1
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Noncanonical function of Capicua as a growth termination signal in Drosophila oogenesis. Proc Natl Acad Sci U S A 2022; 119:e2123467119. [PMID: 35881788 PMCID: PMC9351367 DOI: 10.1073/pnas.2123467119] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Capicua (Cic) proteins are conserved HMG-box transcriptional repressors that control receptor tyrosine kinase (RTK) signaling responses and are implicated in human neurological syndromes and cancer. While Cic is known to exist as short (Cic-S) and long (Cic-L) isoforms with identical HMG-box and associated core regions but distinct N termini, most previous studies have focused on Cic-S, leaving the function of Cic-L unexplored. Here we show that Cic-L acts in two capacities during Drosophila oogenesis: 1) as a canonical sensor of RTK signaling in somatic follicle cells, and 2) as a regulator of postmitotic growth in germline nurse cells. In these latter cells, Cic-L behaves as a temporal signal that terminates endoreplicative growth before they dump their contents into the oocyte. We show that Cic-L is necessary and sufficient for nurse cell endoreplication arrest and induces both stabilization of CycE and down-regulation of Myc. Surprisingly, this function depends mainly on the Cic-L-specific N-terminal module, which is capable of acting independently of the Cic HMG-box-containing core. Mirroring these observations, basal metazoans possess truncated Cic-like proteins composed only of Cic-L N-terminal sequences, suggesting that this module plays unique, ancient roles unrelated to the canonical function of Cic.
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2
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Chakravarti A, Thirimanne HN, Brown S, Calvi BR. Drosophila p53 isoforms have overlapping and distinct functions in germline genome integrity and oocyte quality control. eLife 2022; 11:61389. [PMID: 35023826 PMCID: PMC8758136 DOI: 10.7554/elife.61389] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2020] [Accepted: 12/13/2021] [Indexed: 12/13/2022] Open
Abstract
p53 gene family members in humans and other organisms encode a large number of protein isoforms whose functions are largely undefined. Using Drosophila as a model, we find that a p53B isoform is expressed predominantly in the germline where it colocalizes with p53A into subnuclear bodies. It is only p53A, however, that mediates the apoptotic response to ionizing radiation in the germline and soma. In contrast, p53A and p53B are both required for the normal repair of meiotic DNA breaks, an activity that is more crucial when meiotic recombination is defective. We find that in oocytes with persistent DNA breaks p53A is also required to activate a meiotic pachytene checkpoint. Our findings indicate that Drosophila p53 isoforms have DNA lesion and cell type-specific functions, with parallels to the functions of mammalian p53 family members in the genotoxic stress response and oocyte quality control.
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Affiliation(s)
| | | | - Savanna Brown
- Department of Biology, Indiana University, Bloomington, United States
| | - Brian R Calvi
- Department of Biology, Indiana University, Bloomington, United States
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3
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Liu TH, Dong XL, Chen P, Zhang Q, Zhou XL, Lu C, Pan MH. Geminin is essential for DNA re-replication in the silk gland cells of silkworms. Exp Cell Res 2022; 410:112951. [PMID: 34843715 DOI: 10.1016/j.yexcr.2021.112951] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2021] [Revised: 11/22/2021] [Accepted: 11/25/2021] [Indexed: 11/18/2022]
Abstract
Endoreplication, known as endocycles or endoreduplication, is a cell cycle variant in which the genomic DNA is re-replicated without mitosis leading to polyploidy. Endoreplication is essential for the development and functioning of the different organs in animals and plants. Deletion of Geminin, a DNA replication licensing inhibitor, causes DNA re-replication or damage. However, the role of Geminin in endoreplication is still unclear. Here, we studied the role of Geminin in the endoreplication of the silk gland cells of silkworms by constructing two transgenic silkworm strains, including BmGeminin1-overexpression and BmGeminin1-RNA interference. Interference of BmGeminin1 led to body weight gain, increased silk gland volume, increased DNA content, and enhanced DNA re-replication activity relative to wild-type Dazao. Meanwhile, overexpression of BmGeminin1 showed an opposite phenotype compared to the BmGem1-RNAi strain. Furthermore, RNA-sequencing of the transgenic strains was carried out to explore how BmGeminin1 regulates DNA re-replication. Our data demonstrated a vital role of Geminin in the regulation of endoreplication in the silk gland of silkworms.
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Affiliation(s)
- Tai-Hang Liu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Department of Bioinformatics, Chongqing Medical University, No.1 Yixueyuan Road, Yuzhong District of Chongqing, 400015, China
| | - Xiao-Long Dong
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Peng Chen
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Qian Zhang
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Xiao-Lin Zhou
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China
| | - Cheng Lu
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China.
| | - Min-Hui Pan
- State Key Laboratory of Silkworm Genome Biology, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China; Key Laboratory for Sericulture Functional Genomics and Biotechnology of Agricultural Ministry, Southwest University, No.2 Tiansheng Road, Beibei District of Chongqing, 400716, China.
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4
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Kim M, Delos Santos K, Moon NS. Proper CycE-Cdk2 activity in endocycling tissues requires regulation of the cyclin-dependent kinase inhibitor Dacapo by dE2F1b in Drosophila. Genetics 2021; 217:1-15. [PMID: 33683365 DOI: 10.1093/genetics/iyaa029] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/2020] [Accepted: 12/06/2020] [Indexed: 01/05/2023] Open
Abstract
Polyploidy is an integral part of development and is associated with cellular stress, aging, and pathological conditions. The endocycle, comprised of successive rounds of G and S phases without mitosis, is widely employed to produce polyploid cells in plants and animals. In Drosophila, maintenance of the endocycle is dependent on E2F-governed oscillations of Cyclin E (CycE)-Cdk2 activity, which is known to be largely regulated at the level of transcription. In this study, we report an additional level of E2F-dependent control of CycE-Cdk2 activity during the endocycle. Genetic experiments revealed that an alternative isoform of Drosophila de2f1, dE2F1b, regulates the expression of the p27CIP/KIP-like Cdk inhibitor Dacapo (Dap). We provide evidence showing that dE2F1b-dependent Dap expression in endocycling tissues is necessary for setting proper CycE-Cdk2 activity. Furthermore, we demonstrate that dE2F1b is required for proliferating cell nuclear antigen expression that establishes a negative feedback loop in S phase. Overall, our study reveals previously unappreciated E2F-dependent regulatory networks that are critical for the periodic transition between G and S phases during the endocycle.
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Affiliation(s)
- Minhee Kim
- Department of Biology, Developmental Biology Research Initiative, McGill University, Montreal, Quebec H3A 1B1 Canada
| | - Keemo Delos Santos
- Department of Biology, Developmental Biology Research Initiative, McGill University, Montreal, Quebec H3A 1B1 Canada
| | - Nam-Sung Moon
- Department of Biology, Developmental Biology Research Initiative, McGill University, Montreal, Quebec H3A 1B1 Canada
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5
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Petropoulos M, Champeris Tsaniras S, Taraviras S, Lygerou Z. Replication Licensing Aberrations, Replication Stress, and Genomic Instability. Trends Biochem Sci 2019; 44:752-764. [PMID: 31054805 DOI: 10.1016/j.tibs.2019.03.011] [Citation(s) in RCA: 66] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2019] [Revised: 03/24/2019] [Accepted: 03/27/2019] [Indexed: 01/07/2023]
Abstract
Strict regulation of DNA replication is of fundamental significance for the maintenance of genome stability. Licensing of origins of DNA replication is a critical event for timely genome duplication. Errors in replication licensing control lead to genomic instability across evolution. Here, we present accumulating evidence that aberrant replication licensing is linked to oncogene-induced replication stress and poses a major threat to genome stability, promoting tumorigenesis. Oncogene activation can lead to defects in where along the genome and when during the cell cycle licensing takes place, resulting in replication stress. We also discuss the potential of replication licensing as a specific target for novel anticancer therapies.
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Affiliation(s)
- Michalis Petropoulos
- Department of Biology, School of Medicine, University of Patras, Patras 26504, Greece
| | | | - Stavros Taraviras
- Department of Physiology, School of Medicine, University of Patras, Patras 26504, Greece.
| | - Zoi Lygerou
- Department of Biology, School of Medicine, University of Patras, Patras 26504, Greece.
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6
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Mughal MJ, Mahadevappa R, Kwok HF. DNA replication licensing proteins: Saints and sinners in cancer. Semin Cancer Biol 2018; 58:11-21. [PMID: 30502375 DOI: 10.1016/j.semcancer.2018.11.009] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2018] [Revised: 11/08/2018] [Accepted: 11/26/2018] [Indexed: 12/12/2022]
Abstract
DNA replication is all-or-none process in the cell, meaning, once the DNA replication begins it proceeds to completion. Hence, to achieve maximum control of DNA replication, eukaryotic cells employ a multi-subunit initiator protein complex known as "pre-replication complex or DNA replication licensing complex (DNA replication LC). This complex involves multiple proteins which are origin-recognition complex family proteins, cell division cycle-6, chromatin licensing and DNA replication factor 1, and minichromosome maintenance family proteins. Higher-expression of DNA replication LC proteins appears to be an early event during development of cancer since it has been a common hallmark observed in a wide variety of cancers such as oesophageal, laryngeal, pulmonary, mammary, colorectal, renal, urothelial etc. However, the exact mechanisms leading to the abnormally high expression of DNA replication LC have not been clearly deciphered. Increased expression of DNA replication LC leads to licensing and/or firing of multiple origins thereby inducing replication stress and genomic instability. Therapeutic approaches where the reduction in the activity of DNA replication LC was achieved either by siRNA or shRNA techniques, have shown increased sensitivity of cancer cell lines towards the anti-cancer drugs such as cisplatin, 5-Fluorouracil, hydroxyurea etc. Thus, the expression level of DNA replication LC within the cell determines a cell's fate thereby creating a paradox where DNA replication LC acts as both "Saint" and "Sinner". With a potential to increase sensitivity to chemotherapy drugs, DNA replication LC proteins have prospective clinical importance in fighting cancer. Hence, in this review, we will shed light on importance of DNA replication LC with an aim to use DNA replication LC in diagnosis and prognosis of cancer in patients as well as possible therapeutic targets for cancer therapy.
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Affiliation(s)
- Muhammad Jameel Mughal
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau
| | - Ravikiran Mahadevappa
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau
| | - Hang Fai Kwok
- Cancer Centre, Faculty of Health Sciences, University of Macau, Avenida de Universidade, Taipa, Macau.
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7
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DNA Replication Control During Drosophila Development: Insights into the Onset of S Phase, Replication Initiation, and Fork Progression. Genetics 2017; 207:29-47. [PMID: 28874453 PMCID: PMC5586379 DOI: 10.1534/genetics.115.186627] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2016] [Accepted: 05/19/2017] [Indexed: 12/11/2022] Open
Abstract
Proper control of DNA replication is critical to ensure genomic integrity during cell proliferation. In addition, differential regulation of the DNA replication program during development can change gene copy number to influence cell size and gene expression. Drosophila melanogaster serves as a powerful organism to study the developmental control of DNA replication in various cell cycle contexts in a variety of differentiated cell and tissue types. Additionally, Drosophila has provided several developmentally regulated replication models to dissect the molecular mechanisms that underlie replication-based copy number changes in the genome, which include differential underreplication and gene amplification. Here, we review key findings and our current understanding of the developmental control of DNA replication in the contexts of the archetypal replication program as well as of underreplication and differential gene amplification. We focus on the use of these latter two replication systems to delineate many of the molecular mechanisms that underlie the developmental control of replication initiation and fork elongation.
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8
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Rapid DNA Synthesis During Early Drosophila Embryogenesis Is Sensitive to Maternal Humpty Dumpty Protein Function. Genetics 2017; 207:935-947. [PMID: 28942426 DOI: 10.1534/genetics.117.300318] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 09/20/2017] [Indexed: 12/29/2022] Open
Abstract
Problems with DNA replication cause cancer and developmental malformations. It is not fully understood how DNA replication is coordinated with development and perturbed in disease. We had previously identified the Drosophila gene humpty dumpty (hd), and showed that null alleles cause incomplete DNA replication, tissue undergrowth, and lethality. Animals homozygous for the missense allele, hd272-9 , were viable, but adult females had impaired amplification of eggshell protein genes in the ovary, resulting in the maternal effects of thin eggshells and embryonic lethality. Here, we show that expression of an hd transgene in somatic cells of the ovary rescues amplification and eggshell synthesis but not embryo viability. The germline of these mothers remain mutant for the hd272-9 allele, resulting in reduced maternal Hd protein and embryonic arrest during mitosis of the first few S/M nuclear cleavage cycles with chromosome instability and chromosome bridges. Epistasis analysis of hd with the rereplication mutation plutonium indicates that the chromosome bridges of hd embryos are the result of a failed attempt to segregate incompletely replicated sister chromatids. This study reveals that maternally encoded Humpty dumpty protein is essential for DNA replication and genome integrity during the little-understood embryonic S/M cycles. Moreover, the two hd272-9 maternal-effect phenotypes suggest that ovarian gene amplification and embryonic cleavage are two time periods in development that are particularly sensitive to mild deficits in DNA replication function. This last observation has broader relevance for interpreting why mild mutations in the human ortholog of humpty dumpty and other DNA replication genes cause tissue-specific malformations of microcephalic dwarfisms.
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9
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Parker MW, Botchan MR, Berger JM. Mechanisms and regulation of DNA replication initiation in eukaryotes. Crit Rev Biochem Mol Biol 2017; 52:107-144. [PMID: 28094588 DOI: 10.1080/10409238.2016.1274717] [Citation(s) in RCA: 119] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Cellular DNA replication is initiated through the action of multiprotein complexes that recognize replication start sites in the chromosome (termed origins) and facilitate duplex DNA melting within these regions. In a typical cell cycle, initiation occurs only once per origin and each round of replication is tightly coupled to cell division. To avoid aberrant origin firing and re-replication, eukaryotes tightly regulate two events in the initiation process: loading of the replicative helicase, MCM2-7, onto chromatin by the origin recognition complex (ORC), and subsequent activation of the helicase by its incorporation into a complex known as the CMG. Recent work has begun to reveal the details of an orchestrated and sequential exchange of initiation factors on DNA that give rise to a replication-competent complex, the replisome. Here, we review the molecular mechanisms that underpin eukaryotic DNA replication initiation - from selecting replication start sites to replicative helicase loading and activation - and describe how these events are often distinctly regulated across different eukaryotic model organisms.
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Affiliation(s)
- Matthew W Parker
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
| | - Michael R Botchan
- b Department of Molecular and Cell Biology , University of California Berkeley , Berkeley , CA , USA
| | - James M Berger
- a Department of Biophysics and Biophysical Chemistry , Johns Hopkins University School of Medicine , Baltimore , MD , USA
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10
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Uzcanga G, Lara E, Gutiérrez F, Beaty D, Beske T, Teran R, Navarro JC, Pasero P, Benítez W, Poveda A. Nuclear DNA replication and repair in parasites of the genus Leishmania: Exploiting differences to develop innovative therapeutic approaches. Crit Rev Microbiol 2016; 43:156-177. [PMID: 27960617 DOI: 10.1080/1040841x.2016.1188758] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Leishmaniasis is a common tropical disease that affects mainly poor people in underdeveloped and developing countries. This largely neglected infection is caused by Leishmania spp, a parasite from the Trypanosomatidae family. This parasitic disease has different clinical manifestations, ranging from localized cutaneous to more harmful visceral forms. The main limitations of the current treatments are their high cost, toxicity, lack of specificity, and long duration. Efforts to improve treatments are necessary to deal with this infectious disease. Many approved drugs to combat diseases as diverse as cancer, bacterial, or viral infections take advantage of specific features of the causing agent or of the disease. Recent evidence indicates that the specific characteristics of the Trypanosomatidae replication and repair machineries could be used as possible targets for the development of new treatments. Here, we review in detail the molecular mechanisms of DNA replication and repair regulation in trypanosomatids of the genus Leishmania and the drugs that could be useful against this disease.
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Affiliation(s)
- Graciela Uzcanga
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador.,b Programa Prometeo , SENESCYT, Whymper E7-37 y Alpallana, Quito , Ecuador.,c Facultad de Ciencias Naturales y Ambientales, Universidad Internacional SEK Calle Alberto Einstein sn y 5ta transversal , Quito , Ecuador.,d Fundación Instituto de Estudios Avanzados-IDEA , Caracas , Venezuela
| | - Eliana Lara
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador.,e Institute of Human Genetics , CNRS UPR 1142, 141 rue de la Cardonille, Equipe Labellisée Ligue Contre le Cancer , Montpellier cedex 5 , France
| | - Fernanda Gutiérrez
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
| | - Doyle Beaty
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
| | - Timo Beske
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
| | - Rommy Teran
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
| | - Juan-Carlos Navarro
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador.,f Universidad Central de Venezuela, Instituto de Zoología y Ecología Tropical , Caracas , Venezuela.,g Facultad de Ciencias Naturales y Ambientales, Universidad Internacional SEK, Calle Alberto Einstein sn y 5ta transversal , Quito , Ecuador
| | - Philippe Pasero
- e Institute of Human Genetics , CNRS UPR 1142, 141 rue de la Cardonille, Equipe Labellisée Ligue Contre le Cancer , Montpellier cedex 5 , France
| | - Washington Benítez
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
| | - Ana Poveda
- a Centro Internacional de Zoonosis, Facultad de Ciencias Químicas, Facultad de Medicina Veterinaria , Universidad Central del Ecuador , Quito , Ecuador
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Karavias D, Maroulis I, Papadaki H, Gogos C, Kakkos S, Karavias D, Bravou V. Overexpression of CDT1 Is a Predictor of Poor Survival in Patients with Hepatocellular Carcinoma. J Gastrointest Surg 2016; 20:568-79. [PMID: 26408331 DOI: 10.1007/s11605-015-2960-7] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/24/2015] [Accepted: 09/16/2015] [Indexed: 01/31/2023]
Abstract
BACKGROUND Genomic instability is a common feature in hepatocellular carcinoma. Deregulation of replication licensing factors has been shown to trigger DNA damage response contributing to genomic instability. Overexpression of DNA replication licensing factors chromatin licensing and DNA replication factor 1 (CDT1) and minichromosome maintenance complex component 7 (MCM7) has been previously reported in several human cancers. The aim of the present study was to evaluate the expression and prognostic significance of CDT1 and MCM7 in association with DNA damage response markers and p53 in patients with hepatocellular carcinoma. METHODS Expression of CDT1, MCM7, p-H2A histone family member X (H2AX), phospho-ataxia telangiectasia-mutated (ATM)/ataxia telangiectasia rad3-related (ATR) substrate, and p53 was evaluated by immunohistochemistry on formalin-fixed paraffin-embedded surgical specimens from 111 patients who underwent hepatectomy for hepatocellular carcinoma. Statistical analysis was performed to evaluate associations between the studied proteins, clinicopathological parameters, and patient survival. RESULTS CDT1 expression correlated with p-H2AX (p = 0.038), while MCM7 correlated with p-H2AX and phospho-ATM/ATR substrate (p < 0.001). Increased CDT1 expression was associated with higher tumor grade (p = 0.006) and tumor-node-metastasis (TNM) stage (p = 0.033). High CDT1 expression correlated significantly with reduced overall survival (60.8 and 26.5 % vs 82.8 and 53.0 %, for low CDT1 expression, at 2 and 5 years, respectively, p = 0.012) and was identified by multivariate analysis as an independent predictor of poor overall survival (p = 0.049). CONCLUSIONS Overexpression of CDT1 and MCM7 in hepatocellular carcinoma correlates with DNA damage response, and CDT1 overexpression is a significant prognostic biomarker in hepatocellular carcinoma.
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Affiliation(s)
- Dimitrios Karavias
- Department of Surgery, University Hospital of Patras, Rio, 26500, Greece.
| | - Ioannis Maroulis
- Department of Surgery, University Hospital of Patras, Rio, 26500, Greece
| | - Helen Papadaki
- Department of Anatomy, Histology and Embryology, School of Medicine, University of Patras, Rio, Greece
| | - Charalambos Gogos
- Department of Internal Medicine, University Hospital of Patras, Rio, Greece
| | - Stavros Kakkos
- Department of Vascular Surgery, University Hospital of Patras, Rio, Greece
| | | | - Vasiliki Bravou
- Department of Anatomy, Histology and Embryology, School of Medicine, University of Patras, Rio, Greece
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12
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Re-replication of a centromere induces chromosomal instability and aneuploidy. PLoS Genet 2015; 11:e1005039. [PMID: 25901968 PMCID: PMC4406714 DOI: 10.1371/journal.pgen.1005039] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2014] [Accepted: 01/28/2015] [Indexed: 12/19/2022] Open
Abstract
The faithful inheritance of chromosomes during cell division requires their precise replication and segregation. Numerous mechanisms ensure that each of these fundamental cell cycle events is performed with a high degree of fidelity. The fidelity of chromosomal replication is maintained in part by re-replication controls that ensure there are no more than two copies of every genomic segment to distribute to the two daughter cells. This control is enforced by inhibiting replication initiation proteins from reinitiating replication origins within a single cell cycle. Here we show in Saccharomyces cerevisiae that re-replication control is important for the fidelity of chromosome segregation. In particular, we demonstrate that transient re-replication of centromeric DNA due to disruption of re-replication control greatly induces aneuploidy of the re-replicated chromosome. Some of this aneuploidy arises from missegregation of both sister chromatids to one daughter cell. Aneuploidy can also arise from the generation of an extra sister chromatid via homologous recombination, suggesting that centromeric re-replication can trigger breakage and repair events that expand chromosome number without causing chromosomal rearrangements. Thus, we have identified a potential new non-mitotic source of aneuploidy that can arise from a defect in re-replication control. Given the emerging connections between the deregulation of replication initiation proteins and oncogenesis, this finding may be relevant to the aneuploidy that is prevalent in cancer. The stable inheritance of genetic information requires an elaborate mitotic machinery that acts on the centromeres of chromosomes to ensure their precise segregation. Errors in this segregation can lead to aneuploidy, an unbalanced chromosomal state in which some chromosomes have different copy number than others. Because aneuploidy is associated with developmental abnormalities and diseases such as cancer, there is considerable interest in understanding how these segregation errors arise. Much of this interest has focused on identifying defects in proteins that make up the mitotic machinery. Here, we show that defects in a completely separate process, the control of DNA replication initiation, can lead to chromosome segregation errors as a result of inappropriate re-replication of centromeres. Similar deregulation of replication initiation proteins has been observed in primary human tumors and shown to promote oncogenesis in mouse models. Together, these results raise the possibility that centromeric re-replication may be an additional source of aneuploidy in cancer. In combination with our previous work showing that re-replication is a potent inducer of gene amplification, these results also highlight the versatility of re-replication as a source of genomic instability.
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13
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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.
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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.
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14
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Johansson P, Jeffery J, Al-Ejeh F, Schulz RB, Callen DF, Kumar R, Khanna KK. SCF-FBXO31 E3 ligase targets DNA replication factor Cdt1 for proteolysis in the G2 phase of cell cycle to prevent re-replication. J Biol Chem 2014; 289:18514-25. [PMID: 24828503 DOI: 10.1074/jbc.m114.559930] [Citation(s) in RCA: 43] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
FBXO31 was originally identified as a putative tumor suppressor gene in breast, ovarian, hepatocellular, and prostate cancers. By screening a set of cell cycle-regulated proteins as potential FBXO31 interaction partners, we have now identified Cdt1 as a novel substrate. Cdt1 DNA replication licensing factor is part of the pre-replication complex and essential for the maintenance of genomic integrity. We show that FBXO31 specifically interacts with Cdt1 and regulates its abundance by ubiquitylation leading to subsequent degradation. We also show that Cdt1 regulation by FBXO31 is limited to the G2 phase of the cell cycle and is independent of the pathways previously described for Cdt1 proteolysis in S and G2 phase. FBXO31 targeting of Cdt1 is mediated through the N terminus of Cdt1, a region previously shown to be responsible for its cell cycle regulation. Finally, we show that Cdt1 stabilization due to FBXO31 depletion results in re-replication. Our data present an additional pathway that contributes to the FBXO31 function as a tumor suppressor.
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Affiliation(s)
- Pegah Johansson
- From the Sahlgrenska University Hospital, Department of Clinical Chemistry, Bruna Stråket 16, 41345 Gothenburg, Sweden
| | - Jessie Jeffery
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
| | - Fares Al-Ejeh
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
| | - Renèe B Schulz
- Centre for Personalised Cancer Medicine and Discipline of Medicine, University of Adelaide, Adelaide, South Australia 5000, Australia
| | - David F Callen
- Centre for Personalised Cancer Medicine and Discipline of Medicine, University of Adelaide, Adelaide, South Australia 5000, Australia
| | - Raman Kumar
- School of Paediatrics and Reproductive Health and Discipline of Medicine, University of Adelaide, Adelaide and Women's and Children's Health Research Institute, North Adelaide, South Australia 5006, Australia, and
| | - Kum Kum Khanna
- Signal Transduction Laboratory, QIMR Berghofer Medical Research Institute, Brisbane, Queensland 4006, Australia
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15
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Knockdown of SCF(Skp2) function causes double-parked accumulation in the nucleus and DNA re-replication in Drosophila plasmatocytes. PLoS One 2013; 8:e79019. [PMID: 24205363 PMCID: PMC3812016 DOI: 10.1371/journal.pone.0079019] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2013] [Accepted: 09/18/2013] [Indexed: 12/25/2022] Open
Abstract
In Drosophila, circulating hemocytes are derived from the cephalic mesoderm during the embryonic wave of hematopoiesis. These cells are contributed to the larva and persist through metamorphosis into the adult. To analyze this population of hemocytes, we considered data from a previously published RNAi screen in the hematopoietic niche, which suggested several members of the SCF complex play a role in lymph gland development. eater-Gal4;UAS-GFP flies were crossed to UAS-RNAi lines to knockdown the function of all known SCF complex members in a plasmatocyte-specific fashion, in order to identify which members are novel regulators of plasmatocytes. This specific SCF complex contains five core members: Lin-19-like, SkpA, Skp2, Roc1a and complex activator Nedd8. The complex was identified by its very distinctive large cell phenotype. Furthermore, these large cells stained for anti-P1, a plasmatocyte-specific antibody. It was also noted that the DNA in these cells appeared to be over-replicated. Gamma-tubulin and DAPI staining suggest the cells are undergoing re-replication as they had multiple centrioles and excessive DNA content. Further experimentation determined enlarged cells were BrdU-positive indicating they have progressed through S-phase. To determine how these cells become enlarged and undergo re-replication, cell cycle proteins were analyzed by immunofluorescence. This analysis identified three proteins that had altered subcellular localization in these enlarged cells: Cyclin E, Geminin and Double-parked. Previous research has shown that Double-parked must be degraded to exit S-phase, otherwise the DNA will undergo re-replication. When Double-parked was titrated from the nucleus by an excess of its inhibitor, geminin, the enlarged cells and aberrant protein localization phenotypes were partially rescued. The data in this report suggests that the SCFSkp2 complex is necessary to ubiquitinate Double-parked during plasmatocyte cell division, ensuring proper cell cycle progression and the generation of a normal population of this essential blood cell type.
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16
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Dui W, Wei B, He F, Lu W, Li C, Liang X, Ma J, Jiao R. The Drosophila F-box protein dSkp2 regulates cell proliferation by targeting Dacapo for degradation. Mol Biol Cell 2013; 24:1676-87, S1-7. [PMID: 23552694 PMCID: PMC3667721 DOI: 10.1091/mbc.e12-10-0772] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
dSkp2 regulates cell cycle progression by antagonizing Dap in Drosophila, which resolves the question of whether dSkp2 has a role in regulating Dap stability and suggests the possibility of using Drosophila as a model system in which to study Skp2-mediated tumorigenesis. Cell cycle progression is controlled by a complex regulatory network consisting of interacting positive and negative factors. In humans, the positive regulator Skp2, an F-box protein, has been a subject of intense investigation in part because of its oncogenic activity. By contrast, the molecular and developmental functions of its Drosophila homologue, dSkp2, are poorly understood. Here we investigate the role of dSkp2 by focusing on its functional relationship with Dacapo (Dap), the Drosophila homologue of the cyclin-dependent kinase inhibitors p21cip1/p27kip1/p57kip2. We show that dSkp2 interacts physically with Dap and has a role in targeting Dap for ubiquitination and proteasome-mediated degradation. We present evidence that dSkp2 regulates cell cycle progression by antagonizing Dap in vivo. dSkp2 knockdown reduces cell density in the wing by prolonging the cell doubling time. In addition, the wing phenotype caused by dSkp2 knockdown resembles that caused by dap overexpression and can be partially suppressed by reducing the gene dose of dap. Our study thus documents a conserved functional relationship between dSkp2 and Dap in their control of cell cycle progression, suggesting the possibility of using Drosophila as a model system to study Skp2-mediated tumorigenesis.
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Affiliation(s)
- Wen Dui
- State Key Laboratory of Brain and Cognitive Science, Institute of Biophysics, Chinese Academy of Sciences, Beijing 100101, China
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17
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Ables ET, Drummond-Barbosa D. Cyclin E controls Drosophila female germline stem cell maintenance independently of its role in proliferation by modulating responsiveness to niche signals. Development 2013; 140:530-40. [PMID: 23293285 DOI: 10.1242/dev.088583] [Citation(s) in RCA: 62] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Abstract
Stem cells must proliferate while maintaining 'stemness'; however, much remains to be learned about how factors that control the division of stem cells influence their identity. Multiple stem cell types display cell cycles with short G1 phases, thought to minimize susceptibility to differentiation factors. Drosophila female germline stem cells (GSCs) have short G1 and long G2 phases, and diet-dependent systemic factors often modulate G2. We previously observed that Cyclin E (CycE), a known G1/S regulator, is atypically expressed in GSCs during G2/M; however, it remained unclear whether CycE has cell cycle-independent roles in GSCs or whether it acts exclusively by modulating the cell cycle. In this study, we detected CycE activity during G2/M, reflecting its altered expression pattern, and showed that CycE and its canonical partner, Cyclin-dependent kinase 2 (Cdk2), are required not only for GSC proliferation, but also for GSC maintenance. In genetic mosaics, CycE- and Cdk2-deficient GSCs are rapidly lost from the niche, remain arrested in a G1-like state, and undergo excessive growth and incomplete differentiation. However, we found that CycE controls GSC maintenance independently of its role in the cell cycle; GSCs harboring specific hypomorphic CycE mutations are not efficiently maintained despite normal proliferation rates. Finally, CycE-deficient GSCs have an impaired response to niche bone morphogenetic protein signals that are required for GSC self-renewal, suggesting that CycE modulates niche-GSC communication. Taken together, these results show unequivocally that the roles of CycE/Cdk2 in GSC division cycle regulation and GSC maintenance are separable, and thus potentially involve distinct sets of phosphorylation targets.
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Affiliation(s)
- Elizabeth T Ables
- Department of Biochemistry and Molecular Biology, Bloomberg School of Public Health, Johns Hopkins University, Baltimore, MD 21205, USA
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18
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Abstract
One of the fundamental challenges facing the cell is to accurately copy its genetic material to daughter cells. When this process goes awry, genomic instability ensues in which genetic alterations ranging from nucleotide changes to chromosomal translocations and aneuploidy occur. Organisms have developed multiple mechanisms that can be classified into two major classes to ensure the fidelity of DNA replication. The first class includes mechanisms that prevent premature initiation of DNA replication and ensure that the genome is fully replicated once and only once during each division cycle. These include cyclin-dependent kinase (CDK)-dependent mechanisms and CDK-independent mechanisms. Although CDK-dependent mechanisms are largely conserved in eukaryotes, higher eukaryotes have evolved additional mechanisms that seem to play a larger role in preventing aberrant DNA replication and genome instability. The second class ensures that cells are able to respond to various cues that continuously threaten the integrity of the genome by initiating DNA-damage-dependent "checkpoints" and coordinating DNA damage repair mechanisms. Defects in the ability to safeguard against aberrant DNA replication and to respond to DNA damage contribute to genomic instability and the development of human malignancy. In this article, we summarize our current knowledge of how genomic instability arises, with a particular emphasis on how the DNA replication process can give rise to such instability.
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Affiliation(s)
- Tarek Abbas
- Department of Biochemistry and Molecular Genetics, University of Virginia, Charlottesville, Virginia 22908, USA
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19
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Shi HJ, Wen JK, Miao SB, Liu Y, Zheng B. KLF5 and hhLIM cooperatively promote proliferation of vascular smooth muscle cells. Mol Cell Biochem 2012; 367:185-94. [DOI: 10.1007/s11010-012-1332-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2012] [Accepted: 05/03/2012] [Indexed: 12/11/2022]
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Klotz-Noack K, McIntosh D, Schurch N, Pratt N, Blow JJ. Re-replication induced by geminin depletion occurs from G2 and is enhanced by checkpoint activation. J Cell Sci 2012; 125:2436-45. [PMID: 22366459 PMCID: PMC3481538 DOI: 10.1242/jcs.100883] [Citation(s) in RCA: 50] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To prevent re-replication of DNA in a single cell cycle, the licensing of replication origins by Mcm2-7 is prevented during S and G2 phases. Animal cells achieve this by cell-cycle-regulated proteolysis of the essential licensing factor Cdt1 and inhibition of Cdt1 by geminin. Here we investigate the consequences of ablating geminin in synchronised human U2OS cells. Following geminin loss, cells complete an apparently normal S phase, but a proportion arrest at the G2-M boundary. When Cdt1 accumulates in these cells, DNA re-replicates, suggesting that the key role of geminin is to prevent re-licensing in G2. If cell cycle checkpoints are inhibited in cells lacking geminin, cells progress through mitosis and less re-replication occurs. Checkpoint kinases thereby amplify re-replication into an all-or-nothing response by delaying geminin-depleted cells in G2. Deep DNA sequencing revealed no preferential re-replication of specific genomic regions after geminin depletion. This is consistent with the observation that cells in G2 have lost their replication timing information. By contrast, when Cdt1 is overexpressed or is stabilised by the neddylation inhibitor MLN4924, re-replication can occur throughout S phase.
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Affiliation(s)
- Kathleen Klotz-Noack
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Debbie McIntosh
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
| | - Nicholas Schurch
- Data Analysis Group, College of Life Sciences, University of Dundee DD1 5EH, UK
| | - Norman Pratt
- Department of Human Genetics, Ninewells Hospital, Dundee DD1 9SY, UK
| | - J. Julian Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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21
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Stathopoulou A, Roukos V, Petropoulou C, Kotsantis P, Karantzelis N, Nishitani H, Lygerou Z, Taraviras S. Cdt1 is differentially targeted for degradation by anticancer chemotherapeutic drugs. PLoS One 2012; 7:e34621. [PMID: 22479651 PMCID: PMC3316709 DOI: 10.1371/journal.pone.0034621] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2011] [Accepted: 03/02/2012] [Indexed: 01/01/2023] Open
Abstract
BACKGROUND Maintenance of genome integrity is crucial for the propagation of the genetic information. Cdt1 is a major component of the pre-replicative complex, which controls once per cell cycle DNA replication. Upon DNA damage, Cdt1 is rapidly targeted for degradation. This targeting has been suggested to safeguard genomic integrity and prevent re-replication while DNA repair is in progress. Cdt1 is deregulated in tumor specimens, while its aberrant expression is linked with aneuploidy and promotes tumorigenesis in animal models. The induction of lesions in DNA is a common mechanism by which many cytotoxic anticancer agents operate, leading to cell cycle arrest and apoptosis. METHODOLOGY/PRINCIPAL FINDING In the present study we examine the ability of several anticancer drugs to target Cdt1 for degradation. We show that treatment of HeLa and HepG2 cells with MMS, Cisplatin and Doxorubicin lead to rapid proteolysis of Cdt1, whereas treatment with 5-Fluorouracil and Tamoxifen leave Cdt1 expression unaffected. Etoposide affects Cdt1 stability in HepG2 cells and not in HeLa cells. RNAi experiments suggest that Cdt1 proteolysis in response to MMS depends on the presence of the sliding clamp PCNA. CONCLUSION/SIGNIFICANCE Our data suggest that treatment of tumor cells with commonly used chemotherapeutic agents induces differential responses with respect to Cdt1 proteolysis. Information on specific cellular targets in response to distinct anticancer chemotherapeutic drugs in different cancer cell types may contribute to the optimization of the efficacy of chemotherapy.
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Affiliation(s)
| | - Vassilis Roukos
- Department of General Biology, Medical School, University of Patras, Patras, Greece
| | | | - Panagiotis Kotsantis
- Department of General Biology, Medical School, University of Patras, Patras, Greece
| | | | - Hideo Nishitani
- Department of Biological Signaling, Graduate School of Life Science, University of Hyogo, Hyogo, Japan
| | - Zoi Lygerou
- Department of General Biology, Medical School, University of Patras, Patras, Greece
| | - Stavros Taraviras
- Department of Physiology, Medical School, University of Patras, Patras, Greece
- * E-mail:
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22
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Su TT. Safeguarding genetic information in Drosophila. Chromosoma 2011; 120:547-55. [PMID: 21927823 DOI: 10.1007/s00412-011-0342-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2011] [Revised: 08/24/2011] [Accepted: 08/26/2011] [Indexed: 12/11/2022]
Abstract
Eukaryotic cells employ a plethora of conserved proteins and mechanisms to ensure genome integrity. In metazoa, these mechanisms must operate in the context of organism development. This mini-review highlights two emerging features of DNA damage responses in Drosophila: a crosstalk between DNA damage responses and components of the spindle assembly checkpoint, and increasing evidence for the effect of DNA damage on the developmental program at multiple points during the Drosophila life cycle.
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Affiliation(s)
- Tin Tin Su
- MCD Biology, University of Colorado, Boulder, USA.
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23
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Gardner L, Malik R, Shimizu Y, Mullins N, ElShamy WM. Geminin overexpression prevents the completion of topoisomerase IIα chromosome decatenation, leading to aneuploidy in human mammary epithelial cells. Breast Cancer Res 2011; 13:R53. [PMID: 21595939 PMCID: PMC3218940 DOI: 10.1186/bcr2884] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2010] [Revised: 04/16/2011] [Accepted: 05/19/2011] [Indexed: 11/10/2022] Open
Abstract
INTRODUCTION The nuclear enzyme topoisomerase IIα (TopoIIα) is able to cleave DNA in a reversible manner, making it a valuable target for agents such as etoposide that trap the enzyme in a covalent bond with the 5' DNA end to which it cleaves. This prevents DNA religation and triggers cell death in cancer cells. However, development of resistance to these agents limits their therapeutic use. In this study, we examined the therapeutic targeting of geminin for improving the therapeutic potential of TopoIIα agents. METHODS Human mammary epithelial (HME) cells and several breast cancer cell lines were used in this study. Geminin, TopoIIα and cell division cycle 7 (Cdc7) silencing were done using specific small interfering RNA. Transit or stable inducible overexpression of these proteins and casein kinase Iε (CKIε) were also used, as well as several pharmacological inhibitors that target TopoIIα, Cdc7 or CKIε. We manipulated HME cells that expressed H2B-GFP, or did not, to detect chromosome bridges. Immunoprecipitation and direct Western blot analysis were used to detect interactions between these proteins and their total expression, respectively, whereas interactions on chromosomal arms were detected using a trapped in agarose DNA immunostaining assay. TopoIIα phosphorylation by Cdc7 or CKIε was done using an in vitro kinase assay. The TopoGen decatenation kit was used to measure TopoIIα decatenation activity. Finally, a comet assay and metaphase chromosome spread were used to detect chromosome breakage and changes in chromosome condensation or numbers, respectively. RESULTS We found that geminin and TopoIIα interact primarily in G2/M/early G1 cells on chromosomes, that geminin recruits TopoIIα to chromosomal decatenation sites or vice versa and that geminin silencing in HME cells triggers the formation of chromosome bridges by suppressing TopoIIα access to chromosomal arms. CKIε kinase phosphorylates and positively regulates TopoIIα chromosome localization and function. CKIε kinase overexpression or Cdc7 kinase silencing, which we show phosphorylates TopoIIα in vitro, restored DNA decatenation and chromosome segregation in geminin-silenced cells before triggering cell death. In vivo, at normal concentration, geminin recruits the deSUMOylating sentrin-specific proteases SENP1 and SENP2 enzymes to deSUMOylate chromosome-bound TopoIIα and promote its release from chromosomes following completion of DNA decatenation. In cells overexpressing geminin, premature departure of TopoIIα from chromosomes is thought to be due to the fact that geminin recruits more of these deSUMOylating enzymes, or recruits them earlier, to bound TopoIIα. This triggers premature release of TopoIIα from chromosomes, which we propose induces aneuploidy in HME cells, since chromosome breakage generated through this mechanism were not sensed and/or repaired and the cell cycle was not arrested. Expression of mitosis-inducing proteins such as cyclin A and cell division kinase 1 was also increased in these cells because of the overexpression of geminin. CONCLUSIONS TopoIIα recruitment and its chromosome decatenation function require a normal level of geminin. Geminin silencing induces a cytokinetic checkpoint in which Cdc7 phosphorylates TopoIIα and inhibits its chromosomal recruitment and decatenation and/or segregation function. Geminin overexpression prematurely deSUMOylates TopoIIα, triggering its premature departure from chromosomes and leading to chromosomal abnormalities and the formation of aneuploid, drug-resistant cancer cells. On the basis of our findings, we propose that therapeutic targeting of geminin is essential for improving the therapeutic potential of TopoIIα agents.
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Affiliation(s)
- Lauren Gardner
- Cancer Institute, Department of Biochemistry, University of Mississippi Medical Center, Jackson, 39216, USA
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24
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Deckbar D, Jeggo PA, Löbrich M. Understanding the limitations of radiation-induced cell cycle checkpoints. Crit Rev Biochem Mol Biol 2011; 46:271-83. [PMID: 21524151 PMCID: PMC3171706 DOI: 10.3109/10409238.2011.575764] [Citation(s) in RCA: 151] [Impact Index Per Article: 11.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
The DNA damage response pathways involve processes of double-strand break (DSB) repair and cell cycle checkpoint control to prevent or limit entry into S phase or mitosis in the presence of unrepaired damage. Checkpoints can function to permanently remove damaged cells from the actively proliferating population but can also halt the cell cycle temporarily to provide time for the repair of DSBs. Although efficient in their ability to limit genomic instability, checkpoints are not foolproof but carry inherent limitations. Recent work has demonstrated that the G1/S checkpoint is slowly activated and allows cells to enter S phase in the presence of unrepaired DSBs for about 4–6 h post irradiation. During this time, only a slowing but not abolition of S-phase entry is observed. The G2/M checkpoint, in contrast, is quickly activated but only responds to a level of 10–20 DSBs such that cells with a low number of DSBs do not initiate the checkpoint or terminate arrest before repair is complete. Here, we discuss the limitations of these checkpoints in the context of the current knowledge of the factors involved. We suggest that the time needed to fully activate G1/S arrest reflects the existence of a restriction point in G1-phase progression. This point has previously been defined as the point when mitogen starvation fails to prevent cells from entering S phase. However, cells that passed the restriction point can respond to DSBs, albeit with reduced efficiency.
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Affiliation(s)
- Dorothee Deckbar
- Darmstadt University of Technology, Radiation Biology and DNA Repair, Darmstadt, Germany
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25
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Guernsey DL, Matsuoka M, Jiang H, Evans S, Macgillivray C, Nightingale M, Perry S, Ferguson M, LeBlanc M, Paquette J, Patry L, Rideout AL, Thomas A, Orr A, McMaster CR, Michaud JL, Deal C, Langlois S, Superneau DW, Parkash S, Ludman M, Skidmore DL, Samuels ME. Mutations in origin recognition complex gene ORC4 cause Meier-Gorlin syndrome. Nat Genet 2011; 43:360-4. [PMID: 21358631 DOI: 10.1038/ng.777] [Citation(s) in RCA: 132] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Accepted: 01/14/2011] [Indexed: 12/17/2022]
Abstract
Meier-Gorlin syndrome is a rare autosomal recessive genetic condition whose primary clinical hallmarks include small stature, small external ears and small or absent patellae. Using marker-assisted mapping in multiple families from a founder population and traditional coding exon sequencing of positional candidate genes, we identified three different mutations in the gene encoding ORC4, a component of the eukaryotic origin recognition complex, in five individuals with Meier-Gorlin syndrome. In two such individuals that were negative for mutations in ORC4, we found potential mutations in ORC1 and CDT1, two other genes involved in origin recognition. ORC4 is well conserved in eukaryotes, and the yeast equivalent of the human ORC4 missense mutation was shown to be pathogenic in functional assays of cell growth. This is the first report, to our knowledge, of a germline mutation in any gene of the origin recognition complex in a vertebrate organism.
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Affiliation(s)
- Duane L Guernsey
- Department of Pathology, Dalhousie University, Halifax, Nova Scotia, Canada
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26
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Roukos V, Kinkhabwala A, Colombelli J, Kotsantis P, Taraviras S, Nishitani H, Stelzer E, Bastiaens P, Lygerou Z. Dynamic recruitment of licensing factor Cdt1 to sites of DNA damage. J Cell Sci 2011; 124:422-34. [PMID: 21224399 DOI: 10.1242/jcs.074229] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
For genomic integrity to be maintained, the cell cycle and DNA damage responses must be linked. Cdt1, a G1-specific cell-cycle factor, is targeted for proteolysis by the Cul4-Ddb1(Cdt2) ubiquitin ligase following DNA damage. Using a laser nanosurgery microscope to generate spatially restricted DNA damage within the living cell nucleus, we show that Cdt1 is recruited onto damaged sites in G1 phase cells, within seconds of DNA damage induction. PCNA, Cdt2, Cul4, DDB1 and p21(Cip1) also accumulate rapidly to damaged sites. Cdt1 recruitment is PCNA-dependent, whereas PCNA and Cdt2 recruitment are independent of Cdt1. Fitting of fluorescence recovery after photobleaching profiles to an analytic reaction-diffusion model shows that Cdt1 and p21(Cip1) exhibit highly dynamic binding at the site of damage, whereas PCNA appears immobile. Cdt2 exhibits both a rapidly exchanging and an apparently immobile subpopulation. Our data suggest that PCNA provides an immobile binding interface for dynamic Cdt1 interactions at the site of damage, which leads to rapid Cdt1 recruitment to damaged DNA, preceding Cdt1 degradation.
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Affiliation(s)
- Vassilis Roukos
- Department of General Biology, School of Medicine, University of Patras, 26500 Rio, Patras, Greece
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27
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Maqbool SB, Mehrotra S, Kolpakas A, Durden C, Zhang B, Zhong H, Calvi BR. Dampened activity of E2F1-DP and Myb-MuvB transcription factors in Drosophila endocycling cells. J Cell Sci 2010; 123:4095-106. [PMID: 21045111 DOI: 10.1242/jcs.064519] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
The endocycle is a variant cell cycle comprised of alternating gap (G) and DNA synthesis (S) phases (endoreplication) without mitosis (M), which results in DNA polyploidy and large cell size. Endocycles occur widely in nature, but much remains to be learned about the regulation of this modified cell cycle. Here, we compared gene expression profiles of mitotic cycling larval brain and disc cells with the endocycling cells of fat body and salivary gland of the Drosophila larva. The results indicated that many genes that are positively regulated by the heterodimeric E2F1-DP or Myb-MuvB complex transcription factors are expressed at lower levels in endocycling cells. Many of these target genes have functions in M phase, suggesting that dampened E2F1 and Myb activity promote endocycles. Many other E2F1 target genes that are required for DNA replication were also repressed in endocycling cells, an unexpected result given that these cells must duplicate up to thousands of genome copies during each S phase. For some EF2-regulated genes, the lower level of mRNA in endocycling cells resulted in lower protein concentration, whereas for other genes it did not, suggesting a contribution of post-transcriptional regulation. Both knockdown and overexpression of E2F1-DP and Myb-MuvB impaired endocycles, indicating that transcriptional activation and repression must be balanced. Our data suggest that dampened transcriptional activation by E2F1-DP and Myb-MuvB is important to repress mitosis and coordinate the endocycle transcriptional and protein stability oscillators.
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28
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Ding Q, MacAlpine DM. Preferential re-replication of Drosophila heterochromatin in the absence of geminin. PLoS Genet 2010; 6:e1001112. [PMID: 20838463 PMCID: PMC2936543 DOI: 10.1371/journal.pgen.1001112] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2010] [Accepted: 08/05/2010] [Indexed: 01/04/2023] Open
Abstract
To ensure genomic integrity, the genome must be duplicated exactly once per cell cycle. Disruption of replication licensing mechanisms may lead to re-replication and genomic instability. Cdt1, also known as Double-parked (Dup) in Drosophila, is a key regulator of the assembly of the pre-replicative complex (pre-RC) and its activity is strictly limited to G1 by multiple mechanisms including Cul4-Ddb1 mediated proteolysis and inhibition by geminin. We assayed the genomic consequences of disregulating the replication licensing mechanisms by RNAi depletion of geminin. We found that not all origins of replication were sensitive to geminin depletion and that heterochromatic sequences were preferentially re-replicated in the absence of licensing mechanisms. The preferential re-activation of heterochromatic origins of replication was unexpected because these are typically the last sequences to be duplicated in a normal cell cycle. We found that the re-replication of heterochromatin was regulated not at the level of pre-RC activation, but rather by the formation of the pre-RC. Unlike the global assembly of the pre-RC that occurs throughout the genome in G1, in the absence of geminin, limited pre-RC assembly was restricted to the heterochromatin by elevated cyclin A-CDK activity. These results suggest that there are chromatin and cell cycle specific controls that regulate the re-assembly of the pre-RC outside of G1. Catastrophic consequences may occur if the cell fails to either completely copy the genome or if it duplicates some regions of the genome more than once in a cell cycle. The cell must coordinate thousands of DNA replication start sites (origins) to ensure that the entire genome is copied and that no replication origin is activated more than once in a cell cycle. The cell accomplishes this coordination by confining the selection and activation of replication origins to discrete phases of the cell cycle. Start sites can only be selected or ‘licensed’ for DNA replication in G1 and similarly, they can only be activated for the initiation of DNA replication in S phase. Disruption of the mechanisms that regulate this ‘licensing’ process have been shown to result in extensive re-replication, genomic instability and tumorigenesis in a variety of eukaryotic systems. Here we use genomic approaches in Drosophila to identify which origins of replication are susceptible to re-initiation of DNA replication in the absence of replication licensing controls. Unexpectedly, we find that sequences in the heterochromatin, which were thought to contain only inefficient origins of replication, are preferentially re-replicated. These results provide insights into how origins of replication are selected and regulated in distinct chromatin environments to maintain genomic stability.
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Affiliation(s)
- Queying Ding
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, United States of America
| | - David M. MacAlpine
- Department of Pharmacology and Cancer Biology, Duke University Medical Center, Durham, North Carolina, United States of America
- * E-mail:
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Lee HO, Zacharek SJ, Xiong Y, Duronio RJ. Cell type-dependent requirement for PIP box-regulated Cdt1 destruction during S phase. Mol Biol Cell 2010; 21:3639-53. [PMID: 20826610 PMCID: PMC2965682 DOI: 10.1091/mbc.e10-02-0130] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Previous studies have shown that Cdt1 overexpression in cultured cells can trigger re-replication, but not whether CRL4Cdt2-triggered destruction of Cdt1 is required for normal mitotic cell cycle progression in vivo. We demonstrate that PIP box–mediated destruction of Cdt1Dup during S phase is necessary for the cell division cycle in Drosophila. DNA synthesis–coupled proteolysis of the prereplicative complex component Cdt1 by the CRL4Cdt2 E3 ubiquitin ligase is thought to help prevent rereplication of the genome during S phase. To directly test whether CRL4Cdt2-triggered destruction of Cdt1 is required for normal cell cycle progression in vivo, we expressed a mutant version of Drosophila Cdt1 (Dup), which lacks the PCNA-binding PIP box (DupΔPIP) and which cannot be regulated by CRL4Cdt2. DupΔPIP is inappropriately stabilized during S phase and causes developmental defects when ectopically expressed. DupΔPIP restores DNA synthesis to dup null mutant embryonic epidermal cells, but S phase is abnormal, and these cells do not progress into mitosis. In contrast, DupΔPIP accumulation during S phase did not adversely affect progression through follicle cell endocycles in the ovary. In this tissue the combination of DupΔPIP expression and a 50% reduction in Geminin gene dose resulted in egg chamber degeneration. We could not detect Dup hyperaccumulation using mutations in the CRL4Cdt2 components Cul4 and Ddb1, likely because these cause pleiotropic effects that block cell proliferation. These data indicate that PIP box–mediated destruction of Dup is necessary for the cell division cycle and suggest that Geminin inhibition can restrain DupΔPIP activity in some endocycling cell types.
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Affiliation(s)
- Hyun O Lee
- Curriculum in Genetics and Molecular Biology, Department of Biochemistry and Biophysics, Lineberger Comprehensive Cancer Center, and Program in Molecular Biology and Biotechnology, University of North Carolina, Chapel Hill, NC 27599, USA
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LaFever L, Feoktistov A, Hsu HJ, Drummond-Barbosa D. Specific roles of Target of rapamycin in the control of stem cells and their progeny in the Drosophila ovary. Development 2010; 137:2117-26. [PMID: 20504961 PMCID: PMC2882131 DOI: 10.1242/dev.050351] [Citation(s) in RCA: 111] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/26/2010] [Indexed: 12/21/2022]
Abstract
Stem cells depend on intrinsic and local factors to maintain their identity and activity, but they also sense and respond to changing external conditions. We previously showed that germline stem cells (GSCs) and follicle stem cells (FSCs) in the Drosophila ovary respond to diet via insulin signals. Insulin signals directly modulate the GSC cell cycle at the G2 phase, but additional unknown dietary mediators control both G1 and G2. Target of rapamycin, or TOR, is part of a highly conserved nutrient-sensing pathway affecting growth, proliferation, survival and fertility. Here, we show that optimal TOR activity maintains GSCs but does not play a major role in FSC maintenance, suggesting differential regulation of GSCs versus FSCs. TOR promotes GSC proliferation via G2 but independently of insulin signaling, and TOR is required for the proliferation, growth and survival of differentiating germ cells. We also report that TOR controls the proliferation of FSCs but not of their differentiating progeny. Instead, TOR controls follicle cell number by promoting survival, independently of either the apoptotic or autophagic pathways. These results uncover specific TOR functions in the control of stem cells versus their differentiating progeny, and reveal parallels between Drosophila and mammalian follicle growth.
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Affiliation(s)
- Leesa LaFever
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Biochemistry and Molecular Biology, Division of Reproductive Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
| | - Alexander Feoktistov
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
| | - Hwei-Jan Hsu
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Biochemistry and Molecular Biology, Division of Reproductive Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
| | - Daniela Drummond-Barbosa
- Department of Cell and Developmental Biology, Vanderbilt University Medical Center, Nashville, TN 37232, USA
- Department of Biochemistry and Molecular Biology, Division of Reproductive Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
- Department of Environmental Health Sciences, Division of Reproductive Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
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31
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De Marco V, Gillespie PJ, Li A, Karantzelis N, Christodoulou E, Klompmaker R, van Gerwen S, Fish A, Petoukhov MV, Iliou MS, Lygerou Z, Medema RH, Blow JJ, Svergun DI, Taraviras S, Perrakis A. Quaternary structure of the human Cdt1-Geminin complex regulates DNA replication licensing. Proc Natl Acad Sci U S A 2009; 106:19807-12. [PMID: 19906994 PMCID: PMC2775996 DOI: 10.1073/pnas.0905281106] [Citation(s) in RCA: 62] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2009] [Indexed: 01/12/2023] Open
Abstract
All organisms need to ensure that no DNA segments are rereplicated in a single cell cycle. Eukaryotes achieve this through a process called origin licensing, which involves tight spatiotemporal control of the assembly of prereplicative complexes (pre-RCs) onto chromatin. Cdt1 is a key component and crucial regulator of pre-RC assembly. In higher eukaryotes, timely inhibition of Cdt1 by Geminin is essential to prevent DNA rereplication. Here, we address the mechanism of DNA licensing inhibition by Geminin, by combining X-ray crystallography, small-angle X-ray scattering, and functional studies in Xenopus and mammalian cells. Our findings show that the Cdt1:Geminin complex can exist in two distinct forms, a "permissive" heterotrimer and an "inhibitory" heterohexamer. Specific Cdt1 residues, buried in the heterohexamer, are important for licensing. We postulate that the transition between the heterotrimer and the heterohexamer represents a molecular switch between licensing-competent and licensing-defective states.
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Affiliation(s)
- V. De Marco
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - P. J. Gillespie
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - A. Li
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | | | - E. Christodoulou
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - R. Klompmaker
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - S. van Gerwen
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - A. Fish
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
| | - M. V. Petoukhov
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | - M. S. Iliou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - Z. Lygerou
- Biology, Medical School, University of Patras, 26500 Rio, Patras, Greece
| | - R. H. Medema
- Department of Medical Oncology and Cancer Genomics Center, Laboratory of Experimental Oncology, University Medical Center Utrecht, Universiteitsweg 100, 3584CG Utrecht, The Netherlands; and
| | - J. J. Blow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee DD1 5EH, United Kingdom
| | - D. I. Svergun
- European Molecular Biology Laboratory, Hamburg Outstation, Notkestrasse 85, D-22603 Hamburg, Germany
| | | | - A. Perrakis
- Department of Biochemistry, Netherlands Cancer Institute, Plesmanlaan 121, 1066CX Amsterdam, The Netherlands
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Narasimhachar Y, Coué M. Geminin stabilizes Cdt1 during meiosis in Xenopus oocytes. J Biol Chem 2009; 284:27235-42. [PMID: 19656945 DOI: 10.1074/jbc.m109.008854] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
During the mitotic cell cycle, Geminin can act both as a promoter and inhibitor of initiation of DNA replication. As a promoter, Geminin stabilizes Cdt1 and facilitates its accumulation leading to the assembly of the pre-replication complex on DNA. As an inhibitor, Geminin prevents Cdt1 from loading the mini-chromosome maintenance complex onto pre-replication complexes in late S, G(2), and M phases. Here we show that during meiosis Geminin functions as a stabilizer of Cdt1 promoting its accumulation for the early division cycles of the embryo. Depletion of Geminin in Xenopus immature oocytes leads to a decrease of Cdt1 protein levels during maturation and after activation of these oocytes. Injection of exogenous recombinant Geminin into the depleted oocytes rescues Cdt1 levels demonstrating that Geminin stabilizes Cdt1 during meiosis and after fertilization. Furthermore, Geminin-depleted oocytes did not replicate their DNA after meiosis I indicating that Geminin does not act as an inhibitor of initiation of DNA replication between meiosis I and meiosis II.
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Affiliation(s)
- Yadushyla Narasimhachar
- Department of Cell Biology and Biochemistry, Texas Tech University Health Sciences Center, Lubbock, Texas 79430, USA.
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Abstract
Eukaryotic cells normally restrict genome duplication to once per cell division. In metazoa, re-replication of DNA during a single S phase seems to be prevented solely by suppressing CDT1 activity, a protein required for loading the replicative MCM DNA helicase. However, siRNA suppression of geminin (a specific inhibitor of CDT1) arrested proliferation only of cells derived from cancers by inducing DNA re-replication and DNA damage that spontaneously triggered apoptosis. None of these effects were detected either in cells derived from normal human tissues or in cells immortalized by a viral oncogene. To induce these effects in noncancer cells required suppression of both geminin and cyclin A, another cell cycle regulator. Therefore, initiating DNA replication in some cancer cells is limited solely by regulating the level of CDT1 activity with geminin, whereas noncancer cells contain additional safeguards that prevent DNA re-replication. These results show that inhibition of geminin activity could be used to selectively kill cancer cells without harming other cells.
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Affiliation(s)
- Wenge Zhu
- National Institute of Child Health and Human Development, NIH, Bethesda, Maryland 20892-2753, USA
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34
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Rampakakis E, Arvanitis DN, Di Paola D, Zannis-Hadjopoulos M. Metazoan origins of DNA replication: regulation through dynamic chromatin structure. J Cell Biochem 2009; 106:512-20. [PMID: 19173303 DOI: 10.1002/jcb.22070] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
DNA replication in eukaryotes is initiated at multiple replication origins distributed over the entire genome, which are normally activated once per cell cycle. Due to the complexity of the metazoan genome, the study of metazoan replication origins and their activity profiles has been less advanced than in simpler genome systems. DNA replication in eukaryotes involves many protein-protein and protein-DNA interactions, occurring in multiple stages. As in prokaryotes, control over the timing and frequency of initiation is exerted at the initiation site. A prerequisite for understanding the regulatory mechanisms of eukaryotic DNA replication is the identification and characterization of the cis-acting sequences that serve as replication origins and the trans-acting factors (proteins) that interact with them. Furthermore, in order to understand how DNA replication may become deregulated in malignant cells, the distinguishing features between normal and malignant origins of DNA replication as well as the proteins that interact with them must be determined. Based on advances that were made using simple genome model systems, several proteins involved in DNA replication have been identified. This review summarizes the current findings about metazoan origins of DNA replication and their interacting proteins as well as the role of chromatin structure in their regulation. Furthermore, progress in origin identification and isolation procedures as well as potential mechanisms to inhibit their activation in cancer development and progression are discussed.
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Affiliation(s)
- E Rampakakis
- Department of Biochemistry, Goodman Cancer Centre, Montreal, Quebec, Canada
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35
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Shultz RW, Lee TJ, Allen GC, Thompson WF, Hanley-Bowdoin L. Dynamic localization of the DNA replication proteins MCM5 and MCM7 in plants. PLANT PHYSIOLOGY 2009; 150:658-69. [PMID: 19357199 PMCID: PMC2689970 DOI: 10.1104/pp.109.136614] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/04/2009] [Accepted: 04/02/2009] [Indexed: 05/21/2023]
Abstract
Genome integrity in eukaryotes depends on licensing mechanisms that prevent loading of the minichromosome maintenance complex (MCM2-7) onto replicated DNA during S phase. Although the principle of licensing appears to be conserved across all eukaryotes, the mechanisms that control it vary, and it is not clear how licensing is regulated in plants. In this work, we demonstrate that subunits of the MCM2-7 complex are coordinately expressed during Arabidopsis (Arabidopsis thaliana) development and are abundant in proliferating and endocycling tissues, indicative of a role in DNA replication. We show that endogenous MCM5 and MCM7 proteins are localized in the nucleus during G1, S, and G2 phases of the cell cycle and are released into the cytoplasmic compartment during mitosis. We also show that MCM5 and MCM7 are topologically constrained on DNA and that the MCM complex is stable under high-salt conditions. Our results are consistent with a conserved replicative helicase function for the MCM complex in plants but not with the idea that plants resemble budding yeast by actively exporting the MCM complex from the nucleus to prevent unauthorized origin licensing and rereplication during S phase. Instead, our data show that, like other higher eukaryotes, the MCM complex in plants remains in the nucleus throughout most of the cell cycle and is only dispersed in mitotic cells.
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Affiliation(s)
- Randall W Shultz
- Department of Molecular and Structural Biochemistry , North Carolina State University, Raleigh, North Carolina 27695-7651, USA.
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Sugimoto N, Yoshida K, Tatsumi Y, Yugawa T, Narisawa-Saito M, Waga S, Kiyono T, Fujita M. Redundant and differential regulation of multiple licensing factors ensures prevention of re-replication in normal human cells. J Cell Sci 2009; 122:1184-91. [DOI: 10.1242/jcs.041889] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
When human cells enter S-phase, overlapping differential inhibitory mechanisms downregulate the replication licensing factors ORC1, CDC6 and Cdt1. Such regulation prevents re-replication so that deregulation of any individual factor alone would not be expected to induce overt re-replication. However, this has been challenged by the fact that overexpression of Cdt1 or Cdt1+CDC6 causes re-replication in some cancer cell lines. We thought it important to analyze licensing regulations in human non-cancerous cells that are resistant to Cdt1-induced re-replication and examined whether simultaneous deregulation of these licensing factors induces re-replication in two such cell lines, including human fibroblasts immortalized by telomerase. Individual overexpression of either Cdt1, ORC1 or CDC6 induced no detectable re-replication. However, with Cdt1+ORC1 or Cdt1+CDC6, some re-replication was detectable and coexpression of Cdt1+ORC1+CDC6 synergistically acted to give strong re-replication with increased mini-chromosome maintenance (MCM) loading. Coexpression of ORC1+CDC6 was without effect. These results suggest that, although Cdt1 regulation is the key step, differential regulation of multiple licensing factors ensures prevention of re-replication in normal human cells. Our findings also show for the first time the importance of ORC1 regulation for prevention of re-replication.
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Affiliation(s)
- Nozomi Sugimoto
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
- Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyouku, Tokyo 112-8679, Japan
| | - Kazumasa Yoshida
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Yasutoshi Tatsumi
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
- Division of Biochemistry, Chiba Cancer Center Research Institute, 666-2 Nitona, Chuohku, Chiba 260-8717, Japan
| | - Takashi Yugawa
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Mako Narisawa-Saito
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Shou Waga
- Faculty of Science, Japan Women's University, 2-8-1 Mejirodai, Bunkyouku, Tokyo 112-8679, Japan
| | - Tohru Kiyono
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
| | - Masatoshi Fujita
- Virology Division, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuohku, Tokyo 104-0045, Japan
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Mehrotra S, Maqbool SB, Kolpakas A, Murnen K, Calvi BR. Endocycling cells do not apoptose in response to DNA rereplication genotoxic stress. Genes Dev 2009; 22:3158-71. [PMID: 19056894 DOI: 10.1101/gad.1710208] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Initiation of DNA replication at origins more than once per cell cycle results in rereplication and has been implicated in cancer. Here we use Drosophila to examine the checkpoint responses to rereplication in a developmental context. We find that increased Double-parked (Dup), the Drosophila ortholog of Cdt1, results in rereplication and DNA damage. In most cells, this rereplication triggers caspase activation and apoptotic cell death mediated by both p53-dependent and -independent pathways. Elevated Dup also caused DNA damage in endocycling cells, which switch to a G/S cycle during normal development, indicating that rereplication and the endocycling DNA reduplication program are distinct processes. Unexpectedly, however, endocycling cells do not apoptose regardless of tissue type. Our combined evidence suggests that endocycling apoptosis is repressed in part because proapoptotic gene promoters are silenced. Normal endocycling cells had DNA lesions near heterochromatin, which increased after rereplication, explaining why endocycling cells must constantly repress the genotoxic apoptotic response. Our results reveal a novel regulation of apoptosis in development and new insights into the little-understood endocycle. Similar mechanisms may operate during vertebrate development, with implications for cancer predisposition in certain tissues.
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Affiliation(s)
- Sonam Mehrotra
- Department of Biology, Syracuse University, Syracuse, New York 13244, USA
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38
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Abstract
In mammals, trophoblast giant (TG) cell differentiation is characterized by a physiological endoreduplication, resulting in genome size augmentation. A recent study by Ullah and colleagues (pp. 3024-3036), published in this issue of Genes & Development, now elucidates the role of the cyclin-dependent kinase inhibitors (CKIs), p21 and p57, in mammalian endocycle regulation.
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Narbonne-Reveau K, Lilly M. The Cyclin-dependent kinase inhibitor Dacapo promotes genomic stability during premeiotic S phase. Mol Biol Cell 2009; 20:1960-9. [PMID: 19211840 DOI: 10.1091/mbc.e08-09-0916] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The proper execution of premeiotic S phase is essential to both the maintenance of genomic integrity and accurate chromosome segregation during the meiotic divisions. However, the regulation of premeiotic S phase remains poorly defined in metazoa. Here, we identify the p21(Cip1)/p27(Kip1)/p57(Kip2)-like cyclin-dependent kinase inhibitor (CKI) Dacapo (Dap) as a key regulator of premeiotic S phase and genomic stability during Drosophila oogenesis. In dap(-/-) females, ovarian cysts enter the meiotic cycle with high levels of Cyclin E/cyclin-dependent kinase (Cdk)2 activity and accumulate DNA damage during the premeiotic S phase. High Cyclin E/Cdk2 activity inhibits the accumulation of the replication-licensing factor Doubleparked/Cdt1 (Dup/Cdt1). Accordingly, we find that dap(-/-) ovarian cysts have low levels of Dup/Cdt1. Moreover, mutations in dup/cdt1 dominantly enhance the dap(-/-) DNA damage phenotype. Importantly, the DNA damage observed in dap(-/-) ovarian cysts is independent of the DNA double-strands breaks that initiate meiotic recombination. Together, our data suggest that the CKI Dap promotes the licensing of DNA replication origins for the premeiotic S phase by restricting Cdk activity in the early meiotic cycle. Finally, we report that dap(-/-) ovarian cysts frequently undergo an extramitotic division before meiotic entry, indicating that Dap influences the timing of the mitotic/meiotic transition.
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Affiliation(s)
- Karine Narbonne-Reveau
- Cell Biology and Metabolism Program, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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40
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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.
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Affiliation(s)
- J Julian Blow
- Wellcome Trust Centre for Gene Regulation & Expression, University of Dundee, DD1 5EH, UK.
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41
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The origin recognition complex is dispensable for endoreplication in Drosophila. Proc Natl Acad Sci U S A 2008; 105:12343-8. [PMID: 18711130 DOI: 10.1073/pnas.0805189105] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The origin recognition complex (ORC) is an essential component of the prereplication complex (pre-RC) in mitotic cell cycles. The role of ORC as a foundation to assemble the pre-RC is conserved from yeast to human. Furthermore, in metazoans ORC plays a key role in determining the timing of replication initiation and origin usage. In this report we have produced and analyzed a Drosophila orc1 allele to investigate the roles of ORC1 in three different modes of DNA replication during development. As expected, ORC1 is essential for mitotic replication and proliferation in brains and imaginal discs, as well as for gene amplification in ovarian follicle cells. Surprisingly, however, ORC1 is not required for endoreplication. Decreased cell number in orc1 mutant salivary glands is consistent with the idea that undetectable levels of maternal ORC1 during embryogenesis fail to support further proliferation. Nevertheless, these cells begin endoreplicating normally and reach a final ploidy of >1000C in the absence of zygotic synthesis of ORC1. The dispensability of ORC is further supported by an examination of other ORC members, whereas Double-parked protein/Cdt1 and minichromosome maintenance proteins are apparently essential for endoreplication, implying that some aspects of initiation are shared among the three modes of DNA replication. This study provides insight into the physiologic roles of ORC during metazoan development and proposes that DNA replication initiation is governed differently in mitotic and endocycles.
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42
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Hall JR, Lee HO, Bunker BD, Dorn ES, Rogers GC, Duronio RJ, Cook JG. Cdt1 and Cdc6 are destabilized by rereplication-induced DNA damage. J Biol Chem 2008; 283:25356-25363. [PMID: 18617514 DOI: 10.1074/jbc.m802667200] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The replication factors Cdt1 and Cdc6 are essential for origin licensing, a prerequisite for DNA replication initiation. Mechanisms to ensure that metazoan origins initiate once per cell cycle include degradation of Cdt1 during S phase and inhibition of Cdt1 by the geminin protein. Geminin depletion or overexpression of Cdt1 or Cdc6 in human cells causes rereplication, a form of endogenous DNA damage. Rereplication induced by these manipulations is however uneven and incomplete, suggesting that one or more mechanisms restrain rereplication once it begins. We find that both Cdt1 and Cdc6 are degraded in geminin-depleted cells. We further show that Cdt1 degradation in cells that have rereplicated requires the PCNA binding site of Cdt1 and the Cul4(DDB1) ubiquitin ligase, and Cdt1 can induce its own degradation when overproduced. Cdc6 degradation in geminin-depleted cells requires Huwe1, the ubiquitin ligase that regulates Cdc6 after DNA damage. Moreover, perturbations that specifically disrupt Cdt1 and Cdc6 degradation in response to DNA damage exacerbate rereplication when combined with geminin depletion, and this enhanced rereplication occurs in both human cells and in Drosophila melanogaster cells. We conclude that rereplication-associated DNA damage triggers Cdt1 and Cdc6 ubiquitination and destruction, and propose that this pathway represents an evolutionarily conserved mechanism that minimizes the extent of rereplication.
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Affiliation(s)
- Jonathan R Hall
- Department of Biochemistry and Biophysics, Chapel Hill, North Carolina 27599-7260
| | - Hyun O Lee
- Department of Curriculum in Genetics and Molecular Biology, Chapel Hill, North Carolina 27599-7260
| | - Brandon D Bunker
- Department of Biochemistry and Biophysics, Chapel Hill, North Carolina 27599-7260
| | - Elizabeth S Dorn
- Department of Biochemistry and Biophysics, Chapel Hill, North Carolina 27599-7260
| | - Greg C Rogers
- Department of Biology, Chapel Hill, North Carolina 27599-7260
| | - Robert J Duronio
- Department of Curriculum in Genetics and Molecular Biology, Chapel Hill, North Carolina 27599-7260; Department of Biology, Chapel Hill, North Carolina 27599-7260; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7260
| | - Jeanette Gowen Cook
- Department of Biochemistry and Biophysics, Chapel Hill, North Carolina 27599-7260; Department of Curriculum in Genetics and Molecular Biology, Chapel Hill, North Carolina 27599-7260; Lineberger Comprehensive Cancer Center, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7260.
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43
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Caro E, Gutierrez C. A green GEM: intriguing analogies with animal geminin. Trends Cell Biol 2007; 17:580-5. [PMID: 17997094 DOI: 10.1016/j.tcb.2007.09.008] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2007] [Revised: 09/21/2007] [Accepted: 09/24/2007] [Indexed: 01/16/2023]
Abstract
The transition of precursor cells from an undifferentiated proliferative state to differentiated cells with specific fates is of primary importance for multicellular organisms. Animals and plants have evolved two unrelated proteins, geminin and GEM, respectively, that play analogous roles in regulating this transition. These proteins are involved, probably in early G1 phase of the cell cycle, in regulating the expression of genes involved in cell fate and initiation of differentiation. They also interact with Cdt1, a component of the pre-replication complexes involved in DNA replication licensing in early G1 phase. The interaction of geminin and GEM with Cdt1 and transcriptional regulators is competitive, suggesting that these interactions can play a pivotal role in coordinating DNA replication, cell division and cell fate decisions.
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Affiliation(s)
- Elena Caro
- Centro de Biologia Molecular "Severo Ochoa", Consejo Superior de Investigaciones Cientificas, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain
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The Arabidopsis SET-domain protein ASHR3 is involved in stamen development and interacts with the bHLH transcription factor ABORTED MICROSPORES (AMS). PLANT MOLECULAR BIOLOGY 2007; 66:47-59. [PMID: 17978851 DOI: 10.1007/s11103-007-9251-y] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Accepted: 10/04/2007] [Indexed: 12/24/2022]
Abstract
The Arabidopsis thaliana genome contains more than 30 genes encoding SET-domain proteins that are thought to be epigenetic regulators of gene expression and chromatin structure. SET-domain proteins can be divided into subgroups, and members of the Polycomb group (PcG) and trithorax group (trxG) have been shown to be important regulators of development. Both in animals and plants some of these proteins are components of multimeric protein complexes. Here, we have analyzed the Arabidopsis trxG protein ASHR3 which has a SET domain and pre- and post-SET domains similar to that of Ash1 in Drosophila. In addition to the SET domain, a divergent PHD finger is found in the N-terminus of the ASHR3 protein. As expected from SET-domain proteins involved in transcriptional activation, ASHR3 (coupled to GFP) localizes to euchromatin. A yeast two-hybrid screening revealed that the ASHR3 protein interacts with the putative basic helix-loop-helix (bHLH) transcription factor ABORTED MICROSPORES (AMS), which is involved in anther and stamen development in Arabidopsis. Deletion mapping indicated that both the PHD finger and the SET domain mediate the interaction between the two proteins. Overexpression of ASHR3 led in general to growth arrest, and specifically to degenerated anthers and male sterility. Expression analyses demonstrated that ASHR3 like AMS is expressed in the anther and in stamen filaments. We therefore propose that AMS can target ASHR3 to chromatin and regulate genes involved in stamen development and function.
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Regulatory evolution in proteins by turnover and lineage-specific changes of cyclin-dependent kinase consensus sites. Proc Natl Acad Sci U S A 2007; 104:17713-8. [PMID: 17978194 PMCID: PMC2077061 DOI: 10.1073/pnas.0700997104] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Evolutionary change in gene regulation is a key mechanism underlying the genetic component of organismal diversity. Here, we study evolution of regulation at the posttranslational level by examining the evolution of cyclin-dependent kinase (CDK) consensus phosphorylation sites in the protein subunits of the pre-replicative complex (RC). The pre-RC, an assembly of proteins formed during an early stage of DNA replication, is believed to be regulated by CDKs throughout the animals and fungi. Interestingly, although orthologous pre-RC components often contain clusters of CDK consensus sites, the positions and numbers of sites do not seem conserved. By analyzing protein sequences from both distantly and closely related species, we confirm that consensus sites can turn over rapidly even when the local cluster of sites is preserved, consistent with the notion that precise positioning of phosphorylation events is not required for regulation. We also identify evolutionary changes in the clusters of sites and further examine one replication protein, Mcm3, where a cluster of consensus sites near a nucleocytoplasmic transport signal is confined to a specific lineage. We show that the presence or absence of the cluster of sites in different species is associated with differential regulation of the transport signal. These findings suggest that the CDK regulation of MCM nuclear localization was acquired in the lineage leading to Saccharomyces cerevisiae after the divergence with Candida albicans. Our results begin to explore the dynamics of regulatory evolution at the posttranslational level and show interesting similarities to recent observations of regulatory evolution at the level of transcription.
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46
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Drosophila follicle cell amplicons as models for metazoan DNA replication: a cyclinE mutant exhibits increased replication fork elongation. Proc Natl Acad Sci U S A 2007; 104:16739-46. [PMID: 17940024 DOI: 10.1073/pnas.0707804104] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Gene clusters amplified in the ovarian follicle cells of Drosophila serve as powerful models for metazoan DNA replication. In response to developmental signals, specific genomic regions undergo amplification by repeated firing of replication origins and bidirectional movement of replication forks for approximately 50 kb in each direction. Previous work focused on initiation of amplification, defining replication origins, establishing the role of the prereplication complex and origin recognition complex (ORC), and uncovering regulatory functions for the Myb, E2F1, and Rb transcription factors. Here, we exploit follicle cell amplification to investigate the control of DNA replication fork progression and termination, poorly understood processes in metazoans. We identified a mutant in which, during gene amplification, the replication forks move twice as far from the origin compared with wild type. This phenotype is the result of an amino acid substitution mutation in the cyclinE gene, cyclinE(1f36). The rate of oogenesis is normal in cyclinE(1f36)/cyclinE(Pz8) mutant ovaries, indicating that increased replication fork progression is due to increased replication fork speed, possibly from increased processivity. The increased amplification domains observed in the mutant imply that there are not replication fork barriers preventing replication forks from progressing beyond the normal 100-kb amplified region. These results reveal a previously unrecognized role for CyclinE in controlling replication fork movement.
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Kim Y, Kipreos ET. Cdt1 degradation to prevent DNA re-replication: conserved and non-conserved pathways. Cell Div 2007; 2:18. [PMID: 17565698 PMCID: PMC1913051 DOI: 10.1186/1747-1028-2-18] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2007] [Accepted: 06/12/2007] [Indexed: 11/10/2022] Open
Abstract
In eukaryotes, DNA replication is strictly regulated so that it occurs only once per cell cycle. The mechanisms that prevent excessive DNA replication are focused on preventing replication origins from being reused within the same cell cycle. This regulation involves the temporal separation of the formation of the pre-replicative complex (pre-RC) from the initiation of DNA replication. The replication licensing factors Cdt1 and Cdc6 recruit the presumptive replicative helicase, the Mcm2-7 complex, to replication origins in late M or G1 phase to form pre-RCs. In fission yeast and metazoa, the Cdt1 licensing factor is degraded at the start of S phase by ubiquitin-mediated proteolysis to prevent the reassembly of pre-RCs. In humans, two E3 complexes, CUL4-DDB1CDT2 and SCFSkp2, are redundantly required for Cdt1 degradation. The two E3 complexes use distinct mechanisms to target Cdt1 ubiquitination. Current data suggests that CUL4-DDB1CDT2-mediated degradation of Cdt1 is S-phase specific, while SCFSkp2-mediated Cdt1 degradation occurs throughout the cell cycle. The degradation of Cdt1 by the CUL4-DDB1CDT2 E3 complex is an evolutionarily ancient pathway that is active in fungi and metazoa. In contrast, SCFSkp2-mediated Cdt1 degradation appears to have arisen relatively recently. A role for Skp2 in Cdt1 degradation has only been demonstrated in humans, and the pathway is not conserved in yeast, invertebrates, or even among other vertebrates.
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Affiliation(s)
- Youngjo Kim
- Department of Cellular Biology, University of Georgia, Athens, GA 30602-2607 USA
| | - Edward T Kipreos
- Department of Cellular Biology, University of Georgia, Athens, GA 30602-2607 USA
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48
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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.
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Affiliation(s)
- Emily E Arias
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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Hong A, Narbonne-Reveau K, Riesgo-Escovar J, Fu H, Aladjem MI, Lilly MA. The cyclin-dependent kinase inhibitor Dacapo promotes replication licensing during Drosophila endocycles. EMBO J 2007; 26:2071-82. [PMID: 17380129 PMCID: PMC1852775 DOI: 10.1038/sj.emboj.7601648] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2006] [Accepted: 02/15/2007] [Indexed: 01/08/2023] Open
Abstract
The endocycle is a developmentally programmed variant cell cycle in which cells undergo repeated rounds of DNA replication with no intervening mitosis. In Drosophila, the endocycle is driven by the oscillations of Cyclin E/Cdk2 activity. How the periodicity of Cyclin E/Cdk2 activity is achieved during endocycles is poorly understood. Here, we demonstrate that the p21(cip1)/p27(kip1)/p57(kip2)-like cyclin-dependent kinase inhibitor (CKI), Dacapo (Dap), promotes replication licensing during Drosophila endocycles by reinforcing low Cdk activity during the endocycle Gap-phase. In dap mutants, cells in the endocycle have reduced levels of the licensing factor Double Parked/Cdt1 (Dup/Cdt1), as well as decreased levels of chromatin-bound minichromosome maintenance (MCM2-7) complex. Moreover, mutations in dup/cdt1 dominantly enhance the dap phenotype in several polyploid cell types. Consistent with a reduced ability to complete genomic replication, dap mutants accumulate increased levels of DNA damage during the endocycle S-phase. Finally, genetic interaction studies suggest that dap functions to promote replication licensing in a subset of Drosophila mitotic cycles.
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Affiliation(s)
- Amy Hong
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Karine Narbonne-Reveau
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
| | - Juan Riesgo-Escovar
- Departmento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, Universidad Nacional Antonoma de Mexico, Queretaro, Mexico
| | - Haiqing Fu
- Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Mirit I Aladjem
- Laboratory of Molecular Pharmacology, National Cancer Institute, National Institutes of Health, Bethesda, MD, USA
| | - Mary A Lilly
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD, USA
- Cell Biology and Metabolism Branch, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA. Tel.: +1 301 435 8428; Fax: +1 301 402 0078; E-mail:
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50
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Sivaprasad U, Machida YJ, Dutta A. APC/C--the master controller of origin licensing? Cell Div 2007; 2:8. [PMID: 17319958 PMCID: PMC1810247 DOI: 10.1186/1747-1028-2-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2007] [Accepted: 02/23/2007] [Indexed: 11/15/2022] Open
Abstract
DNA replication must be tightly controlled to prevent initiation of a second round of replication until mitosis is complete. So far, components of the pre-replicative complex (Cdt1, Cdc6 and geminin) were considered key players in this regulation. In a new study, Machida and Dutta have shown that depletion of Emi1 caused cells to replicate their DNA more than once per cell cycle [1]. This effect was dependent on the ability of Emi1 to inhibit the APC/C. In addition to its role in regulating entry into mitosis, oscillation of APC/C activity regulates pre-RC formation: high APC/C activity in late M/G1 allows pre-RC formation and low APC/C activity in S/G2 prevents pre-RC formation for a second time thereby preventing rereplication. Each redundant pathway to prevent rereplication is dependent on regulating one of the pre-RC components, and all of the pathways are co-regulated by Emi1 through the APC/C. In this commentary we discuss how this new role of Emi1 adds to our understanding of the regulation of replication initiation. We also review the literature to analyze whether APC/C has a role in regulating endoreduplication (a normal state of polyploidy in some differentiated cells). Similarly a role of premature APC/C activation in genomic instability of tumors is discussed.
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Affiliation(s)
- Umasundari Sivaprasad
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Yuichi J Machida
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
| | - Anindya Dutta
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA 22908, USA
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