1
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Lee J, Sung K, Joo SY, Jeong JH, Kim SK, Lee H. Dynamic interaction of BRCA2 with telomeric G-quadruplexes underlies telomere replication homeostasis. Nat Commun 2022; 13:3396. [PMID: 35697743 PMCID: PMC9192595 DOI: 10.1038/s41467-022-31156-z] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2021] [Accepted: 05/31/2022] [Indexed: 12/02/2022] Open
Abstract
BRCA2-deficient cells precipitate telomere shortening upon collapse of stalled replication forks. Here, we report that the dynamic interaction between BRCA2 and telomeric G-quadruplex (G4), the non-canonical four-stranded secondary structure, underlies telomere replication homeostasis. We find that the OB-folds of BRCA2 binds to telomeric G4, which can be an obstacle during replication. We further demonstrate that BRCA2 associates with G-triplex (G3)-derived intermediates, which are likely to form during direct interconversion between parallel and non-parallel G4. Intriguingly, BRCA2 binding to G3 intermediates promoted RAD51 recruitment to the telomere G4. Furthermore, MRE11 resected G4-telomere, which was inhibited by BRCA2. Pathogenic mutations at the OB-folds abrogated the binding with telomere G4, indicating that the way BRCA2 associates with telomere is innate to its tumor suppressor activity. Collectively, we propose that BRCA2 binding to telomeric G4 remodels it and allows RAD51-mediated restart of the G4-driven replication fork stalling, simultaneously preventing MRE11-mediated breakdown of telomere. G-quadruplex (G4) can be formed in telomeric DNA. Here the authors show that BRCA2 interacts with telomere G4 structure generated during telomere replication, protecting telomere from nuclease attack.
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Affiliation(s)
- Junyeop Lee
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Keewon Sung
- Department of Chemistry, Seoul National University, Seoul, 08826, South Korea
| | - So Young Joo
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Jun-Hyeon Jeong
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea
| | - Seong Keun Kim
- Department of Chemistry, Seoul National University, Seoul, 08826, South Korea.
| | - Hyunsook Lee
- Department of Biological Sciences & IMBG, Seoul National University, Seoul, 08826, South Korea.
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2
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Izumi H, Funa K. Telomere Function and the G-Quadruplex Formation are Regulated by hnRNP U. Cells 2019; 8:cells8050390. [PMID: 31035352 PMCID: PMC6562495 DOI: 10.3390/cells8050390] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2019] [Revised: 04/22/2019] [Accepted: 04/25/2019] [Indexed: 11/27/2022] Open
Abstract
We examine the role of the heterogenous ribonucleoprotein U (hnRNP U) as a G-quadruplex binding protein in human cell lines. Hypothesizing that hnRNP U is associated with telomeres, we investigate what other telomere-related functions it may have. Telomeric G-quadruplexes have been fully characterized in vitro, but until now no clear evidence of their function or in vivo interactions with proteins has been revealed in mammalian cells. Techniques used were immunoprecipitation, DNA pull-down, binding assay, and Western blots. We identified hnRNP U as a G-quadruplex binding protein. Immunoprecipitations disclosed that endogenous hnRNP U associates with telomeres, and DNA pull-downs showed that the hnRNP U C-terminus specifically binds telomeric G-quadruplexes. We have compared the effect of telomere repeat containing RNA (TERRA) on binding between hnRNP U and telomeric (Tel) or single- stranded Tel (ssTel) oligonucleotides and found that ssTel binds stronger to TERRA than to Tel. We also show that hnRNP U prevents replication protein A (RPA) accumulation at telomeres, and the recognition of telomeric ends by hnRNP suggests that a G-quadruplex promoting protein regulates its accessibility. Thus, hnRNP U-mediated formation has important functions for telomere biology.
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Affiliation(s)
- Hiroto Izumi
- Department of Occupational Pneumology, Institute of Industrial Ecological Sciences, University of Occupational and Environmental Health, Fukuoka 807-8555, Japan.
| | - Keiko Funa
- Department of Medical Biochemistry and Cell Biology, Institute of Biomedicine, University of Gothenburg, SE-40530 Gothenburg, Sweden.
- Oncology Laboratory, University of Gothenburg, Sahlgrenska Hospital, Gula stråket 8, SE-41345 Gothenburg, Sweden.
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3
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Manna S, Srivatsan SG. Fluorescence-based tools to probe G-quadruplexes in cell-free and cellular environments. RSC Adv 2018; 8:25673-25694. [PMID: 30210793 PMCID: PMC6130854 DOI: 10.1039/c8ra03708f] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2018] [Accepted: 07/08/2018] [Indexed: 12/26/2022] Open
Abstract
Biophysical and biochemical investigations provide compelling evidence connecting the four-stranded G-quadruplex (GQ) structure with its role in regulating multiple cellular processes. Hence, modulating the function of GQs by using small molecule binders is being actively pursued as a strategy to develop new chemotherapeutic agents. However, sequence diversity and structural polymorphism of GQs have posed immense challenges in terms of understanding what conformation a G-rich sequence adopts inside the cell and how to specifically target a GQ motif amidst several other GQ-forming sequences. In this context, here we review recent developments in the applications of biophysical tools that use fluorescence readout to probe the GQ structure and recognition in cell-free and cellular environments. First, we provide a detailed discussion on the utility of covalently labeled environment-sensitive fluorescent nucleoside analogs in assessing the subtle difference in GQ structures and their ligand binding abilities. Furthermore, a detailed discussion on structure-specific antibodies and small molecule probes used to visualize and confirm the existence of DNA and RNA GQs in cells is provided. We also highlight the open challenges in the study of tetraplexes (GQ and i-motif structures) and how addressing these challenges by developing new tools and techniques will have a profound impact on tetraplex-directed therapeutic strategies.
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Affiliation(s)
- Sudeshna Manna
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), PuneDr. Homi Bhabha RoadPune 411008India
| | - Seergazhi G. Srivatsan
- Department of Chemistry, Indian Institute of Science Education and Research (IISER), PuneDr. Homi Bhabha RoadPune 411008India
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4
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Tucker BA, Hudson JS, Ding L, Lewis E, Sheardy RD, Kharlampieva E, Graves D. Stability of the Na + Form of the Human Telomeric G-Quadruplex: Role of Adenines in Stabilizing G-Quadruplex Structure. ACS OMEGA 2018; 3:844-855. [PMID: 30023791 PMCID: PMC6045420 DOI: 10.1021/acsomega.7b01649] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 10/26/2017] [Accepted: 01/09/2018] [Indexed: 06/08/2023]
Abstract
G-quadruplexes are higher order DNA structures that play significant roles in gene transcription and telomeric maintenance. The formation and stability of the G-quadruplex structures are under thermodynamic control and may be of biological significance for regulatory function of cellular processes. Here, we report the structural influence and energetic contributions of the adenine bases in the loop sequences that flank G-repeats in human telomeric DNA sequence. Spectroscopic and calorimetric techniques are used to measure the thermal stability and thermodynamic contributions to the stability of human telomeric G-quadruplexes that have been designed with systematic changes of A to T throughout the telomeric sequence. These studies demonstrate that the thermal stability of the G-quadruplex structure is directly related to the number and position of the adenines that are present in the telomeric sequence. The melting temperature (Tm) was reduced from 59 °C for the wild-type sequence to 47 °C for the sequence where all four adenines were replaced with thymines (0123TTT). Furthermore, the enthalpy required for transitioning from the folded to unfolded G-quadruplex structure was reduced by 15 kcal/mol when the adenines were replaced with thymines (37 kcal/mol for the wild-type telomeric sequence reduced to 22 kcal/mol for the sequence where all four adenines were replaced with thymines (0123TTT)). The circular dichroism melting studies for G-quadruplex sequences having a single A to T change showed significantly sloping pretransition baselines and their differential scanning calorimetry (DSC) thermograms revealed biphasic melting profiles. In contrast, the deoxyoligonucleotides having sequences with two or more A to T changes did not exhibit sloping baselines or biphasic DSC thermograms. We attribute the biphasic unfolding profile and reduction in the enthalpy of unfolding to the energetic contributions of adenine hydrogen bonding within the loops as well as the adenine stacking to the G-tetrads of the G-quadruplex structure.
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Affiliation(s)
- Brenna A. Tucker
- Department
of Chemistry, Department of Biochemistry and Molecular Genetics, and Comprehensive
Cancer Center, University of Alabama at
Birmingham, Birmingham, Alabama 35294, United States
| | - Jason S. Hudson
- Department
of Chemistry, Department of Biochemistry and Molecular Genetics, and Comprehensive
Cancer Center, University of Alabama at
Birmingham, Birmingham, Alabama 35294, United States
| | - Lei Ding
- Department
of Chemistry, Department of Biochemistry and Molecular Genetics, and Comprehensive
Cancer Center, University of Alabama at
Birmingham, Birmingham, Alabama 35294, United States
| | - Edwin Lewis
- Department
of Chemistry, Mississippi State University, Mississippi, Mississippi
State 39762, United
States
| | - Richard D. Sheardy
- Department
of Chemistry & Biochemistry, Texas Women’s
University, Denton, Texas 782042, United States
| | - Eugenia Kharlampieva
- Department
of Chemistry, Department of Biochemistry and Molecular Genetics, and Comprehensive
Cancer Center, University of Alabama at
Birmingham, Birmingham, Alabama 35294, United States
| | - David Graves
- Department
of Chemistry, Department of Biochemistry and Molecular Genetics, and Comprehensive
Cancer Center, University of Alabama at
Birmingham, Birmingham, Alabama 35294, United States
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5
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Guan AJ, Shen MJ, Zhang EX, Li Q, Wang LX, Xu LJ, Xiang JF, Tang YL. Stabilizing G-quadruplex DNA by methylazacalix[ n ]pyridine through shape-complementary interaction. Bioorg Med Chem Lett 2016; 26:609-612. [DOI: 10.1016/j.bmcl.2015.11.062] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 11/16/2015] [Accepted: 11/19/2015] [Indexed: 11/26/2022]
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6
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Bazzi S, Novotný J, Yurenko YP, Marek R. Designing a New Class of Bases for Nucleic Acid Quadruplexes and Quadruplex-Active Ligands. Chemistry 2015; 21:9414-25. [PMID: 26032561 DOI: 10.1002/chem.201500743] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2015] [Indexed: 01/13/2023]
Abstract
A new class of quadruplex nucleobases, derived from 3-deazaguanine, has been designed for various applications as smart quadruplex ligands as well as quadruplex-based aptamers, receptors, and sensors. An efficient strategy for modifying the guanine quadruplex core has been developed and tested by using quantum chemistry methods. Several potential guanine derivatives modified at the 3- or 8-position or both are analyzed, and the results compared to reference systems containing natural guanine. Analysis of the formation energies (BLYP-D3(BJ)/def2-TZVPP level of theory, in combination with the COSMO model for water) in model systems consisting of two and three stacked tetrads with Na(+) /K(+) ion(s) inside the internal channel indicates that the formation of structures with 3-halo-3-deazaguanine bases leads to a substantial gain in energy, as compared to the corresponding reference guanine complexes. The results cast light on changes in the noncovalent interactions (hydrogen bonding, stacking, and ion coordination) in a quadruplex stem upon modification of the guanine core. In particular, the enhanced stability of the modified quadruplexes was shown to originate mainly from increased π-π stacking. Our study suggests the 3-halo-3-deazaguanine skeleton as a potential building unit for quadruplex systems and smart G-quadruplex ligands.
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Affiliation(s)
- Sophia Bazzi
- CEITEC-Central European Institute of Technology, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic).,National Center for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic)
| | - Jan Novotný
- CEITEC-Central European Institute of Technology, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic)
| | - Yevgen P Yurenko
- CEITEC-Central European Institute of Technology, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic)
| | - Radek Marek
- CEITEC-Central European Institute of Technology, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic). .,National Center for Biomolecular Research, Faculty of Science, Masaryk University, Kamenice 5, 62500 Brno (Czech Republic).
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7
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Nezu T, Hosomi N, Takahashi T, Anno K, Aoki S, Shimamoto A, Maruyama H, Hayashi T, Matsumoto M, Tahara H. Telomere G-tail Length is a Promising Biomarker Related to White Matter Lesions and Endothelial Dysfunction in Patients With Cardiovascular Risk: A Cross-sectional Study. EBioMedicine 2015; 2:960-7. [PMID: 26425704 PMCID: PMC4563121 DOI: 10.1016/j.ebiom.2015.05.025] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2015] [Revised: 05/22/2015] [Accepted: 05/27/2015] [Indexed: 12/19/2022] Open
Abstract
Background The telomeric 3′-overhang (G-tail) length is essential for the biological effects of telomere dysfunction in vitro, but the association of length with aging and cardiovascular risk is unclear in humans. We investigated the association between the telomere G-tail length of leukocytes and cardiovascular risk, age-related white matter changes (ARWMCs), and endothelial function. Methods Patients with a history of cerebrovascular disease and comorbidity were enrolled (n = 102; 69 males and 33 females, 70.1 ± 9.2 years). Total telomere and telomere G-tail lengths were measured using a hybridization protection assay. Endothelial function was evaluated by ultrasound assessment of brachial flow-mediated dilation (FMD). Findings Shortened telomere G-tail length was associated with age and Framingham risk score (P = 0.018 and P = 0.012). In addition, telomere G-tail length was positively correlated with FMD values (P = 0.031) and negatively with the severity of ARWMCs (P = 0.002). On multivariate regression analysis, telomere G-tail length was independently associated with FMD values (P = 0.022) and the severity of ARWMCs (P = 0.033), whereas total telomere length was not associated with these indicators. Interpretation Telomere G-tail length is associated with age and vascular risk factors, and might be superior to total telomere length as a marker of endothelial dysfunction and ARWMC severity. Telomere G-tail length was measured using a hybridization protection assay in patients with vascular risk factors. Telomere G-tail length was independently related to endothelial function and age-related white matter changes. Telomere G-tail length might be a promising biomarker of vascular damage.
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Affiliation(s)
- Tomohisa Nezu
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Naohisa Hosomi
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Tetsuya Takahashi
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Kumiko Anno
- Department of Cellular and Molecular Biology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Shiro Aoki
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Akira Shimamoto
- Department of Cellular and Molecular Biology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
| | - Hirofumi Maruyama
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Tomonori Hayashi
- Department of Radiobiology/Molecular Epidemiology, Radiation Effects Research Foundation, Hiroshima, Japan
| | - Masayasu Matsumoto
- Department of Clinical Neuroscience and Therapeutics, Hiroshima University Graduate School of Biomedical and Health Sciences, Hiroshima, Japan
| | - Hidetoshi Tahara
- Department of Cellular and Molecular Biology, Institute of Biomedical & Health Sciences, Hiroshima University, Hiroshima, Japan
- Corresponding author at: Department of Cellular and Molecular Biology, Institute of Biomedical & Health Sciences, Hiroshima University, 1-2-3 Kasumi, Minami-ku, Hiroshima 734-8553, Japan.
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8
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Iida K, Majima S, Nakamura T, Seimiya H, Nagasawa K. Evaluation of the interaction between long telomeric DNA and macrocyclic hexaoxazole (6OTD) dimer of a G-quadruplex ligand. Molecules 2013; 18:4328-41. [PMID: 23584054 PMCID: PMC6269967 DOI: 10.3390/molecules18044328] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/2013] [Revised: 04/02/2013] [Accepted: 04/09/2013] [Indexed: 11/19/2022] Open
Abstract
Macrocyclic hexaoxazole dimer of L2H2-6OTD-dimer (3) was newly synthesized as a telomeric G-quadruplex (G4) ligand, and interaction with long telomeric DNAs telo48, 72, and 96 was evaluated by means of electrophoresis mobility shift assay, CD spectra analysis, and CD melting experiments. The L2H2-6OTD-dimer (3) interacted with the long telomeric DNAs by inducing anti-parallel type G4 structure of each unit of 24 bases, i.e., (TTAGGG)₄ sequences. Dimer 3 stabilizes long telomeric DNAs more efficiently than the corresponding monomer of L2H2-6OTD (2). It showed potent inhibitory activity against telomerase, with an IC₅₀ value of 7.5 nm.
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Affiliation(s)
- Keisuke Iida
- Faculty of Technology, Tokyo University of Agriculture and Technology (TUAT), 2-24-16 Naka-cho, Koganei-shi, Tokyo 185-0031, Japan
| | - Satoki Majima
- Faculty of Technology, Tokyo University of Agriculture and Technology (TUAT), 2-24-16 Naka-cho, Koganei-shi, Tokyo 185-0031, Japan
| | - Takahiro Nakamura
- Faculty of Technology, Tokyo University of Agriculture and Technology (TUAT), 2-24-16 Naka-cho, Koganei-shi, Tokyo 185-0031, Japan
| | - Hiroyuki Seimiya
- Cancer Chemotherapy Center, Japanese Foundation for Cancer Research (JFCR), 3-8-31 Ariake, Koto-ku, Tokyo 135-8550, Japan
| | - Kazuo Nagasawa
- Faculty of Technology, Tokyo University of Agriculture and Technology (TUAT), 2-24-16 Naka-cho, Koganei-shi, Tokyo 185-0031, Japan
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9
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Abstract
G-quartets are square planar arrangements of four guanine bases, which can form extraordinarily stable stacks when present in nucleic acid sequences. Such G-quadruplex structures were long regarded as an in vitro phenomenon, but the widespread presence of suitable sequences in genomes and the identification of proteins that stabilize, modify or resolve these nucleic acid structures have provided circumstantial evidence for their physiological relevance. The therapeutic potential of small molecules that can stabilize or disrupt G-quadruplex structures has invigorated the field in recent years. Here we review some of the key observations that support biological functions for G-quadruplex DNA as well as the techniques and tools that have enabled researchers to probe these structures and their interactions with proteins and small molecules.
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Affiliation(s)
- Tracy M Bryan
- Children's Medical Research Institute, University of Sydney, 214 Hawkesbury Road, Westmead, Sydney, NSW 2145, Australia.
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10
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TCAGG, an alternative telomeric sequence in insects. Chromosoma 2011; 120:367-76. [PMID: 21499744 DOI: 10.1007/s00412-011-0317-x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2010] [Revised: 03/06/2011] [Accepted: 03/06/2011] [Indexed: 10/18/2022]
Abstract
The TTAGG repeat, the only determined telomerase-dependent sequence in the Insecta, is generally reputed to be the canonical telomeric motif within the class. By studying the distribution of telomeric DNAs in 30 coleopteran beetles using Southern hybridization, BAL 31 DNA end-degradation assay and fluorescence in situ hybridization, we showed that arrays built of a TCAGG repeat substitute for (TTAGG)n sequences in all tested species within the superfamily Tenebrionoidea. We also provided the experimental evidence that (TCAGG)n repeats represent the terminal sequences on all chromosomes of the model species Tribolium castaneum. (TCAGG)n repeats are therefore promoted as the first sequence-motif alternative to TTAGG-type chromosome ends in insects. Detection of species negative for both TTAGG and TCAGG reveals that, although widespread, these motifs are not ubiquitous telomeric sequences within the order Coleoptera. In addition, Timarcha balearica proved to be a species that harbors (TTAGG)n repeats, but not at telomeric positions, thus further increasing the complexity of telomeric DNAs. Our experiments discarded CTAGG, CTGGG, TTGGG, and TTAGGG variants as potential replacements in TTAGG/TCAGG-negative species, indicating that chromosome termini of these beetles comprise other form(s) of telomeric sequences and telomere maintenance mechanisms.
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11
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Rudimentary G-quadruplex-based telomere capping in Saccharomyces cerevisiae. Nat Struct Mol Biol 2011; 18:478-85. [PMID: 21399640 DOI: 10.1038/nsmb.2033] [Citation(s) in RCA: 93] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2010] [Accepted: 12/29/2010] [Indexed: 11/08/2022]
Abstract
Telomere capping conceals chromosome ends from exonucleases and checkpoints, but the full range of capping mechanisms is not well defined. Telomeres have the potential to form G-quadruplex (G4) DNA, although evidence for telomere G4 DNA function in vivo is limited. In budding yeast, capping requires the Cdc13 protein and is lost at nonpermissive temperatures in cdc13-1 mutants. Here, we use several independent G4 DNA-stabilizing treatments to suppress cdc13-1 capping defects. These include overexpression of three different G4 DNA binding proteins, loss of the G4 DNA unwinding helicase Sgs1, or treatment with small molecule G4 DNA ligands. In vitro, we show that protein-bound G4 DNA at a 3' overhang inhibits 5'→3' resection of a paired strand by exonuclease I. These findings demonstrate that, at least in the absence of full natural capping, G4 DNA can play a positive role at telomeres in vivo.
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12
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Abstract
Telomeric repeat-containing RNA (referred to as TERRA), a noncoding RNA molecule, has recently been found in mammalian cells. The detailed structural features and function of the TERRA RNA at human chromosome ends remain unclear, although this RNA molecule may be a key component of the telomere machinery. In the present studies, we investigated the structural features of human TERRA RNA in living cells. Using a light-switching pyrene probe, we found that human TERRA RNA forms a parallel G-quadruplex structure in living cells, providing the in vivo evidence for the presence of the G-quadruplex in human TERRA RNA. Furthermore, imaging experiments clearly show that TERRA RNA G-quadruplex localizes to telomere DNA at cell nuclei. These results provide valuable information to allow understanding of the structure and function of human TERRA RNA.
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13
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Bombarde O, Boby C, Gomez D, Frit P, Giraud-Panis MJ, Gilson E, Salles B, Calsou P. TRF2/RAP1 and DNA-PK mediate a double protection against joining at telomeric ends. EMBO J 2010; 29:1573-84. [PMID: 20407424 DOI: 10.1038/emboj.2010.49] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2009] [Accepted: 03/04/2010] [Indexed: 11/09/2022] Open
Abstract
DNA-dependent protein kinase (DNA-PK) is a double-strand breaks repair complex, the subunits of which (KU and DNA-PKcs) are paradoxically present at mammalian telomeres. Telomere fusion has been reported in cells lacking these proteins, raising two questions: how is DNA-PK prevented from initiating classical ligase IV (LIG4)-dependent non-homologous end-joining (C-NHEJ) at telomeres and how is the backup end-joining (EJ) activity (B-NHEJ) that operates at telomeres under conditions of C-NHEJ deficiency controlled? To address these questions, we have investigated EJ using plasmid substrates bearing double-stranded telomeric tracks and human cell extracts with variable C-NHEJ or B-NHEJ activity. We found that (1) TRF2/RAP1 prevents C-NHEJ-mediated end fusion at the initial DNA-PK end binding and activation step and (2) DNA-PK counteracts a potent LIG4-independent EJ mechanism. Thus, telomeres are protected against EJ by a lock with two bolts. These results account for observations with mammalian models and underline the importance of alternative non-classical EJ pathways for telomere fusions in cells.
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Affiliation(s)
- Oriane Bombarde
- Institut de Pharmacologie et de Biologie Structurale, Toulouse, France
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14
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Abstract
G-quartets are square planar arrangements of four guanine bases, which can form extraordinarily stable stacks when present in nucleic acid sequences. Such G-quadruplex structures were long regarded as an in vitro phenomenon, but the widespread presence of suitable sequences in genomes and the identification of proteins that stabilize, modify, or resolve these nucleic acid structures have provided circumstantial evidence for their physiological relevance. The therapeutic potential of small molecules that can stabilize or disrupt G-quadruplex structures has invigorated the field in recent years. Here we review some of the key observations that support biological functions for G-quadruplex DNA as well as the techniques and tools that have enabled researchers to probe these structures and their interactions with proteins and small molecules.
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Affiliation(s)
- Tracy M Bryan
- Children's Medical Research Institute and the University of Sydney, Sydney, Australia
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15
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Xu Y, Ishizuka T, Kurabayashi K, Komiyama M. Consecutive formation of G-quadruplexes in human telomeric-overhang DNA: a protective capping structure for telomere ends. Angew Chem Int Ed Engl 2009; 48:7833-6. [PMID: 19757477 DOI: 10.1002/anie.200903858] [Citation(s) in RCA: 104] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Affiliation(s)
- Yan Xu
- Research Center for Advanced Science and Technology, The University of Tokyo, Komaba, Meguro-ku, Tokyo 153-8904, Japan.
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16
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Xu Y, Ishizuka T, Kurabayashi K, Komiyama M. Consecutive Formation of G-Quadruplexes in Human Telomeric-Overhang DNA: A Protective Capping Structure for Telomere Ends. Angew Chem Int Ed Engl 2009. [DOI: 10.1002/ange.200903858] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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17
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Johnson JE, Smith JS, Kozak ML, Johnson FB. In vivo veritas: using yeast to probe the biological functions of G-quadruplexes. Biochimie 2008; 90:1250-63. [PMID: 18331848 DOI: 10.1016/j.biochi.2008.02.013] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2007] [Accepted: 02/07/2008] [Indexed: 12/20/2022]
Abstract
Certain guanine-rich sequences are capable of forming higher order structures known as G-quadruplexes. Moreover, particular genomic regions in a number of highly divergent organisms are enriched for such sequences, raising the possibility that G-quadruplexes form in vivo and affect cellular processes. While G-quadruplexes have been rigorously studied in vitro, whether these structures actually form in vivo and what their roles might be in the context of the cell have remained largely unanswered questions. Recent studies suggest that G-quadruplexes participate in the regulation of such varied processes as telomere maintenance, transcriptional regulation and ribosome biogenesis. Here we review studies aimed at elucidating the in vivo functions of quadruplex structures, with a particular focus on findings in yeast. In addition, we discuss the utility of yeast model systems in the study of the cellular roles of G-quadruplexes.
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Affiliation(s)
- Jay E Johnson
- Department of Pathology and Laboratory Medicine, University of Pennsylvania School of Medicine, Philadelphia, PA 19104, USA
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Patel DJ, Phan AT, Kuryavyi V. Human telomere, oncogenic promoter and 5'-UTR G-quadruplexes: diverse higher order DNA and RNA targets for cancer therapeutics. Nucleic Acids Res 2007; 35:7429-55. [PMID: 17913750 PMCID: PMC2190718 DOI: 10.1093/nar/gkm711] [Citation(s) in RCA: 734] [Impact Index Per Article: 43.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Guanine-rich DNA sequences can form G-quadruplexes stabilized by stacked G–G–G–G tetrads in monovalent cation-containing solution. The length and number of individual G-tracts and the length and sequence context of linker residues define the diverse topologies adopted by G-quadruplexes. The review highlights recent solution NMR-based G-quadruplex structures formed by the four-repeat human telomere in K+ solution and the guanine-rich strands of c-myc, c-kit and variant bcl-2 oncogenic promoters, as well as a bimolecular G-quadruplex that targets HIV-1 integrase. Such structure determinations have helped to identify unanticipated scaffolds such as interlocked G-quadruplexes, as well as novel topologies represented by double-chain-reversal and V-shaped loops, triads, mixed tetrads, adenine-mediated pentads and hexads and snap-back G-tetrad alignments. The review also highlights the recent identification of guanine-rich sequences positioned adjacent to translation start sites in 5′-untranslated regions (5′-UTRs) of RNA oncogenic sequences. The activity of the enzyme telomerase, which maintains telomere length, can be negatively regulated through G-quadruplex formation at telomeric ends. The review evaluates progress related to ongoing efforts to identify small molecule drugs that bind and stabilize distinct G-quadruplex scaffolds associated with telomeric and oncogenic sequences, and outlines progress towards identifying recognition principles based on several X-ray-based structures of ligand–G-quadruplex complexes.
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Affiliation(s)
- Dinshaw J Patel
- Structural Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10021, USA.
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