potential of the cell. Telomeres shorten during each division of the cell, resulting in telomeric damage and replicative senescence. Tumor cells tend to ensure cell proliferation potential and genomic stability by activating telomere maintenance mechanisms (TMMs) for telomere lengthening. The alternative lengthening of telomeres (ALT) pathway is the most frequently activated TMM in tumors of mesenchymal and neuroepithelial origin, and ALT also frequently occurs during experimental cellular immortalization of mesenchymal cells. ALT is a process that relies on homologous recombination (HR) to elongate telomeres. However, some processes in the ALT mechanism remain poorly understood. Here, we review the most recent understanding of ALT mechanisms and processes, which may help us to better understand how the ALT pathway is activated in cancer cells and determine the potential therapeutic targets in ALT pathway-stabilized tumors.
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Affiliation(s)
- Kailong Hou
- Faculty of Life Science and Technology, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China;
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
- First People’s Hospital of Yunnan Province, 157 Jinbi Road, Kunming 650032, China
| | - Yuyang Yu
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
| | - Duda Li
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
| | - Yanduo Zhang
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
| | - Ke Zhang
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
| | - Jinkai Tong
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
| | - Kunxian Yang
- First People’s Hospital of Yunnan Province, 157 Jinbi Road, Kunming 650032, China
- Correspondence: (K.Y.); (S.J.)
| | - Shuting Jia
- Laboratory of Molecular Genetics of Aging and Tumor, Medical School, Kunming University of Science and Technology, 727 Jing Ming Nan Road, Kunming 650500, China; (Y.Y.); (D.L.); (Y.Z.); (K.Z.); (J.T.)
- Correspondence: (K.Y.); (S.J.)
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31
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Break-induced replication: unraveling each step. Trends Genet 2022; 38:752-765. [PMID: 35459559 DOI: 10.1016/j.tig.2022.03.011] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/16/2022] [Revised: 03/11/2022] [Accepted: 03/14/2022] [Indexed: 10/18/2022]
Abstract
Break-induced replication (BIR) repairs one-ended double-strand DNA breaks through invasion into a homologous template followed by DNA synthesis. Different from S-phase replication, BIR copies the template DNA in a migrating displacement loop (D-loop) and results in conservative inheritance of newly synthesized DNA. This unusual mode of DNA synthesis makes BIR a source of various genetic instabilities like those associated with cancer in humans. This review focuses on recent progress in delineating the mechanism of Rad51-dependent BIR in budding yeast. In addition, we discuss new data that describe changes in BIR efficiency and fidelity on encountering replication obstacles as well as the implications of these findings for BIR-dependent processes such as telomere maintenance and the repair of collapsed replication forks.
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32
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A POLD3/BLM dependent pathway handles DSBs in transcribed chromatin upon excessive RNA:DNA hybrid accumulation. Nat Commun 2022; 13:2012. [PMID: 35440629 PMCID: PMC9019021 DOI: 10.1038/s41467-022-29629-2] [Citation(s) in RCA: 16] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2021] [Accepted: 03/25/2022] [Indexed: 12/03/2022] Open
Abstract
Transcriptionally active loci are particularly prone to breakage and mounting evidence suggests that DNA Double-Strand Breaks arising in active genes are handled by a dedicated repair pathway, Transcription-Coupled DSB Repair (TC-DSBR), that entails R-loop accumulation and dissolution. Here, we uncover a function for the Bloom RecQ DNA helicase (BLM) in TC-DSBR in human cells. BLM is recruited in a transcription dependent-manner at DSBs where it fosters resection, RAD51 binding and accurate Homologous Recombination repair. However, in an R-loop dissolution-deficient background, we find that BLM promotes cell death. We report that upon excessive RNA:DNA hybrid accumulation, DNA synthesis is enhanced at DSBs, in a manner that depends on BLM and POLD3. Altogether our work unveils a role for BLM at DSBs in active chromatin, and highlights the toxic potential of RNA:DNA hybrids that accumulate at transcription-associated DSBs. DNA Double Strand breaks in transcriptionally active loci (TC-DSBs) undergo a dedicated repair pathway. Here, the authors show that excessive RNA:DNA hybrid accumulation at TC-DSBs elicits POLD3/BLM-dependent DNA synthesis that induces cell toxicity.
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33
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Malone EG, Thompson MD, Byrd AK. Role and Regulation of Pif1 Family Helicases at the Replication Fork. Int J Mol Sci 2022; 23:ijms23073736. [PMID: 35409096 PMCID: PMC8998199 DOI: 10.3390/ijms23073736] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2022] [Revised: 03/24/2022] [Accepted: 03/25/2022] [Indexed: 02/04/2023] Open
Abstract
Pif1 helicases are a multifunctional family of DNA helicases that are important for many aspects of genomic stability in the nucleus and mitochondria. Pif1 helicases are conserved from bacteria to humans. Pif1 helicases play multiple roles at the replication fork, including promoting replication through many barriers such as G-quadruplex DNA, the rDNA replication fork barrier, tRNA genes, and R-loops. Pif1 helicases also regulate telomerase and promote replication termination, Okazaki fragment maturation, and break-induced replication. This review highlights many of the roles and regulations of Pif1 at the replication fork that promote cellular health and viability.
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Affiliation(s)
- Emory G. Malone
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (E.G.M.); (M.D.T.)
| | - Matthew D. Thompson
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (E.G.M.); (M.D.T.)
| | - Alicia K. Byrd
- Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA; (E.G.M.); (M.D.T.)
- Winthrop P. Rockefeller Cancer Institute, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA
- Correspondence: ; Tel.: +1-501-526-6488
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34
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Aguilera P, Dubarry M, Hardy J, Lisby M, Simon MN, Géli V. Telomeric C-circles localize at nuclear pore complexes in Saccharomyces cerevisiae. EMBO J 2022; 41:e108736. [PMID: 35147992 PMCID: PMC8922269 DOI: 10.15252/embj.2021108736] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2021] [Revised: 01/17/2022] [Accepted: 01/21/2022] [Indexed: 11/09/2022] Open
Abstract
As in human cells, yeast telomeres can be maintained in cells lacking telomerase activity by recombination-based mechanisms known as ALT (Alternative Lengthening of Telomeres). A hallmark of ALT human cancer cells are extrachromosomal telomeric DNA elements called C-circles, whose origin and function have remained unclear. Here, we show that extrachromosomal telomeric C-circles in yeast can be detected shortly after senescence crisis and concomitantly with the production of survivors arising from "type II" recombination events. We uncover that C-circles bind to the nuclear pore complex (NPC) and to the SAGA-TREX2 complex, similar to other non-centromeric episomal DNA. Disrupting the integrity of the SAGA/TREX2 complex affects both C-circle binding to NPCs and type II telomere recombination, suggesting that NPC tethering of C-circles facilitates formation and/or propagation of the long telomere repeats characteristic of type II survivors. Furthermore, we find that disruption of the nuclear diffusion barrier impairs type II recombination. These results support a model in which concentration of C-circles at NPCs benefits type II telomere recombination, highlighting the importance of spatial coordination in ALT-type mechanisms of telomere maintenance.
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Affiliation(s)
- Paula Aguilera
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Marion Dubarry
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Julien Hardy
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Michael Lisby
- Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Marie-Noëlle Simon
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
| | - Vincent Géli
- Marseille Cancer Research Center (CRCM), U1068 Inserm, UMR7258 CNRS, Institut Paoli-Calmettes, Equipe labellisée Ligue, Aix Marseille University, Marseille, France
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Lu R, Pickett HA. Telomeric replication stress: the beginning and the end for alternative lengthening of telomeres cancers. Open Biol 2022; 12:220011. [PMID: 35259951 PMCID: PMC8905155 DOI: 10.1098/rsob.220011] [Citation(s) in RCA: 14] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Telomeres are nucleoprotein structures that cap the ends of linear chromosomes. Telomeric DNA comprises terminal tracts of G-rich tandem repeats, which are inherently difficult for the replication machinery to navigate. Structural aberrations that promote activation of the alternative lengthening of telomeres (ALT) pathway of telomere maintenance exacerbate replication stress at ALT telomeres, driving fork stalling and fork collapse. This form of telomeric DNA damage perpetuates recombination-mediated repair pathways and break-induced telomere synthesis. The relationship between replication stress and DNA repair is tightly coordinated for the purpose of regulating telomere length in ALT cells, but has been shown to be experimentally manipulatable. This raises the intriguing possibility that induction of replication stress can be used as a means to cause toxic levels of DNA damage at ALT telomeres, thereby selectively disrupting the viability of ALT cancers.
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Affiliation(s)
- Robert Lu
- Telomere Length Regulation Unit, Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
| | - Hilda A. Pickett
- Telomere Length Regulation Unit, Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
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Dan J, Zhou Z, Wang F, Wang H, Guo R, Keefe DL, Liu L. Zscan4 Contributes to Telomere Maintenance in Telomerase-Deficient Late Generation Mouse ESCs and Human ALT Cancer Cells. Cells 2022; 11:cells11030456. [PMID: 35159266 PMCID: PMC8834411 DOI: 10.3390/cells11030456] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Revised: 01/24/2022] [Accepted: 01/25/2022] [Indexed: 02/06/2023] Open
Abstract
Proper telomere length is essential for indefinite self-renewal of embryonic stem (ES) cells and cancer cells. Telomerase-deficient late generation mouse ES cells and human ALT cancer cells are able to propagate for numerous passages, suggesting telomerase-independent mechanisms responding for telomere maintenance. However, the underlying mechanisms ensuring the telomere length maintenance are unclear. Here, using late generation telomerase KO (G4 Terc-/-) ESCs as a model, we show that Zscan4, highly upregulated in G4 Terc-/- ESCs, is responsible for the prolonged culture of these cells with stably short telomeres. Mechanistically, G4 Terc-/- ESCs showed reduced levels of DNA methylation and H3K9me3 at Zscan4 promoter and subtelomeres, which relieved the expression of Zscan4. Similarly, human ZSCAN4 was also derepressed by reduced H3K9me3 at its promoter in ALT U2 OS cells, and depletion of ZSCAN4 significantly shortened telomeres. Our results define a similar conserved pathway contributing to the telomere maintenance in telomerase-deficient late generation mESCs and human ALT U2OS cancer cells.
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Affiliation(s)
- Jiameng Dan
- State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China; (Z.Z.); (H.W.); (R.G.)
- State Key Laboratory of Primate Biomedical Research, Institute of Primate Translational Medicine, Kunming University of Science and Technology, Kunming, Yunnan 650500, China; Yunnan Key Laboratory of Primate Biomedical Research, Kunming, Yunnan 650500, China
- Correspondence: (J.D.); (L.L.)
| | - Zhongcheng Zhou
- State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China; (Z.Z.); (H.W.); (R.G.)
| | - Fang Wang
- Department of Obstetrics and Gynecology, New York University Langone Medical Center, New York, NY 10016, USA; (F.W.); (D.L.K.)
| | - Hua Wang
- State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China; (Z.Z.); (H.W.); (R.G.)
| | - Renpeng Guo
- State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China; (Z.Z.); (H.W.); (R.G.)
| | - David L. Keefe
- Department of Obstetrics and Gynecology, New York University Langone Medical Center, New York, NY 10016, USA; (F.W.); (D.L.K.)
| | - Lin Liu
- State Key Laboratory of Medicinal Chemical Biology, Department of Cell Biology and Genetics, College of Life Sciences, Nankai University, Tianjin 300071, China; (Z.Z.); (H.W.); (R.G.)
- Correspondence: (J.D.); (L.L.)
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37
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Epum EA, Haber JE. DNA replication: the recombination connection. Trends Cell Biol 2022; 32:45-57. [PMID: 34384659 PMCID: PMC8688190 DOI: 10.1016/j.tcb.2021.07.005] [Citation(s) in RCA: 30] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2021] [Revised: 07/18/2021] [Accepted: 07/20/2021] [Indexed: 01/03/2023]
Abstract
Failure to complete DNA replication is one of the major sources of genome instability leading to aneuploidy, chromosome breakage, and chromosome rearrangements that are associated with human cancer. One of the surprising revelations of the past decade is that the completion of replication at so-called common fragile sites (CFS) occurs very late in the cell cycle - at mitosis - through a process termed MiDAS (mitotic DNA synthesis). MiDAS is strongly related to another cancer-promoting phenomenon: the activation of alternative lengthening of telomeres (ALT). Our understanding of the mechanisms of ALT and MiDAS in mammalian cells has drawn heavily from recent advances in the study of break-induced replication (BIR), especially in budding yeast. We provide new insights into the BIR, MiDAS, and ALT pathways and their shared similarities.
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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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Barroso-González J, García-Expósito L, Galaviz P, Lynskey ML, Allen JAM, Hoang S, Watkins SC, Pickett HA, O'Sullivan RJ. Anti-recombination function of MutSα restricts telomere extension by ALT-associated homology-directed repair. Cell Rep 2021; 37:110088. [PMID: 34879271 PMCID: PMC8724847 DOI: 10.1016/j.celrep.2021.110088] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2021] [Revised: 09/13/2021] [Accepted: 11/10/2021] [Indexed: 01/02/2023] Open
Abstract
Alternative lengthening of telomeres (ALT) is a telomere-elongation mechanism observed in ~15% of cancer subtypes. Current models indicate that ALT is mediated by homology-directed repair mechanisms. By disrupting MSH6 gene expression, we show that the deficiency of MutSα (MSH2/MSH6) DNA mismatch repair complex causes striking telomere hyperextension. Mechanistically, we show MutSα is specifically recruited to telomeres in ALT cells by associating with the proliferating-cell nuclear antigen (PCNA) subunit of the ALT telomere replisome. We also provide evidence that MutSα counteracts Bloom (BLM) helicase, which adopts a crucial role in stabilizing hyper-extended telomeres and maintaining the survival of MutSα-deficient ALT cancer cells. Lastly, we propose a model in which MutSα deficiency impairs heteroduplex rejection, leading to premature initiation of telomere DNA synthesis that coincides with an accumulation of telomere variant repeats (TVRs). These findings provide evidence that the MutSα DNA mismatch repair complex acts to restrain unwarranted ALT. Barroso-Gonzalez et al. show that the mismatch repair complex MutSα restricts the alternative lengthening of telomeres (ALT) pathway in cancer cells. MutSα has an anti-recombination function and limits recombination between heteroduplex sequences at telomeres, in part by counteracting the Bloom helicase (BLM).
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Affiliation(s)
- Jonathan Barroso-González
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Laura García-Expósito
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Pablo Galaviz
- Bioinformatics Unit, Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
| | - Michelle Lee Lynskey
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Joshua A M Allen
- Telomere Length Regulation Unit, Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
| | - SongMy Hoang
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Simon C Watkins
- Department of Cell Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA
| | - Hilda A Pickett
- Telomere Length Regulation Unit, Children's Medical Research Institute, Faculty of Medicine and Health, University of Sydney, Westmead, NSW 2145, Australia
| | - Roderick J O'Sullivan
- Department of Pharmacology and Chemical Biology, School of Medicine, University of Pittsburgh School of Medicine, Pittsburgh, PA 15261, USA.
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Impact of Chromatin Dynamics and DNA Repair on Genomic Stability and Treatment Resistance in Pediatric High-Grade Gliomas. Cancers (Basel) 2021; 13:cancers13225678. [PMID: 34830833 PMCID: PMC8616465 DOI: 10.3390/cancers13225678] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2021] [Revised: 11/08/2021] [Accepted: 11/11/2021] [Indexed: 02/07/2023] Open
Abstract
Simple Summary Pediatric high-grade gliomas (pHGGs) are the leading cause of mortality in pediatric neuro-oncology, due in great part to treatment resistance driven by complex DNA repair mechanisms. pHGGs have recently been divided into molecular subtypes based on mutations affecting the N-terminal tail of the histone variant H3.3 and the ATRX/DAXX histone chaperone that deposits H3.3 at repetitive heterochromatin loci that are of paramount importance to the stability of our genome. This review addresses the functions of H3.3 and ATRX/DAXX in chromatin dynamics and DNA repair, as well as the impact of mutations affecting H3.3/ATRX/DAXX on treatment resistance and how the vulnerabilities they expose could foster novel therapeutic strategies. Abstract Despite their low incidence, pediatric high-grade gliomas (pHGGs), including diffuse intrinsic pontine gliomas (DIPGs), are the leading cause of mortality in pediatric neuro-oncology. Recurrent, mutually exclusive mutations affecting K27 (K27M) and G34 (G34R/V) in the N-terminal tail of histones H3.3 and H3.1 act as key biological drivers of pHGGs. Notably, mutations in H3.3 are frequently associated with mutations affecting ATRX and DAXX, which encode a chaperone complex that deposits H3.3 into heterochromatic regions, including telomeres. The K27M and G34R/V mutations lead to distinct epigenetic reprogramming, telomere maintenance mechanisms, and oncogenesis scenarios, resulting in distinct subgroups of patients characterized by differences in tumor localization, clinical outcome, as well as concurrent epigenetic and genetic alterations. Contrasting with our understanding of the molecular biology of pHGGs, there has been little improvement in the treatment of pHGGs, with the current mainstays of therapy—genotoxic chemotherapy and ionizing radiation (IR)—facing the development of tumor resistance driven by complex DNA repair pathways. Chromatin and nucleosome dynamics constitute important modulators of the DNA damage response (DDR). Here, we summarize the major DNA repair pathways that contribute to resistance to current DNA damaging agent-based therapeutic strategies and describe the telomere maintenance mechanisms encountered in pHGGs. We then review the functions of H3.3 and its chaperones in chromatin dynamics and DNA repair, as well as examining the impact of their mutation/alteration on these processes. Finally, we discuss potential strategies targeting DNA repair and epigenetic mechanisms as well as telomere maintenance mechanisms, to improve the treatment of pHGGs.
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Kent T, Clynes D. Alternative Lengthening of Telomeres: Lessons to Be Learned from Telomeric DNA Double-Strand Break Repair. Genes (Basel) 2021; 12:1734. [PMID: 34828344 PMCID: PMC8619803 DOI: 10.3390/genes12111734] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2021] [Revised: 10/22/2021] [Accepted: 10/28/2021] [Indexed: 12/25/2022] Open
Abstract
The study of the molecular pathways underlying cancer has given us important insights into how breaks in our DNA are repaired and the dire consequences that can occur when these processes are perturbed. Extensive research over the past 20 years has shown that the key molecular event underpinning a subset of cancers involves the deregulated repair of DNA double-strand breaks (DSBs) at telomeres, which in turn leads to telomere lengthening and the potential for replicative immortality. Here we discuss, in-depth, recent major breakthroughs in our understanding of the mechanisms underpinning this pathway known as the alternative lengthening of telomeres (ALT). We explore how this gives us important insights into how DSB repair at telomeres is regulated, with relevance to the cell-cycle-dependent regulation of repair, repair of stalled replication forks and the spatial regulation of DSB repair.
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Affiliation(s)
- Thomas Kent
- Molecular Haematology Unit, Radcliffe Department of Medicine, The MRC Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK;
| | - David Clynes
- Department of Oncology, The MRC Weatherall Institute of Molecular Medicine, John Radcliffe Hospital, University of Oxford, Oxford OX3 9DS, UK
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42
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Wu X, Malkova A. Break-induced replication mechanisms in yeast and mammals. Curr Opin Genet Dev 2021; 71:163-170. [PMID: 34481360 DOI: 10.1016/j.gde.2021.08.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Revised: 07/17/2021] [Accepted: 08/05/2021] [Indexed: 11/26/2022]
Abstract
Break-induced replication (BIR) is a pathway specialized in repair of double-strand DNA breaks with only one end capable of invading homologous template that can arise following replication collapse, telomere erosion or DNA cutting by site-specific endonucleases. For a long time, yeast remained the only model system to study BIR. Studies in yeast demonstrated that BIR represents an unusual mode of DNA synthesis that is driven by a migrating bubble and leads to conservative inheritance of newly synthesized DNA. This unusual type of DNA synthesis leads to high levels of mutations and chromosome rearrangements. Recently, multiple examples of BIR were uncovered in mammalian cells that allowed the comparison of BIR between organisms. It appeared initially that BIR in mammalian cells is predominantly independent of RAD51, and therefore different from BIR that is predominantly Rad51-dependent in yeast. However, a series of systematic studies utilizing site-specific DNA breaks for BIR initiation in mammalian reporters led to the discovery of highly efficient RAD51-dependent BIR, allowing side-by side comparison with BIR in yeast which is the focus of this review.
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Affiliation(s)
- Xiaohua Wu
- Department of Molecular Medicine, The Scripps Research Institute, La Jolla, CA 92037, United States.
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA 52242, United States.
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43
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Koneru B, Farooqi A, Nguyen TH, Chen WH, Hindle A, Eslinger C, Makena MR, Burrow TA, Wilson J, Smith A, Pilla Reddy V, Cadogan E, Durant ST, Reynolds CP. ALT neuroblastoma chemoresistance due to telomere dysfunction-induced ATM activation is reversible with ATM inhibitor AZD0156. Sci Transl Med 2021; 13:13/607/eabd5750. [PMID: 34408079 DOI: 10.1126/scitranslmed.abd5750] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 03/10/2021] [Accepted: 05/14/2021] [Indexed: 12/26/2022]
Abstract
Cancers overcome replicative immortality by activating either telomerase or an alternative lengthening of telomeres (ALT) mechanism. ALT occurs in ~25% of high-risk neuroblastomas, and progression in patients with ALT neuroblastoma during or after front-line therapy is frequent and often fatal. Temozolomide + irinotecan is commonly used as salvage therapy for neuroblastoma. Patient-derived cell lines and xenografts established from patients with relapsed ALT neuroblastoma demonstrated de novo resistance to temozolomide + irinotecan [SN-38 in vitro, P < 0.05; in vivo mouse event-free survival (EFS), P < 0.0001] vs. telomerase-positive neuroblastomas. We observed that ALT neuroblastoma cells manifested constitutive ataxia-telangiectasia mutated (ATM) activation due to spontaneous telomere dysfunction which was not observed in telomerase-positive neuroblastoma cells. We demonstrated that induction of telomere dysfunction resulted in ATM activation that, in turn, conferred resistance to temozolomide + SN-38 (4.2-fold change in IC50, P < 0.001). ATM knockdown (shRNA) or inhibition using a clinical-stage small-molecule inhibitor (AZD0156) reversed resistance to temozolomide + irinotecan in ALT neuroblastoma cell lines in vitro (P < 0.001) and in four ALT xenografts in vivo (EFS, P < 0.0001). AZD0156 showed modest to no enhancement of temozolomide + irinotecan activity in telomerase-positive neuroblastoma cell lines and xenografts. Ataxia telangiectasia and Rad3 related (ATR) inhibition using AZD6738 did not enhance temozolomide + SN-38 activity in ALT neuroblastoma cells. Thus, ALT neuroblastoma chemotherapy resistance occurs via ATM activation and is reversible with ATM inhibitor AZD0156. Combining AZD0156 with temozolomide + irinotecan warrants clinical testing for neuroblastoma.
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Affiliation(s)
- Balakrishna Koneru
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.,Department of Pediatrics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.,Department of Cell Biology and Biochemistry, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Ahsan Farooqi
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Thinh H Nguyen
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Wan Hsi Chen
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Ashly Hindle
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.,Department of Cell Biology and Biochemistry, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Cody Eslinger
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Monish Ram Makena
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Trevor A Burrow
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
| | - Joanne Wilson
- Early Oncology, R&D AstraZeneca, Cambridge CB10 1XL, UK
| | - Aaron Smith
- Early Oncology, R&D AstraZeneca, Cambridge CB10 1XL, UK
| | - Venkatesh Pilla Reddy
- Clinical Pharmacology and Quantitative Pharmacology, Biopharmaceuticals R&D, AstraZeneca, Cambridge SG8 6EE, UK
| | | | | | - C Patrick Reynolds
- Cancer Center, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA. .,Department of Pediatrics, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.,Department of Cell Biology and Biochemistry, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA.,Department of Internal Medicine, School of Medicine, Texas Tech University Health Sciences Center, Lubbock, TX 79430, USA
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44
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Akter J, Kamijo T. How Do Telomere Abnormalities Regulate the Biology of Neuroblastoma? Biomolecules 2021; 11:1112. [PMID: 34439779 PMCID: PMC8392161 DOI: 10.3390/biom11081112] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 07/20/2021] [Accepted: 07/21/2021] [Indexed: 12/25/2022] Open
Abstract
Telomere maintenance plays important roles in genome stability and cell proliferation. Tumor cells acquire replicative immortality by activating a telomere-maintenance mechanism (TMM), either telomerase, a reverse transcriptase, or the alternative lengthening of telomeres (ALT) mechanism. Recent advances in the genetic and molecular characterization of TMM revealed that telomerase activation and ALT define distinct neuroblastoma (NB) subgroups with adverse outcomes, and represent promising therapeutic targets in high-risk neuroblastoma (HRNB), an aggressive childhood solid tumor that accounts for 15% of all pediatric-cancer deaths. Patients with HRNB frequently present with widely metastatic disease, with tumors harboring recurrent genetic aberrations (MYCN amplification, TERT rearrangements, and ATRX mutations), which are mutually exclusive and capable of promoting TMM. This review provides recent insights into our understanding of TMM in NB tumors, and highlights emerging therapeutic strategies as potential treatments for telomerase- and ALT-positive tumors.
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Affiliation(s)
- Jesmin Akter
- Saitama Cancer Center, Research Institute for Clinical Oncology, Saitama 362-0806, Japan;
| | - Takehiko Kamijo
- Saitama Cancer Center, Research Institute for Clinical Oncology, Saitama 362-0806, Japan;
- Laboratory of Tumor Molecular Biology, Department of Graduate School of Science and Engineering, Saitama University, Saitama 362-0806, Japan
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45
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Ackerson SM, Romney C, Schuck PL, Stewart JA. To Join or Not to Join: Decision Points Along the Pathway to Double-Strand Break Repair vs. Chromosome End Protection. Front Cell Dev Biol 2021; 9:708763. [PMID: 34322492 PMCID: PMC8311741 DOI: 10.3389/fcell.2021.708763] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2021] [Accepted: 06/17/2021] [Indexed: 01/01/2023] Open
Abstract
The regulation of DNA double-strand breaks (DSBs) and telomeres are diametrically opposed in the cell. DSBs are considered one of the most deleterious forms of DNA damage and must be quickly recognized and repaired. Telomeres, on the other hand, are specialized, stable DNA ends that must be protected from recognition as DSBs to inhibit unwanted chromosome fusions. Decisions to join DNA ends, or not, are therefore critical to genome stability. Yet, the processing of telomeres and DSBs share many commonalities. Accordingly, key decision points are used to shift DNA ends toward DSB repair vs. end protection. Additionally, DSBs can be repaired by two major pathways, namely homologous recombination (HR) and non-homologous end joining (NHEJ). The choice of which repair pathway is employed is also dictated by a series of decision points that shift the break toward HR or NHEJ. In this review, we will focus on these decision points and the mechanisms that dictate end protection vs. DSB repair and DSB repair choice.
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Affiliation(s)
- Stephanie M Ackerson
- Department of Biological Sciences, University of South Carolina, Columbia, SC, United States
| | - Carlan Romney
- Department of Biological Sciences, University of South Carolina, Columbia, SC, United States
| | - P Logan Schuck
- Department of Biological Sciences, University of South Carolina, Columbia, SC, United States
| | - Jason A Stewart
- Department of Biological Sciences, University of South Carolina, Columbia, SC, United States
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TERRA transcription destabilizes telomere integrity to initiate break-induced replication in human ALT cells. Nat Commun 2021; 12:3760. [PMID: 34145295 PMCID: PMC8213692 DOI: 10.1038/s41467-021-24097-6] [Citation(s) in RCA: 52] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2020] [Accepted: 05/31/2021] [Indexed: 01/22/2023] Open
Abstract
Alternative Lengthening of Telomeres (ALT) is a Break-Induced Replication (BIR)-based mechanism elongating telomeres in a subset of human cancer cells. While the notion that spontaneous DNA damage at telomeres is required to initiate ALT, the molecular triggers of this physiological telomere instability are largely unknown. We previously proposed that the telomeric long noncoding RNA TERRA may represent one such trigger; however, given the lack of tools to suppress TERRA transcription in cells, our hypothesis remained speculative. We have developed Transcription Activator-Like Effectors able to rapidly inhibit TERRA transcription from multiple chromosome ends in an ALT cell line. TERRA transcription inhibition decreases marks of DNA replication stress and DNA damage at telomeres and impairs ALT activity and telomere length maintenance. We conclude that TERRA transcription actively destabilizes telomere integrity in ALT cells, thereby triggering BIR and promoting telomere elongation. Our data point to TERRA transcription manipulation as a potentially useful target for therapy. TERRA RNA has previously been linked to Alternative lengthening of telomeres (ALT). Here the authors developed a tool to rapidly inhibit TERRA transcription from different chromosome ends in an ALT cell line to show that TERRA transcription actively promotes break induced replication (BIR) and destabilizes telomere integrity in ALT cells.
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47
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Verma P, Greenberg RA. Communication between chromatin and homologous recombination. Curr Opin Genet Dev 2021; 71:1-9. [PMID: 34098484 DOI: 10.1016/j.gde.2021.05.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2021] [Accepted: 05/13/2021] [Indexed: 12/24/2022]
Abstract
Higher-order chromatin packing serves as a structural barrier to the recognition and repair of genomic lesions. The initiation and outcome of the repair response is dictated by a highly coordinated yet complex interplay between chromatin modifying enzymes and their cognate readers, damage induced chemical modifications, nucleosome density, transcriptional state, and cell cycle-dependent availability of DNA repair machinery. The physical and chemical properties of the DNA lesions themselves further regulate the nature of ensuing chromatin responses. Here we review recent discoveries across these various contexts, where chromatin regulates the homology-guided double-strand break repair mechanism, homologous recombination, and also highlight the key knowledge gaps vital to generate a holistic understanding of this process and its contributions to genome integrity.
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Affiliation(s)
- Priyanka Verma
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - Roger A Greenberg
- Department of Cancer Biology, Penn Center for Genome Integrity, Basser Center for BRCA, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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RTEL1 influences the abundance and localization of TERRA RNA. Nat Commun 2021; 12:3016. [PMID: 34021146 PMCID: PMC8140157 DOI: 10.1038/s41467-021-23299-2] [Citation(s) in RCA: 18] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 04/22/2021] [Indexed: 12/13/2022] Open
Abstract
Telomere repeat containing RNAs (TERRAs) are a family of long non-coding RNAs transcribed from the subtelomeric regions of eukaryotic chromosomes. TERRA transcripts can form R-loops at chromosome ends; however the importance of these structures or the regulation of TERRA expression and retention in telomeric R-loops remain unclear. Here, we show that the RTEL1 (Regulator of Telomere Length 1) helicase influences the abundance and localization of TERRA in human cells. Depletion of RTEL1 leads to increased levels of TERRA RNA while reducing TERRA-containing R loops at telomeres. In vitro, RTEL1 shows a strong preference for binding G-quadruplex structures which form in TERRA. This binding is mediated by the C-terminal region of RTEL1, and is independent of the RTEL1 helicase domain. RTEL1 binding to TERRA appears to be essential for cell viability, underscoring the importance of this function. Degradation of TERRA-containing R-loops by overexpression of RNAse H1 partially recapitulates the increased TERRA levels and telomeric instability associated with RTEL1 deficiency. Collectively, these data suggest that regulation of TERRA is a key function of the RTEL1 helicase, and that loss of that function may contribute to the disease phenotypes of patients with RTEL1 mutations. Long non coding RNA TERRA transcripts can form R-loops at chromosome ends. Here, the authors reveal a role for the helicase RTEL in affecting TERRA levels and localization.
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Pham N, Yan Z, Yu Y, Faria Afreen M, Malkova A, Haber JE, Ira G. Mechanisms restraining break-induced replication at two-ended DNA double-strand breaks. EMBO J 2021; 40:e104847. [PMID: 33844333 DOI: 10.15252/embj.2020104847] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 03/04/2021] [Accepted: 03/09/2021] [Indexed: 11/09/2022] Open
Abstract
DNA synthesis during homologous recombination is highly mutagenic and prone to template switches. Two-ended DNA double-strand breaks (DSBs) are usually repaired by gene conversion with a short patch of DNA synthesis, thus limiting the mutation load to the vicinity of the DSB. Single-ended DSBs are repaired by break-induced replication (BIR), which involves extensive and mutagenic DNA synthesis spanning up to hundreds of kilobases. It remains unknown how mutagenic BIR is suppressed at two-ended DSBs. Here, we demonstrate that BIR is suppressed at two-ended DSBs by proteins coordinating the usage of two ends of a DSB: (i) ssDNA annealing proteins Rad52 and Rad59 that promote second end capture, (ii) D-loop unwinding helicase Mph1, and (iii) Mre11-Rad50-Xrs2 complex that promotes synchronous resection of two ends of a DSB. Finally, BIR is also suppressed when Sir2 silences a normally heterochromatic repair template. All of these proteins are particularly important for limiting BIR when recombination occurs between short repetitive sequences, emphasizing the significance of these mechanisms for species carrying many repetitive elements such as humans.
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Affiliation(s)
- Nhung Pham
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Zhenxin Yan
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Yang Yu
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
| | - Mosammat Faria Afreen
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Waltham, MA, USA
| | - Anna Malkova
- Department of Biology, University of Iowa, Iowa City, IA, USA
| | - James E Haber
- Department of Biology, Rosenstiel Basic Medical Sciences Research Center, Waltham, MA, USA
| | - Grzegorz Ira
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX, USA
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Willaume S, Rass E, Fontanilla-Ramirez P, Moussa A, Wanschoor P, Bertrand P. A Link between Replicative Stress, Lamin Proteins, and Inflammation. Genes (Basel) 2021; 12:genes12040552. [PMID: 33918867 PMCID: PMC8070205 DOI: 10.3390/genes12040552] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2021] [Revised: 03/23/2021] [Accepted: 04/08/2021] [Indexed: 12/12/2022] Open
Abstract
Double-stranded breaks (DSB), the most toxic DNA lesions, are either a consequence of cellular metabolism, programmed as in during V(D)J recombination, or induced by anti-tumoral therapies or accidental genotoxic exposure. One origin of DSB sources is replicative stress, a major source of genome instability, especially when the integrity of the replication forks is not properly guaranteed. To complete stalled replication, restarting the fork requires complex molecular mechanisms, such as protection, remodeling, and processing. Recently, a link has been made between DNA damage accumulation and inflammation. Indeed, defects in DNA repair or in replication can lead to the release of DNA fragments in the cytosol. The recognition of this self-DNA by DNA sensors leads to the production of inflammatory factors. This beneficial response activating an innate immune response and destruction of cells bearing DNA damage may be considered as a novel part of DNA damage response. However, upon accumulation of DNA damage, a chronic inflammatory cellular microenvironment may lead to inflammatory pathologies, aging, and progression of tumor cells. Progress in understanding the molecular mechanisms of DNA damage repair, replication stress, and cytosolic DNA production would allow to propose new therapeutical strategies against cancer or inflammatory diseases associated with aging. In this review, we describe the mechanisms involved in DSB repair, the replicative stress management, and its consequences. We also focus on new emerging links between key components of the nuclear envelope, the lamins, and DNA repair, management of replicative stress, and inflammation.
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