1
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Lim CJ. Telomere C-Strand Fill-In Machinery: New Insights into the Human CST-DNA Polymerase Alpha-Primase Structures and Functions. Subcell Biochem 2024; 104:73-100. [PMID: 38963484 DOI: 10.1007/978-3-031-58843-3_5] [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] [Indexed: 07/05/2024]
Abstract
Telomeres at the end of eukaryotic chromosomes are extended by a specialized set of enzymes and telomere-associated proteins, collectively termed here the telomere "replisome." The telomere replisome acts on a unique replicon at each chromosomal end of the telomeres, the 3' DNA overhang. This telomere replication process is distinct from the replisome mechanism deployed to duplicate the human genome. The G-rich overhang is first extended before the complementary C-strand is filled in. This overhang is extended by telomerase, a specialized ribonucleoprotein and reverse transcriptase. The overhang extension process is terminated when telomerase is displaced by CTC1-STN1-TEN1 (CST), a single-stranded DNA-binding protein complex. CST then recruits DNA polymerase α-primase to complete the telomere replication process by filling in the complementary C-strand. In this chapter, the recent structure-function insights into the human telomere C-strand fill-in machinery (DNA polymerase α-primase and CST) will be discussed.
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Affiliation(s)
- Ci Ji Lim
- Department of Biochemistry, College of Agricultural and Life Sciences, University of Wisconsin-Madison, Madison, WI, USA.
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2
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Moreno SP, Fusté JM, Kaiser M, Li JSZ, Nassour J, Haggblom C, Denchi EL, Karlseder J. TZAP overexpression induces telomere dysfunction and ALT-like activity in ATRX/DAXX-deficient cells. iScience 2023; 26:106405. [PMID: 37013192 PMCID: PMC10066556 DOI: 10.1016/j.isci.2023.106405] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2022] [Revised: 11/13/2022] [Accepted: 03/10/2023] [Indexed: 03/14/2023] Open
Abstract
The appropriate regulation of telomere length homeostasis is crucial for the maintenance of genome integrity. The telomere-binding protein TZAP has been suggested to regulate telomere length by promoting t-circle and c-circle excisions through telomere trimming, yet the molecular mechanisms by which TZAP functions at telomeres are not understood. Using a system based on TZAP overexpression, we show that efficient TZAP recruitment to telomeres occurs in the context of open telomeric chromatin caused by loss of ATRX/DAXX independently of H3.3 deposition. Moreover, our data indicate that TZAP binding to telomeres induces telomere dysfunction and ALT-like activity, resulting in the generation of t-circles and c-circles in a Bloom-Topoisomerase IIIα-RMI1-RMI2 (BTR)-dependent manner.
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Affiliation(s)
- Sara Priego Moreno
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Javier Miralles Fusté
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Melanie Kaiser
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Julia Su Zhou Li
- The Ludwig Institute for Cancer Research, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
| | - Joe Nassour
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Candy Haggblom
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
| | - Eros Lazzerini Denchi
- Laboratory for Genome Integrity, National Cancer Institute, Building 37, Room 2144B, Bethesda, MD 20892, USA
| | - Jan Karlseder
- The Salk Institute for Biological Studies, Molecular and Cell Biology Department, 10010 N. Torrey pines Road, La Jolla, CA 92037, USA
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3
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Sohn EJ, Goralsky JA, Shay JW, Min J. The Molecular Mechanisms and Therapeutic Prospects of Alternative Lengthening of Telomeres (ALT). Cancers (Basel) 2023; 15:cancers15071945. [PMID: 37046606 PMCID: PMC10093677 DOI: 10.3390/cancers15071945] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2023] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 04/14/2023] Open
Abstract
As detailed by the end replication problem, the linear ends of a cell's chromosomes, known as telomeres, shorten with each successive round of replication until a cell enters into a state of growth arrest referred to as senescence. To maintain their immortal proliferation capacity, cancer cells must employ a telomere maintenance mechanism, such as telomerase activation or the Alternative Lengthening of Telomeres pathway (ALT). With only 10-15% of cancers utilizing the ALT mechanism, progress towards understanding its molecular components and associated hallmarks has only recently been made. This review analyzes the advances towards understanding the ALT pathway by: (1) detailing the mechanisms associated with engaging the ALT pathway as well as (2) identifying potential therapeutic targets of ALT that may lead to novel cancer therapeutic treatments. Collectively, these studies indicate that the ALT molecular mechanisms involve at least two distinct pathways induced by replication stress and damage at telomeres. We suggest exploiting tumor dependency on ALT is a promising field of study because it suggests new approaches to ALT-specific therapies for cancers with poorer prognosis. While substantial progress has been made in the ALT research field, additional progress will be required to realize these advances into clinical practices to treat ALT cancers and improve patient prognoses.
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Affiliation(s)
- Eric J Sohn
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Julia A Goralsky
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
| | - Jerry W Shay
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390-9039, USA
| | - Jaewon Min
- Institute for Cancer Genetics, Columbia University Irving Medical Center, New York, NY 10032, USA
- Department of Pathology and Cell Biology, Columbia University Irving Medical Center, New York, NY 10032, USA
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4
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Aguilera P, López-Contreras AJ. ATRX, a guardian of chromatin. Trends Genet 2023; 39:505-519. [PMID: 36894374 DOI: 10.1016/j.tig.2023.02.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2022] [Revised: 02/07/2023] [Accepted: 02/14/2023] [Indexed: 03/09/2023]
Abstract
ATRX (alpha-thalassemia mental retardation X-linked) is one of the most frequently mutated tumor suppressor genes in human cancers, especially in glioma, and recent findings indicate roles for ATRX in key molecular pathways, such as the regulation of chromatin state, gene expression, and DNA damage repair, placing ATRX as a central player in the maintenance of genome stability and function. This has led to new perspectives about the functional role of ATRX and its relationship with cancer. Here, we provide an overview of ATRX interactions and molecular functions and discuss the consequences of its impairment, including alternative lengthening of telomeres and therapeutic vulnerabilities that may be exploited in cancer cells.
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Affiliation(s)
- Paula Aguilera
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Consejo Superior de Investigaciones Científicas (CSIC), Universidad de Sevilla - Universidad Pablo de Olavide, Seville, Spain.
| | - Andrés J López-Contreras
- Centro Andaluz de Biología Molecular y Medicina Regenerativa (CABIMER), Consejo Superior de Investigaciones Científicas (CSIC), Universidad de Sevilla - Universidad Pablo de Olavide, Seville, Spain.
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5
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Wieser TA, Wuttke DS. Replication Protein A Utilizes Differential Engagement of Its DNA-Binding Domains to Bind Biologically Relevant ssDNAs in Diverse Binding Modes. Biochemistry 2022; 61:2592-2606. [PMID: 36278947 PMCID: PMC9798700 DOI: 10.1021/acs.biochem.2c00504] [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] [Indexed: 12/31/2022]
Abstract
Replication protein A (RPA) is a ubiquitous ssDNA-binding protein that functions in many DNA processing pathways to maintain genome integrity. Recent studies suggest that RPA forms a highly dynamic complex with ssDNA that can engage with DNA in many modes that are orchestrated by the differential engagement of the four DNA-binding domains (DBDs) in RPA. To understand how these modes influence RPA interaction with biologically relevant ligands, we performed a comprehensive and systematic evaluation of RPA's binding to a diverse set of ssDNA ligands that varied in sequence, length, and structure. These equilibrium binding data show that WT RPA binds structured ssDNA ligands differently from its engagement with minimal ssDNAs. Next, we investigated each DBD's contributions to RPA's binding modes through mutation of conserved, functionally important aromatic residues. Mutations in DBD-A and -B have a much larger effect on binding when ssDNA is embedded into DNA secondary structures compared to their association with unstructured minimal ssDNA. As our data support a complex interplay of binding modes, it is critical to define the trimer core DBDs' role in binding these biologically relevant ligands. We found that DBD-C is important for engaging DNA with diverse binding modes, including, unexpectedly, at short ssDNAs. Thus, RPA uses its constituent DBDs to bind biologically diverse ligands in unanticipated ways. These findings lead to a better understanding of how RPA carries out its functions at diverse locations of the genome and suggest a mechanism through which dynamic recognition can impact differential downstream outcomes.
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Affiliation(s)
- Thomas A Wieser
- Department of Biochemistry, University of Colorado Boulder, Jennie Smoly Caruthers Biotechnology Building, UCB 596, Boulder, Colorado80309, United States
| | - Deborah S Wuttke
- Department of Biochemistry, University of Colorado Boulder, Jennie Smoly Caruthers Biotechnology Building, UCB 596, Boulder, Colorado80309, United States
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6
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Searching for New Z-DNA/Z-RNA Binding Proteins Based on Structural Similarity to Experimentally Validated Zα Domain. Int J Mol Sci 2022; 23:ijms23020768. [PMID: 35054954 PMCID: PMC8775963 DOI: 10.3390/ijms23020768] [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: 11/30/2021] [Revised: 01/03/2022] [Accepted: 01/05/2022] [Indexed: 11/17/2022] Open
Abstract
Z-DNA and Z-RNA are functionally important left-handed structures of nucleic acids, which play a significant role in several molecular and biological processes including DNA replication, gene expression regulation and viral nucleic acid sensing. Most proteins that have been proven to interact with Z-DNA/Z-RNA contain the so-called Zα domain, which is structurally well conserved. To date, only eight proteins with Zα domain have been described within a few organisms (including human, mouse, Danio rerio, Trypanosoma brucei and some viruses). Therefore, this paper aimed to search for new Z-DNA/Z-RNA binding proteins in the complete PDB structures database and from the AlphaFold2 protein models. A structure-based similarity search found 14 proteins with highly similar Zα domain structure in experimentally-defined proteins and 185 proteins with a putative Zα domain using the AlphaFold2 models. Structure-based alignment and molecular docking confirmed high functional conservation of amino acids involved in Z-DNA/Z-RNA, suggesting that Z-DNA/Z-RNA recognition may play an important role in a variety of cellular processes.
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7
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Frank L, Rademacher A, Mücke N, Tirier SM, Koeleman E, Knotz C, Schumacher S, Stainczyk S, Westermann F, Fröhling S, Chudasama P, Rippe K. OUP accepted manuscript. Nucleic Acids Res 2022; 50:e61. [PMID: 35188570 PMCID: PMC9226501 DOI: 10.1093/nar/gkac113] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2021] [Revised: 02/01/2022] [Accepted: 02/05/2022] [Indexed: 11/14/2022] Open
Abstract
Alternative lengthening of telomeres (ALT) occurs in ∼10% of cancer entities. However, little is known about the heterogeneity of ALT activity since robust ALT detection assays with high-throughput in situ readouts are lacking. Here, we introduce ALT-FISH, a method to quantitate ALT activity in single cells from the accumulation of single-stranded telomeric DNA and RNA. It involves a one-step fluorescent in situ hybridization approach followed by fluorescence microscopy imaging. Our method reliably identified ALT in cancer cell lines from different tumor entities and was validated in three established models of ALT induction and suppression. Furthermore, we successfully applied ALT-FISH to spatially resolve ALT activity in primary tissue sections from leiomyosarcoma and neuroblastoma tumors. Thus, our assay provides insights into the heterogeneity of ALT tumors and is suited for high-throughput applications, which will facilitate screening for ALT-specific drugs.
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Affiliation(s)
- Lukas Frank
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Anne Rademacher
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Norbert Mücke
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Stephan M Tirier
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Emma Koeleman
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Caroline Knotz
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Sabrina Schumacher
- Division of Chromatin Networks, German Cancer Research Center (DKFZ) and Bioquant, Heidelberg, Germany
| | - Sabine A Stainczyk
- Hopp Children's Cancer Center (KiTZ), Heidelberg, Germany
- Division of Neuroblastoma Genomics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Frank Westermann
- Hopp Children's Cancer Center (KiTZ), Heidelberg, Germany
- Division of Neuroblastoma Genomics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Stefan Fröhling
- Division of Translational Medical Oncology, National Center for Tumor Diseases (NCT) Heidelberg and German Cancer Research Center (DKFZ), Heidelberg, Germany
- German Cancer Consortium (DKTK), Heidelberg, Germany
| | - Priya Chudasama
- Precision Sarcoma Research Group, German Cancer Research Center (DKFZ) and National Center for Tumor Diseases (NCT), Heidelberg, Germany
| | - Karsten Rippe
- To whom correspondence should be addressed. Tel: +49 6221 5451450;
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8
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Gain-of-Function Mutations in RPA1 Cause a Syndrome with Short Telomeres and Somatic Genetic Rescue. Blood 2021; 139:1039-1051. [PMID: 34767620 PMCID: PMC8854676 DOI: 10.1182/blood.2021011980] [Citation(s) in RCA: 28] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2021] [Accepted: 10/15/2021] [Indexed: 11/20/2022] Open
Abstract
Germline RPA1 gain-of-function missense mutations result in a telomere biology disorder phenotype. Somatic rescue events arise in hematopoiesis secondary to germline RPA1 mutation.
Human telomere biology disorders (TBD)/short telomere syndromes (STS) are heterogeneous disorders caused by inherited loss-of-function mutations in telomere-associated genes. Here, we identify 3 germline heterozygous missense variants in the RPA1 gene in 4 unrelated probands presenting with short telomeres and varying clinical features of TBD/STS, including bone marrow failure, myelodysplastic syndrome, T- and B-cell lymphopenia, pulmonary fibrosis, or skin manifestations. All variants cluster to DNA-binding domain A of RPA1 protein. RPA1 is a single-strand DNA-binding protein required for DNA replication and repair and involved in telomere maintenance. We showed that RPA1E240K and RPA1V227A proteins exhibit increased binding to single-strand and telomeric DNA, implying a gain in DNA-binding function, whereas RPA1T270A has binding properties similar to wild-type protein. To study the mutational effect in a cellular system, CRISPR/Cas9 was used to knock-in the RPA1E240K mutation into healthy inducible pluripotent stem cells. This resulted in severe telomere shortening and impaired hematopoietic differentiation. Furthermore, in patients with RPA1E240K, we discovered somatic genetic rescue in hematopoietic cells due to an acquired truncating cis RPA1 mutation or a uniparental isodisomy 17p with loss of mutant allele, coinciding with stabilized blood counts. Using single-cell sequencing, the 2 somatic genetic rescue events were proven to be independently acquired in hematopoietic stem cells. In summary, we describe the first human disease caused by germline RPA1 variants in individuals with TBD/STS.
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9
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Shiromoto Y, Sakurai M, Minakuchi M, Ariyoshi K, Nishikura K. ADAR1 RNA editing enzyme regulates R-loop formation and genome stability at telomeres in cancer cells. Nat Commun 2021; 12:1654. [PMID: 33712600 PMCID: PMC7955049 DOI: 10.1038/s41467-021-21921-x] [Citation(s) in RCA: 46] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2020] [Accepted: 02/19/2021] [Indexed: 12/12/2022] Open
Abstract
ADAR1 is involved in adenosine-to-inosine RNA editing. The cytoplasmic ADAR1p150 edits 3'UTR double-stranded RNAs and thereby suppresses induction of interferons. Loss of this ADAR1p150 function underlies the embryonic lethality of Adar1 null mice, pathogenesis of the severe autoimmune disease Aicardi-Goutières syndrome, and the resistance developed in cancers to immune checkpoint blockade. In contrast, the biological functions of the nuclear-localized ADAR1p110 remain largely unknown. Here, we report that ADAR1p110 regulates R-loop formation and genome stability at telomeres in cancer cells carrying non-canonical variants of telomeric repeats. ADAR1p110 edits the A-C mismatches within RNA:DNA hybrids formed between canonical and non-canonical variant repeats. Editing of A-C mismatches to I:C matched pairs facilitates resolution of telomeric R-loops by RNase H2. This ADAR1p110-dependent control of telomeric R-loops is required for continued proliferation of telomerase-reactivated cancer cells, revealing the pro-oncogenic nature of ADAR1p110 and identifying ADAR1 as a promising therapeutic target of telomerase positive cancers.
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Affiliation(s)
| | - Masayuki Sakurai
- The Wistar Institute, Philadelphia, PA, USA.,Research Institute for Biomedical Sciences, Tokyo University of Science, Chiba, Japan
| | | | - Kentaro Ariyoshi
- The Wistar Institute, Philadelphia, PA, USA.,Integrated Center for Science and Humanities, Fukushima Medical University, Fukushima, Japan
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10
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Mentegari E, Bertoletti F, Kissova M, Zucca E, Galli S, Tagliavini G, Garbelli A, Maffia A, Bione S, Ferrari E, d’Adda di Fagagna F, Francia S, Sabbioneda S, Chen LY, Lingner J, Bergoglio V, Hoffmann JS, Hübscher U, Crespan E, Maga G. A Role for Human DNA Polymerase λ in Alternative Lengthening of Telomeres. Int J Mol Sci 2021; 22:ijms22052365. [PMID: 33673424 PMCID: PMC7956399 DOI: 10.3390/ijms22052365] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2021] [Revised: 02/13/2021] [Accepted: 02/23/2021] [Indexed: 12/15/2022] Open
Abstract
Telomerase negative cancer cell types use the Alternative Lengthening of Telomeres (ALT) pathway to elongate telomeres ends. Here, we show that silencing human DNA polymerase (Pol λ) in ALT cells represses ALT activity and induces telomeric stress. In addition, replication stress in the absence of Pol λ, strongly affects the survival of ALT cells. In vitro, Pol λ can promote annealing of even a single G-rich telomeric repeat to its complementary strand and use it to prime DNA synthesis. The noncoding telomeric repeat containing RNA TERRA and replication protein A negatively regulate this activity, while the Protection of Telomeres protein 1 (POT1)/TPP1 heterodimer stimulates Pol λ. Pol λ associates with telomeres and colocalizes with TPP1 in cells. In summary, our data suggest a role of Pol λ in the maintenance of telomeres by the ALT mechanism.
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Affiliation(s)
- Elisa Mentegari
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Federica Bertoletti
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Miroslava Kissova
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Elisa Zucca
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Silvia Galli
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Giulia Tagliavini
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Anna Garbelli
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Antonio Maffia
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Silvia Bione
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Elena Ferrari
- Department of Molecular Mechanisms of Disease, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland; (E.F.); (U.H.)
| | - Fabrizio d’Adda di Fagagna
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
- IFOM-The FIRC Institute of Molecular Oncology, 20139 Milan, Italy
| | - Sofia Francia
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Simone Sabbioneda
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
| | - Liuh-Yow Chen
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Frontiers in Genetics National Center of Competence in Research, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 19, CH-1015 Lausanne, Switzerland; (L.-Y.C.); (J.L.)
| | - Joachim Lingner
- Swiss Institute for Experimental Cancer Research (ISREC), School of Life Sciences, Frontiers in Genetics National Center of Competence in Research, Ecole Polytechnique Fédérale de Lausanne (EPFL), Station 19, CH-1015 Lausanne, Switzerland; (L.-Y.C.); (J.L.)
| | - Valerie Bergoglio
- UMR1037 INSERM, Cancer Research Center of Toulouse, 2 Avenue Curien, 31037 Toulouse, France;
| | - Jean-Sébastien Hoffmann
- Laboratoire d’Excellence Toulouse Cancer (TOUCAN), Laboratoire de Pathologie, Institut Universitaire du Cancer-Toulouse, Oncopole, 1 Avenue Irène-Joliot-Curie, 31059 Toulouse, France;
| | - Ulrich Hübscher
- Department of Molecular Mechanisms of Disease, University of Zürich-Irchel, Winterthurerstrasse 190, CH-8057 Zürich, Switzerland; (E.F.); (U.H.)
| | - Emmanuele Crespan
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
- Correspondence: (E.C.); (G.M.)
| | - Giovanni Maga
- Institute of Molecular Genetics IGM-CNR “Luigi Luca Cavalli-Sforza”, via Abbiategrasso 207, 27100 Pavia, Italy; (E.M.); (F.B.); (M.K.); (E.Z.); (S.G.); (G.T.); (A.G.); (A.M.); (S.B.); (F.d.d.F.); (S.F.); (S.S.)
- Correspondence: (E.C.); (G.M.)
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11
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Raghunandan M, Geelen D, Majerova E, Decottignies A. NHP2 downregulation counteracts hTR-mediated activation of the DNA damage response at ALT telomeres. EMBO J 2021; 40:e106336. [PMID: 33595114 DOI: 10.15252/embj.2020106336] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2020] [Revised: 01/15/2021] [Accepted: 01/18/2021] [Indexed: 11/09/2022] Open
Abstract
About 10% of cancer cells employ the "alternative lengthening of telomeres" (ALT) pathway instead of re-activating the hTERT subunit of human telomerase. The hTR RNA subunit is also abnormally silenced in some ALT+ cells not expressing hTERT, suggesting a possible negative non-canonical impact of hTR on ALT. Indeed, we show that ectopically expressed hTR reduces phosphorylation of ssDNA-binding protein RPA (p-RPAS33 ) at ALT telomeres by promoting the hnRNPA1- and DNA-PK-dependent depletion of RPA. The resulting defective ATR checkpoint signaling at telomeres impairs recruitment of the homologous recombination protein, RAD51. This induces ALT telomere fragility, increases POLD3-dependent C-circle production, and promotes the recruitment of the DNA damage marker 53BP1. In ALT+ cells that naturally retain hTR expression, NHP2 H/ACA ribonucleoprotein levels are downregulated, likely in order to restrain DNA damage response (DDR) activation at telomeres through reduced 53BP1 recruitment. This unexpected role of NHP2 is independent from hTR's non-canonical function in modulating telomeric p-RPAS33 . Collectively, our study shines new light on the interference between telomerase- and ALT-dependent pathways and unravels a crucial role for hTR and NHP2 in DDR regulation at ALT telomeres.
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Affiliation(s)
- Maya Raghunandan
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université catholique de Louvain, Brussels, Belgium
| | - Dan Geelen
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université catholique de Louvain, Brussels, Belgium
| | - Eva Majerova
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université catholique de Louvain, Brussels, Belgium
| | - Anabelle Decottignies
- Genetic and Epigenetic Alterations of Genomes, de Duve Institute, Faculty of Pharmacy and Biomedical Sciences, Université catholique de Louvain, Brussels, Belgium
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12
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Functional Diversification of Replication Protein A Paralogs and Telomere Length Maintenance in Arabidopsis. Genetics 2020; 215:989-1002. [PMID: 32532801 DOI: 10.1534/genetics.120.303222] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2020] [Accepted: 06/05/2020] [Indexed: 12/14/2022] Open
Abstract
Replication protein A (RPA) is essential for many facets of DNA metabolism. The RPA gene family expanded in Arabidopsis thaliana with five phylogenetically distinct RPA1 subunits (RPA1A-E), two RPA2 (RPA2A and B), and two RPA3 (RPA3A and B). RPA1 paralogs exhibit partial redundancy and functional specialization in DNA replication (RPA1B and RPA1D), repair (RPA1C and RPA1E), and meiotic recombination (RPA1A and RPA1C). Here, we show that RPA subunits also differentially impact telomere length set point. Loss of RPA1 resets bulk telomeres at a shorter length, with a functional hierarchy for replication group over repair and meiosis group RPA1 subunits. Plants lacking RPA2A, but not RPA2B, harbor short telomeres similar to the replication group. Telomere shortening does not correlate with decreased telomerase activity or deprotection of chromosome ends in rpa mutants. However, in vitro assays show that RPA1B2A3B unfolds telomeric G-quadruplexes known to inhibit replications fork progression. We also found that ATR deficiency can partially rescue short telomeres in rpa2a mutants, although plants exhibit defects in growth and development. Unexpectedly, the telomere shortening phenotype of rpa2a mutants is completely abolished in plants lacking the RTEL1 helicase. RTEL1 has been implicated in a variety of nucleic acid transactions, including suppression of homologous recombination. Thus, the lack of telomere shortening in rpa2a mutants upon RTEL1 deletion suggests that telomere replication defects incurred by loss of RPA may be bypassed by homologous recombination. Taken together, these findings provide new insight into how RPA cooperates with replication and recombination machinery to sustain telomeric DNA.
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13
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Alternative Lengthening of Telomeres: Building Bridges To Connect Chromosome Ends. Trends Cancer 2020; 6:247-260. [PMID: 32101727 DOI: 10.1016/j.trecan.2019.12.009] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 12/16/2019] [Accepted: 12/19/2019] [Indexed: 12/15/2022]
Abstract
Alternative lengthening of telomeres (ALT) is a mechanism of telomere maintenance that is observed in many of the most recalcitrant cancer subtypes. Telomeres in ALT cancer cells exhibit a distinctive nucleoprotein architecture shaped by the mismanagement of chromatin that fosters cycles of DNA damage and replicative stress that activate homology-directed repair (HDR). Mutations in specific chromatin-remodeling factors appear to be key determinants of the emergence and survival of ALT cancer cells. However, these may represent vulnerabilities for the targeted elimination of ALT cancer cells that infiltrate tissues and organs to become devastating tumors. In this review we examine recent findings that provide new insights into the factors and mechanisms that mediate telomere length maintenance and survival of ALT cancer cells.
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14
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Lai Y, Zhu M, Wu W, Rokutanda N, Togashi Y, Liang W, Ohta T. HERC2 regulates RPA2 by mediating ATR-induced Ser33 phosphorylation and ubiquitin-dependent degradation. Sci Rep 2019; 9:14257. [PMID: 31582797 PMCID: PMC6776656 DOI: 10.1038/s41598-019-50812-x] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2019] [Accepted: 09/19/2019] [Indexed: 01/26/2023] Open
Abstract
Replication protein A (RPA) binds to and stabilizes single-stranded DNA and is essential for the genome stability. We reported that an E3 ubiquitin ligase, HERC2, suppresses G-quadruplex (G4) DNA by regulating RPA-helicase complexes. However, the precise mechanism of HERC2 on RPA is as yet largely unknown. Here, we show essential roles for HERC2 on RPA2 status: induction of phosphorylation and degradation of the modified form. HERC2 interacted with RPA through the C-terminal HECT domain. Ubiquitination of RPA2 was inhibited by HERC2 depletion and rescued by reintroduction of the C-terminal fragment of HERC2. ATR-mediated phosphorylation of RPA2 at Ser33 induced by low-level replication stress was inhibited by depletion of HERC2. Contrary, cells lacking HERC2 catalytic residues constitutively expressed an increased level of Ser33-phosphorylated RPA2. HERC2-mediated ubiquitination of RPA2 was abolished by an ATR inhibitor, supporting a hypothesis that the ubiquitinated RPA2 is a phosphorylated subset. Functionally, HERC2 E3 activity has an epistatic relationship with RPA in the suppression of G4 when judged with siRNA knockdown experiments. Together, these results suggest that HERC2 fine-tunes ATR-phosphorylated RPA2 levels through induction and degradation, a mechanism that could be critical for the suppression of secondary DNA structures during cell proliferation.
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Affiliation(s)
- Yongqiang Lai
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.,Department of General Surgery, The People's Hospital of Gaoming District of Foshan City, Foshan city, Guangdong province, China
| | - Mingzhang Zhu
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.,Department of General Surgery, The People's Hospital of Gaoming District of Foshan City, Foshan city, Guangdong province, China
| | - Wenwen Wu
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Nana Rokutanda
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.,Oncology TA Division/Research & Development, AstraZeneca Japan, Osaka, Japan
| | - Yukiko Togashi
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Weixin Liang
- Department of General Surgery, The People's Hospital of Gaoming District of Foshan City, Foshan city, Guangdong province, China
| | - Tomohiko Ohta
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.
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15
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Investigation of Precise Molecular Mechanistic Action of Tobacco-Associated Carcinogen `NNK´ Induced Carcinogenesis: A System Biology Approach. Genes (Basel) 2019; 10:genes10080564. [PMID: 31357510 PMCID: PMC6723528 DOI: 10.3390/genes10080564] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2019] [Revised: 07/22/2019] [Accepted: 07/24/2019] [Indexed: 12/21/2022] Open
Abstract
Cancer is the second deadliest disease listed by the WHO. One of the major causes of cancer disease is tobacco and consumption possibly due to its main component, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK). A plethora of studies have been conducted in the past aiming to decipher the association of NNK with other diseases. However, it is strongly linked with cancer development. Despite these studies, a clear molecular mechanism and the impact of NNK on various system-level networks is not known. In the present study, system biology tools were employed to understand the key regulatory mechanisms and the perturbations that will happen in the cellular processes due to NNK. To investigate the system level influence of the carcinogen, NNK rewired protein–protein interaction network (PPIN) was generated from 544 reported proteins drawn out from 1317 articles retrieved from PubMed. The noise was removed from PPIN by the method of modulation. Gene ontology (GO) enrichment was performed on the seed proteins extracted from various modules to find the most affected pathways by the genes/proteins. For the modulation, Molecular COmplex DEtection (MCODE) was used to generate 19 modules containing 115 seed proteins. Further, scrutiny of the targeted biomolecules was done by the graph theory and molecular docking. GO enrichment analysis revealed that mostly cell cycle regulatory proteins were affected by NNK.
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16
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Abstract
The maintenance of genome stability in eukaryotic cells relies on accurate and efficient replication along each chromosome following every cell division. The terminal position, repetitive sequence, and structural complexities of the telomeric DNA make the telomere an inherently difficult region to replicate within the genome. Thus, despite functioning to protect genome stability mammalian telomeres are also a source of replication stress and have been recognized as common fragile sites within the genome. Telomere fragility is exacerbated at telomeres that rely on the Alternative Lengthening of Telomeres (ALT) pathway. Like common fragile sites, ALT telomeres are prone to chromosome breaks and are frequent sites of recombination suggesting that ALT telomeres are subjected to chronic replication stress. Here, we will review the features of telomeric DNA that challenge the replication machinery and also how the cell overcomes these challenges to maintain telomere stability and ensure the faithful duplication of the human genome.
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Affiliation(s)
- Emily Mason-Osann
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA, USA
- Department of Medicine, Cancer Center, Boston University School of Medicine, Boston, MA, USA
| | - Himabindu Gali
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA, USA
- Department of Medicine, Cancer Center, Boston University School of Medicine, Boston, MA, USA
| | - Rachel Litman Flynn
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA, USA.
- Department of Medicine, Cancer Center, Boston University School of Medicine, Boston, MA, USA.
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17
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Wu W, Rokutanda N, Takeuchi J, Lai Y, Maruyama R, Togashi Y, Nishikawa H, Arai N, Miyoshi Y, Suzuki N, Saeki Y, Tanaka K, Ohta T. HERC2 Facilitates BLM and WRN Helicase Complex Interaction with RPA to Suppress G-Quadruplex DNA. Cancer Res 2018; 78:6371-6385. [PMID: 30279242 DOI: 10.1158/0008-5472.can-18-1877] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2018] [Revised: 08/21/2018] [Accepted: 09/18/2018] [Indexed: 11/16/2022]
Abstract
BLM and WRN are RecQ DNA helicasesessential for genomic stability. Here, we demonstrate that HERC2, a HECT E3 ligase, is critical for their functions to suppress G-quadruplex (G4) DNA. HERC2 interacted with BLM, WRN, and replication protein A (RPA) complexes during the S-phase of the cell cycle. Depletion of HERC2 dissociated RPA from BLM and WRN complexes and significantly increased G4 formation. Triple depletion revealed that HERC2 has an epistatic relationship with BLM and WRN in their G4-suppressing function. In vitro, HERC2 released RPA onto single-stranded DNA (ssDNA) rather than anchoring onto RPA-coated ssDNA. CRISPR/Cas9-mediated deletion of the catalytic ubiquitin-binding site of HERC2 inhibited ubiquitination of RPA2, caused RPA accumulation in the helicase complexes, and increased G4, indicating an essential role for E3 activity in the suppression of G4. Both depletion of HERC2 and inactivation of E3 sensitized cells to the G4-interacting compounds telomestatin and pyridostatin. Overall, these results indicate that HERC2 is a master regulator of G4 suppression that affects the sensitivity of cells to G4 stabilizers. Given that HERC2 expression is frequently reduced in many types of cancers, G4 accumulation as a result of HERC2 deficiency may provide a therapeutic target for G4 stabilizers.Significance: HERC2 is revealed as a master regulator of G-quadruplex, a DNA secondary structure that triggers genomic instability and may serve as a potential molecular target in cancer therapy.Graphical Abstract: http://cancerres.aacrjournals.org/content/canres/78/22/6371/F1.large.jpg Cancer Res; 78(22); 6371-85. ©2018 AACR.
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Affiliation(s)
- Wenwen Wu
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Nana Rokutanda
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Jun Takeuchi
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.,Department of Obstetrics and Gynecology, St. Marianna University School of Medicine, Kawasaki, Japan
| | - Yongqiang Lai
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.,Department of General Surgery, Gaoming People's Hospital in Foshan, Foshan City, Guangdong Province, China
| | - Reo Maruyama
- Project for Cancer Epigenomics, Cancer Institute, Japanese Foundation for Cancer Research, Tokyo, Japan
| | - Yukiko Togashi
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Hiroyuki Nishikawa
- Institute of Advanced Medical Science, St. Marianna University Graduate School of Medicine, Kawasaki, Japan
| | - Naoko Arai
- Laboratory of Protein Metabolism, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Yasuo Miyoshi
- Division of Breast and Endocrine Surgery, Department of Surgery, Hyogo College of Medicine, Hyogo, Japan
| | - Nao Suzuki
- Department of Obstetrics and Gynecology, St. Marianna University School of Medicine, Kawasaki, Japan
| | - Yasushi Saeki
- Laboratory of Protein Metabolism, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Keiji Tanaka
- Laboratory of Protein Metabolism, Tokyo Metropolitan Institute of Medical Science, Tokyo, Japan
| | - Tomohiko Ohta
- Department of Translational Oncology, St. Marianna University Graduate School of Medicine, Kawasaki, Japan.
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18
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Wojtczyk-Miaskowska A, Schlichtholz B. DNA damage and oxidative stress in long-lived aquatic organisms. DNA Repair (Amst) 2018; 69:14-23. [DOI: 10.1016/j.dnarep.2018.07.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2018] [Accepted: 07/09/2018] [Indexed: 12/11/2022]
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19
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Zhu X, Ma X, Tu Y, Huang M, Liu H, Wang F, Gong J, Wang J, Li X, Chen Q, Shen H, Zhu S, Wang Y, Liu Y, Guo C, Tang TS. Parkin regulates translesion DNA synthesis in response to UV radiation. Oncotarget 2018; 8:36423-36437. [PMID: 28430587 PMCID: PMC5482665 DOI: 10.18632/oncotarget.16855] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2017] [Accepted: 03/27/2017] [Indexed: 01/12/2023] Open
Abstract
Deficiency of Parkin is a major cause of early-onset Parkinson's disease (PD). Notably, PD patients also exhibit a significantly higher risk in melanoma and other skin tumors, while the mechanism remains largely unknown. In this study, we show that depletion of Parkin causes compromised cell viability and genome stability after ultraviolet (UV) radiation. We demonstrate that Parkin promotes efficient Rad18-dependent proliferating cell nuclear antigen (PCNA) monoubiquitination by facilitating the formation of Replication protein A (RPA)-coated ssDNA upon UV radiation. Furthermore, Parkin is found to physically interact with NBS1 (Nijmegen breakage syndrome 1), and to be required for optimal recruitment of NBS1 and DNA polymerase eta (Polη) to UV-induced damage sites. Consequently, depletion of Parkin leads to increased UV-induced mutagenesis. These findings unveil an important role of Parkin in protecting genome stability through positively regulating translesion DNA synthesis (TLS) upon UV damage, providing a novel mechanistic link between Parkin deficiency and predisposition to skin cancers in PD patients.
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Affiliation(s)
- Xuefei Zhu
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiaolu Ma
- CAS Key Laboratory of Genomics and Precision Medicine, Beijing Institute of Genomics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Yingfeng Tu
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Min Huang
- CAS Key Laboratory of Genomics and Precision Medicine, Beijing Institute of Genomics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Hongmei Liu
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Fengli Wang
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Juanjuan Gong
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Jiuqiang Wang
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Xiaoling Li
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Qian Chen
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Hongyan Shen
- CAS Key Laboratory of Genomics and Precision Medicine, Beijing Institute of Genomics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Shu Zhu
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Yun Wang
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Yang Liu
- CAS Key Laboratory of Genomics and Precision Medicine, Beijing Institute of Genomics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Caixia Guo
- CAS Key Laboratory of Genomics and Precision Medicine, Beijing Institute of Genomics, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
| | - Tie-Shan Tang
- State Key Laboratory of Membrane Biology, Institute of Zoology, University of Chinese Academy of Sciences, Chinese Academy of Sciences, Beijing 100101, China
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20
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Woodrick J, Gupta S, Camacho S, Parvathaneni S, Choudhury S, Cheema A, Bai Y, Khatkar P, Erkizan HV, Sami F, Su Y, Schärer OD, Sharma S, Roy R. A new sub-pathway of long-patch base excision repair involving 5' gap formation. EMBO J 2017; 36:1605-1622. [PMID: 28373211 DOI: 10.15252/embj.201694920] [Citation(s) in RCA: 46] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2016] [Revised: 02/21/2017] [Accepted: 03/09/2017] [Indexed: 02/06/2023] Open
Abstract
Base excision repair (BER) is one of the most frequently used cellular DNA repair mechanisms and modulates many human pathophysiological conditions related to DNA damage. Through live cell and in vitro reconstitution experiments, we have discovered a major sub-pathway of conventional long-patch BER that involves formation of a 9-nucleotide gap 5' to the lesion. This new sub-pathway is mediated by RECQ1 DNA helicase and ERCC1-XPF endonuclease in cooperation with PARP1 poly(ADP-ribose) polymerase and RPA The novel gap formation step is employed during repair of a variety of DNA lesions, including oxidative and alkylation damage. Moreover, RECQ1 regulates PARP1 auto-(ADP-ribosyl)ation and the choice between long-patch and single-nucleotide BER, thereby modulating cellular sensitivity to DNA damage. Based on these results, we propose a revised model of long-patch BER and a new key regulation point for pathway choice in BER.
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Affiliation(s)
- Jordan Woodrick
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Suhani Gupta
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Sharon Camacho
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Swetha Parvathaneni
- Department of Biochemistry and Molecular Biology, College of Medicine, Howard University, Washington, DC, USA
| | - Sujata Choudhury
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Amrita Cheema
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Yi Bai
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Pooja Khatkar
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Hayriye Verda Erkizan
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
| | - Furqan Sami
- Department of Biochemistry and Molecular Biology, College of Medicine, Howard University, Washington, DC, USA
| | - Yan Su
- Department of Pharmacological Sciences & Department of Chemistry, Stony Brook University, Stony Brook, NY, USA
| | - Orlando D Schärer
- Department of Pharmacological Sciences & Department of Chemistry, Stony Brook University, Stony Brook, NY, USA
| | - Sudha Sharma
- Department of Biochemistry and Molecular Biology, College of Medicine, Howard University, Washington, DC, USA
| | - Rabindra Roy
- Department of Oncology, Lombardi Comprehensive Cancer Center, Georgetown University, Washington, DC, USA
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21
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Krasikova YS, Rechkunova NI, Lavrik OI. Replication protein A as a major eukaryotic single-stranded DNA-binding protein and its role in DNA repair. Mol Biol 2016. [DOI: 10.1134/s0026893316030080] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
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22
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Amorim JP, Santos G, Vinagre J, Soares P. The Role of ATRX in the Alternative Lengthening of Telomeres (ALT) Phenotype. Genes (Basel) 2016; 7:E66. [PMID: 27657132 PMCID: PMC5042396 DOI: 10.3390/genes7090066] [Citation(s) in RCA: 63] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2016] [Revised: 09/07/2016] [Accepted: 09/12/2016] [Indexed: 12/15/2022] Open
Abstract
Telomeres are responsible for protecting chromosome ends in order to prevent the loss of coding DNA. Their maintenance is required for achieving immortality by neoplastic cells and can occur by upregulation of the telomerase enzyme or through a homologous recombination-associated process, the alternative lengthening of telomeres (ALT). The precise mechanisms that govern the activation of ALT or telomerase in tumor cells are not fully understood, although cellular origin may favor one of the other mechanisms that have been found thus far in mutual exclusivity. Specific mutational events influence ALT activation and maintenance: a unifying frequent feature of tumors that acquire this phenotype are the recurrent mutations of the Alpha Thalassemia/Mental Retardation Syndrome X-Linked (ATRX) or Death-Domain Associated Protein (DAXX) genes. This review summarizes the established criteria about this phenotype: its prevalence, theoretical molecular mechanisms and relation with ATRX, DAXX and other proteins (directly or indirectly interacting and resulting in the ALT phenotype).
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Affiliation(s)
- João P Amorim
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto 4200-135, Portugal.
- Instituto de Patologia e Imunologia Molecular da Universidade do Porto (Ipatimup), Porto 4200-135, Portugal.
- Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto, Porto 4050-313, Portugal.
| | - Gustavo Santos
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto 4200-135, Portugal.
- Instituto de Patologia e Imunologia Molecular da Universidade do Porto (Ipatimup), Porto 4200-135, Portugal.
- Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto, Porto 4050-313, Portugal.
| | - João Vinagre
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto 4200-135, Portugal.
- Instituto de Patologia e Imunologia Molecular da Universidade do Porto (Ipatimup), Porto 4200-135, Portugal.
- Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto, Porto 4050-313, Portugal.
| | - Paula Soares
- Instituto de Investigação e Inovação em Saúde (i3S), Universidade do Porto, Porto 4200-135, Portugal.
- Instituto de Patologia e Imunologia Molecular da Universidade do Porto (Ipatimup), Porto 4200-135, Portugal.
- Instituto de Ciências Biomédicas Abel Salazar da Universidade do Porto, Porto 4050-313, Portugal.
- Departamento de Patologia e Oncologia, Faculdade de Medicina da Universidade do Porto, Porto 4200-139, Portugal.
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23
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Safa L, Gueddouda NM, Thiébaut F, Delagoutte E, Petruseva I, Lavrik O, Mendoza O, Bourdoncle A, Alberti P, Riou JF, Saintomé C. 5' to 3' Unfolding Directionality of DNA Secondary Structures by Replication Protein A: G-QUADRUPLEXES AND DUPLEXES. J Biol Chem 2016; 291:21246-21256. [PMID: 27440048 DOI: 10.1074/jbc.m115.709667] [Citation(s) in RCA: 32] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2015] [Indexed: 11/06/2022] Open
Abstract
The replication protein A (RPA) is a single-stranded DNA-binding protein that plays an essential role in DNA metabolism. RPA is able to unfold G-quadruplex (G4) structures formed by telomeric DNA sequences, a function important for telomere maintenance. To elucidate the mechanism through which RPA unfolds telomeric G4s, we studied its interaction with oligonucleotides that adopt a G4 structure extended with a single-stranded tail on either side of the G4. Binding and unfolding was characterized using several biochemical and biophysical approaches and in the presence of specific G4 ligands, such as telomestatin and 360A. Our data show that RPA can bind on each side of the G4 but it unwinds the G4 only from 5' toward 3'. We explain the 5' to 3' unfolding directionality in terms of the 5' to 3' oriented laying out of hRPA subunits along single-stranded DNA. Furthermore, we demonstrate by kinetics experiments that RPA proceeds with the same directionality for duplex unfolding.
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Affiliation(s)
- Layal Safa
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France, the Sorbonne Universités, UPMC University Paris 06, F-75005, Paris, France
| | - Nassima Meriem Gueddouda
- the Laboratoire ARNA-INSERM U1212, UMR 5320, Institut européen de chimie et biologie, 2 rue Robert Escarpit, 33607 Pessac, France
| | - Frédéric Thiébaut
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France, the Sorbonne Universités, UPMC University Paris 06, F-75005, Paris, France, the Ecole Normale Supérieure, PSL Research University, Département de Chimie, 24 rue Lhomond, CNRS, UMR 7203 LBM, 75005 Paris, France, and
| | - Emmanuelle Delagoutte
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France
| | - Irina Petruseva
- the Novosibirsk Institute of Chemical Biology and Fundamental Medecine, Siberian Division of Russian Academy of Science, 630090 Novosibirsk, Russia
| | - Olga Lavrik
- the Novosibirsk Institute of Chemical Biology and Fundamental Medecine, Siberian Division of Russian Academy of Science, 630090 Novosibirsk, Russia
| | - Oscar Mendoza
- the Laboratoire ARNA-INSERM U1212, UMR 5320, Institut européen de chimie et biologie, 2 rue Robert Escarpit, 33607 Pessac, France
| | - Anne Bourdoncle
- the Laboratoire ARNA-INSERM U1212, UMR 5320, Institut européen de chimie et biologie, 2 rue Robert Escarpit, 33607 Pessac, France
| | - Patrizia Alberti
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France,
| | - Jean-François Riou
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France
| | - Carole Saintomé
- From the Structure et Instabilité des Génomes, Sorbonne Universités, Muséum National d'Histoire Naturelle, INSERM U1154, CNRS UMR 7196, CP26, 57 rue Cuvier, 75005, Paris, France, the Sorbonne Universités, UPMC University Paris 06, F-75005, Paris, France,
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24
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Root H, Larsen A, Komosa M, Al-Azri F, Li R, Bazett-Jones DP, Stephen Meyn M. FANCD2 limits BLM-dependent telomere instability in the alternative lengthening of telomeres pathway. Hum Mol Genet 2016; 25:3255-3268. [DOI: 10.1093/hmg/ddw175] [Citation(s) in RCA: 33] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2016] [Revised: 05/02/2016] [Accepted: 06/06/2016] [Indexed: 11/12/2022] Open
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Abstract
Alternative Lengthening of Telomeres (ALT) mechanisms allow telomerase-negative immortal cells to buffer replicative telomere shortening. ALT is naturally active in a number of human cancers and might be selected upon telomerase inactivation. ALT is thought to operate through homologous recombination (HR) occurring between telomeric repeats from independent chromosome ends. Indeed, suppression of a number of HR factors impairs ALT cell proliferation. Yet, how HR is initiated at ALT telomeres remains elusive. Mounting evidence suggests that the long noncoding telomeric RNA TERRA renders ALT telomeres recombinogenic by forming RNA:DNA hybrids with the telomeric C-rich strand. TERRA and telomeric hybrids act in concert with a number of other factors, including the RNA endoribonuclease RNaseH1 and the single stranded DNA binding protein RPA. The functional interaction network built upon these different players seems indispensable for ALT telomere maintenance, and digging into the molecular details of this previously unappreciated network might open the way to novel avenues for cancer treatments.
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Affiliation(s)
- Rajika Arora
- a Institute of Biochemistry; Eidgenössische Technische Hochschule Zürich (ETHZ) ; Zürich , Switzerland
| | - Claus M Azzalin
- a Institute of Biochemistry; Eidgenössische Technische Hochschule Zürich (ETHZ) ; Zürich , Switzerland
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26
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Cox KE, Maréchal A, Flynn RL. SMARCAL1 Resolves Replication Stress at ALT Telomeres. Cell Rep 2016; 14:1032-1040. [PMID: 26832416 PMCID: PMC5051350 DOI: 10.1016/j.celrep.2016.01.011] [Citation(s) in RCA: 79] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2015] [Revised: 11/25/2015] [Accepted: 12/29/2015] [Indexed: 11/20/2022] Open
Abstract
Cancer cells overcome replicative senescence by exploiting mechanisms of telomere elongation, a process often accomplished by reactivation of the enzyme telomerase. However, a subset of cancer cells lack telomerase activity and rely on the alternative lengthening of telomeres (ALT) pathway, a recombination-based mechanism of telomere elongation. Although the mechanisms regulating ALT are not fully defined, chronic replication stress at telomeres might prime these fragile regions for recombination. Here, we demonstrate that the replication stress response protein SMARCAL1 is a critical regulator of ALT activity. SMARCAL1 associates with ALT telomeres to resolve replication stress and ensure telomere stability. In the absence of SMARCAL1, persistently stalled replication forks at ALT telomeres deteriorate into DNA double-strand breaks promoting the formation of chromosome fusions. Our studies not only define a role for SMARCAL1 in ALT telomere maintenance, but also demonstrate that resolution of replication stress is a crucial step in the ALT mechanism.
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Affiliation(s)
- Kelli E Cox
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA 02118, USA; Department of Medicine, Cancer Center, Boston University School of Medicine, Boston, MA 02118, USA
| | - Alexandre Maréchal
- Department of Biology, Université de Sherbrooke, Sherbrooke, QC J1K 2R1, Canada
| | - Rachel Litman Flynn
- Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, MA 02118, USA; Department of Medicine, Cancer Center, Boston University School of Medicine, Boston, MA 02118, USA.
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27
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Maréchal A, Zou L. RPA-coated single-stranded DNA as a platform for post-translational modifications in the DNA damage response. Cell Res 2014; 25:9-23. [PMID: 25403473 DOI: 10.1038/cr.2014.147] [Citation(s) in RCA: 313] [Impact Index Per Article: 31.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
The Replication Protein A (RPA) complex is an essential regulator of eukaryotic DNA metabolism. RPA avidly binds to single-stranded DNA (ssDNA) through multiple oligonucleotide/oligosaccharide-binding folds and coordinates the recruitment and exchange of genome maintenance factors to regulate DNA replication, recombination and repair. The RPA-ssDNA platform also constitutes a key physiological signal which activates the master ATR kinase to protect and repair stalled or collapsed replication forks during replication stress. In recent years, the RPA complex has emerged as a key target and an important regulator of post-translational modifications in response to DNA damage, which is critical for its genome guardian functions. Phosphorylation and SUMOylation of the RPA complex, and more recently RPA-regulated ubiquitination, have all been shown to control specific aspects of DNA damage signaling and repair by modulating the interactions between RPA and its partners. Here, we review our current understanding of the critical functions of the RPA-ssDNA platform in the maintenance of genome stability and its regulation through an elaborate network of covalent modifications.
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Affiliation(s)
- Alexandre Maréchal
- Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA
| | - Lee Zou
- 1] Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, MA 02129, USA [2] Department of Pathology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114, USA
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28
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Arora R, Lee Y, Wischnewski H, Brun CM, Schwarz T, Azzalin CM. RNaseH1 regulates TERRA-telomeric DNA hybrids and telomere maintenance in ALT tumour cells. Nat Commun 2014; 5:5220. [PMID: 25330849 PMCID: PMC4218956 DOI: 10.1038/ncomms6220] [Citation(s) in RCA: 307] [Impact Index Per Article: 30.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2014] [Accepted: 09/10/2014] [Indexed: 12/21/2022] Open
Abstract
A fraction of cancer cells maintain telomeres through the telomerase-independent, ‘Alternative Lengthening of Telomeres’ (ALT) pathway. ALT relies on homologous recombination (HR) between telomeric sequences; yet, what makes ALT telomeres recombinogenic remains unclear. Here we show that the RNA endonuclease RNaseH1 regulates the levels of RNA–DNA hybrids between telomeric DNA and the long noncoding RNA TERRA, and is a key mediator of telomere maintenance in ALT cells. RNaseH1 associated to telomeres specifically in ALT cells and its depletion led to telomeric hybrid accumulation, exposure of single-stranded telomeric DNA, activation of replication protein A at telomeres and abrupt telomere excision. Conversely, overexpression of RNaseH1 weakened the recombinogenic nature of ALT telomeres and led to telomere shortening. Altering cellular RNaseH1 levels did not perturb telomere homoeostasis in telomerase-positive cells. RNaseH1 maintains regulated levels of telomeric RNA–DNA hybrids at ALT telomeres to trigger HR without compromising telomere integrity too severely. A subset of cancers maintains telomere length independently of telomerase by activating alternative lengthening of telomeres (ALT) pathways. Here the authors show that RNaseH1 modulates telomeric homologous recombination frequencies in ALT cells by regulating the levels of RNA–DNA hybrids between TERRA and telomeric DNA.
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Affiliation(s)
- Rajika Arora
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
| | - Yongwoo Lee
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
| | - Harry Wischnewski
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
| | - Catherine M Brun
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
| | - Tobias Schwarz
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
| | - Claus M Azzalin
- Institute of Biochemistry, Eidgenössische Technische Hochschule Zürich (ETHZ), Zürich CH-8093, Switzerland
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29
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Chen R, Wold MS. Replication protein A: single-stranded DNA's first responder: dynamic DNA-interactions allow replication protein A to direct single-strand DNA intermediates into different pathways for synthesis or repair. Bioessays 2014; 36:1156-61. [PMID: 25171654 DOI: 10.1002/bies.201400107] [Citation(s) in RCA: 189] [Impact Index Per Article: 18.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Replication protein A (RPA), the major single-stranded DNA-binding protein in eukaryotic cells, is required for processing of single-stranded DNA (ssDNA) intermediates found in replication, repair, and recombination. Recent studies have shown that RPA binding to ssDNA is highly dynamic and that more than high-affinity binding is needed for function. Analysis of DNA binding mutants identified forms of RPA with reduced affinity for ssDNA that are fully active, and other mutants with higher affinity that are inactive. Single molecule studies showed that while RPA binds ssDNA with high affinity, the RPA complex can rapidly diffuse along ssDNA and be displaced by other proteins that act on ssDNA. Finally, dynamic DNA binding allows RPA to prevent error-prone repair of double-stranded breaks and promote error-free repair. Together, these findings suggest a new paradigm where RPA acts as a first responder at sites with ssDNA, thereby actively coordinating DNA repair and DNA synthesis.
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Affiliation(s)
- Ran Chen
- Department of Biochemistry, Carver College of Medicine, University of Iowa, Iowa City, IA, USA
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30
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Safa L, Delagoutte E, Petruseva I, Alberti P, Lavrik O, Riou JF, Saintomé C. Binding polarity of RPA to telomeric sequences and influence of G-quadruplex stability. Biochimie 2014; 103:80-8. [PMID: 24747047 DOI: 10.1016/j.biochi.2014.04.006] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2013] [Accepted: 04/09/2014] [Indexed: 01/01/2023]
Abstract
Replication protein A (RPA) is a single-stranded DNA binding protein that plays an essential role in telomere maintenance. RPA binds to and unfolds G-quadruplex (G4) structures formed in telomeric DNA, thus facilitating lagging strand DNA replication and telomerase activity. To investigate the effect of G4 stability on the interactions with human RPA (hRPA), we used a combination of biochemical and biophysical approaches. Our data revealed an inverse relationship between G4 stability and ability of hRPA to bind to telomeric DNA; notably small G4 ligands that enhance G4 stability strongly impaired G4 unfolding by hRPA. To gain more insight into the mechanism of binding and unfolding of telomeric G4 structures by RPA, we carried out photo-crosslinking experiments to elucidate the spatial arrangement of the RPA subunits along the DNA strands. Our results showed that RPA1 and RPA2 are arranged from 5' to 3' along the unfolded telomeric G4, as already described for unstructured single-stranded DNA, while no contact is possible with RPA3 on this short oligonucleotide. In addition, these data are compatible with a 5' to 3' directionality in G4 unfolding by hRPA.
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Affiliation(s)
- Layal Safa
- Structure des Acides Nucléiques, Télomères et Evolution, Inserm U1154, CNRS UMR 7196, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris cedex 05, France; Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France
| | - Emmanuelle Delagoutte
- Structure des Acides Nucléiques, Télomères et Evolution, Inserm U1154, CNRS UMR 7196, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris cedex 05, France
| | - Irina Petruseva
- Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of Russian Academy of Science, 630090 Novosibirsk, Russia
| | - Patrizia Alberti
- Structure des Acides Nucléiques, Télomères et Evolution, Inserm U1154, CNRS UMR 7196, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris cedex 05, France
| | - Olga Lavrik
- Novosibirsk Institute of Bioorganic Chemistry, Siberian Division of Russian Academy of Science, 630090 Novosibirsk, Russia
| | - Jean-François Riou
- Structure des Acides Nucléiques, Télomères et Evolution, Inserm U1154, CNRS UMR 7196, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris cedex 05, France.
| | - Carole Saintomé
- Structure des Acides Nucléiques, Télomères et Evolution, Inserm U1154, CNRS UMR 7196, Muséum National d'Histoire Naturelle, 43 rue Cuvier, 75231 Paris cedex 05, France; Université Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France.
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31
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The roles of telomerase in the generation of polyploidy during neoplastic cell growth. Neoplasia 2013; 15:156-68. [PMID: 23441130 DOI: 10.1593/neo.121398] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2012] [Revised: 11/30/2012] [Accepted: 12/03/2012] [Indexed: 01/20/2023] Open
Abstract
Polyploidy contributes to extensive intratumor genomic heterogeneity that characterizes advanced malignancies and is thought to limit the efficiency of current cancer therapies. It has been shown that telomere deprotection in p53-deficient mouse embryonic fibroblasts leads to high rates of polyploidization. We now show that tumor genome evolution through whole-genome duplication occurs in ∼15% of the karyotyped human neoplasms and correlates with disease progression. In a panel of human cancer and transformed cell lines representing the two known types of genomic instability (chromosomal and microsatellite), as well as the two known pathways of telomere maintenance in cancer (telomerase activity and alternative lengthening of telomeres), telomere dysfunction-driven polyploidization occurred independently of the mutational status of p53. Depending on the preexisting context of telomere maintenance, telomerase activity and its major components, human telomerase reverse transcriptase (hTERT) and human telomerase RNA component (hTERC), exert both reverse transcriptase-related (canonical) and noncanonical functions to affect tumor genome evolution through suppression or induction of polyploidization. These new findings provide a more complete mechanistic understanding of cancer progression that may, in the future, lead to novel therapeutic interventions.
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32
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The natural absence of RPA1N domain did not impair Leishmania amazonensis RPA-1 participation in DNA damage response and telomere protection. Parasitology 2013; 140:547-59. [DOI: 10.1017/s0031182012002028] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
SUMMARYWe have previously shown that the subunit 1 of Leishmania amazonensis RPA (LaRPA-1) alone binds the G-rich telomeric strand and is structurally different from other RPA-1. It is analogous to telomere end-binding proteins described in model eukaryotes whose homologues were not identified in the protozoan´s genome. Here we show that LaRPA-1 is involved with damage response and telomere protection although it lacks the RPA1N domain involved with the binding with multiple checkpoint proteins. We induced DNA double-strand breaks (DSBs) in Leishmania using phleomycin. Damage was confirmed by TUNEL-positive nuclei and triggered a G1/S cell cycle arrest that was accompanied by nuclear accumulation of LaRPA-1 and RAD51 in the S phase of hydroxyurea-synchronized parasites. DSBs also increased the levels of RAD51 in non-synchronized parasites and of LaRPA-1 and RAD51 in the S phase of synchronized cells. More LaRPA-1 appeared immunoprecipitating telomeres in vivo and associated in a complex containing RAD51, although this interaction needs more investigation. RAD51 apparently co-localized with few telomeric clusters but it did not immunoprecipitate telomeric DNA. These findings suggest that LaRPA-1 and RAD51 work together in response to DNA DSBs and at telomeres, upon damage, LaRPA-1 works probably to prevent loss of single-stranded DNA and to assume a capping function.
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33
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Rezazadeh S. On BLM helicase in recombination-mediated telomere maintenance. Mol Biol Rep 2012; 40:3049-64. [DOI: 10.1007/s11033-012-2379-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2012] [Accepted: 12/17/2012] [Indexed: 11/29/2022]
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34
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Gocha ARS, Harris J, Groden J. Alternative mechanisms of telomere lengthening: permissive mutations, DNA repair proteins and tumorigenic progression. Mutat Res 2012; 743-744:142-150. [PMID: 23219603 DOI: 10.1016/j.mrfmmm.2012.11.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Revised: 11/22/2012] [Accepted: 11/24/2012] [Indexed: 01/05/2023]
Abstract
Telomeres protect chromosome termini to maintain genomic stability and regulate cellular lifespan. Maintenance of telomere length is required for neoplastic cells after the acquisition of mutations that deregulate cell cycle control and increase cellular proliferation, and can occur through expression of the enzyme telomerase or in a telomerase-independent manner termed alternative lengthening of telomeres (ALT). The precise mechanisms that govern the activation of ALT or telomerase in tumor cells are unknown, although cellular origin may favor one or the other mechanisms. ALT pathways are incompletely understood to date; however, recent publications have increasingly broadened our understanding of how ALT is activated, how it proceeds, and how it influences tumor growth. Specific mutational events influence ALT activation, as mutations in genes that suppress recombination and/or alterations in the regulation of telomerase expression are associated with ALT. Once engaged, ALT uses DNA repair proteins to maintain telomeres in the absence of telomerase; experiments that manipulate the expression of specific proteins in cells using ALT are illuminating some of its mechanisms. Furthermore, ALT may influence tumor growth, as experimental and clinical data suggest that telomerase expression may favor tumor progression. This review summarizes recent findings in mammalian cells and models, as well as clinical data, that identify the genetic mutations permissive to ALT, the DNA repair proteins involved in ALT mechanisms and the importance of telomere maintenance mechanisms for tumor progression. A comprehensive understanding of the mechanisms that permit tumor cell immortalization will be important for identifying novel therapeutic targets in cancer.
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Affiliation(s)
- April Renee Sandy Gocha
- Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States
| | - Julia Harris
- Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States
| | - Joanna Groden
- Department of Molecular Virology, Immunology and Medical Genetics, The Ohio State University College of Medicine, Columbus, OH 43210, United States.
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35
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Organismal propagation in the absence of a functional telomerase pathway in Caenorhabditis elegans. EMBO J 2012; 31:2024-33. [PMID: 22425786 PMCID: PMC3343340 DOI: 10.1038/emboj.2012.61] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 02/14/2012] [Indexed: 11/09/2022] Open
Abstract
To counteract replication-dependent telomere shortening most eukaryotic cells rely on the telomerase pathway, which is crucial for the maintenance of proliferative potential of germ and stem cell populations of multicellular organisms. Likewise, cancer cells usually engage the telomerase pathway for telomere maintenance to gain immortality. However, in ∼10% of human cancers telomeres are maintained through telomerase-independent alternative lengthening of telomeres (ALT) pathways. Here, we describe the generation and characterization of C. elegans survivors in a strain lacking the catalytic subunit of telomerase and the nematode telomere-binding protein CeOB2. These clonal strains, some of which have been propagated for >180 generations, represent the first example of a multicellular organism with canonical telomeres that can survive without a functional telomerase pathway. The animals display the heterogeneous telomere length characteristic for ALT cells, contain single-stranded C-circles, a transcription profile pointing towards an adaptation to chronic stress and are therefore a unique and valuable tool to decipher the ALT mechanism.
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36
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Prakash A, Borgstahl GEO. The structure and function of replication protein A in DNA replication. Subcell Biochem 2012; 62:171-96. [PMID: 22918586 DOI: 10.1007/978-94-007-4572-8_10] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
In all organisms from bacteria and archaea to eukarya, single-stranded DNA binding proteins play an essential role in most, if not all, nuclear metabolism involving single-stranded DNA (ssDNA). Replication protein A (RPA), the major eukaryotic ssDNA binding protein, has two important roles in DNA metabolism: (1) in binding ssDNA to protect it and to keep it unfolded, and (2) in coordinating the assembly and disassembly of numerous proteins and protein complexes during processes such as DNA replication. Since its discovery as a vital player in the process of replication, RPAs roles in recombination and DNA repair quickly became evident. This chapter summarizes the current understanding of RPA's roles in replication by reviewing the available structural data, DNA-binding properties, interactions with various replication proteins, and interactions with DNA repair proteins when DNA replication is stalled.
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Affiliation(s)
- Aishwarya Prakash
- Department of Microbiology and Molecular Genetics, The Markey Center for Molecular Genetics, University of Vermont, Given Medical Building, 89 Beaumont Avenue, Burlington, VT, 05405, USA
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37
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Prakash A, Kieken F, Marky LA, Borgstahl GEO. Stabilization of a G-Quadruplex from Unfolding by Replication Protein A Using Potassium and the Porphyrin TMPyP4. J Nucleic Acids 2011; 2011:529828. [PMID: 21772995 PMCID: PMC3136172 DOI: 10.4061/2011/529828] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/27/2010] [Revised: 03/17/2011] [Accepted: 04/01/2011] [Indexed: 11/20/2022] Open
Abstract
Replication protein A (RPA) plays an essential role in DNA replication by binding and unfolding non-canonical single-stranded DNA (ssDNA) structures. Of the six RPA ssDNA binding domains (labeled A-F), RPA-CDE selectively binds a G-quadruplex forming sequence (5′-TAGGGGAAGGGTTGGAGTGGGTT-3′ called Gq23). In K+, Gq23 forms a mixed parallel/antiparallel conformation, and in Na+ Gq23 has a less stable (TM lowered by ∼20°C), antiparallel conformation. Gq23 is intramolecular and 1D NMR confirms a stable G-quadruplex structure in K+. Full-length RPA and RPA-CDE-core can bind and unfold the Na+ form of Gq23 very efficiently, but complete unfolding is not observed with the K+ form. Studies with G-quadruplex ligands, indicate that TMPyP4 has a thermal stabilization effect on Gq23 in K+, and inhibits complete unfolding by RPA and RPA-CDE-core. Overall these data indicate that G-quadruplexes present a unique problem for RPA to unfold and ligands, such as TMPyP4, could possibly hinder DNA replication by blocking unfolding by RPA.
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Affiliation(s)
- Aishwarya Prakash
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
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38
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Prakash A, Natarajan A, Marky LA, Ouellette MM, Borgstahl GEO. Identification of the DNA-Binding Domains of Human Replication Protein A That Recognize G-Quadruplex DNA. J Nucleic Acids 2011; 2011:896947. [PMID: 21772997 PMCID: PMC3136212 DOI: 10.4061/2011/896947] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2010] [Accepted: 03/11/2011] [Indexed: 12/26/2022] Open
Abstract
Replication protein A (RPA), a key player in DNA metabolism, has 6 single-stranded DNA-(ssDNA-) binding domains (DBDs) A-F. SELEX experiments with the DBDs-C, -D, and -E retrieve a 20-nt G-quadruplex forming sequence. Binding studies show that RPA-DE binds preferentially to the G-quadruplex DNA, a unique preference not observed with other RPA constructs. Circular dichroism experiments show that RPA-CDE-core can unfold the G-quadruplex while RPA-DE stabilizes it. Binding studies show that RPA-C binds pyrimidine- and purine-rich sequences similarly. This difference between RPA-C and RPA-DE binding was also indicated by the inability of RPA-CDE-core to unfold an oligonucleotide containing a TC-region 5′ to the G-quadruplex. Molecular modeling studies of
RPA-DE and telomere-binding proteins Pot1 and Stn1 reveal structural similarities between the proteins and illuminate potential DNA-binding sites for RPA-DE and Stn1. These data indicate that DBDs of RPA have different ssDNA recognition properties.
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Affiliation(s)
- Aishwarya Prakash
- The Eppley Institute for Research in Cancer and Allied Diseases, University of Nebraska Medical Center, 987696 Nebraska Medical Center, Omaha, NE 68198-7696, USA
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39
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Nabetani A, Ishikawa F. Alternative lengthening of telomeres pathway: recombination-mediated telomere maintenance mechanism in human cells. J Biochem 2011; 149:5-14. [PMID: 20937668 DOI: 10.1093/jb/mvq119] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Unlimitedly proliferating cells need to acquire the telomere DNA maintenance mechanism, to counteract possible shortening through multiple rounds of replication and segregation of linear chromosomes. Most human cancer cells express telomerase whereas the other cells utilize the alternative lengthening of telomeres (ALT) pathway to elongate telomere DNA. It is suggested that ALT depends on the recombination between telomere repetitive DNAs. However, the molecular details remain unknown. Recent studies have provided evidence of special structures of telomere DNA and genes essential for the phenotypes of ALT cells. The molecular models of the ALT pathway should be validated to elucidate recombination-mediated telomere maintenance and promote the applications to anti-cancer therapy.
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Affiliation(s)
- Akira Nabetani
- Laboratory of Cell Cycle Regulation, Department of Gene Mechanisms, Graduate School of Biostudies, Kyoto University,Yoshida-Konoe-cho, Sakyo-ku, Kyoto 606-8501, Japan.
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Henson JD, Reddel RR. Assaying and investigating Alternative Lengthening of Telomeres activity in human cells and cancers. FEBS Lett 2010; 584:3800-11. [PMID: 20542034 DOI: 10.1016/j.febslet.2010.06.009] [Citation(s) in RCA: 176] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2010] [Accepted: 06/08/2010] [Indexed: 12/14/2022]
Abstract
Alternative Lengthening of Telomeres (ALT) activity can be deduced from the presence of telomere length maintenance in the absence of telomerase activity. More convenient assays for ALT utilize phenotypic markers of ALT activity, but only a few of these assays are potentially definitive. Here we assess each of the current ALT assays and their implications for understanding the ALT mechanism. We also review the clinical situations where availability of an ALT activity assay would be advantageous. The prevalence of ALT ranges from 25% to 60% in sarcomas and 5% to 15% in carcinomas. Patients with many of these types of ALT[+] tumors have a poor prognosis.
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Affiliation(s)
- Jeremy D Henson
- Children's Medical Research Institute, Sydney, NSW, Australia
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41
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Oakley GG, Patrick SM. Replication protein A: directing traffic at the intersection of replication and repair. FRONT BIOSCI-LANDMRK 2010; 15:883-900. [PMID: 20515732 DOI: 10.2741/3652] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Since the initial discovery of replication protein A (RPA) as a DNA replication factor, much progress has been made on elucidating critical roles for RPA in other DNA metabolic pathways. RPA has been shown to be required for DNA replication, DNA repair, DNA recombination, and the DNA damage response pathway with roles in checkpoint activation. This review summarizes the current understanding of RPA structure, phosphorylation and protein-protein interactions in mediating these DNA metabolic processes.
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Affiliation(s)
- Greg G Oakley
- College of Dentistry, University of Nebraska Medical Center, Lincoln, Nebraska 68583, USA
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42
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Henson JD, Cao Y, Huschtscha LI, Chang AC, Au AYM, Pickett HA, Reddel RR. DNA C-circles are specific and quantifiable markers of alternative-lengthening-of-telomeres activity. Nat Biotechnol 2010; 27:1181-5. [PMID: 19935656 DOI: 10.1038/nbt.1587] [Citation(s) in RCA: 346] [Impact Index Per Article: 24.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2009] [Accepted: 10/15/2009] [Indexed: 11/09/2022]
Abstract
Alternative lengthening of telomeres (ALT) is likely to be an important target for anticancer treatment as approximately 10% of cancers depend on this telomere maintenance mechanism for continued growth, and inhibition of ALT can cause cellular senescence. However, no ALT inhibitors have been developed for therapeutic use because of the lack of a suitable ALT activity assay and of known ALT-specific target molecules. Here we show that partially single-stranded telomeric (CCCTAA)(n) DNA circles (C-circles) are ALT specific. We provide an assay that is rapidly and linearly responsive to ALT activity and that is suitable for screening for ALT inhibitors. We detect C-circles in blood from ALT(+) osteosarcoma patients, suggesting that the C-circle assay (CC assay) may have clinical utility for diagnosis and management of ALT(+) tumors.
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Affiliation(s)
- Jeremy D Henson
- Children's Medical Research Institute, University of Sydney, New South Wales, Australia
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43
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Expression of mutant RPA in human cancer cells causes telomere shortening. Biosci Biotechnol Biochem 2010; 74:382-5. [PMID: 20139621 DOI: 10.1271/bbb.90496] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Replication protein A (RPA) binds to single-stranded DNA generated during DNA replication and other processes. The roles of RPA in telomere maintenance have been demonstrated in yeasts, but not in telomerase-positive human cells. In this study, we found that expression of mutant RPA70 in human cells caused telomere shortening, suggesting that RPA is required for telomere-length regulation in human cancer cells.
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45
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Fan JH, Bochkareva E, Bochkarev A, Gray DM. Circular dichroism spectra and electrophoretic mobility shift assays show that human replication protein A binds and melts intramolecular G-quadruplex structures. Biochemistry 2009; 48:1099-111. [PMID: 19187036 DOI: 10.1021/bi801538h] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Noncanonical DNA structures such as G-quadruplexes might obstruct the binding of hRPA, compromising the accuracy of replication, and be a source of genomic instability. In this study, circular dichroism (CD) and electrophoretic mobility shift assay (EMSA) experiments were used to show that hRPA can bind and melt nontelomeric, intramolecular DNA G-quadruplexes under physiologically germane conditions. EMSA results show that hRPA binds to a 58-mer that includes an embedded quadruplex with an affinity equal to or greater than to nonquadruplex forming 58-mers. Moreover, hRPA binds to a 26-mer purine-rich quadruplex-forming sequence with an affinity indistinguishable from that for binding to the complementary pyrimidine-rich sequence. Under the same conditions, hRPA does not have significant affinity for binding to the duplex formed from the two sequences. Thus, DNA secondary structures can significantly modulate the binding affinity of hRPA over and above its known preference for pyrimidine-rich single-stranded sequences, so that at least some intramolecular G-quadruplex structures may not inhibit hRPA binding during DNA replication. CD spectral changes in combination with EMSA titrations suggest that one hRPA heterotrimer is sufficient to form a stable complex with an unfolded 26-mer G-quadruplex prior to the binding of a second hRPA molecule.
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Affiliation(s)
- Jun-Huei Fan
- Department of Molecular and Cell Biology, Mail Stop FO31, The University of Texas at Dallas, 800 West Campbell Road, Richardson, Texas 75080, USA
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46
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De Boeck G, Forsyth RG, Praet M, Hogendoorn PCW. Telomere-associated proteins: cross-talk between telomere maintenance and telomere-lengthening mechanisms. J Pathol 2009; 217:327-44. [PMID: 19142887 DOI: 10.1002/path.2500] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Telomeres, the ends of eukaryotic chromosomes, have been the subject of intense investigation over the last decade. As telomere dysfunction has been associated with ageing and developing cancer, understanding the exact mechanisms regulating telomere structure and function is essential for the prevention and treatment of human cancers and age-related diseases. The mechanisms by which cells maintain telomere lengthening involve either telomerase or the alternative lengthening of the telomere pathway, although specific mechanisms of the latter and the relationship between the two are as yet unknown. Many cellular factors directly (TRF1/TRF2) and indirectly (shelterin-complex, PinX, Apollo and tankyrase) interact with telomeres, and their interplay influences telomere structure and function. One challenge comes from the observation that many DNA damage response proteins are stably associated with telomeres and contribute to several other aspects of telomere function. This review focuses on the different components involved in telomere maintenance and their role in telomere length homeostasis. Special attention is paid to understanding how these telomere-associated factors, and mainly those involved in double-strand break repair, perform their activities at the telomere ends.
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Affiliation(s)
- Gitte De Boeck
- N. Goormaghtigh Institute of Pathology, University Hospital Ghent, De Pintelaan 185, 9000 Ghent, Belgium
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47
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Pickett HA, Cesare AJ, Johnston RL, Neumann AA, Reddel RR. Control of telomere length by a trimming mechanism that involves generation of t-circles. EMBO J 2009; 28:799-809. [PMID: 19214183 PMCID: PMC2670870 DOI: 10.1038/emboj.2009.42] [Citation(s) in RCA: 154] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2008] [Accepted: 01/23/2009] [Indexed: 01/09/2023] Open
Abstract
Telomere lengths are maintained in many cancer cells by the ribonucleoprotein enzyme telomerase but can be further elongated by increasing telomerase activity through the overexpression of telomerase components. We report here that increased telomerase activity results in increased telomere length that eventually reaches a plateau, accompanied by the generation of telomere length heterogeneity and the accumulation of extrachromosomal telomeric repeat DNA, principally in the form of telomeric circles (t-circles). Telomeric DNA was observed in promyelocytic leukemia bodies, but no intertelomeric copying or telomere exchange events were identified, and there was no increase in telomere dysfunction-induced foci. These data indicate that human cells possess a mechanism to negatively regulate telomere length by trimming telomeric DNA from the chromosome ends, most likely by t-loop resolution to form t-circles. Additionally, these results indicate that some phenotypic characteristics attributed to alternative lengthening of telomeres (ALT) result from increased mean telomere length, rather than from the ALT mechanism itself.
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Affiliation(s)
- Hilda A Pickett
- Cancer Research Group, Children's Medical Research Institute, Westmead, NSW, Australia
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Tomita K, Cooper JP. Fission yeast Ccq1 is telomerase recruiter and local checkpoint controller. Genes Dev 2009; 22:3461-74. [PMID: 19141478 DOI: 10.1101/gad.498608] [Citation(s) in RCA: 79] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Telomeres recruit telomerase and differentiate chromosome ends from sites of DNA damage. Although the DNA damage checkpoint PI3-kinases ATM and ATR localize to telomeres and promote telomerase activation, activation of their downstream checkpoint pathway targets is inhibited. Here, we show that the fission yeast telomeric protein Ccq1 is required for telomerase recruitment and inhibition of ATR target activation at telomeres. The loss of Ccq1 results in progressive telomere shortening and persistent ATR-dependent activation of Chk1. Unlike the checkpoint activation that follows loss of telomerase, this checkpoint activation occurs prior to detectable levels of critically short telomeres. When ccq1Delta telomeres do become critically short, activated Chk1 promotes an unusual homologous recombination-based telomere maintenance process. We find that the previously reported meiotic segregation defects of cells lacking Ccq1 stem from its role in telomere maintenance rather than from a role in formation of the meiotic bouquet. These findings demonstrate the existence of a novel telomerase recruitment factor that also serves to suppress local checkpoint activation.
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Affiliation(s)
- Kazunori Tomita
- Telomere Biology Laboratory, Cancer Research UK, London WC2A 3PX, United Kingdom
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49
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Fan Q, Zhang F, Barrett B, Ren K, Andreassen PR. A role for monoubiquitinated FANCD2 at telomeres in ALT cells. Nucleic Acids Res 2009; 37:1740-54. [PMID: 19129235 PMCID: PMC2665210 DOI: 10.1093/nar/gkn995] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
Both Fanconi anemia (FA) and telomere dysfunction are associated with chromosome instability and an increased risk of cancer. Because of these similarities, we have investigated whether there is a relationship between the FA protein, FANCD2 and telomeres. We find that FANCD2 nuclear foci colocalize with telomeres and PML bodies in immortalized telomerase-negative cells. These cells maintain telomeres by alternative lengthening of telomeres (ALT). In contrast, FANCD2 does not colocalize with telomeres or PML bodies in cells which express telomerase. Using a siRNA approach we find that FANCA and FANCL, which are components of the FA nuclear core complex, regulate FANCD2 monoubiquitination and the telomeric localization of FANCD2 in ALT cells. Transient depletion of FANCD2, or FANCA, results in a dramatic loss of detectable telomeres in ALT cells but not in telomerase-expressing cells. Furthermore, telomere loss following depletion of these proteins in ALT cells is associated with decreased homologous recombination between telomeres (T-SCE). Thus, the FA pathway has a novel function in ALT telomere maintenance related to DNA repair. ALT telomere maintenance is therefore one mechanism by which monoubiquitinated FANCD2 may promote genetic stability.
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Affiliation(s)
- Qiang Fan
- Division of Experimental Hematology and Cancer Biology, Cincinnati Children's Research Foundation, Department of Pediatrics, University of Cincinnati College of Medicine, Cincinnati, OH 45229, USA
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Salas TR, Petruseva I, Lavrik O, Saintomé C. Evidence for direct contact between the RPA3 subunit of the human replication protein A and single-stranded DNA. Nucleic Acids Res 2008; 37:38-46. [PMID: 19010961 PMCID: PMC2615627 DOI: 10.1093/nar/gkn895] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Replication Protein A is a single-stranded (ss) DNA-binding protein that is highly conserved in eukaryotes and plays essential roles in many aspects of nucleic acid metabolism, including replication, recombination, DNA repair and telomere maintenance. It is a heterotrimeric complex consisting of three subunits: RPA1, RPA2 and RPA3. It possesses four DNA-binding domains (DBD), DBD-A, DBD-B and DBD-C in RPA1 and DBD-D in RPA2, and it binds ssDNA via a multistep pathway. Unlike the RPA1 and RPA2 subunits, no ssDNA-RPA3 interaction has as yet been observed although RPA3 contains a structural motif found in the other DBDs. We show here using 4-thiothymine residues as photoaffinity probe that RPA3 interacts directly with ssDNA on the 3'-side on a 31 nt ssDNA.
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Affiliation(s)
- Tonatiuh Romero Salas
- Laboratoire de Biophysique Moléculaire, Cellulaire et Tissulaire, CNRS-ParisVI-Paris XIII-UMR 7033, Paris, France
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