1
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Gala HP, Saha D, Venugopal N, Aloysius A, Purohit G, Dhawan J. A transcriptionally repressed quiescence program is associated with paused RNAPII and is poised for cell cycle reentry. J Cell Sci 2022; 135:275901. [PMID: 35781573 DOI: 10.1242/jcs.259789] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2022] [Accepted: 06/27/2022] [Indexed: 11/20/2022] Open
Abstract
Adult stem cells persist in mammalian tissues by entering a state of reversible quiescence/ G0, associated with low transcription. Using cultured myoblasts and muscle stem cells, we report that in G0, global RNA content and synthesis are substantially repressed, correlating with decreased RNA Polymerase II (RNAPII) expression and activation. Integrating RNAPII occupancy and transcriptome profiling, we identify repressed networks and a role for promoter-proximal RNAPII pausing in G0. Strikingly, RNAPII shows enhanced pausing in G0 on repressed genes encoding regulators of RNA biogenesis (Nucleolin, Rps24, Ctdp1); release of pausing is associated with their increased expression in G1. Knockdown of these transcripts in proliferating cells leads to induction of G0 markers, confirming the importance of their repression in establishment of G0. A targeted screen of RNAPII regulators revealed that knockdown of Aff4 (positive regulator of elongation) unexpectedly enhances expression of G0-stalled genes and hastens S phase; NELF, a regulator of pausing appears to be dispensable. We propose that RNAPII pausing contributes to transcriptional control of a subset of G0-repressed genes to maintain quiescence and impacts the timing of the G0-G1 transition.
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Affiliation(s)
- Hardik P Gala
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India.,Institute for Stem Cell Science and Regenerative Medicine, Bangalore, 560065, India
| | - Debarya Saha
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India
| | - Nisha Venugopal
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India.,Institute for Stem Cell Science and Regenerative Medicine, Bangalore, 560065, India
| | - Ajoy Aloysius
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India.,Institute for Stem Cell Science and Regenerative Medicine, Bangalore, 560065, India.,National Center for Biological Sciences, Bangalore, 560065, India
| | - Gunjan Purohit
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India
| | - Jyotsna Dhawan
- Centre for Cellular and Molecular Biology, Hyderabad, 500007, India.,Institute for Stem Cell Science and Regenerative Medicine, Bangalore, 560065, India
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2
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The Mammalian and Yeast A49 and A34 Heterodimers: Homologous but Not the Same. Genes (Basel) 2021; 12:genes12050620. [PMID: 33921963 PMCID: PMC8143541 DOI: 10.3390/genes12050620] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2021] [Revised: 04/16/2021] [Accepted: 04/20/2021] [Indexed: 11/25/2022] Open
Abstract
Ribosomal RNA synthesis is the rate-limiting step in ribosome biogenesis. In eukaryotes, RNA polymerase I (Pol I) is responsible for transcribing the ribosomal DNA genes that reside in the nucleolus. Aberrations in Pol I activity have been linked to the development of multiple cancers and other genetic diseases. Therefore, it is key that we understand the mechanisms of Pol I transcription. Recent studies have demonstrated that there are many differences between Pol I transcription in yeast and mammals. Our goal is to highlight the similarities and differences between the polymerase-associated factors (PAFs) in yeast and mammalian cells. We focus on the PAF heterodimer A49/34 in yeast and PAF53/49 in mammals. Recent studies have demonstrated that while the structures between the yeast and mammalian orthologs are very similar, they may function differently during Pol I transcription, and their patterns of regulation are different.
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3
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Jung S, von Thülen T, Yang I, Laukemper V, Rupf B, Janga H, Panagiotidis GD, Schoen A, Nicolai M, Schulte LN, Obermann HL, Weber F, Kaufmann A, Bauer S. A ribosomal RNA fragment with 2',3'-cyclic phosphate and GTP-binding activity acts as RIG-I ligand. Nucleic Acids Res 2020; 48:10397-10412. [PMID: 32946572 PMCID: PMC7544222 DOI: 10.1093/nar/gkaa739] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2019] [Revised: 08/19/2020] [Accepted: 08/26/2020] [Indexed: 12/13/2022] Open
Abstract
The RNA helicase RIG-I plays a key role in sensing pathogen-derived RNA. Double-stranded RNA structures bearing 5'-tri- or diphosphates are commonly referred to as activating RIG-I ligands. However, endogenous RNA fragments generated during viral infection via RNase L also activate RIG-I. Of note, RNase-digested RNA fragments bear a 5'-hydroxyl group and a 2',3'-cyclic phosphate. How endogenous RNA fragments activate RIG-I despite the lack of 5'-phosphorylation has not been elucidated. Here we describe an endogenous RIG-I ligand (eRL) that is derived from the internal transcribed spacer 2 region (ITS2) of the 45S ribosomal RNA after partial RNase A digestion in vitro, RNase A protein transfection or RNase L activation. The immunostimulatory property of the eRL is dependent on 2',3'-cyclic phosphate and its sequence is characterized by a G-quadruplex containing sequence motif mediating guanosine-5'-triphosphate (GTP) binding. In summary, RNase generated self-RNA fragments with 2',3'-cyclic phosphate function as nucleotide-5'-triphosphate binding aptamers activating RIG-I.
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Affiliation(s)
- Stephanie Jung
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Tina von Thülen
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Ines Yang
- Institut für Medizinische Mikrobiologie und Krankenhaushygiene, Medizinische Hochschule Hannover, Carl Neuberg Straße 1, 30625 Hannover, Germany
| | - Viktoria Laukemper
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Benjamin Rupf
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Harshavardhan Janga
- Institut für Lungenforschung/iLung, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Georgios-Dimitrios Panagiotidis
- Institut für Virologie, Fachbereich Veterinärmedizin (FB10), Justus-Liebig-Universität Gießen, Schubertstr. 81, 35392 Gießen, Germany
| | - Andreas Schoen
- Institut für Virologie, Fachbereich Veterinärmedizin (FB10), Justus-Liebig-Universität Gießen, Schubertstr. 81, 35392 Gießen, Germany
| | - Marina Nicolai
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Leon N Schulte
- Institut für Lungenforschung/iLung, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
- Deutsches Zentrum für Lungenforschung (DZL), 35392 Gießen, Germany
| | - Hannah-Lena Obermann
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Friedemann Weber
- Institut für Virologie, Fachbereich Veterinärmedizin (FB10), Justus-Liebig-Universität Gießen, Schubertstr. 81, 35392 Gießen, Germany
| | - Andreas Kaufmann
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
| | - Stefan Bauer
- Institut für Immunologie, Philipps-Universität Marburg, BMFZ, Hans-Meerwein-Straße 2, 35043 Marburg, Germany
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McNamar R, Abu-Adas Z, Rothblum K, Knutson BA, Rothblum LI. Conditional depletion of the RNA polymerase I subunit PAF53 reveals that it is essential for mitosis and enables identification of functional domains. J Biol Chem 2019; 294:19907-19922. [PMID: 31727736 PMCID: PMC6937585 DOI: 10.1074/jbc.ra119.009902] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/21/2019] [Revised: 11/05/2019] [Indexed: 12/24/2022] Open
Abstract
Our knowledge of the mechanism of rDNA transcription has benefited from the combined application of genetic and biochemical techniques in yeast. Nomura's laboratory (Nogi, Y., Vu, L., and Nomura, M. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 7026-7030 and Nogi, Y., Yano, R., and Nomura, M. (1991) Proc. Natl. Acad. Sci. U.S.A. 88, 3962-3966) developed a system in yeast to identify genes essential for ribosome biogenesis. Such systems have allowed investigators to determine whether a gene was essential and to determine its function in rDNA transcription. However, there are significant differences in both the structures and components of the transcription apparatus and the patterns of regulation between mammals and yeast. Thus, there are significant deficits in our understanding of mammalian rDNA transcription. We have developed a system combining CRISPR/Cas9 and an auxin-inducible degron that enables combining a "genetics-like"approach with biochemistry to study mammalian rDNA transcription. We now show that the mammalian orthologue of yeast RPA49, PAF53, is required for rDNA transcription and mitotic growth. We have studied the domains of the protein required for activity. We have found that the C-terminal, DNA-binding domain (tandem-winged helix), the heterodimerization, and the linker domain were essential. Analysis of the linker identified a putative helix-turn-helix (HTH) DNA-binding domain. This HTH constitutes a second DNA-binding domain within PAF53. The HTH of the yeast and mammalian orthologues is essential for function. In summary, we show that an auxin-dependent degron system can be used to rapidly deplete nucleolar proteins in mammalian cells, that PAF53 is necessary for rDNA transcription and cell growth, and that all three PAF53 domains are necessary for its function.
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Affiliation(s)
- Rachel McNamar
- Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73104
| | - Zakaria Abu-Adas
- Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73104
| | - Katrina Rothblum
- Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73104
| | - Bruce A Knutson
- Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210
| | - Lawrence I Rothblum
- Department of Cell Biology, University of Oklahoma College of Medicine, Oklahoma City, Oklahoma 73104
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Gaviraghi M, Vivori C, Tonon G. How Cancer Exploits Ribosomal RNA Biogenesis: A Journey beyond the Boundaries of rRNA Transcription. Cells 2019; 8:cells8091098. [PMID: 31533350 PMCID: PMC6769540 DOI: 10.3390/cells8091098] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/27/2019] [Revised: 09/13/2019] [Accepted: 09/15/2019] [Indexed: 02/06/2023] Open
Abstract
The generation of new ribosomes is a coordinated process essential to sustain cell growth. As such, it is tightly regulated according to cell needs. As cancer cells require intense protein translation to ensure their enhanced growth rate, they exploit various mechanisms to boost ribosome biogenesis. In this review, we will summarize how oncogenes and tumor suppressors modulate the biosynthesis of the RNA component of ribosomes, starting from the description of well-characterized pathways that converge on ribosomal RNA transcription while including novel insights that reveal unexpected regulatory networks hacked by cancer cells to unleash ribosome production.
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Affiliation(s)
- Marco Gaviraghi
- Experimental Imaging Center; Ospedale San Raffaele, 20132 Milan, Italy.
- Functional Genomics of Cancer Unit, Division of Experimental Oncology, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) San Raffaele Scientific Institute, 20132 Milan, Italy.
| | - Claudia Vivori
- Centre for Genomic Regulation (CRG), The Barcelona Institute for Science and Technology, 08003 Barcelona, Spain.
| | - Giovanni Tonon
- Functional Genomics of Cancer Unit, Division of Experimental Oncology, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) San Raffaele Scientific Institute, 20132 Milan, Italy.
- Center for Translational Genomics and Bioinformatics, Istituto di Ricovero e Cura a Carattere Scientifico (IRCCS) San Raffaele Scientific Institute, 20132 Milan, Italy.
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6
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Maternally inherited rRNA triggers de novo nucleolus formation in porcine embryos. ZYGOTE 2018; 26:395-402. [PMID: 30311594 DOI: 10.1017/s0967199418000400] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
SummaryThe present study examines the role of RNA polymerase I (RPI)-mediated transcription, maternally inherited rRNA and nucleolar proteins in the resumption of fibrillogranular nucleoli during embryonic genome activation (EGA) in porcine embryos. Late 4-cell embryos were incubated in the absence (control) or presence of actinomycin D (AD) (0.2 μg/ml for inhibition of RPI; 2.0 μg/ml for inhibition of total transcription) and late 2-cell embryos were cultured to the late 4-cell stage with 0.2 μg/ml AD to block EGA. Embryos were then processed for reverse-transcriptase polymerase chain reaction (RT-PCR), and for autoradiography (ARG), transmission electron microscopy (TEM), fluorescence in situ hybridization (FISH), silver staining and immunofluorescence (for RPI). Embryos in the control group displayed extranucleolar and intranucleolar ARG labelling, and exhibited de novo synthesis of rRNA and reticulated functional nucleoli. Nucleolar proteins were located in large foci. After RPI inhibition, nucleolar precursors transformed into segregated fibrillogranular structures, however no fibrillar centres were observed. The localization of rDNA and clusters of rRNA were detected in 57.1% immunoprecipitated (IP) analyzed nucleoli and dispersed RPI; 30.5% of nuclei showed large deposits of nucleolar proteins. Embryos from the AD-2.0 group did not display any transcriptional activity. Nucleolar formation was completely blocked, however 39.4% of nuclei showed rRNA clusters; 85.7% of nuclei were co-localized with nucleolar proteins. Long-term transcriptional inhibition resulted in the lack of ARG and RPI labelling; 40% of analyzed nuclei displayed the accumulation of rRNA molecules into large foci. In conclusion, maternally inherited rRNA co-localized with rDNA and nucleolar proteins can initiate a partial nucleolar assembly, resulting in the formation of fibrilogranular structures independently on activation of RPI-mediated transcription.
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Wang M, Lemos B. Ribosomal DNA copy number amplification and loss in human cancers is linked to tumor genetic context, nucleolus activity, and proliferation. PLoS Genet 2017; 13:e1006994. [PMID: 28880866 PMCID: PMC5605086 DOI: 10.1371/journal.pgen.1006994] [Citation(s) in RCA: 77] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2017] [Revised: 09/19/2017] [Accepted: 08/21/2017] [Indexed: 12/21/2022] Open
Abstract
Ribosomal RNAs (rRNAs) are transcribed from two multicopy DNA arrays: the 5S ribosomal DNA (rDNA) array residing in a single human autosome and the 45S rDNA array residing in five human autosomes. The arrays are among the most variable segments of the genome, exhibit concerted copy number variation (cCNV), encode essential components of the ribosome, and modulate global gene expression. Here we combined whole genome data from >700 tumors and paired normal tissues to provide a portrait of rDNA variation in human tissues and cancers of diverse mutational signatures, including stomach and lung adenocarcinomas, ovarian cancers, and others of the TCGA panel. We show that cancers undergo coupled 5S rDNA array expansion and 45S rDNA loss that is accompanied by increased estimates of proliferation rate and nucleolar activity. These somatic changes in rDNA CN occur in a background of over 10-fold naturally occurring rDNA CN variation across individuals and cCNV of 5S-45S arrays in some but not all tissues. Analysis of genetic context revealed associations between cancer rDNA CN amplification or loss and the presence of specific somatic alterations, including somatic SNPs and copy number gain/losses in protein coding genes across the cancer genome. For instance, somatic inactivation of the tumor suppressor gene TP53 emerged with a strong association with coupled 5S expansion / 45S loss in several cancers. Our results uncover frequent and contrasting changes in the 5S and 45S rDNA along rapidly proliferating cell lineages with high nucleolar activity. We suggest that 5S rDNA amplification facilitates increased proliferation, nucleolar activity, and ribosomal synthesis in cancer, whereas 45S rDNA loss emerges as a byproduct of transcription-replication conflict in rapidly replicating tumor cells. The observations raise the prospects of using the rDNA arrays as re-emerging targets for the design of novel strategies in cancer therapy. The 45S and 5S ribosomal DNA (rDNA) arrays contain hundreds of rDNA copies, with substantial variability across individuals in human populations. Although physically unlinked, the arrays also exhibit joint variation across individual genotypes. However, whether this co-variation in copy number (CN) is universally observed across all tissues is unknown. It also remains unknown if rDNA CN might vary across tissues and in cancer lineages. Here we showed that most cancers undergo coupled 5S rDNA array amplification and 45S rDNA loss, and concerted 5S-45S CN variation in some but not all tissues. The coupled 5S amplification and 45S loss is associated with the presence of certain somatic genetic alterations, as well as increased estimates of cancerous cell proliferation rate and nucleolar activity. Our research uncovers frequent and contrasting changes in rDNA CN in cancers of diverse tissue origin and associated with diverse mutational contexts of tumor suppressors and oncogenes. The observations raise the prospects of using the rDNA arrays as re-emerging targets in novel strategies for cancer therapy.
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Affiliation(s)
- Meng Wang
- Department of Environmental Health & Molecular and Integrative Physiological Sciences program, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, United States of America
| | - Bernardo Lemos
- Department of Environmental Health & Molecular and Integrative Physiological Sciences program, Harvard T. H. Chan School of Public Health, Boston, Massachusetts, United States of America
- * E-mail:
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Moraleva A, Magoulas C, Polzikov M, Hacot S, Mertani HC, Diaz JJ, Zatsepina O. Involvement of the specific nucleolar protein SURF6 in regulation of proliferation and ribosome biogenesis in mouse NIH/3T3 fibroblasts. Cell Cycle 2017; 16:1979-1991. [PMID: 28873013 DOI: 10.1080/15384101.2017.1371880] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
The nucleolar proteins which link cell proliferation to ribosome biogenesis are regarded to be potentially oncogenic. Here, in order to examine the involvement of an evolutionary conserved nucleolar protein SURF6/Rrp14 in proliferation and ribosome biogenesis in mammalian cells, we established stably transfected mouse NIH/3T3 fibroblasts capable of conditional overexpression of the protein. Cell proliferation was monitored in real-time, and various cell cycle parameters were quantified based on flow cytometry, Br-dU-labeling and conventional microscopy data. We show that overexpression of SURF6 accelerates cell proliferation and promotes transition through all cell cycle phases. The most prominent SURF6 pro-proliferative effects include a significant reduction of the population doubling time, from 19.8 ± 0.7 to 16.2 ± 0.5 hours (t-test, p < 0.001), and of the length of cell division cycle, from 17.6 ± 0.6 to 14.0 ± 0.4 hours (t-test, p < 0.001). The later was due to the shortening of all cell cycle phases but the length of G1 period was reduced most, from 5.7 ± 0.4 to 3.8 ± 0.3 hours, or by ∼30%, (t-test, p < 0.05). By Northern blots and qRT-PCR, we further showed that the acceleration of cell proliferation was concomitant with an accumulation of rRNA species along both ribosomal subunit maturation pathways. It is evident, therefore, that like the yeast homologue Rrp14, mammalian SURF6 is involved in various steps of rRNA processing during ribosome biogenesis. We concluded that SURF6 is a novel positive regulator of proliferation and G1/S transition in mammals, implicating that SURF6 is a potential oncogenic protein, which can be further studied as a putative target in anti-cancer therapy.
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Affiliation(s)
- Anastasiia Moraleva
- a Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences , Moscow , Russian Federation
| | - Charalambos Magoulas
- b Centre for Investigative and Diagnostic Oncology, Department of Natural Sciences, School of Science and Technology , Middlesex University , London , United Kingdom
| | - Mikhail Polzikov
- a Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences , Moscow , Russian Federation
| | - Sabine Hacot
- c Centre de Recherche en Cancérologie de Lyon, UMR INSERM 1052-CNRS 5286, Centre Léon Bérard , Université Claude Bernard Lyon I, Université de Lyon , Lyon , France
| | - Hichem C Mertani
- c Centre de Recherche en Cancérologie de Lyon, UMR INSERM 1052-CNRS 5286, Centre Léon Bérard , Université Claude Bernard Lyon I, Université de Lyon , Lyon , France
| | - Jean-Jacques Diaz
- c Centre de Recherche en Cancérologie de Lyon, UMR INSERM 1052-CNRS 5286, Centre Léon Bérard , Université Claude Bernard Lyon I, Université de Lyon , Lyon , France
| | - Olga Zatsepina
- a Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Sciences , Moscow , Russian Federation.,c Centre de Recherche en Cancérologie de Lyon, UMR INSERM 1052-CNRS 5286, Centre Léon Bérard , Université Claude Bernard Lyon I, Université de Lyon , Lyon , France
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9
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Cell cycle and growth stimuli regulate different steps of RNA polymerase I transcription. Gene 2016; 612:36-48. [PMID: 27989772 DOI: 10.1016/j.gene.2016.12.015] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2016] [Revised: 12/09/2016] [Accepted: 12/14/2016] [Indexed: 12/20/2022]
Abstract
Transcription of the ribosomal RNA genes (rDNA) by RNA polymerase I (Pol I) is a major control step for ribosome synthesis and is tightly linked to cellular growth. However, the question of whether this process is modulated primarily at the level of transcription initiation or elongation is controversial. Studies in markedly different cell types have identified either initiation or elongation as the major control point. In this study, we have re-examined this question in NIH3T3 fibroblasts using a combination of metabolic labeling of the 47S rRNA, chromatin immunoprecipitation analysis of Pol I and overexpression of the transcription initiation factor Rrn3. Acute manipulation of growth factor levels altered rRNA synthesis rates over 8-fold without changing Pol I loading onto the rDNA. In fact, robust changes in Pol I loading were only observed under conditions where inhibition of rDNA transcription was associated with chronic serum starvation or cell cycle arrest. Overexpression of the transcription initiation factor Rrn3 increased loading of Pol I on the rDNA but failed to enhance rRNA synthesis in either serum starved, serum treated or G0/G1 arrested cells. Together these data suggest that transcription elongation is rate limiting for rRNA synthesis. We propose that transcription initiation is required for rDNA transcription in response to cell cycle cues, whereas elongation controls the dynamic range of rRNA synthesis output in response to acute growth factor modulation.
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Nguyen LXT, Raval A, Garcia JS, Mitchell BS. Regulation of Ribosomal Gene Expression in Cancer. J Cell Physiol 2015; 230:1181-8. [DOI: 10.1002/jcp.24854] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/09/2014] [Accepted: 10/16/2014] [Indexed: 12/20/2022]
Affiliation(s)
- Le Xuan Truong Nguyen
- Departments of Medicine and Chemical and Systems Biology; Stanford Cancer Institute; Stanford University School of Medicine; Stanford California
| | - Aparna Raval
- Departments of Medicine and Chemical and Systems Biology; Stanford Cancer Institute; Stanford University School of Medicine; Stanford California
| | - Jacqueline S. Garcia
- Departments of Medicine and Chemical and Systems Biology; Stanford Cancer Institute; Stanford University School of Medicine; Stanford California
| | - Beverly S. Mitchell
- Departments of Medicine and Chemical and Systems Biology; Stanford Cancer Institute; Stanford University School of Medicine; Stanford California
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11
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Woods SJ, Hannan KM, Pearson RB, Hannan RD. The nucleolus as a fundamental regulator of the p53 response and a new target for cancer therapy. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2014; 1849:821-9. [PMID: 25464032 DOI: 10.1016/j.bbagrm.2014.10.007] [Citation(s) in RCA: 98] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2014] [Revised: 10/30/2014] [Accepted: 10/31/2014] [Indexed: 01/10/2023]
Abstract
BACKGROUND Recent studies have highlighted the fundamental role that key oncogenes such as MYC, RAS and PI3K occupy in driving RNA Polymerase I transcription in the nucleolus. In addition to maintaining essential levels of protein synthesis, hyperactivated ribosome biogenesis and nucleolar function plays a central role in suppressing p53 activation in response to oncogenic stress. Consequently, disruption of ribosome biogenesis by agents such as the small molecule inhibitor of RNA Polymerase I transcription, CX-5461, has shown unexpected, potent, and selective effects in killing tumour cells via disruption of nucleolar function leading to activation of p53, independent of DNA damage. SCOPE OF REVIEW This review will explore the mechanism of DNA damage-independent activation of p53 via the nucleolar surveillance pathway and how this can be utilised to design novel cancer therapies. MAJOR CONCLUSION AND GENERAL SIGNIFICANCE Non-genotoxic targeting of nucleolar function may provide a new paradigm for treatment of a broad range of oncogene-driven malignancies with improved therapeutic windows. This article is part of a Special Issue entitled: Translation and Cancer.
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Affiliation(s)
- Simone J Woods
- Division of Research, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia
| | - Katherine M Hannan
- Division of Research, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3052, Australia
| | - Richard B Pearson
- Division of Research, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3052, Australia; Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3052, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3168, Australia.
| | - Ross D Hannan
- Division of Research, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, Australia; Sir Peter MacCallum Department of Oncology, University of Melbourne, Parkville, Victoria 3052, Australia; Department of Biochemistry and Molecular Biology, University of Melbourne, Parkville, Victoria 3052, Australia; Department of Biochemistry and Molecular Biology, Monash University, Clayton, Victoria 3168, Australia; School of Biomedical Sciences, University of Queensland, Queensland 4072, Australia.
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12
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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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13
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Hein N, Hannan KM, George AJ, Sanij E, Hannan RD. The nucleolus: an emerging target for cancer therapy. Trends Mol Med 2013; 19:643-54. [PMID: 23953479 DOI: 10.1016/j.molmed.2013.07.005] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Revised: 07/10/2013] [Accepted: 07/15/2013] [Indexed: 02/07/2023]
Abstract
For over 100 years, pathologists have utilised an increase in size and number of nucleoli, the subnuclear site of ribosome synthesis, as a marker of aggressive tumours. Despite this, the contribution of the nucleolus and ribosomal RNA synthesis to cancer has been largely overlooked. This concept has recently changed with the demonstration that the nucleolus indirectly controls numerous other cellular functions, in particular, the cellular activity of the critical tumour suppressor protein, p53. Moreover, selective inhibition of ribosomal gene transcription in the nucleolus has been shown to be an effective therapeutic strategy to promote cancer-specific activation of p53. This article reviews the largely untapped potential of the nucleolus and ribosomal gene transcription as exciting new targets for cancer therapy.
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Affiliation(s)
- Nadine Hein
- Division of Cancer Research, Peter MacCallum Cancer Centre, East Melbourne, 3002, Victoria, Australia; Sir Peter MacCallum Department of Oncology, The University of Melbourne, Parkville, 3010, Victoria, Australia
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14
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Solodushko V, Khader HA, Fouty BW. Serum can overcome contact inhibition in confluent human pulmonary artery smooth muscle cells. PLoS One 2013; 8:e71490. [PMID: 23940764 PMCID: PMC3735496 DOI: 10.1371/journal.pone.0071490] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/15/2013] [Accepted: 07/06/2013] [Indexed: 11/18/2022] Open
Abstract
Pulmonary artery endothelial cells (PAEC) in an intact vessel are continually exposed to serum, but unless injured, do not proliferate, constrained by confluence. In contrast, pulmonary artery smooth muscle cells (PASMC) attain, and maintain, confluence in the presence of minimal serum, protected from serum's stimulatory effects except when the endothelial barrier becomes more permeable. We hypothesized therefore, that confluent PASMC may be less constrained by contact inhibition in the presence of serum than PAEC and tested this idea by exposing confluent non-transformed human PAEC and PASMC to media containing increasing concentrations of fetal bovine serum (FBS) and determining cell growth over 7 days. PAEC that had attained confluence in low serum did not proliferate even when exposed to 5% serum, the highest concentration tested. In contrast, PASMC that attained confluence in low serum did proliferate once serum levels were increased, an effect that was dose dependent. Consistent with this observation, PASMC had more BrdU incorporation and a greater percentage of cells in S phase in 5% compared to 0.2% FBS, whereas no such difference was seen in PAEC. These results suggest that confluent human PAEC are resistant to the stimulatory effects of serum, whereas confluent PASMC can proliferate when serum levels are increased, an effect mediated in part by differences in phosphoinositide 3-kinase activation. This observation may be relevant to understanding the PASMC hyperplasia observed in humans and animals with pulmonary hypertension in which changes in endothelial permeability due to hypoxia or injury expose the underlying smooth muscle to serum.
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MESH Headings
- Cell Proliferation/drug effects
- Cells, Cultured
- Contact Inhibition/drug effects
- Culture Media/pharmacology
- Endothelium, Vascular/cytology
- Endothelium, Vascular/drug effects
- Endothelium, Vascular/physiology
- Humans
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/physiology
- Myocytes, Smooth Muscle/cytology
- Myocytes, Smooth Muscle/drug effects
- Myocytes, Smooth Muscle/physiology
- Oncogene Protein v-akt/metabolism
- Pulmonary Artery/cytology
- Pulmonary Artery/drug effects
- Pulmonary Artery/physiology
- Retinoblastoma Protein/metabolism
- Serum/physiology
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Affiliation(s)
- Victor Solodushko
- Center for Lung Biology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
- Department of Pharmacology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
| | - Heba A. Khader
- Department of Pharmacology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
| | - Brian W. Fouty
- Center for Lung Biology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
- Department of Pharmacology, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
- Department of Medicine/Division of Pulmonary and Critical Care Medicine, University of South Alabama School of Medicine, Mobile, Alabama, United States of America
- * E-mail:
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15
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Lindén M, Segersten U, Runeson M, Wester K, Busch C, Pettersson U, Lind SB, Malmström PU. Tumour expression of bladder cancer-associated urinary proteins. BJU Int 2013; 112:407-15. [DOI: 10.1111/j.1464-410x.2012.11653.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Affiliation(s)
- Mårten Lindén
- Department of Surgical Sciences; Uppsala University; Uppsala; Sweden
| | - Ulrika Segersten
- Department of Surgical Sciences; Uppsala University; Uppsala; Sweden
| | - Marcus Runeson
- Department of Immunology, Genetics and Pathology; Uppsala University; Uppsala; Sweden
| | - Kenneth Wester
- Department of Immunology, Genetics and Pathology; Uppsala University; Uppsala; Sweden
| | - Christer Busch
- Department of Immunology, Genetics and Pathology; Uppsala University; Uppsala; Sweden
| | - Ulf Pettersson
- Department of Immunology, Genetics and Pathology; Uppsala University; Uppsala; Sweden
| | - Sara Bergström Lind
- Department of Immunology, Genetics and Pathology; Uppsala University; Uppsala; Sweden
| | - Per-Uno Malmström
- Department of Surgical Sciences; Uppsala University; Uppsala; Sweden
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16
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Hannan KM, Sanij E, Rothblum LI, Hannan RD, Pearson RB. Dysregulation of RNA polymerase I transcription during disease. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2012; 1829:342-60. [PMID: 23153826 DOI: 10.1016/j.bbagrm.2012.10.014] [Citation(s) in RCA: 100] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2012] [Revised: 10/30/2012] [Accepted: 10/31/2012] [Indexed: 12/13/2022]
Abstract
Transcription of the ribosomal RNA genes by the dedicated RNA polymerase I enzyme and subsequent processing of the ribosomal RNA are fundamental control steps in the synthesis of functional ribosomes. Dysregulation of Pol I transcription and ribosome biogenesis is linked to the etiology of a broad range of human diseases. Diseases caused by loss of function mutations in the molecular constituents of the ribosome, or factors intimately associated with RNA polymerase I transcription and processing are collectively termed ribosomopathies. Ribosomopathies are generally rare and treatment options are extremely limited tending to be more palliative than curative. Other more common diseases are associated with profound changes in cellular growth such as cardiac hypertrophy, atrophy or cancer. In contrast to ribosomopathies, altered RNA polymerase I transcriptional activity in these diseases largely results from dysregulated upstream oncogenic pathways or by direct modulation by oncogenes or tumor suppressors at the level of the RNA polymerase I transcription apparatus itself. Ribosomopathies associated with mutations in ribosomal proteins and ribosomal RNA processing or assembly factors have been covered by recent excellent reviews. In contrast, here we review our current knowledge of human diseases specifically associated with dysregulation of RNA polymerase I transcription and its associated regulatory apparatus, including some cases where this dysregulation is directly causative in disease. We will also provide insight into and discussion of possible therapeutic approaches to treat patients with dysregulated RNA polymerase I transcription. This article is part of a Special Issue entitled: Transcription by Odd Pols.
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Affiliation(s)
- K M Hannan
- Oncogenic Signalling and Growth Control Program, Peter MacCallum Cancer Centre, Locked Bag 1, A'Beckett St, Melbourne, Victoria 8006, Australia
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18
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Poortinga G, Wall M, Sanij E, Siwicki K, Ellul J, Brown D, Holloway TP, Hannan RD, McArthur GA. c-MYC coordinately regulates ribosomal gene chromatin remodeling and Pol I availability during granulocyte differentiation. Nucleic Acids Res 2010; 39:3267-81. [PMID: 21177653 PMCID: PMC3082905 DOI: 10.1093/nar/gkq1205] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Loss of c-MYC is required for downregulation of ribosomal RNA (rRNA) gene (rDNA) transcription by RNA Polymerase I (Pol I) during granulocyte differentiation. Here, we demonstrate a robust reduction of Pol I loading onto rDNA that along with a depletion of the MYC target gene upstream binding factor (UBF) and a switch from epigenetically active to silent rDNA accompanies this MYC reduction. We hypothesized that MYC may coordinate these mechanisms via direct regulation of multiple components of the Pol I transcription apparatus. Using gene expression arrays we identified a ‘regulon’ of Pol I factors that are both downregulated during differentiation and reinduced in differentiated granulocytes upon activation of the MYC-ER transgene. This regulon includes the novel c-MYC target genes RRN3 and POLR1B. Although enforced MYC expression during granulocyte differentiation was sufficient to increase the number of active rRNA genes, its activation in terminally differentiated cells did not alter the active to inactive gene ratio despite increased rDNA transcription. Thus, c-MYC dynamically controls rDNA transcription during granulocytic differentiation through the orchestrated transcriptional regulation of core Pol I factors and epigenetic modulation of number of active rRNA genes.
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Affiliation(s)
- Gretchen Poortinga
- Division of Research, Peter MacCallum Cancer Centre, St Andrews Place, East Melbourne, Victoria, Australia.
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19
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Grummt I. Wisely chosen paths--regulation of rRNA synthesis: delivered on 30 June 2010 at the 35th FEBS Congress in Gothenburg, Sweden. FEBS J 2010; 277:4626-39. [PMID: 20977666 DOI: 10.1111/j.1742-4658.2010.07892.x] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
All cells, from prokaryotes to vertebrates, synthesize enormous amounts of rRNA to produce 1-2 million ribosomes per cell cycle, which are required to maintain the protein synthesis capacity of the daughter cells. In recent years, considerable progress has been made in the elucidation of the basic principles of transcriptional regulation and the pathways that adapt cellular rRNA synthesis to metabolic activity, a process that is essential for understanding the link between nucleolar activity, cell growth, proliferation, and apoptosis. I will survey our present knowledge of the highly coordinated networks that regulate transcription by RNA polymerase I, coordinating rRNA gene transcription and ribosome production with environmental cues. Moreover, I will discuss the epigenetic mechanisms that control the chromatin structure and transcriptional activity of rRNA genes, in particular the role of noncoding RNA in DNA methylation and transcriptional silencing.
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Affiliation(s)
- Ingrid Grummt
- Division of Molecular Biology of the Cell II, German Cancer Research Center, DKFZ-ZMBH-Alliance, Heidelberg, Germany.
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20
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Zhou G, Doçi CL, Lingen MW. Identification and functional analysis of NOL7 nuclear and nucleolar localization signals. BMC Cell Biol 2010; 11:74. [PMID: 20875127 PMCID: PMC2957388 DOI: 10.1186/1471-2121-11-74] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2010] [Accepted: 09/27/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND NOL7 is a candidate tumor suppressor that localizes to a chromosomal region 6p23. This locus is frequently lost in a number of malignancies, and consistent loss of NOL7 through loss of heterozygosity and decreased mRNA and protein expression has been observed in tumors and cell lines. Reintroduction of NOL7 into cells resulted in significant suppression of in vivo tumor growth and modulation of the angiogenic phenotype. Further, NOL7 was observed to localize to the nucleus and nucleolus of cells. However, the mechanisms regulating its subcellular localization have not been elucidated. RESULTS An in vitro import assay demonstrated that NOL7 requires cytosolic machinery for active nuclear transport. Using sequence homology and prediction algorithms, four putative nuclear localization signals (NLSs) were identified. NOL7 deletion constructs and cytoplasmic pyruvate kinase (PK) fusion proteins confirmed the functionality of three of these NLSs. Site-directed mutagenesis of PK fusions and full-length NOL7 defined the minimal functional regions within each NLS. Further characterization revealed that NLS2 and NLS3 were critical for both the rate and efficiency of nuclear targeting. In addition, four basic clusters within NLS2 and NLS3 were independently capable of nucleolar targeting. The nucleolar occupancy of NOL7 revealed a complex balance of rapid nucleoplasmic shuttling but low nucleolar mobility, suggesting NOL7 may play functional roles in both compartments. In support, targeting to the nucleolar compartment was dependent on the presence of RNA, as depletion of total RNA or rRNA resulted in a nucleoplasmic shift of NOL7. CONCLUSIONS These results identify the minimal sequences required for the active targeting of NOL7 to the nucleus and nucleolus. Further, this work characterizes the relative contribution of each sequence to NOL7 nuclear and nucleolar dynamics, the subnuclear constituents that participate in this targeting, and suggests a functional role for NOL7 in both compartments. Taken together, these results identify the requisite protein domains for NOL7 localization, the kinetics that drive this targeting, and suggest NOL7 may function in both the nucleus and nucleolus.
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Affiliation(s)
- Guolin Zhou
- Department of Pathology, The University of Chicago, Chicago, IL, USA
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21
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Abstract
Although now dogma, the idea that nonvertebrate organisms such as yeast, worms, and flies could inform, and in some cases even revolutionize, our understanding of oncogenesis in humans was not immediately obvious. Aided by the conservative nature of evolution and the persistence of a cohort of devoted researchers, the role of model organisms as a key tool in solving the cancer problem has, however, become widely accepted. In this review, we focus on the nematode Caenorhabditis elegans and its diverse and sometimes surprising contributions to our understanding of the tumorigenic process. Specifically, we discuss findings in the worm that address a well-defined set of processes known to be deregulated in cancer cells including cell cycle progression, growth factor signaling, terminal differentiation, apoptosis, the maintenance of genome stability, and developmental mechanisms relevant to invasion and metastasis.
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Affiliation(s)
- Natalia V. Kirienko
- University of Wyoming, College of Agriculture, Department of Molecular Biology, Dept 3944, 1000 E. University Avenue, Laramie, WY 82071
| | - Kumaran Mani
- University of Wyoming, College of Agriculture, Department of Molecular Biology, Dept 3944, 1000 E. University Avenue, Laramie, WY 82071
| | - David S. Fay
- University of Wyoming, College of Agriculture, Department of Molecular Biology, Dept 3944, 1000 E. University Avenue, Laramie, WY 82071
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22
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Drygin D, Rice WG, Grummt I. The RNA polymerase I transcription machinery: an emerging target for the treatment of cancer. Annu Rev Pharmacol Toxicol 2010; 50:131-56. [PMID: 20055700 DOI: 10.1146/annurev.pharmtox.010909.105844] [Citation(s) in RCA: 323] [Impact Index Per Article: 23.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The RNA polymerase I (Pol I) transcription machinery in the nucleolus is the key convergence point that collects and integrates a vast array of information from cellular signaling cascades to regulate ribosome production that in turn guides cell growth and proliferation. Cancer cells commonly harbor mutations that inactivate tumor suppressors, hyperactivate oncogenes, and upregulate protein kinases, all of which promote Pol I transcription and drive cell proliferation. The intimate balance between Pol I transcription and growth-factor signaling is perturbed in cancer cells, indicating that upregulation of rRNA synthesis is mandatory for all tumors. Though the emerging picture of transcriptional regulation reveals an unexpected level of complexity, we are beginning to understand the multiple links between rRNA biogenesis and cancer. In this review, we discuss experimental data and potential strategies to downregulate rRNA synthesis and induce an antiproliferative response in cancer cells.
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Affiliation(s)
- Denis Drygin
- Cylene Pharmaceuticals, San Diego, California, USA.
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23
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Abstract
PURPOSE OF REVIEW This review reports recent findings on the multiple factors that regulate skeletal muscle growth in neonates. RECENT FINDINGS Skeletal muscle is the fastest growing protein mass in neonates. The high rate of neonatal muscle growth is due to accelerated rates of protein synthesis accompanied by the rapid accumulation of muscle nuclei. Feeding profoundly stimulates muscle protein synthesis in neonates and the response decreases with age. The feeding-induced stimulation of muscle protein synthesis is modulated by enhanced sensitivity to the postprandial rise in insulin and amino acids. Insulin and amino acid signaling components have been identified that are involved in the feeding-induced stimulation of protein synthesis in neonatal muscle. The enhanced activation of these signaling components in skeletal muscle of the neonate contributes to the high rate of muscle protein synthesis and rapid gain in muscle protein mass in neonates. SUMMARY Recent findings suggest that the immature muscle has a heightened capacity to activate signaling cascades that promote translation initiation in response to the postprandial rise in insulin and amino acids thereby enabling their efficient utilization for muscle growth. This capacity is further supported by enhanced satellite cell proliferation, but how these two processes are linked remains to be established.
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Affiliation(s)
- Teresa A Davis
- USDA/ARS Children's Nutrition Research Center, Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030, USA.
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24
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RNA polymerases I and III, non-coding RNAs and cancer. Trends Genet 2008; 24:622-9. [PMID: 18980784 DOI: 10.1016/j.tig.2008.10.003] [Citation(s) in RCA: 147] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/02/2008] [Revised: 10/06/2008] [Accepted: 10/06/2008] [Indexed: 12/12/2022]
Abstract
Oncogenically transformed cells overexpress the non-coding RNAs, such as pre-ribosomal RNA (rRNA) and transfer RNA (tRNA), which are produced by RNA polymerases (Pols) I and III. Recent results indicate that levels of pre-rRNA have prognostic value and that a tRNA has oncogenic potential. Transcription by Pols I and III is restrained in healthy cells by the tumour suppressors RB, p53, ARF and PTEN. Such restraints are compromised during cell transformation and the problem is accentuated by oncogene products, such as c-Myc, that stimulate the output of Pol I and Pol III. The resultant increases in rRNA and tRNA expression might promote the generation of cancers.
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25
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Zhang S, Wang J, Tseng H. Basonuclin regulates a subset of ribosomal RNA genes in HaCaT cells. PLoS One 2007; 2:e902. [PMID: 17878937 PMCID: PMC1975673 DOI: 10.1371/journal.pone.0000902] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Accepted: 08/28/2007] [Indexed: 11/20/2022] Open
Abstract
Basonuclin (Bnc1), a cell-type-specific ribosomal RNA (rRNA) gene regulator, is expressed mainly in keratinocytes of stratified epithelium and gametogenic cells of testis and ovary. Previously, basonuclin was shown in vitro to interact with rRNA gene (rDNA) promoter at three highly conserved sites. Basonuclin's high affinity binding site overlaps with the binding site of a dedicated and ubiquitous Pol I transcription regulator, UBF, suggesting that their binding might interfere with each other if they bind to the same promoter. Knocking-down basonuclin in mouse oocytes eliminated approximately one quarter of RNA polymerase I (Pol I) transcription foci, without affecting the BrU incorporation of the remaining ones, suggesting that basonuclin might regulate a subset of rDNA. Here we show, via chromatin immunoprecipitation (ChIP), that basonuclin is associated with rDNA promoters in HaCaT cells, a spontaneously established human keratinocyte line. Immunoprecipitation data suggest that basonuclin is in a complex that also contains the subunits of Pol I (RPA194, RPA116), but not UBF. Knocking-down basonuclin in HaCaT cells partially impairs the association of RPA194 to rDNA promoter, but not that of UBF. Basonuclin-deficiency also reduces the amount of 47S pre-rRNA, but this effect can be seen only after cell-proliferation related rRNA synthesis has subsided at a higher cell density. DNA sequence of basonuclin-bound rDNA promoters shows single nucleotide polymorphisms (SNPs) that differ from those associated with UBF-bound promoters, suggesting that basonuclin and UBF interact with different subsets of promoters. In conclusion, our results demonstrate basonuclin's functional association with rDNA promoters and its interaction with Pol I in vivo. Our data also suggest that basonuclin-Pol I complex transcribes a subset of rDNA.
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Affiliation(s)
- Shengliang Zhang
- Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Junwen Wang
- Center for Bioinformatics, Department of Genetics, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Department of Computer and Information Science, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
| | - Hung Tseng
- Department of Dermatology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Cell and Developmental Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- Center for Research on Reproduction and Women's Health, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America
- * To whom correspondence should be addressed. E-mail:
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Maddox-Hyttel P, Svarcova O, Laurincik J. Ribosomal RNA and nucleolar proteins from the oocyte are to some degree used for embryonic nucleolar formation in cattle and pig. Theriogenology 2007; 68 Suppl 1:S63-70. [PMID: 17466364 DOI: 10.1016/j.theriogenology.2007.03.015] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
The nucleolus is the site of ribosomal RNA (rRNA) and ribosome production. In the bovine primordial follicle oocyte, this organelle is inactive, but in the secondary follicle an active fibrillo-granular nucleolus develops and proteins involved in rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) localize to it. At the end of the oocyte growth phase, the nucleolus is inactivated again and transforms into a solid remnant. The nucleolar remnant is dissolved when meiosis is resumed. Upon fertilization, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities are engaged in the re-establishment of fibrillo-granular nucleoli at the major activation of the embryonic genome. This nucleolar formation can be classified into two different modes: one where nucleolus development occurs inside NPBs (internal; e.g. cattle) and the other where it occurs on the surface of NPBs (external; e.g. pig). Oocyte derived proteins engaged in late rRNA processing (nucleolin and nucleophosmin) may to some degree be re-used for nucleolar formation in the embryo, while the other nucleolar proteins require de novo embryonic transcription in order to be allocated to the developing nucleoli. Moreover, unprocessed rRNA inherited from the oocyte targets to the developing embryonic nucleoli. In conclusion, the nucleolus is important for the development of oocytes and embryos and may serve as a marker for the completion of oocyte growth and the normality of activation of the embryonic genome.
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Affiliation(s)
- P Maddox-Hyttel
- Department of Animal and Veterinary Basic Sciences, Faculty of Life Sciences, University of Copenhagen, Groennegaardsvej 7, DK-1870 Frederiksberg C, Denmark.
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27
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Young DW, Hassan MQ, Pratap J, Galindo M, Zaidi SK, Lee SH, Yang X, Xie R, Javed A, Underwood JM, Furcinitti P, Imbalzano AN, Penman S, Nickerson JA, Montecino MA, Lian JB, Stein JL, van Wijnen AJ, Stein GS. Mitotic occupancy and lineage-specific transcriptional control of rRNA genes by Runx2. Nature 2007; 445:442-6. [PMID: 17251981 DOI: 10.1038/nature05473] [Citation(s) in RCA: 192] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2006] [Accepted: 11/20/2006] [Indexed: 11/09/2022]
Abstract
Regulation of ribosomal RNA genes is a fundamental process that supports the growth of cells and is tightly coupled with cell differentiation. Although rRNA transcriptional control by RNA polymerase I (Pol I) and associated factors is well studied, the lineage-specific mechanisms governing rRNA expression remain elusive. Runt-related transcription factors Runx1, Runx2 and Runx3 establish and maintain cell identity, and convey phenotypic information through successive cell divisions for regulatory events that determine cell cycle progression or exit in progeny cells. Here we establish that mammalian Runx2 not only controls lineage commitment and cell proliferation by regulating genes transcribed by RNA Pol II, but also acts as a repressor of RNA Pol I mediated rRNA synthesis. Within the condensed mitotic chromosomes we find that Runx2 is retained in large discrete foci at nucleolar organizing regions where rRNA genes reside. These Runx2 chromosomal foci are associated with open chromatin, co-localize with the RNA Pol I transcription factor UBF1, and undergo transition into nucleoli at sites of rRNA synthesis during interphase. Ribosomal RNA transcription and protein synthesis are enhanced by Runx2 deficiency that results from gene ablation or RNA interference, whereas induction of Runx2 specifically and directly represses rDNA promoter activity. Runx2 forms complexes containing the RNA Pol I transcription factors UBF1 and SL1, co-occupies the rRNA gene promoter with these factors in vivo, and affects local chromatin histone modifications at rDNA regulatory regions. Thus Runx2 is a critical mechanistic link between cell fate, proliferation and growth control. Our results suggest that lineage-specific control of ribosomal biogenesis may be a fundamental function of transcription factors that govern cell fate.
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Affiliation(s)
- Daniel W Young
- Department of Cell Biology and Cancer Center, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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28
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Bernstein KA, Bleichert F, Bean JM, Cross FR, Baserga SJ. Ribosome biogenesis is sensed at the Start cell cycle checkpoint. Mol Biol Cell 2006; 18:953-64. [PMID: 17192414 PMCID: PMC1805094 DOI: 10.1091/mbc.e06-06-0512] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
In the yeast Saccharomyces cerevisiae it has long been thought that cells must reach a critical cell size, called the "setpoint," in order to allow the Start cell cycle transition. Recent evidence suggests that this setpoint is lowered when ribosome biogenesis is slowed. Here we present evidence that yeast can sense ribosome biogenesis independently of mature ribosome levels and protein synthetic capacity. Our results suggest that ribosome biogenesis directly promotes passage through Start through Whi5, the yeast functional equivalent to the human tumor suppressor Rb. When ribosome biogenesis is inhibited, a Whi5-dependent mechanism inhibits passage through Start before significant decreases in both the number of ribosomes and in overall translation capacity of the cell become evident. This delay at Start in response to decreases in ribosome biogenesis occurs independently of Cln3, the major known Whi5 antagonist. Thus ribosome biogenesis may be sensed at multiple steps in Start regulation. Ribosome biogenesis may thus both delay Start by increasing the cell size setpoint and independently may promote Start by inactivating Whi5.
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Affiliation(s)
- Kara A Bernstein
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA
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29
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Gilkes DM, Chen L, Chen J. MDMX regulation of p53 response to ribosomal stress. EMBO J 2006; 25:5614-25. [PMID: 17110929 PMCID: PMC1679771 DOI: 10.1038/sj.emboj.7601424] [Citation(s) in RCA: 106] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/12/2006] [Accepted: 10/12/2006] [Indexed: 12/15/2022] Open
Abstract
Ribosomal stress such as disruption of rRNA biogenesis activates p53 by release of ribosomal proteins from the nucleoli, which bind to MDM2 and inhibit p53 degradation. We found that p53 activation by ribosomal stress requires degradation of MDMX in an MDM2-dependent fashion. Tumor cells overexpressing MDMX are less sensitive to actinomycin D-induced growth arrest due to formation of inactive p53-MDMX complexes. Knockdown of MDMX increases sensitivity to actinomycin D, whereas MDMX overexpression abrogates p53 activation and prevents growth arrest. Furthermore, MDMX expression promotes resistance to the chemotherapeutic agent 5-fluorouracil (5-FU), which at low concentrations activates p53 by inducing ribosomal stress without significant DNA damage signaling. Knockdown of MDMX abrogates HCT116 tumor xenograft formation in nude mice. MDMX overexpression does not accelerate tumor growth but increases resistance to 5-FU treatment in vivo. Therefore, MDMX is an important regulator of p53 response to ribosomal stress and RNA-targeting chemotherapy agents.
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Affiliation(s)
- Daniele M Gilkes
- Molecular Oncology Program, H Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA
| | - Lihong Chen
- Molecular Oncology Program, H Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA
| | - Jiandong Chen
- Molecular Oncology Program, H Lee Moffitt Cancer Center and Research Institute, Tampa, FL, USA
- Molecular Oncology Program, H Lee Moffitt Cancer Center, MRC3057A, 12902 Magnolia Drive, Tampa, FL 33612, USA. Tel.: +1 813 903 6822; Fax: +1 813 903 6817; E-mail:
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Abstract
The retinoblastoma susceptibility gene was the first tumor suppressor gene identified in humans and the first tumor suppressor gene knocked out by targeted deletion in mice. RB serves as a transducer between the cell cycle machinery and promoter-specific transcription factors, its most documented activity being the repression of the E2F family of transcription factors, which regulate the expression of genes involved in cell proliferation and survival. Recent investigations of RB function suggest that it works as a fundamental regulator to coordinate pathways of cellular growth and differentiation. In this review, we unravel the novel role of an equally important aspect of RB in downregulating the differentiation inhibitor EID-1 during cellular differentiation by teasing apart the signal, which elicit differentiation and limit cell cycle progression, since the molecular mechanisms relating to RB activation of differentiation is much less understood. We review the various roles for RB in differentiation of neurons, muscle, adipose tissue, and the retina. In addition, we provide an update for the current models of the role of RB in cell cycle to entry and exit, extending the view toward chromatin remodeling and expose the dichotomies in the regulation of RB family members. We conclude with a discussion of a novel RB regulatory network, incorporating the dynamic contribution of EID family proteins.
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Affiliation(s)
- L Khidr
- Department of Biological Chemistry, University of California-Irvine Med Sci 1, Irvine, CA 92697, USA
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Ayrault O, Andrique L, Fauvin D, Eymin B, Gazzeri S, Séité P. Human tumor suppressor p14ARF negatively regulates rRNA transcription and inhibits UBF1 transcription factor phosphorylation. Oncogene 2006; 25:7577-86. [PMID: 16924243 DOI: 10.1038/sj.onc.1209743] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
The nucleolar Arf protein has been shown to regulate cell cycle through both p53-dependent and -independent pathways. In addition to the well-characterized Arf-mdm2-p53 pathway, several partners of Arf have recently been described that could participate in alternative regulation process. Among those is the nucleolar protein B23/NPM, involved in the sequential maturation of rRNA. p19ARF can interact with B23/NPM in high molecular complexes and partially inhibit the cleavage of the 32S rRNA, whereas the human p14ARF protein has been shown to participate in the degradation of NPM/B23 by the proteasome. These data led to define Arf as a negative regulator of ribosomal RNA maturation. Our recent finding that the human p14ARF protein was able to specifically interact with the rRNA promoter in a p53-independent context, led us to analyse in vitro and in vivo the consequences of this interaction. Luciferase assay and pulse-chase experiments demonstrated that the rRNA transcription was strongly reduced upon p14ARF overexpression. Investigations on potential interactions between p14ARF and the transcription machinery proteins demonstrated that the upstream binding factor (UBF), required for the initiation of the transcriptional complex, was a new partner of the p14ARF protein. We next examined the phosphorylation status of UBF as UBF phosphorylation is required to recruit on the promoter factors involved in the transcriptional complex. Upon p14ARF overexpression, UBF was found hypophosphorylated, thus unable to efficiently recruit the transcription complex. Taken together, these data define a new p53-independent pathway that could regulate cell cycle through the negative control of rRNA transcription.
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Affiliation(s)
- O Ayrault
- Laboratoire d'Oncologie Moléculaire. EA3805, Pô le Biologie-Santé. 40, Poitiers cedex, France
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Grinstein E, Shan Y, Karawajew L, Snijders PJF, Meijer CJLM, Royer HD, Wernet P. Cell cycle-controlled interaction of nucleolin with the retinoblastoma protein and cancerous cell transformation. J Biol Chem 2006; 281:22223-22235. [PMID: 16698799 DOI: 10.1074/jbc.m513335200] [Citation(s) in RCA: 35] [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
Retinoblastoma protein (Rb) is a multifunctional tumor suppressor, frequently inactivated in certain types of human cancer. Nucleolin is an abundant multifunctional phosphoprotein of proliferating and cancerous cells, recently identified as cell cycle-regulated transcription activator, controlling expression of human papillomavirus type 18 (HPV18) oncogenes in cervical cancer. Here we find that nucleolin is associated with Rb in intact cells in the G1 phase of the cell cycle, and the complex formation is mediated by the growth-inhibitory domain of Rb. Association with Rb inhibits the DNA binding function of nucleolin and in consequence the interaction of nucleolin with the HPV18 enhancer, resulting in Rb-mediated repression of the HPV18 oncogenes. The intracellular distribution of nucleolin in epithelial cells is Rb-dependent, and an altered nucleolin localization in human cancerous tissues results from a loss of Rb. Our findings suggest that deregulated nucleolin activity due to a loss of Rb contributes to tumor development in malignant diseases, thus providing further insights into the molecular network for the Rb-mediated tumor suppression.
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Affiliation(s)
- Edgar Grinstein
- Institute of Transplantation Diagnostics and Cellular Therapeutics, Heinrich Heine University Medical Center, 40225 Düsseldorf, Germany.
| | - Ying Shan
- Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany; Institute of Molecular Pharmacology, 13125 Berlin, Germany
| | - Leonid Karawajew
- Robert-Rossle-Clinic at the HELIOS Klinikum Berlin-Buch, Charite Medical School, 13125 Berlin, Germany
| | - Peter J F Snijders
- Department of Pathology, Vrije Universiteit Medical Center, 1007 MB Amsterdam, The Netherlands
| | - Chris J L M Meijer
- Department of Pathology, Vrije Universiteit Medical Center, 1007 MB Amsterdam, The Netherlands
| | - Hans-Dieter Royer
- Max-Delbrück Center for Molecular Medicine, 13125 Berlin, Germany; Center for Advanced European Studies, 53175 Bonn, Germany
| | - Peter Wernet
- Institute of Transplantation Diagnostics and Cellular Therapeutics, Heinrich Heine University Medical Center, 40225 Düsseldorf, Germany
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Abstract
The rRNAs constitute the catalytic and structural components of the ribosome, the protein synthesis machinery of cells. The level of rRNA synthesis, mediated by Pol I (RNA polymerase I), therefore has a major impact on the life and destiny of a cell. In order to elucidate how cells achieve the stringent control of Pol I transcription, matching the supply of rRNA to demand under different cellular growth conditions, it is essential to understand the components and mechanics of the Pol I transcription machinery. In this review, we discuss: (i) the molecular composition and functions of the Pol I enzyme complex and the two main Pol I transcription factors, SL1 (selectivity factor 1) and UBF (upstream binding factor); (ii) the interplay between these factors during pre-initiation complex formation at the rDNA promoter in mammalian cells; and (iii) the cellular control of the Pol I transcription machinery.
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Ayrault O, Andrique L, Séité P. Involvement of the transcriptional factor E2F1 in the regulation of the rRNA promoter. Exp Cell Res 2006; 312:1185-93. [PMID: 16510138 DOI: 10.1016/j.yexcr.2006.01.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2005] [Revised: 01/25/2006] [Accepted: 01/27/2006] [Indexed: 01/25/2023]
Abstract
p16INK4a-pRB-E2F and ARF-MDM2-p53 are two major tumor suppressor networks involved in cell proliferation control. The nucleolar ARF protein binds to MDM2 to activate the growth suppressive functions of p53, but can also exert its tumor suppressor activity independently of p53, through mechanisms involving other regulators: in that manner, p14ARF has been shown to inhibit the transcriptional activity of E2F1 in vitro, suggesting that the two pathways intersect with one another. More recently, ARF has been shown to inhibit ribosomal RNA processing, and to specifically interact with the rRNA promoter, suggesting a role in the regulation of both maturation and transcription processes. We show here that E2F1 can bind the rRNA promoter and modulate its activity through the interaction with two E2F1-binding sequences we have identified. The regulation of ribosome biogenesis appears as a major p53-independent process, which involves both ARF and E2F1 to control cell proliferation.
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Affiliation(s)
- Olivier Ayrault
- Laboratoire d'Oncologie Moléculaire, EA 3805, Pôle Biologie-Santé, 40, avenue du Recteur Pineau, 86022 Poitiers cedex, France
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David-Pfeuty T. The flexible evolutionary anchorage-dependent Pardee's restriction point of mammalian cells: how its deregulation may lead to cancer. Biochim Biophys Acta Rev Cancer 2005; 1765:38-66. [PMID: 16219425 DOI: 10.1016/j.bbcan.2005.08.008] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2005] [Revised: 08/24/2005] [Accepted: 08/26/2005] [Indexed: 12/12/2022]
Abstract
Living cells oscillate between the two states of quiescence and division that stand poles apart in terms of energy requirements, macromolecular composition and structural organization and in which they fulfill dichotomous activities. Division is a highly dynamic and energy-consuming process that needs be carefully orchestrated to ensure the faithful transmission of the mother genotype to daughter cells. Quiescence is a low-energy state in which a cell may still have to struggle hard to maintain its homeostasis in the face of adversity while waiting sometimes for long periods before finding a propitious niche to reproduce. Thus, the perpetuation of single cells rests upon their ability to elaborate robust quiescent and dividing states. This led yeast and mammalian cells to evolve rigorous Start [L.H. Hartwell, J. Culotti, J. Pringle, B.J. Reid, Genetic control of the cell division cycle in yeast, Science 183 (1974) 46-51] and restriction (R) points [A.B. Pardee, A restriction point for control of normal animal cell proliferation, Proc. Natl. Acad. Sci. U. S. A. 71 (1974) 1286-1290], respectively, that reduce deadly interferences between the two states by enforcing their temporal insulation though still enabling a rapid transition from one to the other upon an unpredictable change in their environment. The constitutive cells of multi-celled organisms are extremely sensitive in addition to the nature of their adhering support that fluctuates depending on developmental stage and tissue specificity. Metazoan evolution has entailed, therefore, the need for exceedingly flexible anchorage-dependent R points empowered to assist cells in switching between quiescence and division at various times, places and conditions in the same organism. Programmed cell death may have evolved concurrently in specific contexts unfit for the operation of a stringent R point that increase the risk of deadly interferences between the two states (as it happens notably during development). But, because of their innate flexibility, anchorage-dependent R points have also the ability to readily adjust to a changing structural context so as to give mutated cells a chance to reproduce, thereby encouraging tumor genesis. The Rb and p53 proteins, which are regulated by the two products of the Ink4a-Arf locus [C.J. Sherr, The INK4a/ARF network in tumor suppression, Nat. Rev., Mol. Cell Biol. 2 (2001) 731-737], govern separable though interconnected pathways that cooperate to restrain cyclin D- and cyclin E-dependent kinases from precipitating untimely R point transit. The expression levels of the Ink4a and Arf proteins are especially sensitive to changes in cellular shape and adhesion that entirely remodel at the time when cells shift between quiescence and division. The Arf proteins further display an extremely high translational sensitivity and can activate the p53 pathway to delay R point transit, but, only when released from the nucleolus, 'an organelle formed by the act of building a ribosome' [T. Mélèse, Z. Xue, The nucleolus: an organelle formed by the act of building a ribosome, Curr. Opin. Cell Biol. 7 (1995) 319-324]. In this way, the Ink4a/Rb and Arf/p53 pathways emerge as key regulators of anchorage-dependent R point transit in mammalian cells and their deregulation is, indeed, a rule in human cancers. Thus, by selecting the nucleolus to mitigate cell cycle control by the Arf proteins, mammalian cells succeeded in forging a highly flexible R point enabling them to match cell division with a growth rate imposed by factors controlling nucleolar assembling, such as nutrients and adhesion. It is noteworthy that nutrient control of critical size at Start in budding yeast has been shown recently to be governed by a nucleolar protein interaction network [P. Jorgensen, J.L. Nishikawa, B.-J. Breitkreutz, M. Tyers, Systematic identification of pathways that couple cell growth and division in yeast, Science 297 (2002) 395-400].
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Affiliation(s)
- Thérèse David-Pfeuty
- UMR 146 du CNRS, Institut Curie-Recherche, Bâtiment 110, Centre Universitaire, 91405 Orsay, France.
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Abstract
This review examines the rationale for targeting the insulin-like growth factor (IGF)-I receptor in the therapy of human tumours and their metastases. The rationale is based on two crucial findings: 1) in experimental animals, normal cells are only partially affected by the deletion of the IGF-I receptor, whereas tumour cells undergo apoptosis when the IGF-I receptor is downregulated; and 2) cells with a deleted IGF-I receptor are refractory to transformation by viral and cellular oncogenes. This review focuses on the mechanisms underlying the experimental findings, and discusses the possibility of extrapolating the results obtained in animals to the cure of human tumours.
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Affiliation(s)
- Renato Baserga
- Thomas Jefferson University, Kimmel Cancer Center, 233 S. 10th Street, 624 BLSB, Philadelphia, PA 19107, USA.
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Benevolenskaya EV, Murray HL, Branton P, Young RA, Kaelin WG. Binding of pRB to the PHD protein RBP2 promotes cellular differentiation. Mol Cell 2005; 18:623-35. [PMID: 15949438 DOI: 10.1016/j.molcel.2005.05.012] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2004] [Revised: 02/02/2005] [Accepted: 05/16/2005] [Indexed: 12/31/2022]
Abstract
pRB can enforce a G1 block by repressing E2F-responsive promoters. It also coactivates certain non-E2F transcription factors and promotes differentiation. Some pRB variants activate transcription and promote differentiation despite impaired E2F binding and transcriptional repression capabilities. We identified RBP2 in a screen for proteins that bind to such pRB variants. RBP2 resembles other chromatin-associated transcriptional regulators and RBP2 binding tracked with pRB's ability to activate transcription and promote differentiation. RBP2 and pRB colocalize and pRB/RBP2 complexes were detected in chromatin isolated from differentiating cells. RBP2 siRNA phenocopied restoration of pRB function in coactivation and differentiation assays, suggesting that pRB prevents RBP2 from repressing genes required for differentiation. In addition, two bromodomain-containing proteins were identified as RBP2 targets that are transcriptionally activated by pRB in an RBP2-dependent manner. Our results suggest that promotion of differentiation by pRB involves neutralization of free RBP2 and transcriptional activation of RBP2 targets linked to euchromatin maintenance.
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Affiliation(s)
- Elizaveta V Benevolenskaya
- Dana-Farber Cancer Institute and Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA
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38
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Abstract
The retinoblastoma protein (pRB) and the pRB-related p107 and p130 comprise the 'pocket protein' family of cell cycle regulators. These proteins are best known for their roles in restraining the G1-S transition through the regulation of E2F-responsive genes. pRB and the p107/p130 pair are required for the repression of distinct sets of genes, potentially due to their selective interactions with E2Fs that are engaged at specific promoter elements. In addition to regulating E2F-responsive genes in a reversible manner, pocket proteins contribute to silencing of such genes in cells that are undergoing senescence or differentiation. Pocket proteins also affect the G1-S transition through E2F-independent mechanisms, such as by inhibiting Cdk2 or by stabilizing p27(Kip1), and they are implicated in the control of G0 exit, the spatial organization of replication, and genomic rereplication. New insights into pocket protein regulation have also been obtained. Kinases previously thought to be crucial to pocket protein phosphorylation have been shown to be redundant, and new modes of phosphorylation and dephosphorylation have been identified. Despite these advances, much remains to be learned about the pocket proteins, particularly with regard to their developmental and tumor suppressor functions. Thus continues the story of the pocket proteins and the cell cycle.
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Affiliation(s)
- David Cobrinik
- Dyson Vision Research Institute and Department of Ophthalmology, Weill Medical College of Cornell University, 1300 York Avenue, LC303, New York, NY 10021, USA.
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39
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Abstract
Transcription of rRNA and tRNA genes by RNA polymerases I and III is essential for sustained protein synthesis and is therefore a fundamental determinant of the capacity of a cell to grow. When cell growth is not required, this transcription is repressed by retinoblastoma protein, p53 and ARF. However, inactivation of these tumour suppressors in cancers deregulates RNA polymerases I and III, and oncoproteins such as Myc can stimulate these systems further. Such events might have a significant impact on the growth potential of tumours.
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Affiliation(s)
- Robert J White
- Institute of Biomedical and Life Sciences, Division of Biochemistry and Molecular Biology, University of Glasgow, Glasgow, G12 8QQ, UK.
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40
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Maddox-Hyttel P, Bjerregaard B, Laurincik J. Meiosis and embryo technology: renaissance of the nucleolus. Reprod Fertil Dev 2005; 17:3-14. [PMID: 15745627 DOI: 10.1071/rd04108] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2004] [Accepted: 10/01/2004] [Indexed: 11/23/2022] Open
Abstract
The nucleolus is the site of rRNA and ribosome production. This organelle presents an active fibrillogranular ultrastructure in the oocyte during the growth of the gamete but, at the end of the growth phase, the nucleolus is transformed into an inactive remnant that is dissolved when meiosis is resumed at germinal vesicle breakdown. Upon meiosis, structures resembling the nucleolar remnant, now referred to as nucleolus precursor bodies (NPBs), are established in the pronuclei. These entities harbour the development of fibrillogranular nucleoli and re-establishment of nucleolar function in conjunction with the major activation of the embryonic genome. This so-called nucleologenesis occurs at a species-specific time of development and can be classified into two different models: one where nucleolus development occurs inside the NPBs (e.g. cattle) and one where the nucleolus is formed on the surface of the NPBs (e.g. pigs). A panel of nucleolar proteins with functions during rDNA transcription (topoisomerase I, RNA polymerase I and upstream binding factor) and early (fibrillarin) or late rRNA processing (nucleolin and nucleophosmin) are localised to specific compartments of the oocyte nucleolus and those engaged in late processing are, to some degree, re-used for nucleologenesis in the embryo, whereas the others require de novo embryonic transcription in order to be allocated to the developing nucleolus. In the oocyte, inactivation of the nucleolus coincides with the acquisition of full meiotic competence, a parameter that may be of importance in relation to in vitro oocyte maturation. In embryo, nucleologenesis may be affected by technological manipulations: in vitro embryo production apparently has no impact on this process in cattle, whereas in the pig this technology results in impaired nucleologenesis. In cattle, reconstruction of embryos by nuclear transfer results in profound disturbances in nucleologenesis. In conclusion, the nucleolus is an organelle of great importance for the developmental competence of oocytes and embryos and may serve as a morphological marker for the completion of oocyte growth and normality of activation of the embryonic genome.
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Affiliation(s)
- Poul Maddox-Hyttel
- Department of Animal and Veterinary Basic Sciences, Royal Veterinary and Agricultural University, Groennegaardsvej 7, DK-1870 Frederiksberg C, Denmark.
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Chapter 2 Regulation of skeletal muscle protein metabolism in growing animals. ACTA ACUST UNITED AC 2005. [DOI: 10.1016/s1877-1823(09)70009-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register]
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Treré D, Ceccarelli C, Montanaro L, Tosti E, Derenzini M. Nucleolar size and activity are related to pRb and p53 status in human breast cancer. J Histochem Cytochem 2004; 52:1601-7. [PMID: 15557214 DOI: 10.1369/jhc.4a6454.2004] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Cell proliferation is tightly coordinated with cell growth. The oncosuppressor proteins pRb and p53 may exert a key role in coupling growth and proliferation by controlling both ribosome biogenesis and cell cycle progression. In the present study we evaluated the relationship between the pRb and p53 status and rRNA transcriptional activity in histological sections of 343 human primary breast carcinomas. Ribosomal biogenesis was quantified by morphometric analysis of silver-stained interphase nucleolar organizer regions (AgNORs). pRb and p53 status was assessed by immunohistochemistry. Twenty-four tumors were considered to be pRb deleted, 260 tumors showed a phosphorylated-pRb labeling index (LI) up to 25%, and 55 tumors an LI >25%. Tumors with deleted pRb or phosphorylated-pRb-LI > or =25% were characterized by significantly greater mean AgNOR area values than those with unaltered pRb (p<0.001). In the 71 tumors with mutated p53 the NOR area mean value was greater than in the 272 tumors with normal p53 (p<0.001). Our results demonstrate, for the first time in vivo, that pRb and p53 status is related to the ribosome biogenesis rate and suggest that in tumors with altered pRb and p53 function the up-regulation of rRNA synthesis may always assure an adequate growth to cancer cells with uncontrolled cell cycle progression.
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Affiliation(s)
- Davide Treré
- Department of Experimental Pathology, Unit of Clinical Pathology, University of Bologna, Bologna, Italy.
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Derenzini M, Ceccarelli C, Santini D, Taffurelli M, Treré D. The prognostic value of the AgNOR parameter in human breast cancer depends on the pRb and p53 status. J Clin Pathol 2004; 57:755-61. [PMID: 15220371 PMCID: PMC1770366 DOI: 10.1136/jcp.2003.015917] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/04/2022]
Abstract
BACKGROUND The amount of argyrophilic nucleolar organiser regions (AgNORs) represents a cell kinetics parameter used in tumour pathology for prognostic purposes. AgNOR expression is directly related to the rate of ribosome biogenesis, which has been recently shown to be controlled also by the tumour suppressor proteins pRb and p53. AIMS To ascertain the relative prognostic value of AgNORs and of pRb and p53 expression in breast carcinoma. METHODS This study was carried out on 335 human primary breast carcinomas with a median follow up time of 108 months. AgNORs were measured by morphometric analysis on sections that had been selectively silver stained; expression of p53 and phosphorylated and non-phosphorylated pRb forms was assessed by immunohistochemistry. RESULTS Patients were divided into groups with low (249) and high (86) AgNOR values; with normal (267) and mutated p53 (68); and with normal (256) and hyperphosphorylated or deleted pRb (79). Univariate analysis of disease free survival showed that AgNORs and the status of pRb and p53 were significantly related to the patients' clinical outcome. However, among the four groups characterised by different pRb and p53 status, the AgNOR parameter was not capable of distinguishing subgroups of patients with different clinical outcomes. CONCLUSIONS These findings indicate that the prognostic value of the AgNOR parameter depends on the status of the tumour suppressor proteins pRb and p53, and it cannot be ascribed to the relation between AgNORs and the cell proliferation rate.
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Affiliation(s)
- M Derenzini
- Department of Experimental Pathology, Unit of Clinical Pathology, University of Bologna, Bologna 40126, Italy.
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44
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Abstract
In vitro production (IVP) of porcine embryos including in vitro maturation (IVM) of oocytes followed by in vitro fertilization (IVF) and in vitro culture (IVC) of the resultant embryos may result in live offspring, but it is still associated with great inefficiencies probably due to incomplete cytoplasmic maturation of the oocytes in vitro. Therefore, fundamental knowledge on the regulation of transcription during the oocyte growth phase when the messengers and protein synthetic machinery necessary for oocyte developmental competence are formed, is of great importance. In mammals, synthesis of RNA, up to 60-70% of which is ribosomal (rRNA), increases during oocyte growth and reaches a peak at the beginning of follicular antrum formation. In oocytes at the end of the growth phase, acquisition of full meiotic competence coincides with a markedly decreased rRNA transcriptional activity in the gametes. Our recent studies on the porcine oocyte growth phase have revealed a deeper molecular and biological insight into the complex regulation of rRNA transcription at different stages of follicular development. The data indicate that the so-called pocket protein, p130, is involved in the down-regulation of rRNA transcription at the end of the oocyte growth phase through an inhibition of the action of upstream binding factor (UBF). The latter protein is necessary for the function of RNA polymerase I (RNA Pol I), which is the actual enzyme driving rRNA gene transcription. Moreover, rRNA transcription also appears to be down-regulated by a decrease in the expression of mRNA encoding PAF53, an RNA Pol I-associated factor also required for the polymerase to exert its action. At the ultrastructural level, these molecular changes are paralleled by marginalization of the fibrillar centres of the oocyte nucleolus followed by compaction of the nucleolus into an inactive sphere of fibrils.
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Affiliation(s)
- B Bjerregaard
- Department of Animal and Veterinary Basic Sciences, The Royal Veterinary and Agricultural University, Groennegaardsvej 7, DK-1870 Frederiksberg C, Denmark
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Prisco M, Maiorana A, Guerzoni C, Calin G, Calabretta B, Voit R, Grummt I, Baserga R. Role of pescadillo and upstream binding factor in the proliferation and differentiation of murine myeloid cells. Mol Cell Biol 2004; 24:5421-33. [PMID: 15169904 PMCID: PMC419857 DOI: 10.1128/mcb.24.12.5421-5433.2004] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2004] [Revised: 02/04/2004] [Accepted: 03/24/2004] [Indexed: 12/13/2022] Open
Abstract
Pescadillo (PES1) and the upstream binding factor (UBF1) play a role in ribosome biogenesis, which regulates cell size, an important component of cell proliferation. We have investigated the effects of PES1 and UBF1 on the growth and differentiation of cell lines derived from 32D cells, an interleukin-3 (IL-3)-dependent murine myeloid cell line. Parental 32D cells and 32D IGF-IR cells (expressing increased levels of the type 1 insulin-like growth factor I [IGF-I] receptor [IGF-IR]) do not express insulin receptor substrate 1 (IRS-1) or IRS-2. 32D IGF-IR cells differentiate when the cells are shifted from IL-3 to IGF-I. Ectopic expression of IRS-1 inhibits differentiation and transforms 32D IGF-IR cells into a tumor-forming cell line. We found that PES1 and UBF1 increased cell size and/or altered the cell cycle distribution of 32D-derived cells but failed to make them IL-3 independent. PES1 and UBF1 also failed to inhibit the differentiation program initiated by the activation of the IGF-IR, which is blocked by IRS-1. 32D IGF-IR cells expressing PES1 or UBF1 differentiate into granulocytes like their parental cells. In contrast, PES1 and UBF1 can transform mouse embryo fibroblasts that have high levels of endogenous IRS-1 and are not prone to differentiation. Our results provide a model for one of the theories of myeloid leukemia, in which both a stimulus of proliferation and a block of differentiation are required for leukemia development.
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Affiliation(s)
- Marco Prisco
- Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA
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46
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Abstract
RNA polymerase (pol) III synthesizes a range of essential products, including tRNA, 5S rRNA and 7SL RNA, which are required for protein synthesis and trafficking. High rates of pol III transcription are necessary for cells to sustain growth. A wide range of transformed and tumour cell types have been shown to express elevated levels of pol III products. This review will summarize what is known about the mechanisms responsible for this deregulation. Some transforming agents have been shown to stimulate expression of the pol III-specific transcription factors TFIIIB or TFIIIC2. In addition, TFIIIB is bound and activated by several oncogenic proteins, including c-Myc. Conversely, TFIIIB interacts in healthy cells with the tumour suppressors RB and p53. Indeed, the ability to limit pol III transcription through TFIIIB may contribute to their growth-suppression capacities. The function of p53 and/or RB is compromised in most if not all transformed cells; the resultant derepression of TFIIIB may provide an almost universal route to deregulate pol III transcription in cancers. In addition to effects on protein synthesis and growth, there is a precedent for a pol III product having oncogenic activity.
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Affiliation(s)
- Robert J White
- Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Davidson Building, Glasgow G12 8QQ, UK.
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Willis IM, Desai N, Upadhya R. Signaling repression of transcription by RNA polymerase III in yeast. PROGRESS IN NUCLEIC ACID RESEARCH AND MOLECULAR BIOLOGY 2004; 77:323-53. [PMID: 15196897 DOI: 10.1016/s0079-6603(04)77009-9] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Affiliation(s)
- Ian M Willis
- Department of Biochemistry, Albert Einstein College of Medicine, 1300 Morris Park Avenue, Bronx, NY 10461 USA
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Dimario PJ. Cell and Molecular Biology of Nucleolar Assembly and Disassembly. INTERNATIONAL REVIEW OF CYTOLOGY 2004; 239:99-178. [PMID: 15464853 DOI: 10.1016/s0074-7696(04)39003-0] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Nucleoli disassemble in prophase of the metazoan mitotic cycle, and they begin their reassembly (nucleologenesis) in late anaphase?early telophase. Nucleolar disassembly and reassembly were obvious to the early cytologists of the eighteenth and nineteenth centuries, and although this has lead to a plethora of literature describing these events, our understanding of the molecular mechanisms regulating nucleolar assembly and disassembly has expanded immensely just within the last 10-15 years. We briefly survey the findings of nineteenth-century cytologists on nucleolar assembly and disassembly, followed by the work of Heitz and McClintock on nucleolar organizers. A primer review of nucleolar structure and functions precedes detailed descriptions of modern molecular and microscopic studies of nucleolar assembly and disassembly. Nucleologenesis is concurrent with the reinitiation of rDNA transcription in telophase. The perichromosomal sheath, prenucleolar bodies, and nucleolar-derived foci serve as repositories for nucleolar processing components used in the previous interphase. Disassembly of the perichromosomal sheath along with the dynamic movements and compositional changes of the prenucleolar bodies and nucleolus-derived foci coincide with reactivation of rDNA synthesis within the chromosomal nucleolar organizers during telophase. Nucleologenesis is considered in various model organisms to provide breadth to our understanding. Nucleolar disassembly occurs at the onset of mitosis primarily as a result of the mitosis-specific phosphorylation of Pol I transcription factors and processing components. Although we have learned much regarding nucleolar assembly and disassembly, many questions still remain, and these questions are as vibrant for us today as early questions were for nineteenth- and early twentieth-century cytologists.
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Affiliation(s)
- Patrick J Dimario
- Department of Biological Sciences, Louisiana State University, Baton Rouge, Louisiana 70803-1715, USA
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Hannan KM, Brandenburger Y, Jenkins A, Sharkey K, Cavanaugh A, Rothblum L, Moss T, Poortinga G, McArthur GA, Pearson RB, Hannan RD. mTOR-dependent regulation of ribosomal gene transcription requires S6K1 and is mediated by phosphorylation of the carboxy-terminal activation domain of the nucleolar transcription factor UBF. Mol Cell Biol 2003; 23:8862-77. [PMID: 14612424 PMCID: PMC262650 DOI: 10.1128/mcb.23.23.8862-8877.2003] [Citation(s) in RCA: 343] [Impact Index Per Article: 16.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Mammalian target of rapamycin (mTOR) is a key regulator of cell growth acting via two independent targets, ribosomal protein S6 kinase 1 (S6K1) and 4EBP1. While each is known to regulate translational efficiency, the mechanism by which they control cell growth remains unclear. In addition to increased initiation of translation, the accelerated synthesis and accumulation of ribosomes are fundamental for efficient cell growth and proliferation. Using the mTOR inhibitor rapamycin, we show that mTOR is required for the rapid and sustained serum-induced activation of 45S ribosomal gene transcription (rDNA transcription), a major rate-limiting step in ribosome biogenesis and cellular growth. Expression of a constitutively active, rapamycin-insensitive mutant of S6K1 stimulated rDNA transcription in the absence of serum and rescued rapamycin repression of rDNA transcription. Moreover, overexpression of a dominant-negative S6K1 mutant repressed transcription in exponentially growing NIH 3T3 cells. Rapamycin treatment led to a rapid dephosphorylation of the carboxy-terminal activation domain of the rDNA transcription factor, UBF, which significantly reduced its ability to associate with the basal rDNA transcription factor SL-1. Rapamycin-mediated repression of rDNA transcription was rescued by purified recombinant phosphorylated UBF and endogenous UBF from exponentially growing NIH 3T3 cells but not by hypophosphorylated UBF from cells treated with rapamycin or dephosphorylated recombinant UBF. Thus, mTOR plays a critical role in the regulation of ribosome biogenesis via a mechanism that requires S6K1 activation and phosphorylation of UBF.
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Affiliation(s)
- Katherine M Hannan
- Trescowthick Research Laboratories, Peter MacCallum Cancer Centre, East Melbourne, Victoria 3002, USA
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Bjerregaard B, Wrenzycki C, Philimonenko VV, Hozak P, Laurincik J, Niemann H, Motlik J, Maddox-Hyttel P. Regulation of Ribosomal RNA Synthesis During the Final Phases of Porcine Oocyte Growth. Biol Reprod 2003; 70:925-35. [PMID: 14627545 DOI: 10.1095/biolreprod.103.020941] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
In porcine oocytes, acquisition of meiotic competence coincides with a decrease of general transcriptional activity at the end of the oocyte growth phase and, specifically, of ribosomal RNA (rRNA) synthesis in the nucleolus. The present study investigated the regulation of rRNA synthesis during porcine oocyte growth. Localization and expression of components involved in regulation of the rRNA synthesis (the RNA polymerase I-associated factor PAF53, upstream binding factor [UBF], and the pocket proteins p130 and pRb) were assessed by immunocytochemistry and semiquantitative reverse transcription-polymerase chain reaction and correlated with ultrastructural analysis and autoradiography following [3H]uridine incubation in growing and fully grown porcine oocytes. In addition, meiotic resumption, ultrastructure, and expression of p130, UBF, and PAF53 were analyzed in growing and fully grown porcine oocytes cultured with 100 microM butyrolactone I (BL-I), a potent inhibitor of cyclin-dependent kinases, to gain insight concerning the regulation of rRNA transcription during meiotic arrest. Immunocytochemical analysis demonstrated that p130 became colocalized with UBF and PAF53 and that the intensity of the PAF53 labeling decreased toward the end of the oocyte growth phase. These data suggest that the decrease in rRNA synthesis is regulated through inhibition of UBF by p130 as well as by decreased availability of PAF53. Moreover, expression of mRNA encoding PAF53 was decreased at the end of the oocyte growth phase. At the morphological level, these events coincided with inactivation of the nucleolus, as visualized by the transformation of the fibrillogranular nucleolus to an electron-dense fibrillar sphere with remnants of the fibrillar centers at the surface. Meiotic inhibition with 100 microM BL-I had a detrimental effect on the ability of porcine oocytes to resume meiosis and on nucleolus morphology, resulting in a lack of RNA synthetic capability as the fibrillar components, where rRNA transcription and initial processing occur, condensed or even disintegrated.
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Affiliation(s)
- Bolette Bjerregaard
- Department of Anatomy and Physiology, Royal Veterinary and Agricultural University, 1870 Frederiksberg, Denmark
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