1
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Endsley CE, Moore KA, Townsley TD, Durston KK, Deweese JE. Bioinformatic Analysis of Topoisomerase IIα Reveals Interdomain Interdependencies and Critical C-Terminal Domain Residues. Int J Mol Sci 2024; 25:5674. [PMID: 38891861 PMCID: PMC11172036 DOI: 10.3390/ijms25115674] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2024] [Revised: 05/01/2024] [Accepted: 05/17/2024] [Indexed: 06/21/2024] Open
Abstract
DNA Topoisomerase IIα (Top2A) is a nuclear enzyme that is a cancer drug target, and there is interest in identifying novel sites on the enzyme to inhibit cancer cells more selectively and to reduce off-target toxicity. The C-terminal domain (CTD) is one potential target, but it is an intrinsically disordered domain, which prevents structural analysis. Therefore, we set out to analyze the sequence of Top2A from 105 species using bioinformatic analysis, including the PSICalc algorithm, Shannon entropy analysis, and other approaches. Our results demonstrate that large (10th-order) interdependent clusters are found including non-proximal positions across the major domains of Top2A. Further, CTD-specific clusters of the third, fourth, and fifth order, including positions that had been previously analyzed via mutation and biochemical assays, were identified. Some of these clusters coincided with positions that, when mutated, either increased or decreased relaxation activity. Finally, sites of low Shannon entropy (i.e., low variation in amino acids at a given site) were identified and mapped as key positions in the CTD. Included in the low-entropy sites are phosphorylation sites and charged positions. Together, these results help to build a clearer picture of the critical positions in the CTD and provide potential sites/regions for further analysis.
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Affiliation(s)
- Clark E. Endsley
- Biological, Physical, and Human Sciences Department, Freed-Hardeman University, Henderson, TN 38340, USA
| | - Kori A. Moore
- Biological, Physical, and Human Sciences Department, Freed-Hardeman University, Henderson, TN 38340, USA
| | | | - Kirk K. Durston
- Department of Research and Publications, Digital Strategies, Langley, BC V2Y 1N5, Canada
| | - Joseph E. Deweese
- Biological, Physical, and Human Sciences Department, Freed-Hardeman University, Henderson, TN 38340, USA
- Department of Biochemistry, Vanderbilt University, Nashville, TN 37232, USA
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2
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Soliman TN, Keifenheim D, Parker PJ, Clarke DJ. Cell cycle responses to Topoisomerase II inhibition: Molecular mechanisms and clinical implications. J Cell Biol 2023; 222:e202209125. [PMID: 37955972 PMCID: PMC10641588 DOI: 10.1083/jcb.202209125] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/22/2023] [Revised: 10/24/2023] [Accepted: 10/25/2023] [Indexed: 11/15/2023] Open
Abstract
DNA Topoisomerase IIA (Topo IIA) is an enzyme that alters the topological state of DNA and is essential for the separation of replicated sister chromatids and the integrity of cell division. Topo IIA dysfunction activates cell cycle checkpoints, resulting in arrest in either the G2-phase or metaphase of mitosis, ultimately triggering the abscission checkpoint if non-disjunction persists. These events, which directly or indirectly monitor the activity of Topo IIA, have become of major interest as many cancers have deficiencies in Topoisomerase checkpoints, leading to genome instability. Recent studies into how cells sense Topo IIA dysfunction and respond by regulating cell cycle progression demonstrate that the Topo IIA G2 checkpoint is distinct from the G2-DNA damage checkpoint. Likewise, in mitosis, the metaphase Topo IIA checkpoint is separate from the spindle assembly checkpoint. Here, we integrate mechanistic knowledge of Topo IIA checkpoints with the current understanding of how cells regulate progression through the cell cycle to accomplish faithful genome transmission and discuss the opportunities this offers for therapy.
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Affiliation(s)
- Tanya N. Soliman
- Barts Cancer Institute, Queen Mary University London, London, UK
| | - Daniel Keifenheim
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
| | | | - Duncan J. Clarke
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN, USA
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3
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Lee J, Wu M, Inman JT, Singh G, Park SH, Lee JH, Fulbright RM, Hong Y, Jeong J, Berger JM, Wang MD. Chromatinization modulates topoisomerase II processivity. Nat Commun 2023; 14:6844. [PMID: 37891161 PMCID: PMC10611788 DOI: 10.1038/s41467-023-42600-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2023] [Accepted: 10/17/2023] [Indexed: 10/29/2023] Open
Abstract
Type IIA topoisomerases are essential DNA processing enzymes that must robustly and reliably relax DNA torsional stress. While cellular processes constantly create varying torsional stress, how this variation impacts type IIA topoisomerase function remains obscure. Using multiple single-molecule approaches, we examined the torsional dependence of eukaryotic topoisomerase II (topo II) activity on naked DNA and chromatin. We observed that topo II is ~50-fold more processive on buckled DNA than previously estimated. We further discovered that topo II relaxes supercoiled DNA prior to plectoneme formation, but with processivity reduced by ~100-fold. This relaxation decreases with diminishing torsion, consistent with topo II capturing transient DNA loops. Topo II retains high processivity on buckled chromatin (~10,000 turns) and becomes highly processive even on chromatin under low torsional stress (~1000 turns), consistent with chromatin's predisposition to readily form DNA crossings. This work establishes that chromatin is a major stimulant of topo II function.
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Affiliation(s)
- Jaeyoon Lee
- Physics Department & LASSP, Cornell University, Ithaca, NY, 14853, USA
| | - Meiling Wu
- Physics Department & LASSP, Cornell University, Ithaca, NY, 14853, USA
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY, 14853, USA
| | - James T Inman
- Physics Department & LASSP, Cornell University, Ithaca, NY, 14853, USA
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY, 14853, USA
| | - Gundeep Singh
- Biophysics Program, Cornell University, Ithaca, NY, 14853, USA
| | - Seong Ha Park
- Biophysics Program, Cornell University, Ithaca, NY, 14853, USA
| | - Joyce H Lee
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | | | - Yifeng Hong
- Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY, 14853, USA
| | - Joshua Jeong
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD, 21205, USA
| | - Michelle D Wang
- Physics Department & LASSP, Cornell University, Ithaca, NY, 14853, USA.
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY, 14853, USA.
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4
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Lee J, Wu M, Inman JT, Singh G, Park SH, Lee JH, Fulbright RM, Hong Y, Jeong J, Berger JM, Wang MD. Chromatinization Modulates Topoisomerase II Processivity. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.10.03.560726. [PMID: 37873421 PMCID: PMC10592930 DOI: 10.1101/2023.10.03.560726] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/25/2023]
Abstract
Type IIA topoisomerases are essential DNA processing enzymes that must robustly and reliably relax DNA torsional stress in vivo. While cellular processes constantly create different degrees of torsional stress, how this stress feeds back to control type IIA topoisomerase function remains obscure. Using a suite of single-molecule approaches, we examined the torsional impact on supercoiling relaxation of both naked DNA and chromatin by eukaryotic topoisomerase II (topo II). We observed that topo II was at least ~ 50-fold more processive on plectonemic DNA than previously estimated, capable of relaxing > 6000 turns. We further discovered that topo II could relax supercoiled DNA prior to plectoneme formation, but with a ~100-fold reduction in processivity; strikingly, the relaxation rate in this regime decreased with diminishing torsion in a manner consistent with the capture of transient DNA loops by topo II. Chromatinization preserved the high processivity of the enzyme under high torsional stress. Interestingly, topo II was still highly processive (~ 1000 turns) even under low torsional stress, consistent with the predisposition of chromatin to readily form DNA crossings. This work establishes that chromatin is a major stimulant of topo II function, capable of enhancing function even under low torsional stress.
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Affiliation(s)
- Jaeyoon Lee
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
| | - Meiling Wu
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA
| | - James T. Inman
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA
| | - Gundeep Singh
- Biophysics Program, Cornell University, Ithaca, NY 14853, USA
| | - Seong ha Park
- Biophysics Program, Cornell University, Ithaca, NY 14853, USA
| | - Joyce H. Lee
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | | | - Yifeng Hong
- Department of Electrical and Computer Engineering, Cornell University, Ithaca, NY 14853, USA
| | - Joshua Jeong
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - James M. Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
| | - Michelle D. Wang
- Physics Department & LASSP, Cornell University, Ithaca, NY 14853, USA
- Howard Hughes Medical Institute, Cornell University, Ithaca, NY 14853, USA
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5
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Sundararajan S, Park H, Kawano S, Johansson M, Lama B, Saito-Fujita T, Saitoh N, Arnaoutov A, Dasso M, Wang Z, Keifenheim D, Clarke DJ, Azuma Y. Methylated histones on mitotic chromosomes promote topoisomerase IIα function for high fidelity chromosome segregation. iScience 2023; 26:106743. [PMID: 37197327 PMCID: PMC10183659 DOI: 10.1016/j.isci.2023.106743] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2022] [Revised: 10/31/2022] [Accepted: 04/21/2023] [Indexed: 05/19/2023] Open
Abstract
DNA Topoisomerase IIα (TopoIIα) decatenates sister chromatids, allowing their segregation in mitosis. Without the TopoIIα Strand Passage Reaction (SPR), chromosome bridges and ultra-fine DNA bridges (UFBs) arise in anaphase. The TopoIIα C-terminal domain is dispensable for the SPR in vitro but essential for mitotic functions in vivo. Here, we present evidence that the Chromatin Tether (ChT) within the CTD interacts with specific methylated nucleosomes and is crucial for high-fidelity chromosome segregation. Mutation of individual αChT residues disrupts αChT-nucleosome interaction, induces loss of segregation fidelity and reduces association of TopoIIα with chromosomes. Specific methyltransferase inhibitors reducing histone H3 or H4 methylation decreased TopoIIα at centromeres and increased segregation errors. Methyltransferase inhibition did not further increase aberrant anaphases in the ChT mutants, indicating a functional connection. The evidence reveals novel cellular regulation whereby TopoIIα specifically interacts with methylated nucleosomes via the αChT to ensure high-fidelity chromosome segregation.
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Affiliation(s)
- Sanjana Sundararajan
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA
| | - Hyewon Park
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA
| | - Shinji Kawano
- Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama 700-0081, Japan
| | - Marnie Johansson
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Bunu Lama
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA
| | - Tomoko Saito-Fujita
- Division of Cancer Biology, The Cancer Institute of Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan
| | - Noriko Saitoh
- Division of Cancer Biology, The Cancer Institute of Japanese Foundation for Cancer Research, Tokyo 135-8550, Japan
| | - Alexei Arnaoutov
- Division of Molecular and Cellular Biology, National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4480, USA
| | - Mary Dasso
- Division of Molecular and Cellular Biology, National Institute for Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892-4480, USA
| | - Zhengqiang Wang
- Center for Drug Design, College of Pharmacy, University of Minnesota, Minneapolis, MN 55455, USA
| | - Daniel Keifenheim
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Duncan J. Clarke
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN 55455, USA
| | - Yoshiaki Azuma
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA
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6
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Super-resolution microscopy reveals the number and distribution of topoisomerase IIα and CENH3 molecules within barley metaphase chromosomes. Chromosoma 2023; 132:19-29. [PMID: 36719450 PMCID: PMC9981516 DOI: 10.1007/s00412-023-00785-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2022] [Revised: 10/25/2022] [Accepted: 12/13/2022] [Indexed: 02/01/2023]
Abstract
Topoisomerase IIα (Topo IIα) and the centromere-specific histone H3 variant CENH3 are key proteins involved in chromatin condensation and centromere determination, respectively. Consequently, they are required for proper chromosome segregation during cell divisions. We combined two super-resolution techniques, structured illumination microscopy (SIM) to co-localize Topo IIα and CENH3, and photoactivated localization microscopy (PALM) to determine their molecule numbers in barley metaphase chromosomes. We detected a dispersed Topo IIα distribution along chromosome arms but an accumulation at centromeres, telomeres, and nucleolus-organizing regions. With a precision of 10-50 nm, we counted ~ 20,000-40,000 Topo IIα molecules per chromosome, 28% of them within the (peri)centromere. With similar precision, we identified ~13,500 CENH3 molecules per centromere where Topo IIα proteins and CENH3-containing chromatin intermingle. In short, we demonstrate PALM as a useful method to count and localize single molecules with high precision within chromosomes. The ultrastructural distribution and the detected amount of Topo IIα and CENH3 are instrumental for a better understanding of their functions during chromatin condensation and centromere determination.
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7
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Jeong J, Lee JH, Carcamo CC, Parker MW, Berger JM. DNA-Stimulated Liquid-Liquid phase separation by eukaryotic topoisomerase ii modulates catalytic function. eLife 2022; 11:e81786. [PMID: 36342377 PMCID: PMC9674351 DOI: 10.7554/elife.81786] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/12/2022] [Accepted: 11/06/2022] [Indexed: 11/09/2022] Open
Abstract
Type II topoisomerases modulate chromosome supercoiling, condensation, and catenation by moving one double-stranded DNA segment through a transient break in a second duplex. How DNA strands are chosen and selectively passed to yield appropriate topological outcomes - for example, decatenation vs. catenation - is poorly understood. Here, we show that at physiological enzyme concentrations, eukaryotic type IIA topoisomerases (topo IIs) readily coalesce into condensed bodies. DNA stimulates condensation and fluidizes these assemblies to impart liquid-like behavior. Condensation induces both budding yeast and human topo IIs to switch from DNA unlinking to active DNA catenation, and depends on an unstructured C-terminal region, the loss of which leads to high levels of knotting and reduced catenation. Our findings establish that local protein concentration and phase separation can regulate how topo II creates or dissolves DNA links, behaviors that can account for the varied roles of the enzyme in supporting transcription, replication, and chromosome compaction.
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Affiliation(s)
- Joshua Jeong
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Joyce H Lee
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Claudia C Carcamo
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of MedicineBaltimoreUnited States
| | - Matthew W Parker
- Department of Biophysics, University of Texas Southwestern Medical CenterDallasUnited States
| | - James M Berger
- Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of MedicineBaltimoreUnited States
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8
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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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9
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Moreira F, Arenas M, Videira A, Pereira F. Evolutionary History of TOPIIA Topoisomerases in Animals. J Mol Evol 2022; 90:149-165. [PMID: 35165762 DOI: 10.1007/s00239-022-10048-2] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2021] [Accepted: 01/26/2022] [Indexed: 01/15/2023]
Abstract
TOPIIA topoisomerases are required for the regulation of DNA topology by DNA cleavage and re-ligation and are important targets of antibiotic and anticancer agents. Humans possess two TOPIIA paralogue genes (TOP2A and TOP2B) with high sequence and structural similarity but distinct cellular functions. Despite their functional and clinical relevance, the evolutionary history of TOPIIA is still poorly understood. Here we show that TOPIIA is highly conserved in Metazoa. We also found that TOPIIA paralogues from jawed and jawless vertebrates had different origins related with tetraploidization events. After duplication, TOP2B evolved under a stronger purifying selection than TOP2A, perhaps promoted by the more specialized role of TOP2B in postmitotic cells. We also detected genetic signatures of positive selection in the highly variable C-terminal domain (CTD), possibly associated with adaptation to cellular interactions. By comparing TOPIIA from modern and archaic humans, we found two amino acid substitutions in the TOP2A CTD, suggesting that TOP2A may have contributed to the evolution of present-day humans, as proposed for other cell cycle-related genes. Finally, we identified six residues conferring resistance to chemotherapy differing between TOP2A and TOP2B. These six residues could be targets for the development of TOP2A-specific inhibitors that would avoid the side effects caused by inhibiting TOP2B. Altogether, our findings clarify the origin, diversification and selection pressures governing the evolution of animal TOPIIA.
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Affiliation(s)
- Filipa Moreira
- Interdisciplinary Centre of Marine and Environmental Research (CIIMAR), University of Porto, Terminal de Cruzeiros do Porto de Leixões, Av. General Norton de Matos s/n, 4450-208, Matosinhos, Portugal
- ICBAS - Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Rua Jorge de Viterbo Ferreira 228, 4050-313, Porto, Portugal
| | - Miguel Arenas
- Department of Biochemistry, Genetics and Immunology, University of Vigo, 36310, Vigo, Spain
- CINBIO, Universidade de Vigo, 36310, Vigo, Spain
- Galicia Sur Health Research Institute (IIS Galicia Sur), 36310, Vigo, Spain
| | - Arnaldo Videira
- ICBAS - Instituto de Ciências Biomédicas de Abel Salazar, Universidade do Porto, Rua Jorge de Viterbo Ferreira 228, 4050-313, Porto, Portugal
- IBMC-Instituto de Biologia Molecular e Celular, Universidade do Porto, Porto, Portugal
- i3S-Instituto de Investigação e Inovação em Saúde, Universidade do Porto, Porto, Portugal
| | - Filipe Pereira
- IDENTIFICA Genetic Testing, Rua Simão Bolívar 259 3º Dir Tras, 4470-214, Maia, Portugal.
- Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456, Coimbra, Portugal.
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10
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Dougherty A, Hawaz MG, Hoang KG, Trac J, Keck JM, Ayes C, Deweese JE. Exploration of the Role of the C-Terminal Domain of Human DNA Topoisomerase IIα in Catalytic Activity. ACS OMEGA 2021; 6:25892-25903. [PMID: 34660952 PMCID: PMC8515377 DOI: 10.1021/acsomega.1c02083] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/19/2021] [Accepted: 09/15/2021] [Indexed: 06/13/2023]
Abstract
Human topoisomerase IIα (TOP2A) is a vital nuclear enzyme involved in resolving knots and tangles in DNA during replication and cell division. TOP2A is a homodimer with a symmetrical, multidomain structure. While the N-terminal and core regions of the protein are well-studied, the C-terminal domain is poorly understood but is involved in enzyme regulation and is predicted to be intrinsically disordered. In addition, it appears to be a major region of post-translational modification and includes several Ser and Thr residues, many of which have not been studied for biochemical effects. Therefore, we generated a series of human TOP2A mutants where we changed specific Ser and Thr residues in the C-terminal domain to Ala, Gly, or Ile residues. We designed, purified, and examined 11 mutant TOP2A enzymes. The amino acid changes were made between positions 1272 and 1525 with 1-7 residues changed per mutant. Several mutants displayed increased levels of DNA cleavage without displaying any change in plasmid DNA relaxation or DNA binding. For example, mutations in the regions 1272-1279, 1324-1343, 1351-1365, and 1374-1377 produced 2-3 times more DNA cleavage in the presence of etoposide than wild-type TOP2A. Further, several mutants displayed changes in relaxation and/or decatenation activity. Together, these results support previous findings that the C-terminal domain of TOP2A influences catalytic activity and interacts with the substrate DNA. Furthermore, we hypothesize that it may be possible to regulate the enzyme by targeting positions in the C-terminal domain. Because the C-terminal domain differs between the two human TOP2 isoforms, this strategy may provide a means for selectively targeting TOP2A for therapeutic inhibition. Additional studies are warranted to explore these results in more detail.
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Affiliation(s)
- Ashley
C. Dougherty
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Mariam G. Hawaz
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Kristine G. Hoang
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Judy Trac
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Jacob M. Keck
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Carmen Ayes
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
| | - Joseph E. Deweese
- Department
of Pharmaceutical Sciences, Lipscomb University
College of Pharmacy and Health Sciences, One University Park Drive, Nashville, Tennessee 37204-3951, United States
- Department
of Biochemistry, Vanderbilt University School
of Medicine, 2215 Garland
Avenue, Nashville, Tennessee 37232-0146, United States
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11
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Choppakatla P, Dekker B, Cutts EE, Vannini A, Dekker J, Funabiki H. Linker histone H1.8 inhibits chromatin binding of condensins and DNA topoisomerase II to tune chromosome length and individualization. eLife 2021; 10:e68918. [PMID: 34406118 PMCID: PMC8416026 DOI: 10.7554/elife.68918] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2021] [Accepted: 08/13/2021] [Indexed: 12/14/2022] Open
Abstract
DNA loop extrusion by condensins and decatenation by DNA topoisomerase II (topo II) are thought to drive mitotic chromosome compaction and individualization. Here, we reveal that the linker histone H1.8 antagonizes condensins and topo II to shape mitotic chromosome organization. In vitro chromatin reconstitution experiments demonstrate that H1.8 inhibits binding of condensins and topo II to nucleosome arrays. Accordingly, H1.8 depletion in Xenopus egg extracts increased condensins and topo II levels on mitotic chromatin. Chromosome morphology and Hi-C analyses suggest that H1.8 depletion makes chromosomes thinner and longer through shortening the average loop size and reducing the DNA amount in each layer of mitotic loops. Furthermore, excess loading of condensins and topo II to chromosomes by H1.8 depletion causes hyper-chromosome individualization and dispersion. We propose that condensins and topo II are essential for chromosome individualization, but their functions are tuned by the linker histone to keep chromosomes together until anaphase.
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Affiliation(s)
- Pavan Choppakatla
- Laboratory of Chromosome and Cell Biology, The Rockefeller UniversityNew YorkUnited States
| | - Bastiaan Dekker
- Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical SchoolWorcesterUnited States
| | - Erin E Cutts
- Division of Structural Biology, The Institute of Cancer ResearchLondonUnited Kingdom
| | - Alessandro Vannini
- Division of Structural Biology, The Institute of Cancer ResearchLondonUnited Kingdom
- Fondazione Human Technopole, Structural Biology Research Centre, 20157MilanItaly
| | - Job Dekker
- Program in Systems Biology, Department of Biochemistry and Molecular Pharmacology, University of Massachusetts Medical SchoolWorcesterUnited States
- Howard Hughes Medical InstituteChevy ChaseUnited States
| | - Hironori Funabiki
- Laboratory of Chromosome and Cell Biology, The Rockefeller UniversityNew YorkUnited States
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12
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Vanden Broeck A, Lotz C, Drillien R, Haas L, Bedez C, Lamour V. Structural basis for allosteric regulation of Human Topoisomerase IIα. Nat Commun 2021; 12:2962. [PMID: 34016969 PMCID: PMC8137924 DOI: 10.1038/s41467-021-23136-6] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/12/2020] [Accepted: 04/15/2021] [Indexed: 12/01/2022] Open
Abstract
The human type IIA topoisomerases (Top2) are essential enzymes that regulate DNA topology and chromosome organization. The Topo IIα isoform is a prime target for antineoplastic compounds used in cancer therapy that form ternary cleavage complexes with the DNA. Despite extensive studies, structural information on this large dimeric assembly is limited to the catalytic domains, hindering the exploration of allosteric mechanism governing the enzyme activities and the contribution of its non-conserved C-terminal domain (CTD). Herein we present cryo-EM structures of the entire human Topo IIα nucleoprotein complex in different conformations solved at subnanometer resolutions (3.6-7.4 Å). Our data unveils the molecular determinants that fine tune the allosteric connections between the ATPase domain and the DNA binding/cleavage domain. Strikingly, the reconstruction of the DNA-binding/cleavage domain uncovers a linker leading to the CTD, which plays a critical role in modulating the enzyme's activities and opens perspective for the analysis of post-translational modifications.
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Affiliation(s)
- Arnaud Vanden Broeck
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France
- Department of Integrated Structural Biology, IGBMC, Illkirch, France
| | - Christophe Lotz
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France
- Department of Integrated Structural Biology, IGBMC, Illkirch, France
| | - Robert Drillien
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France
- Department of Integrated Structural Biology, IGBMC, Illkirch, France
| | - Léa Haas
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France
- Department of Integrated Structural Biology, IGBMC, Illkirch, France
| | - Claire Bedez
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France
- Department of Integrated Structural Biology, IGBMC, Illkirch, France
| | - Valérie Lamour
- Université de Strasbourg, CNRS, INSERM, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), Illkirch, France.
- Department of Integrated Structural Biology, IGBMC, Illkirch, France.
- Hôpitaux Universitaires de Strasbourg, Strasbourg, France.
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13
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McKie SJ, Neuman KC, Maxwell A. DNA topoisomerases: Advances in understanding of cellular roles and multi-protein complexes via structure-function analysis. Bioessays 2021; 43:e2000286. [PMID: 33480441 PMCID: PMC7614492 DOI: 10.1002/bies.202000286] [Citation(s) in RCA: 75] [Impact Index Per Article: 25.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2020] [Revised: 12/06/2020] [Accepted: 12/17/2020] [Indexed: 12/15/2022]
Abstract
DNA topoisomerases, capable of manipulating DNA topology, are ubiquitous and indispensable for cellular survival due to the numerous roles they play during DNA metabolism. As we review here, current structural approaches have revealed unprecedented insights into the complex DNA-topoisomerase interaction and strand passage mechanism, helping to advance our understanding of their activities in vivo. This has been complemented by single-molecule techniques, which have facilitated the detailed dissection of the various topoisomerase reactions. Recent work has also revealed the importance of topoisomerase interactions with accessory proteins and other DNA-associated proteins, supporting the idea that they often function as part of multi-enzyme assemblies in vivo. In addition, novel topoisomerases have been identified and explored, such as topo VIII and Mini-A. These new findings are advancing our understanding of DNA-related processes and the vital functions topos fulfil, demonstrating their indispensability in virtually every aspect of DNA metabolism.
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Affiliation(s)
- Shannon J. McKie
- Department Biological Chemistry, John Innes Centre, Norwich, UK
- Laboratory of Single Molecule Biophysics, NHLBI, Bethesda, Maryland, USA
| | - Keir C. Neuman
- Laboratory of Single Molecule Biophysics, NHLBI, Bethesda, Maryland, USA
| | - Anthony Maxwell
- Department Biological Chemistry, John Innes Centre, Norwich, UK
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14
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Yasuda K, Kato Y, Ikeda S, Kawano S. Regulation of catalytic activity and nucleolar localization of rat DNA topoisomerase IIα through its C-terminal domain. Genes Genet Syst 2021; 95:291-302. [PMID: 33551432 DOI: 10.1266/ggs.20-00038] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
Type II DNA topoisomerase (topo II) catalyzes double-stranded DNA cleavage and re-ligation, thus solving problems in DNA topology. Vertebrates have two isozymes (α and β). Recently, the C-terminal regulatory domain (CRD), which regulates catalytic activity and subnuclear localization by associating with RNA, was identified within the C-terminal domain (CTD) of rat topo IIβ. In contrast, it is unclear whether a β CRD-like domain is present in the CTD of topo IIα. In this study, we aimed to identify an RNA-mediated regulatory domain in the rat topo IIα CTD. First, we exchanged the CTDs of rat topo IIα (amino acids 1,192-1,528) and β (1,201-1,614) and examined the two chimeras' in vitro catalytic activities. Interestingly, the relaxation activities of topo IIα WT enzyme and both of the CTD-swapped mutants were inhibited in the presence of isolated cellular RNA, suggesting that the α CTD is involved in the RNA-mediated regulation of catalytic activity in topo IIα. The results of on-bead assays using a CTD-deleted mutant of rat topo IIα indicated that the RNA-mediated inhibition of the relaxation activity was caused by an interaction between the α CTD and RNA. Further, to identify the domain within the CTD that is associated with subnuclear localization of rat topo IIα, we transiently expressed EGFP-tagged CTD deletion mutants in human cells. The data indicated that the 1,192-1,289 region of rat topo IIα was required for targeting the enzyme to nucleoli. Finally, a relaxation assay using 1-1,289 and Δ1,192-1,289 truncated mutants indicated that the 1,192-1,289 region is involved in RNA-mediated inhibition. These results indicated that the CTD of rat topo IIα, containing the 1,192-1,289 region, is involved in the regulation of catalytic activity by associating with RNA, as well as in the localization to nucleoli in interphase cells.
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Affiliation(s)
- Kazushi Yasuda
- Department of Biochemistry, Faculty of Science, Okayama University of Science
| | - Yuri Kato
- Department of Biochemistry, Faculty of Science, Okayama University of Science
| | - Shogo Ikeda
- Department of Biochemistry, Faculty of Science, Okayama University of Science
| | - Shinji Kawano
- Department of Biochemistry, Faculty of Science, Okayama University of Science
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15
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Johansson M, Azuma Y, Clarke DJ. Role of Aurora B and Haspin kinases in the metaphase Topoisomerase II checkpoint. Cell Cycle 2021; 20:345-352. [PMID: 33459116 DOI: 10.1080/15384101.2021.1875671] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022] Open
Abstract
DNA Topoisomerase II (TopoII) uses ATP hydrolysis to decatenate chromosomes so that sister chromatids can faithfully segregate in mitosis. When the TopoII enzyme cycle stalls due to failed ATP hydrolysis, the onset of anaphase is delayed, presumably to allow extra time for decatenation to be completed. Recent evidence revealed that, unlike the spindle assembly checkpoint, this TopoII checkpoint response requires Aurora B and Haspin kinases and is triggered by SUMOylation of the C-terminal domain of TopoII.
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Affiliation(s)
- M Johansson
- Department of Genetics, Cell Biology & Development, University of Minnesota , Minneapolis, MN, USA
| | - Y Azuma
- Department of Molecular Biosciences, University of Kansas , Lawrence, KS, USA
| | - D J Clarke
- Department of Genetics, Cell Biology & Development, University of Minnesota , Minneapolis, MN, USA
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16
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Kawano S, Fujimoto K, Yasuda K, Ikeda S. DNA binding activity of the proximal C-terminal domain of rat DNA topoisomerase IIβ is involved in ICRF-193-induced closed-clamp formation. PLoS One 2020; 15:e0239466. [PMID: 32960919 PMCID: PMC7508362 DOI: 10.1371/journal.pone.0239466] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Accepted: 09/08/2020] [Indexed: 11/30/2022] Open
Abstract
DNA topoisomerase II (topo II) is an essential enzyme that regulates DNA topology by DNA cleavage and re-ligation. In vertebrates, there are two isozymes, α and β. The C-terminal domain (CTD) of the isozymes, which shows a low degree of sequence homology between α and β, is involved in each isozyme-specific intracellular behavior. The CTD of topo IIβ is supposedly involved in topo II regulation. Topo IIβ is maintained in an inactive state in the nucleoli by the binding of RNA to the 50-residue region termed C-terminal regulatory domain (CRD) present in the CTD. Although in vitro biochemical analysis indicates that the CTD of topo IIβ has DNA binding activity, it is unclear whether CTD influences catalytic reaction in the nucleoplasm. Here, we show that the proximal CTD (hereafter referred to as pCTD) of rat topo IIβ, including the CRD, is involved in the catalytic reaction in the nucleoplasm. We identified the pCTD as a domain with DNA binding activity by in vitro catenation assay and electrophoretic mobility shift assay. Fluorescence recovery after photo-bleaching (FRAP) analysis of pCTD-lacking mutant (ΔpCTD) showed higher mobility in nucleoplasm than that of the wild-type enzyme, indicating that the pCTD also affected the nuclear dynamics of topo IIβ. ICRF-193, one of the topo II catalytic inhibitors, induces the formation of closed-clamp intermediates of topo II. Treatment of ΔpCTD with ICRF-193 significantly decreased the efficiency of closed-clamp formation. Altogether, our data indicate that the binding of topo IIβ to DNA through the pCTD is required for the catalytic reaction in the nucleoplasm.
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Affiliation(s)
- Shinji Kawano
- Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama, Japan
- * E-mail:
| | - Kunpei Fujimoto
- Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama, Japan
| | - Kazushi Yasuda
- Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama, Japan
| | - Shogo Ikeda
- Department of Biochemistry, Faculty of Science, Okayama University of Science, Okayama, Japan
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17
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Pandey N, Keifenheim D, Yoshida MM, Hassebroek VA, Soroka C, Azuma Y, Clarke DJ. Topoisomerase II SUMOylation activates a metaphase checkpoint via Haspin and Aurora B kinases. J Cell Biol 2020; 219:jcb.201807189. [PMID: 31712254 PMCID: PMC7039214 DOI: 10.1083/jcb.201807189] [Citation(s) in RCA: 16] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2018] [Revised: 07/17/2019] [Accepted: 10/03/2019] [Indexed: 12/17/2022] Open
Abstract
To prevent chromosome missegregation, a metaphase checkpoint is activated when topoisomerase II is catalytically inhibited and DNA catenations persist. Pandey et al. dissect the key molecular events triggering this regulatory system. Topoisomerase II (Topo II) is essential for mitosis since it resolves sister chromatid catenations. Topo II dysfunction promotes aneuploidy and drives cancer. To protect from aneuploidy, cells possess mechanisms to delay anaphase onset when Topo II is perturbed, providing additional time for decatenation. Molecular insight into this checkpoint is lacking. Here we present evidence that catalytic inhibition of Topo II, which activates the checkpoint, leads to SUMOylation of the Topo II C-terminal domain (CTD). This modification triggers mobilization of Aurora B kinase from inner centromeres to kinetochore proximal centromeres and the core of chromosome arms. Aurora B recruitment accompanies histone H3 threonine-3 phosphorylation and requires Haspin kinase. Strikingly, activation of the checkpoint depends both on Haspin and Aurora B. Moreover, mutation of the conserved CTD SUMOylation sites perturbs Aurora B recruitment and checkpoint activation. The data indicate that SUMOylated Topo II recruits Aurora B to ectopic sites, constituting the molecular trigger of the metaphase checkpoint when Topo II is catalytically inhibited.
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Affiliation(s)
- Nootan Pandey
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS
| | - Daniel Keifenheim
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN
| | | | | | - Caitlin Soroka
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS
| | - Yoshiaki Azuma
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS
| | - Duncan J Clarke
- Department of Genetics, Cell Biology and Development, University of Minnesota, Minneapolis, MN
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18
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Heldrich J, Sun X, Vale-Silva LA, Markowitz TE, Hochwagen A. Topoisomerases Modulate the Timing of Meiotic DNA Breakage and Chromosome Morphogenesis in Saccharomyces cerevisiae. Genetics 2020; 215:59-73. [PMID: 32152049 PMCID: PMC7198267 DOI: 10.1534/genetics.120.303060] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2019] [Accepted: 03/05/2020] [Indexed: 12/12/2022] Open
Abstract
During meiotic prophase, concurrent transcription, recombination, and chromosome synapsis place substantial topological strain on chromosomal DNA, but the role of topoisomerases in this context remains poorly defined. Here, we analyzed the roles of topoisomerases I and II (Top1 and Top2) during meiotic prophase in Saccharomyces cerevisiae We show that both topoisomerases accumulate primarily in promoter-containing intergenic regions of actively transcribing genes, including many meiotic double-strand break (DSB) hotspots. Despite the comparable binding patterns, top1 and top2 mutations have different effects on meiotic recombination. TOP1 disruption delays DSB induction and shortens the window of DSB accumulation by an unknown mechanism. By contrast, temperature-sensitive top2-1 mutants exhibit a marked delay in meiotic chromosome remodeling and elevated DSB signals on synapsed chromosomes. The problems in chromosome remodeling were linked to altered Top2 binding patterns rather than a loss of Top2 catalytic activity, and stemmed from a defect in recruiting the chromosome remodeler Pch2/TRIP13 to synapsed chromosomes. No chromosomal defects were observed in the absence of TOP1 Our results imply independent roles for Top1 and Top2 in modulating meiotic chromosome structure and recombination.
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Affiliation(s)
- Jonna Heldrich
- Department of Biology, New York University, New York 10003
| | - Xiaoji Sun
- Department of Biology, New York University, New York 10003
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19
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Lotz C, Lamour V. The interplay between DNA topoisomerase 2α post-translational modifications and drug resistance. CANCER DRUG RESISTANCE (ALHAMBRA, CALIF.) 2020; 3:149-160. [PMID: 35582608 PMCID: PMC9090595 DOI: 10.20517/cdr.2019.114] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 12/17/2019] [Revised: 01/19/2020] [Accepted: 02/05/2020] [Indexed: 01/13/2023]
Abstract
The type 2 DNA topoisomerases (Top2) are conserved enzymes and biomarkers for cell proliferation. The catalytic activities of the human isoform Top2α are essential for the regulation of DNA topology during DNA replication, transcription, and chromosome segregation. Top2α is a prominent target for anti-cancer drugs and is highly regulated by post-translational modifications (PTM). Despite an increasing number of proteomic studies, the extent of PTM in cancer cells and its importance in drug response remains largely uncharacterized. In this review, we highlight the different modifications affecting the human Top2α in healthy and cancer cells, taking advantage of the structure-function information accumulated in the past decades. We also overview the regulation of Top2α by PTM, the level of PTM in cancer cells, and the resistance to therapeutic compounds targeting the Top2 enzyme. Altogether, this review underlines the importance of future studies addressing more systematically the interplay between PTM and Top2 drug resistance.
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Affiliation(s)
- Christophe Lotz
- Integrative Structural Biology Department, IGBMC, Université de Strasbourg, CNRS UMR 7104, INSERM U1258, Illkirch 67404, France
| | - Valérie Lamour
- Integrative Structural Biology Department, IGBMC, Université de Strasbourg, CNRS UMR 7104, INSERM U1258, Illkirch 67404, France
- Hôpitaux Universitaires de Strasbourg, Strasbourg 67000, France
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20
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Elton TS, Ozer HG, Yalowich JC. Effects of DNA topoisomerase IIα splice variants on acquired drug resistance. CANCER DRUG RESISTANCE (ALHAMBRA, CALIF.) 2020; 3:161-170. [PMID: 32566920 PMCID: PMC7304410 DOI: 10.20517/cdr.2019.117] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/10/2023]
Abstract
DNA topoisomerase IIα (170 kDa, TOP2α/170) induces transient DNA double-strand breaks in proliferating cells to resolve DNA topological entanglements during chromosome condensation, replication, and segregation. Therefore, TOP2α/170 is a prominent target for anticancer drugs whose clinical efficacy is often compromised due to chemoresistance. Although many resistance mechanisms have been defined, acquired resistance of human cancer cell lines to TOP2α interfacial inhibitors/poisons is frequently associated with a reduction of Top2α/170 expression levels. Recent studies by our laboratory, in conjunction with earlier findings by other investigators, support the hypothesis that a major mechanism of acquired resistance to TOP2α-targeted drugs is due to alternative RNA processing/splicing. Specifically, several TOP2α mRNA splice variants have been reported which retain introns and are translated into truncated TOP2α isoforms lacking nuclear localization sequences and subsequent dysregulated nuclear-cytoplasmic disposition. In addition, intron retention can lead to truncated isoforms that lack both nuclear localization sequences and the active site tyrosine (Tyr805) necessary for forming enzyme-DNA covalent complexes and inducing DNA damage in the presence of TOP2α-targeted drugs. Ultimately, these truncated TOP2α isoforms result in decreased drug activity against TOP2α in the nucleus and manifest drug resistance. Therefore, the complete characterization of the mechanism(s) regulating the alternative RNA processing of TOP2α pre-mRNA may result in new strategies to circumvent acquired drug resistance. Additionally, novel TOP2α splice variants and truncated TOP2α isoforms may be useful as biomarkers for drug resistance, prognosis, and/or direct future TOP2α-targeted therapies.
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Affiliation(s)
- Terry S Elton
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA
| | - Hatice Gulcin Ozer
- Department of Biomedical Informatics, College of Medicine, The Ohio State University, Columbus, OH 43210, USA
| | - Jack C Yalowich
- Division of Pharmaceutics and Pharmacology, College of Pharmacy, The Ohio State University, Columbus, OH 43210, USA
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21
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Zhang M, Liang C, Chen Q, Yan H, Xu J, Zhao H, Yuan X, Liu J, Lin S, Lu W, Wang F. Histone H2A phosphorylation recruits topoisomerase IIα to centromeres to safeguard genomic stability. EMBO J 2020; 39:e101863. [PMID: 31769059 PMCID: PMC6996575 DOI: 10.15252/embj.2019101863] [Citation(s) in RCA: 26] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2019] [Revised: 09/23/2019] [Accepted: 10/29/2019] [Indexed: 01/03/2023] Open
Abstract
Chromosome segregation in mitosis requires the removal of catenation between sister chromatids. Timely decatenation of sister DNAs at mitotic centromeres by topoisomerase IIα (TOP2A) is crucial to maintain genomic stability. The chromatin factors that recruit TOP2A to centromeres during mitosis remain unknown. Here, we show that histone H2A Thr-120 phosphorylation (H2ApT120), a modification generated by the mitotic kinase Bub1, is necessary and sufficient for the centromeric localization of TOP2A. Phosphorylation at residue-120 enhances histone H2A binding to TOP2A in vitro. The C-gate and the extreme C-terminal region are important for H2ApT120-dependent localization of TOP2A at centromeres. Preventing H2ApT120-mediated accumulation of TOP2A at mitotic centromeres interferes with sister chromatid disjunction, as evidenced by increased frequency of anaphase ultra-fine bridges (UFBs) that contain catenated DNA. Tethering TOP2A to centromeres bypasses the requirement for H2ApT120 in suppressing anaphase UFBs. These results demonstrate that H2ApT120 acts as a landmark that recruits TOP2A to mitotic centromeres to decatenate sister DNAs. Our study reveals a fundamental role for histone phosphorylation in resolving centromere DNA entanglements and safeguarding genomic stability during mitosis.
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Affiliation(s)
- Miao Zhang
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Cai Liang
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Qinfu Chen
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Haiyan Yan
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Junfen Xu
- Department of Gynecologic OncologyWomen's HospitalZhejiang University School of MedicineHangzhouZhejiangChina
| | - Hongxia Zhao
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Xueying Yuan
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Jingbo Liu
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Shixian Lin
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
| | - Weiguo Lu
- Department of Gynecologic OncologyWomen's HospitalZhejiang University School of MedicineHangzhouZhejiangChina
- Women's Reproductive Health Key Research Laboratory of Zhejiang ProvinceWomen's HospitalZhejiang University School of MedicineHangzhouZhejiangChina
| | - Fangwei Wang
- MOE Laboratory of Biosystems Homeostasis & Protection and Innovation Center for Cell Signaling NetworkLife Sciences InstituteZhejiang UniversityHangzhouZhejiangChina
- Department of Gynecologic OncologyWomen's HospitalZhejiang University School of MedicineHangzhouZhejiangChina
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22
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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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23
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Antoniou-Kourounioti M, Mimmack ML, Porter ACG, Farr CJ. The Impact of the C-Terminal Region on the Interaction of Topoisomerase II Alpha with Mitotic Chromatin. Int J Mol Sci 2019; 20:ijms20051238. [PMID: 30871006 PMCID: PMC6429393 DOI: 10.3390/ijms20051238] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2019] [Revised: 03/04/2019] [Accepted: 03/08/2019] [Indexed: 02/06/2023] Open
Abstract
Type II topoisomerase enzymes are essential for resolving DNA topology problems arising through various aspects of DNA metabolism. In vertebrates two isoforms are present, one of which (TOP2A) accumulates on chromatin during mitosis. Moreover, TOP2A targets the mitotic centromere during prophase, persisting there until anaphase onset. It is the catalytically-dispensable C-terminal domain of TOP2 that is crucial in determining this isoform-specific behaviour. In this study we show that, in addition to the recently identified chromatin tether domain, several other features of the alpha-C-Terminal Domain (CTD). influence the mitotic localisation of TOP2A. Lysine 1240 is a major SUMOylation target in cycling human cells and the efficiency of this modification appears to be influenced by T1244 and S1247 phosphorylation. Replacement of K1240 by arginine results in fewer cells displaying centromeric TOP2A accumulation during prometaphase-metaphase. The same phenotype is displayed by cells expressing TOP2A in which either of the mitotic phosphorylation sites S1213 or S1247 has been substituted by alanine. Conversely, constitutive modification of TOP2A by fusion to SUMO2 exerts the opposite effect. FRAP analysis of protein mobility indicates that post-translational modification of TOP2A can influence the enzyme's residence time on mitotic chromatin, as well as its subcellular localisation.
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Affiliation(s)
- Melissa Antoniou-Kourounioti
- Department of Genetics, University of Cambridge, Downing St, Cambridge CB2 3EH, UK.
- School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, UK.
| | - Michael L Mimmack
- Department of Genetics, University of Cambridge, Downing St, Cambridge CB2 3EH, UK.
- Metabolic Research Laboratories, Wellcome Trust-Medical Research Council Institute of Metabolic Science, University of Cambridge, Cambridge CB2 0QQ, UK.
| | - Andrew C G Porter
- Centre for Haematology, Faculty of Medicine, Imperial College London, Hammersmith Hospital Campus, Du Cane Rd, London W12 0NN, UK.
| | - Christine J Farr
- Department of Genetics, University of Cambridge, Downing St, Cambridge CB2 3EH, UK.
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24
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Clarke DJ, Azuma Y. Non-Catalytic Roles of the Topoisomerase IIα C-Terminal Domain. Int J Mol Sci 2017; 18:ijms18112438. [PMID: 29149026 PMCID: PMC5713405 DOI: 10.3390/ijms18112438] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/13/2017] [Revised: 11/10/2017] [Accepted: 11/14/2017] [Indexed: 12/26/2022] Open
Abstract
DNA Topoisomerase IIα (Topo IIα) is a ubiquitous enzyme in eukaryotes that performs the strand passage reaction where a double helix of DNA is passed through a second double helix. This unique reaction is critical for numerous cellular processes. However, the enzyme also possesses a C-terminal domain (CTD) that is largely dispensable for the strand passage reaction but is nevertheless important for the fidelity of cell division. Recent studies have expanded our understanding of the roles of the Topo IIα CTD, in particular in mitotic mechanisms where the CTD is modified by Small Ubiquitin-like Modifier (SUMO), which in turn provides binding sites for key regulators of mitosis.
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Affiliation(s)
- Duncan J Clarke
- Department of Genetics, Cell Biology & Development, University of Minnesota, 420 Washington Ave SE, Minneapolis, MN 55455, USA.
| | - Yoshiaki Azuma
- Department of Molecular Biosciences, University of Kansas, Lawrence, KS 66045, USA.
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25
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Emanuelli A, Borroni AP, Apel-Sarid L, Shah PA, Ayyathan DM, Koganti P, Levy-Cohen G, Blank M. Smurf2-Mediated Stabilization of DNA Topoisomerase IIα Controls Genomic Integrity. Cancer Res 2017; 77:4217-4227. [PMID: 28611047 DOI: 10.1158/0008-5472.can-16-2828] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2016] [Revised: 12/13/2016] [Accepted: 06/09/2017] [Indexed: 11/16/2022]
Abstract
DNA topoisomerase IIα (Topo IIα) ensures genomic integrity and unaltered chromosome inheritance and serves as a major target of several anticancer drugs. Topo IIα function is well understood, but how its expression is regulated remains unclear. Here, we identify the E3 ubiquitin ligase Smurf2 as a physiologic regulator of Topo IIα levels. Smurf2 physically interacted with Topo IIα and modified its ubiquitination status to protect Topo IIα from the proteasomal degradation in dose- and catalytically dependent manners. Smurf2-depleted cells exhibited a reduced ability to resolve DNA catenanes and pathological chromatin bridges formed during mitosis, a trait of Topo IIα-deficient cells and a hallmark of chromosome instability. Introducing Topo IIα into Smurf2-depleted cells rescued this phenomenon. Smurf2 was a determinant of Topo IIα protein levels in normal and cancer cells and tissues, and its levels affected cell sensitivity to the Topo II-targeting drug etoposide. Our results identified Smurf2 as an essential regulator of Topo IIα, providing novel insights into its control and into the suggested tumor-suppressor functions of Smurf2. Cancer Res; 77(16); 4217-27. ©2017 AACR.
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Affiliation(s)
- Andrea Emanuelli
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Aurora P Borroni
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Liat Apel-Sarid
- Department of Pathology, The Galilee Medical Center, Nahariya, Israel
| | - Pooja A Shah
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Dhanoop Manikoth Ayyathan
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Praveen Koganti
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Gal Levy-Cohen
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel
| | - Michael Blank
- Laboratory of Molecular and Cellular Cancer Biology, Faculty of Medicine in the Galilee, Bar-Ilan University, Safed, Israel.
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Edgerton H, Johansson M, Keifenheim D, Mukherjee S, Chacón JM, Bachant J, Gardner MK, Clarke DJ. A noncatalytic function of the topoisomerase II CTD in Aurora B recruitment to inner centromeres during mitosis. J Cell Biol 2017; 213:651-64. [PMID: 27325791 PMCID: PMC4915189 DOI: 10.1083/jcb.201511080] [Citation(s) in RCA: 35] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 05/25/2016] [Indexed: 11/22/2022] Open
Abstract
The C-terminal domain (CTD) of Topo II is dispensable for its catalytic activity yet essential for Topo II function in chromosome segregation during mitosis. Here, Edgerton et al. resolve the role of the Topo II CTD during mitosis in yeast, showing that it functions noncatalytically via the Haspin-H3 T3-Phos pathway to recruit Ipl1/Aurora B to mitotic inner centromeres. Faithful chromosome segregation depends on the precise timing of chromatid separation, which is enforced by checkpoint signals generated at kinetochores. Here, we provide evidence that the C-terminal domain (CTD) of DNA topoisomerase IIα (Topo II) provides a novel function at inner centromeres of kinetochores in mitosis. We find that the yeast CTD is required for recruitment of the tension checkpoint kinase Ipl1/Aurora B to inner centromeres in metaphase but is not required in interphase. Conserved CTD SUMOylation sites are required for Ipl1 recruitment. This inner-centromere CTD function is distinct from the catalytic activity of Topo II. Genetic and biochemical evidence suggests that Topo II recruits Ipl1 via the Haspin–histone H3 threonine 3 phosphorylation pathway. Finally, Topo II and Sgo1 are equally important for Ipl1 recruitment to inner centromeres. This indicates H3 T3-Phos/H2A T120-Phos is a universal epigenetic signature that defines the eukaryotic inner centromere and provides the binding site for Ipl1/Aurora B.
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Affiliation(s)
- Heather Edgerton
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Marnie Johansson
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Daniel Keifenheim
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Soumya Mukherjee
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Jeremy M Chacón
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Jeff Bachant
- Department of Cell Biology and Neuroscience, University of California, Riverside, Riverside, CA 92521
| | - Melissa K Gardner
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
| | - Duncan J Clarke
- Department of Genetics, Cell Biology, and Development, University of Minnesota, Minneapolis, MN 55455
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27
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Żabka A, Winnicki K, Polit JT, Maszewski J. The effects of anti-DNA topoisomerase II drugs, etoposide and ellipticine, are modified in root meristem cells of Allium cepa by MG132, an inhibitor of 26S proteasomes. PLANT PHYSIOLOGY AND BIOCHEMISTRY : PPB 2015; 96:72-82. [PMID: 26233708 DOI: 10.1016/j.plaphy.2015.07.016] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/03/2015] [Revised: 06/17/2015] [Accepted: 07/17/2015] [Indexed: 06/04/2023]
Abstract
DNA topoisomerase II (Topo II), a highly specialized nuclear enzyme, resolves various entanglement problems concerning DNA that arise during chromatin remodeling, transcription, S-phase replication, meiotic recombination, chromosome condensation and segregation during mitosis. The genotoxic effects of two Topo II inhibitors known as potent anti-cancer drugs, etoposide (ETO) and ellipticine (EPC), were assayed in root apical meristem cells of Allium cepa. Despite various types of molecular interactions between these drugs and DNA-Topo II complexes at the chromatin level, which have a profound negative impact on the genome integrity (production of double-strand breaks, chromosomal bridges and constrictions, lagging fragments of chromosomes and their uneven segregation to daughter cell nuclei), most of the elicited changes were apparently similar, regarding both their intensity and time characteristics. No essential changes between ETO- and EPC-treated onion roots were noticed in the frequency of G1-, S-, G2-and M-phase cells, nuclear morphology, chromosome structures, tubulin-microtubule systems, extended distribution of mitosis-specific phosphorylation sites of histone H3, and the induction of apoptosis-like programmed cell death (AL-PCD). However, the important difference between the effects induced by the ETO and EPC concerns their catalytic activities in the presence of MG132 (proteasome inhibitor engaged in Topo II-mediated formation of cleavage complexes) and relates to the time-variable changes in chromosomal aberrations and AL-PCD rates. This result implies that proteasome-dependent mechanisms may contribute to the course of physiological effects generated by DNA lesions under conditions that affect the ability of plant cells to resolve topological problems that associated with the nuclear metabolic activities.
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Affiliation(s)
- Aneta Żabka
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236 Łódź, Poland.
| | - Konrad Winnicki
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236 Łódź, Poland.
| | - Justyna Teresa Polit
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236 Łódź, Poland.
| | - Janusz Maszewski
- Department of Cytophysiology, Faculty of Biology and Environmental Protection, University of Łódź, Pomorska 141/143, 90-236 Łódź, Poland.
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28
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Novel kinetochore function of Topoisomerase IIα. Cell Cycle 2015; 14:2875-6. [PMID: 26252448 DOI: 10.1080/15384101.2015.1076303] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
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29
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Lu LY, Kuang H, Korakavi G, Yu X. Topoisomerase II regulates the maintenance of DNA methylation. J Biol Chem 2014; 290:851-60. [PMID: 25451918 DOI: 10.1074/jbc.m114.611509] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The maintenance of DNA methylation in nascent DNA is a critical event for numerous biological processes. Following DNA replication, DNMT1 is the key enzyme that strictly copies the methylation pattern from the parental strand to the nascent DNA. However, the mechanism underlying this highly specific event is not thoroughly understood. In this study, we identified topoisomerase IIα (TopoIIα) as a novel regulator of the maintenance DNA methylation. UHRF1, a protein important for global DNA methylation, interacts with TopoIIα and regulates its localization to hemimethylated DNA. TopoIIα decatenates the hemimethylated DNA following replication, which might facilitate the methylation of the nascent strand by DNMT1. Inhibiting this activity impairs DNA methylation at multiple genomic loci. We have uncovered a novel mechanism during the maintenance of DNA methylation.
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Affiliation(s)
- Lin-Yu Lu
- From the Women's Hospital, School of Medicine, and the Institute of Translational Medicine, Zhejiang University, Hangzhou, Zhejiang 310006, China and
| | - Henry Kuang
- the Division of Molecular Medicine and Genetics, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109
| | - Gautam Korakavi
- the Division of Molecular Medicine and Genetics, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109
| | - Xiaochun Yu
- the Division of Molecular Medicine and Genetics, Department of Internal Medicine, University of Michigan Medical School, Ann Arbor, Michigan 48109
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30
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Zierhut C, Jenness C, Kimura H, Funabiki H. Nucleosomal regulation of chromatin composition and nuclear assembly revealed by histone depletion. Nat Struct Mol Biol 2014; 21:617-25. [PMID: 24952593 PMCID: PMC4082469 DOI: 10.1038/nsmb.2845] [Citation(s) in RCA: 81] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2014] [Accepted: 05/23/2014] [Indexed: 12/13/2022]
Abstract
Nucleosomes are the fundamental unit of chromatin, but analysis of transcription-independent nucleosome functions has been complicated by the gene-expression changes resulting from histone manipulation. Here we solve this dilemma by developing Xenopus laevis egg extracts deficient for nucleosome formation and by analyzing the proteomic landscape and behavior of nucleosomal chromatin and nucleosome-free DNA. We show that although nucleosome-free DNA can recruit nuclear-envelope membranes, nucleosomes are required for spindle assembly and for formation of the lamina and of nuclear pore complexes (NPCs). We show that, in addition to the Ran G-nucleotide exchange factor RCC1, ELYS, the initiator of NPC formation, fails to associate with naked DNA but directly binds histone H2A-H2B dimers and nucleosomes. Tethering ELYS and RCC1 to DNA bypasses the requirement for nucleosomes in NPC formation in a synergistic manner. Thus, the minimal essential function of nucleosomes in NPC formation is to recruit RCC1 and ELYS.
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Affiliation(s)
- Christian Zierhut
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
| | - Christopher Jenness
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
| | - Hiroshi Kimura
- 1] Graduate School of Frontier Biosciences, Osaka University, Suita, Japan. [2] Japan Science and Technology Agency, Core Research for Evolutional Science and Technology, Suita, Japan
| | - Hironori Funabiki
- Laboratory of Chromosome and Cell Biology, Rockefeller University, New York, New York, USA
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