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The CMG helicase and cancer: a tumor "engine" and weakness with missing mutations. Oncogene 2023; 42:473-490. [PMID: 36522488 PMCID: PMC9948756 DOI: 10.1038/s41388-022-02572-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 12/01/2022] [Accepted: 12/07/2022] [Indexed: 12/23/2022]
Abstract
The replicative Cdc45-MCM-GINS (CMG) helicase is a large protein complex that functions in the DNA melting and unwinding steps as a component of replisomes during DNA replication in mammalian cells. Although the CMG performs this important role in cell growth, the CMG is not a simple bystander in cell cycle events. Components of the CMG, specifically the MCM precursors, are also involved in maintaining genomic stability by regulating DNA replication fork speeds, facilitating recovery from replicative stresses, and preventing consequential DNA damage. Given these important functions, MCM/CMG complexes are highly regulated by growth factors such as TGF-ß1 and by signaling factors such as Myc, Cyclin E, and the retinoblastoma protein. Mismanagement of MCM/CMG complexes when these signaling mediators are deregulated, and in the absence of the tumor suppressor protein p53, leads to increased genomic instability and is a contributor to tumorigenic transformation and tumor heterogeneity. The goal of this review is to provide insight into the mechanisms and dynamics by which the CMG is regulated during its assembly and activation in mammalian genomes, and how errors in CMG regulation due to oncogenic changes promote tumorigenesis. Finally, and most importantly, we highlight the emerging understanding of the CMG helicase as an exploitable vulnerability and novel target for therapeutic intervention in cancer.
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Regulation of Mammalian DNA Replication via the Ubiquitin-Proteasome System. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1042:421-454. [PMID: 29357069 DOI: 10.1007/978-981-10-6955-0_19] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Proper regulation of DNA replication ensures the faithful transmission of genetic material essential for optimal cellular and organismal physiology. Central to this regulation is the activity of a set of enzymes that induce or reverse posttranslational modifications of various proteins critical for the initiation, progression, and termination of DNA replication. This is particularly important when DNA replication proceeds in cancer cells with elevated rates of genomic instability and increased proliferative capacities. Here, we describe how DNA replication in mammalian cells is regulated via the activity of the ubiquitin-proteasome system as well as the consequence of derailed ubiquitylation signaling involved in this important cellular activity.
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Kang S, Kang MS, Ryu E, Myung K. Eukaryotic DNA replication: Orchestrated action of multi-subunit protein complexes. Mutat Res 2018; 809:58-69. [PMID: 28501329 DOI: 10.1016/j.mrfmmm.2017.04.002] [Citation(s) in RCA: 18] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 04/13/2017] [Accepted: 04/30/2017] [Indexed: 06/07/2023]
Abstract
Genome duplication is an essential process to preserve genetic information between generations. The eukaryotic cell cycle is composed of functionally distinct phases: G1, S, G2, and M. One of the key replicative proteins that participate at every stage of DNA replication is the Mcm2-7 complex, a replicative helicase. In the G1 phase, inactive Mcm2-7 complexes are loaded on the replication origins by replication-initiator proteins, ORC and Cdc6. Two kinases, S-CDK and DDK, convert the inactive origin-loaded Mcm2-7 complex to an active helicase, the CMG complex in the S phase. The activated CMG complex begins DNA unwinding and recruits enzymes essential for DNA synthesis to assemble a replisome at the replication fork. After completion of DNA synthesis, the inactive CMG complex on the replicated DNA is removed from chromatin to terminate DNA replication. In this review, we will discuss the structure, function, and regulation of the molecular machines involved in each step of DNA replication.
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Affiliation(s)
- Sukhyun Kang
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea.
| | - Mi-Sun Kang
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea
| | - Eunjin Ryu
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea; School of Life Sciences, Ulsan National Institute for Science and Technology, Ulsan 44919, Republic of Korea
| | - Kyungjae Myung
- Center for Genomic Integrity, Institute for Basic Science, Ulsan 44919, Republic of Korea; School of Life Sciences, Ulsan National Institute for Science and Technology, Ulsan 44919, Republic of Korea
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Sonneville R, Moreno SP, Knebel A, Johnson C, Hastie CJ, Gartner A, Gambus A, Labib K. CUL-2 LRR-1 and UBXN-3 drive replisome disassembly during DNA replication termination and mitosis. Nat Cell Biol 2017; 19:468-479. [PMID: 28368371 PMCID: PMC5410169 DOI: 10.1038/ncb3500] [Citation(s) in RCA: 69] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2016] [Accepted: 02/27/2017] [Indexed: 02/06/2023]
Abstract
Replisome disassembly is the final step of DNA replication in eukaryotes, involving the ubiquitylation and CDC48-dependent dissolution of the CMG helicase (CDC45-MCM-GINS). Using Caenorhabditis elegans early embryos and Xenopus laevis egg extracts, we show that the E3 ligase CUL-2LRR-1 associates with the replisome and drives ubiquitylation and disassembly of CMG, together with the CDC-48 cofactors UFD-1 and NPL-4. Removal of CMG from chromatin in frog egg extracts requires CUL2 neddylation, and our data identify chromatin recruitment of CUL2LRR1 as a key regulated step during DNA replication termination. Interestingly, however, CMG persists on chromatin until prophase in worms that lack CUL-2LRR-1, but is then removed by a mitotic pathway that requires the CDC-48 cofactor UBXN-3, orthologous to the human tumour suppressor FAF1. Partial inactivation of lrr-1 and ubxn-3 leads to synthetic lethality, suggesting future approaches by which a deeper understanding of CMG disassembly in metazoa could be exploited therapeutically.
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Affiliation(s)
- Remi Sonneville
- MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Sara Priego Moreno
- Institute of Cancer and Genomic Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Axel Knebel
- MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Clare Johnson
- MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - C James Hastie
- MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Anton Gartner
- Centre for Gene Regulation and Expression, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Agnieszka Gambus
- Institute of Cancer and Genomic Sciences, College of Medical and Dental Sciences, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK
| | - Karim Labib
- MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
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García-Rodríguez N, Wong RP, Ulrich HD. Functions of Ubiquitin and SUMO in DNA Replication and Replication Stress. Front Genet 2016; 7:87. [PMID: 27242895 PMCID: PMC4865505 DOI: 10.3389/fgene.2016.00087] [Citation(s) in RCA: 60] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 04/27/2016] [Indexed: 12/14/2022] Open
Abstract
Complete and faithful duplication of its entire genetic material is one of the essential prerequisites for a proliferating cell to maintain genome stability. Yet, during replication DNA is particularly vulnerable to insults. On the one hand, lesions in replicating DNA frequently cause a stalling of the replication machinery, as most DNA polymerases cannot cope with defective templates. This situation is aggravated by the fact that strand separation in preparation for DNA synthesis prevents common repair mechanisms relying on strand complementarity, such as base and nucleotide excision repair, from working properly. On the other hand, the replication process itself subjects the DNA to a series of hazardous transformations, ranging from the exposure of single-stranded DNA to topological contortions and the generation of nicks and fragments, which all bear the risk of inducing genomic instability. Dealing with these problems requires rapid and flexible responses, for which posttranslational protein modifications that act independently of protein synthesis are particularly well suited. Hence, it is not surprising that members of the ubiquitin family, particularly ubiquitin itself and SUMO, feature prominently in controlling many of the defensive and restorative measures involved in the protection of DNA during replication. In this review we will discuss the contributions of ubiquitin and SUMO to genome maintenance specifically as they relate to DNA replication. We will consider cases where the modifiers act during regular, i.e., unperturbed stages of replication, such as initiation, fork progression, and termination, but also give an account of their functions in dealing with lesions, replication stalling and fork collapse.
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Maculins T, Nkosi PJ, Nishikawa H, Labib K. Tethering of SCF(Dia2) to the Replisome Promotes Efficient Ubiquitylation and Disassembly of the CMG Helicase. Curr Biol 2015; 25:2254-9. [PMID: 26255844 PMCID: PMC4562905 DOI: 10.1016/j.cub.2015.07.012] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2015] [Revised: 06/30/2015] [Accepted: 07/02/2015] [Indexed: 01/27/2023]
Abstract
Disassembly of the Cdc45-MCM-GINS (CMG) DNA helicase, which unwinds the parental DNA duplex at eukaryotic replication forks, is the key regulated step during replication termination but is poorly understood [1, 2]. In budding yeast, the F-box protein Dia2 drives ubiquitylation of the CMG helicase at the end of replication, leading to a disassembly pathway that requires the Cdc48 segregase [3]. The substrate-binding domain of Dia2 comprises leucine-rich repeats, but Dia2 also has a TPR domain at its amino terminus that interacts with the Ctf4 and Mrc1 subunits of the replisome progression complex [4, 5], which assembles around the CMG helicase at replication forks [6]. Previous studies suggested two disparate roles for the TPR domain of Dia2, either mediating replisome-specific degradation of Mrc1 and Ctf4 [4] or else tethering SCFDia2 (SCF [Skp1/cullin/F-box protein]) to the replisome to increase its local concentration at replication forks [5]. Here, we show that SCFDia2 does not mediate replisome-specific degradation of Mrc1 and Ctf4, either during normal S phase or in response to replication stress. Instead, the tethering of SCFDia2 to the replisome progression complex increases the efficiency of ubiquitylation of the Mcm7 subunit of CMG, both in vitro and in vivo. Correspondingly, loss of tethering reduces the efficiency of CMG disassembly in vivo and is synthetic lethal in combination with a disassembly-defective allele of CDC48. Residual ubiquitylation of Mcm7 in dia2-ΔTPR cells is still CMG specific, highlighting the complex regulation of the final stages of chromosome replication, about which much still remains to be learned. Replisome tethering of SCFDia2 promotes efficient ubiquitylation of the CMG helicase Loss of tethering and mutation of Cdc48 cause synthetic CMG disassembly defects
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Affiliation(s)
- Timurs Maculins
- Cancer Research UK Manchester Institute, University of Manchester, Wilmslow Road, Manchester M20 4BX, UK
| | - Pedro Junior Nkosi
- MRC Protein Phosphorylation and Ubiquitylation Unit, Sir James Black Centre, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK
| | - Hiroko Nishikawa
- Cancer Research UK Manchester Institute, University of Manchester, Wilmslow Road, Manchester M20 4BX, UK
| | - Karim Labib
- MRC Protein Phosphorylation and Ubiquitylation Unit, Sir James Black Centre, College of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, UK.
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Abstract
To ensure duplication of the entire genome, eukaryotic DNA replication initiates from thousands of replication origins. The replication forks move through the chromatin until they encounter forks from neighboring origins. During replication fork termination forks converge, the replisomes disassemble and topoisomerase II resolves the daughter DNA molecules. If not resolved efficiently, terminating forks result in genomic instability through the formation of pathogenic structures. Our recent findings shed light onto the mechanism of replisome disassembly upon replication fork termination. We have shown that termination-specific polyubiquitylation of the replicative helicase component – Mcm7, leads to dissolution of the active helicase in a process dependent on the p97/VCP/Cdc48 segregase. The inhibition of terminating helicase disassembly resulted in a replication termination defect. In this extended view we present hypothetical models of replication fork termination and discuss remaining and emerging questions in the DNA replication termination field.
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Key Words
- CMG, Cdc45, Mcm2–7, GINS complex
- CRL, cullin-RING ligase
- D loop, displacement loop
- DDR, DNA damage response
- DNA replication
- DSB, double strand break
- DUB, deubiquitylating enzyme
- ER, endoplasmic reticulum
- ERAD, endoplasmic reticulum associated protein degradation
- GINS, Go-Ichi-Ni-San, complex made of Sld5, Psf1, Psf2, Psf3
- ICL, intra-strand crosslink
- MCM, Minichromosome maintenance
- Mcm2–7
- OriC, chromosomal replication origin
- R loop, RNA:DNA hybrid
- RING, really interesting gene
- RPC, Replisome Progression Complex
- Ter, termination site
- Tus-Ter, terminus utilisation substance - termination
- Xenopus
- p97 segregase
- replication termination
- replicative helicase
- replisome
- ubiquitin
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Affiliation(s)
- Rachael Bailey
- a School of Cancer Sciences; University of Birmingham ; Birmingham , UK
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