1
|
Cui J, Liu X, Shang Q, Sun S, Chen S, Dong J, Zhu Y, Liu L, Xia Y, Wang Y, Xiang L, Fan B, Zhan J, Zhou Y, Chen P, Zhao R, Liu X, Xing N, Wu D, Shi B, Zou Y. Deubiquitination of CDC6 by OTUD6A promotes tumour progression and chemoresistance. Mol Cancer 2024; 23:86. [PMID: 38685067 PMCID: PMC11057083 DOI: 10.1186/s12943-024-01996-y] [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: 12/04/2023] [Accepted: 04/05/2024] [Indexed: 05/02/2024] Open
Abstract
BACKGROUND CDC6 is an oncogenic protein whose expression level fluctuates during the cell cycle. Although several E3 ubiquitin ligases responsible for the ubiquitin-mediated proteolysis of CDC6 have been identified, the deubiquitination pathway for CDC6 has not been investigated. METHODS The proteome-wide deubiquitinase (DUB) screening was used to identify the potential regulator of CDC6. Immunofluorescence, protein half-life and deubiquitination assays were performed to determine the protein stability of CDC6. Gain- and loss-of-function experiments were implemented to analyse the impacts of OUTD6A-CDC6 axis on tumour growth and chemosensitivity in vitro. N-butyl-N-(4-hydroxybutyl) nitrosamine (BBN)-induced conditional Otud6a knockout (CKO) mouse model and tumour xenograft model were performed to analyse the role of OTUD6A-CDC6 axis in vivo. Tissue specimens were used to determine the association between OTUD6A and CDC6. RESULTS OTUD6A interacts with, depolyubiquitinates and stabilizes CDC6 by removing K6-, K33-, and K48-linked polyubiquitination. Moreover, OTUD6A promotes cell proliferation and decreases sensitivity to chemotherapy by upregulating CDC6. CKO mice are less prone to BCa tumorigenesis induced by BBN, and knockdown of OTUD6A inhibits tumour progression in vivo. Furthermore, OTUD6A protein level has a positive correlation with CDC6 protein level, and high protein levels of OTUD6A and CDC6 are associated with poor prognosis in patients with bladder cancer. CONCLUSIONS We reveal an important yet missing piece of novel DUB governing CDC6 stability. In addition, our findings propose a model for the OTUD6A-CDC6 axis that provides novel insights into cell cycle and chemosensitivity regulation, which may become a potential biomarker and promising drug target for cancer treatment.
Collapse
Affiliation(s)
- Jianfeng Cui
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Xiaochen Liu
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
- Department of Clinical laboratory, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Qinghong Shang
- Helmholtz International Lab, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong, 266237, China
| | - Shuna Sun
- Department of Dermatology, The Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Shandong Provincial Hospital of Traditional Chinese Medicine, Jinan, Shandong, 250011, China
| | - Shouzhen Chen
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
| | - Jianping Dong
- Department of Urology, Shouguang People's Hospital, Weifang, Shandong, 262750, China
| | - Yaofeng Zhu
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
| | - Lei Liu
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
| | - Yangyang Xia
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
| | - Yong Wang
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China
| | - Lu Xiang
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Bowen Fan
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Jiafeng Zhan
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Yadi Zhou
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Pengxiang Chen
- Department of Radiation Oncology, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Renchang Zhao
- Department of Thoracic Surgery, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China
| | - Xiaofei Liu
- Departement of Breast and Thyroid Surgery, The Affiliated Hospital of Shandong University of Traditional Chinese Medicine, Shandong Provincial Hospital of Traditional Chinese Medicine, Jinan, Shandong, 250011, China
| | - Nianzeng Xing
- Department of Urology, National Cancer Center/National Clinical Research Center for Cancer/Cancer Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, 100021, China.
| | - Dalei Wu
- Helmholtz International Lab, State Key Laboratory of Microbial Technology, Shandong University, Qingdao, Shandong, 266237, China.
| | - Benkang Shi
- Department of Urology, Qilu Hospital, Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Shandong University, Jinan, Shandong, 250012, China.
| | - Yongxin Zou
- The Key Laboratory of Experimental Teratology, Ministry of Education and Department of Molecular Medicine and Genetics, School of Basic Medical Sciences, Qilu Hospital, Shandong University, Jinan, Shandong, 250012, China.
| |
Collapse
|
2
|
Xiang S, Luo X, Welch D, Reed DR, Alexandrow MG. Identification of Selective ATP-Competitive CMG Helicase Inhibitors for Cancer Intervention that Disrupt CMG-Replisome Function. RESEARCH SQUARE 2023:rs.3.rs-3182731. [PMID: 37609279 PMCID: PMC10441460 DOI: 10.21203/rs.3.rs-3182731/v1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 08/24/2023]
Abstract
The human CMG helicase (Cdc45-MCM-GINS) is a novel target for anti-cancer therapy due to tumor-specific weaknesses in CMG function induced by oncogenic changes and the need for CMG function during recovery from replicative stresses such as chemotherapy. Here, we developed an orthogonal biochemical screening approach and identified selective CMG inhibitors (CMGi) that inhibit ATPase and helicase activities in an ATP-competitive manner at low micromolar concentrations. Structure-activity information and in silico docking indicate that CMGi occupy ATP binding sites and channels within MCM subunits leading to the ATP clefts, which are likely used for ATP/ADP ingress or egress. CMGi inhibit cell growth and DNA replication using multiple molecular mechanisms. CMGi block helicase assembly steps that require ATP binding/hydrolysis by the MCM complex, specifically MCM ring assembly on DNA and GINS recruitment to DNA-loaded MCM hexamers. During S-phase, inhibition of MCM ATP binding/hydrolysis by CMGi causes a 'reverse allosteric' dissociation of Cdc45/GINS from the CMG that destabilizes the replisome and disrupts interactions with Ctf4, Mcm10, and DNA polymerase-α, -δ, -ε, resulting in DNA damage. These novel CMGi are selectively toxic toward tumor cells and define a new class of CMG helicase-targeted anti-cancer compounds with distinct mechanisms of action.
Collapse
Affiliation(s)
- Shengyan Xiang
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Xingju Luo
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Darcy Welch
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Department of Individualized Cancer Management, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Damon R. Reed
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Department of Individualized Cancer Management, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| | - Mark G. Alexandrow
- Cancer Biology and Evolution Program, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
- Molecular Oncology Department, Moffitt Cancer Center and Research Institute, Tampa, FL 33612
| |
Collapse
|
3
|
The CMG helicase and cancer: a tumor "engine" and weakness with missing mutations. Oncogene 2023; 42:473-490. [PMID: 36522488 PMCID: PMC9948756 DOI: 10.1038/s41388-022-02572-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2022] [Revised: 12/01/2022] [Accepted: 12/07/2022] [Indexed: 12/23/2022]
Abstract
The replicative Cdc45-MCM-GINS (CMG) helicase is a large protein complex that functions in the DNA melting and unwinding steps as a component of replisomes during DNA replication in mammalian cells. Although the CMG performs this important role in cell growth, the CMG is not a simple bystander in cell cycle events. Components of the CMG, specifically the MCM precursors, are also involved in maintaining genomic stability by regulating DNA replication fork speeds, facilitating recovery from replicative stresses, and preventing consequential DNA damage. Given these important functions, MCM/CMG complexes are highly regulated by growth factors such as TGF-ß1 and by signaling factors such as Myc, Cyclin E, and the retinoblastoma protein. Mismanagement of MCM/CMG complexes when these signaling mediators are deregulated, and in the absence of the tumor suppressor protein p53, leads to increased genomic instability and is a contributor to tumorigenic transformation and tumor heterogeneity. The goal of this review is to provide insight into the mechanisms and dynamics by which the CMG is regulated during its assembly and activation in mammalian genomes, and how errors in CMG regulation due to oncogenic changes promote tumorigenesis. Finally, and most importantly, we highlight the emerging understanding of the CMG helicase as an exploitable vulnerability and novel target for therapeutic intervention in cancer.
Collapse
|
4
|
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.
Collapse
|
5
|
Sirtuin 5 Is Regulated by the SCF Cyclin F Ubiquitin Ligase and Is Involved in Cell Cycle Control. Mol Cell Biol 2021; 41:MCB.00269-20. [PMID: 33168699 DOI: 10.1128/mcb.00269-20] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Accepted: 11/03/2020] [Indexed: 12/31/2022] Open
Abstract
The ubiquitin-proteasome system is essential for cell cycle progression. Cyclin F is a cell cycle-regulated substrate adapter F-box protein for the Skp1, CUL1, and F-box protein (SCF) family of E3 ubiquitin ligases. Despite its importance in cell cycle progression, identifying cyclin F-bound SCF complex (SCFCyclin F) substrates has remained challenging. Since cyclin F overexpression rescues a yeast mutant in the cdc4 gene, we considered the possibility that other genes that genetically modify cdc4 mutant lethality could also encode cyclin F substrates. We identified the mitochondrial and cytosolic deacylating enzyme sirtuin 5 (SIRT5) as a novel cyclin F substrate. SIRT5 has been implicated in metabolic processes, but its connection to the cell cycle is not known. We show that cyclin F interacts with and controls the ubiquitination, abundance, and stability of SIRT5. We show SIRT5 knockout results in a diminished G1 population and a subsequent increase in both S and G2/M. Global proteomic analyses reveal cyclin-dependent kinase (CDK) signaling changes congruent with the cell cycle changes in SIRT5 knockout cells. Together, these data demonstrate that SIRT5 is regulated by cyclin F and suggest a connection between SIRT5, cell cycle regulation, and metabolism.
Collapse
|
6
|
Yu X, Liu Y, Yin L, Peng Y, Peng Y, Gao Y, Yuan B, Zhu Q, Cao T, Xie B, Sun L, Chen Y, Gong Z, Qiu Y, Fan X, Li X. Radiation-promoted CDC6 protein stability contributes to radioresistance by regulating senescence and epithelial to mesenchymal transition. Oncogene 2018; 38:549-563. [PMID: 30158672 PMCID: PMC6345673 DOI: 10.1038/s41388-018-0460-4] [Citation(s) in RCA: 36] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2017] [Revised: 07/11/2018] [Accepted: 07/24/2018] [Indexed: 12/15/2022]
Abstract
Ionizing radiation (IR) is a conventional cancer therapeutic, to which cancer cells develop radioresistance with exposure. The residual cancer cells after radiation treatment also have increased metastatic potential. The mechanisms by which cancer cells develop radioresistance and gain metastatic potential are still unknown. In this study acute IR exposure induced cancer cell senescence and apoptosis, but after long-term IR exposure, cancer cells exhibited radioresistance. The proliferation of radioresistant cells was retarded, and most cells were arrested in G0/G1 phase. The radioresistant cells simultaneously showed resistance to further IR-induced apoptosis, premature senescence, and epithelial to mesenchymal transformation (EMT). Acute IR exposure steadily elevated CDC6 protein levels due to the attenuation of ubiquitination, while CDC6 overexpression was observed in the radioresistant cells because the insufficiency of CDC6 phosphorylation blocked protein translocation from nucleus to cytoplasm, resulting in subcellular protein accumulation when the cells were arrested in G0/G1 phase. CDC6 ectopic overexpression in CNE2 cells resulted in apoptosis resistance, G0/G1 cell cycle arrest, premature senescence, and EMT, similar to the characteristics of radioresistant CNE2-R cells. Targeting CDC6 with siRNA promoted IR-induced senescence, sensitized cancer cells to IR-induced apoptosis, and reversed EMT. Furthermore, CDC6 depletion synergistically repressed the growth of CNE2-R xenografts when combined with IR. The study describes for the first time cell models for IR-induced senescence, apoptosis resistance, and EMT, three major mechanisms by which radioresistance develops. CDC6 is a novel radioresistance switch regulating senescence, apoptosis, and EMT. These studies suggest that CDC6highKI67low represents a new diagnostic marker of radiosensitivity, and CDC6 represents a new therapeutic target for cancer radiosensitization.
Collapse
Affiliation(s)
- Xiaohui Yu
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Youhong Liu
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Linglong Yin
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Yongbo Peng
- State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University, Changsha, China
| | - Yuchong Peng
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Yingxue Gao
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Bowen Yuan
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Qianling Zhu
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Tuoyu Cao
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Bowen Xie
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Lunquan Sun
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China.,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China
| | - Yan Chen
- Department of Pathology, The Third Xiangya Hospital, Central South University, Changsha, China
| | - Zhicheng Gong
- Department of Pharmacy, Xiangya Hospital, Central South University, Changsha, China
| | - Yuanzheng Qiu
- Department of Otorhinolaryngology, Xiangya Hospital, Central South University, Changsha, China
| | - Xuegong Fan
- Hunan Key Laboratory of Viral Hepatitis, Xiangya Hospital, Central South University, Changsha, China
| | - Xiong Li
- Center for Molecular Medicine, Xiangya Hospital, Central South University, Changsha, China. .,Hunan Key Laboratory of Molecular Radiation Oncology, Xiangya Hospital, Central South University, Changsha, China.
| |
Collapse
|
7
|
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.
Collapse
|
8
|
Fan X, Zhou Y, Chen JJ. Role of Cdc6 in re-replication in cells expressing human papillomavirus E7 oncogene. Carcinogenesis 2016; 37:799-809. [PMID: 27207654 PMCID: PMC4967213 DOI: 10.1093/carcin/bgw059] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2015] [Accepted: 04/29/2016] [Indexed: 11/13/2022] Open
Abstract
The E7 oncoprotein of high-risk human papillomavirus (HPV) types induces DNA re-replication that contributes to carcinogenesis; however, the mechanism is not fully understood. To better understand the mechanism by which E7 induces re-replication, we investigated the expression and function of cell division cycle 6 (Cdc6) in E7-expressing cells. Cdc6 is a DNA replication initiation factor and exhibits oncogenic activities when overexpressed. We found that in E7-expressing cells, the steady-state level of Cdc6 protein was upregulated and its half-life was increased. Cdc6 was localized to the nucleus and associated with chromatin, especially upon DNA damage. Importantly, downregulation of Cdc6 reduced E7-induced re-replication. Interestingly, the level of Cdc6 phosphorylation at serine 54 (S54P) was increased in E7-expressing cells. S54P was associated with an increase in the total amount of Cdc6 and chromatin-bound Cdc6. DNA damage-enhanced upregulation and chromatin binding of Cdc6 appeared to be due to downregulation of cyclin-dependent kinase 1 (Cdk1) as Cdk1 knockdown increased Cdc6 levels. Furthermore, Cdk1 knockdown or inhibition led to re-replication. These findings shed light on the mechanism by which HPV induces genomic instability and may help identify potential targets for drug development.
Collapse
Affiliation(s)
- Xueli Fan
- Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01532, USA, Department of Dermatology, Xijing Hospital, Fourth Military Medical University, Xian 710032, China and
| | - Yunying Zhou
- The Cancer Research Center, Shandong University School of Medicine, Jinan, Shandong 250012, China
| | - Jason J Chen
- Department of Medicine, University of Massachusetts Medical School, Worcester, MA 01532, USA, The Cancer Research Center, Shandong University School of Medicine, Jinan, Shandong 250012, China
| |
Collapse
|
9
|
Kalfalah FM, Berg E, Christensen MO, Linka RM, Dirks WG, Boege F, Mielke C. Spatio-temporal regulation of the human licensing factor Cdc6 in replication and mitosis. Cell Cycle 2016; 14:1704-15. [PMID: 25875233 PMCID: PMC4614858 DOI: 10.1080/15384101.2014.1000182] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023] Open
Abstract
To maintain genome stability, the thousands of replication origins of mammalian genomes must only initiate replication once per cell cycle. This is achieved by a strict temporal separation of ongoing replication in S phase, and the formation of pre-replicative complexes in the preceding G1 phase, which "licenses" each origin competent for replication. The contribution of the loading factor Cdc6 to the timing of the licensing process remained however elusive due to seemingly contradictory findings concerning stabilization, degradation and nuclear export of Cdc6. Using fluorescently tagged Cdc6 (Cdc6-YFP) expressed in living cycling cells, we demonstrate here that Cdc6-YFP is stable and chromatin-associated during mitosis and G1 phase. It undergoes rapid proteasomal degradation during S phase initiation followed by active export to the cytosol during S and G2 phases. Biochemical fractionation abolishes this nuclear exclusion, causing aberrant chromatin association of Cdc6-YFP and, likely, endogenous Cdc6, too. In addition, we demonstrate association of Cdc6 with centrosomes in late G2 and during mitosis. These results show that multiple Cdc6-regulatory mechanisms coexist but are tightly controlled in a cell cycle-specific manner.
Collapse
Affiliation(s)
- Faiza M Kalfalah
- a Institute of Clinical Chemistry and Laboratory Diagnostics; University Düsseldorf; Medical Faculty , Düsseldorf , Germany
| | | | | | | | | | | | | |
Collapse
|
10
|
Walter D, Hoffmann S, Komseli ES, Rappsilber J, Gorgoulis V, Sørensen CS. SCF(Cyclin F)-dependent degradation of CDC6 suppresses DNA re-replication. Nat Commun 2016; 7:10530. [PMID: 26818844 PMCID: PMC4738361 DOI: 10.1038/ncomms10530] [Citation(s) in RCA: 74] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/03/2015] [Accepted: 12/22/2015] [Indexed: 02/06/2023] Open
Abstract
Maintenance of genome stability requires that DNA is replicated precisely once per cell cycle. This is believed to be achieved by limiting replication origin licensing and thereby restricting the firing of each replication origin to once per cell cycle. CDC6 is essential for eukaryotic replication origin licensing, however, it is poorly understood how CDC6 activity is constrained in higher eukaryotes. Here we report that the SCFCyclin F ubiquitin ligase complex prevents DNA re-replication by targeting CDC6 for proteasomal degradation late in the cell cycle. We show that CDC6 and Cyclin F interact through defined sequence motifs that promote CDC6 ubiquitylation and degradation. Absence of Cyclin F or expression of a stable mutant of CDC6 promotes re-replication and genome instability in cells lacking the CDT1 inhibitor Geminin. Together, our work reveals a novel SCFCyclin F-mediated mechanism required for precise once per cell cycle replication. To ensure genome stability, cells need to restrict DNA replication to once per cell cycle. Here the authors show that Cyclin F interacts with and targets the licensing factor CDC6 for degradation, preventing re-firing of replication origins.
Collapse
Affiliation(s)
- David Walter
- Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Ole Maaløes Vej 5, Copenhagen N 2200, Denmark
| | - Saskia Hoffmann
- Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Ole Maaløes Vej 5, Copenhagen N 2200, Denmark
| | - Eirini-Stavroula Komseli
- Department of Histology and Embryology, School of Medicine, University of Athens, Athens GR-11527, Greece
| | - Juri Rappsilber
- Wellcome Trust Centre for Cell Biology, University of Edinburgh, Michael Swann Building, Kings Buildings, Max Born Crescent, Edinburgh EH9 3BF, Scotland.,Department of Bioanalytics, Institute of Biotechnology, Technische Universität Berlin, Berlin 13355, Germany
| | - Vassilis Gorgoulis
- Department of Histology and Embryology, School of Medicine, University of Athens, Athens GR-11527, Greece.,Faculty Institute of Cancer Sciences, University of Manchester, Manchester Academic Health Science Centre, Manchester, UK
| | - Claus Storgaard Sørensen
- Biotech Research and Innovation Centre (BRIC), University of Copenhagen, Ole Maaløes Vej 5, Copenhagen N 2200, Denmark
| |
Collapse
|
11
|
Kim GS, Kang J, Bang SW, Hwang DS. Cdc6 localizes to S- and G2-phase centrosomes in a cell cycle-dependent manner. Biochem Biophys Res Commun 2014; 456:763-7. [PMID: 25498505 DOI: 10.1016/j.bbrc.2014.12.018] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2014] [Accepted: 12/04/2014] [Indexed: 12/24/2022]
Abstract
The Cdc6 protein has been primarily investigated as a component of the pre-replicative complex for the initiation of chromosome replication, which contributes to maintenance of chromosomal integrity. Here, we show that Cdc6 localized to the centrosomes during S and G2 phases of the cell cycle. The centrosomal localization was mediated by Cdc6 amino acid residues 311-366, which are conserved within other Cdc6 homologues and contains a putative nuclear export signal. Deletions or substitutions of the amino acid residues did not allow the proteins to localize to centrosomes. In contrast, DsRed tag fused to the amino acid residues localized to centrosomes. These results indicated that a centrosome localization signal is contained within amino acid residues 311-366. The cell cycle-dependent centrosomal localization of Cdc6 in S and G2 phases suggest a novel function of Cdc6 in centrosomes.
Collapse
Affiliation(s)
- Gwang Su Kim
- Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea
| | - Jeeheon Kang
- Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea
| | - Sung Woong Bang
- Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea
| | - Deog Su Hwang
- Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea.
| |
Collapse
|
12
|
Abstract
DNA replication must be tightly regulated to ensure that the genome is accurately duplicated during each cell cycle. When these regulatory mechanisms fail, replicative stress and DNA damage ensue. Activated oncogenes promote replicative stress, inducing a DNA damage response (DDR) early in tumorigenesis. Senescence or apoptosis result, forming a barrier against tumour progression. This may provide a selective pressure for acquisition of mutations in the DDR pathway during tumorigenesis. Despite its potential importance in early cancer development, the precise nature of oncogene-induced replicative stress remains poorly understood. Here, we review our current understanding of replication initiation and its regulation, describe mechanisms by which activated oncogenes might interfere with these processes and discuss how replicative stress might contribute to the genomic instability seen in cancers.
Collapse
Affiliation(s)
- Stephanie A Hills
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK
| | - John F X Diffley
- Cancer Research UK London Research Institute, Clare Hall Laboratories, South Mimms, Herts, EN6 3LD, UK.
| |
Collapse
|
13
|
CHA HWAJUN, LEE JEONGPYO, LEE KWANGSIK, LEE KUNKOOK, CHOI MYOUNGJUN, LEE DONGKYU, KIM KWANGNYEON, AN SUNGKWAN. Phytosphigosine-1-phosphate increases sensitivity of EGF-dependent cell proliferation. Int J Mol Med 2014; 33:649-53. [DOI: 10.3892/ijmm.2014.1617] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2013] [Accepted: 12/19/2013] [Indexed: 11/05/2022] Open
|
14
|
Abstract
DNA replication is tightly controlled in eukaryotic cells to ensure that an exact copy of the genetic material is inherited by both daughter cells. Oscillating waves of cyclin-dependent kinase (CDK) and anaphase-promoting complex/cyclosome (APC/C) activities provide a binary switch that permits the replication of each chromosome exactly once per cell cycle. Work from several organisms has revealed a conserved strategy whereby inactive replication complexes are assembled onto DNA during periods of low CDK and high APC activity but are competent to execute genome duplication only when these activities are reversed. Periods of high CDK and low APC/C serve an essential function by blocking reassembly of replication complexes, thereby preventing rereplication. Higher eukaryotes have evolved additional CDK-independent mechanisms for preventing rereplication.
Collapse
Affiliation(s)
- Khalid Siddiqui
- Cancer Research UK, London Research Institute, Clare Hall Laboratories, South Mimms, Herts EN6 3LD, United Kingdom
| | | | | |
Collapse
|
15
|
Yim H, Park JW, Woo SU, Kim ST, Liu L, Lee CH, Lee SK. Phosphorylation of Cdc6 at serine 74, but not at serine 106, drives translocation of Cdc6 to the cytoplasm. J Cell Physiol 2013; 228:1221-8. [PMID: 23129444 DOI: 10.1002/jcp.24275] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2012] [Accepted: 10/19/2012] [Indexed: 11/08/2022]
Abstract
Phosphorylation-dependent cytoplasmic translocation of human Cdc6 during S phase is sufficient to control its activity after origin firing. Export from the nucleus also serves as a mechanism for preventing re-replication in mammalian cells. Phosphorylation of the CDK consensus serine residues 54, 74, and 106 has been suggested to be involved in the cytoplasmic translocation of Cdc6. To determine the relative importance of the three phosphorylation sites, we have generated Cdc6 variants by substituting one or more of the three serine residues with alanine or aspartic acid and have assessed their cytoplasmic translocation behavior. Phosphorylation of serine 74 mainly contributes to the cytoplasmic translocation of Cdc6, while serine 54 phosphorylation provides a minor contribution. In contrast, phosphorylation at serine 106 does not affect the nuclear export of Cdc6. Comparative results were found in cells coexpressing the phosphorylation defective mutants of Cdc6 and cyclin A as well as in non-transfected cells synchronized by their release from a double thymidine block. We conclude that Cdk-mediated phosphorylation of Cdc6 at serine 74 is required for the cytoplasmic translocalization of Cdc6 during the cell cycle. Phosphorylation of Cdc6 at serine 54 plays a minor role and phosphorylation of serine 106 plays no role in the cytoplasmic localization of Cdc6. The phosphorylation of S74 in Cdc6 could be important for binding to the nuclear export protein for translocalization.
Collapse
Affiliation(s)
- Hyungshin Yim
- Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul, Republic of Korea.
| | | | | | | | | | | | | |
Collapse
|
16
|
Symeonidou IE, Taraviras S, Lygerou Z. Control over DNA replication in time and space. FEBS Lett 2012; 586:2803-12. [PMID: 22841721 DOI: 10.1016/j.febslet.2012.07.042] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Revised: 07/18/2012] [Accepted: 07/18/2012] [Indexed: 12/23/2022]
Abstract
DNA replication is precisely regulated in time and space, thereby safeguarding genomic integrity. In eukaryotes, replication initiates from multiple sites along the genome, termed origins of replication, and propagates bidirectionally. Dynamic origin bound complexes dictate where and when replication should initiate. During late mitosis and G1 phase, putative origins are recognized and become "licensed" through the assembly of pre-replicative complexes (pre-RCs) that include the MCM2-7 helicases. Subsequently, at the G1/S phase transition, a fraction of pre-RCs are activated giving rise to the establishment of replication forks. Origin location is influenced by chromatin and nuclear organization and origin selection exhibits stochastic features. The regulatory mechanisms that govern these cell cycle events rely on the periodic fluctuation of cyclin dependent kinase (CDK) activity through the cell cycle.
Collapse
|
17
|
Yim H, Erikson RL. Regulation of the final stage of mitosis by components of the pre-replicative complex and a polo kinase. Cell Cycle 2011; 10:1374-7. [PMID: 21519187 PMCID: PMC3117042 DOI: 10.4161/cc.10.9.15489] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2011] [Accepted: 03/15/2011] [Indexed: 11/19/2022] Open
Abstract
The accurate division of duplicated DNA is essential for maintenance of genomic stability in proliferating eukaryotic cells. Errors in DNA replication and chromosomal segregation may lead to cell death or genomic mutations that lead to oncogenic properties. Thus, tight regulation of DNA replication and mitosis is essential for maintaining genomic integrity. Cell division cycle 6 (Cdc6) is an essential factor for initiating DNA replication. Recent work shows that phosphorylation of Cdc6 by polo-like kinase 1 (Plk1), one of the essential mitotic kinases, regulates mitotic exit mediated by Cdk1 and separase. Here we discuss how pre-replicative complex factors are connected with Plk1 and affect mitotic exit.
Collapse
Affiliation(s)
- Hyungshin Yim
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA, USA
| | | |
Collapse
|
18
|
Cdc45 limits replicon usage from a low density of preRCs in mammalian cells. PLoS One 2011; 6:e17533. [PMID: 21390258 PMCID: PMC3046982 DOI: 10.1371/journal.pone.0017533] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2010] [Accepted: 02/08/2011] [Indexed: 12/16/2022] Open
Abstract
Little is known about mammalian preRC stoichiometry, the number of preRCs on chromosomes, and how this relates to replicon size and usage. We show here that, on average, each 100-kb of the mammalian genome contains a preRC composed of approximately one ORC hexamer, 4–5 MCM hexamers, and 2 Cdc6. Relative to these subunits, ∼0.35 total molecules of the pre-Initiation Complex factor Cdc45 are present. Thus, based on ORC availability, somatic cells contain ∼70,000 preRCs of this average total stoichiometry, although subunits may not be juxtaposed with each other. Except for ORC, the chromatin-bound complement of preRC subunits is even lower. Cdc45 is present at very low levels relative to the preRC subunits, but is highly stable, and the same limited number of stable Cdc45 molecules are present from the beginning of S-phase to its completion. Efforts to artificially increase Cdc45 levels through ectopic expression block cell growth. However, microinjection of excess purified Cdc45 into S-phase nuclei activates additional replication foci by three-fold, indicating that Cdc45 functions to activate dormant preRCs and is rate-limiting for somatic replicon usage. Paradoxically, although Cdc45 colocalizes in vivo with some MCM sites and is rate-limiting for DNA replication to occur, neither Cdc45 nor MCMs colocalize with active replication sites. Embryonic metazoan chromatin consists of small replicons that are used efficiently via an excess of preRC subunits. In contrast, somatic mammalian cells contain a low density of preRCs, each containing only a few MCMs that compete for limiting amounts of Cdc45. This provides a molecular explanation why, relative to embryonic replicon dynamics, somatic replicons are, on average, larger and origin efficiency tends to be lower. The stable, continuous, and rate-limiting nature of Cdc45 suggests that Cdc45 contributes to the staggering of replicon usage throughout S-phase, and that replicon activation requires reutilization of existing Cdc45 during S-phase.
Collapse
|
19
|
Bronze-da-Rocha E, Lin CM, Shimura T, Aladjem MI. Interactions of MCP1 with components of the replication machinery in mammalian cells. Int J Biol Sci 2011; 7:193-208. [PMID: 21383955 PMCID: PMC3048848 DOI: 10.7150/ijbs.7.193] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2010] [Accepted: 02/12/2011] [Indexed: 11/18/2022] Open
Abstract
Eukaryotic DNA replication starts with the assembly of a pre-replication complex (pre-RC) at replication origins. We have previously demonstrated that Metaphase Chromosome Protein 1 (MCP1) is involved in the early events of DNA replication. Here we show that MCP1 associates with proteins that are required for the establishment of the pre-replication complex. Reciprocal immunoprecipitation analysis showed that MCP1 interacted with Cdc6, ORC2, ORC4, MCM2, MCM3 and MCM7, with Cdc45 and PCNA. Immunofluorescence studies demonstrated the co-localization of MCP1 with some of those proteins. Moreover, biochemical studies utilizing chromatin-immunoprecipitation (ChIP) revealed that MCP1 preferentially binds replication initiation sites in human cells. Interestingly, although members of the pre-RC are known to interact with some hallmarks of heterochromatin, our co-immunoprecipitation and immunofluorescence analyses showed that MCP1 did not interact and did not co-localize with heterochromatic proteins including HP1β and MetH3K9. These observations suggest that MCP1 is associated with replication factors required for the initiation of DNA replication and binds to the initiation sites in loci that replicate early in S-phase. In addition, immunological assays revealed the association of MCP1 forms with histone H1 variants and mass spectrometry analysis confirmed that MCP1 peptides share common sequences with H1.2 and H1.5 subtypes.
Collapse
Affiliation(s)
- Elsa Bronze-da-Rocha
- Departamento de Ciências Biológicas, Laboratório de Bioquímica, Faculdade de Farmácia da Universidade do Porto, Portugal.
| | | | | | | |
Collapse
|
20
|
Yim H, Erikson RL. Cell division cycle 6, a mitotic substrate of polo-like kinase 1, regulates chromosomal segregation mediated by cyclin-dependent kinase 1 and separase. Proc Natl Acad Sci U S A 2010; 107:19742-7. [PMID: 21041660 PMCID: PMC2993418 DOI: 10.1073/pnas.1013557107] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Defining the links between cell division and DNA replication is essential for understanding normal cell cycle progression and tumorigenesis. In this report we explore the effect of phosphorylation of cell division cycle 6 (Cdc6), a DNA replication initiation factor, by polo-like kinase 1 (Plk1) on the regulation of chromosomal segregation. In mitosis, the phosphorylation of Cdc6 was highly increased, in correlation with the level of Plk1, and conversely, Cdc6 is hypophosphorylated in Plk1-depleted cells, although cyclin A- and cyclin B1-dependent kinases are active. Binding between Cdc6 and Plk1 occurs through the polo-box domain of Plk1, and Cdc6 is phosphorylated by Plk1 on T37. Immunohistochemistry studies reveal that Cdc6 and Plk1 colocalize to the central spindle in anaphase. Expression of T37V mutant of Cdc6 (Cdc6-TV) induces binucleated cells and incompletely separated nuclei. Wild-type Cdc6 but not Cdc6-TV binds cyclin-dependent kinase 1 (Cdk1). Expression of wild-type Plk1 but not kinase-defective mutant promotes the binding of Cdc6 to Cdk1. Cells expressing wild-type Cdc6 display lower Cdk1 activity and higher separase activity than cells expressing Cdc6-TV. These results suggest that Plk1-mediated phosphorylation of Cdc6 promotes the interaction of Cdc6 and Cdk1, leading to the attenuation of Cdk1 activity, release of separase, and subsequent anaphase progression.
Collapse
Affiliation(s)
- Hyungshin Yim
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138
| | - Raymond L. Erikson
- Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138
| |
Collapse
|
21
|
Simian virus 40 activates ATR-Delta p53 signaling to override cell cycle and DNA replication control. J Virol 2010; 84:10727-47. [PMID: 20686026 DOI: 10.1128/jvi.00122-10] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During infection, simian virus 40 (SV40) attempts to take hold of the cell, while the host responds with various defense systems, including the ataxia-telangiectasia mutated/ATM-Rad3 related (ATM/ATR)-mediated DNA damage response pathways. Here we show that upon viral infection, ATR directly activates the p53 isoform Δp53, leading to upregulation of the Cdk inhibitor p21 and downregulation of cyclin A-Cdk2/1 (AK) activity, which force the host to stay in the replicative S phase. Moreover, downregulation of AK activity is a prerequisite for the generation of hypophosphorylated, origin-competent DNA polymerase α-primase (hypo-Polα), which is, unlike AK-phosphorylated Polα (P-Polα), recruited by SV40 large T antigen (T-Ag) to initiate viral DNA replication. Prevention of the downregulation of AK activity by inactivation of ATR-Δp53-p21 signaling significantly reduced the T-Ag-interacting hypo-Polα population and, accordingly, SV40 replication efficiency. Moreover, the ATR-Δp53 pathway facilitates the proteasomal degradation of the 180-kDa catalytic subunit of the non-T-Ag-interacting P-Polα, giving rise to T-Ag-interacting hypo-Polα. Thus, the purpose of activating the ATR-Δp53-p21-mediated intra-S checkpoint is to maintain the host in S phase, an optimal environment for SV40 replication, and to modulate the host DNA replicase, which is indispensable for viral amplification.
Collapse
|
22
|
Cell cycle arrest by transforming growth factor beta1 near G1/S is mediated by acute abrogation of prereplication complex activation involving an Rb-MCM interaction. Mol Cell Biol 2009; 30:845-56. [PMID: 19948884 DOI: 10.1128/mcb.01152-09] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Understanding inhibitory mechanisms of transforming growth factor beta1 (TGF-beta1) has provided insight into cell cycle regulation and how TGF-beta1 sensitivity is lost during tumorigenesis. We show here that TGF-beta1 utilizes a previously unknown mechanism targeting the function of prereplication complexes (pre-RCs) to acutely block S-phase entry when added to cells in late G(1), after most G(1) events have occurred. TGF-beta1 treatment in early G(1) suppresses Myc and CycE-Cdk2 and blocks pre-RC assembly. However, TGF-beta1 treatment in late G(1) acutely blocks S-phase entry by inhibiting activation of fully assembled pre-RCs, with arrest occurring prior to the helicase unwinding step at G(1)/S. This acute block by TGF-beta1 requires the function of Rb in late G(1) but does not involve Myc/CycE-Cdk2 suppression or transcriptional control. Instead, Rb mediates TGF-beta1 late-G(1) arrest by targeting the MCM helicase. Rb binds the MCM complex during late G(1) via a direct interaction with Mcm7, and TGF-beta1 blocks their dissociation at G(1)/S. Loss of Rb or overexpression of Mcm7 or its Rb-binding domain alone abrogates late-G(1) arrest by TGF-beta1. These results demonstrate that TGF-beta1 acutely blocks entry into S phase by inhibiting pre-RC activation and suggest a novel role for Rb in mediating this effect of TGF-beta1 through direct interaction with and control of the MCM helicase.
Collapse
|
23
|
Colin D, Gimazane A, Lizard G, Izard JC, Solary E, Latruffe N, Delmas D. Effects of resveratrol analogs on cell cycle progression, cell cycle associated proteins and 5fluoro-uracil sensitivity in human derived colon cancer cells. Int J Cancer 2009; 124:2780-8. [DOI: 10.1002/ijc.24264] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
|
24
|
Cook JG. Replication licensing and the DNA damage checkpoint. Front Biosci (Landmark Ed) 2009; 14:5013-30. [PMID: 19482602 DOI: 10.2741/3584] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
Accurate and timely duplication of chromosomal DNA requires that replication be coordinated with processes that ensure genome integrity. Significant advances in determining how the earliest steps in DNA replication are affected by DNA damage have highlighted some of the mechanisms to establish that coordination. Recent insights have expanded the relationship between the ATM and ATR-dependent checkpoint pathways and the proteins that bind and function at replication origins. These findings suggest that checkpoints and replication are more intimately associated than previously appreciated, even in the absence of exogenous DNA damage. This review summarizes some of these developments.
Collapse
Affiliation(s)
- Jeanette Gowen Cook
- Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center Campus Box 7260, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
| |
Collapse
|
25
|
Mammalian MCM loading in late-G(1) coincides with Rb hyperphosphorylation and the transition to post-transcriptional control of progression into S-phase. PLoS One 2009; 4:e5462. [PMID: 19421323 PMCID: PMC2674209 DOI: 10.1371/journal.pone.0005462] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2008] [Accepted: 04/15/2009] [Indexed: 01/19/2023] Open
Abstract
Background Control of the onset of DNA synthesis in mammalian cells requires the coordinated assembly and activation of the pre-Replication Complex. In order to understand the regulatory events controlling preRC dynamics, we have investigated how the timing of preRC assembly relates temporally to other biochemical events governing progress into S-phase. Methodology/Principal Finding In murine and Chinese hamster (CHO) cells released from quiescence, the loading of the replicative MCM helicase onto chromatin occurs in the final 3–4 hrs of G1. Cdc45 and PCNA, both of which are required for G1-S transit, bind to chromatin at the G1-S transition or even earlier in G1, when MCMs load. An RNA polymerase II inhibitor (DRB) was added to synchronized murine keratinocytes to show that they are no longer dependent on new mRNA synthesis 3–4 hrs prior to S-phase entry, which is also true for CHO and human cells. Further, CHO cells can progress into S-phase on time, and complete S-phase, under conditions where new mRNA synthesis is significantly compromised, and such mRNA suppression causes no adverse effects on preRC dynamics prior to, or during, S-phase progression. Even more intriguing, hyperphosphorylation of Rb coincides with the start of MCM loading and, paradoxically, with the time in late-G1 when de novo mRNA synthesis is no longer rate limiting for progression into S-phase. Conclusions/Significance MCM, Cdc45, and PCNA loading, and the subsequent transit through G1-S, do not depend on concurrent new mRNA synthesis. These results indicate that mammalian cells pass through a distinct transition in late-G1 at which time Rb becomes hyperphosphorylated and MCM loading commences, but that after this transition the control of MCM, Cdc45, and PCNA loading and the onset of DNA replication are regulated at the post-transcriptional level.
Collapse
|
26
|
Paolinelli R, Mendoza-Maldonado R, Cereseto A, Giacca M. Acetylation by GCN5 regulates CDC6 phosphorylation in the S phase of the cell cycle. Nat Struct Mol Biol 2009; 16:412-20. [PMID: 19343071 DOI: 10.1038/nsmb.1583] [Citation(s) in RCA: 75] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2008] [Accepted: 03/04/2009] [Indexed: 01/21/2023]
Abstract
In eukaryotic cells, the cell-division cycle (CDC)-6 protein is essential to promote the assembly of pre-replicative complexes in the early G1 phase of the cell cycle, a process requiring tight regulation to ensure that proper origin licensing occurs once per cell cycle. Here we show that, in late G1 and early S phase, CDC6 is found in a complex also containing Cyclin A, cyclin-dependent kinase (CDK)-2 and the acetyltransferase general control nonderepressible 5 (GCN5). GCN5 specifically acetylates CDC6 at three lysine residues flanking its cyclin-docking motif, and this modification is crucial for the subsequent phosphorylation of the protein by Cyclin A-CDKs at a specific residue close to the acetylation site. GCN5-mediated acetylation and site-specific phosphorylation of CDC6 are both necessary for the relocalization of the protein to the cell cytoplasm in the S phase, as well as to regulate its stability. This two-step, intramolecular regulatory program by sequential modification of CDC6 seems to be essential for proper S-phase progression.
Collapse
Affiliation(s)
- Roberta Paolinelli
- Molecular Biology Laboratory, Scuola Normale Superiore, AREA della Ricerca del CNR, Pisa, Italy
| | | | | | | |
Collapse
|
27
|
Liu L, Choi JH, Yim H, Choi JS, Park BD, Cho SJ, Lee SK. ATR (AT mutated Rad3 related) activity stabilizes Cdc6 and delays G2/M-phase entry during hydroxyurea-induced S-phase arrest of HeLa cells. Int J Biochem Cell Biol 2008; 41:1410-20. [PMID: 19154794 DOI: 10.1016/j.biocel.2008.12.014] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2008] [Revised: 12/10/2008] [Accepted: 12/10/2008] [Indexed: 11/18/2022]
Abstract
The Cdc6 protein, a key DNA replication initiation factor, contributes to the long-term maintenance of the S-phase checkpoint by anchoring the Rad3-Rad26 complex to chromatin. Here, we demonstrate that ATR (AT mutated and Rad3 related) activity is essential for maintaining high chromatin levels of the Cdc6 protein, thereby delaying entry into mitosis during hydroxyurea (HU)-induced S-phase arrest of HeLa cells. Downregulation of ATR (AT mutated and Rad3 related) (i.e., using ATR-siRNA) reduced the protein levels of chromatin Cdc6 and significantly increased the cellular levels of phospho-histone H3 (Ser 10), an index of mitosis. Downregulation of Cdc6 was completely restored by pretreatment with MG132, a proteasome inhibitor. Moreover, mitotic entry of MG132-pretreated cells was significantly downregulated. Our results also show that ATR (AT mutated and Rad3 related) kinase phosphorylates Cdc6 at serine residue 6. Thus, this ATR (AT mutated and Rad3 related)-mediated phosphorylation of Cdc6 is likely associated with stabilization of Cdc6 protein, thereby maintaining high levels of chromatin Cdc6 and delaying premature mitotic entry. This novel mechanism likely contributes to the functional regulation of chromatin Cdc6, which delays the cell cycle of hydroxyurea-induced cells to enter mitosis at the S-phase checkpoint.
Collapse
Affiliation(s)
- Linhua Liu
- Division of Pharmaceutical Biosciences, Research Institute for Pharmaceutical Sciences, College of Pharmacy, Seoul National University, Seoul 151-742, Republic of Korea.
| | | | | | | | | | | | | |
Collapse
|
28
|
Abstract
Correct regulation of the replication licensing system ensures that chromosomal DNA is precisely duplicated in each cell division cycle. Licensing proteins are inappropriately expressed at an early stage of tumorigenesis in a wide variety of cancers. Here we discuss evidence that misregulation of replication licensing is a consequence of oncogene-induced cell proliferation. This misregulation can cause either under- or over-replication of chromosomal DNA, and could explain the genetic instability commonly seen in cancer cells.
Collapse
Affiliation(s)
- J Julian Blow
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, DD1 5EH, UK.
| | | |
Collapse
|
29
|
Davis AJ, Yan Z, Martinez B, Mumby MC. Protein phosphatase 2A is targeted to cell division control protein 6 by a calcium-binding regulatory subunit. J Biol Chem 2008; 283:16104-14. [PMID: 18397887 PMCID: PMC2414307 DOI: 10.1074/jbc.m710313200] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2007] [Revised: 02/29/2008] [Indexed: 12/19/2022] Open
Abstract
The cell division control protein 6 (Cdc6) is essential for formation of pre-replication complexes at origins of DNA replication. Phosphorylation of Cdc6 by cyclin-dependent kinases inhibits ubiquitination of Cdc6 by APC/C(cdh1) and degradation by the proteasome. Experiments described here show that the PR70 member of the PPP2R3 family of regulatory subunits targets protein phosphatase 2A (PP2A) to Cdc6. Interaction with Cdc6 is mediated by residues within the C terminus of PR70, whereas interaction with PP2A requires N-terminal sequences conserved within the PPP2R3 family. Two functional EF-hand calcium-binding motifs mediate a calcium-enhanced interaction of PR70 with PP2A. Calcium has no effect on the interaction of PR70 with Cdc6 but enhances the association of PP2A with Cdc6 through its effects on PR70. Knockdown of PR70 by RNA interference results in an accumulation of endogenous and expressed Cdc6 protein that is dependent on the cyclin-dependent protein kinase phosphorylation sites on Cdc6. Knockdown of PR70 also causes G(1) arrest, suggesting that PR70 function is critical for progression into S phase. These observations indicate that PP2A can be targeted in a calcium-regulated manner to Cdc6 via the PR70 subunit, where it plays a role in regulating protein phosphorylation and stability.
Collapse
Affiliation(s)
- Anthony J. Davis
- Department of Pharmacology,
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
75390-9041 and the Division of
Cardiology, Department of Medicine, Duke University, Medical Center, Durham,
North Carolina 27710
| | - Zhen Yan
- Department of Pharmacology,
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
75390-9041 and the Division of
Cardiology, Department of Medicine, Duke University, Medical Center, Durham,
North Carolina 27710
| | - Bobbie Martinez
- Department of Pharmacology,
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
75390-9041 and the Division of
Cardiology, Department of Medicine, Duke University, Medical Center, Durham,
North Carolina 27710
| | - Marc C. Mumby
- Department of Pharmacology,
University of Texas Southwestern Medical Center at Dallas, Dallas, Texas
75390-9041 and the Division of
Cardiology, Department of Medicine, Duke University, Medical Center, Durham,
North Carolina 27710
| |
Collapse
|
30
|
Human Rvb1/Tip49 is required for the histone acetyltransferase activity of Tip60/NuA4 and for the downregulation of phosphorylation on H2AX after DNA damage. Mol Cell Biol 2008; 28:2690-700. [PMID: 18285460 DOI: 10.1128/mcb.01983-07] [Citation(s) in RCA: 131] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The role of chromatin-remodeling factors in transcription is well established, but the link between chromatin-remodeling complexes and DNA repair remains unexplored. Human Rvb1 and Rvb2 are highly conserved AAA(+) ATP binding proteins that are part of various chromatin-remodeling complexes, such as Ino80, SNF2-related CBP activator protein (SRCAP), and Tip60/NuA4 complexes, but their molecular function is unclear. The depletion of Rvb1 increases the amount and persistence of phosphorylation on chromatin-associated H2AX after the exposure of cells to UV irradiation or to mitomycin C, cisplatin, camptothecin, or etoposide, without increasing the amount of DNA damage. Tip60 depletion, but not Ino80 or SRCAP depletion, mimics the effect of Rvb1 depletion on H2AX phosphorylation. Rvb1 is required for the histone acetyltransferase (HAT) activity of the Tip60 complex, and histone H4 acetylation is required prior to the dephosphorylation of phospho-H2AX. Thus, Rvb1 is critical for the dephosphorylation of phospho-H2AX due to the role of Rvb1 in maintaining the HAT activity of Tip60/NuA4, implicating the Rvb1-Tip60 complex in the chromatin-remodeling response of cells after DNA damage.
Collapse
|
31
|
Borlado LR, Méndez J. CDC6: from DNA replication to cell cycle checkpoints and oncogenesis. Carcinogenesis 2007; 29:237-43. [PMID: 18048387 DOI: 10.1093/carcin/bgm268] [Citation(s) in RCA: 171] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Cell division cycle 6 (CDC6) is an essential regulator of DNA replication in eukaryotic cells. Its best-characterized function is the assembly of prereplicative complexes at origins of replication during the G(1) phase of the cell division cycle. However, CDC6 also plays important roles in the activation and maintenance of the checkpoint mechanisms that coordinate S phase and mitosis, and recent studies have unveiled its proto-oncogenic activity. CDC6 overexpression interferes with the expression of INK4/ARF tumor suppressor genes through a mechanism involving the epigenetic modification of chromatin at the INK4/ARF locus. In addition, CDC6 overexpression in primary cells may promote DNA hyperreplication and induce a senescence response similar to that caused by oncogene activation. These findings indicate that deregulation of CDC6 expression in human cells poses a serious risk of carcinogenesis.
Collapse
Affiliation(s)
- Luis R Borlado
- DNA replication Group, Molecular Oncology Programme, Spanish National Cancer Research Centre, Melchor Fernández Almagro 3, E-28029 Madrid, Spain
| | | |
Collapse
|
32
|
Park JH, Bang SW, Jeon Y, Kang S, Hwang DS. Knockdown of human MCM10 exhibits delayed and incomplete chromosome replication. Biochem Biophys Res Commun 2007; 365:575-82. [PMID: 17997977 DOI: 10.1016/j.bbrc.2007.11.003] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2007] [Accepted: 11/01/2007] [Indexed: 11/28/2022]
Abstract
In model organisms, MCM10 is required for forming the pre-initiation complex for initiation of chromosome replication and is involved in the elongation step. To investigate the role of MCM10 in human chromosome replication, we used small interfering RNA (siRNA) in MCM10-knockdown experiments and found that knockdown accumulated S and G2 phase cells. The chromosome replication of MCM10-knockdown cells was slowed during early and mid S phases, although Cdc45, Polalpha, and PCNA proteins were loaded onto the chromatin, and was aberrant during late S phase. Our results indicate that MCM10 is essential for the efficient elongation step of chromosome replication.
Collapse
Affiliation(s)
- Jong Hoon Park
- Department of Biological Sciences, Seoul National University, Seoul 151-742, Republic of Korea
| | | | | | | | | |
Collapse
|
33
|
Kim BJ, Kim SY, Lee H. Identification and characterization of human cdc7 nuclear retention and export sequences in the context of chromatin binding. J Biol Chem 2007; 282:30029-38. [PMID: 17711849 DOI: 10.1074/jbc.m703705200] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The Cdc7 serine/threonine kinase activates the initiation of DNA replication by phosphorylating MCM proteins that are bound to the origins of DNA replication. We reported previously that human Cdc7 nuclear import is mediated directly by importin-beta through its binding to the Cdc7 nuclear localization sequence (NLS). Here, we report that human Cdc7 nuclear localization is regulated by two additional elements: nuclear retention (NRS) and export sequences (NES). Cdc7 proteins imported into the nucleus are retained in the nucleus by associating with chromatin, for which NRS-(306-326) is essential. Importantly, this binding appears to be specific to the origin of DNA replication, because the binding of wild-type Cdc7 to origin is 2.4-fold higher than to non-origin DNA. Furthermore, an NRS-defective Cdc7 mutant could not be retained in the nucleus, although it was imported into the nucleus normally. Together, our data suggest that NRS plays an important role in the activation of DNA replication by Cdc7. The Cdc7 proteins unassociated with chromatin are bound by CRM1 via two NES elements: NES1 at 458-467 within kinase insert III, and NES2 at 545-554 within the kinase IX domain. The primary function of the Cdc7-CRM1 association may be to translocate nuclear Cdc7 to the cytoplasm. However, the binding of CRM1 with Cdc7 at NES2 raises an interesting possibility that CRM1 may also down-regulate Cdc7 by masking its kinase domain.
Collapse
Affiliation(s)
- Byung Ju Kim
- Department of Biochemistry, Microbiology and Immunology, the Faculty of Medicine, University of Ottawa, Ottawa, Ontario K1M 8M5, Canada
| | | | | |
Collapse
|
34
|
Kim J, Feng H, Kipreos ET. C. elegans CUL-4 prevents rereplication by promoting the nuclear export of CDC-6 via a CKI-1-dependent pathway. Curr Biol 2007; 17:966-72. [PMID: 17509881 PMCID: PMC1945017 DOI: 10.1016/j.cub.2007.04.055] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/21/2006] [Revised: 04/23/2007] [Accepted: 04/23/2007] [Indexed: 10/23/2022]
Abstract
Genome stability requires that genomic DNA is replicated only once per cell cycle. The replication-licensing system ensures that the formation of prereplicative complexes is temporally separated from the initiation of DNA replication [1-4]. The replication-licensing factors Cdc6 and Cdt1 are required for the assembly of prereplicative complexes during G1 phase. During S phase, metazoan Cdt1 is targeted for degradation by the CUL4 ubiquitin ligase [5-8], and vertebrate Cdc6 is translocated from the nucleus to the cytoplasm [9, 10]. However, because residual vertebrate Cdc6 remains in the nucleus throughout S phase [10-13], it has been unclear whether Cdc6 translocation to the cytoplasm prevents rereplication [1, 2, 14]. The inactivation of C. elegans CUL-4 is associated with dramatic levels of DNA rereplication [5]. Here, we show that C. elegans CDC-6 is exported from the nucleus during S phase in response to the phosphorylation of multiple CDK sites. CUL-4 promotes the phosphorylation and subsequent translocation of CDC-6 via negative regulation of the CDK-inhibitor CKI-1. Rereplication can be induced by coexpression of nonexportable CDC-6 with nondegradable CDT-1, indicating that redundant regulation of CDC-6 and CDT-1 prevents rereplication. This demonstrates that CDC-6 translocation is critical for preventing rereplication and that CUL-4 independently controls both replication-licensing factors.
Collapse
Affiliation(s)
- Jihyun Kim
- Department of Cellular Biology, University of Georgia, Athens, Georgia 30602-2607, USA
| | | | | |
Collapse
|
35
|
Arias EE, Walter JC. Strength in numbers: preventing rereplication via multiple mechanisms in eukaryotic cells. Genes Dev 2007; 21:497-518. [PMID: 17344412 DOI: 10.1101/gad.1508907] [Citation(s) in RCA: 313] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
Abstract
In eukaryotic cells, prereplication complexes (pre-RCs) are assembled on chromatin in the G1 phase, rendering origins of DNA replication competent to initiate DNA synthesis. When DNA replication commences in S phase, pre-RCs are disassembled, and multiple initiations from the same origin do not occur because new rounds of pre-RC assembly are inhibited. In most experimental organisms, multiple mechanisms that prevent pre-RC assembly have now been identified, and rereplication within the same cell cycle can be induced through defined perturbations of these mechanisms. This review summarizes the diverse array of inhibitory pathways used by different organisms to prevent pre-RC assembly, and focuses on the challenge of understanding how in any one cell type, various mechanisms cooperate to strictly enforce once per cell cycle regulation of DNA replication.
Collapse
Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
| | | |
Collapse
|
36
|
Ghosh M, Kemp M, Liu G, Ritzi M, Schepers A, Leffak M. Differential binding of replication proteins across the human c-myc replicator. Mol Cell Biol 2006; 26:5270-83. [PMID: 16809765 PMCID: PMC1592723 DOI: 10.1128/mcb.02137-05] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
The binding of the prereplication complex proteins Orc1, Orc2, Mcm3, Mcm7, and Cdc6 and the novel DNA unwinding element (DUE) binding protein DUE-B to the endogenous human c-myc replicator was studied by chromatin immunoprecipitation. In G(1)-arrested HeLa cells, Mcm3, Mcm7, and DUE-B were prominent near the DUE, while Orc1 and Orc2 were least abundant near the DUE and more abundant at flanking sites. Cdc6 binding mirrored that of Orc2 in G(1)-arrested cells but decreased in asynchronous or M-phase cells. Similarly, the signals from Orc1, Mcm3, and Mcm7 were at background levels in cells arrested in M phase, whereas Orc2 retained the distribution seen in G(1)-phase cells. Previously shown to cause histone hyperacetylation and delocalization of replication initiation, trichostatin A treatment of cells led to a parallel qualitative change in the distribution of Mcm3, but not Orc2, across the c-myc replicator. Orc2, Mcm3, and DUE-B were also bound at an ectopic c-myc replicator, where deletion of sequences essential for origin activity was associated with the loss of DUE-B binding or the alteration of chromatin structure and loss of Mcm3 binding. These results show that proteins implicated in replication initiation are selectively and differentially bound across the c-myc replicator, dependent on discrete structural elements in DNA or chromatin.
Collapse
Affiliation(s)
- Maloy Ghosh
- Department of Biochemistry and Molecular Biology, Wright State University, 3640 Colonel Glenn Highway, Dayton, Ohio 45435, USA
| | | | | | | | | | | |
Collapse
|
37
|
Abstract
Regulation of DNA replication is critical for accurate and timely dissemination of genomic material to daughter cells. The cell uses a variety of mechanisms to control this aspect of the cell cycle. There are various determinants of origin identification, as well as a large number of proteins required to load replication complexes at these defined genomic regions. A pre-Replication Complex (pre-RC) associates with origins in the G1 phase. This complex includes the Origin Recognition Complex (ORC), which serves to recognize origins, the putative helicase MCM2-7, and other factors important for complex assembly. Following pre-RC loading, a pre-Initiation Complex (pre-IC) builds upon the helicase with factors required for eventual loading of replicative polymerases. The chromatin association of these two complexes is temporally distinct, with pre-RC being inhibited, and pre-IC being activated by cyclin-dependent kinases (Cdks). This regulation is the basis for replication licensing, which allows replication to occur at a specific time once, and only once, per cell cycle. By preventing extra rounds of replication within a cell cycle, or by ensuring the cell cycle cannot progress until the environmental and intracellular conditions are most optimal, cells are able to carry out a successful replication cycle with minimal mutations.
Collapse
Affiliation(s)
- Jamie K Teer
- Biological and Biomedical Sciences Program, Harvard Medical School, Boston, MA 02115, USA
| | | |
Collapse
|
38
|
DePamphilis ML, Blow JJ, Ghosh S, Saha T, Noguchi K, Vassilev A. Regulating the licensing of DNA replication origins in metazoa. Curr Opin Cell Biol 2006; 18:231-9. [PMID: 16650748 DOI: 10.1016/j.ceb.2006.04.001] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 04/04/2006] [Indexed: 01/19/2023]
Abstract
Eukaryotic DNA replication is a highly conserved process; the proteins and sequence of events that replicate animal genomes are remarkably similar to those that replicate yeast genomes. Moreover, the assembly of prereplication complexes at DNA replication origins ('DNA licensing') is regulated in all eukaryotes so that no origin fires more than once in a single cell cycle. And yet there are significant differences between species both in the selection of replication origins and in the way in which these origins are licensed to operate. Moreover, these differences impart advantages to multicellular animals and plants that facilitate their development, such as better control over endoreduplication, flexibility in origin selection, and discrimination between quiescent and proliferative states.
Collapse
Affiliation(s)
- Melvin L DePamphilis
- National Institute of Child Health and Human Development, National Institutes of Health, Building 6/3A-15, 9000 Rockville Pike, Bethesda, MD 20892-2753, USA.
| | | | | | | | | | | |
Collapse
|
39
|
McNairn AJ, Gilbert DM. Overexpression of ORC subunits and increased ORC-chromatin association in transformed mammalian cells. J Cell Biochem 2006; 96:879-87. [PMID: 16163736 DOI: 10.1002/jcb.20609] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
The origin recognition complex (ORC) is a conserved heterohexamer required for the formation of pre-replication (pre-RC) complexes at origins of DNA replication. Many studies of ORC subunits have been carried out in transformed human cell lines but the properties of ORC in primary cells have not been addressed. Here, we compare the expression levels and chromatin-association of ORC subunits in HeLa cells to the primary human cell line, WI38, and a virally transformed derivative of WI38, VA13. ORC subunits 2 and 4 were highly overexpressed in both HeLa and VA13, whereas ORC1 levels were elevated in VA13 but considerably higher in HeLa cells. Cellular extraction revealed that the proportion of ORC2 and ORC4 subunits bound to chromatin was similar in all three cell lines throughout the cell-cycle. In contrast, very little ORC1 was associated with chromatin after extraction of primary WI38 cells, whereas the majority of overexpressed ORC1 in both HeLa and VA13 co-fractionated with chromatin throughout the cell-cycle. Although none of the cell lines displayed significant changes in the levels or chromatin-association of ORC during the cell-cycle, the chromatin-associated fraction of ORC1 displayed an increase in apparent molecular weight during S-phase. Similar experiments comparing immortalized CHO cells to an isogenic virally transformed derivative revealed no changes in levels of ORC subunits but an increase in the proportion of all three ORC subunits associated with chromatin. These results demonstrate a complex influence of cellular immortalization and transformation properties on the expression and regulation of ORC subunits. These results extend the potential link between cancer and deregulation of pre-RC proteins, and underscore the importance of considering the transformation status of cell lines when working with these proteins.
Collapse
Affiliation(s)
- Adrian J McNairn
- Department of Biochemistry and Molecular Biology, S.U.N.Y. Upstate Medical University, Syracuse, New York 13210, USA
| | | |
Collapse
|
40
|
Iizuka M, Matsui T, Takisawa H, Smith MM. Regulation of replication licensing by acetyltransferase Hbo1. Mol Cell Biol 2006; 26:1098-108. [PMID: 16428461 PMCID: PMC1347032 DOI: 10.1128/mcb.26.3.1098-1108.2006] [Citation(s) in RCA: 152] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
The initiation of DNA replication is tightly regulated in eukaryotic cells to ensure that the genome is precisely duplicated once and only once per cell cycle. This is accomplished by controlling the assembly of a prereplicative complex (pre-RC) which involves the sequential binding to replication origins of the origin recognition complex (ORC), Cdc6/Cdc18, Cdt1, and the minichromosome maintenance complex (Mcm2-Mcm7, or Mcm2-7). Several mechanisms of pre-RC regulation are known, including ATP utilization, cyclin-dependent kinase levels, protein turnover, and Cdt1 binding by geminin. Histone acetylation may also affect the initiation of DNA replication, but at present neither the enzymes nor the steps involved are known. Here, we show that Hbo1, a member of the MYST histone acetyltransferase family, is a previously unrecognized positive regulatory factor for pre-RC assembly. When Hbo1 expression was inhibited in human cells, Mcm2-7 failed to associate with chromatin even though ORC and Cdc6 loading was normal. When Xenopus egg extracts were immunodepleted of Xenopus Hbo1 (XHbo1), chromatin binding of Mcm2-7 was lost, and DNA replication was abolished. The binding of Mcm2-7 to chromatin in XHbo1-depleted extracts could be restored by the addition of recombinant Cdt1.
Collapse
Affiliation(s)
- Masayoshi Iizuka
- Department of Microbiology, University of Virginia Health System, P.O. Box 800734, Charlottesville, VA 22908-0734, USA
| | | | | | | |
Collapse
|
41
|
Friedrich TD, Bedner E, Darzynkiewicz Z, Lehman JM. Distinct patterns of MCM protein binding in nuclei of S phase and rereplicating SV40-infected monkey kidney cells. Cytometry A 2006; 68:10-8. [PMID: 16184610 DOI: 10.1002/cyto.a.20185] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
BACKGROUND Simian Virus 40 (SV40) infection of growth-arrested monkey kidney cells stimulates S phase entry and the continued synthesis of both viral and cellular DNA. Infected cells can attain total DNA contents as high as DNA Index, DI = 5.0-6.0 (10-12C), with host cell DNA representing 70-80% of the total. In this study, SV40-infected and uninfected control cells were compared to determine whether continued DNA replication beyond DI = 2.0 was associated with rebinding of the minichromosome maintenance (MCM) hexamer, the putative replicative helicase, to chromatin. METHOD Laser scanning cytometry was used to measure the total expression per cell and the chromatin/matrix-association of two MCM subunits in relation to DNA content. RESULTS MCM2 and MCM3 proteins that were associated with the chromatin/matrix fraction in G1 phase of both uninfected and SV40-infected cells were gradually released during progression through S phase. However, in SV40-infected cells that progressed beyond DI = 2.0, chromatin/matrix-associated MCM2 and MCM3 remained at the low levels observed at the end of S phase. Rereplication was not preceded by an obvious rebinding of MCM proteins to chromatin, as was observed in G1 phase. CONCLUSIONS The rereplication of host cell DNA in the absence of the reassociation of MCM proteins with chromatin indicates that SV40 infection induces a novel mechanism of licensing cellular DNA replication.
Collapse
Affiliation(s)
- Thomas D Friedrich
- Albany Medical College, Center for Immunology and Microbial Diseases, Albany, New York 12208, USA.
| | | | | | | |
Collapse
|
42
|
Lau E, Zhu C, Abraham RT, Jiang W. The functional role of Cdc6 in S-G2/M in mammalian cells. EMBO Rep 2006; 7:425-30. [PMID: 16439999 PMCID: PMC1456921 DOI: 10.1038/sj.embor.7400624] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2005] [Revised: 10/18/2005] [Accepted: 12/07/2005] [Indexed: 11/08/2022] Open
Abstract
The Cdc6 protein is required for licensing of replication origins before the onset of DNA replication in eukaryotic cells. Here, we examined whether Cdc6 has other roles in mammalian cell-cycle progression from S to G2/M phase. Using RNA interference, we showed that depletion of Cdc6 in synchronous G1 cells blocks G1 to S transition, confirming the essential role of Cdc6 in the initiation of DNA replication. In contrast, depletion of Cdc6 in synchronous S-phase cells slowed DNA replication and led to mitotic lethality. The Cdc6-depleted S-phase cells showed fewer newly fired origins; however, established replication forks remained active, even during chromatin condensation. Despite such DNA replication abnormalities, loss of Cdc6 failed to activate Chk1 kinase. These results show that Cdc6 is not only required for G1 origin licensing, but is also crucial for proper S-phase DNA replication that is essential for DNA segregation during mitosis.
Collapse
Affiliation(s)
- Eric Lau
- The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
- Graduate Program in Molecular Pathology, University of California, 9500 Gilman Drive 0612, La Jolla, California 92093, USA
| | - Changjun Zhu
- The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Robert T Abraham
- The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
| | - Wei Jiang
- The Burnham Institute, 10901 North Torrey Pines Road, La Jolla, California 92037, USA
- Tel: +1 858 646 3186; Fax: +1 858 713 6247; E-mail:
| |
Collapse
|
43
|
Zhu W, Abbas T, Dutta A. DNA replication and genomic instability. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2006; 570:249-79. [PMID: 18727504 DOI: 10.1007/1-4020-3764-3_9] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Affiliation(s)
- Wenge Zhu
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | | | | |
Collapse
|
44
|
Mailand N, Diffley JFX. CDKs promote DNA replication origin licensing in human cells by protecting Cdc6 from APC/C-dependent proteolysis. Cell 2005; 122:915-26. [PMID: 16153703 DOI: 10.1016/j.cell.2005.08.013] [Citation(s) in RCA: 264] [Impact Index Per Article: 13.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/25/2005] [Revised: 07/19/2005] [Accepted: 08/05/2005] [Indexed: 11/22/2022]
Abstract
Cyclin-dependent kinases (CDKs) restrict DNA replication origin firing to once per cell cycle by preventing the assembly of prereplicative complexes (pre-RCs; licensing) outside of G1 phase. Paradoxically, under certain circumstances, CDKs such as cyclin E-cdk2 are also required to promote licensing. Here, we show that CDK phosphorylation of the essential licensing factor Cdc6 stabilizes it by preventing its association with the anaphase promoting complex/cyclosome (APC/C). APC/C-dependent Cdc6 proteolysis prevents pre-RC assembly in quiescent cells and, when cells reenter the cell cycle from quiescence, CDK-dependent Cdc6 stabilization allows Cdc6 to accumulate before the licensing inhibitors geminin and cyclin A which are also APC/C substrates. This novel mechanism for regulating protein stability establishes a window of time prior to S phase when pre-RCs can assemble which we propose represents a critical function of cyclin E.
Collapse
Affiliation(s)
- Niels Mailand
- Cancer Research UK London Research Institute, Clare Hall Laboratories, Hertfordshire, United Kingdom
| | | |
Collapse
|
45
|
Crevel G, Mathe E, Cotterill S. The Drosophila Cdc6/18 protein has functions in both early and late S phase in S2 cells. J Cell Sci 2005; 118:2451-9. [PMID: 15923658 DOI: 10.1242/jcs.02361] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The Cdc6/18 protein has been mainly characterised for its role in the initiation of DNA replication. Several studies exist, however, which suggest that it may also have a role in controlling the G2/M transition. Here we present studies on the Drosophila Cdc6 (DmCdc6) protein that support this dual function for the protein. First we show that its location is consistent with a cellular role post replication initiation as it remains nuclear throughout G1, S and G2 phases. In addition, we have been able to reduce the level of DmCdc6 protein to nondetectable levels in S2 cells using RNAi. This causes DNA fragmentation and cell cycle abnormalities which have some similarities with phenotypes previously observed in yeasts and are consistent with the cells entering mitosis with incompletely replicated DNA. Finally, we have stably overexpressed the DmCdc6 protein to a high level in S2 cells. Despite a large excess of protein the effects on the S2 cells were minimal. We did, however, detect a slight stalling of the cells in the late S phase of the cell cycle, which further supports the proposal that DmCdc6 has a role in controlling the transition from the S to M phases of the cycle.
Collapse
Affiliation(s)
- Gilles Crevel
- Department Basic Medical Sciences, St Georges Hospital Medical School, London, SW17 0RE, UK
| | | | | |
Collapse
|
46
|
Liku ME, Nguyen VQ, Rosales AW, Irie K, Li JJ. CDK phosphorylation of a novel NLS-NES module distributed between two subunits of the Mcm2-7 complex prevents chromosomal rereplication. Mol Biol Cell 2005; 16:5026-39. [PMID: 16093348 PMCID: PMC1237101 DOI: 10.1091/mbc.e05-05-0412] [Citation(s) in RCA: 85] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2005] [Revised: 07/26/2005] [Accepted: 08/02/2005] [Indexed: 11/11/2022] Open
Abstract
Cyclin-dependent kinases (CDKs) use multiple mechanisms to block reassembly of prereplicative complexes (pre-RCs) at replication origins to prevent inappropriate rereplication. In Saccharomyces cerevisiae, one of these mechanisms promotes the net nuclear export of a pre-RC component, the Mcm2-7 complex, during S, G2, and M phases. Here we identify two partial nuclear localization signals (NLSs) on Mcm2 and Mcm3 that are each necessary, but not sufficient, for nuclear localization of the Mcm2-7 complex. When brought together in cis, however, the two partial signals constitute a potent NLS, sufficient for robust nuclear localization when fused to an otherwise cytoplasmic protein. We also identify a Crm1-dependent nuclear export signal (NES) adjacent to the Mcm3 NLS. Remarkably, the Mcm2-Mcm3 NLS and the Mcm3 NES are sufficient to form a transport module that recapitulates the cell cycle-regulated localization of the entire Mcm2-7 complex. Moreover, we show that CDK regulation promotes net export by phosphorylation of the Mcm3 portion of this module and that nuclear export of the Mcm2-7 complex is sufficient to disrupt replication initiation. We speculate that the distribution of partial transport signals among distinct subunits of a complex may enhance the specificity of protein localization and raises the possibility that previously undetected distributed transport signals are used by other multiprotein complexes.
Collapse
Affiliation(s)
- Muluye E Liku
- Department of Biochemistry, University of California, San Francisco, CA 94143-2200, USA
| | | | | | | | | |
Collapse
|
47
|
Duursma A, Agami R. p53-Dependent regulation of Cdc6 protein stability controls cellular proliferation. Mol Cell Biol 2005; 25:6937-47. [PMID: 16055707 PMCID: PMC1190229 DOI: 10.1128/mcb.25.16.6937-6947.2005] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Activation of tumor suppressor p53 in response to genotoxic stress imposes cellular growth arrest or apoptosis. We identified Cdc6, a licensing factor of the prereplication complex, as a novel target of the p53 pathway. We show that activation of p53 by DNA damage results in enhanced Cdc6 destruction by the anaphase-promoting complex. This destruction is triggered by inhibition of CDK2-mediated CDC6 phosphorylation at serine 54. Conversely, suppression of p53 expression results in stabilization of Cdc6. We demonstrate that loss of p53 results in more replicating cells, an effect that can be reversed by reducing Cdc6 protein levels. Collectively, our data suggest that initiation of DNA replication is regulated by p53 through Cdc6 protein stability.
Collapse
Affiliation(s)
- Anja Duursma
- Division of Tumor Biology, The Netherlands Cancer Institute, Amsterdam
| | | |
Collapse
|
48
|
McNairn AJ, Okuno Y, Misteli T, Gilbert DM. Chinese hamster ORC subunits dynamically associate with chromatin throughout the cell-cycle. Exp Cell Res 2005; 308:345-56. [PMID: 15950218 PMCID: PMC1350721 DOI: 10.1016/j.yexcr.2005.05.009] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2004] [Revised: 05/02/2005] [Accepted: 05/03/2005] [Indexed: 12/11/2022]
Abstract
In yeast, the Origin Recognition Complex (ORC) is bound to replication origins throughout the cell-cycle, but in animal cells, there are conflicting data as to whether and when ORC is removed from chromatin. We find ORC1, 2 and ORC4 to be metabolically stable proteins that co-fractionate with chromatin throughout the cell-cycle in Chinese hamster fibroblasts. Since cellular extraction methods cannot directly examine the chromatin binding properties of proteins in vivo, we examined ORC:chromatin interactions in living cells. Fluorescence loss in photobleaching (FLIP) studies revealed ORC1 and ORC4 to be highly dynamic proteins during the cell-cycle with exchange kinetics similar to other regulatory chromatin proteins. In vivo interaction with chromatin was not significantly altered throughout the cell-cycle, including S-phase. These data support a model in which ORC subunits dynamically interact with chromatin throughout the cell-cycle.
Collapse
Affiliation(s)
- Adrian J. McNairn
- Department of Biochemistry and Molecular Biology, S.U.N.Y. Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| | - Yukiko Okuno
- Department of Biochemistry and Molecular Biology, S.U.N.Y. Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| | - Tom Misteli
- National Cancer Institute, NIH 41 Library Drive Bldg. 41, Bethesda, MD 20892, USA
| | - David M. Gilbert
- Department of Biochemistry and Molecular Biology, S.U.N.Y. Upstate Medical University, 750 East Adams Street, Syracuse, NY 13210, USA
| |
Collapse
|
49
|
Abstract
To ensure its duplication, chromosomal DNA must be precisely duplicated in each cell cycle, with no sections left unreplicated, and no sections replicated more than once. Eukaryotic cells achieve this by dividing replication into two non-overlapping phases. During late mitosis and G1, replication origins are 'licensed' for replication by loading the minichromosome maintenance (Mcm) 2-7 proteins to form a pre-replicative complex. Mcm2-7 proteins are then essential for initiating and elongating replication forks during S phase. Recent data have provided biochemical and structural insight into the process of replication licensing and the mechanisms that regulate it during the cell cycle.
Collapse
Affiliation(s)
- J Julian Blow
- Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, UK.
| | | |
Collapse
|
50
|
Abstract
Initiation and completion of DNA replication defines the beginning and ending of S phase of the cell cycle. Successful progression through S phase requires that replication be properly regulated and monitored to ensure that the entire genome is duplicated exactly once, without errors, in a timely fashion. Given the immense size and complexity of eukaryotic genomes, this presents a significant challenge for the cell. As a result, DNA replication has evolved into a tightly regulated process involving the coordinated action of numerous factors that function in all phases of the cell cycle. We will review our current understanding of these processes from the formation of prereplicative complexes in preparation for S phase to the series of events that culminate in the loading of DNA polymerases during S phase. We will incorporate structural data from archaeal and bacterial replication proteins and discuss their implications for understanding the mechanism of action of their corresponding eukaryotic homologues. We will also describe the concept of replication licensing which protects against genomic instability by limiting initiation events to once per cell cycle. Lastly, we will review our knowledge of checkpoint pathways that maintain the integrity of stalled forks and relay defects in replication to the rest of the cell cycle.
Collapse
Affiliation(s)
- David Y Takeda
- Department of Pathology, Brigham and Women's Hospital, Harvard Medical School, Boston, MA 02115, USA
| | | |
Collapse
|