1
|
Yadav AK, Polasek-Sedlackova H. Quantity and quality of minichromosome maintenance protein complexes couple replication licensing to genome integrity. Commun Biol 2024; 7:167. [PMID: 38336851 PMCID: PMC10858283 DOI: 10.1038/s42003-024-05855-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/05/2023] [Accepted: 01/25/2024] [Indexed: 02/12/2024] Open
Abstract
Accurate and complete replication of genetic information is a fundamental process of every cell division. The replication licensing is the first essential step that lays the foundation for error-free genome duplication. During licensing, minichromosome maintenance protein complexes, the molecular motors of DNA replication, are loaded to genomic sites called replication origins. The correct quantity and functioning of licensed origins are necessary to prevent genome instability associated with severe diseases, including cancer. Here, we delve into recent discoveries that shed light on the novel functions of licensed origins, the pathways necessary for their proper maintenance, and their implications for cancer therapies.
Collapse
Affiliation(s)
- Anoop Kumar Yadav
- Department of Cell Biology and Epigenetics, Institute of Biophysics of the Czech Academy of Sciences, Brno, Czech Republic
- Department of Experimental Biology, Faculty of Science, Masaryk University, Brno, Czech Republic
| | - Hana Polasek-Sedlackova
- Department of Cell Biology and Epigenetics, Institute of Biophysics of the Czech Academy of Sciences, Brno, Czech Republic.
| |
Collapse
|
2
|
Noble TD, Sansam CG, Wittig KA, Majchrzycka B, Sansam CL. Cell Cycle-Dependent TICRR/TRESLIN and MTBP Chromatin Binding Mechanisms and Patterns. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2024:2024.02.02.578516. [PMID: 38370757 PMCID: PMC10871258 DOI: 10.1101/2024.02.02.578516] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/20/2024]
Abstract
The selection of replication origins is a defining characteristic of DNA replication in eukaryotes, yet its mechanism in humans has not been well-defined. In this study, we use Cut&Run to examine genomic binding locations for TICRR/TRESLIN and MTBP, the human orthologs for the yeast DNA replication initiation factors Sld3 and Sld7. We mapped TRESLIN and MTBP binding in HCT116 colorectal cancer cells using asynchronous and G1 synchronized populations. Our data show that TRESLIN and MTBP binding patterns are more defined in a G1 synchronized population compared to asynchronously cycling cells. We also examined whether TRESLIN and MTBP are dependent on one another for binding. Our data suggest MTBP is dependent on TRESLIN for proper association with chromatin during G1 but not S phase. Finally, we asked whether TRESLIN and MTBP binding to chromatin requires licensed origins. Using cell lines with a non-degradable inducible Geminin to inhibit licensing, we show TRESLIN and MTBP binding does not require loaded MCMs. Altogether, our Cut&Run data provides evidence for a chromatin binding mechanism of TRESLIN-MTBP during G1 that is dependent on TRESLIN and does not require interactions with licensed origins.
Collapse
Affiliation(s)
- Tyler D Noble
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Courtney G Sansam
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Kimberlie A Wittig
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Blanka Majchrzycka
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| | - Christopher L Sansam
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104
| |
Collapse
|
3
|
Xiang S, Luo X, Welch D, Reed DR, Alexandrow MG. Identification of Selective ATP-Competitive CMG Helicase Inhibitors for Cancer Intervention that Disrupt CMG-Replisome Function. RESEARCH SQUARE 2023:rs.3.rs-3182731. [PMID: 37609279 PMCID: PMC10441460 DOI: 10.21203/rs.3.rs-3182731/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
The human CMG helicase (Cdc45-MCM-GINS) is a novel target for anti-cancer therapy due to tumor-specific weaknesses in CMG function induced by oncogenic changes and the need for CMG function during recovery from replicative stresses such as chemotherapy. Here, we developed an orthogonal biochemical screening approach and identified selective CMG inhibitors (CMGi) that inhibit ATPase and helicase activities in an ATP-competitive manner at low micromolar concentrations. Structure-activity information and in silico docking indicate that CMGi occupy ATP binding sites and channels within MCM subunits leading to the ATP clefts, which are likely used for ATP/ADP ingress or egress. CMGi inhibit cell growth and DNA replication using multiple molecular mechanisms. CMGi block helicase assembly steps that require ATP binding/hydrolysis by the MCM complex, specifically MCM ring assembly on DNA and GINS recruitment to DNA-loaded MCM hexamers. During S-phase, inhibition of MCM ATP binding/hydrolysis by CMGi causes a 'reverse allosteric' dissociation of Cdc45/GINS from the CMG that destabilizes the replisome and disrupts interactions with Ctf4, Mcm10, and DNA polymerase-α, -δ, -ε, resulting in DNA damage. These novel CMGi are selectively toxic toward tumor cells and define a new class of CMG helicase-targeted anti-cancer compounds with distinct mechanisms of action.
Collapse
Affiliation(s)
- Shengyan Xiang
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Xingju Luo
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Darcy Welch
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Department of Individualized Cancer Management, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Damon R. Reed
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Department of Individualized Cancer Management, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Mark G. Alexandrow
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| |
Collapse
|
4
|
Guilz NC, Ahn YO, Seo S, Mace EM. Unwinding the Role of the CMG Helicase in Inborn Errors of Immunity. J Clin Immunol 2023; 43:847-861. [PMID: 36809597 PMCID: PMC10789183 DOI: 10.1007/s10875-023-01437-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2022] [Accepted: 01/20/2023] [Indexed: 02/23/2023]
Abstract
Inborn errors of immunity (IEI) are a collection of diseases resulting from genetic causes that impact the immune system through multiple mechanisms. Natural killer cell deficiency (NKD) is one such IEI where natural killer (NK) cells are the main immune lineage affected. Though rare, the deficiency of several genes has been described as underlying causes of NKD, including MCM4, GINS1, MCM10 , and GINS4 , all of which are involved in the eukaryotic CMG helicase. The CMG helicase is made up of C DC45 – M CM – G INS and accessory proteins including MCM10. The CMG helicase plays a critical role in DNA replication by unwinding the double helix and enabling access of polymerases to single-stranded DNA, and thus helicase proteins are active in any proliferating cell. Replication stress, DNA damage, and cell cycle arrest are among the cellular phenotypes attributed to loss of function variants in CMG helicase proteins. Despite the ubiquitous function of the CMG helicase, NK cells have an apparent susceptibility to the deficiency of helicase proteins. This review will examine the role of the CMG helicase in inborn errors of immunity through the lens of NKD and further discuss why natural killer cells can be so strongly affected by helicase deficiency.
Collapse
Affiliation(s)
- Nicole C Guilz
- Vagelos College of Physicians and Surgeons, Department of Pediatrics, Columbia University Irving Medical Center, 630 W 168th St., New York, NY, 10032, USA
| | - Yong-Oon Ahn
- Vagelos College of Physicians and Surgeons, Department of Pediatrics, Columbia University Irving Medical Center, 630 W 168th St., New York, NY, 10032, USA
| | - Seungmae Seo
- Vagelos College of Physicians and Surgeons, Department of Pediatrics, Columbia University Irving Medical Center, 630 W 168th St., New York, NY, 10032, USA
| | - Emily M Mace
- Vagelos College of Physicians and Surgeons, Department of Pediatrics, Columbia University Irving Medical Center, 630 W 168th St., New York, NY, 10032, USA.
| |
Collapse
|
5
|
The CMG helicase and cancer: a tumor "engine" and weakness with missing mutations. Oncogene 2023; 42:473-490. [PMID: 36522488 PMCID: PMC9948756 DOI: 10.1038/s41388-022-02572-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 12/01/2022] [Accepted: 12/07/2022] [Indexed: 12/23/2022]
Abstract
The replicative Cdc45-MCM-GINS (CMG) helicase is a large protein complex that functions in the DNA melting and unwinding steps as a component of replisomes during DNA replication in mammalian cells. Although the CMG performs this important role in cell growth, the CMG is not a simple bystander in cell cycle events. Components of the CMG, specifically the MCM precursors, are also involved in maintaining genomic stability by regulating DNA replication fork speeds, facilitating recovery from replicative stresses, and preventing consequential DNA damage. Given these important functions, MCM/CMG complexes are highly regulated by growth factors such as TGF-ß1 and by signaling factors such as Myc, Cyclin E, and the retinoblastoma protein. Mismanagement of MCM/CMG complexes when these signaling mediators are deregulated, and in the absence of the tumor suppressor protein p53, leads to increased genomic instability and is a contributor to tumorigenic transformation and tumor heterogeneity. The goal of this review is to provide insight into the mechanisms and dynamics by which the CMG is regulated during its assembly and activation in mammalian genomes, and how errors in CMG regulation due to oncogenic changes promote tumorigenesis. Finally, and most importantly, we highlight the emerging understanding of the CMG helicase as an exploitable vulnerability and novel target for therapeutic intervention in cancer.
Collapse
|
6
|
Rhind N. DNA replication timing: Biochemical mechanisms and biological significance. Bioessays 2022; 44:e2200097. [PMID: 36125226 PMCID: PMC9783711 DOI: 10.1002/bies.202200097] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2022] [Revised: 08/31/2022] [Accepted: 09/02/2022] [Indexed: 12/27/2022]
Abstract
The regulation of DNA replication is a fascinating biological problem both from a mechanistic angle-How is replication timing regulated?-and from an evolutionary one-Why is replication timing regulated? Recent work has provided significant insight into the first question. Detailed biochemical understanding of the mechanism and regulation of replication initiation has made possible robust hypotheses for how replication timing is regulated. Moreover, technical progress, including high-throughput, single-molecule mapping of replication initiation and single-cell assays of replication timing, has allowed for direct testing of these hypotheses in mammalian cells. This work has consolidated the conclusion that differential replication timing is a consequence of the varying probability of replication origin initiation. The second question is more difficult to directly address experimentally. Nonetheless, plausible hypotheses can be made and one-that replication timing contributes to the regulation of chromatin structure-has received new experimental support.
Collapse
Affiliation(s)
- Nicholas Rhind
- Biochemistry and Molecular Biotechnology, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| |
Collapse
|
7
|
LSD1 is required for euchromatic origin firing and replication timing. Signal Transduct Target Ther 2022; 7:102. [PMID: 35414135 PMCID: PMC9005705 DOI: 10.1038/s41392-022-00927-x] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2021] [Revised: 01/31/2022] [Accepted: 02/13/2022] [Indexed: 11/08/2022] Open
Abstract
The chromatin-based rule governing the selection and activation of replication origins remains to be elucidated. It is believed that DNA replication initiates from open chromatin domains; thus, replication origins reside in open and active chromatin. However, we report here that lysine-specific demethylase 1 (LSD1), which biochemically catalyzes H3K4me1/2 demethylation favoring chromatin condensation, interacts with the DNA replication machinery in human cells. We find that LSD1 level peaks in early S phase, when it is required for DNA replication by facilitating origin firing in euchromatic regions. Indeed, euchromatic zones enriched in H3K4me2 are the preferred sites for the pre-replicative complex (pre-RC) binding. Remarkably, LSD1 deficiency leads to a genome-wide switch of replication from early to late. We show that LSD1-engaged DNA replication is mechanistically linked to the loading of TopBP1-Interacting Checkpoint and Replication Regulator (TICRR) onto the pre-RC and subsequent recruitment of CDC45 during origin firing. Together, these results reveal an unexpected role for LSD1 in euchromatic origin firing and replication timing, highlighting the importance of epigenetic regulation in the activation of replication origins. As selective inhibitors of LSD1 are being exploited as potential cancer therapeutics, our study supports the importance of leveraging an appropriate level of LSD1 to curb the side effects of anti-LSD1 therapy.
Collapse
|
8
|
Wittig KA, Sansam CG, Noble TD, Goins D, Sansam CL. The CRL4DTL E3 ligase induces degradation of the DNA replication initiation factor TICRR/TRESLIN specifically during S phase. Nucleic Acids Res 2021; 49:10507-10523. [PMID: 34534348 PMCID: PMC8501952 DOI: 10.1093/nar/gkab805] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2021] [Revised: 08/26/2021] [Accepted: 09/13/2021] [Indexed: 01/02/2023] Open
Abstract
A DNA replication program, which ensures that the genome is accurately and wholly replicated, is established during G1, before the onset of S phase. In G1, replication origins are licensed, and upon S phase entry, a subset of these will form active replisomes. Tight regulation of the number of active replisomes is crucial to prevent replication stress-induced DNA damage. TICRR/TRESLIN is essential for DNA replication initiation, and the level of TICRR and its phosphorylation determine the number of origins that initiate during S phase. However, the mechanisms regulating TICRR protein levels are unknown. Therefore, we set out to define the TICRR/TRESLIN protein dynamics throughout the cell cycle. Here, we show that TICRR levels are high during G1 and dramatically decrease as cells enter S phase and begin DNA replication. We show that degradation of TICRR occurs specifically during S phase and depends on ubiquitin ligases and proteasomal degradation. Using two targeted siRNA screens, we identify CRL4DTL as a cullin complex necessary for TICRR degradation. We propose that this mechanism moderates the level of TICRR protein available for replication initiation, ensuring the proper number of active origins as cells progress through S phase.
Collapse
Affiliation(s)
- Kimberlie A Wittig
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.,Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
| | - Courtney G Sansam
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
| | - Tyler D Noble
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.,Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
| | - Duane Goins
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
| | - Christopher L Sansam
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA.,Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, OK 73104, USA
| |
Collapse
|
9
|
Alavi S, Ghadiri H, Dabirmanesh B, Moriyama K, Khajeh K, Masai H. G-quadruplex binding protein Rif1, a key regulator of replication timing. J Biochem 2021; 169:1-14. [PMID: 33169133 DOI: 10.1093/jb/mvaa128] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2020] [Accepted: 10/18/2020] [Indexed: 12/19/2022] Open
Abstract
DNA replication is spatially and temporally regulated during S phase to execute efficient and coordinated duplication of entire genome. Various epigenomic mechanisms operate to regulate the timing and locations of replication. Among them, Rif1 plays a major role to shape the 'replication domains' that dictate which segments of the genome are replicated when and where in the nuclei. Rif1 achieves this task by generating higher-order chromatin architecture near nuclear membrane and by recruiting a protein phosphatase. Rif1 is a G4 binding protein, and G4 binding activity of Rif1 is essential for replication timing regulation in fission yeast. In this article, we first summarize strategies by which cells regulate their replication timing and then describe how Rif1 and its interaction with G4 contribute to regulation of chromatin architecture and replication timing.
Collapse
Affiliation(s)
| | - Hamed Ghadiri
- Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Bahareh Dabirmanesh
- Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Kenji Moriyama
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, Japan
| | - Khosro Khajeh
- Department of Nanobiotechnology.,Department of Biochemistry, Faculty of Biological Sciences, Tarbiat Modares University, Tehran, Iran
| | - Hisao Masai
- Genome Dynamics Project, Department of Basic Medical Sciences, Tokyo Metropolitan Institute of Medical Science, 2-1-6 Kamikitazawa, Setagaya-ku, Tokyo, Japan
| |
Collapse
|
10
|
Fan Y, Köberlin MS, Ratnayeke N, Liu C, Deshpande M, Gerhardt J, Meyer T. LRR1-mediated replisome disassembly promotes DNA replication by recycling replisome components. J Cell Biol 2021; 220:212186. [PMID: 34037657 PMCID: PMC8160578 DOI: 10.1083/jcb.202009147] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2020] [Revised: 03/30/2021] [Accepted: 05/04/2021] [Indexed: 11/22/2022] Open
Abstract
After two converging DNA replication forks meet, active replisomes are disassembled and unloaded from chromatin. A key process in replisome disassembly is the unloading of CMG helicases (CDC45–MCM–GINS), which is initiated in Caenorhabditis elegans and Xenopus laevis by the E3 ubiquitin ligase CRL2LRR1. Here, we show that human cells lacking LRR1 fail to unload CMG helicases and accumulate increasing amounts of chromatin-bound replisome components as cells progress through S phase. Markedly, we demonstrate that the failure to disassemble replisomes reduces the rate of DNA replication increasingly throughout S phase by sequestering rate-limiting replisome components on chromatin and blocking their recycling. Continued binding of CMG helicases to chromatin during G2 phase blocks mitosis by activating an ATR-mediated G2/M checkpoint. Finally, we provide evidence that LRR1 is an essential gene for human cell division, suggesting that CRL2LRR1 enzyme activity is required for the proliferation of cancer cells and is thus a potential target for cancer therapy.
Collapse
Affiliation(s)
- Yilin Fan
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA.,Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY
| | - Marielle S Köberlin
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA
| | - Nalin Ratnayeke
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA.,Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY
| | - Chad Liu
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA
| | - Madhura Deshpande
- Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medicine, New York, NY
| | - Jeannine Gerhardt
- Ronald O. Perelman and Claudia Cohen Center for Reproductive Medicine, Weill Cornell Medicine, New York, NY.,Department of Obstetrics and Gynecology, Weill Cornell Medicine, New York, NY
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA.,Department of Cell and Developmental Biology, Weill Cornell Medicine, New York, NY
| |
Collapse
|
11
|
The replicative CMG helicase: the ideal target for cancer therapy. UKRAINIAN BIOCHEMICAL JOURNAL 2020. [DOI: 10.15407/ubj92.06.053] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022] Open
|
12
|
Ocaña-Pallarès E, Vergara Z, Desvoyes B, Tejada-Jimenez M, Romero-Jurado A, Galván A, Fernández E, Ruiz-Trillo I, Gutierrez C. Origin Recognition Complex (ORC) Evolution Is Influenced by Global Gene Duplication/Loss Patterns in Eukaryotic Genomes. Genome Biol Evol 2020; 12:3878-3889. [PMID: 31990293 PMCID: PMC7058166 DOI: 10.1093/gbe/evaa011] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 01/14/2020] [Indexed: 12/29/2022] Open
Abstract
The conservation of orthologs of most subunits of the origin recognition complex (ORC) has served to propose that the whole complex is common to all eukaryotes. However, various uncertainties have arisen concerning ORC subunit composition in a variety of lineages. Also, it is unclear whether the ancestral diversification of ORC in eukaryotes was accompanied by the neofunctionalization of some subunits, for example, role of ORC1 in centriole homeostasis. We have addressed these questions by reconstructing the distribution and evolutionary history of ORC1-5/CDC6 in a taxon-rich eukaryotic data set. First, we identified ORC subunits previously undetected in divergent lineages, which allowed us to propose a series of parsimonious scenarios for the origin of this multiprotein complex. Contrary to previous expectations, we found a global tendency in eukaryotes to increase or decrease the number of subunits as a consequence of genome duplications or streamlining, respectively. Interestingly, parasites show significantly lower number of subunits than free-living eukaryotes, especially those with the lowest genome size and gene content metrics. We also investigated the evolutionary origin of the ORC1 role in centriole homeostasis mediated by the PACT region in human cells. In particular, we tested the consequences of reducing ORC1 levels in the centriole-containing green alga Chlamydomonas reinhardtii. We found that the proportion of centrioles to flagella and nuclei was not dramatically affected. This, together with the PACT region not being significantly more conserved in centriole-bearing eukaryotes, supports the notion that this neofunctionalization of ORC1 would be a recent acquisition rather than an ancestral eukaryotic feature.
Collapse
Affiliation(s)
| | - Zaida Vergara
- Centro de Biologia Molecular Severo Ochoa, CSIC-UAM, Cantoblanco, Madrid, Spain
| | - Bénédicte Desvoyes
- Centro de Biologia Molecular Severo Ochoa, CSIC-UAM, Cantoblanco, Madrid, Spain
| | - Manuel Tejada-Jimenez
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Córdoba, Spain
| | - Ainoa Romero-Jurado
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Córdoba, Spain
| | - Aurora Galván
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Córdoba, Spain
| | - Emilio Fernández
- Departamento de Bioquímica y Biología Molecular, Facultad de Ciencias, Universidad de Córdoba, Córdoba, Spain
| | - Iñaki Ruiz-Trillo
- Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Barcelona, Spain.,Departament de Genètica, Microbiologia i Estadística, Universitat de Barcelona, Barcelona, Spain.,ICREA, Barcelona, Spain
| | - Crisanto Gutierrez
- Centro de Biologia Molecular Severo Ochoa, CSIC-UAM, Cantoblanco, Madrid, Spain
| |
Collapse
|
13
|
MCM family in gastrointestinal cancer and other malignancies: From functional characterization to clinical implication. Biochim Biophys Acta Rev Cancer 2020; 1874:188415. [PMID: 32822825 DOI: 10.1016/j.bbcan.2020.188415] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2020] [Revised: 08/15/2020] [Accepted: 08/15/2020] [Indexed: 02/07/2023]
Abstract
Despite the recent advances in cancer research and treatment, gastrointestinal (GI) cancers remain the most common deadly disease worldwide. The aberrant DNA replication serves as a major source of genomic instability and enhances cell proliferation that contributes to tumor initiation and progression. Minichromosome maintenance family (MCMs) is a well-recognized group of proteins responsible for DNA synthesis. Recent studies suggested that dysregulated MCMs lead to tumor initiation, progression, and chemoresistance via modulating cell cycle and DNA replication stress. Their underlying mechanisms in various cancer types have been gradually identified. Furthermore, multiple studies have investigated the association between MCMs expression and clinicopathological features of cancer patients, implying that MCMs might serve as prominent prognostic biomarkers for GI cancers. This review summarizes the current knowledge on the oncogenic role of MCM proteins and highlights their clinical implications in various malignancies, especially in GI cancers. Targeting MCMs might shed light on the potential for identifying novel therapeutic strategies.
Collapse
|
14
|
Reduced replication origin licensing selectively kills KRAS-mutant colorectal cancer cells via mitotic catastrophe. Cell Death Dis 2020; 11:499. [PMID: 32612138 PMCID: PMC7330027 DOI: 10.1038/s41419-020-2704-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2019] [Revised: 06/01/2020] [Accepted: 06/08/2020] [Indexed: 12/16/2022]
Abstract
To unravel vulnerabilities of KRAS-mutant CRC cells, a shRNA-based screen specifically inhibiting MAPK pathway components and targets was performed in CaCo2 cells harboring conditional oncogenic KRASG12V. The custom-designed shRNA library comprised 121 selected genes, which were previously identified to be strongly regulated in response to MEK inhibition. The screen showed that CaCo2 cells expressing KRASG12V were sensitive to the suppression of the DNA replication licensing factor minichromosome maintenance complex component 7 (MCM7), whereas KRASwt CaCo2 cells were largely resistant to MCM7 suppression. Similar results were obtained in an isogenic DLD-1 cell culture model. Knockdown of MCM7 in a KRAS-mutant background led to replication stress as indicated by increased nuclear RPA focalization. Further investigation showed a significant increase in mitotic cells after simultaneous MCM7 knockdown and KRASG12V expression. The increased percentage of mitotic cells coincided with strongly increased DNA damage in mitosis. Taken together, the accumulation of DNA damage in mitotic cells is due to replication stress that remained unresolved, which results in mitotic catastrophe and cell death. In summary, the data show a vulnerability of KRAS-mutant cells towards suppression of MCM7 and suggest that inhibiting DNA replication licensing might be a viable strategy to target KRAS-mutant cancers.
Collapse
|
15
|
Reed DR, Alexandrow MG. Myc and the Replicative CMG Helicase: The Creation and Destruction of Cancer: Myc Over-Activation of CMG Helicases Drives Tumorigenesis and Creates a Vulnerability in CMGs for Therapeutic Intervention. Bioessays 2020; 42:e1900218. [PMID: 32080866 PMCID: PMC8223603 DOI: 10.1002/bies.201900218] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2019] [Revised: 01/23/2020] [Indexed: 12/27/2022]
Abstract
Myc-driven tumorigenesis involves a non-transcriptional role for Myc in over-activating replicative Cdc45-MCM-GINS (CMG) helicases. Excessive stimulation of CMG helicases by Myc mismanages CMG function by diminishing the number of reserve CMGs necessary for fidelity of DNA replication and recovery from replicative stresses. One potential outcome of these events is the creation of DNA damage that alters genomic structure/function, thereby acting as a driver for tumorigenesis and tumor heterogeneity. Intriguingly, another potential outcome of this Myc-induced CMG helicase over-activation is the creation of a vulnerability in cancer whereby tumor cells specifically lack enough unused reserve CMG helicases to recover from fork-stalling drugs commonly used in chemotherapy. This review provides molecular and clinical support for this provocative hypothesis that excessive activation of CMG helicases by Myc may not only drive tumorigenesis, but also confer an exploitable "reserve CMG helicase vulnerability" that supports developing innovative CMG-focused therapeutic approaches for cancer management.
Collapse
Affiliation(s)
- Damon R Reed
- Department of Interdisciplinary Cancer Management, Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA
| | - Mark G Alexandrow
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, FL, 33612, USA
| |
Collapse
|
16
|
Hulke ML, Massey DJ, Koren A. Genomic methods for measuring DNA replication dynamics. Chromosome Res 2020; 28:49-67. [PMID: 31848781 PMCID: PMC7131883 DOI: 10.1007/s10577-019-09624-y] [Citation(s) in RCA: 17] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 11/30/2019] [Accepted: 12/03/2019] [Indexed: 12/27/2022]
Abstract
Genomic DNA replicates according to a defined temporal program in which early-replicating loci are associated with open chromatin, higher gene density, and increased gene expression levels, while late-replicating loci tend to be heterochromatic and show higher rates of genomic instability. The ability to measure DNA replication dynamics at genome scale has proven crucial for understanding the mechanisms and cellular consequences of DNA replication timing. Several methods, such as quantification of nucleotide analog incorporation and DNA copy number analyses, can accurately reconstruct the genomic replication timing profiles of various species and cell types. More recent developments have expanded the DNA replication genomic toolkit to assays that directly measure the activity of replication origins, while single-cell replication timing assays are beginning to reveal a new level of replication timing regulation. The combination of these methods, applied on a genomic scale and in multiple biological systems, promises to resolve many open questions and lead to a holistic understanding of how eukaryotic cells replicate their genomes accurately and efficiently.
Collapse
Affiliation(s)
- Michelle L Hulke
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Dashiell J Massey
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA
| | - Amnon Koren
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY, 14853, USA.
| |
Collapse
|
17
|
Warren NJH, Eastman A. Comparison of the different mechanisms of cytotoxicity induced by checkpoint kinase I inhibitors when used as single agents or in combination with DNA damage. Oncogene 2020; 39:1389-1401. [PMID: 31659257 PMCID: PMC7023985 DOI: 10.1038/s41388-019-1079-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2019] [Revised: 10/14/2019] [Accepted: 10/15/2019] [Indexed: 12/31/2022]
Abstract
Inhibition of the DNA damage response is an emerging strategy to treat cancer. Understanding how DNA damage response inhibitors cause cytotoxicity in cancer cells is crucial to their further clinical development. This review focuses on three different mechanisms of cell killing by checkpoint kinase I inhibitors (CHK1i). DNA damage induced by chemotherapy drugs, such as topoisomerase I inhibitors, results in S and G2 phase arrest. Addition of CHK1i promotes cell cycle progression before repair is completed resulting in mitotic catastrophe. Ribonucleotide reductase inhibitors such as gemcitabine also arrest cells in S phase by preventing dNTP synthesis. Addition of CHK1i re-activates the DNA helicase to unwind DNA, but in the absence of dNTPs, this leads to excessive single-strand DNA that exceeds the protective capacity of the single-strand-binding protein RPA. Unprotected DNA is subjected to nuclease cleavage, resulting in replication catastrophe. CHK1i alone also kills a subset of cell lines through MRE11 and MUS81-mediated DNA cleavage in S phase cells. The choice of mechanism depends on the activation state of CDK2. Low level activation of CDK2 mediates helicase activation, cell cycle progression, and both replication and mitotic catastrophe. In contrast, high CDK2 activity is required for sensitivity to CHK1i as monotherapy. This high CDK2 activity threshold usually occurs late in the cell cycle to prepare for mitosis, but in CHK1i-sensitive cells, high activity can be attained in early S phase, resulting in DNA cleavage and cell death. This sensitivity to CHK1i has previously been associated with endogenous replication stress, but the dependence on high CDK2 activity, as well as MRE11, contradicts this hypothesis. The major unresolved question is why some cell lines fail to restrain their high CDK2 activity and hence succumb to CHK1i in S phase. Resolving this question will facilitate stratification of patients for treatment with CHK1i as monotherapy.
Collapse
Affiliation(s)
- Nicholas J H Warren
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA
| | - Alan Eastman
- Department of Molecular and Systems Biology, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA.
- Norris Cotton Cancer Center, Geisel School of Medicine at Dartmouth, Lebanon, NH, 03756, USA.
| |
Collapse
|
18
|
Limas JC, Cook JG. Preparation for DNA replication: the key to a successful S phase. FEBS Lett 2019; 593:2853-2867. [PMID: 31556113 PMCID: PMC6817399 DOI: 10.1002/1873-3468.13619] [Citation(s) in RCA: 42] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2019] [Revised: 09/09/2019] [Accepted: 09/17/2019] [Indexed: 12/13/2022]
Abstract
Successful genome duplication is required for cell proliferation and demands extraordinary precision and accuracy. The mechanisms by which cells enter, progress through, and exit S phase are intense areas of focus in the cell cycle and genome stability fields. Key molecular events in the G1 phase of the cell division cycle, especially origin licensing, are essential for pre-establishing conditions for efficient DNA replication during the subsequent S phase. If G1 events are poorly regulated or disordered, then DNA replication can be compromised leading to genome instability, a hallmark of tumorigenesis. Upon entry into S phase, coordinated origin firing and replication progression ensure complete, timely, and precise chromosome replication. Both G1 and S phase progressions are controlled by master cell cycle protein kinases and ubiquitin ligases that govern the activity and abundance of DNA replication factors. In this short review, we describe current understanding and recent developments related to G1 progression and S phase entrance and exit with a particular focus on origin licensing regulation in vertebrates.
Collapse
Affiliation(s)
- Juanita C Limas
- Department of Pharmacology, University of North Carolina at Chapel Hill, NC, USA
| | - Jeanette Gowen Cook
- Department of Pharmacology, University of North Carolina at Chapel Hill, NC, USA
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, NC, USA
| |
Collapse
|
19
|
Sugimoto N, Maehara K, Yoshida K, Ohkawa Y, Fujita M. Genome-wide analysis of the spatiotemporal regulation of firing and dormant replication origins in human cells. Nucleic Acids Res 2019; 46:6683-6696. [PMID: 29893900 PMCID: PMC6061783 DOI: 10.1093/nar/gky476] [Citation(s) in RCA: 46] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2018] [Accepted: 05/16/2018] [Indexed: 12/25/2022] Open
Abstract
In metazoan cells, only a limited number of mini chromosome maintenance (MCM) complexes are fired during S phase, while the majority remain dormant. Several methods have been used to map replication origins, but such methods cannot identify dormant origins. Herein, we determined MCM7-binding sites in human cells using ChIP-Seq, classified them into firing and dormant origins using origin data and analysed their association with various chromatin signatures. Firing origins, but not dormant origins, were well correlated with open chromatin regions and were enriched upstream of transcription start sites (TSSs) of transcribed genes. Aggregation plots of MCM7 signals revealed minimal difference in the efficacy of MCM loading between firing and dormant origins. We also analysed common fragile sites (CFSs) and found a low density of origins at these sites. Nevertheless, firing origins were enriched upstream of the TSSs. Based on the results, we propose a model in which excessive MCMs are actively loaded in a genome-wide manner, irrespective of chromatin status, but only a fraction are passively fired in chromatin areas with an accessible open structure, such as regions upstream of TSSs of transcribed genes. This plasticity in the specification of replication origins may minimize collisions between replication and transcription.
Collapse
Affiliation(s)
- Nozomi Sugimoto
- Department of Cellular Biochemistry, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan
| | - Kazumitsu Maehara
- Division of Transcriptomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan
| | - Kazumasa Yoshida
- Department of Cellular Biochemistry, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan
| | - Yasuyuki Ohkawa
- Division of Transcriptomics, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan
| | - Masatoshi Fujita
- Department of Cellular Biochemistry, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashiku, Fukuoka 812-8582, Japan
| |
Collapse
|
20
|
González Besteiro MA, Calzetta NL, Loureiro SM, Habif M, Bétous R, Pillaire MJ, Maffia A, Sabbioneda S, Hoffmann JS, Gottifredi V. Chk1 loss creates replication barriers that compromise cell survival independently of excess origin firing. EMBO J 2019; 38:e101284. [PMID: 31294866 DOI: 10.15252/embj.2018101284] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Revised: 06/11/2019] [Accepted: 06/19/2019] [Indexed: 01/18/2023] Open
Abstract
The effectiveness of checkpoint kinase 1 (Chk1) inhibitors at killing cancer cells is considered to be fully dependent on their effect on DNA replication initiation. Chk1 inhibition boosts origin firing, presumably limiting the availability of nucleotides and in turn provoking the slowdown and subsequent collapse of forks, thus decreasing cell viability. Here we show that slow fork progression in Chk1-inhibited cells is not an indirect effect of excess new origin firing. Instead, fork slowdown results from the accumulation of replication barriers, whose bypass is impeded by CDK-dependent phosphorylation of the specialized DNA polymerase eta (Polη). Also in contrast to the linear model, the accumulation of DNA damage in Chk1-deficient cells depends on origin density but is largely independent of fork speed. Notwithstanding this, origin dysregulation contributes only mildly to the poor proliferation rates of Chk1-depleted cells. Moreover, elimination of replication barriers by downregulation of helicase components, but not their bypass by Polη, improves cell survival. Our results thus shed light on the molecular basis of the sensitivity of tumors to Chk1 inhibition.
Collapse
Affiliation(s)
- Marina A González Besteiro
- Fundación Instituto Leloir - Instituto de Investigaciones Bioquímicas de Buenos Aires, Consejo de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Nicolás L Calzetta
- Fundación Instituto Leloir - Instituto de Investigaciones Bioquímicas de Buenos Aires, Consejo de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Sofía M Loureiro
- Fundación Instituto Leloir - Instituto de Investigaciones Bioquímicas de Buenos Aires, Consejo de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Martín Habif
- Fundación Instituto Leloir - Instituto de Investigaciones Bioquímicas de Buenos Aires, Consejo de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| | - Rémy Bétous
- Equipe «Labellisée LA LIGUE CONTRE LE CANCER», Laboratoire d'Excellence Toulouse Cancer LABEX TOUCAN - Cancer Research Center of Toulouse, Inserm U1037, CNRS ERL5294, University Paul Sabatier, Toulouse, France
| | - Marie-Jeanne Pillaire
- Equipe «Labellisée LA LIGUE CONTRE LE CANCER», Laboratoire d'Excellence Toulouse Cancer LABEX TOUCAN - Cancer Research Center of Toulouse, Inserm U1037, CNRS ERL5294, University Paul Sabatier, Toulouse, France
| | - Antonio Maffia
- Istituto di Genetica Molecolare "Luigi Luca Cavalli-Sforza" - CNR, Pavia, Italy
| | - Simone Sabbioneda
- Istituto di Genetica Molecolare "Luigi Luca Cavalli-Sforza" - CNR, Pavia, Italy
| | - Jean-Sébastien Hoffmann
- Equipe «Labellisée LA LIGUE CONTRE LE CANCER», Laboratoire d'Excellence Toulouse Cancer LABEX TOUCAN - Cancer Research Center of Toulouse, Inserm U1037, CNRS ERL5294, University Paul Sabatier, Toulouse, France
| | - Vanesa Gottifredi
- Fundación Instituto Leloir - Instituto de Investigaciones Bioquímicas de Buenos Aires, Consejo de Investigaciones Científicas y Técnicas, Buenos Aires, Argentina
| |
Collapse
|
21
|
Duriez B, Chilaka S, Bercher JF, Hercul E, Prioleau MN. Replication dynamics of individual loci in single living cells reveal changes in the degree of replication stochasticity through S phase. Nucleic Acids Res 2019; 47:5155-5169. [PMID: 30926993 PMCID: PMC6547449 DOI: 10.1093/nar/gkz220] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/05/2019] [Revised: 03/18/2019] [Accepted: 03/21/2019] [Indexed: 12/22/2022] Open
Abstract
Eukaryotic genomes are replicated under the control of a highly sophisticated program during the restricted time period corresponding to S phase. The most widely used replication timing assays, which are performed on populations of millions of cells, suggest that most of the genome is synchronously replicated on homologous chromosomes. We investigated the stochastic nature of this temporal program, by comparing the precise replication times of allelic loci within single vertebrate cells progressing through S phase at six loci replicated from very early to very late. We show that replication timing is strictly controlled for the three loci replicated in the first half of S phase. Out of the three loci replicated in the second part of S phase, two present a significantly more stochastic pattern. Surprisingly, we find that the locus replicated at the very end of S phase, presents stochasticity similar to those replicated in early S phase. We suggest that the richness of loci in efficient origins of replication, which decreases from early- to late-replicating regions, and the strength of interaction with the nuclear lamina may underlie the variation of timing control during S phase.
Collapse
Affiliation(s)
- Bénédicte Duriez
- Domaines Chromatiniens et Réplication, Institut Jacques Monod, UMR7592 CNRS – Université Paris Diderot, Paris, France, Equipe labellisée ARC
| | - Sabarinadh Chilaka
- Domaines Chromatiniens et Réplication, Institut Jacques Monod, UMR7592 CNRS – Université Paris Diderot, Paris, France, Equipe labellisée ARC
| | | | - Eslande Hercul
- Domaines Chromatiniens et Réplication, Institut Jacques Monod, UMR7592 CNRS – Université Paris Diderot, Paris, France, Equipe labellisée ARC
| | - Marie-Noëlle Prioleau
- Domaines Chromatiniens et Réplication, Institut Jacques Monod, UMR7592 CNRS – Université Paris Diderot, Paris, France, Equipe labellisée ARC
| |
Collapse
|
22
|
Nepon-Sixt BS, Bryant VL, Alexandrow MG. Myc-driven chromatin accessibility regulates Cdc45 assembly into CMG helicases. Commun Biol 2019; 2:110. [PMID: 30911685 PMCID: PMC6430796 DOI: 10.1038/s42003-019-0353-2] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/25/2018] [Accepted: 02/07/2019] [Indexed: 01/08/2023] Open
Abstract
Myc-driven tumorigenesis involves a non-transcriptional role for Myc in over-activating replication origins. We show here that the mechanism underlying this process involves a direct role for Myc in activation of Cdc45-MCM-GINS (CMG) helicases at Myc-targeted sites. Myc induces decondensation of higher-order chromatin at targeted sites and is required for chromatin access at a chromosomal origin. Myc-driven chromatin accessibility promotes Cdc45/GINS recruitment to resident MCMs, and activation of CMGs. Myc-Box II, which is necessary for Myc-driven transformation, is required for Myc-induced chromatin accessibility, Cdc45/GINS recruitment, and replication stimulation. Myc interactors GCN5, Tip60, and TRRAP are essential for chromatin unfolding and recruitment of Cdc45, and co-expression of GCN5 or Tip60 with MBII-deficient Myc rescues these events and promotes CMG activation. Finally, Myc and Cdc45 interact and physiologic conditions for CMG assembly require the functions of Myc, MBII, and GCN5 for Cdc45 recruitment and initiation of DNA replication.
Collapse
Affiliation(s)
- Brook S. Nepon-Sixt
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, FL 33612 USA
| | - Victoria L. Bryant
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, FL 33612 USA
- University of South Florida Cancer Biology PhD Program, Tampa, FL 33612 USA
- Present Address: AT Still University School of Osteopathic Medicine 27 5850 E Still Circle, Mesa, AZ 85206 USA
| | - Mark G. Alexandrow
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, FL 33612 USA
- University of South Florida Cancer Biology PhD Program, Tampa, FL 33612 USA
| |
Collapse
|
23
|
Origin Firing Regulations to Control Genome Replication Timing. Genes (Basel) 2019; 10:genes10030199. [PMID: 30845782 PMCID: PMC6470937 DOI: 10.3390/genes10030199] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/30/2019] [Revised: 02/25/2019] [Accepted: 02/28/2019] [Indexed: 12/19/2022] Open
Abstract
Complete genome duplication is essential for genetic homeostasis over successive cell generations. Higher eukaryotes possess a complex genome replication program that involves replicating the genome in units of individual chromatin domains with a reproducible order or timing. Two types of replication origin firing regulations ensure complete and well-timed domain-wise genome replication: (1) the timing of origin firing within a domain must be determined and (2) enough origins must fire with appropriate positioning in a short time window to avoid inter-origin gaps too large to be fully copied. Fundamental principles of eukaryotic origin firing are known. We here discuss advances in understanding the regulation of origin firing to control firing time. Work with yeasts suggests that eukaryotes utilise distinct molecular pathways to determine firing time of distinct sets of origins, depending on the specific requirements of the genomic regions to be replicated. Although the exact nature of the timing control processes varies between eukaryotes, conserved aspects exist: (1) the first step of origin firing, pre-initiation complex (pre-IC formation), is the regulated step, (2) many regulation pathways control the firing kinase Dbf4-dependent kinase, (3) Rif1 is a conserved mediator of late origin firing and (4) competition between origins for limiting firing factors contributes to firing timing. Characterization of the molecular timing control pathways will enable us to manipulate them to address the biological role of replication timing, for example, in cell differentiation and genome instability.
Collapse
|
24
|
Abstract
IMPACT STATEMENT This review provides various genetic and cell line data previously published in a way to explain how cellular stress can lead into genetic instability.
Collapse
Affiliation(s)
- Jung Joo Moon
- 1 JS Yoon Memorial Cancer Research Institute LLC, Lutherville, MD 2109, USA
| | - Alexander Lu
- 1 JS Yoon Memorial Cancer Research Institute LLC, Lutherville, MD 2109, USA
| | - Chulso Moon
- 1 JS Yoon Memorial Cancer Research Institute LLC, Lutherville, MD 2109, USA.,2 Department of Otolaryngology-Head and Neck Surgery, The Johns Hopkins Medical Institution, Baltimore, MD 21205, USA
| |
Collapse
|
25
|
Nepon-Sixt BS, Alexandrow MG. TGFβ1 Cell Cycle Arrest Is Mediated by Inhibition of MCM Assembly in Rb-Deficient Conditions. Mol Cancer Res 2018; 17:277-288. [PMID: 30257992 DOI: 10.1158/1541-7786.mcr-18-0558] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2018] [Revised: 08/01/2018] [Accepted: 09/06/2018] [Indexed: 01/14/2023]
Abstract
Transforming growth factor β1 (TGFβ1) is a potent inhibitor of cell growth that targets gene-regulatory events, but also inhibits the function of CDC45-MCM-GINS helicases (CMG; MCM, Mini-Chromosome Maintenance; GINS, Go-Ichi-Ni-San) through multiple mechanisms to achieve cell-cycle arrest. Early in G1, TGFβ1 blocks MCM subunit expression and suppresses Myc and Cyclin E/Cdk2 activity required for CMG assembly, should MCMs be expressed. Once CMGs are assembled in late-G1, TGFβ1 blocks CMG activation using a direct mechanism involving the retinoblastoma (Rb) tumor suppressor. Here, in cells lacking Rb, TGFβ1 does not suppress Myc, Cyclin E/Cdk2 activity, or MCM expression, yet growth arrest remains intact and Smad2/3/4-dependent. Such arrest occurs due to inhibition of MCM hexamer assembly by TGFβ1, which is not seen when Rb is present and MCM subunit expression is normally blocked by TGFβ1. Loss of Smad expression prevents TGFβ1 suppression of MCM assembly. Mechanistically, TGFβ1 blocks a Cyclin E-Mcm7 molecular interaction required for MCM hexamer assembly upstream of CDC10-dependent transcript-1 (CDT1) function. Accordingly, overexpression of CDT1 with an intact MCM-binding domain abrogates TGFβ1 arrest and rescues MCM assembly. The ability of CDT1 to restore MCM assembly and allow S-phase entry indicates that, in the absence of Rb and other canonical mediators, TGFβ1 relies on inhibition of Cyclin E-MCM7 and MCM assembly to achieve cell cycle arrest. IMPLICATIONS: These results demonstrate that the MCM assembly process is a pivotal target of TGFβ1 in eliciting cell cycle arrest, and provide evidence for a novel oncogenic role for CDT1 in abrogating TGFβ1 inhibition of MCM assembly.
Collapse
Affiliation(s)
- Brook S Nepon-Sixt
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, Florida
| | - Mark G Alexandrow
- Department of Molecular Oncology, Moffitt Cancer Center and Research Institute, Tampa, Florida.
| |
Collapse
|
26
|
Aze A, Maiorano D. Recent advances in understanding DNA replication: cell type-specific adaptation of the DNA replication program. F1000Res 2018; 7. [PMID: 30228862 PMCID: PMC6117848 DOI: 10.12688/f1000research.15408.1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 08/20/2018] [Indexed: 12/11/2022] Open
Abstract
DNA replication is an essential process occurring prior to cell division. Cell division coupled to proliferation ensures the growth and renewal of a large variety of specialized cell types generated during embryonic development. Changes in the DNA replication program occur during development. Embryonic undifferentiated cells show a high replication rate and fast proliferation, whereas more differentiated cells are characterized by reduced DNA synthesis and a low proliferation rate. Hence, the DNA replication program must adapt to the specific features of cells committed to different fates. Recent findings on DNA synthesis regulation in different cell types open new perspectives for developing efficient and more adapted therapies to treat various diseases such as genetic diseases and cancer. This review will put the emphasis on recent progress made in this field.
Collapse
Affiliation(s)
- Antoine Aze
- Institute of Human Genetics, UMR9002, CNRS-University of Montpellier, Montpellier, 34396 Cedex 5, France
| | - Domenico Maiorano
- Institute of Human Genetics, UMR9002, CNRS-University of Montpellier, Montpellier, 34396 Cedex 5, France
| |
Collapse
|
27
|
Datta A, Ghatak D, Das S, Banerjee T, Paul A, Butti R, Gorain M, Ghuwalewala S, Roychowdhury A, Alam SK, Das P, Chatterjee R, Dasgupta M, Panda CK, Kundu GC, Roychoudhury S. p53 gain-of-function mutations increase Cdc7-dependent replication initiation. EMBO Rep 2017; 18:2030-2050. [PMID: 28887320 DOI: 10.15252/embr.201643347] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 08/04/2017] [Accepted: 08/09/2017] [Indexed: 12/31/2022] Open
Abstract
Cancer-associated p53 missense mutants confer gain of function (GOF) and promote tumorigenesis by regulating crucial signaling pathways. However, the role of GOF mutant p53 in regulating DNA replication, a commonly altered pathway in cancer, is less explored. Here, we show that enhanced Cdc7-dependent replication initiation enables mutant p53 to confer oncogenic phenotypes. We demonstrate that mutant p53 cooperates with the oncogenic transcription factor Myb in vivo and transactivates Cdc7 in cancer cells. Moreover, mutant p53 cells exhibit enhanced levels of Dbf4, promoting the activity of Cdc7/Dbf4 complex. Chromatin enrichment of replication initiation factors and subsequent increase in origin firing confirm increased Cdc7-dependent replication initiation in mutant p53 cells. Further, knockdown of CDC7 significantly abrogates mutant p53-driven cancer phenotypes in vitro and in vivo Importantly, high CDC7 expression significantly correlates with p53 mutational status and predicts poor clinical outcome in lung adenocarcinoma patients. Collectively, this study highlights a novel functional interaction between mutant p53 and the DNA replication pathway in cancer cells. We propose that increased Cdc7-dependent replication initiation is a hallmark of p53 gain-of-function mutations.
Collapse
Affiliation(s)
- Arindam Datta
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Dishari Ghatak
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Sumit Das
- Laboratory of Tumor Biology, Angiogenesis and Nanomedicine Research, National Centre for Cell Science (NCCS), Pune, India
| | - Taraswi Banerjee
- Laboratory of Molecular Gerontology, National Institute on Aging, NIH Biomedical Research Center, NIH, Baltimore, MD, USA
| | - Anindita Paul
- Department of Biochemistry, University of Calcutta, Kolkata, India
| | - Ramesh Butti
- Laboratory of Tumor Biology, Angiogenesis and Nanomedicine Research, National Centre for Cell Science (NCCS), Pune, India
| | - Mahadeo Gorain
- Laboratory of Tumor Biology, Angiogenesis and Nanomedicine Research, National Centre for Cell Science (NCCS), Pune, India
| | - Sangeeta Ghuwalewala
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Anirban Roychowdhury
- Department of Oncogene Regulation, Chittaranjan National Cancer Institute, Kolkata, India
| | - Sk Kayum Alam
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | - Pijush Das
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India
| | | | | | - Chinmay Kumar Panda
- Department of Oncogene Regulation, Chittaranjan National Cancer Institute, Kolkata, India
| | - Gopal C Kundu
- Laboratory of Tumor Biology, Angiogenesis and Nanomedicine Research, National Centre for Cell Science (NCCS), Pune, India
| | - Susanta Roychoudhury
- Cancer Biology and Inflammatory Disorder Division, CSIR-Indian Institute of Chemical Biology, Kolkata, India .,Saroj Gupta Cancer Centre and Research Institute, Kolkata, India
| |
Collapse
|
28
|
Neves H, Kwok HF. In sickness and in health: The many roles of the minichromosome maintenance proteins. Biochim Biophys Acta Rev Cancer 2017; 1868:295-308. [DOI: 10.1016/j.bbcan.2017.06.001] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2017] [Revised: 05/29/2017] [Accepted: 06/01/2017] [Indexed: 01/09/2023]
|
29
|
Shima N, Pederson KD. Dormant origins as a built-in safeguard in eukaryotic DNA replication against genome instability and disease development. DNA Repair (Amst) 2017; 56:166-173. [PMID: 28641940 PMCID: PMC5547906 DOI: 10.1016/j.dnarep.2017.06.019] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
DNA replication is a prerequisite for cell proliferation, yet it can be increasingly challenging for a eukaryotic cell to faithfully duplicate its genome as its size and complexity expands. Dormant origins now emerge as a key component for cells to successfully accomplish such a demanding but essential task. In this perspective, we will first provide an overview of the fundamental processes eukaryotic cells have developed to regulate origin licensing and firing. With a special focus on mammalian systems, we will then highlight the role of dormant origins in preventing replication-associated genome instability and their functional interplay with proteins involved in the DNA damage repair response for tumor suppression. Lastly, deficiencies in the origin licensing machinery will be discussed in relation to their influence on stem cell maintenance and human diseases.
Collapse
Affiliation(s)
- Naoko Shima
- The University of Minnesota, Twin Cities, Department of Genetics, Cell Biology and Development, Masonic Cancer Center, 6-160 Jackson Hall, 321 Church St SE., Minneapolis, MN 55455, United States.
| | - Kayla D Pederson
- The University of Minnesota, Twin Cities, Department of Genetics, Cell Biology and Development, Masonic Cancer Center, 6-160 Jackson Hall, 321 Church St SE., Minneapolis, MN 55455, United States
| |
Collapse
|
30
|
Köhler C, Koalick D, Fabricius A, Parplys AC, Borgmann K, Pospiech H, Grosse F. Cdc45 is limiting for replication initiation in humans. Cell Cycle 2017; 15:974-85. [PMID: 26919204 PMCID: PMC4889307 DOI: 10.1080/15384101.2016.1152424] [Citation(s) in RCA: 49] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cdc45 is an essential protein that together with Mcm2-7 and GINS forms the eukaryotic replicative helicase CMG. Cdc45 seems to be rate limiting for the initial unwinding or firing of replication origins. In line with this view, Cdc45-overexpressing cells fired at least twice as many origins as control cells. However, these cells displayed an about 2-fold diminished fork elongation rate, a pronounced asymmetry of replication fork extension, and an early S phase arrest. This was accompanied by H2AX-phosphorylation and subsequent apoptosis. Unexpectedly, we did not observe increased ATR/Chk1 signaling but rather a mild ATM/Chk2 response. In addition, we detected accumulation of long stretches of single-stranded DNA, a hallmark of replication catastrophe. We conclude that increased origin firing by upregulated Cdc45 caused exhaustion of the single-strand binding protein RPA, which in consequence diminished the ATR/Chk1 response; the subsequently occurring fork breaks led to an ATM/Chk2 mediated phosphorylation of H2AX and eventually to apoptosis.
Collapse
Affiliation(s)
- Carsten Köhler
- a Research group Biochemistry, Leibniz Institute for Age Research - Fritz Lipmann Institute , Jena , Germany
| | - Dennis Koalick
- a Research group Biochemistry, Leibniz Institute for Age Research - Fritz Lipmann Institute , Jena , Germany
| | - Anja Fabricius
- a Research group Biochemistry, Leibniz Institute for Age Research - Fritz Lipmann Institute , Jena , Germany
| | - Ann Christin Parplys
- b Laboratory of Radiobiology and Experimental Radiation Oncology, University Medical Center Hamburg-Eppendorf , Hamburg , Germany
| | - Kerstin Borgmann
- b Laboratory of Radiobiology and Experimental Radiation Oncology, University Medical Center Hamburg-Eppendorf , Hamburg , Germany
| | - Helmut Pospiech
- a Research group Biochemistry, Leibniz Institute for Age Research - Fritz Lipmann Institute , Jena , Germany.,c Faculty of Biochemistry and Molecular Medicine, University of Oulu , Finland
| | - Frank Grosse
- a Research group Biochemistry, Leibniz Institute for Age Research - Fritz Lipmann Institute , Jena , Germany.,d Centre for Molecular Biomedicine, Friedrich-Schiller University , Jena , Germany
| |
Collapse
|
31
|
The Intra-S Checkpoint Responses to DNA Damage. Genes (Basel) 2017; 8:genes8020074. [PMID: 28218681 PMCID: PMC5333063 DOI: 10.3390/genes8020074] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2017] [Revised: 02/08/2017] [Accepted: 02/08/2017] [Indexed: 02/03/2023] Open
Abstract
Faithful duplication of the genome is a challenge because DNA is susceptible to damage by a number of intrinsic and extrinsic genotoxins, such as free radicals and UV light. Cells activate the intra-S checkpoint in response to damage during S phase to protect genomic integrity and ensure replication fidelity. The checkpoint prevents genomic instability mainly by regulating origin firing, fork progression, and transcription of G1/S genes in response to DNA damage. Several studies hint that regulation of forks is perhaps the most critical function of the intra-S checkpoint. However, the exact role of the checkpoint at replication forks has remained elusive and controversial. Is the checkpoint required for fork stability, or fork restart, or to prevent fork reversal or fork collapse, or activate repair at replication forks? What are the factors that the checkpoint targets at stalled replication forks? In this review, we will discuss the various pathways activated by the intra-S checkpoint in response to damage to prevent genomic instability.
Collapse
|
32
|
Madireddy A, Gerhardt J. Replication Through Repetitive DNA Elements and Their Role in Human Diseases. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2017; 1042:549-581. [PMID: 29357073 DOI: 10.1007/978-981-10-6955-0_23] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Human cells contain various repetitive DNA sequences, which can be a challenge for the DNA replication machinery to travel through and replicate correctly. Repetitive DNA sequence can adopt non-B DNA structures, which could block the DNA replication. Prolonged stalling of the replication fork at the endogenous repeats in human cells can have severe consequences such as genome instability that includes repeat expansions, contractions, and chromosome fragility. Several neurological and muscular diseases are caused by a repeat expansion. Furthermore genome instability is the major cause of cancer. This chapter describes some of the important classes of repetitive DNA sequences in the mammalian genome, their ability to form secondary DNA structures, their contribution to replication fork stalling, and models for repeat expansion as well as chromosomal fragility. Included in this chapter are also some of the strategies currently employed to detect changes in DNA replication and proteins that could prevent the repeat-mediated disruption of DNA replication in human cells. Additionally summarized are the consequences of repeat-associated perturbation of the DNA replication, which could lead to specific human diseases.
Collapse
|
33
|
Inevitability and containment of replication errors for eukaryotic genome lengths spanning megabase to gigabase. Proc Natl Acad Sci U S A 2016; 113:E5765-74. [PMID: 27630194 PMCID: PMC5047159 DOI: 10.1073/pnas.1603241113] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
The replication of DNA is initiated at particular sites on the genome called replication origins (ROs). Understanding the constraints that regulate the distribution of ROs across different organisms is fundamental for quantifying the degree of replication errors and their downstream consequences. Using a simple probabilistic model, we generate a set of predictions on the extreme sensitivity of error rates to the distribution of ROs, and how this distribution must therefore be tuned for genomes of vastly different sizes. As genome size changes from megabases to gigabases, we predict that regularity of RO spacing is lost, that large gaps between ROs dominate error rates but are heavily constrained by the mean stalling distance of replication forks, and that, for genomes spanning ∼100 megabases to ∼10 gigabases, errors become increasingly inevitable but their number remains very small (three or less). Our theory predicts that the number of errors becomes significantly higher for genome sizes greater than ∼10 gigabases. We test these predictions against datasets in yeast, Arabidopsis, Drosophila, and human, and also through direct experimentation on two different human cell lines. Agreement of theoretical predictions with experiment and datasets is found in all cases, resulting in a picture of great simplicity, whereby the density and positioning of ROs explain the replication error rates for the entire range of eukaryotes for which data are available. The theory highlights three domains of error rates: negligible (yeast), tolerable (metazoan), and high (some plants), with the human genome at the extreme end of the middle domain.
Collapse
|
34
|
Selectivity of ORC binding sites and the relation to replication timing, fragile sites, and deletions in cancers. Proc Natl Acad Sci U S A 2016; 113:E4810-9. [PMID: 27436900 DOI: 10.1073/pnas.1609060113] [Citation(s) in RCA: 126] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The origin recognition complex (ORC) binds sites from which DNA replication is initiated. We address ORC binding selectivity in vivo by mapping ∼52,000 ORC2 binding sites throughout the human genome. The ORC binding profile is broader than those of sequence-specific transcription factors, suggesting that ORC is not bound or recruited to specific DNA sequences. Instead, ORC binds nonspecifically to open (DNase I-hypersensitive) regions containing active chromatin marks such as H3 acetylation and H3K4 methylation. ORC sites in early and late replicating regions have similar properties, but there are far more ORC sites in early replicating regions. This suggests that replication timing is due primarily to ORC density and stochastic firing of origins. Computational simulation of stochastic firing from identified ORC sites is in accord with replication timing data. Large genomic regions with a paucity of ORC sites are strongly associated with common fragile sites and recurrent deletions in cancers. We suggest that replication origins, replication timing, and replication-dependent chromosome breaks are determined primarily by the genomic distribution of activator proteins at enhancers and promoters. These activators recruit nucleosome-modifying complexes to create the appropriate chromatin structure that allows ORC binding and subsequent origin firing.
Collapse
|
35
|
Affiliation(s)
- Christian Speck
- a DNA Replication Group, Institute of Clinical Sciences, Imperial College London , London , UK.,b bMRC Clinical Sciences Centre , Du Cane Road, London , UK
| |
Collapse
|
36
|
DNA replication and cancer: From dysfunctional replication origin activities to therapeutic opportunities. Semin Cancer Biol 2016; 37-38:16-25. [DOI: 10.1016/j.semcancer.2016.01.001] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2015] [Revised: 01/04/2016] [Accepted: 01/05/2016] [Indexed: 12/18/2022]
|
37
|
Deciphering DNA replication dynamics in eukaryotic cell populations in relation with their averaged chromatin conformations. Sci Rep 2016; 6:22469. [PMID: 26935043 PMCID: PMC4776152 DOI: 10.1038/srep22469] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2015] [Accepted: 02/16/2016] [Indexed: 12/16/2022] Open
Abstract
We propose a non-local model of DNA replication that takes into account the observed
uncertainty on the position and time of replication initiation in eukaryote cell
populations. By picturing replication initiation as a two-state system and
considering all possible transition configurations, and by taking into account the
chromatin’s fractal dimension, we derive an analytical expression for
the rate of replication initiation. This model predicts with no free parameter the
temporal profiles of initiation rate, replication fork density and fraction of
replicated DNA, in quantitative agreement with corresponding experimental data from
both S. cerevisiae and human cells and provides a quantitative estimate of
initiation site redundancy. This study shows that, to a large extent, the program
that regulates the dynamics of eukaryotic DNA replication is a collective phenomenon
that emerges from the stochastic nature of replication origins initiation.
Collapse
|
38
|
The N Terminus of the Retinoblastoma Protein Inhibits DNA Replication via a Bipartite Mechanism Disrupted in Partially Penetrant Retinoblastomas. Mol Cell Biol 2015; 36:832-45. [PMID: 26711265 DOI: 10.1128/mcb.00636-15] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2015] [Accepted: 12/22/2015] [Indexed: 02/01/2023] Open
Abstract
The N-terminal domain of the retinoblastoma (Rb) tumor suppressor protein (RbN) harbors in-frame exon deletions in partially penetrant hereditary retinoblastomas and is known to impair cell growth and tumorigenesis. However, how such RbN deletions contribute to Rb tumor- and growth-suppressive functions is unknown. Here we establish that RbN directly inhibits DNA replication initiation and elongation using a bipartite mechanism involving N-terminal exons lost in cancer. Specifically, Rb exon 7 is necessary and sufficient to target and inhibit the replicative CMG helicase, resulting in the accumulation of inactive CMGs on chromatin. An independent N-terminal loop domain, which forms a projection, specifically blocks DNA polymerase α (Pol-α) and Ctf4 recruitment without affecting DNA polymerases ε and δ or the CMG helicase. Individual disruption of exon 7 or the projection in RbN or Rb, as occurs in inherited cancers, partially impairs the ability of Rb/RbN to inhibit DNA replication and block G1-to-S cell cycle transit. However, their combined loss abolishes these functions of Rb. Thus, Rb growth-suppressive functions include its ability to block replicative complexes via bipartite, independent, and additive N-terminal domains. The partial loss of replication, CMG, or Pol-α control provides a potential molecular explanation for how N-terminal Rb loss-of-function deletions contribute to the etiology of partially penetrant retinoblastomas.
Collapse
|
39
|
Abstract
DNA replication begins with the assembly of pre-replication complexes (pre-RCs) at thousands of DNA replication origins during the G1 phase of the cell cycle. At the G1-S-phase transition, pre-RCs are converted into pre-initiation complexes, in which the replicative helicase is activated, leading to DNA unwinding and initiation of DNA synthesis. However, only a subset of origins are activated during any S phase. Recent insights into the mechanisms underlying this choice reveal how flexibility in origin usage and temporal activation are linked to chromosome structure and organization, cell growth and differentiation, and replication stress.
Collapse
|
40
|
Bryant VL, Elias RM, McCarthy SM, Yeatman TJ, Alexandrow MG. Suppression of Reserve MCM Complexes Chemosensitizes to Gemcitabine and 5-Fluorouracil. Mol Cancer Res 2015; 13:1296-305. [PMID: 26063742 DOI: 10.1158/1541-7786.mcr-14-0464] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/20/2014] [Accepted: 05/31/2015] [Indexed: 12/29/2022]
Abstract
UNLABELLED Pancreatic ductal adenocarcinoma (PDAC) is one of the deadliest forms of cancer and is very difficult to treat with conventional chemotherapeutic regimens. Gemcitabine and 5-fluorouracil are used in the management of PDAC and act by indirectly blocking replicative forks. However, these drugs are not highly effective at suppressing disease progression, indicating a need for the development of innovative therapeutic approaches. Recent studies indicate that suppression of the MCM helicase may provide a novel means to sensitize cancer cells to chemotherapeutic agents that inhibit replicative fork progression. Mammalian cells assemble more MCM complexes on DNA than are required to start S-phase. The excess MCM complexes function as backup initiation sites under conditions of replicative stress. The current study provides definitive evidence that cosuppression of the excess/backup MCM complexes sensitizes PDAC tumor lines to both gemcitabine and 5-FU, leading to increased loss of proliferative capacity compared with drugs alone. This occurs because reduced MCM levels prevent efficient recovery of DNA replication in tumor cells exposed to drug. PDAC tumor cells are more sensitive to MCM loss in the presence of gemcitabine than are nontumor, immortalized epithelial cells. Similarly, colon tumor cells are rendered less viable when cosuppression of MCM complexes occurs during exposure to the crosslinking agent oxaliplatin or topoisomerase inhibitor etoposide. IMPLICATIONS These studies demonstrate that suppressing the backup complement of MCM complexes provides an effective sensitizing approach with the potential to increase the therapeutic index of drugs used in the clinical management of PDAC and other cancers.
Collapse
Affiliation(s)
- Victoria L Bryant
- University of South Florida Cancer Biology Graduate Program, Moffitt Cancer Center, Tampa, Florida. Molecular Oncology Department, Moffitt Cancer Center, Tampa, Florida
| | - Roy M Elias
- Molecular Oncology Department, Moffitt Cancer Center, Tampa, Florida
| | | | - Timothy J Yeatman
- Gibbs Cancer Center and Research Institute, Spartanburg, South Carolina
| | - Mark G Alexandrow
- University of South Florida Cancer Biology Graduate Program, Moffitt Cancer Center, Tampa, Florida. Molecular Oncology Department, Moffitt Cancer Center, Tampa, Florida.
| |
Collapse
|
41
|
Musiałek MW, Rybaczek D. Behavior of replication origins in Eukaryota - spatio-temporal dynamics of licensing and firing. Cell Cycle 2015; 14:2251-64. [PMID: 26030591 DOI: 10.1080/15384101.2015.1056421] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Although every organism shares some common features of replication, this process varies greatly among eukaryotic species. Current data show that mathematical models of the organization of origins based on possibility theory may be applied (and remain accurate) in every model organism i.e. from yeast to humans. The major differences lie within the dynamics of origin firing and the regulation mechanisms that have evolved to meet new challenges throughout the evolution of the organism. This article elaborates on the relations between chromatin structure, organization of origins, their firing times and the impact that these features can have on genome stability, showing both differences and parallels inside the eukaryotic domain.
Collapse
Key Words
- APC, anaphase promoting complex
- ARS, autonomously replicating sequences
- ATR, ataxia telangiectasia mutated and Rad3-related kinase
- C-Frag, chromosome fragmentation
- CDK, cyclin-dependent kinase
- CDT, C-terminus domain
- CEN, centromere
- CFSs, chromosome fragile sites
- CIN, chromosome instability
- CMG, Cdc45-MCM-GINS complex
- Cdc45, cell division control protein 45
- Cdc6, cell division control protein 6
- Cdt1, chromatin licensing and DNA replication factor 1
- Chk1, checkpoint kinase 1
- Clb2, G2/mitotic-specific cyclin Clb2
- DCR, Ddb1-Cu14a-Roc1 complex
- DDK, Dbf-4-dependent kinase
- DSBs, double strand breaks
- Dbf4, protein Dbf4 homolog A
- Dfp1, Hsk1-Dfp1 kinase complex regulatory subunit Dfp1
- Dpb11, DNA replication regulator Dpb11
- E2F, E2F transcription factor
- EL, early to late origins transition
- ETG1, E2F target gene 1/replisome factor
- Fkh, fork head domain protein
- GCN5, histone acetyltransferase GCN5
- GINS, go-ichi-ni-san
- LE, late to early origins transition
- MCM2–7, minichromosome maintenance helicase complex
- NDT, N-terminus domain
- ORC, origin recognition complex
- ORCA, origin recognition complex subunit A
- PCC, premature chromosome condensation
- PCNA, proliferating cell nuclear antigen
- RO, replication origin
- RPD3, histone deacetylase 3
- RTC, replication timing control
- Rif1, replication timing regulatory factor 1
- SCF, Skp1-Cullin-F-Box ligase
- SIR, sulfite reductase
- Sld2, replication regulator Sld2
- Sld3, replication regulator Sld3
- Swi6, chromatin-associated protein swi6
- Taz1, telomere length regulator taz1
- YKU70, yeast Ku protein.
- dormant origins
- mathematical models of replication
- ori, origin
- origin competence
- origin efficiency
- origin firing
- origin licensing
- p53, tumor suppressor protein p53
- replication timing
Collapse
Affiliation(s)
- Marcelina W Musiałek
- a Department of Cytophysiology ; Institute of Experimental Biology; Faculty of Biology and Environmental Protection; University of Łódź ; Łódź , Poland
| | | |
Collapse
|
42
|
Sansam CG, Goins D, Siefert JC, Clowdus EA, Sansam CL. Cyclin-dependent kinase regulates the length of S phase through TICRR/TRESLIN phosphorylation. Genes Dev 2015; 29:555-66. [PMID: 25737283 PMCID: PMC4358407 DOI: 10.1101/gad.246827.114] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2014] [Accepted: 01/23/2015] [Indexed: 12/22/2022]
Abstract
S-phase cyclin-dependent kinases (CDKs) stimulate replication initiation and accelerate progression through the replication timing program, but it is unknown which CDK substrates are responsible for these effects. CDK phosphorylation of the replication factor TICRR (TopBP1-interacting checkpoint and replication regulator)/TRESLIN is required for DNA replication. We show here that phosphorylated TICRR is limiting for S-phase progression. Overexpression of a TICRR mutant with phosphomimetic mutations at two key CDK-phosphorylated residues (TICRR(TESE)) stimulates DNA synthesis and shortens S phase by increasing replication initiation. This effect requires the TICRR region that is necessary for its interaction with MDM two-binding protein. Expression of TICRR(TESE) does not grossly alter the spatial organization of replication forks in the nucleus but does increase replication clusters and the number of replication forks within each cluster. In contrast to CDK hyperactivation, the acceleration of S-phase progression by TICRR(TESE) does not induce DNA damage. These results show that CDK can stimulate initiation and compress the replication timing program by phosphorylating a single protein, suggesting a simple mechanism by which S-phase length is controlled.
Collapse
Affiliation(s)
- Courtney G Sansam
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA;
| | - Duane Goins
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA
| | - Joseph C Siefert
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
| | - Emily A Clowdus
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
| | - Christopher L Sansam
- Cell Cycle and Cancer Biology Research Program, Oklahoma Medical Research Foundation, Oklahoma City, Oklahoma 73104, USA; Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, Oklahoma 73104, USA
| |
Collapse
|
43
|
Zegerman P. Evolutionary conservation of the CDK targets in eukaryotic DNA replication initiation. Chromosoma 2015; 124:309-21. [PMID: 25575982 DOI: 10.1007/s00412-014-0500-y] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2014] [Revised: 11/27/2014] [Accepted: 12/01/2014] [Indexed: 10/24/2022]
Abstract
A fundamental requirement for all organisms is the faithful duplication and transmission of the genetic material. Failure to accurately copy and segregate the genome during cell division leads to loss of genetic information and chromosomal abnormalities. Such genome instability is the hallmark of the earliest stages of tumour formation. Cyclin-dependent kinase (CDK) plays a vital role in regulating the duplication of the genome within the eukaryotic cell cycle. Importantly, this kinase is deregulated in many cancer types and is an emerging target of chemotherapeutics. In this review, I will consider recent advances concerning the role of CDK in replication initiation across eukaryotes. The implications for strict CDK-dependent regulation of genome duplication in the context of the cell cycle will be discussed.
Collapse
Affiliation(s)
- Philip Zegerman
- Department of Biochemistry, Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, The Henry Wellcome Building of Cancer and Developmental Biology, Cambridge, CB2 1QN, UK,
| |
Collapse
|
44
|
González Besteiro MA, Gottifredi V. The fork and the kinase: a DNA replication tale from a CHK1 perspective. MUTATION RESEARCH-REVIEWS IN MUTATION RESEARCH 2014; 763:168-80. [PMID: 25795119 DOI: 10.1016/j.mrrev.2014.10.003] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2014] [Revised: 10/07/2014] [Accepted: 10/10/2014] [Indexed: 11/30/2022]
Abstract
Replication fork progression is being continuously hampered by exogenously introduced and naturally occurring DNA lesions and other physical obstacles. Checkpoint kinase 1 (Chk1) is activated at replication forks that encounter damaged DNA. Subsequently, Chk1 inhibits the initiation of new replication factories and stimulates the firing of dormant origins (those in the vicinity of stalled forks). Chk1 also avoids fork collapse into DSBs (double strand breaks) and promotes fork elongation. At the molecular level, the current model considers stalled forks as the site of Chk1 activation and the nucleoplasm as the location where Chk1 phosphorylates target proteins. This model certainly serves to explain how Chk1 modulates origin firing, but how Chk1 controls the fate of stalled forks is less clear. Interestingly, recent reports demonstrating that Chk1 phosphorylates chromatin-bound proteins and even holds kinase-independent functions might shed light on how Chk1 contributes to the elongation of damaged DNA. Indeed, such findings have unveiled a puzzling connection between Chk1 and DNA lesion bypass, which might be central to promoting fork elongation and checkpoint attenuation. In summary, Chk1 is a multifaceted and versatile signaling factor that acts at ongoing forks and replication origins to determine the extent and quality of the cellular response to replication stress.
Collapse
Affiliation(s)
- Marina A González Besteiro
- Cell Cycle and Genomic Stability Laboratory, Fundación Instituto Leloir, CONICET, Buenos Aires, Argentina
| | - Vanesa Gottifredi
- Cell Cycle and Genomic Stability Laboratory, Fundación Instituto Leloir, CONICET, Buenos Aires, Argentina.
| |
Collapse
|
45
|
Yoshida K, Bacal J, Desmarais D, Padioleau I, Tsaponina O, Chabes A, Pantesco V, Dubois E, Parrinello H, Skrzypczak M, Ginalski K, Lengronne A, Pasero P. The histone deacetylases sir2 and rpd3 act on ribosomal DNA to control the replication program in budding yeast. Mol Cell 2014; 54:691-7. [PMID: 24856221 DOI: 10.1016/j.molcel.2014.04.032] [Citation(s) in RCA: 75] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2013] [Revised: 03/05/2014] [Accepted: 04/04/2014] [Indexed: 12/16/2022]
Abstract
In S. cerevisiae, replication timing is controlled by epigenetic mechanisms restricting the accessibility of origins to limiting initiation factors. About 30% of these origins are located within repetitive DNA sequences such as the ribosomal DNA (rDNA) array, but their regulation is poorly understood. Here, we have investigated how histone deacetylases (HDACs) control the replication program in budding yeast. This analysis revealed that two HDACs, Rpd3 and Sir2, control replication timing in an opposite manner. Whereas Rpd3 delays initiation at late origins, Sir2 is required for the timely activation of early origins. Moreover, Sir2 represses initiation at rDNA origins, whereas Rpd3 counteracts this effect. Remarkably, deletion of SIR2 restored normal replication in rpd3Δ cells by reactivating rDNA origins. Together, these data indicate that HDACs control the replication timing program in budding yeast by modulating the ability of repeated origins to compete with single-copy origins for limiting initiation factors.
Collapse
Affiliation(s)
- Kazumasa Yoshida
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France; Department of Cellular Biochemistry, Graduate School of Pharmaceutical Sciences, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan
| | - Julien Bacal
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France
| | - Damien Desmarais
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France
| | - Ismaël Padioleau
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France
| | - Olga Tsaponina
- Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå Sweden
| | - Andrei Chabes
- Department of Medical Biochemistry and Biophysics, Umeå University, SE-901 87 Umeå Sweden
| | - Véronique Pantesco
- Inserm U847, Centre Hospitalier Universitaire de Montpellier, Institut de Recherche en Biothérapie, Hôpital Saint Eloi, Université Montpellier 1, Montpellier F-34000, France
| | - Emeric Dubois
- MGX-Montpellier GenomiX, c/o Institut de Génomique Fonctionnelle, 141 rue de la Cardonille, F-34094 Montpellier Cedex 5, France
| | - Hugues Parrinello
- MGX-Montpellier GenomiX, c/o Institut de Génomique Fonctionnelle, 141 rue de la Cardonille, F-34094 Montpellier Cedex 5, France
| | - Magdalena Skrzypczak
- Laboratory of Bioinformatics and Systems Biology, Centre of New Technologies, University of Warsaw, Zwirki i Wigury 93, 02-089 Warsaw, Poland
| | - Krzysztof Ginalski
- Laboratory of Bioinformatics and Systems Biology, Centre of New Technologies, University of Warsaw, Zwirki i Wigury 93, 02-089 Warsaw, Poland
| | - Armelle Lengronne
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France.
| | - Philippe Pasero
- Institute of Human Genetics, UPR 1142, CNRS, 141 rue de la Cardonille, 34396 Montpellier, France; Equipe Labellisée Ligue Contre le Cancer, 14 rue Corvisart, 75013 Paris, France.
| |
Collapse
|
46
|
Alver RC, Chadha GS, Blow JJ. The contribution of dormant origins to genome stability: from cell biology to human genetics. DNA Repair (Amst) 2014; 19:182-9. [PMID: 24767947 PMCID: PMC4065331 DOI: 10.1016/j.dnarep.2014.03.012] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
The ability of a eukaryotic cell to precisely and accurately replicate its DNA is crucial to maintain genome stability. Here we describe our current understanding of the process by which origins are licensed for DNA replication and review recent work suggesting that fork stalling has exerted a strong selective pressure on the positioning of licensed origins. In light of this, we discuss the complex and disparate phenotypes observed in mouse models and humans patients that arise due to defects in replication licensing proteins.
Collapse
Affiliation(s)
- Robert C Alver
- Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Gaganmeet Singh Chadha
- Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - J Julian Blow
- Centre for Gene Regulation & Expression, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
| |
Collapse
|
47
|
Abstract
The MYC oncogene is a multifunctional protein that is aberrantly expressed in a significant fraction of tumors from diverse tissue origins. Because of its multifunctional nature, it has been difficult to delineate the exact contributions of MYC's diverse roles to tumorigenesis. Here, we review the normal role of MYC in regulating DNA replication as well as its ability to generate DNA replication stress when overexpressed. Finally, we discuss the possible mechanisms by which replication stress induced by aberrant MYC expression could contribute to genomic instability and cancer.
Collapse
Affiliation(s)
| | - Jean Gautier
- Institute for Cancer Genetics, Columbia University, New York, New York 10032 Department of Genetics and Development, Columbia University, New York, New York 10032
| |
Collapse
|
48
|
Temporal and spatial regulation of eukaryotic DNA replication: From regulated initiation to genome-scale timing program. Semin Cell Dev Biol 2014; 30:110-20. [DOI: 10.1016/j.semcdb.2014.04.014] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2014] [Accepted: 04/04/2014] [Indexed: 11/23/2022]
|
49
|
Abstract
DNA replication must be tightly regulated to ensure that the genome is accurately duplicated during each cell cycle. When these regulatory mechanisms fail, replicative stress and DNA damage ensue. Activated oncogenes promote replicative stress, inducing a DNA damage response (DDR) early in tumorigenesis. Senescence or apoptosis result, forming a barrier against tumour progression. This may provide a selective pressure for acquisition of mutations in the DDR pathway during tumorigenesis. Despite its potential importance in early cancer development, the precise nature of oncogene-induced replicative stress remains poorly understood. Here, we review our current understanding of replication initiation and its regulation, describe mechanisms by which activated oncogenes might interfere with these processes and discuss how replicative stress might contribute to the genomic instability seen in cancers.
Collapse
Affiliation(s)
- Stephanie A Hills
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK
| | - John F X Diffley
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK.
| |
Collapse
|
50
|
Abstract
While large portions of the mammalian genome are known to replicate sequentially in a distinct, tissue-specific order, recent studies suggest that the inactive X chromosome is duplicated rapidly via random, synchronous DNA synthesis at numerous adjacent regions. The rapid duplication of the inactive X chromosome was observed in high-resolution studies visualizing DNA replication patterns in the nucleus, and by allele-specific DNA sequencing studies measuring the extent of DNA synthesis. These studies conclude that inactive X chromosomes complete replication earlier than previously thought and suggest that the strict order of DNA replication detected in the majority of genomic regions is not preserved in non-transcribed, "silent" chromatin. These observations alter current concepts about the regulation of DNA replication in non-transcribed portions of the genome in general and in the inactive X-chromosome in particular.
Collapse
Affiliation(s)
- Mirit I Aladjem
- Developmental Therapeutic Branch, Center for Cancer Research, National Cancer Institute, Bethesda, MD, USA
| | | |
Collapse
|