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Loss of adipose TET proteins enhances β-adrenergic responses and protects against obesity by epigenetic regulation of β3-AR expression. Proc Natl Acad Sci U S A 2022; 119:e2205626119. [PMID: 35737830 PMCID: PMC9245707 DOI: 10.1073/pnas.2205626119] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
β-adrenergic receptor (β-AR) signaling plays predominant roles in modulating energy expenditure by triggering lipolysis and thermogenesis in adipose tissue, thereby conferring obesity resistance. Obesity is associated with diminished β3-adrenergic receptor (β3-AR) expression and decreased β-adrenergic responses, but the molecular mechanism coupling nutrient overload to catecholamine resistance remains poorly defined. Ten-eleven translocation (TET) proteins are dioxygenases that alter the methylation status of DNA by oxidizing 5-methylcytosine to 5-hydroxymethylcytosine and further oxidized derivatives. Here, we show that TET proteins are pivotal epigenetic suppressors of β3-AR expression in adipocytes, thereby attenuating the responsiveness to β-adrenergic stimulation. Deletion of all three Tet genes in adipocytes led to increased β3-AR expression and thereby enhanced the downstream β-adrenergic responses, including lipolysis, thermogenic gene induction, oxidative metabolism, and fat browning in vitro and in vivo. In mouse adipose tissues, Tet expression was elevated after mice ate a high-fat diet. Mice with adipose-specific ablation of all TET proteins maintained higher levels of β3-AR in both white and brown adipose tissues and remained sensitive to β-AR stimuli under high-fat diet challenge, leading to augmented energy expenditure and decreased fat accumulation. Consequently, they exhibited improved cold tolerance and were substantially protected from diet-induced obesity, inflammation, and metabolic complications, including insulin resistance and hyperlipidemia. Mechanistically, TET proteins directly repressed β3-AR transcription, mainly in an enzymatic activity-independent manner, and involved the recruitment of histone deacetylases to increase deacetylation of its promoter. Thus, the TET-histone deacetylase-β3-AR axis could be targeted to treat obesity and related metabolic diseases.
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Bellefroid M, Rodari A, Galais M, Krijger PHL, Tjalsma SJD, Nestola L, Plant E, Vos ESM, Cristinelli S, Van Driessche B, Vanhulle C, Ait-Ammar A, Burny A, Ciuffi A, de Laat W, Van Lint C. Role of the cellular factor CTCF in the regulation of bovine leukemia virus latency and three-dimensional chromatin organization. Nucleic Acids Res 2022; 50:3190-3202. [PMID: 35234910 PMCID: PMC8989512 DOI: 10.1093/nar/gkac107] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2021] [Revised: 01/31/2022] [Accepted: 02/05/2022] [Indexed: 01/12/2023] Open
Abstract
Bovine leukemia virus (BLV)-induced tumoral development is a multifactorial phenomenon that remains incompletely understood. Here, we highlight the critical role of the cellular CCCTC-binding factor (CTCF) both in the regulation of BLV transcriptional activities and in the deregulation of the three-dimensional (3D) chromatin architecture surrounding the BLV integration site. We demonstrated the in vivo recruitment of CTCF to three conserved CTCF binding motifs along the provirus. Next, we showed that CTCF localized to regions of transitions in the histone modifications profile along the BLV genome and that it is implicated in the repression of the 5′Long Terminal Repeat (LTR) promoter activity, thereby contributing to viral latency, while favoring the 3′LTR promoter activity. Finally, we demonstrated that BLV integration deregulated the host cellular 3D chromatin organization through the formation of viral/host chromatin loops. Altogether, our results highlight CTCF as a new critical effector of BLV transcriptional regulation and BLV-induced physiopathology.
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Affiliation(s)
- Maxime Bellefroid
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Anthony Rodari
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Mathilde Galais
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Peter H L Krijger
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht 3584, CT, The Netherlands
| | - Sjoerd J D Tjalsma
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht 3584, CT, The Netherlands
| | - Lorena Nestola
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Estelle Plant
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Erica S M Vos
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht 3584, CT, The Netherlands
| | - Sara Cristinelli
- Institute of Microbiology, Lausanne University Hospital, University of Lausanne, Lausanne 1011, Switzerland
| | - Benoit Van Driessche
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Caroline Vanhulle
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Amina Ait-Ammar
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Arsène Burny
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
| | - Angela Ciuffi
- Institute of Microbiology, Lausanne University Hospital, University of Lausanne, Lausanne 1011, Switzerland
| | - Wouter de Laat
- Oncode Institute, Hubrecht Institute-KNAW and University Medical Center Utrecht, Utrecht 3584, CT, The Netherlands
| | - Carine Van Lint
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Gosselies 6041, Belgium
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Casale AM, Cappucci U, Piacentini L. Unravelling HP1 functions: post-transcriptional regulation of stem cell fate. Chromosoma 2021; 130:103-111. [PMID: 34128099 PMCID: PMC8426308 DOI: 10.1007/s00412-021-00760-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2021] [Revised: 05/17/2021] [Accepted: 06/01/2021] [Indexed: 12/20/2022]
Abstract
Heterochromatin protein 1 (HP1) is a non-histone chromosomal protein first identified in Drosophila as a major component of constitutive heterochromatin, required for stable epigenetic gene silencing in many species including humans. Over the years, several studies have highlighted additional roles of HP1 in different cellular processes including telomere maintenance, DNA replication and repair, chromosome segregation and, surprisingly, positive regulation of gene expression. In this review, we briefly summarize past research and recent results supporting the unexpected and emerging role of HP1 in activating gene expression. In particular, we discuss the role of HP1 in post-transcriptional regulation of mRNA processing because it has proved decisive in the control of germline stem cells homeostasis in Drosophila and has certainly added a new dimension to our understanding on HP1 targeting and functions in epigenetic regulation of stem cell behaviour.
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Affiliation(s)
- Assunta Maria Casale
- Department of Biology and Biotechnology "C. Darwin", Sapienza University of Rome, Rome, Italy.
| | - Ugo Cappucci
- Department of Biology and Biotechnology "C. Darwin", Sapienza University of Rome, Rome, Italy
| | - Lucia Piacentini
- Department of Biology and Biotechnology "C. Darwin", Sapienza University of Rome, Rome, Italy.
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Fauquenoy S, Robette G, Kula A, Vanhulle C, Bouchat S, Delacourt N, Rodari A, Marban C, Schwartz C, Burny A, Rohr O, Van Driessche B, Van Lint C. Repression of Human T-lymphotropic virus type 1 Long Terminal Repeat sense transcription by Sp1 recruitment to novel Sp1 binding sites. Sci Rep 2017; 7:43221. [PMID: 28256531 PMCID: PMC5335701 DOI: 10.1038/srep43221] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/01/2016] [Accepted: 01/20/2017] [Indexed: 02/07/2023] Open
Abstract
Human T-lymphotropic Virus type 1 (HTLV-1) infection is characterized by viral latency in the majority of infected cells and by the absence of viremia. These features are thought to be due to the repression of viral sense transcription in vivo. Here, our in silico analysis of the HTLV-1 Long Terminal Repeat (LTR) promoter nucleotide sequence revealed, in addition to the four Sp1 binding sites previously identified, the presence of two additional potential Sp1 sites within the R region. We demonstrated that the Sp1 and Sp3 transcription factors bound in vitro to these two sites and compared the binding affinity for Sp1 of all six different HTLV-1 Sp1 sites. By chromatin immunoprecipitation experiments, we showed Sp1 recruitment in vivo to the newly identified Sp1 sites. We demonstrated in the nucleosomal context of an episomal reporter vector that the Sp1 sites interfered with both the sense and antisense LTR promoter activities. Interestingly, the Sp1 sites exhibited together a repressor effect on the LTR sense transcriptional activity but had no effect on the LTR antisense activity. Thus, our results demonstrate the presence of two new functional Sp1 binding sites in the HTLV-1 LTR, which act as negative cis-regulatory elements of sense viral transcription.
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Affiliation(s)
- Sylvain Fauquenoy
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Gwenaëlle Robette
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Anna Kula
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Caroline Vanhulle
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Sophie Bouchat
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Nadège Delacourt
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Anthony Rodari
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Céline Marban
- Biomaterials and Bioengineering, Inserm UMR 1121, Faculty of Dentistry, University of Strasbourg, France
| | - Christian Schwartz
- Institut Universitaire de Technologie Louis Pasteur, University of Strasbourg, Schiltigheim, France
- Laboratory of Dynamic of Host-Pathogen Interactions (DHPI), EA7292, University of Strasbourg, Strasbourg, France
| | - Arsène Burny
- Laboratory of Experimental Hematology, Institut Jules Bordet, Université Libre de Bruxelles (ULB), Brussels, Belgium
| | - Olivier Rohr
- Institut Universitaire de Technologie Louis Pasteur, University of Strasbourg, Schiltigheim, France
- Laboratory of Dynamic of Host-Pathogen Interactions (DHPI), EA7292, University of Strasbourg, Strasbourg, France
| | - Benoit Van Driessche
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Carine Van Lint
- Service of Molecular Virology, Department of Molecular Biology (DBM), Université Libre de Bruxelles (ULB), Rue des Professeurs Jeener et Brachet 12, 6041 Gosselies, Belgium
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Characterization of new RNA polymerase III and RNA polymerase II transcriptional promoters in the Bovine Leukemia Virus genome. Sci Rep 2016; 6:31125. [PMID: 27545598 PMCID: PMC4992882 DOI: 10.1038/srep31125] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2016] [Accepted: 07/11/2016] [Indexed: 12/23/2022] Open
Abstract
Bovine leukemia virus latency is a viral strategy used to escape from the host immune system and contribute to tumor development. However, a highly expressed BLV micro-RNA cluster has been reported, suggesting that the BLV silencing is not complete. Here, we demonstrate the in vivo recruitment of RNA polymerase III to the BLV miRNA cluster both in BLV-latently infected cell lines and in ovine BLV-infected primary cells, through a canonical type 2 RNAPIII promoter. Moreover, by RPC6-knockdown, we showed a direct functional link between RNAPIII transcription and BLV miRNAs expression. Furthermore, both the tumor- and the quiescent-related isoforms of RPC7 subunits were recruited to the miRNA cluster. We showed that the BLV miRNA cluster was enriched in positive epigenetic marks. Interestingly, we demonstrated the in vivo recruitment of RNAPII at the 3′LTR/host genomic junction, associated with positive epigenetic marks. Functionally, we showed that the BLV LTR exhibited a strong antisense promoter activity and identified cis-acting elements of an RNAPII-dependent promoter. Finally, we provided evidence for an in vivo collision between RNAPIII and RNAPII convergent transcriptions. Our results provide new insights into alternative ways used by BLV to counteract silencing of the viral 5′LTR promoter.
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Abstract
Trans-inactivation is the repression of genes on a normal chromosome under the influence of a rearranged homologous chromosome demonstrating the position effect variegation (PEV). This phenomenon was studied in detail on the example of brownDominant allele causing the repression of wild-type brown gene on the opposite chromosome. We have investigated another trans-inactivation-inducing chromosome rearrangement, In(2)A4 inversion. In both cases, brownDominant and In(2)A4, the repression seems to be the result of dragging of the euchromatic region of the normal chromosome into the heterochromatic environment. It was found that cis-inactivation (classical PEV) and trans-inactivation show different patterns of distribution along the chromosome and respond differently to PEV modifying genes. It appears that the causative mechanism of trans-inactivation is de novo heterochromatin assembly on euchromatic sequences dragged into the heterochromatic nuclear compartment. Trans-inactivation turns out to be the result of a combination of heterochromatin-induced position effect and the somatic interphase chromosome pairing that is widespread in Diptera.
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Affiliation(s)
- Aleksei S Shatskikh
- a Department of Molecular Genetics of the Cell , Institute of Molecular Genetics, Russian Academy of Science , Moscow , Russia
| | - Yuriy A Abramov
- a Department of Molecular Genetics of the Cell , Institute of Molecular Genetics, Russian Academy of Science , Moscow , Russia
| | - Sergey A Lavrov
- a Department of Molecular Genetics of the Cell , Institute of Molecular Genetics, Russian Academy of Science , Moscow , Russia
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Han P, Li W, Lin CH, Yang J, Shang C, Nuernberg ST, Jin KK, Xu W, Lin CY, Lin CJ, Xiong Y, Chien H, Zhou B, Ashley E, Bernstein D, Chen PS, Chen HSV, Quertermous T, Chang CP. A long noncoding RNA protects the heart from pathological hypertrophy. Nature 2014; 514:102-106. [PMID: 25119045 PMCID: PMC4184960 DOI: 10.1038/nature13596] [Citation(s) in RCA: 570] [Impact Index Per Article: 57.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/25/2013] [Accepted: 06/17/2014] [Indexed: 01/23/2023]
Abstract
The role of long noncoding RNA (lncRNA) in adult hearts is unknown; also unclear is how lncRNA modulates nucleosome remodeling. An estimated 70% of mouse genes undergo antisense transcription1, including myosin heavy chain 7 (Myh7) that encodes molecular motor proteins for heart contraction2. Here, we identify a cluster of lncRNA transcripts from Myh7 loci and show a new lncRNA–chromatin mechanism for heart failure. In mice, these transcripts, which we named Myosin Heavy Chain Associated RNA Transcripts (MyHEART or Mhrt), are cardiac-specific and abundant in adult hearts. Pathological stress activates the Brg1-Hdac-Parp chromatin repressor complex3 to inhibit Mhrt transcription in the heart. Such stress-induced Mhrt repression is essential for cardiomyopathy to develop: restoring Mhrt to the pre-stress level protects the heart from hypertrophy and failure. Mhrt antagonizes the function of Brg1, a chromatin-remodeling factor that is activated by stress to trigger aberrant gene expression and cardiac myopathy3. Mhrt prevents Brg1 from recognizing its genomic DNA targets, thus inhibiting chromatin targeting and gene regulation by Brg1. Mhrt binds to the helicase domain of Brg1, and this domain is crucial for tethering Brg1 to chromatinized DNA targets. Brg1 helicase has dual nucleic acid-binding specificities: it is capable of binding lncRNA (Mhrt) and chromatinized—but not naked—DNA. This dual-binding feature of helicase enables a competitive inhibition mechanism by which Mhrt sequesters Brg1 from its genomic DNA targets to prevent chromatin remodeling. A Mhrt-Brg1 feedback circuit is thus crucial for heart function. Human MHRT also originates from MYH7 loci and is repressed in various types of myopathic hearts, suggesting a conserved lncRNA mechanism in human cardiomyopathy. Our studies identify the first cardioprotective lncRNA, define a new targeting mechanism for ATP-dependent chromatin-remodeling factors, and establish a new paradigm for lncRNA–chromatin interaction.
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Affiliation(s)
- Pei Han
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305.,Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine
| | - Wei Li
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Chiou-Hong Lin
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Jin Yang
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305.,Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine
| | - Ching Shang
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Sylvia T Nuernberg
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Kevin Kai Jin
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Weihong Xu
- Stanford Genome Technology Center, Stanford University School of Medicine, Stanford, CA 94305
| | - Chieh-Yu Lin
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Chien-Jung Lin
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Yiqin Xiong
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Huanchieh Chien
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Bin Zhou
- Department of Genetics, Pediatrics, and Medicine (Cardiology), Albert Einstein College of Medicine of Yeshiva University, 1301 Morris Park Avenue, Price Center 420, Bronx, NY 10461
| | - Euan Ashley
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Daniel Bernstein
- Department of Pediatrics, Stanford University School of Medicine, Stanford, CA 94305
| | - Peng-Sheng Chen
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine
| | - Huei-Sheng Vincent Chen
- Del E. Webb Neuroscience, Aging & Stem Cell Research Center, Sanford/Burnham Medical Research Institute, La Jolla, California 92037
| | - Thomas Quertermous
- Division of Cardiovascular Medicine, Cardiovascular Institute, Stanford University School of Medicine, Stanford, CA 94305
| | - Ching-Pin Chang
- Krannert Institute of Cardiology and Division of Cardiology, Department of Medicine.,Department of Biochemistry and Molecular Biology.,Department of Medical and Molecular Genetics, Indiana University School of Medicine, Indianapolis, IN 46202, USA
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CtBP and associated LSD1 are required for transcriptional activation by NeuroD1 in gastrointestinal endocrine cells. Mol Cell Biol 2014; 34:2308-17. [PMID: 24732800 DOI: 10.1128/mcb.01600-13] [Citation(s) in RCA: 52] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Gene expression programs required for differentiation depend on both DNA-bound transcription factors and surrounding histone modifications. Expression of the basic helix-loop-helix (bHLH) protein NeuroD1 is restricted to endocrine cells in the gastrointestinal (GI) tract, where it is important for endocrine differentiation. RREB1 (RAS-responsive element binding protein 1), identified as a component of the CtBP corepressor complex, binds to nearby DNA elements to associate with NeuroD and potentiate transcription of a NeuroD1 target gene. Transcriptional activation by RREB1 depends on recruitment of CtBP with its associated proteins, including LSD1, through its PXDLS motifs. The mechanism of transcriptional activation by CtBP has not been previously characterized. Here we found that activation was dependent on the histone H3 lysine 9 (H3K9) demethylase activity of LSD1, which removes repressive methyl marks from dimethylated H3K9 (H3K9Me2), to facilitate subsequent H3K9 acetylation by the NeuroD1-associated histone acetyltransferase, P300/CBP-associated factor (PCAF). The secretin, β-glucokinase, insulin I, and insulin II genes, four known direct targets of NeuroD1 in intestinal and pancreatic endocrine cells, all show similar promoter occupancy by CtBP-associated proteins and PCAF, with acetylation of H3K9. This work may indicate a mechanism for selective regulation of transcription by CtBP and LSD1 involving their association with specific transcription factors and cofactors to drive tissue-specific transcription.
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Choi WI, Jeon BN, Yoon JH, Koh DI, Kim MH, Yu MY, Lee KM, Kim Y, Kim K, Hur SS, Lee CE, Kim KS, Hur MW. The proto-oncoprotein FBI-1 interacts with MBD3 to recruit the Mi-2/NuRD-HDAC complex and BCoR and to silence p21WAF/CDKN1A by DNA methylation. Nucleic Acids Res 2013; 41:6403-20. [PMID: 23658227 PMCID: PMC3711425 DOI: 10.1093/nar/gkt359] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
The tumour-suppressor gene CDKN1A (encoding p21Waf/Cip1) is thought to be epigenetically repressed in cancer cells. FBI-1 (ZBTB7A) is a proto-oncogenic transcription factor repressing the alternative reading frame and p21WAF/CDKN1A genes of the p53 pathway. FBI-1 interacts directly with MBD3 (methyl-CpG–binding domain protein 3) in the nucleus. We demonstrated that FBI-1 binds both non-methylated and methylated DNA and that MBD3 is recruited to the CDKN1A promoter through its interaction with FBI-1, where it enhances transcriptional repression by FBI-1. FBI-1 also interacts with the co-repressors nuclear receptor corepressor (NCoR), silencing mediator for retinoid and thyroid receptors (SMRT) and BCL-6 corepressor (BCoR) to repress transcription. MBD3 regulates a molecular interaction between the co-repressor and FBI-1. MBD3 decreases the interaction between FBI-1 and NCoR/SMRT but increases the interaction between FBI-1 and BCoR. Because MBD3 is a subunit of the Mi-2 autoantigen (Mi-2)/nucleosome remodelling and histone deacetylase (NuRD)-HDAC complex, FBI-1 recruits the Mi-2/NuRD-HDAC complex via MBD3. BCoR interacts with the Mi-2/NuRD-HDAC complex, DNMTs and HP1. MBD3 and BCoR play a significant role in the recruitment of the Mi-2/NuRD-HDAC complex– and the NuRD complex–associated proteins, DNMTs and HP. By recruiting DNMTs and HP1, Mi-2/NuRD-HDAC complex appears to play key roles in epigenetic repression of CDKN1A by DNA methylation.
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Affiliation(s)
- Won-Il Choi
- Department of Biochemistry and Molecular Biology, BK21 Project for Medical Science, Severance Biomedical Research Institute, Yonsei University School of Medicine, 50 Yonsei-Ro, SeoDaeMoon-Gu, Seoul, 120-752, Korea
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Delcuve GP, Khan DH, Davie JR. Targeting class I histone deacetylases in cancer therapy. Expert Opin Ther Targets 2012; 17:29-41. [PMID: 23062071 DOI: 10.1517/14728222.2013.729042] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
INTRODUCTION Class I histone deacetylases (HDACs) are often overexpressed in cancer, and their inhibition typically leads cancer cells, but not normal cells, to apoptosis. Hence, the field of cancer therapy has experienced a continued surge in the development of HDAC inhibitors. AREAS COVERED Class I comprises of HDAC1, 2, 3 and 8. HDAC1, 2 and 3 are active as subunits of multiprotein complexes while an HDAC8 complex has not been identified. Besides being a major contributor to poor prognosis in childhood neuroblastoma, little is known of HDAC8 functions and substrates. The targeting and activities of HDAC1 - 3 are modulated by post-translational modifications and association with numerous proteins. The composition of the various HDAC complexes is cell type dependent and fluctuates with intra- and intercellular stimuli. These HDAC complexes play roles at multiple levels in gene expression and genome stability. The application of isoform-specific HDAC inhibitors has met with varying success in clinical trials. EXPERT OPINION To elucidate the mechanism and cellular impact of HDAC inhibitors, we need to identify the spectrum of class I HDAC complexes and their functions. In the cases of HDAC1 - 3, selectivity of HDAC inhibitors should be directed against relevant complexes. HDAC8 active site unique features facilitate the design of selective inhibitors.
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Affiliation(s)
- Geneviève P Delcuve
- University of Manitoba, Manitoba Institute of Child Health, 715 McDermot Avenue, Room 600A, Winnipeg, Manitoba, R3E 3P4, Canada
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11
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Barkess G, West AG. Chromatin insulator elements: establishing barriers to set heterochromatin boundaries. Epigenomics 2012; 4:67-80. [PMID: 22332659 DOI: 10.2217/epi.11.112] [Citation(s) in RCA: 55] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Epigenomic profiling has revealed that substantial portions of genomes in higher eukaryotes are organized into extensive domains of transcriptionally repressive chromatin. The boundaries of repressive chromatin domains can be fixed by DNA elements known as barrier insulators, to both shield neighboring gene expression and to maintain the integrity of chromosomal silencing. Here, we examine the current progress in identifying vertebrate barrier elements and their binding factors. We overview the design of the reporter assays used to define enhancer-blocking and barrier insulators. We look at the mechanisms vertebrate barrier proteins, such as USF1 and VEZF1, employ to counteract Polycomb- and heterochromatin-associated repression. We also undertake a critical analysis of whether CTCF could also act as a barrier protein. There is good evidence that barrier elements in vertebrates can form repressive chromatin domain boundaries. Future studies will determine whether barriers are frequently used to define repressive domain boundaries in vertebrates.
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Affiliation(s)
- Gráinne Barkess
- Institute of Cancer Sciences, College of Medical, Veterinary & Life Sciences, University of Glasgow, Glasgow, Scotland, UK
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12
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Srinivasan A, Mishra RK. Chromatin domain boundary element search tool for Drosophila. Nucleic Acids Res 2012; 40:4385-95. [PMID: 22287636 PMCID: PMC3378885 DOI: 10.1093/nar/gks045] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Chromatin domain boundary elements prevent inappropriate interaction between distant or closely spaced regulatory elements and restrict enhancers and silencers to correct target promoters. In spite of having such a general role and expected frequent occurrence genome wide, there is no DNA sequence analysis based tool to identify boundary elements. Here, we report chromatin domain Boundary Element Search Tool (cdBEST), to identify boundary elements. cdBEST uses known recognition sequences of boundary interacting proteins and looks for ‘motif clusters’. Using cdBEST, we identified boundary sequences across 12 Drosophila species. Of the 4576 boundary sequences identified in Drosophila melanogaster genome, >170 sequences are repetitive in nature and have sequence homology to transposable elements. Analysis of such sequences across 12 Drosophila genomes showed that the occurrence of repetitive sequences in the context of boundaries is a common feature of drosophilids. We use a variety of genome organization criteria and also experimental test on a subset of the cdBEST boundaries in an enhancer-blocking assay and show that 80% of them indeed function as boundaries in vivo. These observations highlight the role of cdBEST in better understanding of chromatin domain boundaries in Drosophila and setting the stage for comparative analysis of boundaries across closely related species.
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Affiliation(s)
- Arumugam Srinivasan
- Centre for Cellular and Molecular Biology, Council for Scientific and Industrial Research (CSIR), Uppal Road, Hyderabad, 500007, India
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13
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Colin L, Dekoninck A, Reichert M, Calao M, Merimi M, Van den Broeke A, Vierendeel V, Cleuter Y, Burny A, Rohr O, Van Lint C. Chromatin disruption in the promoter of bovine leukemia virus during transcriptional activation. Nucleic Acids Res 2011; 39:9559-73. [PMID: 21890901 PMCID: PMC3239207 DOI: 10.1093/nar/gkr671] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Bovine leukemia virus expression relies on its chromatin organization after integration into the host cell genome. Proviral latency, which results from transcriptional repression in vivo, represents a viral strategy to escape the host immune system and likely allows for tumor progression. Here, we discriminated two types of latency: an easily reactivable latent state of the YR2 provirus and a ‘locked’ latent state of the L267 provirus. The defective YR2 provirus was characterized by the presence of nuclease hypersensitive sites at the U3/R junction and in the R/U5 region of the 5′-long terminal repeat (5′-LTR), whereas the L267 provirus displayed a closed chromatin configuration at the U3/R junction. Reactivation of viral expression in YR2 cells by the phorbol 12-myristate 13-acetate (PMA) plus ionomycin combination was accompanied by a rapid but transient chromatin remodeling in the 5′-LTR, leading to an increased PU.1 and USF-1/USF-2 recruitment in vivo sustained by PMA/ionomycin-mediated USF phosphorylation. In contrast, viral expression was not reactivated by PMA/ionomycin in L267 cells, because the 5′-LTR U3/R region remained inaccessible to nucleases and hypermethylated at CpG dinucleotides. Remarkably, we elucidated the BLV 5′-LTR chromatin organization in PBMCs isolated from BLV-infected cows, thereby depicting the virus hiding in vivo in its natural host.
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Affiliation(s)
- Laurence Colin
- Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
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14
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BRG1 helps RNA polymerase II to overcome a nucleosomal barrier during elongation, in vivo. EMBO Rep 2010; 11:751-7. [PMID: 20829883 DOI: 10.1038/embor.2010.131] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2010] [Revised: 07/06/2010] [Accepted: 07/27/2010] [Indexed: 11/08/2022] Open
Abstract
RNA polymerase II (RNAPII) transcribes genes in a chromatin context. We have designed a system to investigate the role of chromatin remodelling during elongation in vivo, which involves inserting a strong nucleosome-positioning sequence between a promoter and a reporter gene. Our data indicate that a nucleosome positioned in the body of a transcription unit impairs RNAPII progression, provokes RNAPII accumulation upstream to the positioned nucleosome and reduces transcription. By using this system, we show that BRG1, the enzymatic motor of the SWI-SNF chromatin-remodelling complex, is recruited to the positioned nucleosome in a transcription elongation-dependent manner and facilitates traversal of the nucleosome by RNAPII.
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15
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Pierard V, Guiguen A, Colin L, Wijmeersch G, Vanhulle C, Van Driessche B, Dekoninck A, Blazkova J, Cardona C, Merimi M, Vierendeel V, Calomme C, Nguyên TLA, Nuttinck M, Twizere JC, Kettmann R, Portetelle D, Burny A, Hirsch I, Rohr O, Van Lint C. DNA cytosine methylation in the bovine leukemia virus promoter is associated with latency in a lymphoma-derived B-cell line: potential involvement of direct inhibition of cAMP-responsive element (CRE)-binding protein/CRE modulator/activation transcription factor binding. J Biol Chem 2010; 285:19434-49. [PMID: 20413592 PMCID: PMC2885223 DOI: 10.1074/jbc.m110.107607] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2010] [Revised: 03/31/2010] [Indexed: 02/02/2023] Open
Abstract
Bovine leukemia virus (BLV) proviral latency represents a viral strategy to escape the host immune system and allow tumor development. Besides the previously demonstrated role of histone deacetylation in the epigenetic repression of BLV expression, we showed here that BLV promoter activity was induced by several DNA methylation inhibitors (such as 5-aza-2'-deoxycytidine) and that overexpressed DNMT1 and DNMT3A, but not DNMT3B, down-regulated BLV promoter activity. Importantly, cytosine hypermethylation in the 5'-long terminal repeat (LTR) U3 and R regions was associated with true latency in the lymphoma-derived B-cell line L267 but not with defective latency in YR2 cells. Moreover, the virus-encoded transactivator Tax(BLV) decreased DNA methyltransferase expression levels, which could explain the lower level of cytosine methylation observed in the L267(LTaxSN) 5'-LTR compared with the L267 5'-LTR. Interestingly, DNA methylation inhibitors and Tax(BLV) synergistically activated BLV promoter transcriptional activity in a cAMP-responsive element (CRE)-dependent manner. Mechanistically, methylation at the -154 or -129 CpG position (relative to the transcription start site) impaired in vitro binding of CRE-binding protein (CREB) transcription factors to their respective CRE sites. Methylation at -129 CpG alone was sufficient to decrease BLV promoter-driven reporter gene expression by 2-fold. We demonstrated in vivo the recruitment of CREB/CRE modulator (CREM) and to a lesser extent activating transcription factor-1 (ATF-1) to the hypomethylated CRE region of the YR2 5'-LTR, whereas we detected no CREB/CREM/ATF recruitment to the hypermethylated corresponding region in the L267 cells. Altogether, these findings suggest that site-specific DNA methylation of the BLV promoter represses viral transcription by directly inhibiting transcription factor binding, thereby contributing to true proviral latency.
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Affiliation(s)
- Valérie Pierard
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Allan Guiguen
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Laurence Colin
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Gaëlle Wijmeersch
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Caroline Vanhulle
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Benoît Van Driessche
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Ann Dekoninck
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Jana Blazkova
- the Institut de Cancérologie de Marseille, UMR 599 INSERM, Institut Paoli-Calmettes, Université de la Méditerranée, Boulevard Lei Roure 27, 13009 Marseille, France
| | - Christelle Cardona
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Makram Merimi
- the Laboratory of Experimental Hematology, Institut Jules Bordet, Université Libre de Bruxelles, Boulevard de Waterloo 121, 1000 Bruxelles, Belgium
| | - Valérie Vierendeel
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Claire Calomme
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Thi Liên-Anh Nguyên
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
| | - Michèle Nuttinck
- the Département de Biologie Moléculaire, Faculté Universitaire des Sciences Agronomiques de Gembloux, Avenue du Maréchal Juin 6, 5030 Gembloux, Belgium, and
| | - Jean-Claude Twizere
- the Département de Biologie Moléculaire, Faculté Universitaire des Sciences Agronomiques de Gembloux, Avenue du Maréchal Juin 6, 5030 Gembloux, Belgium, and
| | - Richard Kettmann
- the Département de Biologie Moléculaire, Faculté Universitaire des Sciences Agronomiques de Gembloux, Avenue du Maréchal Juin 6, 5030 Gembloux, Belgium, and
| | - Daniel Portetelle
- the Département de Biologie Moléculaire, Faculté Universitaire des Sciences Agronomiques de Gembloux, Avenue du Maréchal Juin 6, 5030 Gembloux, Belgium, and
| | - Arsène Burny
- the Département de Biologie Moléculaire, Faculté Universitaire des Sciences Agronomiques de Gembloux, Avenue du Maréchal Juin 6, 5030 Gembloux, Belgium, and
| | - Ivan Hirsch
- the Institut de Cancérologie de Marseille, UMR 599 INSERM, Institut Paoli-Calmettes, Université de la Méditerranée, Boulevard Lei Roure 27, 13009 Marseille, France
| | - Olivier Rohr
- the Institut Universitaire de Technologie Louis Pasteur de Schiltigheim, University of Strasbourg, 1 Allée d'Athènes, 67300 Schiltigheim, France
| | - Carine Van Lint
- From the Laboratoire de Virologie Moléculaire, Institut de Biologie et de Médecine Moléculaires (IBMM), Université Libre de Bruxelles, Rue des Profs Jeener et Brachet 12, 6041 Gosselies, Belgium
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16
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Evidences for insulator activity of the 5′UTR of the Drosophila melanogaster LTR-retrotransposon ZAM. Mol Genet Genomics 2010; 283:503-9. [DOI: 10.1007/s00438-010-0529-4] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2009] [Accepted: 02/28/2010] [Indexed: 10/19/2022]
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17
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Host cell detection of noncoding stuffer DNA contained in helper-dependent adenovirus vectors leads to epigenetic repression of transgene expression. J Virol 2009; 83:8409-17. [PMID: 19515759 DOI: 10.1128/jvi.00796-09] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Helper-dependent adenovirus (hdAd) vectors have shown great promise as therapeutic gene delivery vehicles in gene therapy applications. However, the level and duration of gene expression from hdAd can differ considerably depending on the nature of the noncoding stuffer DNA contained within the vector. For example, an hdAd containing 22 kb of prokaryotic DNA (hdAd-prok) expresses its transgene 60-fold less efficiently than a similar vector containing eukaryotic DNA (hdAd-euk). Here we have determined the mechanistic basis of this phenomenon. Although neither vector was subjected to CpG methylation and both genomes associated with cellular histones to similar degrees, hdAd-prok chromatin was actively deacetylated. Insertion of an insulator element between the transgene and the bacterial DNA derepressed hdAd-prok, suggesting that foreign DNA nucleates repressive chromatin structures that spread to the transgene. We found that Sp100B/Sp100HMG and Daxx play a role in repressing transgene expression from hdAd and act independently of PML bodies. Thus, we have identified nuclear factors involved in recognizing foreign DNA and have determined the mechanism by which associated genes are repressed.
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18
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Shielding of sleeping beauty DNA transposon-delivered transgene cassettes by heterologous insulators in early embryonal cells. Mol Ther 2008; 17:121-30. [PMID: 18985029 DOI: 10.1038/mt.2008.224] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The Sleeping Beauty (SB) transposon system represents an important alternative to viral integrating vector systems but may, as its viral counterparts, be subject to transcriptional silencing. To investigate shielding of SB-delivered transgene cassettes against transcriptional repression, we establish silencing assays in which SB vector-containing F9 murine teratocarcinoma cell clones are identified by strategies that include or exclude selection for transgene expression. Among clones carrying one or more SB transposon vectors, more than one-third are immediately silenced, and most of the remaining clones move toward silencing during prolonged passage. In line with the lack of an intrinsic ability of SB to resist silencing, we show that the stable transfection rate of SB vectors in F9 cells is significantly improved by flanking the transgene with heterologous 5'-HS4 chicken beta-globin (cHS4) insulators. In approaches based on drug selection and subsequent flow-cytometric detection of transgene expression, clones containing cHS4-insulated vectors are to a much higher degree protected against transcriptional silencing, resulting in long-term expression of the fluorescent marker. Our findings demonstrate that SB vectors, prone for transcriptional silencing by positional effects in F9 cells, are protected by insulators. We believe that insulated SB-derived vectors will become useful tools in transposon-based transgenesis and therapeutic gene transfer.
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19
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Dialynas GK, Vitalini MW, Wallrath LL. Linking Heterochromatin Protein 1 (HP1) to cancer progression. Mutat Res 2008; 647:13-20. [PMID: 18926834 DOI: 10.1016/j.mrfmmm.2008.09.007] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
All cells of a given organism contain nearly identical genetic information, yet tissues display unique gene expression profiles. This specificity is in part due to transcriptional control by epigenetic mechanisms that involve post-translational modifications of histones. These modifications affect the folding of the chromatin fiber and serve as binding sites for non-histone chromosomal proteins. Here we discuss functions of the Heterochromatin Protein 1 (HP1) family of proteins that recognize H3K9me, an epigenetic mark generated by the histone methyltransferases SU(VAR)3-9 and orthologues. Loss of HP1 proteins causes chromosome segregation defects and lethality in some organisms; a reduction in levels of HP1 family members is associated with cancer progression in humans. These consequences are likely due to the role of HP1 in centromere stability, telomere capping and the regulation of euchromatic and heterochromatic gene expression.
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Affiliation(s)
- George K Dialynas
- Department of Biochemistry, 3136 MERF, University of Iowa, Iowa City, IA 52242, USA
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20
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Moreira LS, de Andrade TG, Albuquerque DM, Cunha AF, Fattori A, Saad STO, Costa FF. IDENTIFICATION OF DIFFERENTIALLY EXPRESSED GENES INDUCED BY HYDROXYUREA IN RETICULOCYTES FROM SICKLE CELL ANAEMIA PATIENTS. Clin Exp Pharmacol Physiol 2008; 35:651-5. [DOI: 10.1111/j.1440-1681.2007.04861.x] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
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21
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Oh J, Sohn DH, Ko M, Chung H, Jeon SH, Seong RH. BAF60a interacts with p53 to recruit the SWI/SNF complex. J Biol Chem 2008; 283:11924-34. [PMID: 18303029 DOI: 10.1074/jbc.m705401200] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
To understand the tumor-suppressing mechanism of the SWI/SNF chromatin remodeling complex, we investigated its molecular relationship with p53. Using the pREP4-luc episomal reporter, we first demonstrated that p53 utilizes the chromatin remodeling activity of the SWI/SNF complex to initiate transcription from the chromatin-structured promoter. Among the components of the SWI/SNF complex, we identified BAF60a as a mediator of the interaction with p53 by the yeast two-hybrid assay. p53 directly interacted only with BAF60a, but not with other components of the SWI/SNF complex, such as BRG1, SRG3, SNF5, or BAF57. We found out that multiple residues at the amino acid 108-150 region of BAF60a were involved in the interaction with the tetramerization domain of p53. The N-terminal fragment of BAF60a containing the p53-interacting region as well as small interfering RNA for baf60a inhibited the SWI/SNF complex-mediated transcriptional activity of p53. The uncoupling of p53 with the SWI/SNF complex resulted in the repression of both p53-dependent apoptosis and cell cycle arrest by the regulation of target genes. These results suggest that the SWI/SNF chromatin remodeling complex is involved in the suppression of tumors by the interaction with p53.
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Affiliation(s)
- Jaehak Oh
- Department of Biological Sciences, Institute of Molecular Biology and Genetics, Research Center for Functional Cellulomics, Seoul National University, Seoul 151-742, Korea
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22
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Mateos-Langerak J, Brink MC, Luijsterburg MS, van der Kraan I, van Driel R, Verschure PJ. Pericentromeric heterochromatin domains are maintained without accumulation of HP1. Mol Biol Cell 2007; 18:1464-71. [PMID: 17314413 PMCID: PMC1838966 DOI: 10.1091/mbc.e06-01-0025] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
The heterochromatin protein 1 (HP1) family is thought to be an important structural component of heterochromatin. HP1 proteins bind via their chromodomain to nucleosomes methylated at lysine 9 of histone H3 (H3K9me). To investigate the role of HP1 in maintaining heterochromatin structure, we used a dominant negative approach by expressing truncated HP1alpha or HP1beta proteins lacking a functional chromodomain. Expression of these truncated HP1 proteins individually or in combination resulted in a strong reduction of the accumulation of HP1alpha, HP1beta, and HP1gamma in pericentromeric heterochromatin domains in mouse 3T3 fibroblasts. The expression levels of HP1 did not change. The apparent displacement of HP1alpha, HP1beta, and HP1gamma from pericentromeric heterochromatin did not result in visible changes in the structure of pericentromeric heterochromatin domains, as visualized by DAPI staining and immunofluorescent labeling of H3K9me. Our results show that the accumulation of HP1alpha, HP1beta, and HP1gamma at pericentromeric heterochromatin domains is not required to maintain DAPI-stained pericentromeric heterochromatin domains and the methylated state of histone H3 at lysine 9 in such heterochromatin domains.
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Affiliation(s)
- Julio Mateos-Langerak
- Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, University of Amsterdam, 1098 SM Amsterdam, The Netherlands
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23
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Otte AP, Kwaks THJ, Van Blokland RJM, Sewalt RGAB, Verhees J, Klaren VNA, Siersma TK, Korse HWM, Teunissen NC, Botschuijver S, Van Mer C, Man SY. Various Expression-Augmenting DNA Elements Benefit from STAR-Select, a Novel High Stringency Selection System for Protein Expression. Biotechnol Prog 2007. [DOI: 10.1002/bp070107r] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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24
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Ahn YT, Huang B, McPherson L, Clayberger C, Krensky AM. Dynamic interplay of transcriptional machinery and chromatin regulates "late" expression of the chemokine RANTES in T lymphocytes. Mol Cell Biol 2006; 27:253-66. [PMID: 17074812 PMCID: PMC1800668 DOI: 10.1128/mcb.01071-06] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The chemokine RANTES (regulated upon activation normal T cell expressed and secreted) is expressed "late" (3 to 5 days) after activation in T lymphocytes. In order to understand the molecular events that accompany changes in gene expression, a detailed analysis of the interplay between transcriptional machinery and chromatin on the RANTES promoter over time was undertaken. Krüppel-like factor 13 (KLF13), a sequence-specific DNA binding transcription factor, orchestrates the induction of RANTES expression in T lymphocytes by ordered recruitment of effector molecules, including Nemo-like kinase, p300/cyclic AMP response element binding protein (CBP), p300/CBP-associated factor, and Brahma-related gene 1, that initiate sequential changes in phosphorylation and acetylation of histones and ATP-dependent chromatin remodeling near the TATA box of the RANTES promoter. These events recruit RNA polymerase II to the RANTES promoter and are responsible for late expression of RANTES in T lymphocytes. Therefore, KLF13 is a key regulator of late RANTES expression in T lymphocytes.
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Affiliation(s)
- Yong-Tae Ahn
- Division of Immunology and Transplantation Biology, Department of Pediatrics, Stanford University School of Medicine, 300 Pasteur Drive, Stanford, CA 94305-5164, USA
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25
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Sarkar A, Atapattu A, Belikoff EJ, Heinrich JC, Li X, Horn C, Wimmer EA, Scott MJ. Insulated piggyBac vectors for insect transgenesis. BMC Biotechnol 2006; 6:27. [PMID: 16776846 PMCID: PMC1525164 DOI: 10.1186/1472-6750-6-27] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2005] [Accepted: 06/16/2006] [Indexed: 11/12/2022] Open
Abstract
Background Germ-line transformation of insects is now a widely used method for analyzing gene function and for the development of genetically modified strains suitable for pest control programs. The most widely used transposable element for the germ-line transformation of insects is piggyBac. The site of integration of the transgene can influence gene expression due to the effects of nearby transcription enhancers or silent heterochromatic regions. Position effects can be minimized by flanking a transgene with insulator elements. The scs/scs' and gypsy insulators from Drosophila melanogaster as well as the chicken β-globin HS4 insulator function in both Drosophila and mammalian cells. Results To minimize position effects we have created a set of piggyBac transformation vectors that contain either the scs/scs', gypsy or chicken β-globin HS4 insulators. The vectors contain either fluorescent protein or eye color marker genes and have been successfully used for germ-line transformation of Drosophila melanogaster. A set of the scs/scs' vectors contains the coral reef fluorescent protein marker genes AmCyan, ZsGreen and DsRed that have not been optimized for translation in human cells. These marker genes are controlled by a combined GMR-3xP3 enhancer/promoter that gives particularly strong expression in the eyes. This is also the first report of the use of the ZsGreen and AmCyan reef fluorescent proteins as transformation markers in insects. Conclusion The insulated piggyBac vectors should protect transgenes against position effects and thus facilitate fine control of gene expression in a wide spectrum of insect species. These vectors may also be used for transgenesis in other invertebrate species.
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Affiliation(s)
- Abhimanyu Sarkar
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
| | - Asela Atapattu
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
| | - Esther J Belikoff
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
| | - Jörg C Heinrich
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
| | - Xuelei Li
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
| | - Carsten Horn
- Lehrstuhl für Genetik, Universität Bayreuth, Universitätsstraße 30 NW1, 95447 Bayreuth, Germany
| | - Ernst A Wimmer
- Lehrstuhl für Genetik, Universität Bayreuth, Universitätsstraße 30 NW1, 95447 Bayreuth, Germany
| | - Maxwell J Scott
- Centre for Functional Genomics, Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand
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26
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Kwaks THJ, Otte AP. Employing epigenetics to augment the expression of therapeutic proteins in mammalian cells. Trends Biotechnol 2006; 24:137-42. [PMID: 16460822 DOI: 10.1016/j.tibtech.2006.01.007] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2005] [Revised: 11/09/2005] [Accepted: 01/16/2006] [Indexed: 11/17/2022]
Abstract
Recombinant proteins form an increasingly large part of the portfolio of biopharmaceutical companies. Production of these often complex transgenic proteins is achieved predominantly in mammalian cell lines but the process is hampered by low yields and unstable expression. Some of these problems are caused by gene silencing at the level of chromatin - so-called epigenetic gene silencing. Here, we describe approaches, which have emerged during the past few years, designed to interfere with epigenetic gene silencing with the aim of enhancing and stabilizing transgene expression. These include targeting histones, the inclusion of specific DNA elements and targeting sites of high gene-expression. We conclude that employing epigenetic gene regulation tools, in combination with further process optimization, might represent the next step forward in the production of therapeutic proteins.
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Affiliation(s)
- Ted H J Kwaks
- ChromaGenics, Kruislaan 406, 1098 SM, Amsterdam, The Netherlands
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27
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Inayoshi Y, Miyake K, Machida Y, Kaneoka H, Terajima M, Dohda T, Takahashi M, Iijima S. Mammalian Chromatin Remodeling Complex SWI/SNF Is Essential for Enhanced Expression of the Albumin Gene during Liver Development. ACTA ACUST UNITED AC 2006; 139:177-88. [PMID: 16452305 DOI: 10.1093/jb/mvj015] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
The chromatin remodeling complex SWI/SNF is known to regulate the transcription of several genes by controlling chromatin structure in an ATP-dependent manner. SWI/SNF contains the Swi2p/Snf2p like ATPases BRG1 or BRM exclusively. We found that the expression of BRM gradually increases and that of BRG1 decreases as liver cells differentiate. Chromatin immunoprecipitation assays revealed that the ATPase subunits of SWI/SNF and tumor suppressor retinoblastoma (RB) family proteins bind to the promoter region of the albumin gene in hepatocytes, and that the replacement of BRG1 with BRM and pRB with p130 at this site occurs over the course of differentiation. Small interfering RNA experiments showed that blocking the expression of BRG1 and BRM in fetal and adult hepatocytes, respectively, causes a reduction in albumin expression. In luciferase reporter assays with a pREP4-based reporter plasmid that forms a chromatin structure, BRG1 showed activity stimulating the expression of the albumin promoter mediated by CCAAT/enhancer-binding protein alpha (C/EBPalpha). This enhancement was facilitated by the RB family members pRB and p130. ATPase assays showed that both pRB and C/EBPalpha proteins directly stimulate the ATPase activity of BRG1. Our findings suggest that the mechanism by which the activity of transcription factors is enhanced by RB family members and SWI/SNF includes an increase in the ATPase activity of the chromatin remodeling complex.
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Affiliation(s)
- Yujin Inayoshi
- Department of Biotechnology, Graduate School of Engineering, Japan
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Inayoshi Y, Kaneoka H, Machida Y, Terajima M, Dohda T, Miyake K, Iijima S. Repression of GR-Mediated Expression of the Tryptophan Oxygenase Gene by the SWI/SNF Complex during Liver Development. ACTA ACUST UNITED AC 2005; 138:457-65. [PMID: 16272140 DOI: 10.1093/jb/mvi147] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
The chromatin remodeling complex, SWI/SNF, is known to regulate the transcription of several genes by altering the chromatin structure in an ATP-dependent manner. SWI/SNF exclusively contains BRG1 or BRM as an ATPase subunit. In the present study, we studied the role of SWI/SNF containing BRM or BRG1 in the expression of the liver-specific tryptophan oxygenase (TO) and tyrosine aminotransferase genes. Chromatin remodeling factors significantly repressed the expression of these genes induced by glucocorticoid receptor and dexamethasone. Since the repression was not reversed by trichostatin A treatment, it seemed to be independent of the well-known histone deacetylase pathway. Knock-down of BRG1 by small interfering RNA reversed the repression in primary fetal hepatocytes. These results support a model in which SWI/SNF containing BRG1 represses late stage-specific TO gene expression at an early stage of liver development.
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Affiliation(s)
- Yujin Inayoshi
- Department of Biotechnology, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan
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29
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Abstract
The properties of cis-regulatory elements able to influence gene transcription over large distances have led to the hypothesis that elements called insulators should exist to limit the action of enhancers and silencers. During the last decades, insulators have been identified in many eukaryotes from yeast to human. Insulators possess two main properties: (i) they can block enhancer-promoter communication ('enhancer blocker activity'), and (ii) they can prevent the spread of repressive chromatin ('barrier activity'). This review focuses on recent studies designed to elucidate the molecular mechanisms of the insulator function, and gives an overview of the critical role of insulators in nuclear organization and functional identity of chromatin.
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Affiliation(s)
- E Brasset
- INSERM U384, Faculté de Médecine, BP38, Clermont-Ferrand 63001, France
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30
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Verschure PJ, van der Kraan I, de Leeuw W, van der Vlag J, Carpenter AE, Belmont AS, van Driel R. In vivo HP1 targeting causes large-scale chromatin condensation and enhanced histone lysine methylation. Mol Cell Biol 2005; 25:4552-64. [PMID: 15899859 PMCID: PMC1140641 DOI: 10.1128/mcb.25.11.4552-4564.2005] [Citation(s) in RCA: 143] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Changes in chromatin structure are a key aspect in the epigenetic regulation of gene expression. We have used a lac operator array system to visualize by light microscopy the effect of heterochromatin protein 1 (HP1) alpha (HP1alpha) and HP1beta on large-scale chromatin structure in living mammalian cells. The structure of HP1, containing a chromodomain, a chromoshadow domain, and a hinge domain, allows it to bind to a variety of proteins. In vivo targeting of an enhanced green fluorescent protein-tagged HP1-lac repressor fusion to a lac operator-containing, gene-amplified chromosome region causes local condensation of the higher-order chromatin structure, recruitment of the histone methyltransferase SETDB1, and enhanced trimethylation of histone H3 lysine 9. Polycomb group proteins of both the HPC/HPH and the EED/EZH2 complexes, which are involved in the heritable repression of gene activity, are not recruited to the amplified chromosome region by HP1alpha and HP1beta in vivo targeting. HP1alpha targeting causes the recruitment of endogenous HP1beta to the chromatin region and vice versa, indicating a direct interaction between the two HP1 homologous proteins. Our findings indicate that HP1alpha and HP1beta targeting is sufficient to induce heterochromatin formation.
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Affiliation(s)
- Pernette J Verschure
- Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, University of Amsterdam, P.O. Box 94062, 1090 GB Amsterdam, The Netherlands.
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31
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Wen J, Huang S, Pack SD, Yu X, Brandt SJ, Noguchi CT. Tal1/SCL binding to pericentromeric DNA represses transcription. J Biol Chem 2005; 280:12956-66. [PMID: 15677454 DOI: 10.1074/jbc.m412721200] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Tal1/SCL is a basic helix-loop-helix transcription factor critical for normal hematopoiesis. To understand the mechanisms underlying transcriptional regulation by Tal1/SCL, we combined an in vitro DNA binding strategy and an in vivo chromatin immunoprecipitation analysis to search for Tal1/SCL target regions in K562 erythroleukemia cells. A 0.4-kb genomic DNA clone containing two Tal1/SCL binding E-boxes and GATA- and SATB1-binding motifs (EEGS) was identified that localized to the pericentromeric region with high homology to satellite 2 DNA. Pericentric DNA is related to heterochromatin and gene inactivation. We found that Tal1/SCL could complex with the histone H3 lysine 9 (H3K9)-specific methyltransferase Suv39H1. Binding of Tal1/SCL to EEGS chromatin correlated with hypermethylation of H3K9 and the association of heterochromatin protein HP1 to this region. In Rep4 reporter gene assays, EEGS affected repression in a manner dependent on the expression level of Tal1/SCL that was accompanied by increased H3K9 methylation in chromatin associated with EEGS and a linked promoter. A specific histone deacetylase inhibitor, trichostatin A, relieved Tal1/SCL-mediated repression by EEGS. In addition, SATB1 bound EEGS chromatin and promoted Tal1/SCL EEGS-dependent repression. We expand the list of potential interacting partners for Tal1/SCL by demonstrating direct associations of Tal1/SCL with SATB1 and with Suv39H1. These results reveal a novel mechanism of action for Tal1/SCL and implicate heterochromatin-like silencing via a cis-acting binding motif for transcriptional repression.
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Affiliation(s)
- Jie Wen
- Molecular Medicine Branch, NIDDK, National Institutes of Health, Bethesda, Maryland 20892, USA
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32
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Wen J, Huang S, Rogers H, Dickinson LA, Kohwi-Shigematsu T, Noguchi CT. SATB1 family protein expressed during early erythroid differentiation modifies globin gene expression. Blood 2004; 105:3330-9. [PMID: 15618465 DOI: 10.1182/blood-2004-08-2988] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Special AT-rich binding protein 1 (SATB1) nuclear protein, expressed predominantly in T cells, regulates genes through targeting chromatin remodeling during T-cell maturation. Here we show SATB1 family protein induction during early human adult erythroid progenitor cell differentiation concomitant with epsilon-globin expression. Erythroid differentiation of human erythroleukemia K562 cells by hemin simultaneously increases gamma-globin and down-regulates SATB1 family protein and epsilon-globin gene expression. Chromatin immunoprecipitation using anti-SATB1 anti-body shows selective binding in vivo in the beta-globin cluster to the hypersensitive site 2 (HS2) in the locus control region (LCR) and to the epsilon-globin promoter. SATB1 overexpression increases epsilon-globin and decreases gamma-globin gene expression accompanied by histone hyperacetylation and hypomethylation in chromatin from the epsilon-globin promoter and HS2, and histone hypoacetylation and hypermethylation associated with the gamma-globin promoter. In K562 cells SATB1 family protein forms a complex with CREB-binding protein (CBP) important in transcriptional activation. In cotransfection experiments, increase in epsilon-promoter activity by SATB1 was amplified by CBP and blocked by E1A, a CBP inhibitor. Our results suggest that SATB1 can up-regulate the epsilon-globin gene by interaction with specific sites in the beta-globin cluster and imply that SATB1 family protein expressed in the erythroid progenitor cells may have a role in globin gene expression during early erythroid differentiation.
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Affiliation(s)
- Jie Wen
- National Institutes of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892, USA
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33
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Calomme C, Dekoninck A, Nizet S, Adam E, Nguyên TLA, Van Den Broeke A, Willems L, Kettmann R, Burny A, Van Lint C. Overlapping CRE and E box motifs in the enhancer sequences of the bovine leukemia virus 5' long terminal repeat are critical for basal and acetylation-dependent transcriptional activity of the viral promoter: implications for viral latency. J Virol 2004; 78:13848-64. [PMID: 15564493 PMCID: PMC533944 DOI: 10.1128/jvi.78.24.13848-13864.2004] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2004] [Accepted: 08/04/2004] [Indexed: 11/20/2022] Open
Abstract
Bovine leukemia virus (BLV) infection is characterized by viral latency in a large proportion of cells containing an integrated provirus. In this study, we postulated that mechanisms directing the recruitment of deacetylases to the BLV 5' long terminal repeat (LTR) could explain the transcriptional repression of viral expression in vivo. Accordingly, we showed that BLV promoter activity was induced by several deacetylase inhibitors (such as trichostatin A [TSA]) in the context of episomal LTR constructs and in the context of an integrated BLV provirus. Moreover, treatment of BLV-infected cells with TSA increased H4 acetylation at the viral promoter, showing a close correlation between the level of histone acetylation and transcriptional activation of the BLV LTR. Among the known cis-regulatory DNA elements located in the 5' LTR, three E box motifs overlapping cyclic AMP responsive elements (CREs) in U3 were shown to be involved in transcriptional repression of BLV basal gene expression. Importantly, the combined mutations of these three E box motifs markedly reduced the inducibility of the BLV promoter by TSA. E boxes are susceptible to recognition by transcriptional repressors such as Max-Mad-mSin3 complexes that repress transcription by recruiting deacetylases. However, our in vitro binding studies failed to reveal the presence of Mad-Max proteins in the BLV LTR E box-specific complexes. Remarkably, TSA increased the occupancy of the CREs by CREB/ATF. Therefore, we postulated that the E box-specific complexes exerted their negative cooperative effect on BLV transcription by steric hindrance with the activators CREB/ATF and/or their transcriptional coactivators possessing acetyltransferase activities. Our results thus suggest that the overlapping CRE and E box elements in the BLV LTR were selected during evolution as a novel strategy for BLV to allow better silencing of viral transcription and to escape from the host immune response.
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Affiliation(s)
- Claire Calomme
- Université Libre de Bruxelles (ULB), Institut de Biologie et de Médecine Moléculaires (IBMM), Service de Chimie Biologique, Laboratoire de Virologie Moléculaire, Rue des Profs Jeener et Brachet, 12, 6041 Gosselies, Belgium
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34
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Golovnin A, Melnick E, Mazur A, Georgiev P. Drosophila Su(Hw) insulator can stimulate transcription of a weakened yellow promoter over a distance. Genetics 2004; 170:1133-42. [PMID: 15520254 PMCID: PMC1451172 DOI: 10.1534/genetics.104.034587] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The insulator element from the gypsy transposon is a DNA sequence that blocks activation of a promoter by a transcriptional enhancer when placed between them. The insulator contains reiterated binding sites for the Suppressor of Hairy-wing [Su(Hw)] zinc-finger protein. A protein encoded by another gene, modifier of mdg4 [mod(mdg4)], is also required for the enhancer-blocking activity of the Su(Hw) insulator. Here we present evidence that the Su(Hw) insulator activates a weakened yellow promoter at a distance. Deletion of the upstream promoter region (UPR), located close by the TATA box, significantly reduces yellow expression. The Su(Hw) insulator placed at different positions relative to the yellow promoter partially compensates for loss of the UPR. Su(Hw) is able to stimulate yellow expression even if it is located at a 5-kb distance from the promoter. The stimulatory activity depends on the number of Su(Hw)-binding sites. Mutational analysis demonstrates that only the DNA-binding domain and adjacent regions of the Su(Hw) protein are required for stimulation of yellow transcription.
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Affiliation(s)
- Anton Golovnin
- Institute of Gene Biology, Russian Academy of Sciences, Moscow 119334, Russia
- Center for Medical Studies of Oslo University, Moscow 199334, Russia
| | - Elena Melnick
- Institute of Gene Biology, Russian Academy of Sciences, Moscow 119334, Russia
| | - Alexander Mazur
- Institute of Gene Biology, Russian Academy of Sciences, Moscow 119334, Russia
| | - Pavel Georgiev
- Institute of Gene Biology, Russian Academy of Sciences, Moscow 119334, Russia
- Corresponding author: Institute of Gene Biology, Russian Academy of Sciences, 34/5 Vavilov St., Moscow 119334, Russia. E-mail:
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35
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Ma Z, Chang MJ, Shah R, Adamski J, Zhao X, Benveniste EN. Brg-1 Is Required for Maximal Transcription of the Human Matrix Metalloproteinase-2 Gene. J Biol Chem 2004; 279:46326-34. [PMID: 15317818 DOI: 10.1074/jbc.m405438200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Matrix metalloproteinases (MMPs) are zinc-dependent endopeptidases whose aberrant expression are correlated with tumor invasion and angiogenesis. The transcription factors Sp1, Sp3, and AP-2 are required for constitutive expression of MMP-2 in tumor cells; however, the regulatory mechanisms of MMP-2 expression are not well understood. We investigated the involvement of Brg-1, the ATPase subunit of the SWI/SNF complex, in human MMP-2 gene transcription. Reconstitution of Brg-1 enhances MMP-2 transcription in Brg-1-deficient SW-13 cells. Chromatin immunoprecipitation assay demonstrates that Brg-1 is required for recruitment of Sp1, AP-2, and polymerase II to the MMP-2 promoter, whereas the binding of Sp3 to the MMP-2 promoter is decreased upon Brg-1 reconstitution. Furthermore, Sp1 interacts with Brg-1 in vivo. Restriction enzyme accessibility assays indicate that accessibility of the MMP-2 promoter region is not changed in the absence or presence of Brg-1. These results illustrate the connection between the SWI/SNF complex and optimal expression of MMP-2 and highlight the critical function of Brg-1 in regulating the recruitment of Sp1, Sp3, AP-2, and polymerase II to the MMP-2 promoter.
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Affiliation(s)
- Zhendong Ma
- Department of Cell Biology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0005, USA
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36
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Zhao H, Dean A. An insulator blocks spreading of histone acetylation and interferes with RNA polymerase II transfer between an enhancer and gene. Nucleic Acids Res 2004; 32:4903-19. [PMID: 15371553 PMCID: PMC519119 DOI: 10.1093/nar/gkh832] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
We studied the mechanism by which an insulator interrupts enhancer signaling to a gene using stably replicated chromatin templates containing the human beta-globin locus control region HS2 enhancer and a target globin gene. The chicken beta-globin 5' HS4 (cHS4) insulator acted as a positional enhancer blocker, inhibiting promoter remodeling and transcription activation only when placed between the enhancer and gene. Enhancer blocking by cHS4 reduced histone hyperacetylation across a zone extending from the enhancer to the gene and inhibited recruitment of CBP and p300 to HS2. Enhancer blocking also led to accumulation of RNA polymerase II at HS2 and within cHS4, accompanied by its diminution at the gene promoter. The enhancer blocking effects were completely attributable to the CTCF binding site in cHS4. These findings provide experimental evidence for the involvement of spreading in establishment of a broad zone of histone modification by an enhancer, as well as for blocking by an insulator of the transfer of RNA polymerase II from an enhancer to a promoter.
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Affiliation(s)
- Hui Zhao
- Laboratory of Cellular and Developmental Biology, NIDDK, NIH, Bethesda, MD 20892, USA
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37
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Abstract
Heterochromatin Protein 1 (HP1) is a structural component of silent chromatin at telomeres and centromeres. Euchromatic genes repositioned near heterochromatin by chromosomal rearrangements are typically silenced in an HP1-dependent manner. Silencing is thought to involve the spreading of heterochromatin proteins over the rearranged genes. HP1 associates with centric heterochromatin through an interaction with methylated lysine 9 of histone H3, a modification generated by SU(VAR)3-9. The current model for spreading of silent chromatin involves HP1-dependent recruitment of SU(VAR)3-9, resulting in the methylation of adjacent nucleosomes and association of HP1 along the chromatin fiber. To address mechanisms of silent chromatin formation and spreading, HP1 was fused to the DNA-binding domain of the E. coli lacI repressor and expressed in Drosophila melanogaster stocks carrying heat shock reporter genes positioned 1.9 and 3.7 kb downstream of lac operator repeats. Association of lacI-HP1 with the repeats resulted in silencing of both reporter genes and correlated with a closed chromatin structure consisting of regularly spaced nucleosomes, similar to that observed in centric heterochromatin. Chromatin immunoprecipitation experiments demonstrated that HP1 spread bi-directionally from the tethering site and associated with the silenced reporter transgenes. To examine mechanisms of spreading, the effects of a mutation in Su(var)3-9 were investigated. Silencing was minimally affected at 1.9 kb, but eliminated at 3.7 kb, suggesting that HP1-mediated silencing can operate in a SU(VAR)3-9-independent and -dependent manner.
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Affiliation(s)
- John R Danzer
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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38
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Scott MJ, Heinrich JC, Li X. Progress towards the development of a transgenic strain of the Australian sheep blowfly (Lucilia cuprina) suitable for a male-only sterile release program. INSECT BIOCHEMISTRY AND MOLECULAR BIOLOGY 2004; 34:185-192. [PMID: 14871615 DOI: 10.1016/j.ibmb.2003.11.001] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/03/2003] [Indexed: 05/24/2023]
Abstract
The Australian sheep blowfly Lucilia cuprina is the most important pest species involved in cutaneous myiasis (flystrike) of sheep in Australia and New Zealand. In New Zealand L. cuprina is primarily controlled through the application of insecticides. However, there is an increased interest in biological methods of control of this species. We have proposed to develop a genetically modified strain of L. cuprina that would be ideal for a male-only sterile release program. To that end we have developed a method for making transgenic L. cuprina using a piggyBac vector and an EGFP marker gene. We have also developed in Drosophila melanogaster a 2-component genetic system for controlling female viability. Females carrying both components of the system die unless fed a diet that contains tetracycline. We anticipate that the female-killing system will need to be optimised for L. cuprina in order to make a strain with the properties required for a male-only release program.
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Affiliation(s)
- Maxwell J Scott
- Institute of Molecular BioSciences, Massey University, Private Bag 11222, Palmerston North, New Zealand.
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39
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van Driel R, Fransz PF, Verschure PJ. The eukaryotic genome: a system regulated at different hierarchical levels. J Cell Sci 2003; 116:4067-75. [PMID: 12972500 DOI: 10.1242/jcs.00779] [Citation(s) in RCA: 138] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023] Open
Abstract
Eukaryotic gene expression can be viewed within a conceptual framework in which regulatory mechanisms are integrated at three hierarchical levels. The first is the sequence level, i.e. the linear organization of transcription units and regulatory sequences. Here, developmentally co-regulated genes seem to be organized in clusters in the genome, which constitute individual functional units. The second is the chromatin level, which allows switching between different functional states. Switching between a state that suppresses transcription and one that is permissive for gene activity probably occurs at the level of the gene cluster, involving changes in chromatin structure that are controlled by the interplay between histone modification, DNA methylation, and a variety of repressive and activating mechanisms. This regulatory level is combined with control mechanisms that switch individual genes in the cluster on and off, depending on the properties of the promoter. The third level is the nuclear level, which includes the dynamic 3D spatial organization of the genome inside the cell nucleus. The nucleus is structurally and functionally compartmentalized and epigenetic regulation of gene expression may involve repositioning of loci in the nucleus through changes in large-scale chromatin structure.
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Affiliation(s)
- Roel van Driel
- Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, University of Amsterdam, Kruislaan 318,1098SM Amsterdam, The Netherlands.
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40
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Yao S, Osborne CS, Bharadwaj RR, Pasceri P, Sukonnik T, Pannell D, Recillas-Targa F, West AG, Ellis J. Retrovirus silencer blocking by the cHS4 insulator is CTCF independent. Nucleic Acids Res 2003; 31:5317-23. [PMID: 12954767 PMCID: PMC203325 DOI: 10.1093/nar/gkg742] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Silencing of retrovirus vectors poses a significant obstacle to genetic manipulation of stem cells and their use in gene therapy. We describe a mammalian silencer blocking assay using insulator elements positioned between retrovirus silencer elements and an LCRbeta-globin reporter transgene. In transgenic mice, we show that retrovirus silencers are blocked by the cHS4 insulator. Silencer blocking is independent of the CTCF binding site and is most effective when flanking the internal reporter transgene. These data distinguish silencer blocking activity by cHS4 from its enhancer blocking activity. Retrovirus vectors can be created at high titer with one but not two internal dimer cHS4 cores. cHS4 in the LTRs has no effect on expression in transduced F9 cells, suggesting that position effect blocking is not sufficient to escape silencing. The Drosophila insulators gypsy and Scs fail to block silencing in transgenic mice, but gypsy stimulates vector expression 2-fold when located in the LTRs of an infectious retrovirus. The silencer blocking assay complements existing insulator assays in mammalian cells, provides new insight into mechanisms of insulation and is a valuable tool to identify additional silencer blocking insulators that cooperate with cHS4 to improve stem cell retrovirus vector design.
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Affiliation(s)
- Shuyuan Yao
- Developmental Biology Program, Hospital for Sick Children, 555 University Avenue, Toronto, Ontario M5G 1X8, Canada
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41
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Xia ZB, Anderson M, Diaz MO, Zeleznik-Le NJ. MLL repression domain interacts with histone deacetylases, the polycomb group proteins HPC2 and BMI-1, and the corepressor C-terminal-binding protein. Proc Natl Acad Sci U S A 2003; 100:8342-7. [PMID: 12829790 PMCID: PMC166231 DOI: 10.1073/pnas.1436338100] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
The MLL (mixed-lineage leukemia) gene is involved in many chromosomal translocations associated with acute myeloid and lymphoid leukemia. We previously identified a transcriptional repression domain in MLL, which contains a region with homology to DNA methyltransferase. In chromosomal translocations, the MLL repression domain is retained in the leukemogenic fusion protein and is required for transforming activity of MLL fusion proteins. We explored the mechanism of action of the MLL repression domain. Histone deacetylase 1 interacts with the MLL repression domain, partially mediating its activity; binding of Cyp33 to the adjacent MLL-PHD domain potentiates this binding. Because the MLL repression domain activity was only partially relieved with the histone deacetylase inhibitor trichostatin A, we explored other protein interactions with this domain. Polycomb group proteins HPC2 and BMI-1 and the corepressor C-terminal-binding protein also bind the MLL repression domain. Expression of exogenous BMI-1 potentiates MLL repression domain activity. Functional antagonism between Mll and Bmi-1 has been shown genetically in murine knockout models for Mll and Bmi-1. Our new data suggest a model whereby recruitment of BMI-1 to the MLL protein may be able to modulate its function. Furthermore, repression mediated by histone deacetylases and that mediated by polycomb group proteins may act either independently or together for MLL function in vivo.
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Affiliation(s)
| | | | | | - Nancy J. Zeleznik-Le
- To whom correspondence should be addressed at: Cardinal Bernardin Cancer
Center, Loyola University Medical Center, 2160 South First Avenue, 112-337,
Maywood, IL 60153. E-mail:
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42
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Li Y, Danzer JR, Alvarez P, Belmont AS, Wallrath LL. Effects of tethering HP1 to euchromatic regions of the Drosophila genome. Development 2003; 130:1817-24. [PMID: 12642487 DOI: 10.1242/dev.00405] [Citation(s) in RCA: 116] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Heterochromatin protein 1 (HP1) is a conserved non-histone chromosomal protein enriched in heterochromatin. On Drosophila polytene chromosomes, HP1 localizes to centric and telomeric regions, along the fourth chromosome, and to specific sites within euchromatin. HP1 associates with centric regions through an interaction with methylated lysine nine of histone H3, a modification generated by the histone methyltransferase SU(VAR)3-9. This association correlates with a closed chromatin configuration and silencing of euchromatic genes positioned near heterochromatin. To determine whether HP1 is sufficient to nucleate the formation of silent chromatin at non-centric locations, HP1 was tethered to sites within euchromatic regions of Drosophila chromosomes. At 25 out of 26 sites tested, tethered HP1 caused silencing of a nearby reporter gene. The site that did not support silencing was upstream of an active gene, suggesting that the local chromatin environment did not support the formation of silent chromatin. Silencing correlated with the formation of ectopic fibers between the site of tethered HP1 and other chromosomal sites, some containing HP1. The ability of HP1 to bring distant chromosomal sites into proximity with each other suggests a mechanism for chromatin packaging. Silencing was not dependent on SU(VAR)3-9 dosage, suggesting a bypass of the requirement for histone methylation.
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Affiliation(s)
- Yuhong Li
- Department of Biochemistry, University of Iowa, Iowa City, IA 52242, USA
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43
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Kwaks THJ, Barnett P, Hemrika W, Siersma T, Sewalt RGAB, Satijn DPE, Brons JF, van Blokland R, Kwakman P, Kruckeberg AL, Kelder A, Otte AP. Identification of anti-repressor elements that confer high and stable protein production in mammalian cells. Nat Biotechnol 2003; 21:553-8. [PMID: 12679786 DOI: 10.1038/nbt814] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/04/2002] [Accepted: 02/14/2003] [Indexed: 11/08/2022]
Abstract
The expression of transgenic proteins is often low and unstable over time, a problem that may be due to integration of the transgene in repressed chromatin. We developed a screening technology to identify genetic elements that efficiently counteract chromatin-associated repression. When these elements were used to flank a transgene, we observed a substantial increase in the number of mammalian cell colonies that expressed the transgenic protein. Expression of the shielded transgene was, in a copy number-dependent fashion, substantially higher than the expression of unprotected transgenes. Also, protein production remained stable over an extended time period. The DNA elements are small, not exceeding 2,100 base pairs (bp), and they are highly conserved between human and mouse, at both the functional and sequence levels. Our results demonstrate the existence of a class of genetic elements that can readily be applied to more efficient transgenic protein production in mammalian cells.
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Affiliation(s)
- Ted H J Kwaks
- Swammerdam Institute for Life Sciences, BioCentrum Amsterdam, University of Amsterdam, Plantage Muidergracht 12, 1018 TV Amsterdam, The Netherlands
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44
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Engel N, Bartolomei MS. Mechanisms of Insulator Function in Gene Regulation and Genomic Imprinting. INTERNATIONAL REVIEW OF CYTOLOGY 2003; 232:89-127. [PMID: 14711117 DOI: 10.1016/s0074-7696(03)32003-0] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Correct temporal and spatial patterns of gene expression are required to establish unique cell types. Several levels of genome organization are involved in achieving this intricate regulatory feat. Insulators are elements that modulate interactions between other cis-acting sequences and separate chromatin domains with distinct condensation states. Thus, they are proposed to play an important role in the partitioning of the genome into discrete realms of expression. This review focuses on the roles that insulators have in vivo and reviews models of insulator mechanisms in the light of current understanding of gene regulation.
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Affiliation(s)
- Nora Engel
- Howard Hughes Medical Institute and Department of Cell and Developmental Biology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, USA
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Chromatin insulators and position effects. ACTA ACUST UNITED AC 2003. [DOI: 10.1016/s0167-7306(03)38023-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/29/2023]
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Sewalt RG, Kwaks TH, Hamer K, Otte AP. Biochemical Analysis of Mammalian Polycomb Group Protein Complexes and the Identification of Genetic Elements that Block Polycomb-Mediated Gene Repression. Methods Enzymol 2003; 377:282-96. [PMID: 14979032 DOI: 10.1016/s0076-6879(03)77017-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/29/2023]
Affiliation(s)
- Richard G Sewalt
- Swammerdam Institute for Life Sciences, University of Amsterdam, 1018 TV Amsterdam, The Netherlands
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Li Y, Kirschmann DA, Wallrath LL. Does heterochromatin protein 1 always follow code? Proc Natl Acad Sci U S A 2002; 99 Suppl 4:16462-9. [PMID: 12151603 PMCID: PMC139909 DOI: 10.1073/pnas.162371699] [Citation(s) in RCA: 154] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Heterochromatin protein 1 (HP1) is a conserved chromosomal protein that participates in chromatin packaging and gene silencing. A loss of HP1 leads to lethality in Drosophila and correlates with metastasis in human breast cancer cells. On Drosophila polytene chromosomes HP1 is localized to centric regions, telomeric regions, in a banded pattern along the fourth chromosome, and at many sites scattered throughout the euchromatic arms. Recently, one mechanism of HP1 chromosome association was revealed; the amino-terminal chromo domain of HP1 interacts with methylated lysine nine of histone H3, consistent with the histone code hypothesis. Compelling data support this mechanism of HP1 association at centric regions. Is this the only mechanism by which HP1 associates with chromosomes? Interest is now shifting toward the role of HP1 within euchromatic domains. Accumulating evidence in Drosophila and mammals suggests that HP1 associates with chromosomes through interactions with nonhistone chromosomal proteins at locations other than centric heterochromatin. Does HP1 play a similar role in chromatin packaging and gene regulation at these sites as it does in centric heterochromatin? Does HP1 associate with the same proteins at these sites as it does in centric heterochromatin? A first step toward answering these questions is the identification of sequences associated with HP1 within euchromatic domains. Such sequences are likely to include HP1 "target genes" whose discovery will aid in our understanding of HP1 lethality in Drosophila and metastasis of breast cancer cells.
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Affiliation(s)
- Yuhong Li
- Department of Biochemistry, University of Iowa, Iowa City 52242, USA
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Liu H, Kang H, Liu R, Chen X, Zhao K. Maximal induction of a subset of interferon target genes requires the chromatin-remodeling activity of the BAF complex. Mol Cell Biol 2002; 22:6471-9. [PMID: 12192045 PMCID: PMC135632 DOI: 10.1128/mcb.22.18.6471-6479.2002] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The mammalian SWI/SNF-like chromatin-remodeling BAF complex plays several important roles in controlling cell proliferation and differentiation. Interferons (IFNs) are key mediators of cellular antiviral and antiproliferative activities. In this report, we demonstrate that the BAF complex is required for the maximal induction of a subset of IFN target genes by alpha IFN (IFN-alpha). The BAF complex is constitutively associated with the IFITM3 promoter in vivo and facilitates the chromatin remodeling of the promoter upon IFN-alpha induction. Furthermore, we show that the ubiquitous transcription activator Sp1 interacts with the BAF complex in vivo and augments the BAF-mediated activation of the IFITM3 promoter. Sp1 binds constitutively to the IFITM3 promoter in the absence of the BAF complex, suggesting that it may recruit and/or stabilize the BAF complex binding to the IFITM3 promoter. Our results bring new mechanistic insights into the antiproliferative effects of the chromatin-remodeling BAF complex.
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Affiliation(s)
- Hong Liu
- Laboratory of Molecular Immunology, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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Wei W, Brennan MD. The gypsy insulator can act as a promoter-specific transcriptional stimulator. Mol Cell Biol 2001; 21:7714-20. [PMID: 11604507 PMCID: PMC99942 DOI: 10.1128/mcb.21.22.7714-7720.2001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2001] [Accepted: 08/13/2001] [Indexed: 11/20/2022] Open
Abstract
Insulators define chromosomal domains such that an enhancer in one domain cannot activate a promoter in a different domain. We show that the Drosophila gypsy insulator behaves as a cis-stimulatory element in the larval fat body. Transcriptional stimulation by the insulator is distance dependent, as expected for a promoter element as opposed to an enhancer. Stimulation of a test alcohol dehydrogenase promoter requires a binding site for a GATA transcription factor, suggesting that the insulator may be facilitating access of this DNA binding protein to the promoter. Short-range stimulation requires both the Suppressor of Hairy-wing protein and the Mod(mdg4)-62.7 protein encoded by the trithorax group gene mod(mdg4). In the absence of interaction with Mod(mdg4)-62.7, the insulator is converted into a short-range transcriptional repressor but retains some cis-stimulatory activity over longer distances. These results indicate that insulator and promoter sequences share important characteristics and are not entirely distinct. We propose that the gypsy insulator can function as a promoter element and may be analogous to promoter-proximal regulatory modules that integrate input from multiple distal enhancer sequences.
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Affiliation(s)
- W Wei
- Department of Biochemistry and Molecular Biology, University of Louisville, Kentucky 40202, USA
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50
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Abstract
The opposing actions of polycomb (PcG) and trithorax group (trxG) gene products maintain essential gene expression patterns during Drosophila development. PcG proteins are thought to establish repressive chromatin structures, but the mechanisms by which this occurs are not known. Polycomb repressive complex 1 (PRC1) contains several PcG proteins and inhibits chromatin remodeling by trxG-related SWI/SNF complexes. We have defined a functional core of PRC1 by reconstituting a stable complex using four recombinant PcG proteins. One subunit, PSC, can also inhibit chromatin remodeling on its own. These PcG proteins create a chromatin structure that has normal nucleosome organization and is accessible to nucleases but excludes hSWI/SNF.
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Affiliation(s)
- N J Francis
- Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA
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