1
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Dörner K, Badertscher L, Horváth B, Hollandi R, Molnár C, Fuhrer T, Meier R, Sárazová M, van den Heuvel J, Zamboni N, Horvath P, Kutay U. Genome-wide RNAi screen identifies novel players in human 60S subunit biogenesis including key enzymes of polyamine metabolism. Nucleic Acids Res 2022; 50:2872-2888. [PMID: 35150276 PMCID: PMC8934630 DOI: 10.1093/nar/gkac072] [Citation(s) in RCA: 11] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2021] [Revised: 01/18/2022] [Accepted: 01/25/2022] [Indexed: 12/19/2022] Open
Abstract
Ribosome assembly is an essential process that is linked to human congenital diseases and tumorigenesis. While great progress has been made in deciphering mechanisms governing ribosome biogenesis in eukaryotes, an inventory of factors that support ribosome synthesis in human cells is still missing, in particular regarding the maturation of the large 60S subunit. Here, we performed a genome-wide RNAi screen using an imaging-based, single cell assay to unravel the cellular machinery promoting 60S subunit assembly in human cells. Our screen identified a group of 310 high confidence factors. These highlight the conservation of the process across eukaryotes and reveal the intricate connectivity of 60S subunit maturation with other key cellular processes, including splicing, translation, protein degradation, chromatin organization and transcription. Intriguingly, we also identified a cluster of hits comprising metabolic enzymes of the polyamine synthesis pathway. We demonstrate that polyamines, which have long been used as buffer additives to support ribosome assembly in vitro, are required for 60S maturation in living cells. Perturbation of polyamine metabolism results in early defects in 60S but not 40S subunit maturation. Collectively, our data reveal a novel function for polyamines in living cells and provide a rich source for future studies on ribosome synthesis.
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Affiliation(s)
- Kerstin Dörner
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland.,Molecular Life Sciences Ph.D. Program, 8057 Zurich, Switzerland
| | - Lukas Badertscher
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland.,Molecular Life Sciences Ph.D. Program, 8057 Zurich, Switzerland
| | - Bianka Horváth
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland.,Molecular Life Sciences Ph.D. Program, 8057 Zurich, Switzerland
| | - Réka Hollandi
- Synthetic and Systems Biology Unit, Biological Research Center, 6726 Szeged, Hungary
| | - Csaba Molnár
- Synthetic and Systems Biology Unit, Biological Research Center, 6726 Szeged, Hungary
| | - Tobias Fuhrer
- Institute of Molecular Systems Biology, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Roger Meier
- ScopeM, ETH Zürich, 8093 Zürich, Switzerland
| | - Marie Sárazová
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Jasmin van den Heuvel
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland
| | - Nicola Zamboni
- Institute of Molecular Systems Biology, Department of Biology, ETH Zürich, 8093 Zürich, Switzerland
| | - Peter Horvath
- Synthetic and Systems Biology Unit, Biological Research Center, 6726 Szeged, Hungary.,Institute for Molecular Medicine Finland, University of Helsinki, 00014 Helsinki, Finland
| | - Ulrike Kutay
- Institute of Biochemistry, Department of Biology, ETH Zurich, 8093 Zurich, Switzerland
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2
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Thoms HC, Stark LA. The NF-κB Nucleolar Stress Response Pathway. Biomedicines 2021; 9:biomedicines9091082. [PMID: 34572268 PMCID: PMC8471347 DOI: 10.3390/biomedicines9091082] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 08/09/2021] [Accepted: 08/20/2021] [Indexed: 12/20/2022] Open
Abstract
The nuclear organelle, the nucleolus, plays a critical role in stress response and the regulation of cellular homeostasis. P53 as a downstream effector of nucleolar stress is well defined. However, new data suggests that NF-κB also acts downstream of nucleolar stress to regulate cell growth and death. In this review, we will provide insight into the NF-κB nucleolar stress response pathway. We will discuss apoptosis mediated by nucleolar sequestration of RelA and new data demonstrating a role for p62 (sequestosome (SQSTM1)) in this process. We will also discuss activation of NF-κB signalling by degradation of the RNA polymerase I (PolI) complex component, transcription initiation factor-IA (TIF-IA (RRN3)), and contexts where TIF-IA-NF-κB signalling may be important. Finally, we will discuss how this pathway is targeted by aspirin to mediate apoptosis of colon cancer cells.
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3
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Chen W, Shen T, Wang L, Lu K. Oligomerization of Selective Autophagy Receptors for the Targeting and Degradation of Protein Aggregates. Cells 2021; 10:cells10081989. [PMID: 34440758 PMCID: PMC8394947 DOI: 10.3390/cells10081989] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2021] [Revised: 07/31/2021] [Accepted: 08/02/2021] [Indexed: 02/05/2023] Open
Abstract
The selective targeting and disposal of solid protein aggregates are essential for cells to maintain protein homoeostasis. Autophagy receptors including p62, NBR1, Cue5/TOLLIP (CUET), and Tax1-binding protein 1 (TAX1BP1) proteins function in selective autophagy by targeting ubiquitinated aggregates through ubiquitin-binding domains. Here, we summarize previous beliefs and recent findings on selective receptors in aggregate autophagy. Since there are many reviews on selective autophagy receptors, we focus on their oligomerization, which enables receptors to function as pathway determinants and promotes phase separation.
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Affiliation(s)
- Wenjun Chen
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China; (W.C.); (T.S.); (L.W.)
- Department of Neurology, Shanxi Provincial People’s Hospital, Taiyuan 030012, China
| | - Tianyun Shen
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China; (W.C.); (T.S.); (L.W.)
| | - Lijun Wang
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China; (W.C.); (T.S.); (L.W.)
| | - Kefeng Lu
- Department of Neurosurgery, State Key Laboratory of Biotherapy, West China Hospital, Sichuan University, Chengdu 610041, China; (W.C.); (T.S.); (L.W.)
- Correspondence:
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Chen J, Stark LA. Insights into the Relationship between Nucleolar Stress and the NF-κB Pathway. Trends Genet 2019; 35:768-780. [PMID: 31434627 DOI: 10.1016/j.tig.2019.07.009] [Citation(s) in RCA: 21] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Revised: 07/22/2019] [Accepted: 07/24/2019] [Indexed: 02/06/2023]
Abstract
The nuclear organelle the nucleolus and the transcription factor nuclear factor of κ-light-chain-enhancer of activated B cells (NF-κB) are both central to the control of cellular homeostasis, dysregulated in common diseases and implicated in the ageing process. Until recently, it was believed that they acted independently to regulate homeostasis in health and disease. However, there is an emerging body of evidence suggesting that nucleoli and NF-κB signalling converge at multiple levels. Here we will review current understanding of this crosstalk. We will discuss activation of the NF-κB pathway by nucleolar stress and induction of apoptosis by nucleolar sequestration of NF-κB/RelA. We will also discuss the role of TIF-IA, COMMD1, and nucleophosmin, which are key players in this crosstalk, and the therapeutic relevance, particularly with respect to the antitumour effects of aspirin.
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Affiliation(s)
- Jingyu Chen
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Road, Edinburgh, Scotland EH4 2XU, UK
| | - Lesley A Stark
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Road, Edinburgh, Scotland EH4 2XU, UK.
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5
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Chen J, Lobb IT, Morin P, Novo SM, Simpson J, Kennerknecht K, von Kriegsheim A, Batchelor EE, Oakley F, Stark LA. Identification of a novel TIF-IA-NF-κB nucleolar stress response pathway. Nucleic Acids Res 2019; 46:6188-6205. [PMID: 29873780 PMCID: PMC6158704 DOI: 10.1093/nar/gky455] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Accepted: 05/14/2018] [Indexed: 12/13/2022] Open
Abstract
p53 as an effector of nucleolar stress is well defined, but p53 independent mechanisms are largely unknown. Like p53, the NF-κB transcription factor plays a critical role in maintaining cellular homeostasis under stress. Many stresses that stimulate NF-κB also disrupt nucleoli. However, the link between nucleolar function and activation of the NF-κB pathway is as yet unknown. Here we demonstrate that artificial disruption of the PolI complex stimulates NF-κB signalling. Unlike p53 nucleolar stress response, this effect does not appear to be linked to inhibition of rDNA transcription. We show that specific stress stimuli of NF-κB induce degradation of a critical component of the PolI complex, TIF-IA. This degradation precedes activation of NF-κB and is associated with increased nucleolar size. It is mimicked by CDK4 inhibition and is dependent upon a novel pathway involving UBF/p14ARF and S44 of the protein. We show that blocking TIF-IA degradation blocks stress effects on nucleolar size and NF-κB signalling. Finally, using ex vivo culture, we show a strong correlation between degradation of TIF-IA and activation of NF-κB in freshly resected, human colorectal tumours exposed to the chemopreventative agent, aspirin. Together, our study provides compelling evidence for a new, TIF-IA-NF-κB nucleolar stress response pathway that has in vivo relevance and therapeutic implications.
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Affiliation(s)
- Jingyu Chen
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Ian T Lobb
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Pierre Morin
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Sonia M Novo
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - James Simpson
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Kathrin Kennerknecht
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Alex von Kriegsheim
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Emily E Batchelor
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
| | - Fiona Oakley
- Liver Research Group, Institute of Cellular Medicine, 4th Floor, William Leech Building, Framlington Place, Newcastle University, Newcastle Upon Tyne NE2 4HH, UK
| | - Lesley A Stark
- University of Edinburgh Cancer Research Centre, Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Rd., Edinburgh EH4 2XU, UK
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6
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von Walden F. Ribosome biogenesis in skeletal muscle: coordination of transcription and translation. J Appl Physiol (1985) 2019; 127:591-598. [PMID: 31219775 DOI: 10.1152/japplphysiol.00963.2018] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Skeletal muscle mass responds in a remarkable manner to alterations in loading and use. It has long been clear that skeletal muscle hypertrophy can be prevented by inhibiting RNA synthesis. Since 80% of the cell's total RNA has been estimated to be rRNA, this finding indicates that de novo production of rRNA via transcription of the corresponding genes is important for such hypertrophy to occur. Transcription of rDNA by RNA Pol I is the rate-limiting step in ribosome biogenesis, indicating in turn that this biogenesis strongly influences the hypertrophic response. The present minireview focuses on 1) a brief description of the key steps in ribosome biogenesis and the relationship of this process to skeletal muscle mass and 2) the coordination of ribosome biogenesis and protein synthesis for growth or atrophy, as exemplified by the intracellular AMPK and mTOR pathways.
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Affiliation(s)
- Ferdinand von Walden
- Division of Pediatric Neurology, Department of Women's and Children's Health, Karolinska Institute, Stockholm, Sweden
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7
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Azkanaz M, Rodríguez López A, de Boer B, Huiting W, Angrand PO, Vellenga E, Kampinga HH, Bergink S, Martens JH, Schuringa JJ, van den Boom V. Protein quality control in the nucleolus safeguards recovery of epigenetic regulators after heat shock. eLife 2019; 8:45205. [PMID: 31199242 PMCID: PMC6570483 DOI: 10.7554/elife.45205] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2019] [Accepted: 05/21/2019] [Indexed: 12/19/2022] Open
Abstract
Maintenance of epigenetic modifiers is of utmost importance to preserve the epigenome and consequently appropriate cellular functioning. Here, we analyzed Polycomb group protein (PcG) complex integrity in response to heat shock (HS). Upon HS, various Polycomb Repressive Complex (PRC)1 and PRC2 subunits, including CBX proteins, but also other chromatin regulators, are found to accumulate in the nucleolus. In parallel, binding of PRC1/2 to target genes is strongly reduced, coinciding with a dramatic loss of H2AK119ub and H3K27me3 marks. Nucleolar-accumulated CBX proteins are immobile, but remarkably both CBX protein accumulation and loss of PRC1/2 epigenetic marks are reversible. This post-heat shock recovery of pan-nuclear CBX protein localization and reinstallation of epigenetic marks is HSP70 dependent. Our findings demonstrate that the nucleolus is an essential protein quality control center, which is indispensable for recovery of epigenetic regulators and maintenance of the epigenome after heat shock.
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Affiliation(s)
- Maria Azkanaz
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Aida Rodríguez López
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Bauke de Boer
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Wouter Huiting
- Department of Biomedical Sciences of Cells and Systems, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | | | - Edo Vellenga
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Harm H Kampinga
- Department of Biomedical Sciences of Cells and Systems, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Steven Bergink
- Department of Biomedical Sciences of Cells and Systems, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Joost Ha Martens
- Department of Molecular Biology, Faculty of Science and Medicine, Radboud Institute for Molecular Life Sciences, Radboud University Nijmegen, Nijmegen, Netherlands
| | - Jan Jacob Schuringa
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
| | - Vincent van den Boom
- Department of Experimental Hematology, Cancer Research Center Groningen, University Medical Center Groningen, University of Groningen, Groningen, Netherlands
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8
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Urdaneta EC, Vieira-Vieira CH, Hick T, Wessels HH, Figini D, Moschall R, Medenbach J, Ohler U, Granneman S, Selbach M, Beckmann BM. Purification of cross-linked RNA-protein complexes by phenol-toluol extraction. Nat Commun 2019; 10:990. [PMID: 30824702 PMCID: PMC6397201 DOI: 10.1038/s41467-019-08942-3] [Citation(s) in RCA: 140] [Impact Index Per Article: 28.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2018] [Accepted: 02/11/2019] [Indexed: 12/30/2022] Open
Abstract
Recent methodological advances allowed the identification of an increasing number of RNA-binding proteins (RBPs) and their RNA-binding sites. Most of those methods rely, however, on capturing proteins associated to polyadenylated RNAs which neglects RBPs bound to non-adenylate RNA classes (tRNA, rRNA, pre-mRNA) as well as the vast majority of species that lack poly-A tails in their mRNAs (including all archea and bacteria). We have developed the Phenol Toluol extraction (PTex) protocol that does not rely on a specific RNA sequence or motif for isolation of cross-linked ribonucleoproteins (RNPs), but rather purifies them based entirely on their physicochemical properties. PTex captures RBPs that bind to RNA as short as 30 nt, RNPs directly from animal tissue and can be used to simplify complex workflows such as PAR-CLIP. Finally, we provide a global RNA-bound proteome of human HEK293 cells and the bacterium Salmonella Typhimurium.
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Affiliation(s)
- Erika C Urdaneta
- IRI Life Sciences, Humboldt University, Philippstr. 13, 10115, Berlin, Germany
| | - Carlos H Vieira-Vieira
- Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Timon Hick
- IRI Life Sciences, Humboldt University, Philippstr. 13, 10115, Berlin, Germany
| | - Hans-Herrmann Wessels
- Berlin Institute for Medical Systems Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, 13125, Berlin, Germany
- Department of Biology, Humboldt University, Philippstr. 13, 10115, Berlin, Germany
| | - Davide Figini
- IRI Life Sciences, Humboldt University, Philippstr. 13, 10115, Berlin, Germany
| | - Rebecca Moschall
- Biochemistry I, University of Regensburg, Universitätsstrasse 31, 93053, Regensburg, Germany
| | - Jan Medenbach
- Biochemistry I, University of Regensburg, Universitätsstrasse 31, 93053, Regensburg, Germany
| | - Uwe Ohler
- Berlin Institute for Medical Systems Biology, Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, 13125, Berlin, Germany
- Department of Biology, Humboldt University, Philippstr. 13, 10115, Berlin, Germany
| | - Sander Granneman
- Centre for Systems and Synthetic Biology (SynthSys), University of Edinburgh, Max Born Crescent, Edinburgh, EH9 3BF, UK
| | - Matthias Selbach
- Max-Delbrück-Center for Molecular Medicine, Robert-Rössle-Str. 10, 13125, Berlin, Germany
| | - Benedikt M Beckmann
- IRI Life Sciences, Humboldt University, Philippstr. 13, 10115, Berlin, Germany.
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9
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Crosstalk between NF-κB and Nucleoli in the Regulation of Cellular Homeostasis. Cells 2018; 7:cells7100157. [PMID: 30301139 PMCID: PMC6210184 DOI: 10.3390/cells7100157] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2018] [Revised: 09/28/2018] [Accepted: 10/03/2018] [Indexed: 12/30/2022] Open
Abstract
Nucleoli are emerging as key sensors of cellular stress and regulators of the downstream consequences on proliferation, metabolism, senescence, and apoptosis. NF-κB signalling is activated in response to a similar plethora of stresses, which leads to modulation of cell growth and death programs. While nucleolar and NF-κB pathways are distinct, it is increasingly apparent that they converge at multiple levels. Exposure of cells to certain insults causes a specific type of nucleolar stress that is characterised by degradation of the PolI complex component, TIF-IA, and increased nucleolar size. Recent studies have shown that this atypical nucleolar stress lies upstream of cytosolic IκB degradation and NF-κB nuclear translocation. Under these stress conditions, the RelA component of NF-κB accumulates within functionally altered nucleoli to trigger a nucleophosmin dependent, apoptotic pathway. In this review, we will discuss these points of crosstalk and their relevance to anti-tumour mechanism of aspirin and small molecule CDK4 inhibitors. We will also briefly the discuss how crosstalk between nucleoli and NF-κB signalling may be more broadly relevant to the regulation of cellular homeostasis and how it may be exploited for therapeutic purpose.
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10
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Montacié C, Durut N, Opsomer A, Palm D, Comella P, Picart C, Carpentier MC, Pontvianne F, Carapito C, Schleiff E, Sáez-Vásquez J. Nucleolar Proteome Analysis and Proteasomal Activity Assays Reveal a Link between Nucleolus and 26S Proteasome in A. thaliana. FRONTIERS IN PLANT SCIENCE 2017; 8:1815. [PMID: 29104584 PMCID: PMC5655116 DOI: 10.3389/fpls.2017.01815] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/30/2017] [Accepted: 10/06/2017] [Indexed: 05/23/2023]
Abstract
In all eukaryotic cells, the nucleolus is functionally and structurally linked to rRNA synthesis and ribosome biogenesis. This compartment contains as well factors involved in other cellular activities, but the functional interconnection between non-ribosomal activities and the nucleolus (structure and function) still remains an open question. Here, we report a novel mass spectrometry analysis of isolated nucleoli from Arabidopsis thaliana plants using the FANoS (Fluorescence Assisted Nucleolus Sorting) strategy. We identified many ribosome biogenesis factors (RBF) and proteins non-related with ribosome biogenesis, in agreement with the recognized multi-functionality of the nucleolus. Interestingly, we found that 26S proteasome subunits localize in the nucleolus and demonstrated that proteasome activity and nucleolus organization are intimately linked to each other. Proteasome subunits form discrete foci in the disorganized nucleolus of nuc1.2 plants. Nuc1.2 protein extracts display reduced proteasome activity in vitro compared to WT protein extracts. Remarkably, proteasome activity in nuc1.2 is similar to proteasome activity in WT plants treated with proteasome inhibitors (MG132 or ALLN). Finally, we show that MG132 treatment induces disruption of nucleolar structures in WT but not in nuc1.2 plants. Altogether, our data suggest a functional interconnection between nucleolus structure and proteasome activity.
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Affiliation(s)
- Charlotte Montacié
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Nathalie Durut
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Alison Opsomer
- Laboratoire de Spectrométrie de Masse BioOrganique, Institut Pluridisciplinaire Hubert Curien, UMR7178 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Denise Palm
- Institute for Molecular Biosciences, Cluster of Excellence Macromolecular Complexes, Buchman Institute for Molecular Life Sciences, Goethe University Frankfurt, Frankfurt, Germany
| | - Pascale Comella
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Claire Picart
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Marie-Christine Carpentier
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Frederic Pontvianne
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
| | - Christine Carapito
- Laboratoire de Spectrométrie de Masse BioOrganique, Institut Pluridisciplinaire Hubert Curien, UMR7178 Centre National de la Recherche Scientifique, Université de Strasbourg, Strasbourg, France
| | - Enrico Schleiff
- Institute for Molecular Biosciences, Cluster of Excellence Macromolecular Complexes, Buchman Institute for Molecular Life Sciences, Goethe University Frankfurt, Frankfurt, Germany
| | - Julio Sáez-Vásquez
- Laboratoire Génome et Développement des Plantes, Centre National de la Recherche Scientifique, UMR 5096, Perpignan, France
- Laboratoire Génome et Développement des Plantes, University of Perpignan Via Domitia, UMR 5096, Perpignan, France
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11
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Natisvili T, Yandim C, Silva R, Emanuelli G, Krueger F, Nageshwaran S, Festenstein R. Transcriptional Activation of Pericentromeric Satellite Repeats and Disruption of Centromeric Clustering upon Proteasome Inhibition. PLoS One 2016; 11:e0165873. [PMID: 27806100 PMCID: PMC5091837 DOI: 10.1371/journal.pone.0165873] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/17/2016] [Accepted: 10/19/2016] [Indexed: 12/27/2022] Open
Abstract
Heterochromatinisation of pericentromeres, which in mice consist of arrays of major satellite repeats, are important for centromere formation and maintenance of genome stability. The dysregulation of this process has been linked to genomic stress and various cancers. Here we show in mice that the proteasome binds to major satellite repeats and proteasome inhibition by MG132 results in their transcriptional de-repression; this de-repression is independent of cell-cycle perturbation. The transcriptional activation of major satellite repeats upon proteasome inhibition is accompanied by delocalisation of heterochromatin protein 1 alpha (HP1α) from chromocentres, without detectable change in the levels of histone H3K9me3, H3K4me3, H3K36me3 and H3 acetylation on the major satellite repeats. Moreover, inhibition of the proteasome was found to increase the number of chromocentres per cell, reflecting destabilisation of the chromocentre structures. Our findings suggest that the proteasome plays a role in maintaining heterochromatin integrity of pericentromeres.
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Affiliation(s)
- Theona Natisvili
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
| | - Cihangir Yandim
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
| | - Raquel Silva
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
| | - Giulia Emanuelli
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
| | - Felix Krueger
- Bioinformatics Group, Babraham Institute, Cambridge, United Kingdom
| | - Sathiji Nageshwaran
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
| | - Richard Festenstein
- Gene Control Mechanisms and Disease Group, Department of Medicine, Division of Brain Sciences and MRC Clinical Sciences Centre, Imperial College London, Hammersmith Hospital, London, United Kingdom
- * E-mail:
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12
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Jin R, Zhou W. TIF-IA: An oncogenic target of pre-ribosomal RNA synthesis. Biochim Biophys Acta Rev Cancer 2016; 1866:189-196. [PMID: 27641688 DOI: 10.1016/j.bbcan.2016.09.003] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/2016] [Revised: 09/13/2016] [Accepted: 09/14/2016] [Indexed: 12/30/2022]
Abstract
Cancer cells devote the majority of their energy consumption to ribosome biogenesis, and pre-ribosomal RNA transcription accounts for 30-50% of all transcriptional activity. This aberrantly elevated biological activity is an attractive target for cancer therapeutic intervention if approaches can be developed to circumvent the development of side effects in normal cells. TIF-IA is a transcription factor that connects RNA polymerase I with the UBF/SL-1 complex to initiate the transcription of pre-ribosomal RNA. Its function is conserved in eukaryotes from yeast to mammals, and its activity is promoted by the phosphorylation of various oncogenic kinases in cancer cells. The depletion of TIF-IA induces cell death in lung cancer cells and mouse embryonic fibroblasts but not in several other normal tissue types evaluated in knock-out studies. Furthermore, the nuclear accumulation of TIF-IA under UTP down-regulated conditions requires the activity of LKB1 kinase, and LKB1-inactivated cancer cells are susceptible to cell death under such stress conditions. Therefore, TIF-IA may be a unique target to suppress ribosome biogenesis without significantly impacting the survival of normal tissues.
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Affiliation(s)
- Rui Jin
- Department of Hematology and Medical Oncology, The Winship Cancer Institute of Emory University, Atlanta, GA 30322, USA
| | - Wei Zhou
- Department of Hematology and Medical Oncology, The Winship Cancer Institute of Emory University, Atlanta, GA 30322, USA; Department of Pathology and Laboratory Medicine and Department of Human Genetics, Emory University School of Medicine, Atlanta, GA, USA.
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13
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Regulation of energy homeostasis by the ubiquitin-independent REGγ proteasome. Nat Commun 2016; 7:12497. [PMID: 27511885 PMCID: PMC4987533 DOI: 10.1038/ncomms12497] [Citation(s) in RCA: 52] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2016] [Accepted: 07/07/2016] [Indexed: 12/30/2022] Open
Abstract
Maintenance of energy homeostasis is essential for cell survival. Here, we report that the ATP- and ubiquitin-independent REGγ-proteasome system plays a role in maintaining energy homeostasis and cell survival during energy starvation via repressing rDNA transcription, a major intracellular energy-consuming process. Mechanistically, REGγ-proteasome limits cellular rDNA transcription and energy consumption by targeting the rDNA transcription activator SirT7 for ubiquitin-independent degradation under normal conditions. Moreover, energy starvation induces an AMPK-directed SirT7 phosphorylation and subsequent REGγ-dependent SirT7 subcellular redistribution and degradation, thereby further reducing rDNA transcription to save energy to overcome cell death. Energy starvation is a promising strategy for cancer therapy. Our report also shows that REGγ knockdown markedly improves the anti-tumour activity of energy metabolism inhibitors in mice. Our results underscore a control mechanism for an ubiquitin-independent process in maintaining energy homeostasis and cell viability under starvation conditions, suggesting that REGγ-proteasome inhibition has a potential to provide tumour-starving benefits. In conditions of energy stress cells reduce transcription of ribosomal RNA (rRNA) to maintain cell survival. Here, the authors show that energy stress induces an AMPK-dependent phosphorylation of Sirt7, which promotes its ubiquitin-independent degradation by REGγ, resulting in the down-regulation of rRNA transcription and cell survival.
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14
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Badertscher L, Wild T, Montellese C, Alexander L, Bammert L, Sarazova M, Stebler M, Csucs G, Mayer T, Zamboni N, Zemp I, Horvath P, Kutay U. Genome-wide RNAi Screening Identifies Protein Modules Required for 40S Subunit Synthesis in Human Cells. Cell Rep 2015; 13:2879-91. [DOI: 10.1016/j.celrep.2015.11.061] [Citation(s) in RCA: 61] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2015] [Revised: 10/11/2015] [Accepted: 11/18/2015] [Indexed: 02/08/2023] Open
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15
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Laribee RN, Hosni-Ahmed A, Workman JJ, Chen H. Ccr4-not regulates RNA polymerase I transcription and couples nutrient signaling to the control of ribosomal RNA biogenesis. PLoS Genet 2015; 11:e1005113. [PMID: 25815716 PMCID: PMC4376722 DOI: 10.1371/journal.pgen.1005113] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2014] [Accepted: 03/02/2015] [Indexed: 11/19/2022] Open
Abstract
Ribosomal RNA synthesis is controlled by nutrient signaling through the mechanistic target of rapamycin complex 1 (mTORC1) pathway. mTORC1 regulates ribosomal RNA expression by affecting RNA Polymerase I (Pol I)-dependent transcription of the ribosomal DNA (rDNA) but the mechanisms involved remain obscure. This study provides evidence that the Ccr4-Not complex, which regulates RNA Polymerase II (Pol II) transcription, also functions downstream of mTORC1 to control Pol I activity. Ccr4-Not localizes to the rDNA and physically associates with the Pol I holoenzyme while Ccr4-Not disruption perturbs rDNA binding of multiple Pol I transcriptional regulators including core factor, the high mobility group protein Hmo1, and the SSU processome. Under nutrient rich conditions, Ccr4-Not suppresses Pol I initiation by regulating interactions with the essential transcription factor Rrn3. Additionally, Ccr4-Not disruption prevents reduced Pol I transcription when mTORC1 is inhibited suggesting Ccr4-Not bridges mTORC1 signaling with Pol I regulation. Analysis of the non-essential Pol I subunits demonstrated that the A34.5 subunit promotes, while the A12.2 and A14 subunits repress, Ccr4-Not interactions with Pol I. Furthermore, ccr4Δ is synthetically sick when paired with rpa12Δ and the double mutant has enhanced sensitivity to transcription elongation inhibition suggesting that Ccr4-Not functions to promote Pol I elongation. Intriguingly, while low concentrations of mTORC1 inhibitors completely inhibit growth of ccr4Δ, a ccr4Δ rpa12Δ rescues this growth defect suggesting that the sensitivity of Ccr4-Not mutants to mTORC1 inhibition is at least partially due to Pol I deregulation. Collectively, these data demonstrate a novel role for Ccr4-Not in Pol I transcriptional regulation that is required for bridging mTORC1 signaling to ribosomal RNA synthesis. All cells communicate their environmental nutrient status to the gene expression machinery so that transcription occurs in proportion to the nutrients available to support cell growth and proliferation. mTORC1 signaling, which is essential for this process, regulates Pol I-dependent rRNA expression. We provide evidence that the RNA polymerase II regulatory complex, Ccr4-Not, also is a novel Pol I regulator required for mTORC1-dependent control of Pol I activity. Ccr4-Not disruption increases Pol I transcription due to an inability to decrease Pol I interactions with the transcription factor Rrn3 when mTORC1 signaling is reduced. Additionally, genetic and biochemical evidence supports a role for Ccr4-Not as a positive regulator of Pol I transcription elongation as well. Surprisingly, while Ccr4-Not mutations profoundly inhibit growth when mTORC1 activity is reduced, this phenotype is reversed by simultaneously impairing Pol I transcription. Overall, our data demonstrate that the evolutionarily conserved Ccr4-Not complex mediates environmental signaling through mTORC1 to control Pol I transcription initiation and, additionally, to regulate Pol I elongation. These studies further suggest that uncoupling Pol I from upstream mTORC1 activity by targeting Ccr4-Not sensitizes cells to mTORC1 inhibitors which is a concept that could have implications for anti-cancer drug development.
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Affiliation(s)
- R. Nicholas Laribee
- University of Tennessee Health Science Center Department of Pathology and Laboratory Medicine and the UT Center for Cancer Research, Memphis, Tennessee, United States of America
- * E-mail:
| | - Amira Hosni-Ahmed
- University of Tennessee Health Science Center Department of Pathology and Laboratory Medicine and the UT Center for Cancer Research, Memphis, Tennessee, United States of America
| | - Jason J. Workman
- University of Tennessee Health Science Center Department of Pathology and Laboratory Medicine and the UT Center for Cancer Research, Memphis, Tennessee, United States of America
| | - Hongfeng Chen
- University of Tennessee Health Science Center Department of Pathology and Laboratory Medicine and the UT Center for Cancer Research, Memphis, Tennessee, United States of America
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16
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Functions of the proteasome on chromatin. Biomolecules 2014; 4:1026-44. [PMID: 25422899 PMCID: PMC4279168 DOI: 10.3390/biom4041026] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2014] [Revised: 09/11/2014] [Accepted: 11/10/2014] [Indexed: 12/11/2022] Open
Abstract
The proteasome is a large self-compartmentalized protease complex that recognizes, unfolds, and destroys ubiquitylated substrates. Proteasome activities are required for a host of cellular functions, and it has become clear in recent years that one set of critical actions of the proteasome occur on chromatin. In this review, we discuss some of the ways in which proteasomes directly regulate the structure and function of chromatin and chromatin regulatory proteins, and how this influences gene transcription. We discuss lingering controversies in the field, the relative importance of proteolytic versus non-proteolytic proteasome activities in this process, and highlight areas that require further investigation. Our intention is to show that proteasomes are involved in major steps controlling the expression of the genetic information, that proteasomes use both proteolytic mechanisms and ATP-dependent protein remodeling to accomplish this task, and that much is yet to be learned about the full spectrum of ways that proteasomes influence the genome.
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17
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Akt activation enhances ribosomal RNA synthesis through casein kinase II and TIF-IA. Proc Natl Acad Sci U S A 2013; 110:20681-6. [PMID: 24297901 DOI: 10.1073/pnas.1313097110] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Transcription initiation factor I (TIF-IA) plays an essential role in regulating ribosomal RNA (rRNA) synthesis by tethering RNA polymerase I (Pol I) to the rDNA promoter. We have found that activated Akt enhances rRNA synthesis through the phosphorylation of casein kinase IIα (CK2α) on a threonine residue near its N terminus. CK2 in turn phosphorylates TIF-IA, thereby increasing rDNA transcription. Activated Akt also stabilizes TIF-IA, induces its translocation to the nucleolus, and enhances its interaction with Pol I. Treatment with AZD8055, an inhibitor of both Akt and mammalian target of rapamycin phosphorylation, but not with rapamycin, disrupts Akt-mediated TIF-IA stability, translocation, and activity. These data support a model in which activated Akt enhances rRNA synthesis both by preventing TIF-IA degradation and phosphorylating CK2α, which in turn phosphorylates TIF-IA. This model provides an explanation for the ability of activated Akt to promote cell proliferation and, potentially, transformation.
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18
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Brooks PJ. Blinded by the UV light: how the focus on transcription-coupled NER has distracted from understanding the mechanisms of Cockayne syndrome neurologic disease. DNA Repair (Amst) 2013; 12:656-71. [PMID: 23683874 PMCID: PMC4240003 DOI: 10.1016/j.dnarep.2013.04.018] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Cockayne syndrome (CS) is a devastating neurodevelopmental disorder, with growth abnormalities, progeriod features, and sun sensitivity. CS is typically considered to be a DNA repair disorder, since cells from CS patients have a defect in transcription-coupled nucleotide excision repair (TC-NER). However, cells from UV-sensitive syndrome patients also lack TC-NER, but these patients do not suffer from the neurologic and other abnormalities that CS patients do. Also, the neurologic abnormalities that affect CS patients (CS neurologic disease) are qualitatively different from those seen in NER-deficient XP patients. Therefore, the TC-NER defect explains the sun sensitive phenotype common to both CS and UVsS, but cannot explain CS neurologic disease. However, as CS neurologic disease is of much greater clinical significance than the sun sensitivity, there is a pressing need to understand its molecular basis. While there is evidence for defective repair of oxidative DNA damage and mitochondrial abnormalities in CS cells, here I propose that the defects in transcription by both RNA polymerases I and II that have been documented in CS cells provide a better explanation for many of the severe growth and neurodevelopmental defects in CS patients than defective DNA repair. The implications of these ideas for interpreting results from mouse models of CS, and for the development of treatments and therapies for CS patients are discussed.
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Affiliation(s)
- P J Brooks
- Laboratory of Neurogenetics, National Institute on Alcohol Abuse and Alcoholism, NIH, 5625 Fishers Lane, 3S-32, Bethesda, MD 20892, USA.
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19
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Abstract
Nucleoli are the sites where synthesis of rRNA and ribosomal assembly take place. Along with these "traditional" roles, the nucleolus controls cellular physiology and homeostasis. The cellular and molecular alterations associated with impaired nucleolar activity ("nucleolar stress") have just started to be systematically explored in the nervous system taking advantage of newly available animal models lacking rRNA synthesis in specific neurons. These studies showed that nucleolar function is necessary for neuronal survival and that its modality of action differs between and within cell types. Nucleolar function is also crucial in pathology as it controls mitochondrial activity and critical stress signaling pathways mimicking hallmarks of human neurodegenerative diseases. This mini-review will focus on the modes of action of nucleolar stress and discuss how the manipulation of nucleolar activity might underscore novel strategies to extend neuronal function and survival.
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Affiliation(s)
- Rosanna Parlato
- Department of Molecular Biology of the Cell I, DKFZ-ZMBH Alliance, German Cancer Research Center, Im Neuenheimer Feld, 581, 69120, Heidelberg, Germany.
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20
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Gaur K, Li J, Wang D, Dutta P, Yan SJ, Tsurumi A, Land H, Wu G, Li WX. The Birt-Hogg-Dubé tumor suppressor Folliculin negatively regulates ribosomal RNA synthesis. Hum Mol Genet 2012; 22:284-99. [PMID: 23077212 DOI: 10.1093/hmg/dds428] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Birt-Hogg-Dubé syndrome (BHD) is a human cancer disorder caused by mutations in the tumor suppressor gene Folliculin (FLCN) with unknown biological functions. Here, we show that the Drosophila homolog of FLCN, dFLCN (a.k.a. dBHD) localizes to the nucleolus and physically interacts with the 19S proteasomal ATPase, Rpt4, a nucleolar resident and known regulator of rRNA transcription. Downregulation of dFLCN resulted in an increase in nucleolar volume and upregulation of rRNA synthesis, whereas dFLCN overexpression reduced rRNA transcription and counteracted the effects of Rpt4 on rRNA production by preventing the association of Rpt4 with the rDNA locus. We further show that human FLCN exhibited evolutionarily conserved function and that Rpt4 knockdown inhibits the growth of FLCN-deficient human renal cancer cells in mouse xenografts. Our study suggests that FLCN functions as a tumor suppressor by negatively regulating rRNA synthesis.
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Affiliation(s)
- Kriti Gaur
- Department of Medicine, University of California San Diego, La Jolla, CA 92093, USA
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21
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Tsai YC, Greco TM, Boonmee A, Miteva Y, Cristea IM. Functional proteomics establishes the interaction of SIRT7 with chromatin remodeling complexes and expands its role in regulation of RNA polymerase I transcription. Mol Cell Proteomics 2012; 11:60-76. [PMID: 22586326 DOI: 10.1074/mcp.a111.015156] [Citation(s) in RCA: 135] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Among mammalian sirtuins, SIRT7 is the only enzyme residing in nucleoli where ribosomal DNA is transcribed. Recent reports established that SIRT7 associates with RNA Pol I machinery and is required for rDNA transcription. Although defined by its homology to the yeast histone deacetylase Sir2, current knowledge suggests that SIRT7 itself has little to no deacetylase activity. Because only two SIRT7 interactions have been thus far described: RNA Pol I and upstream binding factor, identification of proteins and complexes associating with SIRT7 is critical to understanding its functions. Here, we present the first characterization of SIRT7 interaction networks. We have systematically investigated protein interactions of three EGFP-tagged SIRT7 constructs: wild type, a point mutation affecting rDNA transcription, and a deletion mutant lacking the predicted coiled-coil domain. A combinatorial proteomics and bioinformatics approach was used to integrate gene ontology classifications, functional protein networks, and normalized abundances of proteins co-isolated with SIRT7. The resulting refined proteomic data set confirmed SIRT7 interactions with RNA Pol I and upstream binding factor and highlighted association with factors involved in RNA Pol I- and II-dependent transcriptional processes and several nucleolus-localized chromatin remodeling complexes. Particularly enriched were members of the B-WICH complex, such as Mybbp1a, WSTF, and SNF2h. Prominent interactions were validated by a selected reaction monitoring-like approach using metabolic labeling with stable isotopes, confocal microscopy, reciprocal immunoaffinity precipitation, and co-isolation with endogenous SIRT7. To extend the current knowledge of mechanisms involved in SIRT7-dependent regulation of rDNA transcription, we showed that small interfering RNA-mediated SIRT7 knockdown leads to reduced levels of RNA Pol I protein, but not messenger RNA, which was confirmed in diverse cell types. The down-regulation of RNA Pol I protein levels placed in the context of SIRT7 interaction networks led us to propose that SIRT7 plays a crucial role in connecting the function of chromatin remodeling complexes to RNA Pol I machinery during transcription.
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Affiliation(s)
- Yuan-Chin Tsai
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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22
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Richardson LA, Reed BJ, Charette JM, Freed EF, Fredrickson EK, Locke MN, Baserga SJ, Gardner RG. A conserved deubiquitinating enzyme controls cell growth by regulating RNA polymerase I stability. Cell Rep 2012; 2:372-85. [PMID: 22902402 DOI: 10.1016/j.celrep.2012.07.009] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2012] [Revised: 06/11/2012] [Accepted: 07/25/2012] [Indexed: 12/22/2022] Open
Abstract
Eukaryotic ribosome biogenesis requires hundreds of trans-acting factors and dozens of RNAs. Although most factors required for ribosome biogenesis have been identified, little is known about their regulation. Here, we reveal that the yeast deubiquitinating enzyme Ubp10 is localized to the nucleolus and that ubp10Δ cells have reduced pre-rRNAs, mature rRNAs, and translating ribosomes. Through proteomic analyses, we found that Ubp10 interacts with proteins that function in rRNA production and ribosome biogenesis. In particular, we discovered that the largest subunit of RNA polymerase I (RNAPI) is stabilized via Ubp10-mediated deubiquitination and that this is required in order to achieve optimal levels of ribosomes and cell growth. USP36, the human ortholog of Ubp10, complements the ubp10Δ allele for RNAPI stability, pre-rRNA processing, and cell growth in yeast, suggesting that deubiquitination of RNAPI may be conserved in eukaryotes. Our work implicates Ubp10/USP36 as a key regulator of rRNA production through control of RNAPI stability.
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23
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Abstract
Regulation of gene transcription is vitally important for the maintenance of normal cellular homeostasis. Failure to correctly regulate gene expression, or to deal with problems that arise during the transcription process, can lead to cellular catastrophe and disease. One of the ways cells cope with the challenges of transcription is by making extensive use of the proteolytic and nonproteolytic activities of the ubiquitin-proteasome system (UPS). Here, we review recent evidence showing deep mechanistic connections between the transcription and ubiquitin-proteasome systems. Our goal is to leave the reader with a sense that just about every step in transcription-from transcription initiation through to export of mRNA from the nucleus-is influenced by the UPS and that all major arms of the system--from the first step in ubiquitin (Ub) conjugation through to the proteasome-are recruited into transcriptional processes to provide regulation, directionality, and deconstructive power.
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Affiliation(s)
- Fuqiang Geng
- Department of Cell and Developmental Biology, Vanderbilt University School of Medicine, Nashville, Tennessee 37232-8240, USA.
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24
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Tsai YC, Greco TM, Boonmee A, Miteva Y, Cristea IM. Functional proteomics establishes the interaction of SIRT7 with chromatin remodeling complexes and expands its role in regulation of RNA polymerase I transcription. Mol Cell Proteomics 2011; 11:M111.015156. [PMID: 22147730 DOI: 10.1074/mcp.m111.015156] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Among mammalian sirtuins, SIRT7 is the only enzyme residing in nucleoli where ribosomal DNA is transcribed. Recent reports established that SIRT7 associates with RNA Pol I machinery and is required for rDNA transcription. Although defined by its homology to the yeast histone deacetylase Sir2, current knowledge suggests that SIRT7 itself has little to no deacetylase activity. Because only two SIRT7 interactions have been thus far described: RNA Pol I and upstream binding factor, identification of proteins and complexes associating with SIRT7 is critical to understanding its functions. Here, we present the first characterization of SIRT7 interaction networks. We have systematically investigated protein interactions of three EGFP-tagged SIRT7 constructs: wild type, a point mutation affecting rDNA transcription, and a deletion mutant lacking the predicted coiled-coil domain. A combinatorial proteomics and bioinformatics approach was used to integrate gene ontology classifications, functional protein networks, and normalized abundances of proteins co-isolated with SIRT7. The resulting refined proteomic data set confirmed SIRT7 interactions with RNA Pol I and upstream binding factor and highlighted association with factors involved in RNA Pol I- and II-dependent transcriptional processes and several nucleolus-localized chromatin remodeling complexes. Particularly enriched were members of the B-WICH complex, such as Mybbp1a, WSTF, and SNF2h. Prominent interactions were validated by a selected reaction monitoring-like approach using metabolic labeling with stable isotopes, confocal microscopy, reciprocal immunoaffinity precipitation, and co-isolation with endogenous SIRT7. To extend the current knowledge of mechanisms involved in SIRT7-dependent regulation of rDNA transcription, we showed that small interfering RNA-mediated SIRT7 knockdown leads to reduced levels of RNA Pol I protein, but not messenger RNA, which was confirmed in diverse cell types. The down-regulation of RNA Pol I protein levels placed in the context of SIRT7 interaction networks led us to propose that SIRT7 plays a crucial role in connecting the function of chromatin remodeling complexes to RNA Pol I machinery during transcription.
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Affiliation(s)
- Yuan-Chin Tsai
- Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA
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25
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Scharf A, Grozdanov PN, Veith R, Kubitscheck U, Meier UT, von Mikecz A. Distant positioning of proteasomal proteolysis relative to actively transcribed genes. Nucleic Acids Res 2011; 39:4612-27. [PMID: 21306993 PMCID: PMC3113580 DOI: 10.1093/nar/gkr069] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
While it is widely acknowledged that the ubiquitin–proteasome system plays an important role in transcription, little is known concerning the mechanistic basis, in particular the spatial organization of proteasome-dependent proteolysis at the transcription site. Here, we show that proteasomal activity and tetraubiquitinated proteins concentrate to nucleoplasmic microenvironments in the euchromatin. Such proteolytic domains are immobile and distinctly positioned in relation to transcriptional processes. Analysis of gene arrays and early genes in Caenorhabditis elegans embryos reveals that proteasomes and proteasomal activity are distantly located relative to transcriptionally active genes. In contrast, transcriptional inhibition generally induces local overlap of proteolytic microdomains with components of the transcription machinery and degradation of RNA polymerase II. The results establish that spatial organization of proteasomal activity differs with respect to distinct phases of the transcription cycle in at least some genes, and thus might contribute to the plasticity of gene expression in response to environmental stimuli.
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Affiliation(s)
- Andrea Scharf
- IUF - Leibniz Research Institute for Environmental Medicine at Heinrich-Heine University Duesseldorf, D-40225 Duesseldorf, Germany
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26
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Shcherbik N, Pestov DG. Ubiquitin and ubiquitin-like proteins in the nucleolus: multitasking tools for a ribosome factory. Genes Cancer 2010; 1:681-689. [PMID: 21113400 DOI: 10.1177/1947601910381382] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Synthesis of new ribosomes is an essential process upregulated during cell growth and proliferation. Here, we review our current understanding of the role that ubiquitin and ubiquitin-like proteins (UBLs) play in ribosome biogenesis, with a focus on mammalian cells. One important function of the nuclear ubiquitin-proteasome system is to control the supply of ribosomal proteins for the assembly of new ribosomal subunits in the nucleolus. Mutations in ribosomal proteins or ribosome assembly factors, stress, and many anticancer drugs have been shown to disrupt normal ribosome biogenesis, triggering a p53-dependent response. We discuss how p53 can be activated by the aberrant ribosome formation, centering on the current models of the interaction between ribosomal proteins released from the nucleolus and the ubiquitin ligase Mdm2. Recent studies also revealed multiple ubiquitin- and UBL-conjugated forms of nucleolar proteins with largely unknown functions, indicating that many new details about the role of these modifications in the nucleolus await to be discovered.
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Affiliation(s)
- Natalia Shcherbik
- Department of Cell Biology, University of Medicine and Dentistry of New Jersey, Stratford, NJ 08084
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27
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Kwak J, Workman JL, Lee D. The proteasome and its regulatory roles in gene expression. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2010; 1809:88-96. [PMID: 20723625 DOI: 10.1016/j.bbagrm.2010.08.001] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/20/2009] [Revised: 07/30/2010] [Accepted: 08/07/2010] [Indexed: 12/21/2022]
Abstract
Cumulative evidence indicates that the proteasome, which is mainly known as a protein-degrading machine, is very essential for gene expression. Destructive functions of the proteasome, i.e., ubiquitin-dependent proteolytic activity, are significant for activator localization, activator destruction, co-activator/repressor destruction and PIC disassembly. Non-proteolytic functions of the proteasome are important for recruitment of activators and co-activators to promoters, ubiquitin-dependent histone modification, transcription elongation and possibly maturation of mRNA via the facilitation of mRNA export from the nucleus to the cytoplasm. In this review, we discuss how the proteasome regulates transcription at numerous stages during gene expression. This article is part of a Special Issue entitled The 26S Proteasome: When degradation is just not enough!
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Affiliation(s)
- Jaechan Kwak
- Department of Biological Sciences, KAIST, Yuseong-Gu, Daejeon, 305-701, Korea
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28
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Philippi A, Steinbauer R, Reiter A, Fath S, Leger-Silvestre I, Milkereit P, Griesenbeck J, Tschochner H. TOR-dependent reduction in the expression level of Rrn3p lowers the activity of the yeast RNA Pol I machinery, but does not account for the strong inhibition of rRNA production. Nucleic Acids Res 2010; 38:5315-26. [PMID: 20421203 PMCID: PMC2938223 DOI: 10.1093/nar/gkq264] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Ribosome biogenesis is tightly linked to cellular growth. A crucial step in the regulation of ribosomal RNA (rRNA) gene transcription is the formation of the complex between RNA polymerase I (Pol I) and the Pol I-dependent transcription factor Rrn3p. We found that TOR inactivation leads to proteasome-dependent degradation of Rrn3p and a strong reduction in initiation competent Pol I-Rrn3p complexes affecting yeast rRNA gene transcription. Using a mutant expressing non-degradable Rrn3p or a strain in which defined endogenous Rrn3p levels can be adjusted by the Tet-off system, we can demonstrate that Rrn3p levels influence the number of Pol I-Rrn3p complexes and consequently rRNA gene transcription. However, our analysis reveals that the dramatic reduction of rRNA synthesis in the immediate cellular response to impaired TOR signalling cannot be explained by the simple down-regulation of Rrn3p and Pol I-Rrn3p levels.
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Affiliation(s)
- Anja Philippi
- Institut für Biochemie, Genetik und Mikrobiologie, Universität Regensburg, Universitätsstr. 31, 93053 Regensburg, Germany
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