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Breindl M, Spitzer D, Gerasimaitė R, Kairys V, Schubert T, Henfling R, Schwartz U, Lukinavičius G, Manelytė L. Biochemical and cellular insights into the Baz2B protein, a non-catalytic subunit of the chromatin remodeling complex. Nucleic Acids Res 2024; 52:337-354. [PMID: 38000389 PMCID: PMC10783490 DOI: 10.1093/nar/gkad1096] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2023] [Revised: 09/21/2023] [Accepted: 11/06/2023] [Indexed: 11/26/2023] Open
Abstract
Baz2B is a regulatory subunit of the ATP-dependent chromatin remodeling complexes BRF1 and BRF5, which control access to DNA during DNA-templated processes. Baz2B has been implicated in several diseases and also in unhealthy ageing, however limited information is available on the domains and cellular roles of Baz2B. To gain more insight into the Baz2B function, we biochemically characterized the TAM (Tip5/ARBP/MBD) domain with the auxiliary AT-hook motifs and the bromodomain (BRD). We observed alterations in histone code recognition in bromodomains carrying cancer-associated point mutations, suggesting their potential involvement in disease. Furthermore, the depletion of Baz2B in the Hap1 cell line resulted in altered cell morphology, reduced colony formation and perturbed transcriptional profiles. Despite that, super-resolution microscopy images revealed no changes in the overall chromatin structure in the absence of Baz2B. These findings provide insights into the biological function of Baz2B.
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Affiliation(s)
- Matthias Breindl
- Biochemistry III, University of Regensburg, Regensburg DE-93053, Germany
| | - Dominika Spitzer
- Biochemistry III, University of Regensburg, Regensburg DE-93053, Germany
| | - Rūta Gerasimaitė
- Chromatin Labeling and Imaging Group, Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, DE-37077 Göttingen, Germany
| | - Visvaldas Kairys
- Institute of Biotechnology, Life Sciences Center, Vilnius University, Vilnius LT-10257, Lithuania
| | | | - Ramona Henfling
- Biochemistry III, University of Regensburg, Regensburg DE-93053, Germany
| | - Uwe Schwartz
- NGS Analysis Center, University of Regensburg, Regensburg DE-93053, Germany
| | - Gražvydas Lukinavičius
- Chromatin Labeling and Imaging Group, Department of NanoBiophotonics, Max Planck Institute for Multidisciplinary Sciences, Am Fassberg 11, DE-37077 Göttingen, Germany
| | - Laura Manelytė
- Biochemistry III, University of Regensburg, Regensburg DE-93053, Germany
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Chen N, Yang S, You D, Shen J, Ruan B, Wu M, Zhang J, Luo X, Tang H. Systematic genetic modifications of cell wall biosynthesis enhanced the secretion and surface-display of polysaccharide degrading enzymes in Saccharomyces cerevisiae. Metab Eng 2023; 77:273-282. [PMID: 37100192 DOI: 10.1016/j.ymben.2023.04.011] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2022] [Revised: 03/31/2023] [Accepted: 04/15/2023] [Indexed: 04/28/2023]
Abstract
Saccharomyces cerevisiae is a robust cell factory to secrete or surface-display cellulase and amylase for the conversion of agricultural residues into valuable chemicals. Engineering the secretory pathway is a well-known strategy for overproducing these enzymes. Although cell wall biosynthesis can be tightly linked to the secretory pathway by regulation of all involved processes, the effect of its modifications on protein production has not been extensively studied. In this study, we systematically studied the effect of engineering cell wall biosynthesis on the activity of cellulolytic enzyme β-glucosidase (BGL1) by comparing seventy-nine gene knockout S. cerevisiae strains and newly identified that inactivation of DFG5, YPK1, FYV5, CCW12 and KRE1 obviously improved BGL1 secretion and surface-display. Combinatorial modifications of these genes, particularly double deletion of FVY5 and CCW12, along with the use of rich medium, increased the activity of secreted and surface-displayed BGL1 by 6.13-fold and 7.99-fold, respectively. Additionally, we applied this strategy to improve the activity of the cellulolytic cellobiohydrolase and amylolytic α-amylase. Through proteomic analysis coupled with reverse engineering, we found that in addition to the secretory pathway, regulation of translation processes may also involve in improving enzyme activity by engineering cell wall biosynthesis. Our work provides new insight into the construction of a yeast cell factory for efficient production of polysaccharide degrading enzymes.
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Affiliation(s)
- Nanzhu Chen
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Shuo Yang
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China; State Key Laboratory of Biobased Material and Green Papermaking, School of Bioengineering, Key Laboratory of Shandong Microbial Engineering, Qilu University of Technology, 3501 Daxue Road, Jinan, 250353, China
| | - Dawei You
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Junfeng Shen
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Banlai Ruan
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Mei Wu
- Synceres Biosciences (Shenzhen) Co., Ltd, Nanshan Medical Device Industrial Park, Nanhai Avenue, Shenzhen, 518067, China
| | - Jianzhi Zhang
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China
| | - Xiaozhou Luo
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
| | - Hongting Tang
- CAS Key Laboratory of Quantitative Engineering Biology, Shenzhen Institute of Synthetic Biology, Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences, Shenzhen, 518055, China.
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In vivo CRISPR screening identifies BAZ2 chromatin remodelers as druggable regulators of mammalian liver regeneration. Cell Stem Cell 2022; 29:372-385.e8. [PMID: 35090595 PMCID: PMC8897233 DOI: 10.1016/j.stem.2022.01.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 12.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2020] [Revised: 09/17/2021] [Accepted: 12/30/2021] [Indexed: 12/17/2022]
Abstract
Identifying new pathways that regulate mammalian regeneration is challenging due to the paucity of in vivo screening approaches. We employed pooled CRISPR knockout and activation screening in the regenerating liver to evaluate 165 chromatin regulatory proteins. Both screens identified the imitation-SWI chromatin remodeling components Baz2a and Baz2b, not previously implicated in regeneration. In vivo sgRNA, siRNA, and knockout strategies against either paralog confirmed increased regeneration. Distinct BAZ2-specific bromodomain inhibitors, GSK2801 and BAZ2-ICR, resulted in accelerated liver healing after diverse injuries. Inhibitor-treated mice also exhibited improved healing in an inflammatory bowel disease model, suggesting multi-tissue applicability. Transcriptomics on regenerating livers showed increases in ribosomal and cell cycle mRNAs. Surprisingly, CRISPRa screening to define mechanisms showed that overproducing Rpl10a or Rpl24 was sufficient to drive regeneration, whereas Rpl24 haploinsufficiency was rate limiting for BAZ2 inhibition-mediated regeneration. The discovery of regenerative roles for imitation-SWI components provides immediate strategies to enhance tissue repair.
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Faria TC, Maldonado HL, Santos LC, DeLabio R, Payao SLM, Turecki G, Mechawar N, Santana DA, Gigek CO, Lemos B, Smith MAC, Chen ES. Characterization of Cerebellum-Specific Ribosomal DNA Epigenetic Modifications in Alzheimer's Disease: Should the Cerebellum Serve as a Control Tissue After All? Mol Neurobiol 2020; 57:2563-2571. [PMID: 32232768 DOI: 10.1007/s12035-020-01902-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2019] [Accepted: 03/09/2020] [Indexed: 11/26/2022]
Abstract
Alzheimer's disease (AD) is a neurodegenerative disease, known as the most common form of dementia. In AD onset, abnormal rRNA expression has been reported to be linked in pathogenesis. Although region-specific expression patterns have previously been reported in AD, it is not until recently that the cerebellum has come under the spotlight. Specifically, it is unclear whether DNA methylation is the mechanism involved in rRNA expression regulation in AD. Hence, we sought to explore the rDNA methylation pattern of two different brain regions - auditory cortex and cerebellum - from AD and age-/sex-matched controls. Our results showed differential hypermethylation at an upstream CpG region to the rDNA promoter when comparing cerebellum controls to auditory cortex controls. This suggests a possible regulatory region from rDNA expression regulation. Moreover, when comparing between AD and control cerebellum samples, we observed hypermethylation of the rDNA promoter region as well as an increase in rDNA content. In addition, we also observed increased rRNA levels in AD compared to control cerebellum. Although still considered a pathology-free brain region, there are growing findings that continue to suggest otherwise. Indeed, cerebellum from AD has been recently described as affected by the disease, presenting a unique pattern of molecular alterations. Given that we observed that increased rDNA promoter methylation did not silence rDNA gene expression, we suggest that rDNA promoter hypermethylation is playing a protective role in rDNA genomic stability and, therefore, increasing rRNA levels in AD cerebellum.
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Affiliation(s)
- Tathyane C Faria
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil
| | - Héctor L Maldonado
- Department of Environmental Health, Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA
| | - Leonardo C Santos
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil
| | - Roger DeLabio
- Faculdade de Medicina de Marília (FAMEMA), Marília, SP, Brazil
| | | | - Gustavo Turecki
- Department of Psychiatry, Douglas Hospital Research Center, McGill University, Montreal, QC, Canada
| | - Naguib Mechawar
- Department of Psychiatry, Douglas Hospital Research Center, McGill University, Montreal, QC, Canada
| | - Dalileia A Santana
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil
| | - Carolina O Gigek
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil
| | - Bernardo Lemos
- Department of Environmental Health, Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA
- Broad Institute of Harvard and MIT, Cambridge, MA, USA
| | - Marilia A C Smith
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil
| | - Elizabeth S Chen
- Departamento de Morfologia e Genética, Programa de Pós-Graduação em Biologia Estrutural e Funcional da UNIFESP/EPM, Disciplina de Genética, Universidade Federal de São Paulo (UNIFESP/EPM), São Paulo, SP, Brazil.
- Department of Environmental Health, Program in Molecular and Integrative Physiological Sciences, Harvard T.H. Chan School of Public Health, Boston, MA, USA.
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NoRC Recruitment by H2A.X Deposition at rRNA Gene Promoter Limits Embryonic Stem Cell Proliferation. Cell Rep 2019; 23:1853-1866. [PMID: 29742439 DOI: 10.1016/j.celrep.2018.04.023] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2017] [Revised: 01/16/2018] [Accepted: 04/04/2018] [Indexed: 01/22/2023] Open
Abstract
Embryonic stem cells (ESCs) display an abbreviated cell cycle, resulting in a short doubling time and rapid proliferation. The histone variant H2A.X is critical for proliferation of stem cells, although mechanistic insights have remained obscure. Here, we show that H2A.X defines the rate of mouse ESC proliferation independently of the DNA damage response pathway, and it associates with three major chromatin-modifying complexes. Our functional and biochemical analyses demonstrate that H2A.X-associated factors mediate the H2A.X-dependent effect on ESC proliferation and involve the nucleolar remodeling complex (NoRC). A specific H2A.X deposition at rDNA promoters determines the chromatin recruitment of the NoRC, histone modifications, the rRNA transcription, and the rate of proliferation. Collectively, our results suggest that NoRC assembly by H2A.X deposition at rRNA promoters silences transcription, and this represents an important regulatory component for ESC proliferation.
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Dyomin A, Galkina S, Fillon V, Cauet S, Lopez-Roques C, Rodde N, Klopp C, Vignal A, Sokolovskaya A, Saifitdinova A, Gaginskaya E. Structure of the intergenic spacers in chicken ribosomal DNA. Genet Sel Evol 2019; 51:59. [PMID: 31655542 PMCID: PMC6815422 DOI: 10.1186/s12711-019-0501-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Accepted: 10/14/2019] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Ribosomal DNA (rDNA) repeats are situated in the nucleolus organizer regions (NOR) of chromosomes and transcribed into rRNA for ribosome biogenesis. Thus, they are an essential component of eukaryotic genomes. rDNA repeat units consist of rRNA gene clusters that are transcribed into single pre-rRNA molecules, each separated by intergenic spacers (IGS) that contain regulatory elements for rRNA gene cluster transcription. Because of their high repeat content, rDNA sequences are usually absent from genome assemblies. In this work, we used the long-read sequencing technology to describe the chicken IGS and fill the knowledge gap on rDNA sequences of one of the key domesticated animals. METHODS We used the long-read PacBio RSII technique to sequence the BAC clone WAG137G04 (Wageningen BAC library) known to contain chicken NOR elements and the HGAP workflow software suit to assemble the PacBio RSII reads. Whole-genome sequence contigs homologous to the chicken rDNA repetitive unit were identified based on the Gallus_gallus-5.0 assembly with BLAST. We used the Geneious 9.0.5 and Mega software, maximum likelihood method and Chickspress project for sequence evolution analysis, phylogenetic tree construction and analysis of the raw transcriptome data. RESULTS Three complete IGS sequences in the White Leghorn chicken genome and one IGS sequence in the red junglefowl contig AADN04001305.1 (Gallus_gallus-5.0) were detected. They had various lengths and contained three groups of tandem repeats (some of them being very GC rich) that form highly organized arrays. Initiation and termination sites of rDNA transcription were located within small and large unique regions (SUR and LUR), respectively. No functionally significant sites were detected within the tandem repeat sequences. CONCLUSIONS Due to the highly organized GC-rich repeats, the structure of the chicken IGS differs from that of IGS in human, apes, Xenopus or fish rDNA. However, the chicken IGS shares some molecular organization features with that of the turtles, which are other representatives of the Sauropsida clade that includes birds and reptiles. Our current results on the structure of chicken IGS together with the previously reported ribosomal gene cluster sequence provide sufficient data to consider that the complete chicken rDNA sequence is assembled with confidence in terms of molecular DNA organization.
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Affiliation(s)
- Alexander Dyomin
- Saint Petersburg State University, Universitetskaya emb. 7/9, Saint Petersburg, 199034, Russian Federation.,Saratov State Medical University, Bolshaya Kazachia Str. 112, Saratov, Russian Federation
| | - Svetlana Galkina
- Saint Petersburg State University, Universitetskaya emb. 7/9, Saint Petersburg, 199034, Russian Federation
| | - Valerie Fillon
- INRA, GenPhySE, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Stephane Cauet
- INRA, CNRGV, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Celine Lopez-Roques
- INRA, GeT-PlaGe, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Nathalie Rodde
- INRA, CNRGV, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Christophe Klopp
- INRA, Sigenae, MIAT, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Alain Vignal
- INRA, GenPhySE, 24 Chemin de Borde Rouge, Auzeville, 31326, Castanet Tolosan, France
| | - Anastasia Sokolovskaya
- Saint Petersburg State University, Universitetskaya emb. 7/9, Saint Petersburg, 199034, Russian Federation
| | - Alsu Saifitdinova
- Herzen State Pedagogical University of Russia, Moika Emb. 48, Saint Petersburg, 191186, Russian Federation
| | - Elena Gaginskaya
- Saint Petersburg State University, Universitetskaya emb. 7/9, Saint Petersburg, 199034, Russian Federation.
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Coleman O, Suda S, Meiller J, Henry M, Riedl M, Barron N, Clynes M, Meleady P. Increased growth rate and productivity following stable depletion of miR-7 in a mAb producing CHO cell line causes an increase in proteins associated with the Akt pathway and ribosome biogenesis. J Proteomics 2019; 195:23-32. [PMID: 30641232 DOI: 10.1016/j.jprot.2019.01.003] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2018] [Revised: 12/06/2018] [Accepted: 01/07/2019] [Indexed: 12/21/2022]
Abstract
Cell line engineering using microRNAs represents a desirable route for improving the efficiency of recombinant protein production by CHO cells. In this study we generated stable CHO DP12 cells expressing a miR-7 sponge transcript which sequesters miR-7 from its endogenous targets. Depletion of miR-7 results in a 65% increase in cell growth and >3-fold increase in yield of secreted IgG protein. Quantitative labelfree LC-MS/MS proteomic profiling was carried out to identify the targets of miR-7 and understand the functional drivers of the improved CHO cell phenotypes. Subcellular enrichment and total proteome analysis identified more than 3000 proteins per fraction resulting in over 5000 unique proteins identified per timepoint analysed. Early stage culture analysis identified 117 proteins overexpressed in miR-7 depleted cells. A subset of these proteins are involved in the Akt pathway which could be the underlying route for cell density improvement and may be exploited more specifically in the future. Late stage culture identified 160 proteins overexpressed in miR-7 depleted cells with some of these involved in ribosome biogenesis which may be causing the increased productivity through improved translational efficiency. This is the first in-depth proteomic profiling of the IgG producing CHO DP12 cell line stably depleted of miR-7. SIGNIFICANCE: Chinese hamster ovary (CHO) cells are the mammalian cell expression system of choice for production of recombinant therapeutic proteins. There is much research ongoing to characterise CHO cell factories through the application of systems biology approaches that will enable a fundamental understanding of CHO cell physiology, and as a result, a better knowledge and understanding of recombinant protein production. This study profiles the proteomic effects of microRNA-7 depletion on the IgG producing CHO DP12 cell line. This is one of the very few studies that attempts to identify the functioning proteins driving improved CHO cell phenotypes resulting from microRNA manipulation. Using subcellular enrichment and total proteome analysis we identified over 5000 unique proteins in miR-7 depleted CHO cells. This work has identified a cohort of proteins involved in the Akt pathway and ribosome biogenesis. These proteins may drive improved CHO cell phenotypes and are of great interest for future work.
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Affiliation(s)
- Orla Coleman
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland.
| | - Srinivas Suda
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Justine Meiller
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Michael Henry
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Markus Riedl
- Department of Biotechnology, BOKU University of Natural Resources and Life Sciences, Vienna, Austria
| | - Niall Barron
- National Institute for Bioprocessing Research & Training, Foster Avenue, Mount Merrion, Blackrock, Co. Dublin, Ireland; School of Chemical and Bioprocess Engineering, University College Dublin, Dublin 4, Ireland
| | - Martin Clynes
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland
| | - Paula Meleady
- National Institute for Cellular Biotechnology, Dublin City University, Glasnevin, Dublin 9, Ireland
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Polysome profiling of mAb producing CHO cell lines links translational control of cell proliferation and recombinant mRNA loading onto ribosomes with global and recombinant protein synthesis. Biotechnol J 2017; 12. [DOI: 10.1002/biot.201700177] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2017] [Revised: 05/07/2017] [Accepted: 05/15/2017] [Indexed: 12/13/2022]
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9
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Insights into the prevalence and underlying causes of clonal variation through transcriptomic analysis in Pichia pastoris. Appl Microbiol Biotechnol 2017; 101:5045-5058. [PMID: 28534062 PMCID: PMC5486821 DOI: 10.1007/s00253-017-8317-2] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2016] [Revised: 04/04/2017] [Accepted: 04/29/2017] [Indexed: 02/02/2023]
Abstract
Clonal variation, wherein a range of specific productivities of secreted proteins are observed from supposedly identical transformants, is an accepted aspect of working with Pichia pastoris. It means that a significant number of transformants need to be tested to obtain a representative sample, and in commercial protein production, companies regularly screen thousands of transformants to select for the highest secretor. Here, we have undertaken a detailed investigation of this phenomenon by characterising clones transformed with the human serum albumin gene. The titers of nine clones, each containing a single copy of the human serum albumin gene (identified by qPCR), were measured and the clones grouped into three categories, namely, high-, mid- and low-level secretors. Transcriptomic analysis, using microarrays, showed that no regulatory patterns consistently correlated with titer, suggesting that the causes of clonal variation are varied. However, a number of physiological changes appeared to underlie the differences in titer, suggesting there is more than one biochemical signature for a high-secreting strain. An anomalous low-secreting strain displaying high transcript levels that appeared to be nutritionally starved further emphasises the complicated nature of clonal variation.
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10
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Fischer S, Marquart KF, Pieper LA, Fieder J, Gamer M, Gorr I, Schulz P, Bradl H. miRNA engineering of CHO cells facilitates production of difficult-to-express proteins and increases success in cell line development. Biotechnol Bioeng 2017; 114:1495-1510. [PMID: 28262952 PMCID: PMC6084326 DOI: 10.1002/bit.26280] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2016] [Revised: 01/25/2017] [Accepted: 03/01/2017] [Indexed: 01/05/2023]
Abstract
In recent years, coherent with growing biologics portfolios also the number of complex and thus difficult-to-express (DTE) therapeutic proteins has increased considerably. DTE proteins challenge bioprocess development and can include various therapeutic protein formats such as monoclonal antibodies (mAbs), multi-specific affinity scaffolds (e.g., bispecific antibodies), cytokines, or fusion proteins. Hence, the availability of robust and versatile Chinese hamster ovary (CHO) host cell factories is fundamental for high-yielding bioprocesses. MicroRNAs (miRNAs) have emerged as potent cell engineering tools to improve process performance of CHO manufacturing cell lines. However, there has not been any report demonstrating the impact of beneficial miRNAs on industrial cell line development (CLD) yet. To address this question, we established novel CHO host cells constitutively expressing a pro-productive miRNA: miR-557. Novel host cells were tested in two independent CLD campaigns using two different mAb candidates including a normal as well as a DTE antibody. Presence of miR-557 significantly enhanced each process step during CLD in a product independent manner. Stable expression of miR-557 increased the probability to identify high-producing cell clones. Furthermore, production cell lines derived from miR-557 expressing host cells exhibited significantly increased final product yields in fed-batch cultivation processes without compromising product quality. Strikingly, cells co-expressing miR-557 and a DTE antibody achieved a twofold increase in product titer compared to clones co-expressing a negative control miRNA. Thus, host cell engineering using miRNAs represents a promising tool to overcome limitations in industrial CLD especially with regard to DTE proteins. Biotechnol. Bioeng. 2017;114: 1495-1510. © 2017 Wiley Periodicals, Inc.
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Affiliation(s)
- Simon Fischer
- Early Stage Bioprocess Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany.,Cell Culture Development CMB, Boehringer Ingelheim GmbH & Co. KG, Biberach, Germany
| | - Kim F Marquart
- Early Stage Bioprocess Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Lisa A Pieper
- Institute of Cell Biology and Immunology, University of Stuttgart, Stuttgart, Germany
| | - Juergen Fieder
- Early Stage Bioprocess Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Martin Gamer
- Early Stage Bioprocess Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Ingo Gorr
- Early Stage Bioprocess Development, Boehringer Ingelheim GmbH & Co. KG, Birkendorfer Strasse 65, 88397, Biberach, Germany
| | - Patrick Schulz
- Cell Culture Development CMB, Boehringer Ingelheim GmbH & Co. KG, Biberach, Germany
| | - Harald Bradl
- Cell Culture Development CMB, Boehringer Ingelheim GmbH & Co. KG, Biberach, Germany
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11
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mTORC1 signalling and eIF4E/4E-BP1 translation initiation factor stoichiometry influence recombinant protein productivity from GS-CHOK1 cells. Biochem J 2016; 473:4651-4664. [PMID: 27760840 PMCID: PMC5147049 DOI: 10.1042/bcj20160845] [Citation(s) in RCA: 41] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2016] [Revised: 10/17/2016] [Accepted: 10/19/2016] [Indexed: 12/14/2022]
Abstract
Many protein-based biotherapeutics are produced in cultured Chinese hamster ovary (CHO) cell lines. Recent reports have demonstrated that translation of recombinant mRNAs and global control of the translation machinery via mammalian target of rapamycin (mTOR) signalling are important determinants of the amount and quality of recombinant protein such cells can produce. mTOR complex 1 (mTORC1) is a master regulator of cell growth/division, ribosome biogenesis and protein synthesis, but the relationship between mTORC1 signalling, cell growth and proliferation and recombinant protein yields from mammalian cells, and whether this master regulating signalling pathway can be manipulated to enhance cell biomass and recombinant protein production (rPP) are not well explored. We have investigated mTORC1 signalling and activity throughout batch culture of a panel of sister recombinant glutamine synthetase-CHO cell lines expressing different amounts of a model monoclonal IgG4, to evaluate the links between mTORC1 signalling and cell proliferation, autophagy, recombinant protein expression, global protein synthesis and mRNA translation initiation. We find that the expression of the mTORC1 substrate 4E-binding protein 1 (4E-BP1) fluctuates throughout the course of cell culture and, as expected, that the 4E-BP1 phosphorylation profiles change across the culture. Importantly, we find that the eIF4E/4E-BP1 stoichiometry positively correlates with cell productivity. Furthermore, eIF4E amounts appear to be co-regulated with 4E-BP1 amounts. This may reflect a sensing of either change at the mRNA level as opposed to the protein level or the fact that the phosphorylation status, as well as the amount of 4E-BP1 present, is important in the co-regulation of eIF4E and 4E-BP1.
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12
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Gu L, Frommel SC, Oakes CC, Simon R, Grupp K, Gerig CY, Bär D, Robinson MD, Baer C, Weiss M, Gu Z, Schapira M, Kuner R, Sültmann H, Provenzano M, Yaspo ML, Brors B, Korbel J, Schlomm T, Sauter G, Eils R, Plass C, Santoro R. BAZ2A (TIP5) is involved in epigenetic alterations in prostate cancer and its overexpression predicts disease recurrence. Nat Genet 2014; 47:22-30. [PMID: 25485837 DOI: 10.1038/ng.3165] [Citation(s) in RCA: 110] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2014] [Accepted: 11/17/2014] [Indexed: 12/14/2022]
Abstract
Prostate cancer is driven by a combination of genetic and/or epigenetic alterations. Epigenetic alterations are frequently observed in all human cancers, yet how aberrant epigenetic signatures are established is poorly understood. Here we show that the gene encoding BAZ2A (TIP5), a factor previously implicated in epigenetic rRNA gene silencing, is overexpressed in prostate cancer and is paradoxically involved in maintaining prostate cancer cell growth, a feature specific to cancer cells. BAZ2A regulates numerous protein-coding genes and directly interacts with EZH2 to maintain epigenetic silencing at genes repressed in metastasis. BAZ2A overexpression is tightly associated with a molecular subtype displaying a CpG island methylator phenotype (CIMP). Finally, high BAZ2A levels serve as an independent predictor of biochemical recurrence in a cohort of 7,682 individuals with prostate cancer. This work identifies a new aberrant role for the epigenetic regulator BAZ2A, which can also serve as a useful marker for metastatic potential in prostate cancer.
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Affiliation(s)
- Lei Gu
- 1] Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Heidelberg, Germany. [2] Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Sandra C Frommel
- 1] Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland. [2] Molecular Life Science Program, Life Science Zurich Graduate School, University of Zurich, Zurich, Switzerland
| | - Christopher C Oakes
- Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Ronald Simon
- Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Katharina Grupp
- Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Cristina Y Gerig
- Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland
| | - Dominik Bär
- Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland
| | - Mark D Robinson
- 1] Institute of Molecular Life Sciences, University of Zurich, Zurich, Switzerland. [2] Swiss Institute of Bioinformatics (SIB), University of Zurich, Zurich, Switzerland
| | - Constance Baer
- Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Melanie Weiss
- Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Zuguang Gu
- Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Matthieu Schapira
- Department of Pharmacology and Toxicology, University of Toronto, Toronto, Ontario, Canada
| | - Ruprecht Kuner
- Unit of Cancer Genome Research, German Cancer Research Center (DKFZ) and National Center of Tumour Diseases, Heidelberg, Germany
| | - Holger Sültmann
- Unit of Cancer Genome Research, German Cancer Research Center (DKFZ) and National Center of Tumour Diseases, Heidelberg, Germany
| | - Maurizio Provenzano
- Oncology Research Unit, Division of Urology, University Hospital of Zurich, Zurich, Switzerland
| | | | | | - Benedikt Brors
- Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Jan Korbel
- Genome Biology Unit, European Molecular Biology Laboratory (EMBL), Heidelberg, Germany
| | - Thorsten Schlomm
- Martini Clinic, Prostate Cancer Center, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Guido Sauter
- Institute of Pathology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
| | - Roland Eils
- 1] Division of Theoretical Bioinformatics, German Cancer Research Center (DKFZ), Heidelberg, Germany. [2] Department for Bioinformatics and Functional Genomics, Institute for Pharmacy and Molecular Biotechnology (IPMB) and BioQuant, Heidelberg University, Heidelberg, Germany
| | - Christoph Plass
- Division of Epigenomics and Cancer Risk Factors, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - Raffaella Santoro
- Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland
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13
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Role of epigenetics in expression of recombinant proteins from mammalian cells. ACTA ACUST UNITED AC 2014. [DOI: 10.4155/pbp.14.47] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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14
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Abstract
Chromatin immunoprecipitation (ChIP) is a powerful method that allows to probe specific protein-DNA interactions in vivo and to estimate the occupancy of proteins at specific sites of the genome. However, the traditional ChIP assay is not able to distinguish whether repeats that share identical sequences display a different composition of associated factors and, consequently, different functions. The ChIP-chop method provides a useful application to analyze the interaction of proteins with repetitive sequences based on their CpG methylation content. The detailed ChIP-chop protocol that serves to determine the chromatin composition of active and silent ribosomal RNA (rRNA) genes, repeats that share identical sequences but display distinct functions and chromatin compositions, is reported here.
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Affiliation(s)
- Raffaella Santoro
- Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland
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15
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Carroll AJ. The Arabidopsis Cytosolic Ribosomal Proteome: From form to Function. FRONTIERS IN PLANT SCIENCE 2013; 4:32. [PMID: 23459595 PMCID: PMC3585428 DOI: 10.3389/fpls.2013.00032] [Citation(s) in RCA: 53] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/01/2012] [Accepted: 02/10/2013] [Indexed: 05/20/2023]
Abstract
The cytosolic ribosomal proteome of Arabidopsis thaliana has been studied intensively by a range of proteomics approaches and is now one of the most well characterized eukaryotic ribosomal proteomes. Plant cytosolic ribosomes are distinguished from other eukaryotic ribosomes by unique proteins, unique post-translational modifications and an abundance of ribosomal proteins for which multiple divergent paralogs are expressed and incorporated. Study of the A. thaliana ribosome has now progressed well beyond a simple cataloging of protein parts and is focused strongly on elucidating the functions of specific ribosomal proteins, their paralogous isoforms and covalent modifications. This review summarises current knowledge concerning the Arabidopsis cytosolic ribosomal proteome and highlights potentially fruitful areas of future research in this fast moving and important area.
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Affiliation(s)
- Adam J. Carroll
- Australian Research Council Centre of Excellence in Plant Energy Biology, Australian National UniversityCanberra, ACT, Australia
- *Correspondence: Adam J. Carroll, Australian Research Council Centre of Excellence in Plant Energy Biology, Australian National University, ACT 0200, Canberra, Australia. e-mail:
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16
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Guetg C, Scheifele F, Rosenthal F, Hottiger MO, Santoro R. Inheritance of silent rDNA chromatin is mediated by PARP1 via noncoding RNA. Mol Cell 2012; 45:790-800. [PMID: 22405650 DOI: 10.1016/j.molcel.2012.01.024] [Citation(s) in RCA: 121] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2011] [Revised: 11/14/2011] [Accepted: 01/10/2012] [Indexed: 01/13/2023]
Abstract
Faithful propagation of specific chromatin states requires re-establishment of epigenetic marks after every cell division. How the original epigenetic signature is inherited after disruption during DNA replication is still poorly understood. Here, we show that the poly(ADP-ribose)-polymerase-1 (PARP1/ARTD1) is implicated in the maintenance of silent rDNA chromatin during cell division. We demonstrate that PARP1 associates with TIP5, a subunit of the NoRC complex, via the noncoding pRNA and binds to silent rRNA genes after their replication in mid-late S phase. PARP1 represses rRNA transcription and is implicated in the formation of silent rDNA chromatin. Silent rDNA chromatin is a specific substrate for ADP-ribosylation and the enzymatic activity of PARP1 is necessary to establish rDNA silencing. The data unravel a function of PARP1 and ADP-ribosylation that serves to allow for the inheritance of silent chromatin structures, shedding light on how epigenetic marks are transmitted during each cell cycle.
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Affiliation(s)
- Claudio Guetg
- Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Winterthurerstrasse 190, 8057 Zurich, Switzerland
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17
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Zhai N, Zhao ZL, Cheng MB, Di YW, Yan HX, Cao CY, Dai H, Zhang Y, Shen YF. Human PIH1 associates with histone H4 to mediate the glucose-dependent enhancement of pre-rRNA synthesis. J Mol Cell Biol 2012; 4:231-41. [PMID: 22368283 DOI: 10.1093/jmcb/mjs003] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Ribosome biogenesis is critical in the growth of eukaryotic cells, in which the synthesis of precursor ribosomal RNA is the first and rate-limiting step. Here, we show that human PIH1 domain-containing protein 1 (PIH1) interacts directly with histone H4 and recruits the Brg1-SWI/SNF complex via SNF5 to human rRNA genes. This process is likely involved in PIH1-dependent DNase I-hypersensitive chromatin remodeling at the core promoter of the rRNA genes. PIH1 mediates the occupancy of not only the Brg1 complex but also the Pol I complex at the core promoter and enhances transcription initiation of rRNA genes. Additionally, the interaction between PIH1 and H4K16 expels TIP5, a component of the silencing nucleolar remodeling complex (NoRC), from the core region, suggesting that PIH1 is involved in the derepression of NoRC-silenced rRNA genes. These data indicate that PIH1 is a positive regulator of human rRNA genes and is of great importance for the recovery of human cells from nutrient starvation and the transition to glucose-induced exponential growth in vivo.
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Affiliation(s)
- Niu Zhai
- Department of Biochemistry and Molecular Biology, National Laboratory of Medical Molecular Biology, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences and Peking Union Medical College, 5 Dongdan Santiao, Beijing 100005, China
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18
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Pietrzak M, Rempala G, Nelson PT, Zheng JJ, Hetman M. Epigenetic silencing of nucleolar rRNA genes in Alzheimer's disease. PLoS One 2011; 6:e22585. [PMID: 21799908 PMCID: PMC3142181 DOI: 10.1371/journal.pone.0022585] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2010] [Accepted: 06/30/2011] [Indexed: 11/25/2022] Open
Abstract
Background Ribosomal deficits are documented in mild cognitive impairment (MCI), which often represents an early stage Alzheimer's disease (AD), as well as in advanced AD. The nucleolar rRNA genes (rDNA), transcription of which is critical for ribosomal biogenesis, are regulated by epigenetic silencing including promoter CpG methylation. Methodology/Principal Findings To assess whether CpG methylation of the rDNA promoter was dysregulated across the AD spectrum, we analyzed brain samples from 10 MCI-, 23 AD-, and, 24 age-matched control individuals using bisulfite mapping. The rDNA promoter became hypermethylated in cerebro-cortical samples from MCI and AD groups. In parietal cortex, the rDNA promoter was hypermethylated more in MCI than in advanced AD. The cytosine methylation of total genomic DNA was similar in AD, MCI, and control samples. Consistent with a notion that hypermethylation-mediated silencing of the nucleolar chromatin stabilizes rDNA loci, preventing their senescence-associated loss, genomic rDNA content was elevated in cerebrocortical samples from MCI and AD groups. Conclusions/Significance In conclusion, rDNA hypermethylation could be a new epigenetic marker of AD. Moreover, silencing of nucleolar chromatin may occur during early stages of AD pathology and play a role in AD-related ribosomal deficits and, ultimately, dementia.
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Affiliation(s)
- Maciej Pietrzak
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, Kentucky United States of America
| | - Grzegorz Rempala
- Department of Biostatistics, Medical College of Georgia, Augusta, Georgia, United States of America
| | - Peter T. Nelson
- Sanders-Brown Center on Aging, University of Kentucky, Lexington, Kentucky, United States of America
| | - Jing-Juan Zheng
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, Kentucky United States of America
| | - Michal Hetman
- Department of Neurological Surgery and Kentucky Spinal Cord Injury Research Center, University of Louisville, Louisville, Kentucky United States of America
- Department of Pharmacology and Toxicology, University of Louisville, Louisville, Kentucky United States of America
- * E-mail:
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Dreesen IAJ, Fussenegger M. Ectopic expression of human mTOR increases viability, robustness, cell size, proliferation, and antibody production of chinese hamster ovary cells. Biotechnol Bioeng 2010; 108:853-66. [PMID: 21404259 DOI: 10.1002/bit.22990] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/16/2010] [Revised: 10/11/2010] [Accepted: 10/18/2010] [Indexed: 01/14/2023]
Abstract
Engineering of mammalian production cell lines to improve titer and quality of biopharmaceuticals is a top priority of the biopharmaceutical manufacturing industry providing protein therapeutics to patients worldwide. While many engineering strategies have been successful in the past decade they were often based on the over-expression of a single transgene and therefore limited to addressing a single bottleneck in the cell's production capacity. We provide evidence that ectopic expression of the global metabolic sensor and processing protein mammalian target of rapamycin (mTOR), simultaneously improves key bioprocess-relevant characteristics of Chinese hamster ovary (CHO) cell-derived production cell lines such as cell growth (increased cell size and protein content), proliferation (increased cell-cycle progression), viability (decreased apoptosis), robustness (decreased sensitivity to sub-optimal growth factor and oxygen supplies) and specific productivity of secreted human glycoproteins. Cultivation of mTOR-transgenic CHO-derived cell lines engineered for secretion of a therapeutic IgG resulted in antibody titers of up to 50 pg/cell/day, which represents a four-fold increase compared to the parental production cell line. mTOR-based engineering of mammalian production cell lines may therefore have a promising future in biopharmaceutical manufacturing of human therapeutic proteins.
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Affiliation(s)
- Imke A J Dreesen
- Department of Biosystems Science and Engineering, ETH Zurich, Mattenstrasse 26, CH-4058 Basel, Switzerland
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RNA Interference in Pigs: Comparison of RNAi Test Systems and Expression Vectors. Mol Biotechnol 2010; 48:38-48. [DOI: 10.1007/s12033-010-9346-6] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
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21
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The NoRC complex mediates the heterochromatin formation and stability of silent rRNA genes and centromeric repeats. EMBO J 2010; 29:2135-46. [PMID: 20168299 DOI: 10.1038/emboj.2010.17] [Citation(s) in RCA: 141] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2009] [Accepted: 01/26/2010] [Indexed: 11/08/2022] Open
Abstract
Maintenance of specific heterochromatic domains is crucial for genome stability. In eukaryotic cells, a fraction of the tandem-repeated ribosomal RNA (rRNA) genes is organized in the heterochromatic structures. The principal determinant of rDNA silencing is the nucleolar remodelling complex, NoRC, that consists of TIP5 (TTF-1-interacting protein-5) and the ATPase SNF2h. Here we showed that TIP5 not only mediates the establishment of rDNA silencing but also the formation of perinucleolar heterochromatin that contains centric and pericentric repeats. Our data indicated that the TIP5-mediated heterochromatin is indispensable for stability of silent rRNA genes and of major and minor satellite repeats. Moreover, depletion of TIP5 impairs rDNA silencing, upregulates rDNA transcription levels and induces cell transformation. These findings point to a role of TIP5 in protecting genome stability and suggest that it can play a role in the cellular transformation process.
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