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Custer SK, Gilson T, Astroski JW, Nanguneri SR, Iurillo AM, Androphy EJ. COPI coatomer subunit α-COP interacts with the RNA binding protein Nucleolin via a C-terminal dilysine motif. Hum Mol Genet 2023; 32:3263-3275. [PMID: 37658769 PMCID: PMC10656708 DOI: 10.1093/hmg/ddad140] [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: 04/17/2023] [Revised: 08/07/2023] [Accepted: 08/30/2023] [Indexed: 09/05/2023] Open
Abstract
The COPI coatomer subunit α-COP has been shown to co-precipitate mRNA in multiple settings, but it was unclear whether the interaction with mRNA was direct or mediated by interaction with an adapter protein. The COPI complex often interacts with proteins via C-terminal dilysine domains. A search for candidate RNA binding proteins with C-terminal dilysine motifs yielded Nucleolin, which terminates in a KKxKxx sequence. This protein was an especially intriguing candidate as it has been identified as an interacting partner for Survival Motor Neuron protein (SMN). Loss of SMN causes the neurodegenerative disease Spinal Muscular Atrophy. We have previously shown that SMN and α-COP interact and co-migrate in axons, and that overexpression of α-COP reduced phenotypic severity in cell culture and animal models of SMA. We show here that in an mRNA independent manner, endogenous Nucleolin co-precipitates endogenous α-COP and ε-COP but not β-COP which may reflect an interaction with the so-called B-subcomplex rather a complete COPI heptamer. The ability of Nucleolin to bind to α-COP requires the presence of the C-terminal KKxKxx domain of Nucleolin. Furthermore, we have generated a point mutant in the WD40 domain of α-COP which eliminates its ability to co-precipitate Nucleolin but does not interfere with precipitation of partners mediated by non-KKxKxx motifs such as the kainate receptor subunit 2. We propose that via interaction between the C-terminal dilysine motif of Nucleolin and the WD40 domain of α-COP, Nucleolin acts an adaptor to allow α-COP to interact with a population of mRNA.
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Affiliation(s)
- Sara K Custer
- Dermatology, Indiana University School of Medicine, 545 Barnhill Drive, Emerson Hall 139, Indianapolis, IN 46202, United States
| | - Timra Gilson
- Dermatology, Indiana University School of Medicine, 545 Barnhill Drive, Emerson Hall 139, Indianapolis, IN 46202, United States
| | - Jacob W Astroski
- Dermatology, Indiana University School of Medicine, 545 Barnhill Drive, Emerson Hall 139, Indianapolis, IN 46202, United States
| | - Siddarth R Nanguneri
- Dermatology, Indiana University School of Medicine, 545 Barnhill Drive, Emerson Hall 139, Indianapolis, IN 46202, United States
| | - Alyssa M Iurillo
- Indiana University School of Medicine, 340 West 10 St, Indianapolis, IN 46202, United States
| | - Elliot J Androphy
- Dermatology, Indiana University School of Medicine, 545 Barnhill Drive, Emerson Hall 139, Indianapolis, IN 46202, United States
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2
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Kim N. The Interplay between G-quadruplex and Transcription. Curr Med Chem 2019; 26:2898-2917. [PMID: 29284393 PMCID: PMC6026074 DOI: 10.2174/0929867325666171229132619] [Citation(s) in RCA: 83] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2017] [Revised: 11/22/2017] [Accepted: 12/21/2017] [Indexed: 12/25/2022]
Abstract
G4 DNA is a non-canonical DNA structure consisting of a stacked array of Gquartets held together by base pairing between guanine bases. The formation of G4 DNA requires a cluster of guanine-runs within a strand of DNA. Even though the chemistry of this remarkable DNA structure has been under investigation for decades, evidence supporting the biological relevance of G4 DNA has only begun to emerge and point to very important and conserved biological functions. This review will specifically focus on the interplay between transcription and G4 DNA and discuss two alternative but interconnected perspectives. The first part of the review will describe the evidence substantiating the intriguing idea that a shift in DNA structural conformation could be another layer of non-genetic or epigenetic regulator of gene expression and thereby an important determinant of cell fate. The second part will describe the recent genetic studies showing that those genomic loci containing G4 DNA-forming guanine-rich sequences are potential hotspots of genome instability and that the level and orientation of transcription is critical in the materialization of genome instability associated with these sequences.
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Affiliation(s)
- Nayun Kim
- Department of Microbiology and Molecular Genetics, The University of Texas Health Science Center at Houston; The University of Texas Graduate School of Biomedical Sciences, Houston, TX, United States
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3
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Fob1p recruits DNA topoisomerase I to ribosomal genes locus and contributes to its transcriptional silencing maintenance. Int J Biochem Cell Biol 2019; 110:143-148. [PMID: 30880168 DOI: 10.1016/j.biocel.2019.03.006] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Revised: 03/08/2019] [Accepted: 03/12/2019] [Indexed: 11/20/2022]
Abstract
S. cerevisiae ribosomal DNA (rDNA) locus hosts a series of highly complex regulatory machineries for RNA polymerase I, II and III transcription, DNA replication and units recombination, all acting in the Non Transcribed Spacers (NTSs) interposed between the repeated units by which it is composed. DNA topoisomerase I (Top1p) contributes, recruiting Sir2p, to the maintenance of transcriptional silencing occurring at the RNA Polymerase II cryptic promoters, located in the NTS region. In this paper we found that Fob1p presence is crucial for Top1p recruitment at NTS, allowing transcriptional silencing to be established and maintained. We also showed the role of Nsr1p in Top1p recruitment to rDNA locus. Our work allows to hypothesize that Nsr1p targets Top1p into the nucleolus while Fob1p is responsible for its preferential distribution at RFB.
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4
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Sharma VR, Thomas SD, Miller DM, Rezzoug F. Nucleolin Overexpression Confers Increased Sensitivity to the Anti-Nucleolin Aptamer, AS1411. Cancer Invest 2018; 36:475-491. [PMID: 30396283 PMCID: PMC6396827 DOI: 10.1080/07357907.2018.1527930] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2018] [Accepted: 09/20/2018] [Indexed: 02/04/2023]
Abstract
AS1411 is an antiproliferative DNA aptamer, which binds the ubiquitous protein, nucleolin. In this study, we show that constitutive overexpression of nucleolin confers increased sensitivity to the growth inhibitory effects of AS1411. HeLa cells overexpressing nucleolin have an increased growth rate and invasiveness relative to control cells. Nucleolin overexpressing cells demonstrate increased growth inhibition in response to the AS1411 treatment, which correlates with increased apoptosis and cell cycle arrest, when compared to non-transfected cells. AS1411 induces nucleolin expression at the RNA and protein level in HeLa cells, suggesting a feedback loop with important implications for the clinical use of AS1411.
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Affiliation(s)
- Vivek R. Sharma
- University of Louisville, Division of Medical Oncology/Hematology, Department of Medicine, James Graham Brown Cancer Center, Louisville, Kentucky, USA
| | - Shelia D. Thomas
- University of Louisville, Division of Medical Oncology/Hematology, Department of Medicine, James Graham Brown Cancer Center, Louisville, Kentucky, USA
| | - Donald M. Miller
- University of Louisville, Division of Medical Oncology/Hematology, Department of Medicine, James Graham Brown Cancer Center, Louisville, Kentucky, USA
| | - Francine Rezzoug
- University of Louisville, Division of Medical Oncology/Hematology, Department of Medicine, James Graham Brown Cancer Center, Louisville, Kentucky, USA
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5
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Ko CY, Lin CH, Chuang JY, Chang WC, Hsu TI. MDM2 Degrades Deacetylated Nucleolin Through Ubiquitination to Promote Glioma Stem-Like Cell Enrichment for Chemotherapeutic Resistance. Mol Neurobiol 2018; 55:3211-3223. [PMID: 28478507 DOI: 10.1007/s12035-017-0569-4] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 04/20/2017] [Indexed: 12/20/2022]
Abstract
Glioblastoma multiforme (GBM) is the most fatal of all brain cancers, and the standard care protocol for GBM patients is surgical tumor resection followed by radiotherapy and temozolomide (TMZ)-mediated chemotherapy. However, tumor recurrence frequently occurs, and recurrent GBM exhibits more malignancy and less sensitivity in response to chemotherapy. The malignancy and drug resistance primarily reflect the small population of glioma stem-like cells (GSC). Therefore, understanding the mechanism that controls GSC enrichment is important to benefit the prognosis of GBM patients. Nucleolin (NCL), which is responsible for ribosome biogenesis and RNA maturation, is overexpressed in gliomas. However, the role of NCL in GSC development and drug resistance is still unclear. In this study, we demonstrate that NCL attenuated GSC enrichment to enhance the sensitivity of GBM cells in response to TMZ. In GSC enrichment, NCL was significantly reduced at the protein level as a result of decreased protein stability. In particular, the inhibition of HDAC activity by suberoylanilide hydroxamic acid rescued NCL acetylation accompanied by the loss of mouse double minute 2 homolog (MDM2)-mediated ubiquitination. In addition, we found that NCL ubiquitination resulted from the activation of STAT3- and JNK-mediated signaling in GSC. Moreover, NCL inhibited the formation of stem-like spheres by attenuating the expression of Sox2, Oct4, and Bmi1. Furthermore, NCL sensitized the response of GBM cells to TMZ. Based on these findings, NCL expression is a potential indicator to predict chemotherapeutic efficiency in GBM patients.
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MESH Headings
- Acetylation
- Brain Neoplasms/metabolism
- Brain Neoplasms/pathology
- Cell Line, Tumor
- Down-Regulation/genetics
- Drug Resistance, Neoplasm/drug effects
- Drug Resistance, Neoplasm/genetics
- Gene Expression Regulation, Neoplastic/drug effects
- Glioma/genetics
- Glioma/metabolism
- Glioma/pathology
- Histone Deacetylase Inhibitors/pharmacology
- Humans
- JNK Mitogen-Activated Protein Kinases/metabolism
- Models, Biological
- Neoplasm Recurrence, Local/genetics
- Neoplasm Recurrence, Local/pathology
- Neoplastic Stem Cells/metabolism
- Neoplastic Stem Cells/pathology
- Phosphoproteins/metabolism
- Phosphorylation/drug effects
- Proteolysis/drug effects
- Proto-Oncogene Proteins c-mdm2/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA-Binding Proteins/metabolism
- STAT3 Transcription Factor/metabolism
- Spheroids, Cellular/metabolism
- Spheroids, Cellular/pathology
- Temozolomide/pharmacology
- Ubiquitination
- Vorinostat/pharmacology
- Nucleolin
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Affiliation(s)
- Chiung-Yuan Ko
- The Ph.D. Program for Neural Regenerative Medicine, College of Medical Science and Technology, Taipei Medical University and National Health Research Institutes, Taipei, Taiwan
| | - Chao-Han Lin
- Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, Taiwan
| | - Jian-Ying Chuang
- The Ph.D. Program for Neural Regenerative Medicine, College of Medical Science and Technology, Taipei Medical University and National Health Research Institutes, Taipei, Taiwan
- Comprehensive Cancer Center, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Wen-Chang Chang
- The Ph.D. Program for Neural Regenerative Medicine, College of Medical Science and Technology, Taipei Medical University and National Health Research Institutes, Taipei, Taiwan
- Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, Taiwan
- Comprehensive Cancer Center, College of Medicine, Taipei Medical University, Taipei, Taiwan
| | - Tsung-I Hsu
- The Ph.D. Program for Neural Regenerative Medicine, College of Medical Science and Technology, Taipei Medical University and National Health Research Institutes, Taipei, Taiwan.
- Comprehensive Cancer Center, College of Medicine, Taipei Medical University, Taipei, Taiwan.
- Center for Neurotrauma and Neuroregeneration, College of Medical Science and Technology, Taipei Medical University, Taipei, Taiwan.
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6
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A Screen for Candidate Targets of Lysine Polyphosphorylation Uncovers a Conserved Network Implicated in Ribosome Biogenesis. Cell Rep 2018; 22:3427-3439. [DOI: 10.1016/j.celrep.2018.02.104] [Citation(s) in RCA: 44] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2017] [Revised: 01/12/2018] [Accepted: 02/27/2018] [Indexed: 11/22/2022] Open
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7
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Wolfson E, Solomon S, Schmukler E, Goldshmit Y, Pinkas-Kramarski R. Nucleolin and ErbB2 inhibition reduces tumorigenicity of ErbB2-positive breast cancer. Cell Death Dis 2018; 9:47. [PMID: 29352243 PMCID: PMC5833446 DOI: 10.1038/s41419-017-0067-7] [Citation(s) in RCA: 26] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/25/2017] [Revised: 10/01/2017] [Accepted: 10/17/2017] [Indexed: 12/14/2022]
Abstract
ErbB2, a member of the ErbB family of receptor tyrosine kinases, is an essential player in the cell's growth and proliferation signaling pathways. Amplification or overexpression of ErbB2 is observed in ∼30% of breast cancer patients, and often drives cellular transformation and cancer development. Recently, we have shown that ErbB2 interacts with the nuclear-cytoplasmic shuttling protein nucleolin, an interaction which enhances cell transformation in vitro, and increases mortality risk and disease progression rate in human breast cancer patients. Given these results, and since acquired resistance to anti-ErbB2-targeted therapy is a major obstacle in treatment of breast cancer, we have examined the therapeutic potential of targeting the ErbB2-nucleolin complex. The effect of the nucleolin-specific inhibitor GroA (AS1411) on ErbB2-positive breast cancer was tested in vivo, in a mouse xenograft model for breast cancer; as well as in vitro, alone and in combination with the ErbB2 kinase-inhibitor tyrphostin AG-825. Here, we show that in vivo treatment of ErbB2-positive breast tumor xenografts with GroA reduces tumor size and leads to decreased ErbB2-mediated signaling. Moreover, we found that co-treatment of breast cancer cell lines with GroA and the ErbB2 kinase-inhibitor tyrphostin AG-825 enhances the anti-cancer effects exerted by GroA alone in terms of cell viability, mortality, migration, and invasiveness. We, therefore, suggest a novel therapeutic approach, consisting of combined inhibition of ErbB2 and nucleolin, which has the potential to improve breast cancer treatment efficacy.
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Affiliation(s)
- Eya Wolfson
- Department of Neurobiology, Faculty of Life Science, Tel-Aviv University, Ramat-Aviv, 69978, Israel
| | - Shira Solomon
- Department of Neurobiology, Faculty of Life Science, Tel-Aviv University, Ramat-Aviv, 69978, Israel
| | - Eran Schmukler
- Department of Neurobiology, Faculty of Life Science, Tel-Aviv University, Ramat-Aviv, 69978, Israel
| | - Yona Goldshmit
- Department of Neurobiology, Faculty of Life Science, Tel-Aviv University, Ramat-Aviv, 69978, Israel
| | - Ronit Pinkas-Kramarski
- Department of Neurobiology, Faculty of Life Science, Tel-Aviv University, Ramat-Aviv, 69978, Israel.
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8
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Antiviral screen identifies EV71 inhibitors and reveals camptothecin-target, DNA topoisomerase 1 as a novel EV71 host factor. Antiviral Res 2017; 143:122-133. [PMID: 28427827 DOI: 10.1016/j.antiviral.2017.04.008] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2017] [Revised: 04/12/2017] [Accepted: 04/14/2017] [Indexed: 11/23/2022]
Abstract
Enterovirus 71 (EV71) is one of the causative agents of hand, foot and mouth disease (HFMD) associated with severe neurological disease. EV71's pathogenesis remains poorly understood and the lack of approved antiviral has led to its emergence as a clinically important neurotropic virus. The goals of this study were to: (i) identify novel anti-EV71 compounds that may serve as lead molecules for therapeutics; and (ii) investigate their targets in downstream studies. We screened a 502-compound library of highly purified natural products for anti-EV71 activities in a cell-based immunofluorescence assay that were then confirmed in viral plaque reduction assays. Along with known antivirals, novel inhibitors of EV71 were also identified. We selected camptothecin for downstream studies and found that it is a limited spectrum enterovirus inhibitor that inhibits coxsackievirus A16 but not ECHOvirus 7. Camptothecin, a DNA topoisomerase 1 (TOP1) inhibitor, inhibits both viral RNA replication and translation based on luciferase replicon studies. Depletion of TOP1 using siRNA was then able to rescue EV71 infection from camptothecin inhibition. Interestingly, EV71 viral RNA replication and translation were also in TOP1 depleted cells. We found that nuclear TOP1 was relocalized to cytoplasmic replication vesicles during EV71 infection and localized with viral 3CD using confocal microscopy and proximity-ligation assays. Our findings reveal camptothecin to be a limited spectrum antiviral against enteroviruses that functions in a TOP1-dependent but cytotoxicity-independent manner. TOP1 is in turn needed for maximal EV71 viral RNA replication and viral protein synthesis.
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9
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Molecular Mechanism of DNA Topoisomerase I-Dependent rDNA Silencing: Sir2p Recruitment at Ribosomal Genes. J Mol Biol 2016; 428:4905-4916. [PMID: 27825925 DOI: 10.1016/j.jmb.2016.10.032] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2016] [Revised: 10/25/2016] [Accepted: 10/30/2016] [Indexed: 11/24/2022]
Abstract
Saccharomyces cerevisiae sir2Δ or top1Δ mutants exhibit similar phenotypes involving ribosomal DNA, including (i) loss of transcriptional silencing, resulting in non-coding RNA hyperproduction from cryptic RNA polymerase II promoters; (ii) alterations in recombination; and (iii) a general increase in histone acetylation. Given the distinct enzymatic activities of Sir2 and Top1 proteins, a histone deacetylase and a DNA topoisomerase, respectively, we investigated whether genetic and/or physical interactions between the two proteins could explain the shared ribosomal RNA genes (rDNA) phenotypes. We employed an approach of complementing top1Δ cells with yeast, human, truncated, and chimeric yeast/human TOP1 constructs and of assessing the extent of non-coding RNA silencing and histone H4K16 deacetylation. Our findings demonstrate that residues 115-125 within the yeast Top1p N-terminal domain are required for the complementation of the top1∆ rDNA phenotypes. In chromatin immunoprecipitation and co-immunoprecipitation experiments, we further demonstrate the physical interaction between Top1p and Sir2p. Our genetic and biochemical studies support a model whereby Top1p recruits Sir2p to the rDNA and clarifies a structural role of DNA topoisomerase I in the epigenetic regulation of rDNA, independent of its known catalytic activity.
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10
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Azevedo C, Livermore T, Saiardi A. Protein Polyphosphorylation of Lysine Residues by Inorganic Polyphosphate. Mol Cell 2015; 58:71-82. [DOI: 10.1016/j.molcel.2015.02.010] [Citation(s) in RCA: 80] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2014] [Revised: 12/02/2014] [Accepted: 02/03/2015] [Indexed: 10/23/2022]
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11
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The L1TD1 protein interactome reveals the importance of post-transcriptional regulation in human pluripotency. Stem Cell Reports 2015; 4:519-28. [PMID: 25702638 PMCID: PMC4376047 DOI: 10.1016/j.stemcr.2015.01.014] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2014] [Revised: 01/16/2015] [Accepted: 01/16/2015] [Indexed: 11/24/2022] Open
Abstract
The RNA-binding protein L1TD1 is one of the most specific and abundant proteins in pluripotent stem cells and is essential for the maintenance of pluripotency in human cells. Here, we identify the protein interaction network of L1TD1 in human embryonic stem cells (hESCs) and provide insights into the interactome network constructed in human pluripotent cells. Our data reveal that L1TD1 has an important role in RNA splicing, translation, protein traffic, and degradation. L1TD1 interacts with multiple stem-cell-specific proteins, many of which are still uncharacterized in the context of development. Further, we show that L1TD1 is a part of the pluripotency interactome network of OCT4, SOX2, and NANOG, bridging nuclear and cytoplasmic regulation and highlighting the importance of RNA biology in pluripotency. A protein interactome is constructed in human embryonic stem cells L1TD1 interacts with U2af1 and Srsf3, which are vital for somatic cell reprogramming L1TD1 is involved in the high proteasome activity of pluripotent cells L1TD1 connects uncharacterized factors to the OCT4, SOX2, and NANOG network
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12
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Durut N, Sáez-Vásquez J. Nucleolin: dual roles in rDNA chromatin transcription. Gene 2015; 556:7-12. [PMID: 25225127 DOI: 10.1016/j.gene.2014.09.023] [Citation(s) in RCA: 49] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2014] [Revised: 09/08/2014] [Accepted: 09/09/2014] [Indexed: 01/17/2023]
Abstract
Nucleolin is a major nucleolar protein conserved in all eukaryotic organisms. It is a multifunctional protein involved in different cellular aspects like chromatin organization and stability, DNA and RNA metabolism, assembly of ribonucleoprotein complexes, cytokinesis, cell proliferation and stress response. The multifunctionality of nucleolin is linked to its tripartite structure, post-translational modifications and its ability of shuttling from and to the nucleolus/nucleoplasm and cytoplasm. Nucleolin has been now studied for many years and its activities and properties have been described in a number of excellent reviews. Here, we overview the role of nucleolin in RNA polymerase I (RNAPI) transcription and describe recent results concerning its functional interaction with rDNA chromatin organization. For a long time, nucleolin has been associated with rRNA gene expression and pre-rRNA processing. However, the functional connection between nucleolin and active versus inactive rRNA genes is still not fully understood. Novel evidence indicates that the nucleolin protein might be required for controlling the transcriptional ON/OFF states of rDNA chromatin in both mammals and plants.
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Affiliation(s)
- Nathalie Durut
- CNRS, Laboratoire Génome et Développement des Plantes, UMR 5096, 66860 Perpignan, France; Univ. Perpignan Via Domitia, Laboratoire Génome et Développement des Plantes, UMR 5096, F-66860 Perpignan, France
| | - Julio Sáez-Vásquez
- CNRS, Laboratoire Génome et Développement des Plantes, UMR 5096, 66860 Perpignan, France; Univ. Perpignan Via Domitia, Laboratoire Génome et Développement des Plantes, UMR 5096, F-66860 Perpignan, France.
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13
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Quin JE, Devlin JR, Cameron D, Hannan KM, Pearson RB, Hannan RD. Targeting the nucleolus for cancer intervention. Biochim Biophys Acta Mol Basis Dis 2014; 1842:802-16. [PMID: 24389329 DOI: 10.1016/j.bbadis.2013.12.009] [Citation(s) in RCA: 170] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/28/2013] [Accepted: 12/17/2013] [Indexed: 12/17/2022]
Abstract
The contribution of the nucleolus to cancer is well established with respect to its traditional role in facilitating ribosome biogenesis and proliferative capacity. More contemporary studies however, infer that nucleoli contribute a much broader role in malignant transformation. Specifically, extra-ribosomal functions of the nucleolus position it as a central integrator of cellular proliferation and stress signaling, and are emerging as important mechanisms for modulating how oncogenes and tumor suppressors operate in normal and malignant cells. The dependence of certain tumor cells to co-opt nucleolar processes to maintain their cancer phenotypes has now clearly been demonstrated by the application of small molecule inhibitors of RNA Polymerase I to block ribosomal DNA transcription and disrupt nucleolar function (Bywater et al., 2012 [1]). These drugs, which selectively kill tumor cells in vivo while sparing normal cells, have now progressed to clinical trials. It is likely that we have only just begun to scratch the surface of the potential of the nucleolus as a new target for cancer therapy, with "suppression of nucleolar stress" representing an emerging "hallmark" of cancer. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.
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Affiliation(s)
- Jaclyn E Quin
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Jennifer R Devlin
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Donald Cameron
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia
| | - Kate M Hannan
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, Australia
| | - Richard B Pearson
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, Victoria, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia
| | - Ross D Hannan
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, East Melbourne, Victoria, Australia; Department of Biochemistry and Molecular Biology, The University of Melbourne, Parkville, Victoria, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, Victoria, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria, Australia; Department of Pathology, The University of Melbourne, Parkville, Victoria, Australia; School of Biomedical Sciences, The University of Queensland, St Lucia, Queensland, Australia.
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14
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Tacheny A, Michel S, Dieu M, Payen L, Arnould T, Renard P. Unbiased proteomic analysis of proteins interacting with the HIV-1 5'LTR sequence: role of the transcription factor Meis. Nucleic Acids Res 2012; 40:e168. [PMID: 22904091 PMCID: PMC3505963 DOI: 10.1093/nar/gks733] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
To depict the largest picture of a core promoter interactome, we developed a one-step DNA-affinity capture method coupled with an improved mass spectrometry analysis process focused on the identification of low abundance proteins. As a proof of concept, this method was developed through the analysis of 230 bp contained in the 5′long terminal repeat (LTR) of the human immunodeficiency virus 1 (HIV-1). Beside many expected interactions, many new transcriptional regulators were identified, either transcription factors (TFs) or co-regulators, which interact directly or indirectly with the HIV-1 5′LTR. Among them, the homeodomain-containing TF myeloid ectopic viral integration site was confirmed to functionally interact with a specific binding site in the HIV-1 5′LTR and to act as a transcriptional repressor, probably through recruitment of the repressive Sin3A complex. This powerful and validated DNA-affinity approach could also be used as an efficient screening tool to identify a large set of proteins that physically interact, directly or indirectly, with a DNA sequence of interest. Combined with an in silico analysis of the DNA sequence of interest, this approach provides a powerful approach to select the interacting candidates to validate functionally by classical approaches.
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Affiliation(s)
- A Tacheny
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences, University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
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15
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Zhao J, Yu H, Lin L, Tu J, Cai L, Chen Y, Zhong F, Lin C, He F, Yang P. Interactome study suggests multiple cellular functions of hepatoma-derived growth factor (HDGF). J Proteomics 2011; 75:588-602. [DOI: 10.1016/j.jprot.2011.08.021] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2011] [Revised: 08/14/2011] [Accepted: 08/25/2011] [Indexed: 02/05/2023]
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16
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Chou SM, Huang TH, Chen HC, Li TK. Calcium-induced cleavage of DNA topoisomerase I involves the cytoplasmic-nuclear shuttling of calpain 2. Cell Mol Life Sci 2011; 68:2769-84. [PMID: 21086148 PMCID: PMC11114693 DOI: 10.1007/s00018-010-0591-4] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 10/29/2010] [Accepted: 11/02/2010] [Indexed: 12/18/2022]
Abstract
Important to the function of calpains is temporal and spatial regulation of their proteolytic activity. Here, we demonstrate that cytoplasm-resident calpain 2 cleaves human nuclear topoisomerase I (hTOP1) via Ca(2+)-activated proteolysis and nucleoplasmic shuttling of proteases. This proteolysis of hTOP1 was induced by either ionomycin-caused Ca(2+) influx or addition of Ca(2+) in cellular extracts. Ca(2+) failed to induce hTOP1 proteolysis in calpain 2-knockdown cells. Moreover, calpain 2 cleaved hTOP1 in vitro. Furthermore, calpain 2 entered the nucleus upon Ca(2+) influx, and calpastatin interfered with this process. Calpain 2 cleavage sites were mapped at K(158) and K(183) of hTOP1. Calpain 2-truncated hTOP1 exhibited greater relaxation activity but remained able to interact with nucleolin and to form cleavable complexes. Interestingly, calpain 2 appears to be involved in ionomycin-induced protection from camptothecin-induced cytotoxicity. Thus, our data suggest that nucleocytoplasmic shuttling may serve as a novel type of regulation for calpain 2-mediated nuclear proteolysis.
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Affiliation(s)
- Shang-Min Chou
- Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan
| | - Ting-Hsiang Huang
- Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan
| | - Hsiang-Chin Chen
- Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan
| | - Tsai-Kun Li
- Department and Graduate Institute of Microbiology, College of Medicine, Taipei, Taiwan
- Center for Biotechnology, National Taiwan University, Taipei, Taiwan
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17
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Bernstein KA, Reid RJD, Sunjevaric I, Demuth K, Burgess RC, Rothstein R. The Shu complex, which contains Rad51 paralogues, promotes DNA repair through inhibition of the Srs2 anti-recombinase. Mol Biol Cell 2011; 22:1599-607. [PMID: 21372173 PMCID: PMC3084681 DOI: 10.1091/mbc.e10-08-0691] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
The Shu complex, which contains RAD51 paralogues, is involved in the decision between homologous recombination and error-prone repair. We discovered a link to ribosomal DNA (rDNA) recombination when we found an interaction between one member of the Shu complex, SHU1, and UAF30, a component of the upstream activating factor complex (UAF), which regulates rDNA transcription. In the absence of Uaf30, rDNA copy number increases, and this increase depends on several functional subunits of the Shu complex. Furthermore, in the absence of Uaf30, we find that Shu1 and Srs2, an anti-recombinase DNA helicase with which the Shu complex physically interacts, act in the same pathway regulating rDNA recombination. In addition, Shu1 modulates Srs2 recruitment to both induced and spontaneous foci correlating with a decrease in Rad51 foci, demonstrating that the Shu complex is an important regulator of Srs2 activity. Last, we show that Shu1 regulation of Srs2 to double-strand breaks is not restricted to the rDNA, indicating a more general function for the Shu complex in the regulation of Srs2. We propose that the Shu complex shifts the balance of repair toward Rad51 filament stabilization by inhibiting the disassembly reaction of Srs2.
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Affiliation(s)
- Kara A Bernstein
- Department of Genetics & Development, Columbia University Medical Center, New York, NY 10032, USA
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18
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Abstract
Loss of heterozygosity (LOH) can be a driving force in the evolution of mitotic/somatic diploid cells, and cellular changes that increase the rate of LOH have been proposed to facilitate this process. In the yeast Saccharomyces cerevisiae, spontaneous LOH occurs by a number of mechanisms including chromosome loss and reciprocal and nonreciprocal recombination. We performed a screen in diploid yeast to identify mutants with increased rates of LOH using the collection of homozygous deletion alleles of nonessential genes. Increased LOH was quantified at three loci (MET15, SAM2, and MAT) on three different chromosomes, and the LOH events were analyzed as to whether they were reciprocal or nonreciprocal in nature. Nonreciprocal LOH was further characterized as chromosome loss or truncation, a local mutational event (gene conversion or point mutation), or break-induced replication (BIR). The 61 mutants identified could be divided into several groups, including ones that had locus-specific effects. Mutations in genes involved in DNA replication and chromatin assembly led to LOH predominantly via reciprocal recombination. In contrast, nonreciprocal LOH events with increased chromosome loss largely resulted from mutations in genes implicated in kinetochore function, sister chromatid cohesion, or relatively late steps of DNA recombination. Mutants of genes normally involved in early steps of DNA damage repair and signaling produced nonreciprocal LOH without an increased proportion of chromosome loss. Altogether, this study defines a genetic landscape for the basis of increased LOH and the processes by which it occurs.
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19
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Role of a tryptophan anchor in human topoisomerase I structure, function and inhibition. Biochem J 2008; 411:523-30. [PMID: 18215123 DOI: 10.1042/bj20071436] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Human Top1 (topoisomerase I) relaxes supercoiled DNA during cell division and transcription. Top1 is composed of 765 amino acids and contains an unstructured N-terminal domain of 200 amino acids, and a structured functional domain of 565 amino acids that binds and relaxes supercoiled DNA. In the present study we examined the region spanning the junction of the N-terminal domain and functional domain (junction region). Analysis of several published Top1 structures revealed that three tryptophan residues formed a network of aromatic stacking interactions and electrostatic interactions that anchored the N-terminus of the functional domain to sub-domains containing the nose cone and active site. Mutation of the three tryptophan residues (Trp(203)/Trp(205)/Trp(206)) to an alanine residue, either individually or together, in silico revealed that the individual tryptophan residue's contribution to the tryptophan 'anchor' was additive. When the three tryptophan residues were mutated to alanine in vitro, the resulting mutant Top1 differed from wild-type Top1 in that it lacked processivity, exhibited resistance to camptothecin and was inactivated by urea. The results indicated that the tryptophan anchor stabilized the N-terminus of the functional domain and prevented the loss of Top1 structure and function.
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20
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Miao ZH, Player A, Shankavaram U, Wang YH, Zimonjic DB, Lorenzi PL, Liao ZY, Liu H, Shimura T, Zhang HL, Meng LH, Zhang YW, Kawasaki ES, Popescu NC, Aladjem MI, Goldstein DJ, Weinstein JN, Pommier Y. Nonclassic functions of human topoisomerase I: genome-wide and pharmacologic analyses. Cancer Res 2007; 67:8752-61. [PMID: 17875716 DOI: 10.1158/0008-5472.can-06-4554] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The biological functions of nuclear topoisomerase I (Top1) have been difficult to study because knocking out TOP1 is lethal in metazoans. To reveal the functions of human Top1, we have generated stable Top1 small interfering RNA (siRNA) cell lines from colon and breast carcinomas (HCT116-siTop1 and MCF-7-siTop1, respectively). In those clones, Top1 is reduced approximately 5-fold and Top2alpha compensates for Top1 deficiency. A prominent feature of the siTop1 cells is genomic instability, with chromosomal aberrations and histone gamma-H2AX foci associated with replication defects. siTop1 cells also show rDNA and nucleolar alterations and increased nuclear volume. Genome-wide transcription profiling revealed 55 genes with consistent changes in siTop1 cells. Among them, asparagine synthetase (ASNS) expression was reduced in siTop1 cells and in cells with transient Top1 down-regulation. Conversely, Top1 complementation increased ASNS, indicating a causal link between Top1 and ASNS expression. Correspondingly, pharmacologic profiling showed L-asparaginase hypersensitivity in the siTop1 cells. Resistance to camptothecin, indenoisoquinoline, aphidicolin, hydroxyurea, and staurosporine and hypersensitivity to etoposide and actinomycin D show that Top1, in addition to being the target of camptothecins, also regulates DNA replication, rDNA stability, and apoptosis. Overall, our studies show the pleiotropic nature of human Top1 activities. In addition to its classic DNA nicking-closing functions, Top1 plays critical nonclassic roles in genomic stability, gene-specific transcription, and response to various anticancer agents. The reported cell lines and approaches described in this article provide new tools to perform detailed functional analyses related to Top1 function.
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Affiliation(s)
- Ze-Hong Miao
- Laboratories of Molecular Pharmacology, National Institute of Diabetes and Digestive and Kidney Diseases, NIH, Bethesda, Maryland, USA
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21
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Pungaliya P, Kulkarni D, Park HJ, Marshall H, Zheng H, Lackland H, Saleem A, Rubin EH. TOPORS functions as a SUMO-1 E3 ligase for chromatin-modifying proteins. J Proteome Res 2007; 6:3918-23. [PMID: 17803295 DOI: 10.1021/pr0703674] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
TOPORS is the first example of a protein with both ubiquitin and SUMO-1 E3 ligase activity and has been implicated as a tumor suppressor in several different malignancies. To gain insight into the cellular role of TOPORS, a proteomic screen was performed to identify candidate sumoylation substrates. The results indicate that many of the putative substrates are involved in chromatin modification or transcriptional regulation. Transfection studies confirmed mammalian Sin3A as a sumoylation substrate for TOPORS. These findings suggest that TOPORS may function as a tumor suppressor by regulating mSin3A and other proteins involved in chromatin modification.
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Affiliation(s)
- Pooja Pungaliya
- Department of Pharmacology, The Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, 195 Little Albany Street, New Brunswick, New Jersey 08901, USA
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22
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Storck S, Shukla M, Dimitrov S, Bouvet P. Functions of the histone chaperone nucleolin in diseases. Subcell Biochem 2007; 41:125-44. [PMID: 17484127 DOI: 10.1007/1-4020-5466-1_7] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022]
Abstract
Alteration of nuclear morphology is often used by pathologist as diagnostic marker for malignancies like cancer. In particular, the staining of cells by the silver staining methods (AgNOR) has been proved to be an important tool for predicting the clinical outcome of some cancer diseases. Two major argyrophilic proteins responsible for the strong staining of cells in interphase are the nucleophosmin (B23) and the nucleolin (C23) nucleolar proteins. Interestingly these two proteins have been described as chromatin associated proteins with histone chaperone activities and also as proteins able to regulate chromatin transcription. Nucleolin seems to be over-expressed in highly proliferative cells and is involved in many aspect of gene expression: chromatin remodeling, DNA recombination and replication, RNA transcription by RNA polymerase I and II, rRNA processing, mRNA stabilisation, cytokinesis and apoptosis. Interestingly, nucleolin is also found on the cell surface in a wide range of cancer cells, a property which is being used as a marker for the diagnosis of cancer and for the development of anti-cancer drugs to inhibit proliferation of cancer cells. In addition to its implication in cancer, nucleolin has been described not only as a marker or as a protein being involved in many diseases like viral infections, autoimmune diseases, Alzheimer's disease pathology but also in drug resistance. In this review we will focus on the chromatin associated functions of nucleolin and discuss the functions of nucleolin or its use as diagnostic marker and as a target for therapy
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Affiliation(s)
- Sébastien Storck
- Laboratoire Joliot-Curie, Ecole Normale Supérieure de Lyon, 46 Allée d'Italie, 69007 Lyon, France
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23
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Staub E, Mackowiak S, Vingron M. An inventory of yeast proteins associated with nucleolar and ribosomal components. Genome Biol 2006; 7:R98. [PMID: 17067374 PMCID: PMC1794573 DOI: 10.1186/gb-2006-7-10-r98] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2006] [Revised: 07/26/2006] [Accepted: 10/26/2006] [Indexed: 11/24/2022] Open
Abstract
BACKGROUND Although baker's yeast is a primary model organism for research on eukaryotic ribosome assembly and nucleoli, the list of its proteins that are functionally associated with nucleoli or ribosomes is still incomplete. We trained a naïve Bayesian classifier to predict novel proteins that are associated with yeast nucleoli or ribosomes based on parts lists of nucleoli in model organisms and large-scale protein interaction data sets. Phylogenetic profiling and gene expression analysis were carried out to shed light on evolutionary and regulatory aspects of nucleoli and ribosome assembly. RESULTS We predict that, in addition to 439 known proteins, a further 62 yeast proteins are associated with components of the nucleolus or the ribosome. The complete set comprises a large core of archaeal-type proteins, several bacterial-type proteins, but mostly eukaryote-specific inventions. Expression of nucleolar and ribosomal genes tends to be strongly co-regulated compared to other yeast genes. CONCLUSION The number of proteins associated with nucleolar or ribosomal components in yeast is at least 14% higher than known before. The nucleolus probably evolved from an archaeal-type ribosome maturation machinery by recruitment of several bacterial-type and mostly eukaryote-specific factors. Not only expression of ribosomal protein genes, but also expression of genes encoding the 90S processosome, are strongly co-regulated and both regulatory programs are distinct from each other.
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Affiliation(s)
- Eike Staub
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - Sebastian Mackowiak
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
| | - Martin Vingron
- Department of Computational Molecular Biology, Max Planck Institute for Molecular Genetics, Berlin, Germany
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24
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Girvan AC, Teng Y, Casson LK, Thomas SD, Jüliger S, Ball MW, Klein JB, Pierce WM, Barve SS, Bates PJ. AGRO100 inhibits activation of nuclear factor-kappaB (NF-kappaB) by forming a complex with NF-kappaB essential modulator (NEMO) and nucleolin. Mol Cancer Ther 2006; 5:1790-9. [PMID: 16891465 DOI: 10.1158/1535-7163.mct-05-0361] [Citation(s) in RCA: 183] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
AGRO100, also known as AS1411, is an experimental anticancer drug that recently entered human clinical trials. It is a member of a novel class of antiproliferative agents known as G-rich oligonucleotides (GRO), which are non-antisense, guanosine-rich phosphodiester oligodeoxynucleotides that form stable G-quadruplex structures. The biological activity of GROs results from their binding to specific cellular proteins as aptamers. One important target protein of GROs has been previously identified as nucleolin, a multifunctional protein expressed at high levels by cancer cells. Here, we report that AGRO100 also associates with nuclear factor-kappaB (NF-kappaB) essential modulator (NEMO), which is a regulatory subunit of the inhibitor of kappaB (IkappaB) kinase (IKK) complex, and also called IKKgamma. In the classic NF-kappaB pathway, the IKK complex is required for phosphorylation of IkappaBalpha and subsequent activation of the transcription factor NF-kappaB. We found that treatment of cancer cells with AGRO100 inhibits IKK activity and reduces phosphorylation of IkappaBalpha in response to tumor necrosis factor-alpha stimulation. Using a reporter gene assay, we showed that AGRO100 blocks both tumor necrosis factor-alpha-induced and constitutive NF-kappaB activity in human cancer cell lines derived from cervical, prostate, breast, and lung carcinomas. In addition, we showed that, in AGRO100-treated cancer cells, NEMO is coprecipitated by nucleolin, indicating that both proteins are present in the same complex. Our studies suggest that abrogation of NF-kappaB activity may contribute to the anticancer effects of AGRO100 and that nucleolin may play a previously unknown role in regulating the NF-kappaB pathway.
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Affiliation(s)
- Allicia C Girvan
- University of Louisville, 580 South Preston Street, Delia Baxter Building 321, Louisville, KY 40202-1756, USA
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25
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St-Amant C, Lussier S, Lehoux J, Laberge RM, Boissonneault G. Altered phosphorylation of topoisomerase I following overexpression in an ovarian cancer cell line. Biochem Cell Biol 2006; 84:55-66. [PMID: 16462890 DOI: 10.1139/o05-157] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
There is a growing interest regarding the use of camptothecins (CPTs) for the management of ovarian cancer. Since topoisomerase I has been established as a prime target of these drugs in other experimental models, it was important to determine whether sensitivity to CPTs in ovarian cancer cells is also correlated with the cellular level of this enzyme. Despite the 7-fold increase in topoisomerase expression achieved by adenovirus-mediated expression, the sensitivity to a CPT derivative (topotecan), was not improved compared with control cells harboring an endogenous level of the enzyme. This observation is in accordance with the similar level of topoisomerase I activity found in control and overexpressing cells and suggests that these cells may efficiently regulate the enzyme activity. Indeed, topoisomerase I overexpressing cells are characterized by a lack of alkaline phosphatase sensitivity and elimination of the hyperphosphorylated form of the protein. Taken together, these observations strongly suggest that an alteration in the phosphorylation state of topoisomerase I could limit its activity and prevent improvement of CPT response in ovarian cancer cells. In addition, a limited extent of topoisomerase I phosphorylating activity was found in nuclear extract of OVCAR-3 cells. Hence, providing enhancement in topoisomerase I expression may not result in improvement of CPT response in ovarian cancer cells because of an efficient control of the phosphorylation state of the enzyme.
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Affiliation(s)
- Christiane St-Amant
- Département de Biochimie, Faculté de Médecine, Université de Sherbrooke, QC, Canada
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26
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Czubaty A, Girstun A, Kowalska-Loth B, Trzcińska AM, Purta E, Winczura A, Grajkowski W, Staroń K. Proteomic analysis of complexes formed by human topoisomerase I. BIOCHIMICA ET BIOPHYSICA ACTA-PROTEINS AND PROTEOMICS 2005; 1749:133-41. [PMID: 15848144 DOI: 10.1016/j.bbapap.2005.03.007] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/05/2005] [Revised: 03/08/2005] [Accepted: 03/09/2005] [Indexed: 10/25/2022]
Abstract
Human topoisomerase I is a nuclear enzyme that catalyses DNA relaxation and phosphorylation of SR proteins. Topoisomerase I participates in several protein-protein interactions. We performed a proteomic analysis of protein partners of topoisomerase I. Two methods were applied to proteins of the nuclear extract of HeLa cells: a co-immunoprecipitation and an affinity chromatography combined with mass spectrometry. Complexes formed by topoisomerase I with its protein partners were immunoprecipitated by scleroderma anti-topoisomerase I antibodies. To identify binding sites for the protein partners, baits corresponding to fragments of topoisomerase I were constructed and used in the affinity chromatography. The N-terminal domain and the cap region of the core domain appeared to be the main regions that bound proteins. We identified 36 nuclear proteins that were associated with topoisomerase I. The proteins were mainly involved in RNA metabolism. We found 29 new and confirmed 7 previously identified protein partners of topoisomerase I. More than 40% proteins that associate with the cap region contain two closely spaced RRM domains. Docking calculations identified the RRM domains as a possible site for the interaction of these proteins with the cap region.
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Affiliation(s)
- Alicja Czubaty
- Institute of Biochemistry, Warsaw University, ul. Miecznikowa 1, 02-096 Warszawa, Poland
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27
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Yu D, Khan E, Khaleque MA, Lee J, Laco G, Kohlhagen G, Kharbanda S, Cheng YC, Pommier Y, Bharti A. Phosphorylation of DNA topoisomerase I by the c-Abl tyrosine kinase confers camptothecin sensitivity. J Biol Chem 2004; 279:51851-61. [PMID: 15448168 DOI: 10.1074/jbc.m404396200] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
DNA topoisomerase I (topo I) is involved in the regulation of DNA supercoiling, gene transcription, recombination, and DNA repair. The anticancer agent camptothecin specifically targets topo I. The mechanisms responsible for the regulation of topo I in cells, however, are not known. This study demonstrates that c-Abl-dependent phosphorylation up-regulates topo I activity. The c-Abl SH3 domain bound directly to the N-terminal region of topo I. The results demonstrate that c-Abl phosphorylated topo I at Tyr268 in core subdomain II. c-Abl-mediated phosphorylation of topo I Tyr268 in vitro and in cells conferred activation of the topo I isomerase function. Moreover, activation of c-Abl by treatment of cells with ionizing radiation was associated with c-Abl-dependent phosphorylation of topo I and induction of topo I activity. The functional significance of the c-Abl/topo I interaction is supported by the findings that (i) mutant topo I(Y268F) exhibited loss of c-Abl-induced topo I activity, and (ii) c-Abl-/- cells were deficient in the accumulation of protein-linked DNA breaks. In addition, loss of topo I phosphorylation in c-Abl-deficient cells conferred resistance to camptothecin-induced apoptosis. These findings collectively support a model in which c-Abl-mediated phosphorylation of topo I is functionally important to topo I activity and sensitivity to topo I poisons.
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Affiliation(s)
- Donghui Yu
- Department of Adult Oncology, Dana-Farber Cancer Institute, Harvard Medical School, Boston, Massachusetts 02115, USA
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28
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Rajendra R, Malegaonkar D, Pungaliya P, Marshall H, Rasheed Z, Brownell J, Liu LF, Lutzker S, Saleem A, Rubin EH. Topors functions as an E3 ubiquitin ligase with specific E2 enzymes and ubiquitinates p53. J Biol Chem 2004; 279:36440-4. [PMID: 15247280 DOI: 10.1074/jbc.c400300200] [Citation(s) in RCA: 148] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The human topoisomerase I- and p53-binding protein topors contains a highly conserved, N-terminal C3HC4-type RING domain that is homologous to the RING domains of known E3 ubiquitin ligases. We demonstrate that topors functions in vitro as a RING-dependent E3 ubiquitin ligase with the E2 enzymes UbcH5a, UbcH5c, and UbcH6 but not with UbcH7, CDC34, or UbcH2b. Additional studies indicate that a conserved tryptophan within the topors RING domain is required for ubiquitination activity. Furthermore, both in vitro and cellular studies implicate p53 as a ubiquitination substrate for topors. Similar to MDM2, overexpression of topors results in a proteasome-dependent decrease in p53 protein expression in a human osteosarcoma cell line. These results are similar to the recent finding that a Drosophila topors orthologue ubiquitinates the Hairy transcriptional repressor and suggest that topors functions as a ubiquitin ligase for multiple transcription factors.
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Affiliation(s)
- Rajeev Rajendra
- Department of Pharmacology, The Cancer Institute of New Jersey, Robert Wood Johnson Medical School, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ 08901, USA
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29
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Alessandri M, Beretta GL, Ferretti E, Mancia A, Khobta A, Capranico G. Enhanced CPT Sensitivity of Yeast Cells and Selective Relaxation of Gal4 Motif-containing DNA by Novel Gal4–Topoisomerase I Fusion Proteins. J Mol Biol 2004; 337:295-305. [PMID: 15003448 DOI: 10.1016/j.jmb.2004.01.032] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/01/2003] [Revised: 01/14/2004] [Accepted: 01/20/2004] [Indexed: 10/26/2022]
Abstract
Human topoisomerase I-B (Top1) efficiently relaxes DNA supercoils during basic cellular processes, and can be transformed into a DNA-damaging agent by antitumour drugs, enzyme mutations and DNA lesions. Here, we describe Gal4-Top1 chimeric proteins (GalTop) with an N-terminal truncation of Top1, and mutations of the Gal4 Zn-cluster and/or Top1 domains that impair their respective DNA-binding activities. Expression levels of chimeras were similar in yeast cells, however, GalTop conferred an increased CPT sensitivity to RAD52- yeast cells as compared to a GalTop with mutations of the Gal4 domain, showing that a functional Gal4 domain can alter in vivo functions of Top1. In vitro enzyme activity was tested with a DNA relaxation assay using negatively supercoiled plasmids with 0 to 5 Gal4 consensus motifs. Only GalTop with a functional Gal4 domain could direct DNA relaxation activity of Top1 specifically to DNA molecules containing Gal4 motifs. By using a substrate competition assay, we could demonstrate that the Gal4-anchored Top1 remains functional and efficiently relax DNA substrates in cis. The enhanced CPT sensitivity of GalTop in yeast cells may then be due to alterations of the chromatin-binding activity of Top1. The GalTop chimeras may indeed mimic a normal mechanism by which Top1 is recruited to chromatin sites in living cells. Such hybrid Top1s may be helpful in further dissecting enzyme functions, and constitute a prototype of a site-specific DNA cutter endowed with high cell lethality.
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Affiliation(s)
- Marco Alessandri
- Alma Mater Studiorum-University of Bologna, G. Moruzzi Department of Biochemistry, via S. Giacomo 11, 40126 Bologna, Italy
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30
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Christensen MO, Barthelmes HU, Boege F, Mielke C. Residues 190-210 of human topoisomerase I are required for enzyme activity in vivo but not in vitro. Nucleic Acids Res 2004; 31:7255-63. [PMID: 14654701 PMCID: PMC291868 DOI: 10.1093/nar/gkg927] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
DNA-topoisomerase I (topo I) unwinds the DNA- double helix by cutting one strand and allowing rotation of the other. In vitro, this function does not require the N-terminal domain of the enzyme, which is believed to regulate cellular properties. To assess this role, we studied the cellular distribution and mobility of green fluorescent protein-chimera of human topo I lacking either the entire N-terminal domain or a portion of it. We find that topo I truncated up to position 210 is not stabilized by camptothecin in covalent DNA-complexes inside a living cell, whereas in vitro it retains full DNA-relaxation activity, and is targeted by camptothecin in the usual manner. This difference is not shared with a fragment lacking the N-terminal domain up to position 190, indicating that residues 190-210 play a crucial role for the activity of the enzyme in its physiological environment, but not in vitro. Since it is impossible to discriminate in vivo whether this region is required for topo I to form covalent DNA intermediates in the cell, or just for camptothecin to bind and stabilize such complexes, we could not explain precisely these cellular observations. However, inactivity in vivo of the enzyme lacking this region is indicated by a lesser cytotoxicity.
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Affiliation(s)
- Morten O Christensen
- Institute of Clinical Chemistry and Laboratory Diagnostics, Heinrich-Heine-University, Medical School, Moorenstrasse 5, D-40225 Duesseldorf, Germany
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31
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Abstract
DNA topoisomerases are a class of enzymes that alter the topology of DNA and are targets of several anticancer drugs. Camptothecins (CPTs) are a relatively new family of compounds that specifically target topoisomerase I (Top1). These compounds "poison" Top1 by binding to the Top1-DNA complex in a manner that prevents the religation of DNA. Topotecan and irinotecan are two CPTs that are approved for the treatment of a variety of malignancies, including colorectal, ovarian, and small cell lung cancers, as well as myeloid malignancies. Although CPTs have proven to be effective anticancer drugs, resistance is still a critical clinical problem. The mechanisms underlying de novo and acquired clinical resistance to CPTs and the newer classes of Top1 poisons are unclear. However, based on preclinical studies, it is likely that clinical resistance to these drugs is the result of: (1) inadequate accumulation of drug in the tumor, (2) resistance-conferring alterations in Top1, or (3) alterations in the cellular response to the Top1-CPT interaction. This review will focus on the current knowledge regarding mechanisms of resistance to CPTs and other Top1-targeting drugs.
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Affiliation(s)
- Zeshaan A Rasheed
- The Cancer Institute of New Jersey, Department of Molecular and Cellular Pharmacology, UMDNJ-Robert Wood Johnson Medical School, 195 Little Albany Street, New Brunswick, NJ 08901, USA.
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Rallabhandi P, Hashimoto K, Mo YY, Beck WT, Moitra PK, D'Arpa P. Sumoylation of topoisomerase I is involved in its partitioning between nucleoli and nucleoplasm and its clearing from nucleoli in response to camptothecin. J Biol Chem 2002; 277:40020-6. [PMID: 12149243 DOI: 10.1074/jbc.m200388200] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Previous studies identified a small fraction of putatively sumoylated topoisomerase I (TOP1) under basal conditions ( approximately 1%), and anticancer camptothecins that trap the TOP1-DNA covalent intermediate markedly increase the sumoylation of TOP1 (<or=10%). To study the role of the sumoylation of TOP1, we mutated sites on green fluorescent protein (GFP)-TOP1 corresponding to the consensus sequence for protein sumoylation (PsiKXE, where Psi is a hydrophobic residue) and assayed the mutants for basal and camptothecin-induced sumoylation. Only one of the eight mutants, K117R, located in the highly charged NH2-terminal region, showed a substantial reduction ( approximately 5-fold) in basal and camptothecin-induced sumoylation; thus, Lys-117 appears to be the major sumoylation site. A triple mutant having the PsiKXE sequences flanking K117R additionally mutated (K103R/K117R/K153R) showed little if any sumoylation, but was degraded like wild-type GFP-TOP1 during camptothecin treatment. However, K103R/K117R/K153R-GFP-TOP1 was markedly concentrated within nucleoli, depleted from the remainder of nucleus, and failed to be cleared from nucleoli in response to camptothecin treatment. These data are consistent with a model wherein basal transient sumoylation of the NH2-terminal, highly charged, disordered region prevents TOP1 binding to sites in nucleoli, thus driving it to bind in the nucleoplasm; and camptothecin treatment, which increases TOP1 sumoylation, further shifts the binding resulting in delocalization of TOP1 from nucleoli to nucleoplasm.
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Affiliation(s)
- Prasad Rallabhandi
- Department of Biochemistry and Molecular Biology, Uniformed Services University of the Health Sciences, Bethesda, Maryland 20814-4799, USA
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Shibata Y, Muramatsu T, Hirai M, Inui T, Kimura T, Saito H, McCormick LM, Bu G, Kadomatsu K. Nuclear targeting by the growth factor midkine. Mol Cell Biol 2002; 22:6788-96. [PMID: 12215536 PMCID: PMC134045 DOI: 10.1128/mcb.22.19.6788-6796.2002] [Citation(s) in RCA: 106] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2002] [Accepted: 06/17/2002] [Indexed: 01/08/2023] Open
Abstract
Ligand-receptor internalization has been traditionally regarded as part of the cellular desensitization system. Low-density lipoprotein receptor-related protein (LRP) is a large endocytosis receptor with a diverse array of ligands. We recently showed that LRP binds heparin-binding growth factor midkine. Here we demonstrate that LRP mediates nuclear targeting by midkine and that the nuclear targeting is biologically important. Exogenous midkine reached the nucleus, where intact midkine was detected, within 20 min. Midkine was not internalized in LRP-deficient cells, whereas transfection of an LRP expression vector restored midkine internalization and subsequent nuclear translocation. Internalized midkine in the cytoplasm bound to nucleolin, a nucleocytoplasmic shuttle protein. The midkine-binding sites were mapped to acidic stretches in the N-terminal domain of nucleolin. When the nuclear localization signal located next to the acidic stretches was deleted, we found that the mutant nucleolin not only accumulated in the cytoplasm but also suppressed the nuclear translocation of midkine. By using cells that overexpressed the mutant nucleolin, we further demonstrated that the nuclear targeting was necessary for the full activity of midkine in the promotion of cell survival. This study therefore reveals a novel role of LRP in intracellular signaling by its ligand and the importance of nucleolin in this process.
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Affiliation(s)
- Yoshihisa Shibata
- Department of Biochemistry, Nagoya University School of Medicine, Showa-ku, Japan
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Christensen MO, Barthelmes HU, Boege F, Mielke C. The N-terminal domain anchors human topoisomerase I at fibrillar centers of nucleoli and nucleolar organizer regions of mitotic chromosomes. J Biol Chem 2002; 277:35932-8. [PMID: 12119295 DOI: 10.1074/jbc.m204738200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA topoisomerase I releases torsion stress created by DNA transcription. In principle, this activity is required in the nucleoplasm for mRNA synthesis and in the nucleoli for rRNA synthesis. Yet, topoisomerase I is mostly a nucleolar protein. Current belief holds that this preference is triggered by the N-terminal domain of the enzyme, which constitutes a nucleolar import signal. Contradicting this view, we show here that nucleolar accumulation of various fragments of topoisomerase I is correlated with their lesser mobility in this compartment and not with the N-terminal domain being intact or present. Therefore, the N-terminal domain is not likely a nucleolar import signal. We show that it rather serves as an adaptor that anchors a subpopulation of topoisomerase I at fibrillar centers of nucleoli and nucleolar organizer regions of mitotic chromosomes. Thus, it provides a steady association of topoisomerase I with the rDNA and with RNA polymerase I, which is maintained in a living cell during the entire cell cycle.
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Affiliation(s)
- Morten O Christensen
- Department of Clinical Chemistry, Medizinische Poliklinik, University of Würzburg, Klinikstrasse 6-8, D-97070 Würzburg, Germany
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Rasheed ZA, Saleem A, Ravee Y, Pandolfi PP, Rubin EH. The topoisomerase I-binding RING protein, topors, is associated with promyelocytic leukemia nuclear bodies. Exp Cell Res 2002; 277:152-60. [PMID: 12083797 DOI: 10.1006/excr.2002.5550] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We previously identified topors as a topoisomerase I-binding protein that localizes in punctate nuclear regions when expressed as a GFP fusion protein. We now demonstrate that both the GFP-topors fusion protein and endogenous topors are associated with promyelocytic leukemia (PML) nuclear bodies in exponentially growing HeLa cells. Studies using isogenic PML+/+ and PML-/- murine embryonic fibroblasts indicate that the punctate nuclear localization of topors is dependent on PML. A basic C-terminal region but not the N-terminal RING domain of topors is required for the punctate nuclear localization of this protein. Additional studies indicate that topors, but not PML, rapidly relocalizes from nuclear bodies to the nucleoplasm in cells exposed to the transcription inhibitor dichloro-1-beta-d-ribofuranolsylbenzimidazole or to the topoisomerase I-targeting drug camptothecin. These results identify topors as a new member of the group of proteins that associate dynamically with PML nuclear bodies and suggest that topors may be involved in the cellular response to camptothecin.
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Affiliation(s)
- Zeshaan A Rasheed
- Department of Pharmacology, Robert Wood Johnson Medical School, New Brunswick, New Jersey 08903-2681, USA
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Marchand C, Pourquier P, Laco GS, Jing N, Pommier Y. Interaction of human nuclear topoisomerase I with guanosine quartet-forming and guanosine-rich single-stranded DNA and RNA oligonucleotides. J Biol Chem 2002; 277:8906-11. [PMID: 11756434 DOI: 10.1074/jbc.m106372200] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Human nuclear DNA topoisomerase I (top1) plays a crucial role in DNA replication, transcription, and chromosome condensation. In this study, we show that intra- and intermolecular guanosine quartets (G-quartets) can inhibit top1-mediated DNA cleavage at a high affinity site. Top1-mediated DNA cleavage was also inhibited by a 16-mer single-stranded oligodeoxynucleotide (ODN) containing a G-rich sequence (G(2)T(2)G(5)TG(2)TG(3)) and by its RNA equivalent, neither of which form G-quartet structures. A comparison of various single-stranded ODN for their ability to inhibit top1-mediated DNA cleavage indicated that G-rich sequences containing repeats of 2 or 3 consecutive guanines interspaced with thymines specifically inhibited top1. We also found that both single-stranded and G-quartet-forming ODNs bind to top1 without being cleaved by the enzyme. These results demonstrate that either DNA or RNA G-rich single-stranded and G-quartet-forming oligonucleotides can bind to top1 and prevent cleavage of duplex DNA.
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Affiliation(s)
- Christophe Marchand
- Laboratory of Molecular Pharmacology, Center for Cancer Research, NCI, National Institutes of Health, Bethesda, Maryland 20892-4255, USA
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Woo MH, Vance JR, Marcos ARO, Bailly C, Bjornsti MA. Active site mutations in DNA topoisomerase I distinguish the cytotoxic activities of camptothecin and the indolocarbazole, rebeccamycin. J Biol Chem 2002; 277:3813-22. [PMID: 11733535 DOI: 10.1074/jbc.m110484200] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DNA topoisomerase I (Top1p) catalyzes topological changes in DNA and is the cellular target of the antitumor agent camptothecin (CPT). Non-CPT drugs that target Top1p, such as indolocarbazoles, are under clinical development. However, whether the cytotoxicity of indolocarbazoles derives from Top1p poisoning remains unclear. To further investigate indolocarbazole mechanism, rebeccamycin R-3 activity was examined in vitro and in yeast. Using a series of Top1p mutants, where substitution of residues around the active site tyrosine has well-defined effects on enzyme catalysis, we show that catalytically active, CPT-resistant enzymes remain sensitive to R-3. This indolocarbazole did not inhibit yeast Top1p activity, yet was effective in stabilizing Top1p-DNA complexes. Similar results were obtained with human Top1p, when Ser or His were substituted for Asn-722. The mutations altered enzyme function and sensitivity to CPT, yet R-3 poisoning of Top1p was unaffected. Moreover, top1delta, rad52delta yeast cells expressing human Top1p, but not catalytically inactive Top1Y723Fp, were sensitive to R-3. These data support hTop1p as the cellular target of R-3 and indicate that distinct drug-enzyme interactions at the active site are required for efficient poisoning by R-3 or CPT. Furthermore, resistance to one poison may potentiate cell sensitivity to structurally distinct compounds that also target Top1p.
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Affiliation(s)
- Michael H Woo
- Department of Molecular Pharmacology, St. Jude Children's Research Hospital, Memphis, Tennessee 38105, USA
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Xu L, Yang L, Hashimoto K, Anderson M, Kohlhagen G, Pommier Y, D'Arpa P. Characterization of BTBD1 and BTBD2, two similar BTB-domain-containing Kelch-like proteins that interact with Topoisomerase I. BMC Genomics 2002; 3:1. [PMID: 11818025 PMCID: PMC64781 DOI: 10.1186/1471-2164-3-1] [Citation(s) in RCA: 44] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2001] [Accepted: 01/07/2002] [Indexed: 12/04/2022] Open
Abstract
BACKGROUND Two-hybrid screening for proteins that interact with the core domain of human topoisomerase I identified two novel proteins, BTBD1 and BTBD2, which share 80% amino acid identities. RESULTS The interactions were confirmed by co-precipitation assays demonstrating the physical interaction of BTBD1 and BTBD2 with 100 kDa topoisomerase I from HeLa cells. Deletion mapping using two-hybrid and GST-pulldown assays demonstrated that less than the C-terminal half of BTBD1 is sufficient for binding topoisomerase I. The topoisomerase I sequences sufficient to bind BTBD2 were mapped to residues 215 to 329. BTBD2 with an epitope tag localized to cytoplasmic bodies. Using truncated versions that direct BTBD2 and TOP1 to the same cellular compartment, either the nucleus or the cytoplasm, co-localization was demonstrated in co-transfected Hela cells. The supercoil relaxation and DNA cleavage activities of topoisomerase I in vitro were affected little or none by co-incubation with BTBD2. Northern analysis revealed only a single sized mRNA for each BTBD1 and BTBD2 in all human tissues tested. Characterization of BTBD2 mRNA revealed a 255 nucleotide 90% GC-rich region predicted to encode the N-terminus. BTBD1 and BTBD2 are widely if not ubiquitously expressed in human tissues, and have two paralogs as well as putative orthologs in C. elegans and D. melanogaster. CONCLUSIONS BTBD1 and BTBD2 belong to a small family of uncharacterized proteins that appear to be specific to animals. Epitope-tagged BTBD2 localized to cytoplasmic bodies. The characterization of BTBD1 and BTBD2 and their interaction with TOP1 is underway.
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Affiliation(s)
- Lixin Xu
- Department of Biochemistry and Molecular Biology Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA
| | - Lihong Yang
- Department of Biochemistry and Molecular Biology Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, Bldg. 37/Rm. 1C18, Bethesda, MD 20892-4255, USA
| | - Keiko Hashimoto
- Department of Biochemistry and Molecular Biology Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA
| | - Melvin Anderson
- Department of Biochemistry and Molecular Biology Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA
| | - Glenda Kohlhagen
- Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA
| | - Yves Pommier
- Laboratory of Molecular Pharmacology, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-4255, USA
| | - Peter D'Arpa
- Department of Biochemistry and Molecular Biology Uniformed Services University of the Health Sciences 4301 Jones Bridge Road, Bethesda, MD 20814-4799, USA
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