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Regulation of the mitotic chromosome folding machines. Biochem J 2022; 479:2153-2173. [PMID: 36268993 DOI: 10.1042/bcj20210140] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Revised: 09/30/2022] [Accepted: 10/03/2022] [Indexed: 11/17/2022]
Abstract
Over the last several years enormous progress has been made in identifying the molecular machines, including condensins and topoisomerases that fold mitotic chromosomes. The discovery that condensins generate chromatin loops through loop extrusion has revolutionized, and energized, the field of chromosome folding. To understand how these machines fold chromosomes with the appropriate dimensions, while disentangling sister chromatids, it needs to be determined how they are regulated and deployed. Here, we outline the current understanding of how these machines and factors are regulated through cell cycle dependent expression, chromatin localization, activation and inactivation through post-translational modifications, and through associations with each other, with other factors and with the chromatin template itself. There are still many open questions about how condensins and topoisomerases are regulated but given the pace of progress in the chromosome folding field, it seems likely that many of these will be answered in the years ahead.
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2
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Swan RL, Cowell IG, Austin CA. Mechanisms to repair stalled Topoisomerase II-DNA covalent complexes. Mol Pharmacol 2021; 101:24-32. [PMID: 34689119 DOI: 10.1124/molpharm.121.000374] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Accepted: 10/11/2021] [Indexed: 11/22/2022] Open
Abstract
DNA topoisomerases regulate the topological state of DNA, relaxing DNA supercoils and resolving catenanes and knots that result from biological processes such as transcription and replication. DNA topoisomerase II (TOP2) enzymes achieve this by binding DNA and introducing an enzyme-bridged DNA double-strand break (DSB) where each protomer of the dimeric enzyme is covalently attached to the 5' end of the cleaved DNA via an active site tyrosine phosphodiester linkage. The enzyme then passes a second DNA duplex though the DNA break, before religation and release of the enzyme. However, this activity is potentially hazardous to the cell, as failure to complete religation leads to persistent TOP2 protein-DNA covalent complexes which are cytotoxic. Indeed, this property of topoisomerase has been exploited in cancer therapy in the form of topoisomerase poisons which block the religation stage of the reaction cycle, leading to an accumulation of topoisomerase-DNA adducts. A number of parallel cellular processes have been identified that lead to removal of these covalent TOP2-DNA complexes facilitating repair of the resulting protein-free DSB by standard DNA repair pathways. These pathways presumably arose to repair spontaneous stalled or poisoned TOP2-DNA complexes, but understanding their mechanisms also has implications for cancer therapy, particularly resistance to anti-cancer TOP2 poisons and the genotoxic side effects of these drugs. Here we review recent progress in the understanding of the processing to TOP2 DNA covalent complexes., The basic components and mechanisms plus the additional layer of complexity posed by the post-translational modifications that modulate these pathways. Significance Statement Multiple pathways have been reported for removal and repair of TOP2-DNA covalent complexes to ensure the timely and efficient repair of TOP2-DNA covalent adducts to protect the genome. Post-translational modifications such as ubiquitination and SUMOylation are involved in the regulation of TOP2-DNA complex repair. Small molecule inhibitors of these post translational modifications may help to improve outcomes of TOP2 poison chemotherapy, for example by increasing TOP2 poison cytotoxicity and reducing genotoxicity, but this remains to be determined.
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Affiliation(s)
- Rebecca L Swan
- Biosciences Institute, Newcastle University, United Kingdom
| | - Ian G Cowell
- Institute for Cell and Molecular Biosciences, Newcastle University, United Kingdom
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3
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Duprey A, Groisman EA. The regulation of DNA supercoiling across evolution. Protein Sci 2021; 30:2042-2056. [PMID: 34398513 PMCID: PMC8442966 DOI: 10.1002/pro.4171] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/21/2021] [Revised: 08/04/2021] [Accepted: 08/04/2021] [Indexed: 11/11/2022]
Abstract
DNA supercoiling controls a variety of cellular processes, including transcription, recombination, chromosome replication, and segregation, across all domains of life. As a physical property, DNA supercoiling alters the double helix structure by under- or over-winding it. Intriguingly, the evolution of DNA supercoiling reveals both similarities and differences in its properties and regulation across the three domains of life. Whereas all organisms exhibit local, constrained DNA supercoiling, only bacteria and archaea exhibit unconstrained global supercoiling. DNA supercoiling emerges naturally from certain cellular processes and can also be changed by enzymes called topoisomerases. While structurally and mechanistically distinct, topoisomerases that dissipate excessive supercoils exist in all domains of life. By contrast, topoisomerases that introduce positive or negative supercoils exist only in bacteria and archaea. The abundance of topoisomerases is also transcriptionally and post-transcriptionally regulated in domain-specific ways. Nucleoid-associated proteins, metabolites, and physicochemical factors influence DNA supercoiling by acting on the DNA itself or by impacting the activity of topoisomerases. Overall, the unique strategies that organisms have evolved to regulate DNA supercoiling hold significant therapeutic potential, such as bactericidal agents that target bacteria-specific processes or anticancer drugs that hinder abnormal DNA replication by acting on eukaryotic topoisomerases specialized in this process. The investigation of DNA supercoiling therefore reveals general principles, conserved mechanisms, and kingdom-specific variations relevant to a wide range of biological questions.
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Affiliation(s)
- Alexandre Duprey
- Department of Microbial PathogenesisYale School of MedicineNew HavenConnecticutUSA
| | - Eduardo A. Groisman
- Department of Microbial PathogenesisYale School of MedicineNew HavenConnecticutUSA
- Yale Microbial Sciences InstituteWest HavenConnecticutUSA
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4
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Ma Y, North BJ, Shu J. Regulation of topoisomerase II stability and activity by ubiquitination and SUMOylation: clinical implications for cancer chemotherapy. Mol Biol Rep 2021; 48:6589-6601. [PMID: 34476738 DOI: 10.1007/s11033-021-06665-7] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 08/17/2021] [Indexed: 12/09/2022]
Abstract
DNA topoisomerases II (TOP2) are peculiar enzymes (TOP2α and TOP2β) that modulate the conformation of DNA by momentarily breaking double-stranded DNA to allow another strand to pass through, and then rejoins the DNA phosphodiester backbone. TOP2α and TOP2β play vital roles in nearly all events involving DNA metabolism, including DNA transcription, replication, repair, and chromatin remodeling. Beyond these vital functions, TOP2 enzymes are therapeutic targets for various anticancer drugs, termed TOP2 poisons, such as teniposide, etoposide, and doxorubicin. These drugs exert their antitumor activity by inhibiting the activity of TOP2-DNA cleavage complexes (TOP2ccs) containing DNA double-strand breaks (DSBs), subsequently leading to the degradation of TOP2 by the 26S proteasome, thereby exposing the DSBs and eliciting a DNA damage response. Failure of the DSBs to be appropriately repaired leads to genomic instability. Due to this mechanism, patients treated with TOP2-based drugs have a high incidence of secondary malignancies and cardiotoxicity. While the cytotoxicity associated with TOP2 poisons appears to be TOP2α-dependent, the DNA sequence rearrangements and formation of DSBs appear to be mediated primarily through TOP2β inhibition, likely due to the differential degradation patterns of TOP2α and TOP2β. Research over the past few decades has shown that under various conditions, the ubiquitin-proteasome system (UPS) and the SUMOylation pathway are primarily responsible for regulating the stability and activity of TOP2 and are therefore critical regulators of the therapeutic effect of TOP2-targeting drugs. In this review, we summarize the current progress on the regulation of TOP2α and TOP2β by ubiquitination and SUMOylation. By fully elucidating the basic biology of these essential and complex molecular mechanisms, better strategies may be developed to improve the therapeutic efficacy of TOP2 poisons and minimize the risks of therapy-related secondary malignancy.
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Affiliation(s)
- Ying Ma
- Department of Medical Oncology, The First Affiliated Hospital of Zhejiang University, Hangzhou, 310029, China
- Zhejiang University School of Medicine, Hangzhou, 310029, China
| | - Brian J North
- Biomedical Sciences Department, Creighton University School of Medicine, 2500 California Plaza, Omaha, NE, 68178, USA.
| | - Jianfeng Shu
- HwaMei Hospital, University of Chinese Academy of Sciences, Ningbo, 315010, China.
- Ningbo Institute of Life and Health Industry, University of Chinese Academy of Sciences, Ningbo, 315020, China.
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5
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Zhao W, Duan Y, Li HM, Li S, Shen Y, Zhang Y, Li YZ, Tang YJ. Triazole/thiadiazole substituted 4'-demethylepipodophyllotoxin derivatives induced apoptosis in HeLa cells by up-regulating TMEM133. Eur J Pharmacol 2021; 905:174189. [PMID: 34033816 DOI: 10.1016/j.ejphar.2021.174189] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/02/2020] [Revised: 05/06/2021] [Accepted: 05/12/2021] [Indexed: 11/23/2022]
Abstract
Heterocycle modification has been widely and successfully employed in the antitumor drugs. However, the different antitumor efficacy was corelated with the heterocycle substituted, and the genetic mechanism underlying these effects has not been elucidated. In this study, the intrinsic regularity between different types of heterocycle-substituted DMEP derivative compounds and the mechanisms of their antitumor activity was preliminarily disclosed. Triazole/thiadiazole substituted 4'-demethylepipodophyllotoxin derivatives induced more severe DNA damage and higher levels of 26S proteasomal Topo IIβ degradation, though inhibited the recruition of γH2AX to resist the DNA damage. The reduced DNA repair led to higher up-regulation of cell cycle arrest proteins, and ultimately DNA damage mediated-ATM/ATR apoptotic pathways and specifically activated DNA damage response gene TMEM133, which induced apoptosis through up-regulation of G2/M cell cycle arrest-related genes. Over-expression and knock-out of TMEM133 demonstrated that TMEM133 is essential for inhibition of the tumor cell growth during treatment with triazole/thiadiazole substituted 4'-demethylepipodophyllotoxin derivatives.
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Affiliation(s)
- Wei Zhao
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Ying Duan
- Hubei Key Laboratory of Industrial Microbiology, Hubei Provincial Cooperative Innovation Center of Industrial Fermentation, Key Laboratory of Fermentation Engineering (Ministry of Education), Hubei University of Technology, Wuhan, 430068, China
| | - Hong-Mei Li
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Shengying Li
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Yuemao Shen
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Youming Zhang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Yue-Zhong Li
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China
| | - Ya-Jie Tang
- State Key Laboratory of Microbial Technology, Shandong University, Qingdao, 266237, China.
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6
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Cell Cycle-Dependent Control and Roles of DNA Topoisomerase II. Genes (Basel) 2019; 10:genes10110859. [PMID: 31671531 PMCID: PMC6896119 DOI: 10.3390/genes10110859] [Citation(s) in RCA: 97] [Impact Index Per Article: 19.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Revised: 10/25/2019] [Accepted: 10/28/2019] [Indexed: 12/13/2022] Open
Abstract
Type II topoisomerases are ubiquitous enzymes in all branches of life that can alter DNA superhelicity and unlink double-stranded DNA segments during processes such as replication and transcription. In cells, type II topoisomerases are particularly useful for their ability to disentangle newly-replicated sister chromosomes. Growing lines of evidence indicate that eukaryotic topoisomerase II (topo II) activity is monitored and regulated throughout the cell cycle. Here, we discuss the various roles of topo II throughout the cell cycle, as well as mechanisms that have been found to govern and/or respond to topo II function and dysfunction. Knowledge of how topo II activity is controlled during cell cycle progression is important for understanding how its misregulation can contribute to genetic instability and how modulatory pathways may be exploited to advance chemotherapeutic development.
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7
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Lee KC, Bramley RL, Cowell IG, Jackson GH, Austin CA. Proteasomal inhibition potentiates drugs targeting DNA topoisomerase II. Biochem Pharmacol 2016; 103:29-39. [PMID: 26794000 PMCID: PMC5071433 DOI: 10.1016/j.bcp.2015.12.015] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2015] [Accepted: 12/22/2015] [Indexed: 01/15/2023]
Abstract
The reaction mechanism of DNA topoisomerase II (TOP2) involves a covalent double-strand break intermediate in which the enzyme is coupled to DNA via a 5′-phosphotyrosyl bond. This normally transient enzyme-bridged break is stabilised by drugs such as mitoxantrone, mAMSA, etoposide, doxorubicin, epirubicin and idarubicin, which are referred to as TOP2 poisons. Removal of topoisomerase II by the proteasome is involved in the repair of these lesions. In K562 cells, inhibiting the proteasome with MG132 significantly potentiated the growth inhibition by these six drugs that target topoisomerase II, and the highest level of potentiation was observed with mitoxantrone. Mitoxantrone also showed the greatest potentiation by MG132 in three Nalm 6 cell lines with differing levels of TOP2A or TOP2B. Mitoxantrone was also potentiated by the clinically used proteasome inhibitor PS341 (Velcade). We have also shown that proteasome inhibition with MG132 in K562 cells reduces the rate of removal of mitoxantrone or etoposide stabilised topoisomerase complexes from DNA, suggesting a possible mechanism for the potentiation of topoisomerase II drugs by proteasomal inhibition.
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Affiliation(s)
- Ka C Lee
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Rebecca L Bramley
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Ian G Cowell
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Graham H Jackson
- Institute for Cellular Medicine, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom
| | - Caroline A Austin
- Institute for Cell and Molecular Biosciences, Newcastle University, Newcastle upon Tyne NE2 4HH, United Kingdom.
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8
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Shen Y, Chen W, Zhao B, Hao H, Li Z, Lu C, Shen Y. CS1 is a novel topoisomerase IIα inhibitor with favorable drug resistance profiles. Biochem Biophys Res Commun 2014; 453:302-8. [DOI: 10.1016/j.bbrc.2014.09.042] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2014] [Accepted: 09/11/2014] [Indexed: 01/26/2023]
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9
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Painuly U, Kumar S. Efficacy of bortezomib as first-line treatment for patients with multiple myeloma. CLINICAL MEDICINE INSIGHTS-ONCOLOGY 2013; 7:53-73. [PMID: 23492937 PMCID: PMC3588852 DOI: 10.4137/cmo.s7764] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Recent years have seen a dramatic change in the approach towards diagnosing and treating Multiple Myeloma. Newer and more target specific approach to treatment has prolonged the survival for patients with multiple myeloma. The proteasome inhibitors make an important class of anti-myeloma drugs that disrupts the proteolytic machinery of the tumor cells preferentially, enhancing their susceptibility to apoptosis. Bortezomib, in particular has shown significant clinical efficacy in myeloma treatment. It is the most commonly used proteasome inhibitor and has been tested to be effective in prolonging the overall survival in several trials. Its combinations with cyclophosphamide and dexamethasone are the treatment of choice for standard risk patients following the mSMART guidelines. The success with its lower dosage in elderly and its proven efficacious subcutaneous usage makes Bortezomib a useful agent for maximizing patient compliance and minimizing therapy related toxicity and costs. This review discusses several trials where Bortezomib has been used as a single/combination agent for front-line treatment of multiple myeloma.
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Affiliation(s)
- Utkarsh Painuly
- Division of Hematology, Department of Internal Medicine, Mayo Clinic, Rochester, MN, USA. ; 4th Department of Internal Medicine, University Hospital and Charles University Faculty of Medicine, Hradec Králové, Czech Republic
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Schonn I, Hennesen J, Dartsch DC. Ku70 and Rad51 vary in their importance for the repair of doxorubicin- versus etoposide-induced DNA damage. Apoptosis 2011; 16:359-69. [PMID: 21107697 DOI: 10.1007/s10495-010-0564-y] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
For DNA targeting anticancer drugs, cellular DNA repair mechanisms may cause resistance and hamper the therapeutic outcome. DNA damage induced by topoisomerase IIα inhibitors like etoposide and anthracyclines, which are a mainstay of cancer therapy, is also repaired in many cell types, but the impact and precise mechanisms of this repair are still obscure. To investigate the DNA damage response of human adenocarcinoma HT29-cells to doxorubicin and to compare the involvement of Ku70 and Rad51 in the repair of doxorubicin- versus etoposide-induced DNA damage, we assessed cell cycle distribution and cell death, DNA damage, proteins relevant for repair by homologous recombination and non-homologous end-joining, and clonogenicity following exposure to doxorubicin at clinically achievable concentrations. Also, we assessed changes in the repair kinetics after siRNA-mediated attenuation of Ku70 or Rad51 expression. We found that exposure to doxorubicin for 24 h induced a substantial amount of DNA damage that was largely repaired when doxorubicin was removed and the cells were maintained in drug-free medium. Nevertheless, a pronounced G(2)/M arrest occurred at times when repair was maximal. This was followed by a distinct increase in cell death and loss of clonogenicity. In this regard, responses to doxorubicin and etoposide were similar. However, distinct differences in the repair process following doxorubicin versus etoposide were seen in concentration dependency, time-course and requirement of Ku70 and Rad51 proteins. In spite of the shared molecular target of doxorubicin and etoposide, DNA lesions induced by these compounds are repaired differently.
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Affiliation(s)
- Ilona Schonn
- Clinical Pharmacy, Institute of Pharmacy, Hamburg University, Bundesstrasse 45, Hamburg, Germany.
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Sabisz M, Wesierska-Gadek J, Skladanowski A. Increased cytotoxicity of an unusual DNA topoisomerase II inhibitor compound C-1305 toward HeLa cells with downregulated PARP-1 activity results from re-activation of the p53 pathway and modulation of mitotic checkpoints. Biochem Pharmacol 2010; 79:1387-97. [PMID: 20067769 DOI: 10.1016/j.bcp.2009.12.023] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/24/2009] [Revised: 12/30/2009] [Accepted: 12/31/2009] [Indexed: 11/25/2022]
Abstract
Our previous studies have shown that murine fibroblast cells, in which PARP-1 gene was inactivated by gene disruption, are extremely sensitive to triazoloacridone compound C-1305, an inhibitor of DNA topoisomerase II with unusual properties. Here, we show that pharmacological inhibition of PARP-1 activity by its inhibitor compound NU1025, sensitizes human cervical carcinoma HeLa cells to compound C-1305 compared to treatment with drug alone. Cytotoxic effect of drug/NU1025 of other topoisomerase II inhibitors varied depending on the dose of PARP-1 inhibitor. Increased cytotoxicity of topoisomerase II inhibitor/NU1025 combinations was attributable to the re-activation of the p53 pathway in drug-treated HeLa cells. This lead to a more stringent cell cycle checkpoint control during G2 and M and enhanced cell death by mitotic catastrophe induced by drug/NU1025 combinations. Interestingly, treatment of HeLa cells with NU1025 alone also increased p53 expression. This effect is, at least in part, related to the inhibition of proteasome activity by drug treatments. Together, our results show that concomitant inhibition of topoisomerase II and PARP-1 leads to the synergistic cytotoxic effect toward tumor cells that may be important for combination therapies with NU1025 and topoisomerase II inhibitors. We also confirmed our earlier work and show the important role of PARP-1 activity in the maintenance of the G2 arrest induced by DNA damaging drugs. Finally, based on our studies we propose that NU1025 and possibly other inhibitors of PARP-1 may be used as non-genotoxic agents to activate p53 in tumor cells with non-functional p53 pathways.
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Affiliation(s)
- Michal Sabisz
- Department of Pharmaceutical Technology and Biochemistry, Gdansk University of Technology, Poland
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12
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Shinagawa H, Miki Y, Yoshida K. BRCA1-mediated ubiquitination inhibits topoisomerase II alpha activity in response to oxidative stress. Antioxid Redox Signal 2008; 10:939-49. [PMID: 18162055 DOI: 10.1089/ars.2007.1851] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Topoisomerase IIalpha is known to be critically involved in both cell proliferation and cell death. The mechanisms responsible for stress-dependent topoisomerase IIalpha alterations, however, remain unclear. This study focused on the behavior of topoisomerase IIalpha in response to oxidative stress induced by hydrogen peroxide (H(2)O(2)). The catalytic activity of topoisomerase IIalpha in MOLT-4 cells treated with H(2)O(2) decreased in parallel with the alteration of topoisomerase IIalpha expression. The ubiquitination of topoisomerase IIalpha was dependent on oxidative stress. BRCA1, a tumor-suppressor gene, appeared to be involved in these alterations in topoisomerase IIalpha. Furthermore, the retinoblastoma protein (pRb) was required for the ubiquitination of topoisomerase IIalpha by BRCA1. We conclude that the functions of topoisomerase IIalpha are regulated by ubiquitination on exposure to oxidative stress.
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Affiliation(s)
- Hirokuni Shinagawa
- Department of Molecular Genetics, Medical Research Institute, Tokyo Medical and Dental University, Tokyo, Japan
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13
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Congdon LM, Pourpak A, Escalante AM, Dorr RT, Landowski TH. Proteasomal inhibition stabilizes topoisomerase IIalpha protein and reverses resistance to the topoisomerase II poison ethonafide (AMP-53, 6-ethoxyazonafide). Biochem Pharmacol 2008; 75:883-90. [PMID: 18062937 PMCID: PMC2271051 DOI: 10.1016/j.bcp.2007.10.026] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2007] [Revised: 10/08/2007] [Accepted: 10/24/2007] [Indexed: 11/26/2022]
Abstract
Multiple myeloma (MM) is an incurable malignancy of plasma cells. Although multiple myeloma patients often respond to initial therapy, the majority of patients will relapse with disease that is refractory to further drug treatment. Thus, new therapeutic strategies are needed. One common mechanism of acquired drug resistance involves a reduction in the expression or function of the drug target. We hypothesized that the cytotoxic activity of topoisomerase II (topo II) poisons could be enhanced, and drug resistance overcome, by increasing the expression and activity of the drug target, topo II in myeloma cells. To test this hypothesis, we evaluated the cytotoxicity of the anthracene-containing topo II poison, ethonafide (AMP-53/6-ethoxyazonafide), in combination with the proteasome inhibitor bortezomib (PS-341/Velcade). Combination drug activity studies were done in 8226/S myeloma cells and its drug resistant subclone, 8226/Dox1V. We found that a 24-h treatment of cells with bortezomib maximally increased topo IIalpha protein expression and activity, and consistently increased the cytotoxicity of ethonafide in the 8226/S and 8226/Dox1V cell lines. This increase in cytotoxicity corresponded to an increase in DNA double-strand breaks, as measured by the neutral comet assay. Therefore, increasing topo IIalpha expression through inhibition of proteasomal degradation increased DNA double-strand breaks and enhanced the cytotoxicity of the topo II poison ethonafide. These data suggest that bortezomib-mediated stabilization of topo IIalpha expression may potentiate the cytotoxic activity of topo II poisons and thereby, provide a strategy to circumvent drug resistance.
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Affiliation(s)
- Lauren M. Congdon
- Department of Biochemistry and Molecular Biophysics, The University of Arizona, Tucson, AZ, USA
- Arizona Cancer Center, The University of Arizona, Tucson, AZ, USA
| | - Alan Pourpak
- Department of Pharmacology, The University of Arizona, Tucson, AZ, USA
- Arizona Cancer Center, The University of Arizona, Tucson, AZ, USA
| | | | - Robert T. Dorr
- Department of Pharmacology, The University of Arizona, Tucson, AZ, USA
- College of Medicine, The University of Arizona, Tucson, AZ, USA
- Arizona Cancer Center, The University of Arizona, Tucson, AZ, USA
| | - Terry H. Landowski
- College of Medicine, The University of Arizona, Tucson, AZ, USA
- Arizona Cancer Center, The University of Arizona, Tucson, AZ, USA
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Dartsch DC, Gieseler F. Repair of idarubicin-induced DNA damage: A cause of resistance? DNA Repair (Amst) 2007; 6:1618-28. [PMID: 17616443 DOI: 10.1016/j.dnarep.2007.05.007] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2006] [Revised: 05/23/2007] [Accepted: 05/24/2007] [Indexed: 10/23/2022]
Abstract
Idarubicin, a widely used anticancer drug inhibits topoisomerase (topo) IIalpha and induces DNA double strand breaks. The finding that idarubicin-induced DNA damage is repaired before cell death is initiated encouraged us to examine the role of DNA repair for the cytotoxicity of idarubicin in human promyelocytic HL60 leukaemia cells. We found that DNA double strand breaks induced by a 90 min transient exposure to 0.5 microgml(-1) idarubicin were rapidly repaired throughout the whole population, while topo IIalpha itself was degraded. In spite of DNA repair, the vast majority of cells died within 40 h. Using differential staining of the chromatids and microscopic evaluation of DNA break points, we found evidence for a high number of false ligations of loose DNA strands arising from the inhibition of topo IIalpha action by idarubicin. If mainly actively transcribed genes are affected, this results in a disruption of vital genetic information, of regulatory sequences and, ultimately, in induction of the cell death pathway. Our results confirm the hypothesis that misrepair of DNA damage is a decisive event in idarubicin-induced cell death. They are discussed in the context of topo IIalpha-function and the currently known mechanisms of DNA double strand break repair.
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Affiliation(s)
- Dorothee C Dartsch
- Hamburg University, Institute of Pharmacy, Bundesstr. 45, 20146 Hamburg, Germany.
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15
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Tedesco D, Zhang J, Trinh L, Lalehzadeh G, Meisner R, Yamaguchi KD, Ruderman DL, Dinter H, Zajchowski DA. The ubiquitin-conjugating enzyme E2-EPF is overexpressed in primary breast cancer and modulates sensitivity to topoisomerase II inhibition. Neoplasia 2007; 9:601-13. [PMID: 17710163 PMCID: PMC1939933 DOI: 10.1593/neo.07385] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Revised: 06/05/2007] [Accepted: 06/07/2007] [Indexed: 12/30/2022] Open
Abstract
We identified the ubiquitin-conjugating enzyme E2-EPF mRNA as differentially expressed in breast tumors relative to normal tissues and performed studies to elucidate its putative role in cancer. We demonstrated that overexpression of E2-EPF protein correlated with estrogen receptor (ER) negativity in breast cancer specimens and that its expression is cell cycle-regulated, suggesting a potential function for E2-EPF in cell cycle progression. However, reduction of E2-EPF protein levels by > 80% using RNAi had no significant effects on the proliferation of HeLa cervical cancer cells or ER(-) MDA-MB-231 or MDA-MB-453 breast cancer cells. Because E2-EPF protein levels were elevated during the G(2)/M phase of the cell cycle and because E2-EPF mRNA in tumor specimens was frequently coexpressed with genes involved in cell cycle control, spindle assembly, and mitotic surveillance, the possibility that E2-EPF might have a function in the cellular response to agents that induce a G(2) checkpoint or an M checkpoint was investigated. E2-EPF knockdown sensitized HeLa cells to the topoisomerase (topo) II inhibitors etoposide and doxorubicin and also increased topo IIalpha protein levels. These data suggest that combined administration of topo II-directed drugs and E2-EPF inhibitors may enhance their clinical effectiveness.
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Affiliation(s)
- Donato Tedesco
- Department of Cancer Research, Berlex Biosciences, Richmond, CA 94804, USA
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Dimov ND, Zynger DL, Luan C, Kozlowski JM, Yang XJ. Topoisomerase II Alpha Expression in Testicular Germ Cell Tumors. Urology 2007; 69:955-61. [PMID: 17482942 DOI: 10.1016/j.urology.2007.01.068] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2006] [Revised: 11/22/2006] [Accepted: 01/23/2007] [Indexed: 11/29/2022]
Abstract
OBJECTIVES Inhibitors of topoisomerase II alpha (TopoIIalpha), an enzyme with a crucial role in DNA maintenance, are included in the chemotherapy protocols for testicular germ cell tumors (GCTs). Despite the success of current chemotherapy regimens, a significant number of patients experience relapse. We analyzed TopoIIalpha expression in primary and metastatic testicular GCTs because this enzyme is a target for some antineoplastic agents. METHODS Primary GCT specimens from 109 patients, including 57 seminomas and 52 mixed GCTs (41 embryonal carcinomas, 23 yolk sac tumors, 19 seminomas, 8 choriocarcinomas, 17 teratomas with immature elements, and 16 teratomas with mature elements), were obtained from our archives. The metastatic lesions from 11 of the patients with mixed GCTs included seven teratomas with mature components, five embryonal carcinomas, one yolk sac tumor, one choriocarcinoma, and one teratoma with immature components. Representative sections were subjected to immunohistochemistry with monoclonal antibody against TopoIIalpha, and the nuclear staining findings were evaluated. RESULTS Most embryonal carcinoma (100%), yolk sac tumor (95%), seminoma (88%), and choriocarcinoma (62%) components of the GCTs were TopoIIalpha immunoreactive. None of the teratoma specimens with mature elements expressed TopoIIalpha. CONCLUSIONS The results of our study have shown that TopoIIalpha is expressed in most seminomas, embryonal carcinomas, yolk sac tumors, and choriocarcinomas, suggesting a possible mechanism of sensitivity of these components to TopoIIalpha inhibitors. Teratomas with mature and immature elements expressed low levels of TopoIIalpha, which might contribute to their chemoresistance. These findings imply that the variable chemoresponsiveness of testicular GCTs could have an underlying molecular basis.
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MESH Headings
- Adolescent
- Adult
- Antigens, Neoplasm/metabolism
- Biomarkers, Tumor/analysis
- Biopsy, Needle
- Carcinoma, Embryonal/drug therapy
- Carcinoma, Embryonal/enzymology
- Carcinoma, Embryonal/pathology
- Choriocarcinoma/drug therapy
- Choriocarcinoma/enzymology
- Choriocarcinoma/pathology
- DNA Topoisomerases, Type II/metabolism
- DNA-Binding Proteins/antagonists & inhibitors
- DNA-Binding Proteins/metabolism
- Endodermal Sinus Tumor/drug therapy
- Endodermal Sinus Tumor/enzymology
- Endodermal Sinus Tumor/pathology
- Gene Expression Regulation, Neoplastic
- Humans
- Immunohistochemistry
- Male
- Middle Aged
- Neoplasms, Germ Cell and Embryonal/drug therapy
- Neoplasms, Germ Cell and Embryonal/enzymology
- Neoplasms, Germ Cell and Embryonal/pathology
- Prognosis
- Sampling Studies
- Seminoma/drug therapy
- Seminoma/enzymology
- Seminoma/pathology
- Sensitivity and Specificity
- Teratoma/drug therapy
- Teratoma/enzymology
- Teratoma/pathology
- Testicular Neoplasms/drug therapy
- Testicular Neoplasms/enzymology
- Topoisomerase II Inhibitors
- Treatment Outcome
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Affiliation(s)
- Nikolay D Dimov
- Department of Pathology, Northwestern University Feinberg School of Medicine, Chicago, Illinois, USA
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17
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Yoshida K, Yamaguchi T, Shinagawa H, Taira N, Nakayama KI, Miki Y. Protein kinase C delta activates topoisomerase IIalpha to induce apoptotic cell death in response to DNA damage. Mol Cell Biol 2006; 26:3414-31. [PMID: 16611985 PMCID: PMC1447416 DOI: 10.1128/mcb.26.9.3414-3431.2006] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
DNA topoisomerase II is an essential nuclear enzyme that modulates DNA processes by altering the topological state of double-stranded DNA. This enzyme is required for chromosome condensation and segregation; however, the regulatory mechanism of its activation is largely unknown. Here we demonstrate that topoisomerase IIalpha is activated in response to genotoxic stress. Concomitant with the activation, the expression of topoisomerase IIalpha is increased following DNA damage. The results also demonstrate that the proapoptotic kinase protein kinase C delta (PKCdelta) interacts with topoisomerase IIalpha. This association is in an S-phase-specific manner and is required for stabilization and catalytic activation of topoisomerase IIalpha in response to DNA damage. Conversely, inhibition of PKCdelta activity attenuates DNA damage-induced activation of topoisomerase IIalpha. Finally, aberrant activation of topoisomerase IIalpha by PKCdelta is associated with induction of apoptosis upon exposure to genotoxic agents. These findings indicate that PKCdelta regulates topoisomerase IIalpha and thereby cell fate in the genotoxic stress response.
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Affiliation(s)
- Kiyotsugu Yoshida
- Department of Molecular Genetics, Medical Research Institute, Tokyo Medical and Dental University, 1-5-45, Yushima, Bunkyo-ku, Tokyo 113-8510, Japan.
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18
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Barker CR, Mouchel NAP, Jenkins JR. The identification and characterisation of a functional interaction between arginyl-tRNA-protein transferase and topoisomerase II. Biochem Biophys Res Commun 2006; 342:596-604. [PMID: 16488395 DOI: 10.1016/j.bbrc.2006.02.006] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2006] [Accepted: 02/03/2006] [Indexed: 01/22/2023]
Abstract
Topoisomerase II is required for the viability of all eukaryotic cells. It plays important roles in DNA replication, recombination, chromosome segregation, and the maintenance of the nuclear scaffold. Proteins that interact with and regulate this essential enzyme are of great interest. To investigate the role of proteins interacting with the N-terminal domain of the Saccharomyces cerevisiae topoisomerase II, we used a yeast two-hybrid protein interaction screen. We identified an interaction between arginyl-tRNA-protein transferase (Ate1) and the N-terminal domain of the S. cerevisiae topoisomerase II, including the potential site of interaction. Ate1 is a component of the N-end rule protein degradation pathway which targets proteins for degradation. We also propose a previously unidentified role for Ate1 in modulating the level of topoisomerase II through the cell cycle.
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Affiliation(s)
- Catherine R Barker
- School of Clinical Sciences, Division of Gastroenterology, The University of Liverpool, Henry Wellcome Laboratory of Molecular and Cellular Gastroenterology, Crown Street, Liverpool L69 3BX, UK
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19
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Gray MD, Mann M, Nitiss JL, Hendershot LM. Activation of the unfolded protein response is necessary and sufficient for reducing topoisomerase IIalpha protein levels and decreasing sensitivity to topoisomerase-targeted drugs. Mol Pharmacol 2005; 68:1699-707. [PMID: 16141312 DOI: 10.1124/mol.105.014753] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A wide range of chemotherapeutic agents has been identified that are active against solid tumors. However, resistance remains an important obstacle to the development of curative regimens. Whereas much attention has been paid to acquired drug resistance, a variety of physiological pathways also have been described that reduce the sensitivity of previously untreated tumors to cytotoxic antitumor agents. Treatment of cells with pharmacological agents that alter the environment of the endoplasmic reticulum (ER) and activate the unfolded protein response (UPR) can render cells resistant to topoisomerase II poisons. We describe experiments showing that activation of the mammalian ER stress response is both necessary and sufficient to decrease topoisomerase IIalpha protein levels and to render cells resistant to etoposide, a topoisomerase II-targeting drug. This is not caused by the elevated levels of BiP that are a hallmark of this response, because a cell line that has been engineered to overexpress BiP does not show increased resistance to etoposide. The UPR was shown to be required for altered drug sensitivity, because the BiP-overexpressing cell line, which is unable to activate the UPR, did not show decreased topoisomerase II levels or increased resistance to etoposide in response to stress conditions. The transient overexpression of an unfolded protein activated the UPR and led to the concomitant loss of topoisomerase IIalpha protein from the cells, demonstrating that UPR activation is sufficient for the changes in topoisomerase II levels that had been observed previously with pharmacological induction of the UPR.
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Affiliation(s)
- Miranda D Gray
- Department of Molecular Pharmacology, St. Jude Children's Research Hospital, 332 N. Lauderdale, Memphis, Tennessee 38105, USA
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20
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Lou Z, Minter-Dykhouse K, Chen J. BRCA1 participates in DNA decatenation. Nat Struct Mol Biol 2005; 12:589-93. [PMID: 15965487 DOI: 10.1038/nsmb953] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/28/2005] [Accepted: 05/18/2005] [Indexed: 11/08/2022]
Abstract
The tumor suppressor BRCA1 has an important function in the maintenance of genomic stability. Increasing evidence suggests that BRCA1 regulates cell cycle checkpoints and DNA repair after DNA damage. However, little is known about its normal function in the absence of DNA damage. Here we show that BRCA1 interacts and colocalizes with topoisomerase IIalpha in S phase cells. Similar to cells treated with the topoisomerase IIalpha inhibitor ICRF-193, BRCA1-deficient cells show lagging chromosomes, indicating a defect in DNA decatenation and chromosome segregation. More directly, BRCA1 deficiency results in defective DNA decatenation in vitro. Finally, topoisomerase IIalpha is ubiquitinated in a BRCA1-dependent manner, and topoisomerase IIalpha ubiquitination correlates with higher DNA decatenation activity. Together these results suggest an important role of BRCA1 in DNA decatenation and reveal a previously unknown function of BRCA1 in the maintenance of genomic stability.
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Affiliation(s)
- Zhenkun Lou
- Department of Oncology, Mayo Clinic and Foundation, Rochester, Minnesota 55905, USA
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21
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Krasikova A, Kulikova T, Saifitdinova A, Derjusheva S, Gaginskaya E. Centromeric protein bodies on avian lampbrush chromosomes contain a protein detectable with an antibody against DNA topoisomerase II. Chromosoma 2004; 113:316-23. [PMID: 15616868 DOI: 10.1007/s00412-004-0321-5] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2004] [Revised: 10/01/2004] [Accepted: 10/06/2004] [Indexed: 10/26/2022]
Abstract
In the oocyte nuclei (germinal vesicle or GV) of a variety of avian species, prominent spherical entities termed protein bodies (PBs) arise at the centromeric regions of the lampbrush chromosomes (LBCs). In spite of the obvious protein nature of PBs, nothing is known about their composition. We show that an antibody against DNA topoisomerase II (topo II), the DNA unwinding enzyme, recognizes PBs from chaffinch and pigeon oocytes. In later chaffinch oocytes, the PBs fuse to form a karyosphere, which is also labeled by the anti-topo II antibody. Furthermore, we show that proteins characteristic of Cajal bodies and B-snurposomes are not found in PBs, despite morphological similarities among these structures. Using immunoelectron microscopy and immunofluorescent laser scanning microscopy we demonstrated that topo II localizes predominantly in the dense material of PBs. Two antigens of approximately 170 kDa (which corresponds to topo II) and approximately 100 kDa were revealed with the antibody against topo II on immunoblots of avian GV proteins. We propose that the smaller protein results from oocyte specific topo II cleavage, since it was not detected in nuclei from testis cells. This represents the first report of a defined protein in the centromeric PBs on avian LBCs.
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Affiliation(s)
- Alla Krasikova
- Biological Research Institute, Saint-Petersburg State University, Saint Petersburg, 198504, Russia
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22
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Yun J, Tomida A, Andoh T, Tsuruo T. Interaction between glucose-regulated destruction domain of DNA topoisomerase IIalpha and MPN domain of Jab1/CSN5. J Biol Chem 2004; 279:31296-303. [PMID: 15126503 DOI: 10.1074/jbc.m401411200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA topoisomerase (topo) IIalpha, an essential enzyme for cell proliferation, is targeted to a proteasome-dependent degradation pathway when human tumor cells are glucose-starved. Here we show that the topo IIalpha destabilization depends on the newly identified domain, GRDD (glucose-regulated destruction domain), which was mapped to the N-terminal 70-170 amino acid sequence. Indeed, the deletion of GRDD conferred a stable feature on topo IIalpha, whereas the fusion of GRDD rendered green fluorescent protein unstable under glucose starvation conditions. Nuclear localization was a prerequisite for GRDD function, because the inhibition of nuclear translocation resulted in the suppression of GRDD-mediated topo IIalpha degradation. Further, GRDD was identified as an interactive domain for Jab1/CSN5, which promoted the degradation of topo IIalpha in a manner dependent on the MPN (Mpr1p/Prd1p N terminus) domain. Depleting Jab1/CSN5 by antisense oligonucleotide and treating cells with the CSN-associated kinase inhibitor, curcumin, inhibited topo IIalpha degradation induced by glucose starvation. These findings demonstrate that GRDD can act as a stress-activated degron for regulating topo IIalpha stability, possibly through interaction with the MPN domain of Jab1/CSN5.
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Affiliation(s)
- Jisoo Yun
- Institute of Molecular and Cellular Biosciences, The University of Tokyo, 1-1-1,Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan
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23
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Abstract
It is thought that when tumor cells are treated with anticancer drugs, they die through the apoptotic pathway and that cell resistance to cancer chemotherapy is mainly a resistance to apoptosis commitment. p53 is not functional in nearly half of the tumors examined and because of its involvement (directly or through its target genes) in the apoptotic pathway, drug resistance to chemotherapy has been largely attributed to the status of this "tumor suppressor protein". Topoisomerase II (topo II) inhibitors are widely used not only as single agents, but also in the majority of combination treatment protocols for hematologic malignancies and solid tumors. The relationship between p53 and topo II raises many questions about basic regulatory, biochemical, structural and functional characteristics that could be different in cells in different tissues, and most importantly, between different tumor cell types and their normal tissue counterpart. Understanding these relationships may lead to strategies for chemotherapy optimization and further precision targeting of tumor cells in order to avoid drug resistance and thereby chemotherapy failure.
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Affiliation(s)
- Nikola I Valkov
- Department of Interdisciplinary Oncology, H Lee Moffitt Cancer Center and Research Institute, University of South Florida, 12902 Magnolia Drive, Tampa, FL 33612, USA
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Wu HM, Chi KH, Lin WW. Proteasome inhibitors stimulate activator protein-1 pathway via reactive oxygen species production. FEBS Lett 2002; 526:101-5. [PMID: 12208513 DOI: 10.1016/s0014-5793(02)03151-4] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
In this report we explored the effects of proteasome inhibitors (MG132, aLLN, lactacystin and MG262) on interleukin-8 (IL-8) induction. In HEK293 cells, proteasome inhibitors could concentration-dependently increase IL-8 promoter and activator protein-1 (AP-1) activities, but inhibited nuclear factor (NF)-kappa B activation induced by cytokines. The stimulating effects on IL-8 promoter and AP-1 were reduced by N-acetylcysteine, glutathione, diphenyleneiodonium, rotenone and antimycin A. Fluorescent analysis using 2',7'-dichlorodihydrofluorescin diacetate further confirmed the abilities of proteasome inhibitors to induce reactive oxygen species (ROS) production. These results suggest that ROS production by proteasome inhibitors leads to AP-1 activation, which in the absence of NF-kappa B activation still transactivates IL-8 gene expression.
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Affiliation(s)
- Hsiao-Mei Wu
- Department of Pharmacology, College of Medicine, National Taiwan University, Taipei, Taiwan
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25
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St Pierre J, Wright DJ, Rowe TC, Wright SJ. DNA topoisomerase II distribution in mouse preimplantation embryos. Mol Reprod Dev 2002; 61:335-46. [PMID: 11835579 DOI: 10.1002/mrd.10016] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
DNA topoisomerase II (topo II) is an essential enzyme that mediates a variety of chromosome activities including DNA replication, transcription, recombination, and chromosome condensation and segregation. Isoform-specific anti-topo II antibodies were used to determine the distribution of topo II alpha and beta in mouse gametes and embryos. Immunoblot analysis with two anti-topo IIalpha antibodies revealed that a 170 kDa topo IIalpha band was present in ovary and testis. Mature sperm exhibited an 89 kDa band only, which may be a degradation product of topo IIalpha. Immunoblots probed with a monoclonal antibody that recognizes both isoforms, showed bands at 170 and 180 kDa, which correspond to topo IIalpha and beta, respectively. An additional 100 kDa band was also present in ovary and testis. Mature sperm did not exhibit staining with this antibody. We also localized topo II in mouse gametes and embryos up to the blastocyst stage using immunofluorescence microscopy. While both isoforms were found in nuclei and nucleoli of germinal vesicle oocytes, topo IIalpha localized to metaphase chromosomes during meiosis, and only to nucleoli during embryonic interphase. Topo IIbeta was absent from chromosomes of metaphase II oocytes, but localized to embryonic interphase nuclei. Both full-length isoforms were absent from sperm, indicating topo II is stored maternally. These results identify topo II as an important component of mouse oocyte and embryonic chromatin, and suggest its involvement in oocyte maturation and preimplantation embryonic development. The different immunofluorescent staining patterns indicate topo IIalpha and beta may serve different roles during the embryonic cell cycle.
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Affiliation(s)
- Jason St Pierre
- Department of Biology, University of Dayton, Dayton, Ohio 45469-2320, USA
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26
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Abstract
Although the proteasome is responsible for the majority of intracellular protein degradation, and has been demonstrated to play a pivotal role in a diverse array of cellular activities, the role of the proteasome in the central nervous system is only beginning to be elucidated. Recent studies have demonstrated that proteasome inhibition occurs in numerous neurodegenerative conditions, and that proteasome inhibition is sufficient to induce neuron death, elevate intracellular levels of protein oxidation, and increase neural vulnerability to subsequent injury. The focus of this review is to describe what is currently known about proteasome biology in the central nervous system and to discuss the possible role of proteasome inhibition in the neurodegenerative process.
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Affiliation(s)
- Q Ding
- Department of Anatomy, University of Kentucky, Lexington, KY, USA
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