1
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Khayat F, Alshmery M, Pal M, Oliver AW, Bianchi A. Binding of the TRF2 iDDR motif to RAD50 highlights a convergent evolutionary strategy to inactivate MRN at telomeres. Nucleic Acids Res 2024:gkae509. [PMID: 38884214 DOI: 10.1093/nar/gkae509] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2023] [Revised: 05/07/2024] [Accepted: 06/07/2024] [Indexed: 06/18/2024] Open
Abstract
Telomeres protect chromosome ends from unscheduled DNA repair, including from the MRN (MRE11, RAD50, NBS1) complex, which processes double-stranded DNA breaks (DSBs) via activation of the ATM kinase, promotes DNA end-tethering aiding the non-homologous end-joining (NHEJ) pathway, and initiates DSB resection through the MRE11 nuclease. A protein motif (MIN, for MRN inhibitor) inhibits MRN at budding yeast telomeres by binding to RAD50 and evolved at least twice, in unrelated telomeric proteins Rif2 and Taz1. We identify the iDDR motif of human shelterin protein TRF2 as a third example of convergent evolution for this telomeric mechanism for binding MRN, despite the iDDR lacking sequence homology to the MIN motif. CtIP is required for activation of MRE11 nuclease action, and we provide evidence for binding of a short C-terminal region of CtIP to a RAD50 interface that partly overlaps with the iDDR binding site, indicating that the interaction is mutually exclusive. In addition, we show that the iDDR impairs the DNA binding activity of RAD50. These results highlight direct inhibition of MRN action as a crucial role of telomeric proteins across organisms and point to multiple mechanisms enforced by the iDDR to disable the many activities of the MRN complex.
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Affiliation(s)
- Freddy Khayat
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
| | - Majedh Alshmery
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
- Department of Life Sciences, Hafr Al Batin University, Saudi Arabia
| | - Mohinder Pal
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
- School of Biosciences, University of Kent, Canterbury, UK
| | - Antony W Oliver
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
| | - Alessandro Bianchi
- Genome Damage and Stability Centre, School of Life Sciences, University of Sussex, Brighton, UK
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2
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Sonmez C, Toia B, Eickhoff P, Matei AM, El Beyrouthy M, Wallner B, Douglas ME, de Lange T, Lottersberger F. DNA-PK controls Apollo's access to leading-end telomeres. Nucleic Acids Res 2024; 52:4313-4327. [PMID: 38407308 PMCID: PMC11077071 DOI: 10.1093/nar/gkae105] [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: 05/19/2023] [Revised: 01/23/2024] [Accepted: 02/01/2024] [Indexed: 02/27/2024] Open
Abstract
The complex formed by Ku70/80 and DNA-PKcs (DNA-PK) promotes the synapsis and the joining of double strand breaks (DSBs) during canonical non-homologous end joining (c-NHEJ). In c-NHEJ during V(D)J recombination, DNA-PK promotes the processing of the ends and the opening of the DNA hairpins by recruiting and/or activating the nuclease Artemis/DCLRE1C/SNM1C. Paradoxically, DNA-PK is also required to prevent the fusions of newly replicated leading-end telomeres. Here, we describe the role for DNA-PK in controlling Apollo/DCLRE1B/SNM1B, the nuclease that resects leading-end telomeres. We show that the telomeric function of Apollo requires DNA-PKcs's kinase activity and the binding of Apollo to DNA-PK. Furthermore, AlphaFold-Multimer predicts that Apollo's nuclease domain has extensive additional interactions with DNA-PKcs, and comparison to the cryo-EM structure of Artemis bound to DNA-PK phosphorylated on the ABCDE/Thr2609 cluster suggests that DNA-PK can similarly grant Apollo access to the DNA end. In agreement, the telomeric function of DNA-PK requires the ABCDE/Thr2609 cluster. These data reveal that resection of leading-end telomeres is regulated by DNA-PK through its binding to Apollo and its (auto)phosphorylation-dependent positioning of Apollo at the DNA end, analogous but not identical to DNA-PK dependent regulation of Artemis at hairpins.
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Affiliation(s)
- Ceylan Sonmez
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping 58 183, Sweden
| | - Beatrice Toia
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping 58 183, Sweden
| | - Patrik Eickhoff
- Chester Beatty Laboratories, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
| | - Andreea Medeea Matei
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping 58 183, Sweden
| | - Michael El Beyrouthy
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping 58 183, Sweden
| | - Björn Wallner
- Department of Physics, Chemistry and Biology, Linköping University, Linköping 58 183, Sweden
| | - Max E Douglas
- Chester Beatty Laboratories, The Institute of Cancer Research, 237 Fulham Road, London SW3 6JB, UK
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, The Rockefeller University, 1230 York Avenue, NY, NY 10021, USA
| | - Francisca Lottersberger
- Department of Biomedical and Clinical Sciences, Linköping University, Linköping 58 183, Sweden
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3
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Bories C, Lejour T, Adolphe F, Kermasson L, Couvé S, Tanguy L, Luszczewska G, Watzky M, Poillerat V, Garnier P, Groisman R, Ferlicot S, Richard S, Saparbaev M, Revy P, Gad S, Renaud F. DCLRE1B/Apollo germline mutations associated with renal cell carcinoma impair telomere protection. Biochim Biophys Acta Mol Basis Dis 2024; 1870:167107. [PMID: 38430974 DOI: 10.1016/j.bbadis.2024.167107] [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: 07/05/2023] [Revised: 02/14/2024] [Accepted: 02/25/2024] [Indexed: 03/05/2024]
Abstract
Hereditary renal cell carcinoma (RCC) is caused by germline mutations in a subset of genes, including VHL, MET, FLCN, and FH. However, many familial RCC cases do not harbor mutations in the known predisposition genes. Using Whole Exome Sequencing, we identified two germline missense variants in the DCLRE1B/Apollo gene (ApolloN246I and ApolloY273H) in two unrelated families with several RCC cases. Apollo encodes an exonuclease involved in DNA Damage Response and Repair (DDRR) and telomere integrity. We characterized these two functions in the human renal epithelial cell line HKC8. The decrease or inhibition of Apollo expression sensitizes these cells to DNA interstrand crosslink damage (ICLs). HKC8 Apollo-/- cells appear defective in the DDRR and present an accumulation of telomere damage. Wild-type and mutated Apollo forms could interact with TRF2, a shelterin protein involved in telomere protection. However, only ApolloWT can rescue the telomere damage in HKC8 Apollo-/- cells. Our results strongly suggest that ApolloN246I and ApolloY273H are loss-of-function mutants that cause impaired telomere integrity and could lead to genomic instability. Altogether, our results suggest that mutations in Apollo could induce renal oncogenesis.
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Affiliation(s)
- Charlie Bories
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Thomas Lejour
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Florine Adolphe
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Laëtitia Kermasson
- Laboratory of Genome Dynamics in the Immune System, Laboratoire labellisé Ligue Nationale contre le Cancer, INSERM UMR 1163, Université de Paris, Imagine Institute, Paris, France
| | - Sophie Couvé
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Laura Tanguy
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Gabriela Luszczewska
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Manon Watzky
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Victoria Poillerat
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Pauline Garnier
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Regina Groisman
- UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Sophie Ferlicot
- UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France; Département de Pathologie, AP-HP, Université Paris-Saclay, Hôpital de Bicêtre, Le Kremlin-Bicêtre, France
| | - Stéphane Richard
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France; Réseau National de Référence pour Cancers Rares de l'Adulte PREDIR labellisé par l'INCa, Hôpital de Bicêtre, AP-HP, et Service d'Urologie, Le Kremlin-Bicêtre, France
| | - Murat Saparbaev
- UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Patrick Revy
- Laboratory of Genome Dynamics in the Immune System, Laboratoire labellisé Ligue Nationale contre le Cancer, INSERM UMR 1163, Université de Paris, Imagine Institute, Paris, France
| | - Sophie Gad
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France
| | - Flore Renaud
- EPHE, PSL Université, Paris, France; UMR 9019 CNRS, Gustave Roussy, Université Paris-Saclay, 114 rue Edouard Vaillant, Villejuif 94800, France.
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4
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Benson CW, Sheltra MR, Huff DR. The genome of Salmacisia buchloëana, the parasitic puppet master pulling strings of sexual phenotypic monstrosities in buffalograss. G3 (BETHESDA, MD.) 2024; 14:jkad238. [PMID: 37847611 PMCID: PMC10849329 DOI: 10.1093/g3journal/jkad238] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/28/2023] [Revised: 10/04/2023] [Accepted: 10/06/2023] [Indexed: 10/19/2023]
Abstract
To complete its parasitic lifecycle, Salmacisia buchloëana, a biotrophic fungus, manipulates reproductive organ development, meristem determinacy, and resource allocation in its dioecious plant host, buffalograss (Bouteloua dactyloides; Poaceae). To gain insight into S. buchloëana's ability to manipulate its host, we sequenced and assembled the 20.1 Mb genome of S. buchloëana into 22 chromosome-level pseudomolecules. Phylogenetic analysis suggests that S. buchloëana is nested within the genus Tilletia and diverged from Tilletia caries and Tilletia walkeri ∼40 MYA. We find that S. buchloëana contains a novel chromosome arm with no syntenic relationship to other publicly available Tilletia genomes, and that genes on the novel arm are upregulated upon infection, suggesting that this unique chromosomal segment may have played a critical role in S. buchloëana's evolution and host specificity. Salmacisia buchloëana has one of the largest fractions of serine peptidases (1.53% of the proteome) and one of the highest GC contents (62.3%) in all classified fungi. Analysis of codon base composition indicated that GC content is controlled more by selective constraints than directional mutation, and that S. buchloëana has a unique bias for the serine codon UCG. Finally, we identify 3 inteins within the S. buchloëana genome, 2 of which are located in a gene often used in fungal taxonomy. The genomic and transcriptomic resources generated here will aid plant pathologists and breeders by providing insight into the extracellular components contributing to sex determination in dioecious grasses.
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Affiliation(s)
- Christopher W Benson
- Department of Plant Science, Pennsylvania State University, University Park, PA 16801, USA
- Intercollegiate Graduate Degree Program in Plant Biology, Pennsylvania State University, University Park, PA 16801, USA
| | - Matthew R Sheltra
- Department of Plant Science, Pennsylvania State University, University Park, PA 16801, USA
- Intercollegiate Graduate Degree Program in Plant Biology, Pennsylvania State University, University Park, PA 16801, USA
| | - David R Huff
- Department of Plant Science, Pennsylvania State University, University Park, PA 16801, USA
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5
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Li B. Telomere maintenance in African trypanosomes. Front Mol Biosci 2023; 10:1302557. [PMID: 38074093 PMCID: PMC10704157 DOI: 10.3389/fmolb.2023.1302557] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2023] [Accepted: 11/15/2023] [Indexed: 02/12/2024] Open
Abstract
Telomere maintenance is essential for genome integrity and chromosome stability in eukaryotic cells harboring linear chromosomes, as telomere forms a specialized structure to mask the natural chromosome ends from DNA damage repair machineries and to prevent nucleolytic degradation of the telomeric DNA. In Trypanosoma brucei and several other microbial pathogens, virulence genes involved in antigenic variation, a key pathogenesis mechanism essential for host immune evasion and long-term infections, are located at subtelomeres, and expression and switching of these major surface antigens are regulated by telomere proteins and the telomere structure. Therefore, understanding telomere maintenance mechanisms and how these pathogens achieve a balance between stability and plasticity at telomere/subtelomere will help develop better means to eradicate human diseases caused by these pathogens. Telomere replication faces several challenges, and the "end replication problem" is a key obstacle that can cause progressive telomere shortening in proliferating cells. To overcome this challenge, most eukaryotes use telomerase to extend the G-rich telomere strand. In addition, a number of telomere proteins use sophisticated mechanisms to coordinate the telomerase-mediated de novo telomere G-strand synthesis and the telomere C-strand fill-in, which has been extensively studied in mammalian cells. However, we recently discovered that trypanosomes lack many telomere proteins identified in its mammalian host that are critical for telomere end processing. Rather, T. brucei uses a unique DNA polymerase, PolIE that belongs to the DNA polymerase A family (E. coli DNA PolI family), to coordinate the telomere G- and C-strand syntheses. In this review, I will first briefly summarize current understanding of telomere end processing in mammals. Subsequently, I will describe PolIE-mediated coordination of telomere G- and C-strand synthesis in T. brucei and implication of this recent discovery.
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Affiliation(s)
- Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Arts and Sciences, Cleveland State University, Cleveland, OH, United States
- Case Comprehensive Cancer Center, Case Western Reserve University, Cleveland, OH, United States
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, Cleveland, OH, United States
- Center for RNA Science and Therapeutics, Case Western Reserve University, Cleveland, OH, United States
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6
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Li P, Zhong R, Yu J, Wang Y, Wang C, Geng W, Bao S, Wang S, Zhang G, Zhu X, Ji M, Guan H. DCLRE1A Contributes to DNA Damage Repair and Apoptosis in Age-Related Cataracts by Regulating the lncRNA/miRNA/mRNA Axis. Curr Eye Res 2023; 48:992-1005. [PMID: 37503815 DOI: 10.1080/02713683.2023.2241159] [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: 03/10/2023] [Accepted: 07/23/2023] [Indexed: 07/29/2023]
Abstract
PURPOSE Age-related cataract (ARC) is associated with the deregulation of transcription and defects in DNA repair in lens epithelial cells (LECs). DCLRE1A acted in DNA interstrand cross-links pathway to improve DNA replication and transcription. The aim of this study was to examined the further regulatory effect on DCLRE1A in the lncRNA-miRNA-mRNA network using a cell model of DCLRE1A overexpression (OE-DCLRE1A) in LECs. METHODS The expression level of DCLRE1A in ARC tissues and SRA01/04 cells after H2O2 treatment was measured as protein and mRNA by qRT-PCR and Western Blot(WB). CCK8, and TUNEL assays detected the change in cell viability and apoptosis, respectively. Furthermore, Immunofluorescence assays detect the expression of DNA damaged and repair marker proteins after OE-DCLRE1A. The global expression profiles of lncRNAs, miRNAs, and mRNAs were determined using high-throughput sequencing. KEGG and GO enrichment analysis disclose the possible function of differentially expressed (DE) lncRNA, miRNA, and mRNA. RESULTS The protein and mRNA of DCLRE1A were decreased in the anterior capsule of ARC and SRA01/04 cells treated by H2O2. OE-DCLRE1A improved damaged-DNA repair and enhanced cell viability against apoptosis after H2O2 treatment. Furthermore, we demonstrated the DE-molecules between the OE-DCLRE1A and control groups including 595 DE-lncRNAs, 221 DE-miRNAs, and 4718 DE-mRNAs. Next, bioinformatics analysis not only found that the DE-mRNAs are mainly involved in DNA repair-related signaling pathways after OE-DCLRE1A, but also screened two lncRNA-miRNA-mRNA networks focusing on DNA damage activated by OE-DCLRE1A, which involved 2 lncRNAs, 2 miRNAs, and 53 mRNAs. CONCLUSION We revealed that DCLRE1A activated the lncRNA/miRNA/DNA-repair network to take part in DNA repair processes, which not only represents a new regulatory mechanism employed by DCLRE1A but also uncovers the screening lncRNA may hold potential therapeutic values in ARC formation. However, these conclusions will need to be confirmed by future studies in vitro and in vivo models.
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Affiliation(s)
- Pengfei Li
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Renhao Zhong
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Jianfeng Yu
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Ying Wang
- Department of Ophthalmology, The Affiliated Hospital of Yangzhou University, Yangzhou University, Yangzhou, China
| | - Congyu Wang
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Wenjing Geng
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Sijie Bao
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Siwen Wang
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Guowei Zhang
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Xi Zhu
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Min Ji
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
| | - Huaijin Guan
- Eye Institute, Affiliated Hospital of Nantong University, Medical School of Nantong University, Nantong, Jiangsu, China
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7
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Myler LR, Toia B, Vaughan CK, Takai K, Matei AM, Wu P, Paull TT, de Lange T, Lottersberger F. DNA-PK and the TRF2 iDDR inhibit MRN-initiated resection at leading-end telomeres. Nat Struct Mol Biol 2023; 30:1346-1356. [PMID: 37653239 PMCID: PMC10497418 DOI: 10.1038/s41594-023-01072-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Accepted: 07/18/2023] [Indexed: 09/02/2023]
Abstract
Telomeres replicated by leading-strand synthesis lack the 3' overhang required for telomere protection. Surprisingly, resection of these blunt telomeres is initiated by the telomere-specific 5' exonuclease Apollo rather than the Mre11-Rad50-Nbs1 (MRN) complex, the nuclease that acts at DNA breaks. Without Apollo, leading-end telomeres undergo fusion, which, as demonstrated here, is mediated by alternative end joining. Here, we show that DNA-PK and TRF2 coordinate the repression of MRN at blunt mouse telomeres. DNA-PK represses an MRN-dependent long-range resection, while the endonuclease activity of MRN-CtIP, which could cleave DNA-PK off of blunt telomere ends, is inhibited in vitro and in vivo by the iDDR of TRF2. AlphaFold-Multimer predicts a conserved association of the iDDR with Rad50, potentially interfering with CtIP binding and MRN endonuclease activation. We propose that repression of MRN-mediated resection is a conserved aspect of telomere maintenance and represents an ancient feature of DNA-PK and the iDDR.
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Affiliation(s)
- Logan R Myler
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY, USA
| | - Beatrice Toia
- Department of Biomedical and Clinical Sciences, Faculty of Medicine and Health Sciences, Linköping University, Linköping, Sweden
| | - Cara K Vaughan
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA
| | - Kaori Takai
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY, USA
| | - Andreea M Matei
- Department of Biomedical and Clinical Sciences, Faculty of Medicine and Health Sciences, Linköping University, Linköping, Sweden
| | - Peng Wu
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY, USA
- Department of Pediatrics, Stanford University School of Medicine, Stanford, CA, USA
| | - Tanya T Paull
- Department of Molecular Biosciences, University of Texas at Austin, Austin, TX, USA
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, NY, USA.
| | - Francisca Lottersberger
- Department of Biomedical and Clinical Sciences, Faculty of Medicine and Health Sciences, Linköping University, Linköping, Sweden.
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8
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Abstract
It has been known for decades that telomerase extends the 3' end of linear eukaryotic chromosomes and dictates the telomeric repeat sequence based on the template in its RNA. However, telomerase does not mitigate sequence loss at the 5' ends of chromosomes, which results from lagging strand DNA synthesis and nucleolytic processing. Therefore, a second enzyme is needed to keep telomeres intact: DNA polymerase α/Primase bound to Ctc1-Stn1-Ten1 (CST). CST-Polα/Primase maintains telomeres through a fill-in reaction that replenishes the lost sequences at the 5' ends. CST not only serves to maintain telomeres but also determines their length by keeping telomerase from overelongating telomeres. Here we discuss recent data on the evolution, structure, function, and recruitment of mammalian CST-Polα/Primase, highlighting the role of this complex and telomere length control in human disease.
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Affiliation(s)
- Sarah W Cai
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
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9
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Revy P, Kannengiesser C, Bertuch AA. Genetics of human telomere biology disorders. Nat Rev Genet 2023; 24:86-108. [PMID: 36151328 DOI: 10.1038/s41576-022-00527-z] [Citation(s) in RCA: 43] [Impact Index Per Article: 43.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/11/2022] [Indexed: 01/24/2023]
Abstract
Telomeres are specialized nucleoprotein structures at the ends of linear chromosomes that prevent the activation of DNA damage response and repair pathways. Numerous factors localize at telomeres to regulate their length, structure and function, to avert replicative senescence or genome instability and cell death. In humans, Mendelian defects in several of these factors can result in abnormally short or dysfunctional telomeres, causing a group of rare heterogeneous premature-ageing diseases, termed telomeropathies, short-telomere syndromes or telomere biology disorders (TBDs). Here, we review the TBD-causing genes identified so far and describe their main functions associated with telomere biology. We present molecular aspects of TBDs, including genetic anticipation, phenocopy, incomplete penetrance and somatic genetic rescue, which underlie the complexity of these diseases. We also discuss the implications of phenotypic and genetic features of TBDs on fundamental aspects related to human telomere biology, ageing and cancer, as well as on diagnostic, therapeutic and clinical approaches.
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Affiliation(s)
- Patrick Revy
- INSERM UMR 1163, Laboratory of Genome Dynamics in the Immune System, Equipe Labellisée Ligue Nationale contre le Cancer, Paris, France.
- Université Paris Cité, Imagine Institute, Paris, France.
| | - Caroline Kannengiesser
- APHP Service de Génétique, Hôpital Bichat, Paris, France
- Inserm U1152, Université Paris Cité, Paris, France
| | - Alison A Bertuch
- Departments of Paediatrics and Molecular & Human Genetics, Baylor College of Medicine, Houston, TX, USA
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10
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Abstract
Shelterin is a multiprotein complex that plays central roles in telomere biology. Mutations in shelterin result in premature aging diseases and familial cancer predisposition. Mechanistic understanding of these so-called telomereopathies is hampered by our lack of knowledge regarding the structure and stoichiometry of shelterin. Here, we use multiple methods to probe the stoichiometry and conformational states of shelterin and reveal that it forms a fully dimeric complex with extensive conformational heterogeneity. Our results highlight the dynamic nature of this essential complex and explain why its high-resolution structure determination has yet to be achieved. Human shelterin is a six-subunit complex—composed of TRF1, TRF2, Rap1, TIN2, TPP1, and POT1—that binds telomeres, protects them from the DNA-damage response, and regulates the maintenance of telomeric DNA. Although high-resolution structures have been generated of the individual structured domains within shelterin, the architecture and stoichiometry of the full complex are currently unknown. Here, we report the purification of shelterin subcomplexes and reconstitution of the entire complex using full-length, recombinant subunits. By combining negative-stain electron microscopy (EM), cross-linking mass spectrometry (XLMS), AlphaFold modeling, mass photometry, and native mass spectrometry (MS), we obtain stoichiometries as well as domain-scale architectures of shelterin subcomplexes and determine that they feature extensive conformational heterogeneity. For POT1/TPP1 and POT1/TPP1/TIN2, we observe high variability in the positioning of the POT1 DNA-binding domain, the TPP1 oligonucleotide/oligosaccharide–binding (OB) fold, and the TIN2 TRFH domain with respect to the C-terminal domains of POT1. Truncation of unstructured linker regions in TIN2, TPP1, and POT1 did not reduce the conformational variability of the heterotrimer. Shelterin and TRF1-containing subcomplexes form fully dimeric stoichiometries, even in the absence of DNA substrates. Shelterin and its subcomplexes showed extensive conformational variability, regardless of the presence of DNA substrates. We conclude that shelterin adopts a multitude of conformations and argue that its unusual architectural variability is beneficial for its many functions at telomeres.
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11
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Paul T, Opresko PL, Ha T, Myong S. Vectorial folding of telomere overhang promotes higher accessibility. Nucleic Acids Res 2022; 50:6271-6283. [PMID: 35687089 PMCID: PMC9226509 DOI: 10.1093/nar/gkac401] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2022] [Revised: 04/20/2022] [Accepted: 06/08/2022] [Indexed: 11/13/2022] Open
Abstract
Human telomere overhang composed of tandem repeats of TTAGGG folds into G-quadruplex (G4). Unlike in an experimental setting in the test tube in which the entire length is allowed to fold at once, inside the cell, the overhang is expected to fold as it is synthesized directionally (5' to 3') and released segmentally by a specialized enzyme, the telomerase. To mimic such vectorial G4 folding process, we employed a superhelicase, Rep-X which can unwind DNA to release the TTAGGG repeats in 5' to 3' direction. We demonstrate that the folded conformation achieved by the refolding of full sequence is significantly different from that of the vectorial folding for two to eight TTAGGG repeats. Strikingly, the vectorially folded state leads to a remarkably higher accessibility to complementary C-rich strand and the telomere binding protein POT1, reflecting a less stably folded state resulting from the vectorial folding. Importantly, our study points to an inherent difference between the co-polymerizing and post-polymerized folding of telomere overhang that can impact telomere architecture and downstream processes.
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Affiliation(s)
- Tapas Paul
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA
| | - Patricia L Opresko
- Department of Environmental and Occupational Health, University of Pittsburgh Graduate School of Public Health, and UPMC Hillman Cancer Center, Pittsburgh, PA15213, USA
| | - Taekjip Ha
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA.,Physics Frontier Center (Center for Physics of Living Cells), University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA.,Howard Hughes Medical Institute, Johns Hopkins University, Baltimore, MD, USA
| | - Sua Myong
- Department of Biophysics, Johns Hopkins University, Baltimore, MD21218, USA.,Physics Frontier Center (Center for Physics of Living Cells), University of Illinois, 1110 W. Green St., Urbana, IL 61801, USA
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12
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Kermasson L, Churikov D, Awad A, Smoom R, Lainey E, Touzot F, Audebert-Bellanger S, Haro S, Roger L, Costa E, Mouf M, Bottero A, Oleastro M, Abdo C, de Villartay JP, Géli V, Tzfati Y, Callebaut I, Danielian S, Soares G, Kannengiesser C, Revy P. Inherited human Apollo deficiency causes severe bone marrow failure and developmental defects. Blood 2022; 139:2427-2440. [PMID: 35007328 PMCID: PMC11022855 DOI: 10.1182/blood.2021010791] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Accepted: 12/13/2021] [Indexed: 11/20/2022] Open
Abstract
Inherited bone marrow failure syndromes (IBMFSs) are a group of disorders typified by impaired production of 1 or several blood cell types. The telomere biology disorders dyskeratosis congenita (DC) and its severe variant, Høyeraal-Hreidarsson (HH) syndrome, are rare IBMFSs characterized by bone marrow failure, developmental defects, and various premature aging complications associated with critically short telomeres. We identified biallelic variants in the gene encoding the 5'-to-3' DNA exonuclease Apollo/SNM1B in 3 unrelated patients presenting with a DC/HH phenotype consisting of early-onset hypocellular bone marrow failure, B and NK lymphopenia, developmental anomalies, microcephaly, and/or intrauterine growth retardation. All 3 patients carry a homozygous or compound heterozygous (in combination with a null allele) missense variant affecting the same residue L142 (L142F or L142S) located in the catalytic domain of Apollo. Apollo-deficient cells from patients exhibited spontaneous chromosome instability and impaired DNA repair that was complemented by CRISPR/Cas9-mediated gene correction. Furthermore, patients' cells showed signs of telomere fragility that were not associated with global reduction of telomere length. Unlike patients' cells, human Apollo KO HT1080 cell lines showed strong telomere dysfunction accompanied by excessive telomere shortening, suggesting that the L142S and L142F Apollo variants are hypomorphic. Collectively, these findings define human Apollo as a genome caretaker and identify biallelic Apollo variants as a genetic cause of a hitherto unrecognized severe IBMFS that combines clinical hallmarks of DC/HH with normal telomere length.
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Affiliation(s)
- Laëtitia Kermasson
- Laboratory of Genome Dynamics in the Immune System, Laboratoire labellisé Ligue Naionale contre le Cancer, INSERM UMR 1163, Université de Paris, Imagine Institute, Paris, France
| | - Dmitri Churikov
- U1068 INSERM, Unité Mixte de Recherche (UMR) 7258 (CNRS), Equipe Labellisée Ligue Nationale Contre le Cancer, Marseille Cancer Research Center (CRCM), Institut Paoli-Calmettes, Aix Marseille University, Marseille, France
| | - Aya Awad
- Department of Genetics, The Silberman Institute of Life Science, The Hebrew University of Jerusalem, Safra Campus-Givat Ram, Jerusalem, Israel
| | - Riham Smoom
- Department of Genetics, The Silberman Institute of Life Science, The Hebrew University of Jerusalem, Safra Campus-Givat Ram, Jerusalem, Israel
| | - Elodie Lainey
- Hematology Laboratory, Robert Debré Hospital-Assistance Publique-Hôpitaux de Paris (APHP); INSERM UMR 1131-Hematology University Institute-Denis Diderot School of Medicine, Paris, France
| | - Fabien Touzot
- Department of Immunology-Rheumatology, Department of Pediatrics, Centre Hospitalier Universitaire (CHU), Sainte Justine Research Center, Université de Montréal, Montréal, Quebec, Canada
| | | | - Sophie Haro
- Department of Paediatrics and Medical Genetics, CHU de Brest, Brest, France
| | - Lauréline Roger
- Structure and Instability of Genomes laboratory, “Muséum National d'Histoire Naturelle” (MNHN), INSERM U1154, CNRS UMR 7196, Paris, France
| | - Emilia Costa
- Serviço de Pediatria, Centro Hospitalar e Universitário do Porto, Porto, Portugal
| | - Maload Mouf
- 68HAL Meddle Laboratory, Zenon Skelter Institute, Green Hills, Eggum, Norway
| | | | - Matias Oleastro
- Rheumathology and Immunology Service, Hospital Nacional de Pediatría JP Garrahan, Buenos Aires, Argentina
| | - Chrystelle Abdo
- Onco-Hematology, Assistance Publique-Hôpitaux de Paris, Université de Paris and Institut Necker Enfants Malades, Paris, France
| | - Jean-Pierre de Villartay
- Laboratory of Genome Dynamics in the Immune System, Laboratoire labellisé Ligue Naionale contre le Cancer, INSERM UMR 1163, Université de Paris, Imagine Institute, Paris, France
| | - Vincent Géli
- U1068 INSERM, Unité Mixte de Recherche (UMR) 7258 (CNRS), Equipe Labellisée Ligue Nationale Contre le Cancer, Marseille Cancer Research Center (CRCM), Institut Paoli-Calmettes, Aix Marseille University, Marseille, France
| | - Yehuda Tzfati
- Department of Genetics, The Silberman Institute of Life Science, The Hebrew University of Jerusalem, Safra Campus-Givat Ram, Jerusalem, Israel
| | - Isabelle Callebaut
- UMR CNRS 7590, Institut de Minéralogie, de Physique des Matériaux et de Cosmochimie (IMPMC), Muséum National d'Histoire Naturelle, Sorbonne Université, Paris, France
| | - Silvia Danielian
- Department of Immunology, JP Garrahan National Hospital of Pediatrics, Buenos Aires, Argentina
| | - Gabriela Soares
- Centro de Genética Médica Jacinto de Magalhães, Centro Hospitalar e Universitário do Porto, Porto, Portugal
| | - Caroline Kannengiesser
- Service de Génétique, Assistance Publique des Hôpitaux de Paris, Hôpital Bichat, Université Paris Diderot, Paris, France
| | - Patrick Revy
- Laboratory of Genome Dynamics in the Immune System, Laboratoire labellisé Ligue Naionale contre le Cancer, INSERM UMR 1163, Université de Paris, Imagine Institute, Paris, France
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13
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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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14
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Rabbani MAG, Tonini ML, Afrin M, Li B. POLIE suppresses telomerase-mediated telomere G-strand extension and helps ensure proper telomere C-strand synthesis in trypanosomes. Nucleic Acids Res 2022; 50:2036-2050. [PMID: 35061898 PMCID: PMC8887473 DOI: 10.1093/nar/gkac023] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2021] [Revised: 01/05/2022] [Accepted: 01/07/2022] [Indexed: 11/15/2022] Open
Abstract
Trypanosoma brucei causes human African trypanosomiasis and sequentially expresses distinct VSGs, its major surface antigen, to achieve host immune evasion. VSGs are monoallelically expressed from subtelomeric loci, and telomere proteins regulate VSG monoallelic expression and VSG switching. T. brucei telomerase is essential for telomere maintenance, but no regulators of telomerase have been identified. T. brucei appears to lack OB fold-containing telomere-specific ssDNA binding factors that are critical for coordinating telomere G- and C-strand syntheses in higher eukaryotes. We identify POLIE as a telomere protein essential for telomere integrity. POLIE-depleted cells have more frequent VSG gene conversion-mediated VSG switching and an increased amount of telomeric circles (T-circles), indicating that POLIE suppresses DNA recombination at the telomere/subtelomere. POLIE-depletion elongates telomere 3' overhangs dramatically, indicating that POLIE is essential for coordinating DNA syntheses of the two telomere strands. POLIE depletion increases the level of telomerase-dependent telomere G-strand extension, identifying POLIE as the first T. brucei telomere protein that suppresses telomerase. Furthermore, depletion of POLIE results in an elevated telomeric C-circle level, suggesting that the telomere C-strand experiences replication stress and that POLIE may promote telomere C-strand synthesis. Therefore, T. brucei uses a novel mechanism to coordinate the telomere G- and C-strand DNA syntheses.
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Affiliation(s)
- M A G Rabbani
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
| | - Maiko Luis Tonini
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
| | - Marjia Afrin
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
| | - Bibo Li
- Center for Gene Regulation in Health and Disease, Department of Biological, Geological, and Environmental Sciences, College of Sciences and Health Professions, Cleveland State University, 2121 Euclid Avenue, Cleveland, OH 44115, USA
- Case Comprehensive Cancer Center, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
- Department of Inflammation and Immunity, Lerner Research Institute, Cleveland Clinic, 9500 Euclid Avenue, Cleveland OH 44195, USA
- Center for RNA Science and Therapeutics, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106, USA
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15
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Telomerase in Cancer: Function, Regulation, and Clinical Translation. Cancers (Basel) 2022; 14:cancers14030808. [PMID: 35159075 PMCID: PMC8834434 DOI: 10.3390/cancers14030808] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/10/2021] [Revised: 01/29/2022] [Accepted: 02/02/2022] [Indexed: 02/04/2023] Open
Abstract
Simple Summary Cells undergoing malignant transformation must circumvent replicative senescence and eventual cell death associated with progressive telomere shortening that occurs through successive cell division. To do so, malignant cells reactivate telomerase to extend their telomeres and achieve cellular immortality, which is a “Hallmark of Cancer”. Here we review the telomere-dependent and -independent functions of telomerase in cancer, as well as its potential as a biomarker and therapeutic target to diagnose and treat cancer patients. Abstract During the process of malignant transformation, cells undergo a series of genetic, epigenetic, and phenotypic alterations, including the acquisition and propagation of genomic aberrations that impart survival and proliferative advantages. These changes are mediated in part by the induction of replicative immortality that is accompanied by active telomere elongation. Indeed, telomeres undergo dynamic changes to their lengths and higher-order structures throughout tumor formation and progression, processes overseen in most cancers by telomerase. Telomerase is a multimeric enzyme whose function is exquisitely regulated through diverse transcriptional, post-transcriptional, and post-translational mechanisms to facilitate telomere extension. In turn, telomerase function depends not only on its core components, but also on a suite of binding partners, transcription factors, and intra- and extracellular signaling effectors. Additionally, telomerase exhibits telomere-independent regulation of cancer cell growth by participating directly in cellular metabolism, signal transduction, and the regulation of gene expression in ways that are critical for tumorigenesis. In this review, we summarize the complex mechanisms underlying telomere maintenance, with a particular focus on both the telomeric and extratelomeric functions of telomerase. We also explore the clinical utility of telomeres and telomerase in the diagnosis, prognosis, and development of targeted therapies for primary, metastatic, and recurrent cancers.
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16
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Wu HY, Zheng Y, Laciak AR, Huang NN, Koszelak-Rosenblum M, Flint AJ, Carr G, Zhu G. Structure and Function of SNM1 Family Nucleases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2022; 1414:1-26. [PMID: 35708844 DOI: 10.1007/5584_2022_724] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
Abstract
Three human nucleases, SNM1A, SNM1B/Apollo, and SNM1C/Artemis, belong to the SNM1 gene family. These nucleases are involved in various cellular functions, including homologous recombination, nonhomologous end-joining, cell cycle regulation, and telomere maintenance. These three proteins share a similar catalytic domain, which is characterized as a fused metallo-β-lactamase and a CPSF-Artemis-SNM1-PSO2 domain. SNM1A and SNM1B/Apollo are exonucleases, whereas SNM1C/Artemis is an endonuclease. This review contains a summary of recent research on SNM1's cellular and biochemical functions, as well as structural biology studies. In addition, protein structure prediction by the artificial intelligence program AlphaFold provides a different view of the proteins' non-catalytic domain features, which may be used in combination with current results from X-ray crystallography and cryo-EM to understand their mechanism more clearly.
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17
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Vicari MR, Bruschi DP, Cabral-de-Mello DC, Nogaroto V. Telomere organization and the interstitial telomeric sites involvement in insects and vertebrates chromosome evolution. Genet Mol Biol 2022; 45:e20220071. [DOI: 10.1590/1678-4685-gmb-2022-0071] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2022] [Accepted: 09/24/2022] [Indexed: 11/16/2022] Open
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18
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Lee L, Perez Oliva AB, Martinez-Balsalobre E, Churikov D, Peter J, Rahmouni D, Audoly G, Azzoni V, Audebert S, Camoin L, Mulero V, Cayuela ML, Kulathu Y, Geli V, Lachaud C. UFMylation of MRE11 is essential for telomere length maintenance and hematopoietic stem cell survival. SCIENCE ADVANCES 2021; 7:eabc7371. [PMID: 34559557 PMCID: PMC8462904 DOI: 10.1126/sciadv.abc7371] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/25/2020] [Accepted: 08/03/2021] [Indexed: 06/13/2023]
Abstract
Ubiquitin-fold modifier 1 (UFM1) is involved in neural and erythroid development, yet its biological roles in these processes are unknown. Here, we generated zebrafish models deficient in Ufm1 and Ufl1 that exhibited telomere shortening associated with developmental delay, impaired hematopoiesis and premature aging. We further report that HeLa cells lacking UFL1 have instability of telomeres replicated by leading-strand synthesis. We uncover that MRE11 UFMylation is necessary for the recruitment of the phosphatase PP1-α leading to dephosphorylation of NBS1. In the absence of UFMylation, NBS1 remains phosphorylated, thereby reducing MRN recruitment to telomeres. The absence of MRN at telomeres favors the formation of the TRF2-Apollo/SNM1 complex consistent with the loss of leading telomeres. These results suggest that MRE11-UFMylation may serve as module to recruit PP1-α. Last, zebrafish expressing Mre11 that cannot be UFMylated phenocopy Ufm1-deficient zebrafish, demonstrating that UFMylation of MRE11 is a previously undescribed evolutionarily conserved mechanisms regulating telomere length.
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Affiliation(s)
- Lara Lee
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Ana Belen Perez Oliva
- Hospital Clínico Universitario Virgen de la Arrixaca, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
- Departamento de Biología Celular e Histología, Facultad de Biología, Universidad de Murcia, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
| | - Elena Martinez-Balsalobre
- Hospital Clínico Universitario Virgen de la Arrixaca, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
| | - Dmitri Churikov
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Joshua Peter
- MRC Protein Phosphorylation & Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee, UK
| | - Dalicya Rahmouni
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Gilles Audoly
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Violette Azzoni
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Stephane Audebert
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Luc Camoin
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Victoriano Mulero
- Hospital Clínico Universitario Virgen de la Arrixaca, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
- Departamento de Biología Celular e Histología, Facultad de Biología, Universidad de Murcia, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
| | - Maria L. Cayuela
- Hospital Clínico Universitario Virgen de la Arrixaca, IMIB-Arrixaca, Centro de Investigación Biomédica en Red de Enfermedades Raras, Murcia, Spain
| | - Yogesh Kulathu
- MRC Protein Phosphorylation & Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee, UK
| | - Vincent Geli
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
| | - Christophe Lachaud
- Aix-Marseille Univ, INSERM, CNRS, Institut Paoli-Calmettes, CRCM, Marseille, France
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19
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Baddock H, Newman J, Yosaatmadja Y, Bielinski M, Schofield C, Gileadi O, McHugh P. A phosphate binding pocket is a key determinant of exo- versus endo-nucleolytic activity in the SNM1 nuclease family. Nucleic Acids Res 2021; 49:9294-9309. [PMID: 34387694 PMCID: PMC8450094 DOI: 10.1093/nar/gkab692] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 07/21/2021] [Accepted: 07/27/2021] [Indexed: 12/02/2022] Open
Abstract
The SNM1 nucleases which help maintain genome integrity are members of the metallo-β-lactamase (MBL) structural superfamily. Their conserved MBL-β-CASP-fold SNM1 core provides a molecular scaffold forming an active site which coordinates the metal ions required for catalysis. The features that determine SNM1 endo- versus exonuclease activity, and which control substrate selectivity and binding are poorly understood. We describe a structure of SNM1B/Apollo with two nucleotides bound to its active site, resembling the product state of its exonuclease reaction. The structure enables definition of key SNM1B residues that form contacts with DNA and identifies a 5' phosphate binding pocket, which we demonstrate is important in catalysis and which has a key role in determining endo- versus exonucleolytic activity across the SNM1 family. We probed the capacity of SNM1B to digest past sites of common endogenous DNA lesions and find that base modifications planar to the nucleobase can be accommodated due to the open architecture of the active site, but lesions axial to the plane of the nucleobase are not well tolerated due to constriction around the altered base. We propose that SNM1B/Apollo might employ its activity to help remove common oxidative lesions from telomeres.
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Affiliation(s)
- Hannah T Baddock
- Department of Oncology, MRC Weatherall Institute of Molecular Medicine, University of Oxford, OX3 9DS, UK
| | - Joseph A Newman
- Centre for Medicines Discovery, University of Oxford, ORCRB, OX3 7DQ, UK
| | | | - Marcin Bielinski
- Chemistry Research Laboratory, University of Oxford, Mansfield Road, Oxford OX1 3TA, UK
| | | | - Opher Gileadi
- Centre for Medicines Discovery, University of Oxford, ORCRB, OX3 7DQ, UK
| | - Peter J McHugh
- Department of Oncology, MRC Weatherall Institute of Molecular Medicine, University of Oxford, OX3 9DS, UK
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20
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Distinct functions of POT1 proteins contribute to the regulation of telomerase recruitment to telomeres. Nat Commun 2021; 12:5514. [PMID: 34535663 PMCID: PMC8448735 DOI: 10.1038/s41467-021-25799-7] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2021] [Accepted: 08/27/2021] [Indexed: 01/07/2023] Open
Abstract
Human shelterin components POT1 and TPP1 form a stable heterodimer that protects telomere ends from ATR-dependent DNA damage responses and regulates telomerase-dependent telomere extension. Mice possess two functionally distinct POT1 proteins. POT1a represses ATR/CHK1 DNA damage responses and the alternative non-homologous end-joining DNA repair pathway while POT1b regulates C-strand resection and recruits the CTC1-STN1-TEN1 (CST) complex to telomeres to mediate C-strand fill-in synthesis. Whether POT1a and POT1b are involved in regulating the length of the telomeric G-strand is unclear. Here we demonstrate that POT1b, independent of its CST function, enhances recruitment of telomerase to telomeres through three amino acids in its TPP1 interacting C-terminus. POT1b thus coordinates the synthesis of both telomeric G- and C-strands. In contrast, POT1a negatively regulates telomere length by inhibiting telomerase recruitment to telomeres. The identification of unique amino acids between POT1a and POT1b helps us understand mechanistically how human POT1 switches between end protective functions and promoting telomerase recruitment.
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21
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Rachakonda S, Hoheisel JD, Kumar R. Occurrence, functionality and abundance of the TERT promoter mutations. Int J Cancer 2021; 149:1852-1862. [PMID: 34313327 DOI: 10.1002/ijc.33750] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2021] [Revised: 06/14/2021] [Accepted: 07/16/2021] [Indexed: 12/18/2022]
Abstract
Telomere shortening at chromosomal ends due to the constraints of the DNA replication process acts as a tumor suppressor by restricting the replicative potential in primary cells. Cancers evade that limitation primarily through the reactivation of telomerase via different mechanisms. Mutations within the promoter of the telomerase reverse transcriptase (TERT) gene represent a definite mechanism for the ribonucleic enzyme regeneration predominantly in cancers that arise from tissues with low rates of self-renewal. The promoter mutations cause a moderate increase in TERT transcription and consequent telomerase upregulation to the levels sufficient to delay replicative senescence but not prevent bulk telomere shortening and genomic instability. Since the discovery, a staggering number of studies have resolved the discrete aspects, effects and clinical relevance of the TERT promoter mutations. The promoter mutations link transcription of TERT with oncogenic pathways, associate with markers of poor outcome and define patients with reduced survivals in several cancers. In this review, we discuss the occurrence and impact of the promoter mutations and highlight the mechanism of TERT activation. We further deliberate on the foundational question of the abundance of the TERT promoter mutations and a general dearth of functional mutations within noncoding sequences, as evident from pan-cancer analysis of the whole-genomes. We posit that the favorable genomic constellation within the TERT promoter may be less than a common occurrence in other noncoding functional elements. Besides, the evolutionary constraints limit the functional fraction within the human genome, hence the lack of abundant mutations outside the coding sequences.
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Affiliation(s)
| | - Jörg D Hoheisel
- Division of Functional Genome Analysis, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Rajiv Kumar
- Division of Functional Genome Analysis, German Cancer Research Center (DKFZ), Heidelberg, Germany.,Department of Molecular Biology of Cancer, Institute of Experimental Medicine of the Czech Academy of Sciences, Prague, Czech Republic
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22
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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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23
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Nelson CB, Alturki TM, Luxton JJ, Taylor LE, Maranon DG, Muraki K, Murnane JP, Bailey SM. Telomeric Double Strand Breaks in G1 Human Cells Facilitate Formation of 5' C-Rich Overhangs and Recruitment of TERRA. Front Genet 2021; 12:644803. [PMID: 33841503 PMCID: PMC8027502 DOI: 10.3389/fgene.2021.644803] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Accepted: 02/08/2021] [Indexed: 12/12/2022] Open
Abstract
Telomeres, repetitive nucleoprotein complexes that protect chromosomal termini and prevent them from activating inappropriate DNA damage responses (DDRs), shorten with cell division and thus with aging. Here, we characterized the human cellular response to targeted telomeric double-strand breaks (DSBs) in telomerase-positive and telomerase-independent alternative lengthening of telomere (ALT) cells, specifically in G1 phase. Telomeric DSBs in human G1 cells elicited early signatures of a DDR; however, localization of 53BP1, an important regulator of resection at broken ends, was not observed at telomeric break sites. Consistent with this finding and previously reported repression of classical non-homologous end-joining (c-NHEJ) at telomeres, evidence for c-NHEJ was also lacking. Likewise, no evidence of homologous recombination (HR)-dependent repair of telomeric DSBs in G1 was observed. Rather, and supportive of rapid truncation events, telomeric DSBs in G1 human cells facilitated formation of extensive tracks of resected 5′ C-rich telomeric single-stranded (ss)DNA, a previously proposed marker of the recombination-dependent ALT pathway. Indeed, induction of telomeric DSBs in human ALT cells resulted in significant increases in 5′ C-rich (ss)telomeric DNA in G1, which rather than RPA, was bound by the complementary telomeric RNA, TERRA, presumably to protect these exposed ends so that they persist into S/G2 for telomerase-mediated or HR-dependent elongation, while also circumventing conventional repair pathways. Results demonstrate the remarkable adaptability of telomeres, and thus they have important implications for persistent telomeric DNA damage in normal human G1/G0 cells (e.g., lymphocytes), as well as for therapeutically relevant targets to improve treatment of ALT-positive tumors.
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Affiliation(s)
- Christopher B Nelson
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States.,Cell and Molecular Biology Program, Colorado State University, Fort Collins, CO, United States
| | - Taghreed M Alturki
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States.,Cell and Molecular Biology Program, Colorado State University, Fort Collins, CO, United States
| | - Jared J Luxton
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States.,Cell and Molecular Biology Program, Colorado State University, Fort Collins, CO, United States
| | - Lynn E Taylor
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States
| | - David G Maranon
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States
| | - Keiko Muraki
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, United States
| | - John P Murnane
- Department of Radiation Oncology, University of California, San Francisco, San Francisco, CA, United States
| | - Susan M Bailey
- Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO, United States.,Cell and Molecular Biology Program, Colorado State University, Fort Collins, CO, United States
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24
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Tomasova K, Kroupa M, Forsti A, Vodicka P, Vodickova L. Telomere maintenance in interplay with DNA repair in pathogenesis and treatment of colorectal cancer. Mutagenesis 2021; 35:261-271. [PMID: 32083302 DOI: 10.1093/mutage/geaa005] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2019] [Accepted: 01/29/2020] [Indexed: 12/14/2022] Open
Abstract
Colorectal cancer (CRC) continues to be one of the leading malignancies and causes of tumour-related deaths worldwide. Both impaired DNA repair mechanisms and disrupted telomere length homeostasis represent key culprits in CRC initiation, progression and prognosis. Mechanistically, altered DNA repair results in the accumulation of mutations in the genome and, ultimately, in genomic instability. DNA repair also determines the response to chemotherapeutics in CRC treatment, suggesting its utilisation in the prediction of therapy response and individual approach to patients. Telomere attrition resulting in replicative senescence, simultaneously by-passing cell cycle checkpoints, is a hallmark of malignant transformation of the cell. Telomerase is almost ubiquitous in advanced solid cancers, including CRC, and its expression is fundamental to cell immortalisation. Therefore, there is a persistent effort to develop therapeutics, which are telomerase-specific and gentle to non-malignant tissues. However, in practice, we are still at the level of clinical trials. The current state of knowledge and the route, which the research takes, gives us a positive perspective that the problem of molecular models of telomerase activation and telomere length stabilisation will finally be solved. We summarise the current literature herein, by pointing out the crosstalk between proteins involved in DNA repair and telomere length homeostasis in relation to CRC.
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Affiliation(s)
- Kristyna Tomasova
- Department of Molecular Biology of Cancer, Institute of Experimental Medicine, The Czech Academy of Sciences, Vídeňská, Praha, Czech Republic.,Faculty of Medicine and Biomedical Center in Pilsen, Charles University, Pilsen, Alej Svobody, Plzeň, Czech Republic
| | - Michal Kroupa
- Department of Molecular Biology of Cancer, Institute of Experimental Medicine, The Czech Academy of Sciences, Vídeňská, Praha, Czech Republic.,Faculty of Medicine and Biomedical Center in Pilsen, Charles University, Pilsen, Alej Svobody, Plzeň, Czech Republic
| | - Asta Forsti
- Hopp Children's Cancer Center (KiTZ), Im Neuenheimer Feld, Heidelberg, Germany.,Division of Pediatric Neurooncology, German Cancer Research Center (DKFZ), German Cancer Consortium (DKTK), Im Neuenheimer Feld, Heidelberg, Germany
| | - Pavel Vodicka
- Department of Molecular Biology of Cancer, Institute of Experimental Medicine, The Czech Academy of Sciences, Vídeňská, Praha, Czech Republic.,Faculty of Medicine and Biomedical Center in Pilsen, Charles University, Pilsen, Alej Svobody, Plzeň, Czech Republic.,Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University, Albertov, Praha, Czech Republic
| | - Ludmila Vodickova
- Department of Molecular Biology of Cancer, Institute of Experimental Medicine, The Czech Academy of Sciences, Vídeňská, Praha, Czech Republic.,Faculty of Medicine and Biomedical Center in Pilsen, Charles University, Pilsen, Alej Svobody, Plzeň, Czech Republic.,Institute of Biology and Medical Genetics, First Faculty of Medicine, Charles University, Albertov, Praha, Czech Republic
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25
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Abstract
In this perspective, we introduce shelterin and the mechanisms of ATM activation and NHEJ at telomeres, before discussing the following questions: How are t-loops proposed to protect chromosome ends and what is the evidence for this model? Can other models explain how TRF2 mediates end protection? Could t-loops be pathological structures? How is end protection achieved in pluripotent cells? What do the insights into telomere end protection in pluripotent cells mean for the t-loop model of end protection? Why might different cell states have evolved different mechanisms of end protection? Finally, we offer support for an updated t-loop model of end protection, suggesting that the data is supportive of a critical role for t-loops in protecting chromosome ends from NHEJ and ATM activation, but that other mechanisms are involved. Finally, we propose that t-loops are likely dynamic, rather than static, structures.
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Affiliation(s)
- Phil Ruis
- The Francis Crick Institute, London NW1 1AT, United Kingdom
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26
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Cicconi A, Rai R, Xiong X, Broton C, Al-Hiyasat A, Hu C, Dong S, Sun W, Garbarino J, Bindra RS, Schildkraut C, Chen Y, Chang S. Microcephalin 1/BRIT1-TRF2 interaction promotes telomere replication and repair, linking telomere dysfunction to primary microcephaly. Nat Commun 2020; 11:5861. [PMID: 33203878 PMCID: PMC7672075 DOI: 10.1038/s41467-020-19674-0] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2020] [Accepted: 10/22/2020] [Indexed: 01/07/2023] Open
Abstract
Telomeres protect chromosome ends from inappropriately activating the DNA damage and repair responses. Primary microcephaly is a key clinical feature of several human telomere disorder syndromes, but how microcephaly is linked to dysfunctional telomeres is not known. Here, we show that the microcephalin 1/BRCT-repeats inhibitor of hTERT (MCPH1/BRIT1) protein, mutated in primary microcephaly, specifically interacts with the TRFH domain of the telomere binding protein TRF2. The crystal structure of the MCPH1-TRF2 complex reveals that this interaction is mediated by the MCPH1 330YRLSP334 motif. TRF2-dependent recruitment of MCPH1 promotes localization of DNA damage factors and homology directed repair of dysfunctional telomeres lacking POT1-TPP1. Additionally, MCPH1 is involved in the replication stress response, promoting telomere replication fork progression and restart of stalled telomere replication forks. Our work uncovers a previously unrecognized role for MCPH1 in promoting telomere replication, providing evidence that telomere replication defects may contribute to the onset of microcephaly.
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Affiliation(s)
- Alessandro Cicconi
- grid.47100.320000000419368710Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
| | - Rekha Rai
- grid.47100.320000000419368710Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
| | - Xuexue Xiong
- grid.507739.fState Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031 China
| | - Cayla Broton
- grid.47100.320000000419368710Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.5386.8000000041936877XTri- Institutional MD/PhD Program, Weill Cornell Medical College, New York, NY 10065 USA
| | - Amer Al-Hiyasat
- grid.47100.320000000419368710Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.47100.320000000419368710Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
| | - Chunyi Hu
- grid.507739.fState Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031 China
| | - Siying Dong
- grid.507739.fState Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031 China
| | - Wenqi Sun
- grid.507739.fState Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031 China
| | - Jennifer Garbarino
- grid.47100.320000000419368710Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.47100.320000000419368710Department of Therapeutic Radiology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
| | - Ranjit S. Bindra
- grid.47100.320000000419368710Department of Therapeutic Radiology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.47100.320000000419368710Department of Experimental Pathology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
| | - Carl Schildkraut
- grid.251993.50000000121791997Department of Cell Biology, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461 USA
| | - Yong Chen
- grid.507739.fState Key Laboratory of Molecular Biology, Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031 China
| | - Sandy Chang
- grid.47100.320000000419368710Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.47100.320000000419368710Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA ,grid.47100.320000000419368710Department of Pathology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520 USA
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27
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Aramburu T, Plucinsky S, Skordalakes E. POT1-TPP1 telomere length regulation and disease. Comput Struct Biotechnol J 2020; 18:1939-1946. [PMID: 32774788 PMCID: PMC7385035 DOI: 10.1016/j.csbj.2020.06.040] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 06/24/2020] [Accepted: 06/27/2020] [Indexed: 12/27/2022] Open
Abstract
Telomeres are DNA repeats at the ends of linear chromosomes and are replicated by telomerase, a ribonucleoprotein reverse transcriptase. Telomere length regulation and chromosome end capping are essential for genome stability and are mediated primarily by the shelterin and CST complexes. POT1-TPP1, a subunit of shelterin, binds the telomeric overhang, suppresses ATR-dependent DNA damage response, and recruits telomerase to telomeres for DNA replication. POT1 localization to telomeres and chromosome end protection requires its interaction with TPP1. Therefore, the POT1-TPP1 complex is critical to telomere maintenance and full telomerase processivity. The aim of this mini-review is to summarize recent POT1-TPP1 structural studies and discuss how the complex contributes to telomere length regulation. In addition, we review how disruption of POT1-TPP1 function leads to human disease.
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Key Words
- ATM, Ataxia Telangiectasia Mutated protein
- ATR, Ataxia Telangiectasia and Rad3-related Protein
- CST, CTC1, Stn1 and Ten1
- CTC1, Conserved Telomere Capping Protein 1
- POT1
- POT1, Protection of telomere 1
- RAP1, Repressor/Activator Protein 1
- RPA, Replication Protein A
- SMCHD1, Structural Maintenance Of Chromosomes Flexible Hinge Domain Containing 1
- Shelterin
- Stn1, Suppressor of Cdc Thirteen
- TERC, Telomerase RNA
- TERT, Telomerase Reverse Transcriptase
- TIN2, TRF1- and TRF2-Interacting Nuclear Protein 2
- TPP1
- TPP1 also known as ACD, Adrenocortical Dysplasia Protein Homolog
- TRF1, Telomere Repeat binding Factor 1
- TRF2, Telomere Repeat binding Factor 2
- TSPYL5, Testis-specific Y-encoded-like protein 5
- Telomerase
- Telomeres
- Ten1, Telomere Length Regulation Protein
- USP7, ubiquitin-specific-processing protease 7
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28
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Long-lived post-mitotic cell aging: is a telomere clock at play? Mech Ageing Dev 2020; 189:111256. [PMID: 32380018 DOI: 10.1016/j.mad.2020.111256] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2020] [Revised: 04/25/2020] [Accepted: 04/27/2020] [Indexed: 12/27/2022]
Abstract
Senescence is a cellular response to stress for both dividing and post-mitotic cells. Noteworthy, long-lived post-mitotic cells (collectively named LLPMCs), which can live for decades in the organism, can exhibit a distinct type of cellular aging characterized by a progressive functional decline not associated to an overt senescence phenotype. The age-related drivers of senescence and aging in LLPMCs remain largely unknown. There is evidence that an increased production of reactive oxygen species (ROS) due to dysfunctional mitochondria, coupled with an inherent inability of cellular-degradation mechanisms to remove damaged molecules, is responsible for senescence and aging in LLPMC. Although telomeric DNA shortening, by nature linked to cell division, is generally not considered as a driver of LLPMC aging and senescence, we discuss recent reports revealing the existence of age-related telomere changes in LLPMC. These findings reveal unexpected roles for telomeres in LLPMC function and invite us to consider the hypothesis of a complex telomere clock involved in both dividing and non-dividing cell aging.
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29
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Cicconi A, Chang S. Shelterin and the replisome: at the intersection of telomere repair and replication. Curr Opin Genet Dev 2020; 60:77-84. [PMID: 32171974 DOI: 10.1016/j.gde.2020.02.016] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2019] [Revised: 02/10/2020] [Accepted: 02/12/2020] [Indexed: 12/30/2022]
Abstract
Telomeres are G-rich repetitive sequences that are difficult to replicate, resulting in increased replication stress that can threaten genome stability. Shelterin protects telomeres from engaging in aberrant DNA repair and dictates the choice of DNA repair pathway at dysfunctional telomeres. Recently, shelterin has been shown to participate in telomere replication. Here we review the most recent discoveries documenting the mechanisms by which shelterin represses DNA repair pathways at telomeres while assisting its replication. The interplay between shelterin and the replisome complex highlights a novel connection between telomere maintenance and repair.
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Affiliation(s)
- Alessandro Cicconi
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520, USA
| | - Sandy Chang
- Department of Laboratory Medicine, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520, USA; Department of Pathology, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520, USA; Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, 330 Cedar St., New Haven, CT 06520, USA.
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30
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Abstract
In this review, Mirman et al. summarize the current understanding of the role of 53BP1 in DSB repair at deprotected telomeres, in class switch recombination in the immune system, and in the context of PARPi-treated BRCA1-deficient cells. They argue that the primary function of 53BP1 is not to regulate the choice between c-NHEJ and HDR, but to ensure the fidelity of DSB repair, a function that is corrupted in diseases where DNA repair is rewired. 53BP1 is an enigmatic DNA damage response factor that gained prominence because it determines the efficacy of PARP1 inhibitory drugs (PARPi) in BRCA1-deficient cancers. Recent studies have elevated 53BP1 from its modest status of (yet another) DNA damage factor to master regulator of double-strand break (DSB) repair pathway choice. Our review of the literature suggests an alternative view. We propose that 53BP1 has evolved to avoid mutagenic repair outcomes and does so by controlling the processing of DNA ends and the dynamics of DSBs. The consequences of 53BP1 deficiency, such as diminished PARPi efficacy in BRCA1-deficient cells and altered repair of damaged telomeres, can be explained from this viewpoint. We further propose that some of the fidelity functions of 53BP1 coevolved with class switch recombination (CSR) in the immune system. We speculate that, rather than being deterministic in DSB repair pathway choice, 53BP1 functions as a DSB escort that guards against illegitimate and potentially tumorigenic recombination.
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Affiliation(s)
- Zachary Mirman
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
| | - Titia de Lange
- Laboratory for Cell Biology and Genetics, The Rockefeller University, New York, New York 10065, USA
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31
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Sui J, Zhang S, Chen BPC. DNA-dependent protein kinase in telomere maintenance and protection. Cell Mol Biol Lett 2020; 25:2. [PMID: 31988640 PMCID: PMC6969447 DOI: 10.1186/s11658-020-0199-0] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Accepted: 01/02/2020] [Indexed: 12/12/2022] Open
Abstract
This review focuses on DNA-dependent protein kinase (DNA-PK), which is the key regulator of canonical non-homologous end-joining (NHEJ), the predominant mechanism of DNA double-strand break (DSB) repair in mammals. DNA-PK consists of the DNA-binding Ku70/80 heterodimer and the catalytic subunit DNA-PKcs. They assemble at DNA ends, forming the active DNA-PK complex, which initiates NHEJ-mediated DSB repair. Paradoxically, both Ku and DNA-PKcs are associated with telomeres, and they play crucial roles in protecting the telomere against fusions. Herein, we discuss possible mechanisms and contributions of Ku and DNA-PKcs in telomere regulation.
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Affiliation(s)
- Jiangdong Sui
- 1Radiation Oncology Center, Chongqing University Cancer Hospital, Chongqing, 400030 China
| | - Shichuan Zhang
- 2Department of Radiation Oncology, Sichuan Cancer Hospital, Chengdu, China
| | - Benjamin P C Chen
- 3Department of Radiation Oncology, University of Texas Southwestern Medical Center, 2201 Inwood Rd., Dallas, TX 75390-9187 USA
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32
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Stroik S, Kurtz K, Hendrickson EA. CtIP is essential for telomere replication. Nucleic Acids Res 2019; 47:8927-8940. [PMID: 31378812 PMCID: PMC6755089 DOI: 10.1093/nar/gkz652] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 07/08/2019] [Accepted: 07/16/2019] [Indexed: 01/10/2023] Open
Abstract
The maintenance of telomere length is critical to longevity and survival. Specifically, the failure to properly replicate, resect, and/or form appropriate telomeric structures drives telomere shortening and, in turn, genomic instability. The endonuclease CtIP is a DNA repair protein that is well-known to promote genome stability through the resection of endogenous DNA double-stranded breaks. Here, we describe a novel role for CtIP. We show that in the absence of CtIP, human telomeres shorten rapidly to non-viable lengths. This telomere dysfunction results in an accumulation of fusions, breaks, and frank telomere loss. Additionally, CtIP suppresses the generation of circular, extrachromosomal telomeric DNA. These latter structures appear to arise from arrested DNA replication forks that accumulate in the absence of CtIP. Hence, CtIP is required for faithful replication through telomeres via its roles at stalled replication tracts. Our findings demonstrate a new role for CtIP as a protector of human telomere integrity.
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Affiliation(s)
- Susanna Stroik
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, USA
| | - Kevin Kurtz
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, USA
| | - Eric A Hendrickson
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota Medical School, Minneapolis, MN 55455, USA
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33
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The Replisome Mediates A-NHEJ Repair of Telomeres Lacking POT1-TPP1 Independently of MRN Function. Cell Rep 2019; 29:3708-3725.e5. [PMID: 31825846 PMCID: PMC7001145 DOI: 10.1016/j.celrep.2019.11.012] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2019] [Revised: 09/22/2019] [Accepted: 11/04/2019] [Indexed: 02/07/2023] Open
Abstract
Telomeres use shelterin to protect chromosome ends from activating the DNA damage sensor MRE11-RAD50-NBS1 (MRN), repressing ataxia-telangiectasia, mutated (ATM) and ATM and Rad3-related (ATR) dependent DNA damage checkpoint responses. The MRE11 nuclease is thought to be essential for the resection of the 5′ C-strand to generate the microhomologies necessary for alternative non-homologous end joining (A-NHEJ) repair. In the present study, we uncover DNA damage signaling and repair pathways engaged by components of the replisome complex to repair dysfunctional telomeres. In cells lacking MRN, single-stranded telomeric overhangs devoid of POT1-TPP1 do not recruit replication protein A (RPA), ATR-interacting protein (ATRIP), and RAD 51. Rather, components of the replisome complex, including Claspin, Proliferating cell nuclear antigen (PCNA), and Downstream neighbor of SON (DONSON), initiate DNA-PKcs-mediated p-CHK1 activation and A-NHEJ repair. In addition, Claspin directly interacts with TRF2 and recruits EXO1 to newly replicated telomeres to promote 5′ end resection. Our data indicate that MRN is dispensable for the repair of dysfunctional telomeres lacking POT1-TPP1 and highlight the contributions of the replisome in telomere repair. Rai et al. define roles for the DNA replisome components Claspin, PCNA, and DONSON in the sensing and repair of telomeres lacking POT1-TPP1. In cells lacking MRN, CPD initiates DNA-PKcs-mediated p-CHK1 activation and A-NHEJ repair. Claspin directly interacts with TRF2 and recruits EXO1 to promote 5′ C-strand end resection.
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34
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Barbero Barcenilla B, Shippen DE. Back to the future: The intimate and evolving connection between telomere-related factors and genotoxic stress. J Biol Chem 2019; 294:14803-14813. [PMID: 31434740 DOI: 10.1074/jbc.aw119.008145] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The conversion of circular genomes to linear chromosomes during molecular evolution required the invention of telomeres. This entailed the acquisition of factors necessary to fulfill two new requirements: the need to fully replicate terminal DNA sequences and the ability to distinguish chromosome ends from damaged DNA. Here we consider the multifaceted functions of factors recruited to perpetuate and stabilize telomeres. We discuss recent theories for how telomere factors evolved from existing cellular machineries and examine their engagement in nontelomeric functions such as DNA repair, replication, and transcriptional regulation. We highlight the remarkable versatility of protection of telomeres 1 (POT1) proteins that was fueled by gene duplication and divergence events that occurred independently across several eukaryotic lineages. Finally, we consider the relationship between oxidative stress and telomeres and the enigmatic role of telomere-associated proteins in mitochondria. These findings point to an evolving and intimate connection between telomeres and cellular physiology and the strong drive to maintain chromosome integrity.
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Affiliation(s)
- Borja Barbero Barcenilla
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
| | - Dorothy E Shippen
- Department of Biochemistry and Biophysics, Texas A&M University, College Station, Texas 77843-2128
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35
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Doksani Y. The Response to DNA Damage at Telomeric Repeats and Its Consequences for Telomere Function. Genes (Basel) 2019; 10:genes10040318. [PMID: 31022960 PMCID: PMC6523756 DOI: 10.3390/genes10040318] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2019] [Revised: 04/13/2019] [Accepted: 04/18/2019] [Indexed: 01/17/2023] Open
Abstract
Telomeric repeats, coated by the shelterin complex, prevent inappropriate activation of the DNA damage response at the ends of linear chromosomes. Shelterin has evolved distinct solutions to protect telomeres from different aspects of the DNA damage response. These solutions include formation of t-loops, which can sequester the chromosome terminus from DNA-end sensors and inhibition of key steps in the DNA damage response. While blocking the DNA damage response at chromosome ends, telomeres make wide use of many of its players to deal with exogenous damage and replication stress. This review focuses on the interplay between the end-protection functions and the response to DNA damage occurring inside the telomeric repeats, as well as on the consequences that telomere damage has on telomere structure and function.
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Affiliation(s)
- Ylli Doksani
- IFOM, The FIRC Institute of Molecular Oncology, via Adamello 16, 20139 Milan, Italy.
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36
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Herwest S, Albers C, Schmiester M, Salewsky B, Hopfenmüller W, Meyer A, Bertram L, Demuth I. The hSNM1B/Apollo variant rs11552449 is associated with cellular sensitivity towards mitomycin C and ionizing radiation. DNA Repair (Amst) 2018; 72:93-98. [DOI: 10.1016/j.dnarep.2018.09.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2018] [Revised: 08/03/2018] [Accepted: 09/10/2018] [Indexed: 11/30/2022]
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37
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Kosebent EG, Uysal F, Ozturk S. Telomere length and telomerase activity during folliculogenesis in mammals. J Reprod Dev 2018; 64:477-484. [PMID: 30270279 PMCID: PMC6305847 DOI: 10.1262/jrd.2018-076] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Telomeres are repetitive non-coding DNA sequences located at the ends of chromosomes in eukaryotic cells. Their most important function is to protect chromosome ends from being recognized
as DNA damage. They are also implicated in meiosis and synapse formation. The length of telomeres inevitably shortens at the end of each round of DNA replication and, also, as a consequence
of the exposure to oxidative stress and/or genotoxic agents. The enzyme telomerase contributes to telomere lengthening. It has been reported that telomerase is exclusively expressed in germ
cells, granulosa cells, early embryos, stem cells, and various types of cancerous cells. Granulosa cells undergo many mitotic divisions and either granulosa cells or oocytes are exposed to a
variety of genotoxic agents throughout folliculogenesis; thus, telomerase plays an important role in the maintenance of telomere length. In this review article, we have comprehensively
evaluated the studies focusing on the regulation of telomerase expression and activity, as well as telomere length, during folliculogenesis from primordial to antral follicles, in several
mammalian species including mice, bovines, and humans. Also, the possible relationships between female infertility caused by follicular development defects and alterations in the telomeres
and/or telomerase activity are discussed.
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Affiliation(s)
- Esra Gozde Kosebent
- Department of Histology and Embryology, Akdeniz University School of Medicine, Antalya 07070, Turkey
| | - Fatma Uysal
- Department of Histology and Embryology, Ankara University School of Medicine, Ankara, Turkey
| | - Saffet Ozturk
- Department of Histology and Embryology, Akdeniz University School of Medicine, Antalya 07070, Turkey
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Abstract
For more than a decade, it has been known that mammalian cells use shelterin to protect chromosome ends. Much progress has been made on the mechanism by which shelterin prevents telomeres from inadvertently activating DNA damage signaling and double-strand break (DSB) repair pathways. Shelterin averts activation of three DNA damage response enzymes [the ataxia-telangiectasia-mutated (ATM) and ataxia telangiectasia and Rad3-related (ATR) kinases and poly(ADP-ribose) polymerase 1 (PARP1)], blocks three DSB repair pathways [classical nonhomologous end joining (c-NHEJ), alternative (alt)-NHEJ, and homology-directed repair (HDR)], and prevents hyper-resection at telomeres. For several of these functions, mechanistic insights have emerged. In addition, much has been learned about how shelterin maintains the telomeric 3' overhang, forms and protects the t-loop structure, and promotes replication through telomeres. These studies revealed that shelterin is compartmentalized, with individual subunits dedicated to distinct aspects of the end-protection problem. This review focuses on the current knowledge of shelterin-mediated telomere protection, highlights differences between human and mouse shelterin, and discusses some of the questions that remain.
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Affiliation(s)
- Titia de Lange
- Laboratory of Cell Biology and Genetics, Rockefeller University, New York, NY 10065, USA;
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SNM1B/Apollo in the DNA damage response and telomere maintenance. Oncotarget 2018; 8:48398-48409. [PMID: 28430596 PMCID: PMC5564657 DOI: 10.18632/oncotarget.16864] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2017] [Accepted: 03/27/2017] [Indexed: 01/26/2023] Open
Abstract
hSNM1B/Apollo is a member of the highly conserved β-CASP subgroup within the MBL superfamily of proteins. It interacts with several DNA repair proteins and functions within the Fanconi anemia pathway in response to DNA interstrand crosslinks. As a shelterin accessory protein, hSNM1B/Apollo is also vital for the generation and maintenance of telomeric overhangs. In this review, we will summarize studies on hSNM1B/Apollo's function, including its contribution to DNA damage signaling, replication fork maintenance, control of topological stress and telomere protection. Furthermore, we will highlight recent studies illustrating hSNM1B/Apollo's putative role in human disease.
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40
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Song S, Johnson FB. Epigenetic Mechanisms Impacting Aging: A Focus on Histone Levels and Telomeres. Genes (Basel) 2018; 9:genes9040201. [PMID: 29642537 PMCID: PMC5924543 DOI: 10.3390/genes9040201] [Citation(s) in RCA: 38] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2018] [Revised: 03/27/2018] [Accepted: 03/29/2018] [Indexed: 12/13/2022] Open
Abstract
Aging and age-related diseases pose some of the most significant and difficult challenges to modern society as well as to the scientific and medical communities. Biological aging is a complex, and, under normal circumstances, seemingly irreversible collection of processes that involves numerous underlying mechanisms. Among these, chromatin-based processes have emerged as major regulators of cellular and organismal aging. These include DNA methylation, histone modifications, nucleosome positioning, and telomere regulation, including how these are influenced by environmental factors such as diet. Here we focus on two interconnected categories of chromatin-based mechanisms impacting aging: those involving changes in the levels of histones or in the functions of telomeres.
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Affiliation(s)
- Shufei Song
- Biochemistry and Molecular Biophysics Graduate Group, Biomedical Graduate Studies, University of Pennsylvania, Philadelphia, PA 19104, USA.
- Department of Pathology and Laboratory Medicine, and Institute on Aging, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
| | - F Brad Johnson
- Department of Pathology and Laboratory Medicine, and Institute on Aging, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA 19104, USA.
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41
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Stewart JA, Wang Y, Ackerson SM, Schuck PL. Emerging roles of CST in maintaining genome stability and human disease. Front Biosci (Landmark Ed) 2018; 23:1564-1586. [PMID: 29293451 DOI: 10.2741/4661] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
The human CTC1-STN1-TEN1 (CST) complex is a single-stranded DNA binding protein that shares homology with RPA and interacts with DNA polymerase alpha/primase. CST complexes are conserved from yeasts to humans and function in telomere maintenance. A common role of CST across species is in the regulation of telomere extension by telomerase and C-strand fill-in synthesis. However, recent studies also indicate that CST promotes telomere duplex replication as well the rescue of stalled DNA replication at non-telomeric sites. Furthermore, CST dysfunction and mutation is associated with several genetic diseases and cancers. In this review, we will summarize what is known about CST with a particular focus on the emerging roles of CST in DNA replication and human disease.
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Affiliation(s)
- Jason A Stewart
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA,
| | - Yilin Wang
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Stephanie M Ackerson
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Percy Logan Schuck
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
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42
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Cleal K, Norris K, Baird D. Telomere Length Dynamics and the Evolution of Cancer Genome Architecture. Int J Mol Sci 2018; 19:E482. [PMID: 29415479 PMCID: PMC5855704 DOI: 10.3390/ijms19020482] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2017] [Revised: 01/29/2018] [Accepted: 01/31/2018] [Indexed: 02/06/2023] Open
Abstract
Telomeres are progressively eroded during repeated rounds of cell division due to the end replication problem but also undergo additional more substantial stochastic shortening events. In most cases, shortened telomeres induce a cell-cycle arrest or trigger apoptosis, although for those cells that bypass such signals during tumour progression, a critical length threshold is reached at which telomere dysfunction may ensue. Dysfunction of the telomere nucleoprotein complex can expose free chromosome ends to the DNA double-strand break (DSB) repair machinery, leading to telomere fusion with both telomeric and non-telomeric loci. The consequences of telomere fusions in promoting genome instability have long been appreciated through the breakage-fusion-bridge (BFB) cycle mechanism, although recent studies using high-throughput sequencing technologies have uncovered evidence of involvement in a wider spectrum of genomic rearrangements including chromothripsis. A critical step in cancer progression is the transition of a clone to immortality, through the stabilisation of the telomere repeat array. This can be achieved via the reactivation of telomerase, or the induction of the alternative lengthening of telomeres (ALT) pathway. Whilst telomere dysfunction may promote genome instability and tumour progression, by limiting the replicative potential of a cell and enforcing senescence, telomere shortening can act as a tumour suppressor mechanism. However, the burden of senescent cells has also been implicated as a driver of ageing and age-related pathology, and in the promotion of cancer through inflammatory signalling. Considering the critical role of telomere length in governing cancer biology, we review questions related to the prognostic value of studying the dynamics of telomere shortening and fusion, and discuss mechanisms and consequences of telomere-induced genome rearrangements.
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Affiliation(s)
- Kez Cleal
- Division of Cancer and Genetics, School of Medicine, UHW Main Building, Cardiff CF14 4XN, UK.
| | - Kevin Norris
- Division of Cancer and Genetics, School of Medicine, UHW Main Building, Cardiff CF14 4XN, UK.
| | - Duncan Baird
- Division of Cancer and Genetics, School of Medicine, UHW Main Building, Cardiff CF14 4XN, UK.
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43
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Telomeres: Implications for Cancer Development. Int J Mol Sci 2018; 19:ijms19010294. [PMID: 29351238 PMCID: PMC5796239 DOI: 10.3390/ijms19010294] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2017] [Revised: 01/12/2018] [Accepted: 01/16/2018] [Indexed: 12/31/2022] Open
Abstract
Telomeres facilitate the protection of natural ends of chromosomes from constitutive exposure to the DNA damage response (DDR). This is most likely achieved by a lariat structure that hides the linear telomeric DNA through protein-protein and protein-DNA interactions. The telomere shortening associated with DNA replication in the absence of a compensatory mechanism culminates in unmasked telomeres. Then, the subsequent activation of the DDR will define the fate of cells according to the functionality of cell cycle checkpoints. Dysfunctional telomeres can suppress cancer development by engaging replicative senescence or apoptotic pathways, but they can also promote tumour initiation. Studies in telomere dynamics and karyotype analysis underpin telomere crisis as a key event driving genomic instability. Significant attainment of telomerase or alternative lengthening of telomeres (ALT)-pathway to maintain telomere length may be permissive and required for clonal evolution of genomically-unstable cells during progression to malignancy. We summarise current knowledge of the role of telomeres in the maintenance of chromosomal stability and carcinogenesis.
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44
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Heterozygous RTEL1 variants in bone marrow failure and myeloid neoplasms. Blood Adv 2018; 2:36-48. [PMID: 29344583 DOI: 10.1182/bloodadvances.2017008110] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2017] [Accepted: 10/17/2017] [Indexed: 12/22/2022] Open
Abstract
Biallelic germline mutations in RTEL1 (regulator of telomere elongation helicase 1) result in pathologic telomere erosion and cause dyskeratosis congenita. However, the role of RTEL1 mutations in other bone marrow failure (BMF) syndromes and myeloid neoplasms, and the contribution of monoallelic RTEL1 mutations to disease development are not well defined. We screened 516 patients for germline mutations in telomere-associated genes by next-generation sequencing in 2 independent cohorts; one constituting unselected patients with idiopathic BMF, unexplained cytopenia, or myeloid neoplasms (n = 457) and a second cohort comprising selected patients on the basis of the suspicion of constitutional/familial BMF (n = 59). Twenty-three RTEL1 variants were identified in 27 unrelated patients from both cohorts: 7 variants were likely pathogenic, 13 were of uncertain significance, and 3 were likely benign. Likely pathogenic RTEL1 variants were identified in 9 unrelated patients (7 heterozygous and 2 biallelic). Most patients were suspected to have constitutional BMF, which included aplastic anemia (AA), unexplained cytopenia, hypoplastic myelodysplastic syndrome, and macrocytosis with hypocellular bone marrow. In the other 18 patients, RTEL1 variants were likely benign or of uncertain significance. Telomeres were short in 21 patients (78%), and 3' telomeric overhangs were significantly eroded in 4. In summary, heterozygous RTEL1 variants were associated with marrow failure, and telomere length measurement alone may not identify patients with telomere dysfunction carrying RTEL1 variants. Pathogenicity assessment of heterozygous RTEL1 variants relied on a combination of clinical, computational, and functional data required to avoid misinterpretation of common variants.
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45
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Telomerase activity is required for the telomere G-overhang structure in Trypanosoma brucei. Sci Rep 2017; 7:15983. [PMID: 29167542 PMCID: PMC5700094 DOI: 10.1038/s41598-017-16182-y] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2017] [Accepted: 11/08/2017] [Indexed: 01/24/2023] Open
Abstract
Trypanosoma brucei causes fatal human African trypanosomiasis and evades the host immune response by regularly switching its major surface antigen, VSG, which is expressed exclusively from subtelomeric loci. Telomere length and telomere proteins play important roles in regulating VSG silencing and switching. T. brucei telomerase plays a key role in maintaining telomere length, and T. brucei telomeres terminate in a single-stranded 3′ G-rich overhang. Understanding the detailed structure of the telomere G-overhang and its maintenance will contribute greatly to better understanding telomere maintenance mechanisms. Using an optimized adaptor ligation assay, we found that most T. brucei telomere G-overhangs end in 5′ TTAGGG 3′, while a small portion of G-overhangs end in 5′ TAGGGT 3′. Additionally, the protein and the RNA components of the telomerase (TbTERT and TbTR) and TbKu are required for telomere G-overhangs that end in 5′ TTAGGG 3′ but do not significantly affect the 5′ TAGGGT 3′-ending overhangs, indicating that telomerase-mediated telomere synthesis is important for the telomere G-overhang structure. Furthermore, using telomere oligo ligation-mediated PCR, we showed for the first time that the T. brucei telomere 5′ end sequence – an important feature of the telomere terminal structure – is not random but preferentially 5′ CCTAAC 3′.
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46
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Arnoult N, Correia A, Ma J, Merlo A, Garcia-Gomez S, Maric M, Tognetti M, Benner CW, Boulton SJ, Saghatelian A, Karlseder J. Regulation of DNA repair pathway choice in S and G2 phases by the NHEJ inhibitor CYREN. Nature 2017; 549:548-552. [PMID: 28959974 PMCID: PMC5624508 DOI: 10.1038/nature24023] [Citation(s) in RCA: 161] [Impact Index Per Article: 23.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 08/10/2017] [Indexed: 01/21/2023]
Abstract
Classical non-homologous end joining (cNHEJ) and homologous recombination compete for the repair of double-stranded DNA breaks during the cell cycle. Homologous recombination is inhibited during the G1 phase of the cell cycle, but both pathways are active in the S and G2 phases. However, it is unclear why cNHEJ does not always outcompete homologous recombination during the S and G2 phases. Here we show that CYREN (cell cycle regulator of NHEJ) is a cell-cycle-specific inhibitor of cNHEJ. Suppression of CYREN allows cNHEJ to occur at telomeres and intrachromosomal breaks during the S and G2 phases, and cells lacking CYREN accumulate chromosomal aberrations upon damage induction, specifically outside the G1 phase. CYREN acts by binding to the Ku70/80 heterodimer and preferentially inhibits cNHEJ at breaks with overhangs by protecting them. We therefore propose that CYREN is a direct cell-cycle-dependent inhibitor of cNHEJ that promotes error-free repair by homologous recombination during cell cycle phases when sister chromatids are present.
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Affiliation(s)
- Nausica Arnoult
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Adriana Correia
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Jiao Ma
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Anna Merlo
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Sara Garcia-Gomez
- Dsb Repair Metabolism Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Marija Maric
- Dsb Repair Metabolism Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Marco Tognetti
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Christopher W Benner
- Department of Medicine, University of California San Diego, 9500 Gilman Drive, La Jolla, California 92093, USA
| | - Simon J Boulton
- Dsb Repair Metabolism Laboratory, The Francis Crick Institute, 1 Midland Road, London NW1 1AT, UK
| | - Alan Saghatelian
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
| | - Jan Karlseder
- The Salk Institute for Biological Studies, 10010 North Torrey Pines Rd., La Jolla, California 92037, USA
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47
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Min J, Wright WE, Shay JW. Alternative lengthening of telomeres can be maintained by preferential elongation of lagging strands. Nucleic Acids Res 2017; 45:2615-2628. [PMID: 28082393 PMCID: PMC5389697 DOI: 10.1093/nar/gkw1295] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2015] [Accepted: 01/04/2017] [Indexed: 11/14/2022] Open
Abstract
Alternative lengthening of telomeres (ALT) is a telomerase independent telomere maintenance mechanism that occurs in ∼15% of cancers. The potential mechanism of ALT is homology-directed telomere synthesis, but molecular mechanisms of how ALT maintains telomere length in human cancer is poorly understood. Here, we generated TERC (telomerase RNA) gene knockouts in telomerase positive cell lines that resulted in long-term surviving clones acquiring the ALT pathway but at a very low frequency. By comparing these ALT cells with parental telomerase positive cells, we observed that ALT cells possess excessively long telomeric overhangs derived from telomere elongation processes that mostly occur during S phase. ALT cells exhibited preferential elongation of the telomeric lagging strands, whereas telomerase positive cells exhibited similar elongation between leading and lagging strands. We propose that the ALT pathway preferentially occurs at telomeric lagging strands leading to heterogeneous telomere lengths observed in most ALT cancers.
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Affiliation(s)
- Jaewon Min
- Department of Cell Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - Woodring E Wright
- Department of Cell Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
| | - Jerry W Shay
- Department of Cell Biology, University of Texas Southwestern Medical Center, 5323 Harry Hines Boulevard, Dallas, TX 75390-9039, USA
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48
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Yalçin Z, Selenz C, Jacobs JJL. Ubiquitination and SUMOylation in Telomere Maintenance and Dysfunction. Front Genet 2017; 8:67. [PMID: 28588610 PMCID: PMC5440461 DOI: 10.3389/fgene.2017.00067] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2016] [Accepted: 05/10/2017] [Indexed: 12/14/2022] Open
Abstract
Telomeres are essential nucleoprotein structures at linear chromosomes that maintain genome integrity by protecting chromosome ends from being recognized and processed as damaged DNA. In addition, they limit the cell’s proliferative capacity, as progressive loss of telomeric DNA during successive rounds of cell division eventually causes a state of telomere dysfunction that prevents further cell division. When telomeres become critically short, the cell elicits a DNA damage response resulting in senescence, apoptosis or genomic instability, thereby impacting on aging and tumorigenesis. Over the past years substantial progress has been made in understanding the role of post-translational modifications in telomere-related processes, including telomere maintenance, replication and dysfunction. This review will focus on recent findings that establish an essential role for ubiquitination and SUMOylation at telomeres.
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Affiliation(s)
- Zeliha Yalçin
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
| | - Carolin Selenz
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
| | - Jacqueline J L Jacobs
- Department of Molecular Oncology, Netherlands Cancer InstituteAmsterdam, Netherlands
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49
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DNA Replication Origins and Fork Progression at Mammalian Telomeres. Genes (Basel) 2017; 8:genes8040112. [PMID: 28350373 PMCID: PMC5406859 DOI: 10.3390/genes8040112] [Citation(s) in RCA: 47] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2017] [Revised: 03/23/2017] [Accepted: 03/24/2017] [Indexed: 12/20/2022] Open
Abstract
Telomeres are essential chromosomal regions that prevent critical shortening of linear chromosomes and genomic instability in eukaryotic cells. The bulk of telomeric DNA is replicated by semi-conservative DNA replication in the same way as the rest of the genome. However, recent findings revealed that replication of telomeric repeats is a potential cause of chromosomal instability, because DNA replication through telomeres is challenged by the repetitive telomeric sequences and specific structures that hamper the replication fork. In this review, we summarize current understanding of the mechanisms by which telomeres are faithfully and safely replicated in mammalian cells. Various telomere-associated proteins ensure efficient telomere replication at different steps, such as licensing of replication origins, passage of replication forks, proper fork restart after replication stress, and dissolution of post-replicative structures. In particular, shelterin proteins have central roles in the control of telomere replication. Through physical interactions, accessory proteins are recruited to maintain telomere integrity during DNA replication. Dormant replication origins and/or homology-directed repair may rescue inappropriate fork stalling or collapse that can cause defects in telomere structure and functions.
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50
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NBS1 Phosphorylation Status Dictates Repair Choice of Dysfunctional Telomeres. Mol Cell 2017; 65:801-817.e4. [PMID: 28216226 PMCID: PMC5639704 DOI: 10.1016/j.molcel.2017.01.016] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2016] [Revised: 11/22/2016] [Accepted: 01/05/2017] [Indexed: 01/07/2023]
Abstract
Telomeres employ TRF2 to protect chromosome ends from activating the DNA damage sensor MRE11-RAD50-NBS1 (MRN), thereby repressing ATM-dependent DNA damage checkpoint responses. How TRF2 prevents MRN activation at dysfunctional telomeres is unclear. Here, we show that the phosphorylation status of NBS1 determines the repair pathway choice of dysfunctional telomeres. The crystal structure of the TRF2-NBS1 complex at 3.0 Å resolution shows that the NBS1 429YQLSP433 motif interacts specifically with the TRF2TRFH domain. Phosphorylation of NBS1 serine 432 by CDK2 in S/G2 dissociates NBS1 from TRF2, promoting TRF2-Apollo/SNM1B complex formation and the protection of leading-strand telomeres. Classical-NHEJ-mediated repair of telomeres lacking TRF2 requires phosphorylated NBS1S432 to activate ATM, while interaction of de-phosphorylated NBS1S432 with TRF2 promotes alternative-NHEJ repair of telomeres lacking POT1-TPP1. Our work advances understanding of how the TRF2TRFH domain orchestrates telomere end protection and reveals how the phosphorylation status of the NBS1S432 dictates repair pathway choice of dysfunctional telomeres.
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