1
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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.
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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.
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2
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Ratnayeke N, Baris Y, Chung M, Yeeles JTP, Meyer T. CDT1 inhibits CMG helicase in early S phase to separate origin licensing from DNA synthesis. Mol Cell 2023; 83:26-42.e13. [PMID: 36608667 DOI: 10.1016/j.molcel.2022.12.004] [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: 07/12/2022] [Revised: 09/16/2022] [Accepted: 12/08/2022] [Indexed: 01/07/2023]
Abstract
Human cells license tens of thousands of origins of replication in G1 and then must stop all licensing before DNA synthesis in S phase to prevent re-replication and genome instability that ensue when an origin is licensed on replicated DNA. However, the E3 ubiquitin ligase CRL4Cdt2 only starts to degrade the licensing factor CDT1 after origin firing, raising the question of how cells prevent re-replication before CDT1 is fully degraded. Here, using quantitative microscopy and in-vitro-reconstituted human DNA replication, we show that CDT1 inhibits DNA synthesis during an overlap period when CDT1 is still present after origin firing. CDT1 inhibits DNA synthesis by suppressing CMG helicase at replication forks, and DNA synthesis commences once CDT1 is degraded. Thus, in contrast to the prevailing model that human cells prevent re-replication by strictly separating licensing from firing, licensing and firing overlap, and cells instead separate licensing from DNA synthesis.
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Affiliation(s)
- Nalin Ratnayeke
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Cell and Developmental Biology, Weill Cornell Medical College, New York, NY 10065, USA
| | - Yasemin Baris
- Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, UK
| | - Mingyu Chung
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA
| | - Joseph T P Yeeles
- Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, UK
| | - Tobias Meyer
- Department of Chemical and Systems Biology, Stanford University School of Medicine, Stanford, CA 94305, USA; Department of Cell and Developmental Biology, Weill Cornell Medical College, New York, NY 10065, USA.
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3
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Karantzelis N, Petropoulos M, De Marco V, Egan DA, Fish A, Christodoulou E, Will DW, Lewis JD, Perrakis A, Lygerou Z, Taraviras S. Small Molecule Inhibitor Targeting CDT1/Geminin Protein Complex Promotes DNA Damage and Cell Death in Cancer Cells. Front Pharmacol 2022; 13:860682. [PMID: 35548337 PMCID: PMC9083542 DOI: 10.3389/fphar.2022.860682] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 03/30/2022] [Indexed: 01/18/2023] Open
Abstract
DNA replication initiation requires the loading of MCM2-7 complexes at the origins of replication during G1. Replication licensing renders chromatin competent for DNA replication and its tight regulation is essential to prevent aberrant DNA replication and genomic instability. CDT1 is a critical factor of licensing and its activity is controlled by redundant mechanisms, including Geminin, a protein inhibitor of CDT1. Aberrant CDT1 and Geminin expression have been shown to promote tumorigenesis in vivo and are also evident in multiple human tumors. In this study, we developed an in vitro AlphaScreen™ high-throughput screening (HTS) assay for the identification of small-molecule inhibitors targeting the CDT1/Geminin protein complex. Biochemical characterization of the most potent compound, AF615, provided evidence of specific, dose-dependent inhibition of Geminin binding to CDT1 both in-vitro and in cells. Moreover, compound AF615 induces DNA damage, inhibits DNA synthesis and reduces viability selectively in cancer cell lines, and this effect is CDT1-dependent. Taken together, our data suggest that AF615 may serve as a useful compound to elucidate the role of CDT1/Geminin protein complex in replication licensing and origin firing as well as a scaffold for further medicinal chemistry optimisation.
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Affiliation(s)
| | - Michalis Petropoulos
- Department of General Biology, Medical School, University of Patras, Patras, Greece
| | - Valeria De Marco
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - David A Egan
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Alexander Fish
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | | | - David W Will
- Chemical Biology Core Facility, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Joe D Lewis
- Chemical Biology Core Facility, European Molecular Biology Laboratory, Heidelberg, Germany
| | - Anastassis Perrakis
- Division of Biochemistry, Netherlands Cancer Institute, Amsterdam, Netherlands
| | - Zoi Lygerou
- Department of General Biology, Medical School, University of Patras, Patras, Greece
| | - Stavros Taraviras
- Department of Physiology, Medical School, University of Patras, Patras, Greece
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4
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Nguyen H, Wu H, Ung A, Yamazaki Y, Fogelgren B, Ward WS. Deletion of Orc4 during oogenesis severely reduces polar body extrusion and blocks zygotic DNA replication†. Biol Reprod 2022; 106:730-740. [PMID: 34977916 PMCID: PMC9040667 DOI: 10.1093/biolre/ioab237] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2021] [Revised: 09/21/2021] [Accepted: 12/15/2021] [Indexed: 11/14/2022] Open
Abstract
Origin recognition complex subunit 4 (ORC4) is a DNA-binding protein required for DNA replication. During oocyte maturation, after the last oocyte DNA replication step and before zygotic DNA replication, the oocyte undergoes two meiotic cell divisions in which half the DNA is ejected in much smaller polar bodies. We previously demonstrated that ORC4 forms a cytoplasmic cage around the DNA that is ejected in both polar body extrusion (PBE) events. Here, we used ZP3 activated Cre to delete exon 7 of Orc4 during oogenesis to test how it affected both predicted functions of ORC4: its recently discovered role in PBE and its well-known role in DNA synthesis. Orc4 deletion severely reduced PBE. Almost half of Orc4-depleted germinal vesicle (GV) oocytes cultured in vitro were arrested before anaphase I (48%), and only 25% produced normal first polar bodies. This supports the role of ORC4 in PBE and suggests that transcription of the full-length Orc4 during oogenesis is required for efficient PBE. Orc4 deletion also abolished zygotic DNA synthesis. Fewer Orc4-depleted oocytes developed to the metaphase II (MII) stage, and after activation these oocytes were arrested at the two-cell stage without undergoing DNA synthesis. This confirms that transcription of full-length Orc4 after the primary follicle stage is required for zygotic DNA replication. The data also suggest that MII oocytes do not have a replication licensing checkpoint as cytokinesis progressed without DNA synthesis. Together, the data confirm that oocyte ORC4 is important for both PBE and zygotic DNA synthesis.
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Affiliation(s)
- Hieu Nguyen
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
| | - Hongwen Wu
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
| | - Anna Ung
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
| | - Yukiko Yamazaki
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
| | - Ben Fogelgren
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
| | - W Steven Ward
- Department of Anatomy, Biochemistry & Physiology, Institute for Biogenesis Research, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
- Department of Obstetrics, Gynecology & Women’s Health, John A. Burns School of Medicine, University of Hawaii at Manoa, Honolulu, HI, USA
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5
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Connolly C, Takahashi S, Miura H, Hiratani I, Gilbert N, Donaldson AD, Hiraga SI. SAF-A promotes origin licensing and replication fork progression to ensure robust DNA replication. J Cell Sci 2022; 135:jcs258991. [PMID: 34888666 DOI: 10.1242/jcs.258991] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2021] [Accepted: 12/02/2021] [Indexed: 11/20/2022] Open
Abstract
The organisation of chromatin is closely intertwined with biological activities of chromosome domains, including transcription and DNA replication status. Scaffold-attachment factor A (SAF-A), also known as heterogeneous nuclear ribonucleoprotein U (HNRNPU), contributes to the formation of open chromatin structure. Here, we demonstrate that SAF-A promotes the normal progression of DNA replication and enables resumption of replication after inhibition. We report that cells depleted of SAF-A show reduced origin licensing in G1 phase and, consequently, reduced origin activation frequency in S phase. Replication forks also progress less consistently in cells depleted of SAF-A, contributing to reduced DNA synthesis rate. Single-cell replication timing analysis revealed two distinct effects of SAF-A depletion: first, the boundaries between early- and late-replicating domains become more blurred; and second, SAF-A depletion causes replication timing changes that tend to bring regions of discordant domain compartmentalisation and replication timing into concordance. Associated with these defects, SAF-A-depleted cells show elevated formation of phosphorylated histone H2AX (γ-H2AX) and tend to enter quiescence. Overall, we find that SAF-A protein promotes robust DNA replication to ensure continuing cell proliferation.
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Affiliation(s)
- Caitlin Connolly
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK
| | - Saori Takahashi
- RIKEN Center for Biosystems Dynamics Research, Kobe, Hyogo 650-0047, Japan
| | - Hisashi Miura
- RIKEN Center for Biosystems Dynamics Research, Kobe, Hyogo 650-0047, Japan
| | - Ichiro Hiratani
- RIKEN Center for Biosystems Dynamics Research, Kobe, Hyogo 650-0047, Japan
| | - Nick Gilbert
- MRC Human Genetics Unit, The University of Edinburgh, Crewe Rd, Edinburgh EH4 2XU, UK
| | - Anne D Donaldson
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK
| | - Shin-Ichiro Hiraga
- Institute of Medical Sciences, University of Aberdeen, Foresterhill, Aberdeen AB25 2ZD, UK
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6
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Efficiency and equity in origin licensing to ensure complete DNA replication. Biochem Soc Trans 2021; 49:2133-2141. [PMID: 34545932 DOI: 10.1042/bst20210161] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2021] [Revised: 08/19/2021] [Accepted: 08/31/2021] [Indexed: 12/21/2022]
Abstract
The cell division cycle must be strictly regulated during both development and adult maintenance, and efficient and well-controlled DNA replication is a key event in the cell cycle. DNA replication origins are prepared in G1 phase of the cell cycle in a process known as origin licensing which is essential for DNA replication initiation in the subsequent S phase. Appropriate origin licensing includes: (1) Licensing enough origins at adequate origin licensing speed to complete licensing before G1 phase ends; (2) Licensing origins such that they are well-distributed on all chromosomes. Both aspects of licensing are critical for replication efficiency and accuracy. In this minireview, we will discuss recent advances in defining how origin licensing speed and distribution are critical to ensure DNA replication completion and genome stability.
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7
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Replication initiation: Implications in genome integrity. DNA Repair (Amst) 2021; 103:103131. [PMID: 33992866 DOI: 10.1016/j.dnarep.2021.103131] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 05/07/2021] [Accepted: 05/07/2021] [Indexed: 02/01/2023]
Abstract
In every cell cycle, billions of nucleotides need to be duplicated within hours, with extraordinary precision and accuracy. The molecular mechanism by which cells regulate the replication event is very complicated, and the entire process begins way before the onset of S phase. During the G1 phase of the cell cycle, cells prepare by assembling essential replication factors to establish the pre-replicative complex at origins, sites that dictate where replication would initiate during S phase. During S phase, the replication process is tightly coupled with the DNA repair system to ensure the fidelity of replication. Defects in replication and any error must be recognized by DNA damage response and checkpoint signaling pathways in order to halt the cell cycle before cells are allowed to divide. The coordination of these processes throughout the cell cycle is therefore critical to achieve genomic integrity and prevent diseases. In this review, we focus on the current understanding of how the replication initiation events are regulated to achieve genome stability.
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8
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Lee PH, Osley MA. Who gets a license: DNA synthesis in quiescent cells re-entering the cell cycle. Curr Genet 2021; 67:539-543. [PMID: 33682029 DOI: 10.1007/s00294-021-01170-7] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2021] [Revised: 02/24/2021] [Accepted: 02/26/2021] [Indexed: 12/23/2022]
Abstract
The precise regulation of the entry into S phase is critical for preventing genome instability. The first step in the initiation of eukaryotic DNA synthesis occurs in G1 phase cells and involves the loading of the conserved MCM helicase onto multiple origins of replication in a process known as origin licensing. In proliferating metazoan cells, an origin-licensing checkpoint delays initiation until high levels of MCM loading occur, with excess origins being licensed. One function of this checkpoint is to ensure that S phase can be completed in the face of replication stress by activation of dormant MCM bound origins. However, when both metazoan and yeast cells enter S phase from quiescence or G0 phase, a non-growing but reversible cell cycle state, origins are significantly under-licensed. In metazoan cells, under-licensing is the result of a compromised origin-licensing checkpoint. In budding yeast, our study has revealed that under-licensing can be attributed to the chromatin structure at a class of origins that is inhibitory to the binding of MCM. Thus, defects in multiple pathways may contribute to the failure to fully license origins in quiescent cells re-entering the cell cycle, thereby promoting a higher risk of genome instability.
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Affiliation(s)
- Po-Hsuen Lee
- Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131, USA
| | - Mary Ann Osley
- Molecular Genetics and Microbiology, University of New Mexico Health Sciences Center, Albuquerque, NM, 87131, USA.
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9
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Liao M, Zhang J, Wang G, Wang L, Liu J, Ouyang L, Liu B. Small-Molecule Drug Discovery in Triple Negative Breast Cancer: Current Situation and Future Directions. J Med Chem 2021; 64:2382-2418. [PMID: 33650861 DOI: 10.1021/acs.jmedchem.0c01180] [Citation(s) in RCA: 58] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
Triple negative breast cancer (TNBC) is the most aggressive subtype of breast cancer, but an effective targeted therapy has not been well-established so far. Considering the lack of effective targets, where do we go next in the current TNBC drug development? A promising intervention for TNBC might lie in de novo small-molecule drugs that precisely target different molecular characteristics of TNBC. However, an ideal single-target drug discovery still faces a huge challenge. Alternatively, other new emerging strategies, such as dual-target drug, drug repurposing, and combination strategies, may provide new insight into the improvement of TNBC therapeutics. In this review, we focus on summarizing the current situation of a series of candidate small-molecule drugs in TNBC therapy, including single-target drugs, dual-target drugs, as well as drug repurposing and combination strategies that will together shed new light on the future directions targeting TNBC vulnerabilities with small-molecule drugs for future therapeutic purposes.
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Affiliation(s)
- Minru Liao
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Jin Zhang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Guan Wang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Leiming Wang
- The Institute of Chemical Biology, Shenzhen Bay Laboratory, Shenzhen 518107, China
| | - Jie Liu
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Liang Ouyang
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
| | - Bo Liu
- State Key Laboratory of Biotherapy and Cancer Center, West China Hospital, Sichuan University, Chengdu 610041, China
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10
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Prospect of reprogramming replication licensing for cancer drug development. Biomed Pharmacother 2021; 136:111190. [PMID: 33497909 DOI: 10.1016/j.biopha.2020.111190] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2020] [Revised: 12/15/2020] [Accepted: 12/26/2020] [Indexed: 12/15/2022] Open
Abstract
Eukaryotic chromosomal DNA replication is preceded by replication licensing which involves the identification of the origin of replication by origin recognition complex (ORC). The ORC loads pre-replication complexes (pre-RCs) through a series of tightly regulated mechanisms where the ORC interacts with Cdc6 to recruit cdt1-MCM2-7 complexes to the origin of replication. In eukaryotes, adherence to regulatory mechanisms of the replication program is required to ensure that all daughter cells carry the exact copy of genetic material as the parent cell. Failure of which leads to the development of genome instability syndromes like cancer, diabetes, etc. In an event of such occurrence, preventing cells from carrying the defaulted genetic material and passing it to other cells hinges on the regulation of chromosomal DNA replication. Thus, understanding the mechanisms underpinning chromosomal DNA replication and particularly replication licensing can expose druggable enzymes, effector molecules, and secondary messengers that can be targeted for diagnosis and therapeutic purposes. Effectively drugging these molecular markers to reprogram pre-replication events can be used to control the fate of chromosomal DNA replication for the treatment of genome instability disorders and in this case, cancer. This review discusses available knowledge of replication licensing in the contest of molecular drug discovery for the treatment of cancer.
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11
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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
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12
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Zhou Y, Pei F, Ji M, Zhang F, Sun Y, Zhao Q, Wang X, Hong Y, Tian J, Wang Y, Chen JJ. WDHD1 facilitates G1 checkpoint abrogation in HPV E7 expressing cells by modulating GCN5. BMC Cancer 2020; 20:840. [PMID: 32883234 PMCID: PMC7469104 DOI: 10.1186/s12885-020-07287-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/04/2019] [Accepted: 08/10/2020] [Indexed: 12/15/2022] Open
Abstract
Background Genomic instability is a hallmark of cancer. The G1 checkpoint allows cells to repair damaged DNA that may lead to genomic instability. The high-risk human papillomavirus (HPV) E7 gene can abrogate the G1 checkpoint, yet the mechanism is still not fully understood. Our recent study showed that WDHD1 (WD repeat and high mobility group [HMG]-box DNA-binding protein 1) plays a role in regulating G1 checkpoint of E7 expressing cells. In this study, we explored the mechanism by which WDHD1 regulates G1 checkpoint in HPV E7 expressing cells. Methods NIKS and RPE1 derived cell lines were used. Real-time PCR, Rescue experiment, FACS and BrdU labeling experiments were performed to examine role of GCN5 in G1 checkpoint abrogation in HPV-16 E7 expressing cells. Results In this study, we observed that WDHD1 facilitates G1 checkpoint abrogation by modulating GCN5 in HPV E7 expressing cells. Notably, depletion of WDHD1 caused G1 arrest while overexpression of GCN5 rescued the inhibitory effects of WDHD1 knockdown on G1/S progression. Furthermore, siWDHD1 significantly decreased cell cycle proliferation and DNA synthesis that was correlated with Akt phosphorylation (p-Akt), which was reversed by GCN5 overexpression in HPV E7 expressing cells. Conclusions In summary, our data identified a WDHD1/GCN5/Akt pathway leading to the abrogation of G1 checkpoint in the presence of damaged DNA, which may cause genomic instability and eventually HPV induced tumorigenesis.
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Affiliation(s)
- Yunying Zhou
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Department of Microbiology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, 250012, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China.,Shandong LaiBo Biotechnology co., Ltd, Jinan, China
| | - Fengyan Pei
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Mingyu Ji
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Fang Zhang
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Yingshuo Sun
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China
| | - Qianqian Zhao
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Xiao Wang
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Yatian Hong
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Juanjuan Tian
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China.,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China
| | - Yunshan Wang
- Medical Research & Laboratory Diagnostic Center, Jinan Central Hospital, Cheeloo College of Medicine, Shandong University, Jinan, Shandong, China. .,Department of Microbiology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, 250012, Shandong, China. .,Microbiology Department, Jinan Central Hospital Affiliated to Shandong first medical university, Jinan, China.
| | - Jason J Chen
- Department of Microbiology, School of Basic Medical Sciences, Cheeloo College of Medicine, Shandong University, Jinan, 250012, Shandong, China.
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13
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Rainey MD, Bennett D, O’Dea R, Zanchetta ME, Voisin M, Seoighe C, Santocanale C. ATR Restrains DNA Synthesis and Mitotic Catastrophe in Response to CDC7 Inhibition. Cell Rep 2020; 32:108096. [DOI: 10.1016/j.celrep.2020.108096] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2019] [Revised: 06/19/2020] [Accepted: 08/10/2020] [Indexed: 12/31/2022] Open
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14
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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.
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15
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Guerra SL, Maertens O, Kuzmickas R, De Raedt T, Adeyemi RO, Guild CJ, Guillemette S, Redig AJ, Chambers ES, Xu M, Tiv H, Santagata S, Jänne PA, Elledge SJ, Cichowski K. A Deregulated HOX Gene Axis Confers an Epigenetic Vulnerability in KRAS-Mutant Lung Cancers. Cancer Cell 2020; 37:705-719.e6. [PMID: 32243838 PMCID: PMC10805385 DOI: 10.1016/j.ccell.2020.03.004] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/23/2018] [Revised: 11/12/2019] [Accepted: 03/03/2020] [Indexed: 01/02/2023]
Abstract
While KRAS mutations are common in non-small cell lung cancer (NSCLC), effective treatments are lacking. Here, we report that half of KRAS-mutant NSCLCs aberrantly express the homeobox protein HOXC10, largely due to unappreciated defects in PRC2, which confers sensitivity to combined BET/MEK inhibitors in xenograft and PDX models. Efficacy of the combination is dependent on suppression of HOXC10 by BET inhibitors. We further show that HOXC10 regulates the expression of pre-replication complex (pre-RC) proteins in sensitive tumors. Accordingly, BET/MEK inhibitors suppress pre-RC proteins in cycling cells, triggering stalled replication, DNA damage, and death. These studies reveal a promising therapeutic strategy for KRAS-mutant NSCLCs, identify a predictive biomarker of response, and define a subset of NSCLCs with a targetable epigenetic vulnerability.
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Affiliation(s)
- Stephanie L Guerra
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Ophélia Maertens
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Ryan Kuzmickas
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Thomas De Raedt
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Richard O Adeyemi
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Caroline J Guild
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Shawna Guillemette
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA
| | - Amanda J Redig
- Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Emily S Chambers
- Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Man Xu
- Belfer Center for Applied Cancer Science, Boston, MA 02115, USA
| | - Hong Tiv
- Experimental Therapeutic Core, Dana-Farber Cancer Institute, Boston, MA 02115, USA
| | - Sandro Santagata
- Harvard Medical School, Boston, MA 02115, USA; Departments of Pathology, Brigham and Women's Hospital, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Ludwig Center at Harvard, Harvard Medical School, Boston, MA 02115, USA
| | - Pasi A Jänne
- Harvard Medical School, Boston, MA 02115, USA; Lowe Center for Thoracic Oncology, Dana-Farber Cancer Institute, Boston, MA 02115, USA; Belfer Center for Applied Cancer Science, Boston, MA 02115, USA
| | - Stephen J Elledge
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Ludwig Center at Harvard, Harvard Medical School, Boston, MA 02115, USA; Department of Genetics, Harvard Medical School, Boston, MA 02115, USA; Howard Hughes Medical Institute, 77 Avenue Louis Pasteur, Boston, MA 02115, USA
| | - Karen Cichowski
- Genetics Division, Department of Medicine, Brigham and Women's Hospital, Boston, MA 02115, USA; Harvard Medical School, Boston, MA 02115, USA; Ludwig Center at Harvard, Harvard Medical School, Boston, MA 02115, USA.
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16
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Ovejero S, Bueno A, Sacristán MP. Working on Genomic Stability: From the S-Phase to Mitosis. Genes (Basel) 2020; 11:E225. [PMID: 32093406 PMCID: PMC7074175 DOI: 10.3390/genes11020225] [Citation(s) in RCA: 29] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2020] [Revised: 02/17/2020] [Accepted: 02/18/2020] [Indexed: 12/15/2022] Open
Abstract
Fidelity in chromosome duplication and segregation is indispensable for maintaining genomic stability and the perpetuation of life. Challenges to genome integrity jeopardize cell survival and are at the root of different types of pathologies, such as cancer. The following three main sources of genomic instability exist: DNA damage, replicative stress, and chromosome segregation defects. In response to these challenges, eukaryotic cells have evolved control mechanisms, also known as checkpoint systems, which sense under-replicated or damaged DNA and activate specialized DNA repair machineries. Cells make use of these checkpoints throughout interphase to shield genome integrity before mitosis. Later on, when the cells enter into mitosis, the spindle assembly checkpoint (SAC) is activated and remains active until the chromosomes are properly attached to the spindle apparatus to ensure an equal segregation among daughter cells. All of these processes are tightly interconnected and under strict regulation in the context of the cell division cycle. The chromosomal instability underlying cancer pathogenesis has recently emerged as a major source for understanding the mitotic processes that helps to safeguard genome integrity. Here, we review the special interconnection between the S-phase and mitosis in the presence of under-replicated DNA regions. Furthermore, we discuss what is known about the DNA damage response activated in mitosis that preserves chromosomal integrity.
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Affiliation(s)
- Sara Ovejero
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca-CSIC, Campus Miguel de Unamuno, 37007 Salamanca, Spain
- Institute of Human Genetics, CNRS, University of Montpellier, 34000 Montpellier, France
- Department of Biological Hematology, CHU Montpellier, 34295 Montpellier, France
| | - Avelino Bueno
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca-CSIC, Campus Miguel de Unamuno, 37007 Salamanca, Spain
- Departamento de Microbiología y Genética, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain
| | - María P. Sacristán
- Instituto de Biología Molecular y Celular del Cáncer (IBMCC), Universidad de Salamanca-CSIC, Campus Miguel de Unamuno, 37007 Salamanca, Spain
- Departamento de Microbiología y Genética, Universidad de Salamanca, Campus Miguel de Unamuno, 37007 Salamanca, Spain
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17
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Primo LMF, Teixeira LK. DNA replication stress: oncogenes in the spotlight. Genet Mol Biol 2019; 43:e20190138. [PMID: 31930281 PMCID: PMC7197996 DOI: 10.1590/1678-4685gmb-2019-0138] [Citation(s) in RCA: 27] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2019] [Accepted: 07/09/2019] [Indexed: 01/21/2023] Open
Abstract
Precise replication of genetic material is essential to maintain genome stability. DNA replication is a tightly regulated process that ensues faithful copies of DNA molecules to daughter cells during each cell cycle. Perturbation of DNA replication may compromise the transmission of genetic information, leading to DNA damage, mutations, and chromosomal rearrangements. DNA replication stress, also referred to as DNA replicative stress, is defined as the slowing or stalling of replication fork progression during DNA synthesis as a result of different insults. Oncogene activation, one hallmark of cancer, is able to disturb numerous cellular processes, including DNA replication. In fact, extensive work has indicated that oncogene-induced replication stress is an important source of genomic instability in human carcinogenesis. In this review, we focus on main oncogenes that induce DNA replication stress, such as RAS, MYC, Cyclin E, MDM2, and BCL-2 among others, and the molecular mechanisms by which these oncogenes interfere with normal DNA replication and promote genomic instability.
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Affiliation(s)
- Luiza M. F. Primo
- Group of Cell Cycle Control, Program of Immunology and Tumor
Biology. Brazilian National Cancer Institute (INCA), Rio de Janeiro, RJ,
Brazil
| | - Leonardo K. Teixeira
- Group of Cell Cycle Control, Program of Immunology and Tumor
Biology. Brazilian National Cancer Institute (INCA), Rio de Janeiro, RJ,
Brazil
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18
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Abstract
Precise replication of genetic material is essential to maintain genome stability. DNA replication is a tightly regulated process that ensues faithful copies of DNA molecules to daughter cells during each cell cycle. Perturbation of DNA replication may compromise the transmission of genetic information, leading to DNA damage, mutations, and chromosomal rearrangements. DNA replication stress, also referred to as DNA replicative stress, is defined as the slowing or stalling of replication fork progression during DNA synthesis as a result of different insults. Oncogene activation, one hallmark of cancer, is able to disturb numerous cellular processes, including DNA replication. In fact, extensive work has indicated that oncogene-induced replication stress is an important source of genomic instability in human carcinogenesis. In this review, we focus on main oncogenes that induce DNA replication stress, such as RAS, MYC, Cyclin E, MDM2, and BCL-2 among others, and the molecular mechanisms by which these oncogenes interfere with normal DNA replication and promote genomic instability.
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Affiliation(s)
- Luiza M F Primo
- Group of Cell Cycle Control, Program of Immunology and Tumor Biology. Brazilian National Cancer Institute (INCA), Rio de Janeiro, RJ, Brazil
| | - Leonardo K Teixeira
- Group of Cell Cycle Control, Program of Immunology and Tumor Biology. Brazilian National Cancer Institute (INCA), Rio de Janeiro, RJ, Brazil
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19
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WEE1 kinase inhibitor AZD1775 induces CDK1 kinase-dependent origin firing in unperturbed G1- and S-phase cells. Proc Natl Acad Sci U S A 2019; 116:23891-23893. [PMID: 31712441 PMCID: PMC6883772 DOI: 10.1073/pnas.1915108116] [Citation(s) in RCA: 50] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
WEE1 kinase is a key regulator of the G2/M transition. The WEE1 kinase inhibitor AZD1775 (WEE1i) induces origin firing in replicating cells. We show that WEE1i induces CDK1-dependent RIF1 phosphorylation and CDK2- and CDC7-dependent activation of the replicative helicase. WEE1 suppresses CDK1 and CDK2 kinase activities to regulate the G1/S transition after the origin licensing is complete. We identify a role for WEE1 in cell cycle regulation and important effects of AZD1775, which is in clinical trials.
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20
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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.
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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
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21
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Abstract
The full licensing of replication origins in late G1 is normally enforced by the licensing checkpoint. In this issue, Matson et al. (2019. J. Cell Biol. https://doi.org/10.1083/jcb.201902143) show that this checkpoint is inoperative in cells exiting from G0, resulting in incomplete origin licensing and consequent replicative stress.
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Affiliation(s)
- J Julian Blow
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dundee, UK
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22
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Matson JP, House AM, Grant GD, Wu H, Perez J, Cook JG. Intrinsic checkpoint deficiency during cell cycle re-entry from quiescence. J Cell Biol 2019; 218:2169-2184. [PMID: 31186278 PMCID: PMC6605788 DOI: 10.1083/jcb.201902143] [Citation(s) in RCA: 34] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 05/08/2019] [Accepted: 05/17/2019] [Indexed: 12/19/2022] Open
Abstract
To maintain tissue homeostasis, cells transition between cell cycle quiescence and proliferation. An essential G1 process is minichromosome maintenance complex (MCM) loading at DNA replication origins to prepare for S phase, known as origin licensing. A p53-dependent origin licensing checkpoint normally ensures sufficient MCM loading before S phase entry. We used quantitative flow cytometry and live cell imaging to compare MCM loading during the long first G1 upon cell cycle entry and the shorter G1 phases in the second and subsequent cycles. We discovered that despite the longer G1 phase, the first G1 after cell cycle re-entry is significantly underlicensed. Consequently, the first S phase cells are hypersensitive to replication stress. This underlicensing results from a combination of slow MCM loading with a severely compromised origin licensing checkpoint. The hypersensitivity to replication stress increases over repeated rounds of quiescence. Thus, underlicensing after cell cycle re-entry from quiescence distinguishes a higher-risk first cell cycle that likely promotes genome instability.
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Affiliation(s)
- Jacob Peter Matson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Amy M House
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Gavin D Grant
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Huaitong Wu
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC
| | - Joanna Perez
- Biochemistry, Cell and Developmental Biology Program, Emory University, Atlanta, GA
| | - Jeanette Gowen Cook
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC
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23
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Petropoulos M, Champeris Tsaniras S, Taraviras S, Lygerou Z. Replication Licensing Aberrations, Replication Stress, and Genomic Instability. Trends Biochem Sci 2019; 44:752-764. [PMID: 31054805 DOI: 10.1016/j.tibs.2019.03.011] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 03/24/2019] [Accepted: 03/27/2019] [Indexed: 01/07/2023]
Abstract
Strict regulation of DNA replication is of fundamental significance for the maintenance of genome stability. Licensing of origins of DNA replication is a critical event for timely genome duplication. Errors in replication licensing control lead to genomic instability across evolution. Here, we present accumulating evidence that aberrant replication licensing is linked to oncogene-induced replication stress and poses a major threat to genome stability, promoting tumorigenesis. Oncogene activation can lead to defects in where along the genome and when during the cell cycle licensing takes place, resulting in replication stress. We also discuss the potential of replication licensing as a specific target for novel anticancer therapies.
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Affiliation(s)
- Michalis Petropoulos
- Department of Biology, School of Medicine, University of Patras, Patras 26504, Greece
| | | | - Stavros Taraviras
- Department of Physiology, School of Medicine, University of Patras, Patras 26504, Greece.
| | - Zoi Lygerou
- Department of Biology, School of Medicine, University of Patras, Patras 26504, Greece.
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24
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Pozo PN, Matson JP, Cole Y, Kedziora KM, Grant GD, Temple B, Cook JG. Cdt1 variants reveal unanticipated aspects of interactions with cyclin/CDK and MCM important for normal genome replication. Mol Biol Cell 2018; 29:2989-3002. [PMID: 30281379 PMCID: PMC6333176 DOI: 10.1091/mbc.e18-04-0242] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The earliest step in DNA replication is origin licensing, which is the DNA loading of minichromosome maintenance (MCM) helicase complexes. The Cdc10-dependent transcript 1 (Cdt1) protein is essential for MCM loading during the G1 phase of the cell cycle, but the mechanism of Cdt1 function is still incompletely understood. We examined a collection of rare Cdt1 variants that cause a form of primordial dwarfism (the Meier-Gorlin syndrome) plus one hypomorphic Drosophila allele to shed light on Cdt1 function. Three hypomorphic variants load MCM less efficiently than wild-type (WT) Cdt1, and their lower activity correlates with impaired MCM binding. A structural homology model of the human Cdt1-MCM complex positions the altered Cdt1 residues at two distinct interfaces rather than the previously described single MCM interaction domain. Surprisingly, one dwarfism allele (Cdt1-A66T) is more active than WT Cdt1. This hypermorphic variant binds both cyclin A and SCFSkp2 poorly relative to WT Cdt1. Detailed quantitative live-cell imaging analysis demonstrated no change in the stability of this variant, however. Instead, we propose that cyclin A/CDK inhibits the Cdt1 licensing function independent of the creation of the SCFSkp2 phosphodegron. Together, these findings identify key Cdt1 interactions required for both efficient origin licensing and tight Cdt1 regulation to ensure normal cell proliferation and genome stability.
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Affiliation(s)
- Pedro N Pozo
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jacob P Matson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Yasemin Cole
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Katarzyna M Kedziora
- Department of Genetics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Gavin D Grant
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Brenda Temple
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,R. L. Juliano Structural Bioinformatics Core Facility, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Center for Structural Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
| | - Jeanette Gowen Cook
- Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599.,Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599
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25
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Champeris Tsaniras S, Villiou M, Giannou AD, Nikou S, Petropoulos M, Pateras IS, Tserou P, Karousi F, Lalioti ME, Gorgoulis VG, Patmanidi AL, Stathopoulos GT, Bravou V, Lygerou Z, Taraviras S. Geminin ablation in vivo enhances tumorigenesis through increased genomic instability. J Pathol 2018; 246:134-140. [PMID: 29952003 DOI: 10.1002/path.5128] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/26/2018] [Revised: 05/29/2018] [Accepted: 06/01/2018] [Indexed: 11/09/2022]
Abstract
Geminin, a DNA replication licensing inhibitor, ensures faithful DNA replication in vertebrates. Several studies have shown that geminin depletion in vitro results in rereplication and DNA damage, whereas increased expression of geminin has been observed in human cancers. However, conditional inactivation of geminin during embryogenesis has not revealed any detectable DNA replication defects. In order to examine its role in vivo, we conditionally inactivated geminin in the murine colon and lung, and assessed chemically induced carcinogenesis. We show here that mice lacking geminin develop a significantly higher number of tumors and bear a larger tumor burden than sham-treated controls in urethane-induced lung and azoxymethane/dextran sodium sulfate-induced colon carcinogenesis. Survival is also significantly reduced in mice lacking geminin during lung carcinogenesis. A significant increase in the total number and grade of lesions (hyperplasias, adenomas, and carcinomas) was also confirmed by hematoxylin and eosin staining. Moreover, increased genomic aberrations, identified by increased ATR and γH2AX expression, was detected with immunohistochemistry analysis. In addition, we analyzed geminin expression in human colon cancer, and found increased expression, as well as a positive correlation with ATM/ATR levels and a non-monotonic association with γH2AX. Taken together, our data demonstrate that geminin acts as a tumor suppressor by safeguarding genome stability, whereas its overexpression is also associated with genomic instability. Copyright © 2018 Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.
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Affiliation(s)
| | - Maria Villiou
- Department of Physiology, Medical School, University of Patras, Patras, Greece
| | - Anastassios D Giannou
- Laboratory for Molecular Respiratory Carcinogenesis, Department of Physiology, Faculty of Medicine, University of Patras, Patras, Greece
| | - Sofia Nikou
- Department of Anatomy-Histology-Embryology, School of Medicine, University of Patras, Patras, Greece
| | | | - Ioannis S Pateras
- Department of Histology and Embryology, School of Medicine, National Kapodistrian University of Athens, Athens, Greece
| | - Paraskevi Tserou
- Department of Physiology, Medical School, University of Patras, Patras, Greece
| | - Foteini Karousi
- Department of Physiology, Medical School, University of Patras, Patras, Greece
| | - Maria-Eleni Lalioti
- Department of Physiology, Medical School, University of Patras, Patras, Greece
| | - Vassilis G Gorgoulis
- Department of Histology and Embryology, School of Medicine, National Kapodistrian University of Athens, Athens, Greece.,Biomedical Research Foundation of the Academy of Athens, Athens, Greece.,Faculty of Biology, Medicine and Health, University of Manchester, Manchester Academic Health Science Centre, Manchester, UK
| | | | - Georgios T Stathopoulos
- Laboratory for Molecular Respiratory Carcinogenesis, Department of Physiology, Faculty of Medicine, University of Patras, Patras, Greece
| | - Vasiliki Bravou
- Department of Anatomy-Histology-Embryology, School of Medicine, University of Patras, Patras, Greece
| | - Zoi Lygerou
- Department of Biology, Medical School, University of Patras, Patras, Greece
| | - Stavros Taraviras
- Department of Physiology, Medical School, University of Patras, Patras, Greece
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26
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The Temporal Regulation of S Phase Proteins During G 1. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1042:335-369. [PMID: 29357066 DOI: 10.1007/978-981-10-6955-0_16] [Citation(s) in RCA: 20] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Successful DNA replication requires intimate coordination with cell-cycle progression. Prior to DNA replication initiation in S phase, a series of essential preparatory events in G1 phase ensures timely, complete, and precise genome duplication. Among the essential molecular processes are regulated transcriptional upregulation of genes that encode replication proteins, appropriate post-transcriptional control of replication factor abundance and activity, and assembly of DNA-loaded protein complexes to license replication origins. In this chapter we describe these critical G1 events necessary for DNA replication and their regulation in the context of both cell-cycle entry and cell-cycle progression.
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27
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Lemmens B, Hegarat N, Akopyan K, Sala-Gaston J, Bartek J, Hochegger H, Lindqvist A. DNA Replication Determines Timing of Mitosis by Restricting CDK1 and PLK1 Activation. Mol Cell 2018; 71:117-128.e3. [PMID: 30008317 PMCID: PMC6039720 DOI: 10.1016/j.molcel.2018.05.026] [Citation(s) in RCA: 81] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2018] [Revised: 04/27/2018] [Accepted: 05/21/2018] [Indexed: 12/26/2022]
Abstract
To maintain genome stability, cells need to replicate their DNA before dividing. Upon completion of bulk DNA synthesis, the mitotic kinases CDK1 and PLK1 become active and drive entry into mitosis. Here, we have tested the hypothesis that DNA replication determines the timing of mitotic kinase activation. Using an optimized double-degron system, together with kinase inhibitors to enforce tight inhibition of key proteins, we find that human cells unable to initiate DNA replication prematurely enter mitosis. Preventing DNA replication licensing and/or firing causes prompt activation of CDK1 and PLK1 in S phase. In the presence of DNA replication, inhibition of CHK1 and p38 leads to premature activation of mitotic kinases, which induces severe replication stress. Our results demonstrate that, rather than merely a cell cycle output, DNA replication is an integral signaling component that restricts activation of mitotic kinases. DNA replication thus functions as a brake that determines cell cycle duration.
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Affiliation(s)
- Bennie Lemmens
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden; Division of Genome Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet and Science for Life Laboratory, Stockholm, Sweden
| | - Nadia Hegarat
- Genome Damage and Stability Centre, University of Sussex, Brighton, UK
| | - Karen Akopyan
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
| | - Joan Sala-Gaston
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden
| | - Jiri Bartek
- Division of Genome Biology, Department of Medical Biochemistry and Biophysics, Karolinska Institutet and Science for Life Laboratory, Stockholm, Sweden; Danish Cancer Society Research Center, Copenhagen, Denmark
| | - Helfrid Hochegger
- Genome Damage and Stability Centre, University of Sussex, Brighton, UK.
| | - Arne Lindqvist
- Department of Cell and Molecular Biology, Karolinska Institutet, Stockholm, Sweden.
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28
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Carroll TD, Newton IP, Chen Y, Blow JJ, Näthke I. Lgr5 + intestinal stem cells reside in an unlicensed G 1 phase. J Cell Biol 2018; 217:1667-1685. [PMID: 29599208 PMCID: PMC5940300 DOI: 10.1083/jcb.201708023] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2017] [Revised: 01/23/2018] [Accepted: 02/27/2018] [Indexed: 12/21/2022] Open
Abstract
During late mitosis and the early G1 phase, the origins of replication are licensed by binding to double hexamers of MCM2-7. In this study, we investigated how licensing and proliferative commitment are coupled in the epithelium of the small intestine. We developed a method for identifying cells in intact tissue containing DNA-bound MCM2-7. Interphase cells above the transit-amplifying compartment had no DNA-bound MCM2-7, but still expressed the MCM2-7 protein, suggesting that licensing is inhibited immediately upon differentiation. Strikingly, we found most proliferative Lgr5+ stem cells are in an unlicensed state. This suggests that the elongated cell-cycle of intestinal stem cells is caused by an increased G1 length, characterized by dormant periods with unlicensed origins. Significantly, the unlicensed state is lost in Apc-mutant epithelium, which lacks a functional restriction point, causing licensing immediately upon G1 entry. We propose that the unlicensed G1 phase of intestinal stem cells creates a temporal window when proliferative fate decisions can be made.
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Affiliation(s)
- Thomas D Carroll
- Cell and Developmental Biology, University of Dundee, Dundee, Scotland, UK
| | - Ian P Newton
- Cell and Developmental Biology, University of Dundee, Dundee, Scotland, UK
| | - Yu Chen
- Cell and Developmental Biology, University of Dundee, Dundee, Scotland, UK
| | - J Julian Blow
- Centre for Gene Regulation and Expression, University of Dundee, Dundee, Scotland, UK
| | - Inke Näthke
- Cell and Developmental Biology, University of Dundee, Dundee, Scotland, UK
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29
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MCM10 overexpression implicates adverse prognosis in urothelial carcinoma. Oncotarget 2018; 7:77777-77792. [PMID: 27780919 PMCID: PMC5363620 DOI: 10.18632/oncotarget.12795] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Accepted: 10/12/2016] [Indexed: 12/12/2022] Open
Abstract
Urothelial carcinoma (UC) occurs in the upper urinary tract (UTUC) and the urinary bladder (UBUC). The molecular pathogenesis of UC has not been fully elucidated. Through data mining of a published transcriptome of UBUC (GSE31684), we identified Minichromosome Maintenance Complex Component 2 (MCM2) and MCM10 as the two most significantly upregulated genes in UC progression among the MCM gene family, the key factors for the initiation of DNA replication. To validate the clinical significance of MCM2 and MCM10, immunohistochemistry, evaluated by H-score, was used in a pilot study of 50 UTUC and 50 UBUC samples. Only a high expression level of MCM10 predicted worse disease-specific survival (DSS) and inferior metastasis-free survival (MeFS) for both UTUC and UBUC. Correspondingly, evaluation of MCM10 mRNA expression in 36 UTUCs and 30 UBUCs showed significantly upregulated levels in high stage UC, suggesting its role in tumor progression. Evaluation of 340 UTUC and 296 UBUC tissue samples, respectively, demonstrated that high MCM10 immunoexpression was significantly associated with advanced primary tumors, nodal status, and the presence of vascular invasion in both groups of UCs. In multivariate Cox regression analyses, adjusted for standard clinicopathological features, MCM10 overexpression was independently associated with DSS (UTUC hazard ratio [HR]=2.401, P = 0.013; UBUC HR=4.323, P=0.001) and with MeFS (UTUC HR=3.294, P<0.001; UBUC HR=1.972, P=0.015). In vitro, knockdown of MCM10 gene significantly suppressed cell proliferation in both J82 and TCCSUP cells. In conclusion, MCM10 overexpression was associated with unfavorable clinicopathological characteristics and independent negative prognostic effects, justifying its potential theranostic value in UC.
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Arbi M, Pefani DE, Taraviras S, Lygerou Z. Controlling centriole numbers: Geminin family members as master regulators of centriole amplification and multiciliogenesis. Chromosoma 2017; 127:151-174. [PMID: 29243212 DOI: 10.1007/s00412-017-0652-7] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2017] [Revised: 11/06/2017] [Accepted: 11/07/2017] [Indexed: 01/18/2023]
Abstract
To ensure that the genetic material is accurately passed down to daughter cells during mitosis, dividing cells must duplicate their chromosomes and centrosomes once and only once per cell cycle. The same key steps-licensing, duplication, and segregation-control both the chromosome and the centrosome cycle, which must occur in concert to safeguard genome integrity. Aberrations in genome content or centrosome numbers lead to genomic instability and are linked to tumorigenesis. Such aberrations, however, can also be part of the normal life cycle of specific cell types. Multiciliated cells best exemplify the deviation from a normal centrosome cycle. They are post-mitotic cells which massively amplify their centrioles, bypassing the rule for once-per-cell-cycle centriole duplication. Hundreds of centrioles dock to the apical cell surface and generate motile cilia, whose concerted movement ensures fluid flow across epithelia. The early steps that control the generation of multiciliated cells have lately started to be elucidated. Geminin and the vertebrate-specific GemC1 and McIdas are distantly related coiled-coil proteins, initially identified as cell cycle regulators associated with the chromosome cycle. Geminin is required to ensure once-per-cell-cycle genome replication, while McIdas and GemC1 bind to Geminin and are implicated in DNA replication control. Recent findings highlight Geminin family members as early regulators of multiciliogenesis. GemC1 and McIdas specify the multiciliate cell fate by forming complexes with the E2F4/5 transcription factors to switch on a gene expression program leading to centriole amplification and cilia formation. Positive and negative interactions among Geminin family members may link cell cycle control to centriole amplification and multiciliogenesis, acting close to the point of transition from proliferation to differentiation. We review key steps of centrosome duplication and amplification, present the role of Geminin family members in the centrosome and chromosome cycle, and discuss links with disease.
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Affiliation(s)
- Marina Arbi
- Laboratory of Biology, School of Medicine, University of Patras, 26504 Rio, Patras, Greece
| | - Dafni-Eleftheria Pefani
- Laboratory of Biology, School of Medicine, University of Patras, 26504 Rio, Patras, Greece.,CRUK/MRC Oxford Institute, Department of Oncology, University of Oxford, Oxford, OX3 7DQ, UK
| | - Stavros Taraviras
- Laboratory of Physiology, School of Medicine, University of Patras, 26504 Rio, Patras, Greece
| | - Zoi Lygerou
- Laboratory of Biology, School of Medicine, University of Patras, 26504 Rio, Patras, Greece.
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Matson JP, Dumitru R, Coryell P, Baxley RM, Chen W, Twaroski K, Webber BR, Tolar J, Bielinsky AK, Purvis JE, Cook JG. Rapid DNA replication origin licensing protects stem cell pluripotency. eLife 2017; 6:30473. [PMID: 29148972 PMCID: PMC5720591 DOI: 10.7554/elife.30473] [Citation(s) in RCA: 59] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2017] [Accepted: 11/16/2017] [Indexed: 11/24/2022] Open
Abstract
Complete and robust human genome duplication requires loading minichromosome maintenance (MCM) helicase complexes at many DNA replication origins, an essential process termed origin licensing. Licensing is restricted to G1 phase of the cell cycle, but G1 length varies widely among cell types. Using quantitative single-cell analyses, we found that pluripotent stem cells with naturally short G1 phases load MCM much faster than their isogenic differentiated counterparts with long G1 phases. During the earliest stages of differentiation toward all lineages, MCM loading slows concurrently with G1 lengthening, revealing developmental control of MCM loading. In contrast, ectopic Cyclin E overproduction uncouples short G1 from fast MCM loading. Rapid licensing in stem cells is caused by accumulation of the MCM loading protein, Cdt1. Prematurely slowing MCM loading in pluripotent cells not only lengthens G1 but also accelerates differentiation. Thus, rapid origin licensing is an intrinsic characteristic of stem cells that contributes to pluripotency maintenance. From red blood cells to nerve cells, animals’ bodies contain many different types of specialized cells. These all begin as stem cells, which have the potential to divide and make more stem cells or to specialize. All dividing cells must first unwind their DNA so that it can be copied. To achieve this, cells load DNA-unwinding enzymes called helicases onto their DNA during the part of the cell cycle known as G1 phase. Cells must load enough helicase enzymes to ensure that their DNA is copied completely and in time. Stem cells divide faster than their specialized descendants, and have a much shorter G1 phase too. Yet these cells still manage to load enough helicases to copy their DNA. Little is known about how the amount, rate and timing of helicase loading varies between cells that divide at different speeds. Now Matson et al. have measured how quickly helicase enzymes are loaded onto DNA in individual human cells, including stem cells and specialized or “differentiated” cells. Stem cells loaded helicases rapidly to make up for the short time they spent in G1 phase, while differentiated cells loaded the enzymes more slowly. Measuring how the loading rate changed when stem cells were triggered to specialize showed that helicase loading slowed as the G1 phase got longer. Matson et al. found that the levels of key proteins required for helicase loading correlated with the rates of loading. Altering the levels of the proteins changed how quickly the enzymes were loaded and how the cells behaved – for example, slowing down the loading of helicases made the stem cells specialize quicker. These findings show that the processes of cell differentiation and DNA replication are closely linked. This study and future ones will help scientists understand what is happening during early animal development, when specialization first takes place, as well as what has gone wrong in cancer cells, which also divide quickly. A better understanding of this process also helps in regenerative medicine – where one of the challenges is to make enough specialized cells to transplant into a patient with tissue damage without those cells becoming cancerous.
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Affiliation(s)
- Jacob Peter Matson
- Department of Biochemistry and Biophysics, The University of North Carolina, Chapel Hill, United States
| | - Raluca Dumitru
- Human Pluripotent Stem Cell Core Facility, The University of North Carolina, Chapel Hill, United States
| | - Philip Coryell
- Department of Genetics, The University of North Carolina, Chapel Hill, United States
| | - Ryan M Baxley
- Department of Biochemistry, Molecular Biology, and Biophysics, The University of Minnesota, Minneapolis, United States
| | - Weili Chen
- Stem Cell Institute, University of Minnesota, Minnesota, United States
| | - Kirk Twaroski
- Stem Cell Institute, University of Minnesota, Minnesota, United States
| | - Beau R Webber
- Stem Cell Institute, University of Minnesota, Minnesota, United States
| | - Jakub Tolar
- Stem Cell Institute, University of Minnesota, Minnesota, United States
| | - Anja-Katrin Bielinsky
- Department of Biochemistry, Molecular Biology, and Biophysics, The University of Minnesota, Minneapolis, United States
| | - Jeremy E Purvis
- Department of Genetics, The University of North Carolina, Chapel Hill, United States.,Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, United States
| | - Jeanette Gowen Cook
- Department of Biochemistry and Biophysics, The University of North Carolina, Chapel Hill, United States.,Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, United States
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32
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Jiang S, Huang Y, Qi Y, He R, Liu Z, Ma Y, Guo X, Shao Y, Sun Z, Ruan Q. Human cytomegalovirus miR-US5-1 inhibits viral replication by targeting Geminin mRNA. Virol Sin 2017; 32:431-439. [PMID: 29116593 DOI: 10.1007/s12250-017-4064-x] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2017] [Accepted: 10/26/2017] [Indexed: 11/25/2022] Open
Abstract
Viruses commonly create favorable cellular conditions for their survival through multiple mechanisms. MicroRNAs (miRNAs), which function as post-transcriptional regulators, are utilized by human cytomegalovirus (HCMV) in its infection and pathogenesis. In the present study, the DNA replication inhibitor Geminin (GMNN) was identified to be a direct target of hcmv-miR-US5-1. Overexpression of hcmv-miR-US5-1 could block the accumulation of GMNN during HCMV infection, and the decrease of GMNN expression caused by hcmv-miR-US5-1 or GMNN specific siRNA reduced HCMV DNA copies in U373 cells. Meanwhile, ectopic expression of hcmv-miR-US5-1 and consequent lower expression of GMNN influenced host cell cycle and proliferation. These results imply that hcmv-miR-US5-1 may affect viral replication and host cellular environment by regulating expression kinetics of GMNN during HCMV infection.
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Affiliation(s)
- Shujuan Jiang
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
- Clinical Genetics, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yujing Huang
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Ying Qi
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Rong He
- Clinical Genetics, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China.
| | - Zhongyang Liu
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yanping Ma
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Xin Guo
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Yaozhong Shao
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Zhengrong Sun
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China
| | - Qiang Ruan
- Virus Laboratory, the Affiliated Shengjing Hospital, China Medical University, Shenyang, 110122, China.
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33
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Riera A, Barbon M, Noguchi Y, Reuter LM, Schneider S, Speck C. From structure to mechanism-understanding initiation of DNA replication. Genes Dev 2017; 31:1073-1088. [PMID: 28717046 PMCID: PMC5538431 DOI: 10.1101/gad.298232.117] [Citation(s) in RCA: 72] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
In this Review, Riera et al. review recent structural and biochemical insights that start to explain how specific proteins recognize DNA replication origins, load the replicative helicase on DNA, unwind DNA, synthesize new DNA strands, and reassemble chromatin. DNA replication results in the doubling of the genome prior to cell division. This process requires the assembly of 50 or more protein factors into a replication fork. Here, we review recent structural and biochemical insights that start to explain how specific proteins recognize DNA replication origins, load the replicative helicase on DNA, unwind DNA, synthesize new DNA strands, and reassemble chromatin. We focus on the minichromosome maintenance (MCM2–7) proteins, which form the core of the eukaryotic replication fork, as this complex undergoes major structural rearrangements in order to engage with DNA, regulate its DNA-unwinding activity, and maintain genome stability.
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Affiliation(s)
- Alberto Riera
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Marta Barbon
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom.,Medical Research Council (MRC) London Institute of Medical Sciences (LMS), London W12 0NN, United Kingdom
| | - Yasunori Noguchi
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - L Maximilian Reuter
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Sarah Schneider
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom
| | - Christian Speck
- DNA Replication Group, Institute of Clinical Sciences (ICS), Faculty of Medicine, Imperial College London, London W12 0NN, United Kingdom.,Medical Research Council (MRC) London Institute of Medical Sciences (LMS), London W12 0NN, United Kingdom
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34
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Gardner NJ, Gillespie PJ, Carrington JT, Shanks EJ, McElroy SP, Haagensen EJ, Frearson JA, Woodland A, Blow JJ. The High-Affinity Interaction between ORC and DNA that Is Required for Replication Licensing Is Inhibited by 2-Arylquinolin-4-Amines. Cell Chem Biol 2017; 24:981-992.e4. [PMID: 28781123 PMCID: PMC5563080 DOI: 10.1016/j.chembiol.2017.06.019] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2016] [Revised: 06/13/2017] [Accepted: 06/30/2017] [Indexed: 01/10/2023]
Abstract
In late mitosis and G1, origins of DNA replication must be "licensed" for use in the upcoming S phase by being encircled by double hexamers of the minichromosome maintenance proteins MCM2-7. A "licensing checkpoint" delays cells in G1 until sufficient origins have been licensed, but this checkpoint is lost in cancer cells. Inhibition of licensing can therefore kill cancer cells while only delaying normal cells in G1. In a high-throughput cell-based screen for licensing inhibitors we identified a family of 2-arylquinolin-4-amines, the most potent of which we call RL5a. The binding of the origin recognition complex (ORC) to origin DNA is the first step of the licensing reaction. We show that RL5a prevents ORC forming a tight complex with DNA that is required for MCM2-7 loading. Formation of this ORC-DNA complex requires ATP, and we show that RL5a inhibits ORC allosterically to mimic a lack of ATP.
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Affiliation(s)
- Nicola J Gardner
- Centre for Gene Regulation & Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Peter J Gillespie
- Centre for Gene Regulation & Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Jamie T Carrington
- Centre for Gene Regulation & Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Emma J Shanks
- Drug Discovery Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Stuart P McElroy
- Drug Discovery Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Emma J Haagensen
- Centre for Gene Regulation & Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Julie A Frearson
- Drug Discovery Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Andrew Woodland
- Drug Discovery Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
| | - J Julian Blow
- Centre for Gene Regulation & Expression, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
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35
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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.
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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
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36
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Blumenfeld B, Ben-Zimra M, Simon I. Perturbations in the Replication Program Contribute to Genomic Instability in Cancer. Int J Mol Sci 2017; 18:E1138. [PMID: 28587102 PMCID: PMC5485962 DOI: 10.3390/ijms18061138] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2017] [Revised: 05/08/2017] [Accepted: 05/21/2017] [Indexed: 12/14/2022] Open
Abstract
Cancer and genomic instability are highly impacted by the deoxyribonucleic acid (DNA) replication program. Inaccuracies in DNA replication lead to the increased acquisition of mutations and structural variations. These inaccuracies mainly stem from loss of DNA fidelity due to replication stress or due to aberrations in the temporal organization of the replication process. Here we review the mechanisms and impact of these major sources of error to the replication program.
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Affiliation(s)
- Britny Blumenfeld
- Department of Microbiology and Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel.
| | - Micha Ben-Zimra
- Department of Microbiology and Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel.
- Pharmacology and Experimental Therapeutics Unit, The Institute for Drug Research, School of Pharmacy, Faculty of Medicine, The Hebrew University of Jerusalem, Jerusalem 91120, Israel.
| | - Itamar Simon
- Department of Microbiology and Molecular Genetics, IMRIC, Faculty of Medicine, Hebrew University of Jerusalem, Jerusalem 91120, Israel.
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37
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Tang XF, Chen XY, Zhang CD, Li YF, Liu TH, Zhou XL, Wang L, Zhang Q, Chen P, Lu C, Pan MH. Two Geminin homologs regulate DNA replication in silkworm, Bombyx mori. Cell Cycle 2017; 16:830-840. [PMID: 28379781 DOI: 10.1080/15384101.2017.1282582] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
DNA replication is rigorously controlled in cells to ensure that the genome duplicates exactly once per cell cycle. Geminin is a small nucleoprotein, which prevents DNA rereplication by directly binding to and inhibiting the DNA replication licensing factor, Cdt1. In this study, we have identified 2 Geminin genes, BmGeminin1 and BmGeminn2, in silkworm, Bombyx mori. These genes contain the Geminin conserved coiled-coil domain and are periodically localized in the nucleus during the S-G2 phase but are degraded at anaphase in mitosis. Both BmGeminin1 and BmGeminin2 are able to homodimerize and interact with BmCdt1 in cells. In addition, BmGeminin1 and BmGeminin2 can interact with each other. Overexpression of BmGeminin1 affects cell cycle progression: cell cycle is arrested in S phase, and RNA interference of BmGeminin1 leads to rereplication. In contrast, overexpression or knockdown of BmGeminin2 with RNAi did not significantly affect cell cycle, while more rereplication occurred when BmGeminin1 and BmGeminin2 together were knocked down in cells than when only BmGeminin1 was knocked down. These data suggest that both BmGeminin1 and BmGeminin2 are involved in the regulation of DNA replication. These findings provide insight into the function of Geminin and contribute to our understanding of the regulation mechanism of cell cycle in silkworm.
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Affiliation(s)
- Xiao-Fang Tang
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China
| | - Xiang-Yun Chen
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,b Basic Medical School , Guiyang College of Traditional Chinese Medicine , Guiyang , China
| | - Chun-Dong Zhang
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,c Department of Biochemistry and Molecular Biology , Chongqing Medical University , Chongqing , China
| | - Yao-Feng Li
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,b Basic Medical School , Guiyang College of Traditional Chinese Medicine , Guiyang , China
| | - Tai-Hang Liu
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China
| | - Xiao-Lin Zhou
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China
| | - La Wang
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China
| | - Qian Zhang
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China
| | - Peng Chen
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,d Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry , Southwest University , Chongqing , China
| | - Cheng Lu
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,d Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry , Southwest University , Chongqing , China
| | - Min-Hui Pan
- a State Key Laboratory of Silkworm Genome Biology , Southwest University , Chongqing , China.,d Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry , Southwest University , Chongqing , China
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38
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Matson JP, Cook JG. Cell cycle proliferation decisions: the impact of single cell analyses. FEBS J 2017; 284:362-375. [PMID: 27634578 PMCID: PMC5296213 DOI: 10.1111/febs.13898] [Citation(s) in RCA: 107] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2016] [Revised: 08/23/2016] [Accepted: 09/13/2016] [Indexed: 12/16/2022]
Abstract
Cell proliferation is a fundamental requirement for organismal development and homeostasis. The mammalian cell division cycle is tightly controlled to ensure complete and precise genome duplication and segregation of replicated chromosomes to daughter cells. The onset of DNA replication marks an irreversible commitment to cell division, and the accumulated efforts of many decades of molecular and cellular studies have probed this cellular decision, commonly called the restriction point. Despite a long-standing conceptual framework of the restriction point for progression through G1 phase into S phase or exit from G1 phase to quiescence (G0), recent technical advances in quantitative single cell analysis of mammalian cells have provided new insights. Significant intercellular heterogeneity revealed by single cell studies and the discovery of discrete subpopulations in proliferating cultures suggests the need for an even more nuanced understanding of cell proliferation decisions. In this review, we describe some of the recent developments in the cell cycle field made possible by quantitative single cell experimental approaches.
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Affiliation(s)
- Jacob P. Matson
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill. Chapel Hill, North Carolina 27599
| | - Jeanette G. Cook
- Department of Biochemistry and Biophysics, University of North Carolina at Chapel Hill. Chapel Hill, North Carolina 27599
- Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill. Chapel Hill, North Carolina 27599
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39
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Pozo PN, Cook JG. Regulation and Function of Cdt1; A Key Factor in Cell Proliferation and Genome Stability. Genes (Basel) 2016; 8:genes8010002. [PMID: 28025526 PMCID: PMC5294997 DOI: 10.3390/genes8010002] [Citation(s) in RCA: 65] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2016] [Revised: 12/13/2016] [Accepted: 12/14/2016] [Indexed: 12/30/2022] Open
Abstract
Successful cell proliferation requires efficient and precise genome duplication followed by accurate chromosome segregation. The Cdc10-dependent transcript 1 protein (Cdt1) is required for the first step in DNA replication, and in human cells Cdt1 is also required during mitosis. Tight cell cycle controls over Cdt1 abundance and activity are critical to normal development and genome stability. We review here recent advances in elucidating Cdt1 molecular functions in both origin licensing and kinetochore–microtubule attachment, and we describe the current understanding of human Cdt1 regulation.
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Affiliation(s)
- Pedro N Pozo
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| | - Jeanette Gowen Cook
- Curriculum in Genetics and Molecular Biology, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
- Department of Biochemistry and Biophysics, The University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
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40
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Patmanidi AL, Champeris Tsaniras S, Karamitros D, Kyrousi C, Lygerou Z, Taraviras S. Concise Review: Geminin-A Tale of Two Tails: DNA Replication and Transcriptional/Epigenetic Regulation in Stem Cells. Stem Cells 2016; 35:299-310. [DOI: 10.1002/stem.2529] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2016] [Revised: 09/18/2016] [Accepted: 10/01/2016] [Indexed: 12/14/2022]
Affiliation(s)
| | | | - Dimitris Karamitros
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
| | - Christina Kyrousi
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
| | - Zoi Lygerou
- Department of Biology; Medical School, University of Patras; Rio Patras Greece
| | - Stavros Taraviras
- Department of Physiology; Medical School, University of Patras; Rio Patras Greece
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41
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Tudzarova S, Mulholland P, Dey A, Stoeber K, Okorokov AL, Williams GH. p53 controls CDC7 levels to reinforce G1 cell cycle arrest upon genotoxic stress. Cell Cycle 2016; 15:2958-2972. [PMID: 27611229 PMCID: PMC5105930 DOI: 10.1080/15384101.2016.1231281] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
DNA replication initiation is a key event in the cell cycle, which is dependent on 2 kinases - CDK2 and CDC7. Here we report a novel mechanism in which p53 induces G1 checkpoint and cell cycle arrest by downregulating CDC7 kinase in response to genotoxic stress. We demonstrate that p53 controls CDC7 stability post-transcriptionally via miR-192/215 and post-translationally via Fbxw7β E3 ubiquitin ligase. The p53-dependent pathway of CDC7 downregulation is interlinked with the p53-p21-CDK2 pathway, as p21-mediated inhibition of CDK2-dependent phosphorylation of CDC7 on Thr376 is required for GSK3ß-phosphorylation and Fbxw7ß-dependent degradation of CDC7. Notably, sustained oncogenic high levels of active CDC7 exert a negative feedback onto p53, leading to unrestrained S-phase progression and accumulation of DNA damage. Thus, p53-dependent control of CDC7 levels is essential for blocking G1/S cell-cycle transition upon genotoxic stress, thereby safeguarding the genome from instability and thus representing a novel general stress response.
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Affiliation(s)
- Slavica Tudzarova
- a Wolfson Institute for Biomedical Research, Division of Medicine, University College London , London , UK.,b Division of Endocrinology, David Geffen School of Medicine, University of California Los Angeles , Los Angeles , CA , USA
| | - Paul Mulholland
- c Department of Pathology , UCL Cancer Institute, University College London , London , UK
| | - Ayona Dey
- a Wolfson Institute for Biomedical Research, Division of Medicine, University College London , London , UK
| | - Kai Stoeber
- c Department of Pathology , UCL Cancer Institute, University College London , London , UK
| | - Andrei L Okorokov
- a Wolfson Institute for Biomedical Research, Division of Medicine, University College London , London , UK
| | - Gareth H Williams
- c Department of Pathology , UCL Cancer Institute, University College London , London , UK.,d Oncologica Ltd, The Science Village, Chesterford Research Park , Cambridge , UK
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Htike NTT, Maekawa F, Soutome H, Sano K, Maejima S, Aung KH, Tokuda M, Tsukahara S. Arsenic Exposure Induces Unscheduled Mitotic S Phase Entry Coupled with Cell Death in Mouse Cortical Astrocytes. Front Neurosci 2016; 10:297. [PMID: 27445668 PMCID: PMC4926759 DOI: 10.3389/fnins.2016.00297] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2016] [Accepted: 06/13/2016] [Indexed: 11/16/2022] Open
Abstract
There is serious concern about arsenic in the natural environment, which exhibits neurotoxicity and increases the risk of neurodevelopmental disorders. Adverse effects of arsenic have been demonstrated in neurons, but it is not fully understood how arsenic affects other cell types in the brain. In the current study, we examined whether sodium arsenite (NaAsO2) affects the cell cycle, viability, and apoptosis of in vitro-cultured astrocytes isolated from the cerebral cortex of mice. Cultured astrocytes from transgenic mice expressing fluorescent ubiquitination-based cell cycle indicator (Fucci) were subjected to live imaging analysis to assess the effects of NaAsO2 (0, 1, 2, and 4 μM) on the cell cycle and number of cells. Fucci was designed to express monomeric Kusabira Orange2 (mKO2) fused with the ubiquitylation domain of hCdt1, a marker of G1 phase, and monomeric Azami Green (mAG) fused with the ubiquitylation domain of hGem, a marker of S, G2, and M phases. NaAsO2 concentration-dependently decreased the peak levels of the mAG/mKO2 emission ratio when the ratio had reached a peak in astrocytes without NaAsO2 exposure, which was due to attenuating the increase in the mAG-expressing cell number. In contrast, the mAG/mKO2 emission ratio and number of mAG-expressing cells were concentration-dependently increased by NaAsO2 before their peak levels, indicating unscheduled S phase entry. We further examined the fate of cells forced to enter S phase by NaAsO2. We found that most of these cells died up to the end of live imaging. In addition, quantification of the copy number of the glial fibrillary acidic protein gene expressed specifically in astrocytes revealed a concentration-dependent decrease caused by NaAsO2. However, NaAsO2 did not increase the amount of nucleosomes generated from DNA fragmentation and failed to alter the gene expression of molecules relevant to unscheduled S phase entry-coupled apoptosis (p21, p53, E2F1, E2F4, and Gm36566). These findings suggest that NaAsO2 adversely affects the cell cycle and viability of astrocytes by inducing unscheduled S phase entry coupled with cell death that may be caused by mechanisms other than apoptosis.
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Affiliation(s)
- Nang T T Htike
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University Saitama, Japan
| | - Fumihiko Maekawa
- Center for Health and Environmental Risk Research, National Institute for Environmental Studies Tsukuba, Japan
| | - Haruka Soutome
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University Saitama, Japan
| | - Kazuhiro Sano
- Center for Health and Environmental Risk Research, National Institute for Environmental Studies Tsukuba, Japan
| | - Sho Maejima
- Area of Life-NanoBio, Division of Strategy Research, Graduate School of Science and Engineering, Saitama University Saitama, Japan
| | - Kyaw H Aung
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University Saitama, Japan
| | - Masaaki Tokuda
- Department of Cell Physiology, Faculty of Medicine/Graduate School of Medicine, Kagawa University Kagawa, Japan
| | - Shinji Tsukahara
- Area of Regulatory Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama UniversitySaitama, Japan; Area of Life-NanoBio, Division of Strategy Research, Graduate School of Science and Engineering, Saitama UniversitySaitama, Japan
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Role of WDHD1 in Human Papillomavirus-Mediated Oncogenesis Identified by Transcriptional Profiling of E7-Expressing Cells. J Virol 2016; 90:6071-6084. [PMID: 27099318 DOI: 10.1128/jvi.00513-16] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 04/16/2016] [Indexed: 01/04/2023] Open
Abstract
UNLABELLED The E7 oncoprotein of the high-risk human papillomavirus (HPV) plays a major role in HPV-induced carcinogenesis. E7 abrogates the G1 cell cycle checkpoint and induces genomic instability, but the mechanism is not fully understood. In this study, we performed RNA sequencing (RNA-seq) to characterize the transcriptional profile of keratinocytes expressing HPV 16 (HPV-16) E7. At the transcriptome level, 236 genes were differentially expressed between E7 and vector control cells. A subset of the differentially expressed genes, most of them novel to E7-expressing cells, was further confirmed by real-time PCR. Of interest, the activities of multiple transcription factors were altered in E7-expressing cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were investigated. The upregulated genes were enriched in cell cycle and DNA replication, as well as in the DNA metabolic process, transcription, DNA damage, DNA repair, and nucleotide metabolism. Specifically, we focused our studies on the gene encoding WDHD1 (WD repeat and high mobility group [HMG]-box DNA-binding protein), one of the genes that was upregulated in E7-expressing cells. WDHD1 is a component of the replisome that regulates DNA replication. Recent studies suggest that WDHD1 may also function as a DNA replication initiation factor as well as a G1 checkpoint regulator. We found that in E7-expressing cells, the steady-state level of WDHD1 protein was increased along with the half-life. Moreover, downregulation of WDHD1 reduced E7-induced G1 checkpoint abrogation and rereplication, demonstrating a novel function for WDHD1. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications. IMPORTANCE The high-risk HPV types induce cervical cancer and encode an E7 oncoprotein that plays a major role in HPV-induced carcinogenesis. However, the mechanism by which E7 induces carcinogenesis is not fully understood; specific anti-HPV agents are not available. In this study, we performed RNA-seq to characterize transcriptional profiling of keratinocytes expressing HPV-16 E7 and identified more than 200 genes that were differentially expressed between E7 and vector control cells. Through bioinformatics analysis, pathways altered in E7-expressing cells were identified. Significantly, the WDHD1 gene, one of the genes that is upregulated in E7-expressing cells, was found to play an important role in E7-induced G1 checkpoint abrogation and rereplication. These studies shed light on mechanisms by which HPV induces genomic instability and have therapeutic implications.
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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]
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Muñoz S, Méndez J. DNA replication stress: from molecular mechanisms to human disease. Chromosoma 2016; 126:1-15. [PMID: 26797216 DOI: 10.1007/s00412-016-0573-x] [Citation(s) in RCA: 48] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2015] [Revised: 01/04/2016] [Accepted: 01/05/2016] [Indexed: 12/29/2022]
Abstract
The genome of proliferating cells must be precisely duplicated in each cell division cycle. Chromosomal replication entails risks such as the possibility of introducing breaks and/or mutations in the genome. Hence, DNA replication requires the coordinated action of multiple proteins and regulatory factors, whose deregulation causes severe developmental diseases and predisposes to cancer. In recent years, the concept of "replicative stress" (RS) has attracted much attention as it impinges directly on genomic stability and offers a promising new avenue to design anticancer therapies. In this review, we summarize recent progress in three areas: (1) endogenous and exogenous factors that contribute to RS, (2) molecular mechanisms that mediate the cellular responses to RS, and (3) the large list of diseases that are directly or indirectly linked to RS.
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Affiliation(s)
- Sergio Muñoz
- DNA Replication Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain
| | - Juan Méndez
- DNA Replication Group, Molecular Oncology Programme, Spanish National Cancer Research Centre (CNIO), Melchor Fernández Almagro 3, E-28029, Madrid, Spain.
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Bai G, Smolka MB, Schimenti JC. Chronic DNA Replication Stress Reduces Replicative Lifespan of Cells by TRP53-Dependent, microRNA-Assisted MCM2-7 Downregulation. PLoS Genet 2016; 12:e1005787. [PMID: 26765334 PMCID: PMC4713100 DOI: 10.1371/journal.pgen.1005787] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2015] [Accepted: 12/15/2015] [Indexed: 11/18/2022] Open
Abstract
Circumstances that compromise efficient DNA replication, such as disruptions to replication fork progression, cause a state known as DNA replication stress (RS). Whereas normally proliferating cells experience low levels of RS, excessive RS from intrinsic or extrinsic sources can trigger cell cycle arrest and senescence. Here, we report that a key driver of RS-induced senescence is active downregulation of the Minichromosome Maintenance 2–7 (MCM2-7) factors that are essential for replication origin licensing and which constitute the replicative helicase core. Proliferating cells produce high levels of MCM2-7 that enable formation of dormant origins that can be activated in response to acute, experimentally-induced RS. However, little is known about how physiological RS levels impact MCM2-7 regulation. We found that chronic exposure of primary mouse embryonic fibroblasts (MEFs) to either genetically-encoded or environmentally-induced RS triggered gradual MCM2-7 repression, followed by inhibition of replication and senescence that could be accelerated by MCM hemizygosity. The MCM2-7 reduction in response to RS is TRP53-dependent, and involves a group of Trp53-dependent miRNAs, including the miR-34 family, that repress MCM expression in replication-stressed cells before they undergo terminal cell cycle arrest. miR-34 ablation partially rescued MCM2-7 downregulation and genomic instability in mice with endogenous RS. Together, these data demonstrate that active MCM2-7 repression is a physiologically important mechanism for RS-induced cell cycle arrest and genome maintenance on an organismal level. Duplication of the genome by DNA replication is essential for cell proliferation. DNA replication is initiated from many sites (“origins”) along chromosomes that are bound by replication licensing proteins, including MCM2-7. They are also core components of the replication helicase complex that unwinds double stranded DNA to expose single stranded DNA that is the template for DNA polymerase. Eukaryotic DNA replication machinery faces many challenges to duplicate the complex and massive genome. Circumstances that inhibit progression of the replication machinery cause “replication stress” (RS). Cells can counteract RS by utilizing “dormant” or “backup” origins. Abundant MCM2-7 expression sufficiently licenses dormant origins, but reducing MCMs compromises cellular responses to RS. We show that MCM2-7 expression is downregulated in cells experiencing chronic RS, and this depends on the TRP53 tumor suppressor and microRNAs it regulates. Extended RS eventually reduces MCMs to a point that terminal cell cycle arrest occurs. We propose that this mechanism is a crucial protection against neoplasia.
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Affiliation(s)
- Gongshi Bai
- Department of Biomedical Sciences, Cornell University, Ithaca, New York, United States of America
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
| | - Marcus B. Smolka
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
- Weill Institute for Cellular and Molecular Biology, Cornell University, Ithaca, New York, United States of America
- Center for Vertebrate Genomics, Cornell University, Ithaca, New York, United States of America
| | - John C. Schimenti
- Department of Biomedical Sciences, Cornell University, Ithaca, New York, United States of America
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, New York, United States of America
- Center for Vertebrate Genomics, Cornell University, Ithaca, New York, United States of America
- * E-mail:
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Burrage LC, Charng WL, Eldomery MK, Willer JR, Davis EE, Lugtenberg D, Zhu W, Leduc MS, Akdemir ZC, Azamian M, Zapata G, Hernandez PP, Schoots J, de Munnik SA, Roepman R, Pearring JN, Jhangiani S, Katsanis N, Vissers LELM, Brunner HG, Beaudet AL, Rosenfeld JA, Muzny DM, Gibbs RA, Eng CM, Xia F, Lalani SR, Lupski JR, Bongers EMHF, Yang Y. De Novo GMNN Mutations Cause Autosomal-Dominant Primordial Dwarfism Associated with Meier-Gorlin Syndrome. Am J Hum Genet 2015; 97:904-13. [PMID: 26637980 PMCID: PMC4678788 DOI: 10.1016/j.ajhg.2015.11.006] [Citation(s) in RCA: 56] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 11/05/2015] [Indexed: 12/21/2022] Open
Abstract
Meier-Gorlin syndrome (MGS) is a genetically heterogeneous primordial dwarfism syndrome known to be caused by biallelic loss-of-function mutations in one of five genes encoding pre-replication complex proteins: ORC1, ORC4, ORC6, CDT1, and CDC6. Mutations in these genes cause disruption of the origin of DNA replication initiation. To date, only an autosomal-recessive inheritance pattern has been described in individuals with this disorder, with a molecular etiology established in about three-fourths of cases. Here, we report three subjects with MGS and de novo heterozygous mutations in the 5' end of GMNN, encoding the DNA replication inhibitor geminin. We identified two truncating mutations in exon 2 (the 1(st) coding exon), c.16A>T (p.Lys6(∗)) and c.35_38delTCAA (p.Ile12Lysfs(∗)4), and one missense mutation, c.50A>G (p.Lys17Arg), affecting the second-to-last nucleotide of exon 2 and possibly RNA splicing. Geminin is present during the S, G2, and M phases of the cell cycle and is degraded during the metaphase-anaphase transition by the anaphase-promoting complex (APC), which recognizes the destruction box sequence near the 5' end of the geminin protein. All three GMNN mutations identified alter sites 5' to residue Met28 of the protein, which is located within the destruction box. We present data supporting a gain-of-function mechanism, in which the GMNN mutations result in proteins lacking the destruction box and hence increased protein stability and prolonged inhibition of replication leading to autosomal-dominant MGS.
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Affiliation(s)
- Lindsay C Burrage
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Department of Pediatrics, Texas Children's Hospital, Houston, TX 77030, USA
| | - Wu-Lin Charng
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Mohammad K Eldomery
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jason R Willer
- Center for Human Disease Modeling, Duke University Medical Center, Durham, NC 27701, USA
| | - Erica E Davis
- Center for Human Disease Modeling, Duke University Medical Center, Durham, NC 27701, USA
| | - Dorien Lugtenberg
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Wenmiao Zhu
- Exome Laboratory, Baylor Miraca Genetics Laboratories, Houston, TX 77030, USA
| | - Magalie S Leduc
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Zeynep C Akdemir
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Mahshid Azamian
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Gladys Zapata
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Patricia P Hernandez
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jeroen Schoots
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Sonja A de Munnik
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Ronald Roepman
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Jillian N Pearring
- Department of Ophthalmology, Duke University Medical Center, Durham, NC 27701, USA
| | - Shalini Jhangiani
- Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA
| | - Nicholas Katsanis
- Center for Human Disease Modeling, Duke University Medical Center, Durham, NC 27701, USA
| | - Lisenka E L M Vissers
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Han G Brunner
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands
| | - Arthur L Beaudet
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Jill A Rosenfeld
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA
| | - Donna M Muzny
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA
| | - Richard A Gibbs
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA
| | - Christine M Eng
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Exome Laboratory, Baylor Miraca Genetics Laboratories, Houston, TX 77030, USA
| | - Fan Xia
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Exome Laboratory, Baylor Miraca Genetics Laboratories, Houston, TX 77030, USA
| | - Seema R Lalani
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Exome Laboratory, Baylor Miraca Genetics Laboratories, Houston, TX 77030, USA
| | - James R Lupski
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Human Genome Sequencing Center, Baylor College of Medicine, Houston, TX 77030, USA; Department of Pediatrics, Texas Children's Hospital, Houston, TX 77030, USA
| | - Ernie M H F Bongers
- Department of Human Genetics, Radboud university medical center, P.O. Box 9101, 6500 HB, Nijmegen, the Netherlands.
| | - Yaping Yang
- Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030, USA; Exome Laboratory, Baylor Miraca Genetics Laboratories, Houston, TX 77030, USA.
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Das M, Prasad SB, Yadav SS, Modi A, Singh S, Pradhan S, Narayan G. HPV-type-specific response of cervical cancer cells to cisplatin after silencing replication licensing factor MCM4. Tumour Biol 2015; 36:9987-94. [PMID: 26188903 DOI: 10.1007/s13277-015-3782-7] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 07/08/2015] [Indexed: 12/25/2022] Open
Abstract
Minichoromosome maintenance (MCM) proteins play key role in cell cycle progression by licensing DNA replication only once per cell cycle. These proteins are found to be overexpressed in cervical cancer cells. In this study, we depleted MCM4, one of the MCM 2-7 complex components by RNA interference (RNAi) in four cervical cancer cell lines. The four cell lines were selected on the basis of their human papillomavirus (HPV) infection: HPV16-positive SiHa, HPV18-positive ME-180, HPV16- and HPV18-positive CaSki, and HPV-negative C-33A. The MCM4-deficient cells irrespective of their HPV status grow for several generations and maintain regular cell cycle. We did not find any evidence of augmented response to a short-term (48 h) cisplatin treatment in these MCM4-deficient cells. However, MCM4-/HPV16+ SiHa cells cannot withstand a prolonged treatment (up to 5 days) of even a sublethal dosage of cisplatin. They show increased chromosomal instability compared to their control counterparts. On the other hand, MCM4-deficient CaSki cells (both HPV16+ and 18+) remain resistant to a prolonged exposure to cisplatin. Our study indicates that cervical cancer cells may be using excess MCMs as a backup for replicative stress; however, its regulatory mechanism is dependent on the HPV status of the cells.
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Affiliation(s)
- Mitali Das
- Cancer Genetics Laboratory, Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India
| | - Shyam Babu Prasad
- Cancer Genetics Laboratory, Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India.,Division of Molecular Oncology, Institute of Cytology and Preventive Oncology, I-7, Sector-39, Noida, 201 301, India
| | - Suresh Singh Yadav
- Cancer Genetics Laboratory, Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India
| | - Arusha Modi
- Cancer Genetics Laboratory, Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India
| | - Sunita Singh
- Department of Zoology, Mahila Mahavidyalaya, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India
| | - Satyajit Pradhan
- Department of Radiotherapy and Radiation Medicine, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India
| | - Gopeshwar Narayan
- Cancer Genetics Laboratory, Department of Molecular and Human Genetics, Banaras Hindu University, Varanasi, 221 005, Uttar Pradesh, India.
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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.
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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
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Affiliation(s)
- Marcelina W Musiałek
- a Department of Cytophysiology ; Institute of Experimental Biology; Faculty of Biology and Environmental Protection; University of Łódź ; Łódź , Poland
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50
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Morino M, Nukina K, Sakaguchi H, Maeda T, Takahara M, Shiomi Y, Nishitani H. Mitotic UV irradiation induces a DNA replication-licensing defect that potentiates G1 arrest response. PLoS One 2015; 10:e0120553. [PMID: 25798850 PMCID: PMC4370595 DOI: 10.1371/journal.pone.0120553] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 02/05/2015] [Indexed: 11/19/2022] Open
Abstract
Cdt1 begins to accumulate in M phase and has a key role in establishing replication licensing at the end of mitosis or in early G1 phase. Treatments that damage the DNA of cells, such as UV irradiation, induce Cdt1 degradation through PCNA-dependent CRL4-Cdt2 ubiquitin ligase. How Cdt1 degradation is linked to cell cycle progression, however, remains unclear. In G1 phase, when licensing is established, UV irradiation leads to Cdt1 degradation, but has little effect on the licensing state. In M phase, however, UV irradiation does not induce Cdt1 degradation. When mitotic UV-irradiated cells were released into G1 phase, Cdt1 was degraded before licensing was established. Thus, these cells exhibited both defective licensing and G1 cell cycle arrest. The frequency of G1 arrest increased in cells expressing extra copies of Cdt2, and thus in cells in which Cdt1 degradation was enhanced, whereas the frequency of G1 arrest was reduced in cell expressing an extra copy of Cdt1. The G1 arrest response of cells irradiated in mitosis was important for cell survival by preventing the induction of apoptosis. Based on these observations, we propose that mammalian cells have a DNA replication-licensing checkpoint response to DNA damage induced during mitosis.
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Affiliation(s)
- Masayuki Morino
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Kohei Nukina
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Hiroki Sakaguchi
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Takeshi Maeda
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Michiyo Takahara
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Yasushi Shiomi
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
| | - Hideo Nishitani
- Graduate School of Life Science, University of Hyogo, Kamigori, Ako-gun, Hyogo, Japan
- * E-mail:
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