101
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Sulli G, Di Micco R, d'Adda di Fagagna F. Crosstalk between chromatin state and DNA damage response in cellular senescence and cancer. Nat Rev Cancer 2012; 12:709-20. [PMID: 22952011 DOI: 10.1038/nrc3344] [Citation(s) in RCA: 158] [Impact Index Per Article: 13.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
The generation of DNA lesions and the resulting activation of DNA damage response (DDR) pathways are both affected by the chromatin status at the site of damaged DNA. In turn, DDR activation affects the chromatin at both the damaged site and across the whole genome. Cellular senescence and cancer are associated with the engagement of the DDR pathways and with profound chromatin changes. In this Opinion article, we discuss the interplay between chromatin and DDR factors in the context of cellular senescence that is induced by oncogenes and in cancer.
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Affiliation(s)
- Gabriele Sulli
- IFOM Foundation-FIRC Institute of Molecular Oncology Foundation, Milan 20139, Italy
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102
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Talluri S, Dick FA. Regulation of transcription and chromatin structure by pRB: here, there and everywhere. Cell Cycle 2012; 11:3189-98. [PMID: 22895179 PMCID: PMC3466518 DOI: 10.4161/cc.21263] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Commitment to divide is one of the most crucial steps in the mammalian cell division cycle. It is critical for tissue and organismal homeostasis, and consequently is highly regulated. The vast majority of cancers evade proliferative control, further emphasizing the importance of the commitment step in cell cycle regulation. The Retinoblastoma (RB) tumor suppressor pathway regulates this decision-making step. Since being the subject of Knudson's 'two hit hypothesis', there has been considerable interest in understanding pRB's role in cancer. It is best known for repressing E2F dependent transcription of cell cycle genes. However, pRB's role in controlling chromatin structure is expanding and bringing it into new regulatory paradigms. In this review we discuss pRB function through protein-protein interactions, at the level of transcriptional regulation of individual promoters and in organizing higher order chromatin domains.
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Affiliation(s)
- Srikanth Talluri
- London Regional Cancer Program; Western University; London, ON Canada
- Department of Biochemistry; Western University; London, ON Canada
| | - Frederick A. Dick
- London Regional Cancer Program; Western University; London, ON Canada
- Department of Biochemistry; Western University; London, ON Canada
- Children’s Health Research Institute; Western University; London, ON Canada
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103
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Contrepois K, Thuret JY, Courbeyrette R, Fenaille F, Mann C. Deacetylation of H4-K16Ac and heterochromatin assembly in senescence. Epigenetics Chromatin 2012; 5:15. [PMID: 22932127 PMCID: PMC3487866 DOI: 10.1186/1756-8935-5-15] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2012] [Accepted: 08/02/2012] [Indexed: 01/20/2023] Open
Abstract
Background Cellular senescence is a stress response of mammalian cells leading to a durable arrest of cell proliferation that has been implicated in tumor suppression, wound healing, and aging. The proliferative arrest is mediated by transcriptional repression of genes essential for cell division by the retinoblastoma protein family. This repression is accompanied by varying degrees of heterochromatin assembly, but little is known regarding the molecular mechanisms involved. Results We found that both deacetylation of H4-K16Ac and expression of HMGA1/2 can contribute to DNA compaction during senescence. SIRT2, an NAD-dependent class III histone deacetylase, contributes to H4-K16Ac deacetylation and DNA compaction in human fibroblast cell lines that assemble striking senescence-associated heterochromatin foci (SAHFs). Decreased H4-K16Ac was observed in both replicative and oncogene-induced senescence of these cells. In contrast, this mechanism was inoperative in a fibroblast cell line that did not assemble extensive heterochromatin during senescence. Treatment of senescent cells with trichostatin A, a class I/II histone deacetylase inhibitor, also induced rapid and reversible decondensation of SAHFs. Inhibition of DNA compaction did not significantly affect the stability of the senescent state. Conclusions Variable DNA compaction observed during senescence is explained in part by cell-type specific regulation of H4 deacetylation and HMGA1/2 expression. Deacetylation of H4-K16Ac during senescence may explain reported decreases in this mark during mammalian aging and in cancer cells.
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Affiliation(s)
- Kévin Contrepois
- CEA, iBiTecS, Service de Biologie Intégrative et de Génétique Moléculaire (SBIGeM), F-91191, Gif-sur-Yvette, France.
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104
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Chandra T, Kirschner K, Thuret JY, Pope BD, Ryba T, Newman S, Ahmed K, Samarajiwa SA, Salama R, Carroll T, Stark R, Janky R, Narita M, Xue L, Chicas A, Nũnez S, Janknecht R, Hayashi-Takanaka Y, Wilson MD, Marshall A, Odom DT, Babu MM, Bazett-Jones DP, Tavaré S, Edwards PA, Lowe SW, Kimura H, Gilbert DM, Narita M. Independence of repressive histone marks and chromatin compaction during senescent heterochromatic layer formation. Mol Cell 2012; 47:203-14. [PMID: 22795131 PMCID: PMC3701408 DOI: 10.1016/j.molcel.2012.06.010] [Citation(s) in RCA: 221] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2012] [Revised: 04/17/2012] [Accepted: 06/06/2012] [Indexed: 01/02/2023]
Abstract
The expansion of repressive epigenetic marks has been implicated in heterochromatin formation during embryonic development, but the general applicability of this mechanism is unclear. Here we show that nuclear rearrangement of repressive histone marks H3K9me3 and H3K27me3 into nonoverlapping structural layers characterizes senescence-associated heterochromatic foci (SAHF) formation in human fibroblasts. However, the global landscape of these repressive marks remains unchanged upon SAHF formation, suggesting that in somatic cells, heterochromatin can be formed through the spatial repositioning of pre-existing repressively marked histones. This model is reinforced by the correlation of presenescent replication timing with both the subsequent layered structure of SAHFs and the global landscape of the repressive marks, allowing us to integrate microscopic and genomic information. Furthermore, modulation of SAHF structure does not affect the occupancy of these repressive marks, nor vice versa. These experiments reveal that high-order heterochromatin formation and epigenetic remodeling of the genome can be discrete events.
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Affiliation(s)
- Tamir Chandra
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
| | - Kristina Kirschner
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | | | - Benjamin D. Pope
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Tyrone Ryba
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Scott Newman
- Department of Pathology and Hutchison/MRC Research Centre, University of Cambridge, Cambridge CB2 0XZ, UK
| | - Kashif Ahmed
- The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
| | - Shamith A. Samarajiwa
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
| | - Rafik Salama
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | - Thomas Carroll
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | - Rory Stark
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | - Rekin’s Janky
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
| | - Masako Narita
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | - Lixiang Xue
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
| | - Agustin Chicas
- Cancer Biology and Genetics Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
| | - Sabrina Nũnez
- Cold Spring Harbor Laboratory, Cold Spring Harbor, NY 11724, USA
| | - Ralf Janknecht
- Department of Cell Biology, University of Oklahoma Health Sciences Center, Oklahoma City, OK 73104, USA
| | | | - Michael D. Wilson
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
- The Hospital for Sick Children, Toronto, ON M5G 1X8, Canada
| | - Aileen Marshall
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Cambridge Hepatobiliary Unit, Addenbrooke’s Hospital, Cambridge CB2 2QQ, UK
| | - Duncan T. Odom
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
| | - M. Madan Babu
- MRC Laboratory of Molecular Biology, Cambridge CB2 0QH, UK
| | | | - Simon Tavaré
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
| | - Paul A.W. Edwards
- Department of Pathology and Hutchison/MRC Research Centre, University of Cambridge, Cambridge CB2 0XZ, UK
| | - Scott W. Lowe
- Cancer Biology and Genetics Program, Memorial Sloan Kettering Cancer Center, New York, NY 10065, USA
- Howard Hughes Medical Institute
| | - Hiroshi Kimura
- Graduate School of Frontier Biosciences, Osaka University, Osaka 565-0871, Japan
| | - David M. Gilbert
- Department of Biological Science, Florida State University, Tallahassee, FL 32306, USA
| | - Masashi Narita
- Cancer Research UK Cambridge Research Institute, Li Ka Shing Centre, Robinson Way, Cambridge CB2 0RE, UK
- Department of Oncology, University of Cambridge, Cambridge CB2 0RE, UK
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105
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David G. Regulation of oncogene-induced cell cycle exit and senescence by chromatin modifiers. Cancer Biol Ther 2012; 13:992-1000. [PMID: 22825329 DOI: 10.4161/cbt.21116] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
Oncogene activation leads to dramatic changes in numerous biological pathways controlling cellular division, and results in the initiation of a transcriptional program that promotes transformation. Conversely, it also triggers an irreversible cell cycle exit called cellular senescence, which allows the organism to counteract the potentially detrimental uncontrolled proliferation of damaged cells. Therefore, a tight transcriptional control is required at the onset of oncogenic signal, coordinating both positive and negative regulation of gene expression. Not surprisingly, numerous chromatin modifiers contribute to the cellular response to oncogenic stress. While these chromatin modifiers were initially thought of as mere mediators of the cellular response to oncogenic stress, recent studies have uncovered a direct and specific regulation of chromatin modifiers by oncogenic signals. We review here the diverse functions of chromatin modifiers in the cellular response to oncogenic stress, and discuss the implications of these findings on the regulation of cell cycle progression and proliferation by activated oncogenes.
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Affiliation(s)
- Gregory David
- Department of Pharmacology and NYU Cancer Institute, NYU Langone Medical Center, New York, NY, USA.
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106
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Abstract
A major goal in cancer and aging research is to discriminate the biochemical modifications that happen locally that could account for the healthiness or malignancy of tissues. Senescence is one general antiproliferative cellular process that acts as a strong barrier for cancer progression, playing a crucial role in aging. Here, we focus on the current methods to assess cellular senescence, discriminating the advantages and disadvantages of several senescence biomarkers.
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Affiliation(s)
- Bruno Bernardes de Jesus
- Telomeres and Telomerase Group, Molecular Oncology Program, Spanish National Cancer Centre, Madrid, Spain
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107
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Aging Process in Chromatin of Animals. ANNALS OF ANIMAL SCIENCE 2012. [DOI: 10.2478/v10220-012-0025-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Aging Process in Chromatin of AnimalsThe aging process is a variable, stochastic and pleiotropic phenomenon which is regulated by different environmental and genetic factors. The age-associated changes, which occur at the molecular and cellular levels and disturb biological homeostasis, may directly or indirectly contribute to aging, causing apoptosis or cellular senescence and consequently leading to the death of the organism. In this context, it is particularly interesting to observe changes in somatic cell chromatin. In the present paper, we summarized the knowledge on the biological aspects of aging with special consideration of age-related changes in chromatin like DNA damage, shortening telomeres or age-related changes in methylation of DNA.
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108
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Salminen A, Kauppinen A, Kaarniranta K. Emerging role of NF-κB signaling in the induction of senescence-associated secretory phenotype (SASP). Cell Signal 2012; 24:835-45. [PMID: 22182507 DOI: 10.1016/j.cellsig.2011.12.006] [Citation(s) in RCA: 451] [Impact Index Per Article: 37.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/2011] [Accepted: 12/04/2011] [Indexed: 11/17/2022]
Abstract
The major hallmark of cellular senescence is an irreversible cell cycle arrest and thus it is a potent tumor suppressor mechanism. Genotoxic insults, e.g. oxidative stress, are important inducers of the senescent phenotype which is characterized by an accumulation of senescence-associated heterochromatic foci (SAHF) and DNA segments with chromatin alterations reinforcing senescence (DNA-SCARS). Interestingly, senescent cells secrete pro-inflammatory factors and thus the condition has been called the senescence-associated secretory phenotype (SASP). Emerging data has revealed that NF-κB signaling is the major signaling pathway which stimulates the appearance of SASP. It is known that DNA damage provokes NF-κB signaling via a variety of signaling complexes containing NEMO protein, an NF-κB essential modifier, as well as via the activation of signaling pathways of p38MAPK and RIG-1, retinoic acid inducible gene-1. Genomic instability evoked by cellular stress triggers epigenetic changes, e.g. release of HMGB1 proteins which are also potent enhancers of inflammatory responses. Moreover, environmental stress and chronic inflammation can stimulate p38MAPK and ceramide signaling and induce cellular senescence with pro-inflammatory responses. On the other hand, two cyclin-dependent kinase inhibitors, p16INK4a and p14ARF, are effective inhibitors of NF-κB signaling. We will review in detail the signaling pathways which activate NF-κB signaling and trigger SASP in senescent cells.
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Affiliation(s)
- Antero Salminen
- Department of Neurology, Institute of Clinical Medicine, University of Eastern Finland, P.O. Box 1627, FIN-70211 Kuopio, Finland.
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109
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The retinoblastoma family of proteins and their regulatory functions in the mammalian cell division cycle. Cell Div 2012; 7:10. [PMID: 22417103 PMCID: PMC3325851 DOI: 10.1186/1747-1028-7-10] [Citation(s) in RCA: 183] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2012] [Accepted: 03/14/2012] [Indexed: 12/15/2022] Open
Abstract
The retinoblastoma (RB) family of proteins are found in organisms as distantly related as humans, plants, and insects. These proteins play a key role in regulating advancement of the cell division cycle from the G1 to S-phases. This is achieved through negative regulation of two important positive regulators of cell cycle entry, E2F transcription factors and cyclin dependent kinases. In growth arrested cells transcriptional activity by E2Fs is repressed by RB proteins. Stimulation of cell cycle entry by growth factor signaling leads to activation of cyclin dependent kinases. They in turn phosphorylate and inactivate the RB family proteins, leading to E2F activation and additional cyclin dependent kinase activity. This propels the cell cycle irreversibly forward leading to DNA synthesis. This review will focus on the basic biochemistry and cell biology governing the regulation and activity of mammalian RB family proteins in cell cycle control.
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110
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Kato K, Okuwaki M, Nagata K. Role of Template Activating Factor-I as a chaperone in linker histone dynamics. J Cell Sci 2012; 124:3254-65. [PMID: 21940793 DOI: 10.1242/jcs.083139] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/10/2023] Open
Abstract
Linker histone H1 is a fundamental chromosomal protein involved in the maintenance of higher-ordered chromatin organization. The exchange dynamics of histone H1 correlates well with chromatin plasticity. A variety of core histone chaperones involved in core histone dynamics has been identified, but the identity of the linker histone chaperone in the somatic cell nucleus has been a long-standing unanswered question. Here we show that Template Activating Factor-I (TAF-I, also known as protein SET) is involved in histone H1 dynamics as a linker histone chaperone. Among previously identified core histone chaperones and linker histone chaperone candidates, only TAF-I was found to be associated specifically with histone H1 in mammalian somatic cell nuclei. TAF-I showed linker histone chaperone activity in vitro. Fluorescence recovery after photobleaching analyses revealed that TAF-I is involved in the regulation of histone H1 dynamics in the nucleus. Therefore, we propose that TAF-I is a key molecule that regulates linker histone-mediated chromatin assembly and disassembly.
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Affiliation(s)
- Kohsuke Kato
- Department of Infection Biology, Graduate School of Comprehensive Human Sciences, University of Tsukuba, 1-1-1 Tennodai, Tsukuba 305-8575, Japan
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111
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Sato S, Takahashi S, Asamoto M, Nakanishi M, Wakita T, Ogura Y, Yatabe Y, Shirai T. Histone H1 expression in human prostate cancer tissues and cell lines. Pathol Int 2011; 62:84-92. [DOI: 10.1111/j.1440-1827.2011.02755.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
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112
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Pichugin A, Beaujean N, Vignon X, Vassetzky Y. Ring-like distribution of constitutive heterochromatin in bovine senescent cells. PLoS One 2011; 6:e26844. [PMID: 22132080 PMCID: PMC3223162 DOI: 10.1371/journal.pone.0026844] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2011] [Accepted: 10/05/2011] [Indexed: 11/29/2022] Open
Abstract
Background Cells that reach “Hayflick limit” of proliferation, known as senescent cells, possess a particular type of nuclear architecture. Human senescent cells are characterized by the presence of highly condensed senescent associated heterochromatin foci (SAHF) that can be detected both by immunostaining for histone H3 three-methylated at lysine 9 (H3K9me3) and by DAPI counterstaining. Methods We have studied nuclear architecture in bovine senescent cells using a combination of immunofluorescence and 3D fluorescent in-situ hybridization (FISH). Results Analysis of heterochromatin distribution in bovine senescent cells using fluorescent in situ hybridization for pericentric chromosomal regions, immunostaining of H3K9me3, centromeric proteins CENP A/B and DNA methylation showed a lower level of heterochromatin condensation as compared to young cells. No SAHF foci were observed. Instead, we observed fibrous ring-like or ribbon-like heterochromatin patterns that were undetectable with DAPI counterstaining. These heterochromatin fibers were associated with nucleoli. Conclusions Constitutive heterochromatin in bovine senescent cells is organized in ring-like structures.
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Affiliation(s)
- Andrey Pichugin
- INRA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
- ENVA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
- Centre National de la Recherche Scientifique UMR 8126, Université Paris-Sud 11, Institut de Cancérologie Gustave-Roussy, Villejuif, France
- * E-mail: (AP); (YV)
| | - Nathalie Beaujean
- INRA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
- ENVA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
| | - Xavier Vignon
- INRA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
- ENVA UMR 1198 Groupe Biologie du Développement et Reproduction, Jouy en Josas, France
| | - Yegor Vassetzky
- Centre National de la Recherche Scientifique UMR 8126, Université Paris-Sud 11, Institut de Cancérologie Gustave-Roussy, Villejuif, France
- * E-mail: (AP); (YV)
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113
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Histone H1 recruitment by CHD8 is essential for suppression of the Wnt-β-catenin signaling pathway. Mol Cell Biol 2011; 32:501-12. [PMID: 22083958 DOI: 10.1128/mcb.06409-11] [Citation(s) in RCA: 101] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
Members of the chromodomain helicase DNA-binding (CHD) family of proteins are thought to regulate gene expression. Among mammalian CHD proteins, CHD8 was originally isolated as a negative regulator of the Wnt-β-catenin signaling pathway that binds directly to β-catenin and suppresses its transactivation activity. The mechanism by which CHD8 inhibits β-catenin-dependent transcription has been unclear, however. Here we show that CHD8 promotes the association of β-catenin and histone H1, with formation of the trimeric complex on chromatin being required for inhibition of β-catenin-dependent transactivation. A CHD8 mutant that lacks the histone H1 binding domain did not show such inhibitory activity, indicating that histone H1 recruitment is essential for the inhibitory effect of CHD8. Furthermore, either depletion of histone H1 or expression of a dominant negative mutant of this protein resulted in enhancement of the response to Wnt signaling. These observations reveal a new mode of regulation of the Wnt signaling pathway by CHD8, which counteracts β-catenin function through recruitment of histone H1 to Wnt target genes. Given that CHD8 is expressed predominantly during embryogenesis, it may thus contribute to setting a threshold for responsiveness to Wnt signaling that operates in a development-dependent manner.
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114
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Simboeck E, Ribeiro JD, Teichmann S, Di Croce L. Epigenetics and senescence: Learning from the INK4-ARF locus. Biochem Pharmacol 2011; 82:1361-70. [DOI: 10.1016/j.bcp.2011.07.084] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2011] [Revised: 07/14/2011] [Accepted: 07/15/2011] [Indexed: 11/30/2022]
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115
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Jeanblanc M, Ragu S, Gey C, Contrepois K, Courbeyrette R, Thuret JY, Mann C. Parallel pathways in RAF-induced senescence and conditions for its reversion. Oncogene 2011; 31:3072-85. [PMID: 22020327 DOI: 10.1038/onc.2011.481] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
We developed a clonal WI-38hTERT/GFP-RAF1-ER immortal cell line to study RAF-induced senescence of human fibroblasts. Activation of the GFP-RAF1-ER kinase by addition of 4-hydroxy-tamoxifen led to a robust induction of senescence within one population doubling, accompanied by the assembly of heterochromatic foci. At least two pathways contribute in parallel to this senescence leading to the accumulation of p15, p16, p21 and p27 inhibitors of cyclin-dependent kinases (CKIs). Cells that traversed S phase after RAF1 kinase activation experienced a replicative stress manifested by phosphorylation of H2AX and Chk2 and synthesis of p21. However, about half the cells in the population were blocked without passing through S phase and did not show activation of DNA-damage checkpoints. When the cells were cultivated in 5% oxygen, RAF1 activation generated minimal reactive oxygen species, but RAF-induced senescence occurred efficiently in these conditions even in the presence of anti-oxidants or inhibitors of DNA checkpoint pathways. Despite the presence of heterochromatic foci, simultaneous knockdown of p16 and p21 with inactivation of the GFP-RAF1-ER kinase led to rapid reversion of the senescent state with the majority of cells becoming competent for long-term proliferation. These results demonstrate that replicative and oxidative stresses are not required for RAF-induced senescence, and this senescence is readily reversed upon loss of CKIs.
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Affiliation(s)
- M Jeanblanc
- CEA, iBiTec-S, Service de Biologie Intégrative et Génétique Moléculaire-Bât, 142, CEA/Saclay, Gif-sur-Yvette, France
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116
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Rai TS, Adams PD. Lessons from senescence: Chromatin maintenance in non-proliferating cells. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2011; 1819:322-31. [PMID: 21839870 DOI: 10.1016/j.bbagrm.2011.07.014] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2011] [Revised: 07/25/2011] [Accepted: 07/27/2011] [Indexed: 02/08/2023]
Abstract
Cellular senescence is an irreversible proliferation arrest, thought to contribute to tumor suppression, proper wound healing and, perhaps, tissue and organismal aging. Two classical tumor suppressors, p53 and pRB, control cell cycle arrest associated with senescence. Profound molecular changes occur in cells undergoing senescence. At the level of chromatin, for example, senescence associated heterochromatic foci (SAHF) form in some cell types. Chromatin is inherently dynamic and likely needs to be actively maintained to achieve a stable cell phenotype. In proliferating cells chromatin is maintained in conjunction with DNA replication, but how non-proliferating cells maintain chromatin structure is poorly understood. Some histone variants, such as H3.3 and macroH2A increase as cells undergo senescence, suggesting histone variants and their associated chaperones could be important in chromatin structure maintenance in senescent cells. Here, we discuss options available for senescent cells to maintain chromatin structure and the relative contribution of histone variants and chaperones in this process. This article is part of a Special Issue entitled: Histone chaperones and chromatin assembly.
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117
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Abstract
The RB1 gene is the first tumor suppressor gene identified whose mutational inactivation is the cause of a human cancer, the pediatric cancer retinoblastoma. The 25 years of research since its discovery has not only illuminated a general role for RB1 in human cancer, but also its critical importance in normal development. Understanding the molecular function of the RB1 encoded protein, pRb, is a long-standing goal that promises to inform our understanding of cancer, its relationship to normal development, and possible therapeutic strategies to combat this disease. Achieving this goal has been difficult, complicated by the complexity of pRb and related proteins. The goal of this review is to explore the hypothesis that, at its core, the molecular function of pRb is to dynamically regulate the location-specific assembly or disassembly of protein complexes on the DNA in response to the output of various signaling pathways. These protein complexes participate in a variety of molecular processes relevant to DNA including gene transcription, DNA replication, DNA repair, and mitosis. Through regulation of these processes, RB1 plays a uniquely prominent role in normal development and cancer.
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Affiliation(s)
- Meenalakshmi Chinnam
- Department of Pharmacology and Therapeutics, Roswell Park Cancer Institute, Buffalo, New York, USA
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118
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Kreiling JA, Tamamori-Adachi M, Sexton AN, Jeyapalan JC, Munoz-Najar U, Peterson AL, Manivannan J, Rogers ES, Pchelintsev NA, Adams PD, Sedivy JM. Age-associated increase in heterochromatic marks in murine and primate tissues. Aging Cell 2011; 10:292-304. [PMID: 21176091 DOI: 10.1111/j.1474-9726.2010.00666.x] [Citation(s) in RCA: 113] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Chromatin is highly dynamic and subject to extensive remodeling under many physiologic conditions. Changes in chromatin that occur during the aging process are poorly documented and understood in higher organisms, such as mammals. We developed an immunofluorescence assay to quantitatively detect, at the single cell level, changes in the nuclear content of chromatin-associated proteins. We found increased levels of the heterochromatin-associated proteins histone macro H2A (mH2A) and heterochromatin protein 1 beta (HP1β) in human fibroblasts during replicative senescence in culture, and for the first time, an age-associated increase in these heterochromatin marks in several tissues of mice and primates. Mouse lung was characterized by monophasic mH2A expression histograms at both ages, and an increase in mean staining intensity at old age. In the mouse liver, we observed increased age-associated localization of mH2A to regions of pericentromeric heterochromatin. In the skeletal muscle, we found two populations of cells with either low or high mH2A levels. This pattern of expression was similar in mouse and baboon, and showed a clear increase in the proportion of nuclei with high mH2A levels in older animals. The frequencies of cells displaying evidence of increased heterochromatinization are too high to be readily accounted for by replicative or oncogene-induced cellular senescence, and are prominently found in terminally differentiated, postmitotic tissues that are not conventionally thought to be susceptible to senescence. Our findings distinguish specific chromatin states in individual cells of mammalian tissues, and provide a foundation to investigate further the progressive epigenetic changes that occur during aging.
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119
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Kreiling JA, Tamamori-Adachi M, Sexton AN, Jeyapalan JC, Munoz-Najar U, Peterson AL, Manivannan J, Rogers ES, Pchelintsev NA, Adams PD, Sedivy JM. Age-associated increase in heterochromatic marks in murine and primate tissues. Aging Cell 2011. [PMID: 21176091 DOI: 10.1111/j.1474-9726.2010.00666.x.age-associated] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/20/2023] Open
Abstract
Chromatin is highly dynamic and subject to extensive remodeling under many physiologic conditions. Changes in chromatin that occur during the aging process are poorly documented and understood in higher organisms, such as mammals. We developed an immunofluorescence assay to quantitatively detect, at the single cell level, changes in the nuclear content of chromatin-associated proteins. We found increased levels of the heterochromatin-associated proteins histone macro H2A (mH2A) and heterochromatin protein 1 beta (HP1β) in human fibroblasts during replicative senescence in culture, and for the first time, an age-associated increase in these heterochromatin marks in several tissues of mice and primates. Mouse lung was characterized by monophasic mH2A expression histograms at both ages, and an increase in mean staining intensity at old age. In the mouse liver, we observed increased age-associated localization of mH2A to regions of pericentromeric heterochromatin. In the skeletal muscle, we found two populations of cells with either low or high mH2A levels. This pattern of expression was similar in mouse and baboon, and showed a clear increase in the proportion of nuclei with high mH2A levels in older animals. The frequencies of cells displaying evidence of increased heterochromatinization are too high to be readily accounted for by replicative or oncogene-induced cellular senescence, and are prominently found in terminally differentiated, postmitotic tissues that are not conventionally thought to be susceptible to senescence. Our findings distinguish specific chromatin states in individual cells of mammalian tissues, and provide a foundation to investigate further the progressive epigenetic changes that occur during aging.
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Affiliation(s)
- Jill A Kreiling
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, 70 Ship Street, Providence, RI 02903, USA.
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120
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Abstract
Cellular senescence is a specialized form of growth arrest, confined to mitotic cells, induced by various stressful stimuli and characterized by a permanent growth arrest, resistance to apoptosis, an altered pattern of gene expression and the expression of some markers that are characteristic, although not exclusive, to the senescent state. Senescent cells profoundly modify neighboring and remote cells through the production of an altered secretome, eventually leading to inflammation, fibrosis and possibly growth of neoplastic cells. Mammalian aging has been defined as a reduction in the capacity to adequately maintain tissue homeostasis or to repair tissues after injury. Tissue homeostasis and regenerative capacity are nowadays considered to be related to the stem cell pool present in every tissue. For this reason, pathological and patho-physiological conditions characterized by altered tissue homeostasis and impaired regenerative capacity can be viewed as a consequence of the reduction in stem cell number and/or function. Last, cellular senescence is a double-edged sword, since it may inhibit the growth of transformed cells, preventing the occurrence of cancer, while it may facilitate growth of preneoplastic lesions in a paracrine fashion; therefore, interventions targeting this cell response to stress may have a profound impact on many age-related pathologies, ranging from cardiovascular disease to oncology. Aim of this review is to discuss both molecular mechanisms associated with stem cell senescence and interventions that may attenuate or reverse this process.
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121
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Abrass CK, Hansen K, Popov V, Denisenko O. Alterations in chromatin are associated with increases in collagen III expression in aging nephropathy. Am J Physiol Renal Physiol 2010; 300:F531-9. [PMID: 20610530 DOI: 10.1152/ajprenal.00237.2010] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
Aging nephropathy is a slowly progressive fibrotic process that affects all compartments of the kidney and eventually impairs kidney function; however, little is known about the mechanisms that contribute to this process. These studies examined the epigenetic control of expression of collagen III (Col3a1), a matrix protein that contributes to kidney fibrosis. Using real-time PCR, Western blotting, and chromatin immunoprecipitation assay of kidneys harvested from 4- and 24-mo-old ad libitum-fed F344 rats, we found increased transcription of Col3a1 that was associated with increased RNA polymerase II recruitment despite elevated posttranslational histone modification (H3K27me3) normally associated with gene silencing. A reduction in the density of another repressive modification (H3K9me3) at the Col3a1 locus in aged rats suggests that cooperation between Polycomb- and heterochromatin-mediated systems are required to maintain repression of the Col3a1 gene. These findings demonstrate alterations in epigenetic control of gene expression in association with the fibrosis of aging nephropathy.
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Affiliation(s)
- Christine K Abrass
- Primary and Specialty Care Medicine, Department of Veterans Affairs Puget Sound Health Care System, Seattle, Washington, USA.
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122
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Identification of target genes for wild type and truncated HMGA2 in mesenchymal stem-like cells. BMC Cancer 2010; 10:329. [PMID: 20576167 PMCID: PMC2912264 DOI: 10.1186/1471-2407-10-329] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2010] [Accepted: 06/25/2010] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND The HMGA2 gene, coding for an architectural transcription factor involved in mesenchymal embryogenesis, is frequently deranged by translocation and/or amplification in mesenchymal tumours, generally leading to over-expression of shortened transcripts and a truncated protein. METHODS To identify pathways that are affected by sarcoma-associated variants of HMGA2, we have over-expressed wild type and truncated HMGA2 protein in an immortalized mesenchymal stem-like cell (MSC) line, and investigated the localisation of these proteins and their effects on differentiation and gene expression patterns. RESULTS Over-expression of both transgenes blocked adipogenic differentiation of these cells, and microarray analysis revealed clear changes in gene expression patterns, more pronounced for the truncated protein. Most of the genes that showed altered expression in the HMGA2-overexpressing cells fell into the group of NF-kappaB-target genes, suggesting a central role for HMGA2 in this pathway. Of particular interest was the pronounced up-regulation of SSX1, already implicated in mesenchymal oncogenesis and stem cell functions, only in cells expressing the truncated protein. Furthermore, over-expression of both HMGA2 forms was associated with a strong repression of the epithelial marker CD24, consistent with the reported low level of CD24 in cancer stem cells. CONCLUSIONS We conclude that the c-terminal part of HMGA2 has important functions at least in mesenchymal cells, and the changes in gene expression resulting from overexpressing a protein lacking this domain may add to the malignant potential of sarcomas.
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123
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CENP-A reduction induces a p53-dependent cellular senescence response to protect cells from executing defective mitoses. Mol Cell Biol 2010; 30:2090-104. [PMID: 20160010 DOI: 10.1128/mcb.01318-09] [Citation(s) in RCA: 77] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cellular senescence is an irreversible growth arrest and is presumed to be a natural barrier to tumor development. Like telomere shortening, certain defects in chromosome integrity can trigger senescence; however, the roles of centromere proteins in regulating commitment to the senescent state remains to be established. We examined chromatin structure in senescent human primary fibroblasts and found that CENP-A protein levels are diminished in senescent cells. Senescence-associated reduction of CENP-A is caused by transcriptional and posttranslational control. Surprisingly, forced reduction of CENP-A by short-hairpin RNA was found to cause premature senescence in human primary fibroblasts. This premature senescence is dependent on a tumor suppressor, p53, but not on p16(INK4a)-Rb; the depletion of CENP-A in p53-deficient cells results in aberrant mitosis with chromosome missegregation. We propose that p53-dependent senescence that arises from CENP-A reduction acts as a "self-defense mechanism" to prevent centromere-defective cells from undergoing mitotic proliferation that potentially leads to massive generation of aneuploid cells.
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124
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Talluri S, Isaac CE, Ahmad M, Henley SA, Francis SM, Martens AL, Bremner R, Dick FA. A G1 checkpoint mediated by the retinoblastoma protein that is dispensable in terminal differentiation but essential for senescence. Mol Cell Biol 2010; 30:948-60. [PMID: 20008551 PMCID: PMC2815577 DOI: 10.1128/mcb.01168-09] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/28/2009] [Revised: 09/23/2009] [Accepted: 12/07/2009] [Indexed: 11/20/2022] Open
Abstract
Terminally differentiated cell types are needed to live and function in a postmitotic state for a lifetime. Cellular senescence is another type of permanent arrest that blocks the proliferation of cells in response to genotoxic stress. Here we show that the retinoblastoma protein (pRB) uses a mechanism to block DNA replication in senescence that is distinct from its role in permanent cell cycle exit associated with terminal differentiation. Our work demonstrates that a subtle mutation in pRB that cripples its ability to interact with chromatin regulators impairs heterochromatinization and repression of E2F-responsive promoters during senescence. In contrast, terminally differentiated nerve and muscle cells bearing the same mutation fully exit the cell cycle and block E2F-responsive gene expression by a different mechanism. Remarkably, this reveals that pRB recruits chromatin regulators primarily to engage a stress-responsive G(1) arrest program.
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Affiliation(s)
- Srikanth Talluri
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Christian E. Isaac
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Mohammad Ahmad
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Shauna A. Henley
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Sarah M. Francis
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Alison L. Martens
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Rod Bremner
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
| | - Frederick A. Dick
- London Regional Cancer Program, Children's Health Research Institute, Department of Biochemistry, University of Western Ontario, London, Ontario, Canada, Genetics and Development Division, Toronto Western Research Institute, Department of Ophthalmology and Visual Science, Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Ontario, Canada
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125
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PARP is involved in replicative aging in Neurospora crassa. Fungal Genet Biol 2010; 47:297-309. [PMID: 20045739 DOI: 10.1016/j.fgb.2009.12.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/08/2009] [Revised: 12/10/2009] [Accepted: 12/29/2009] [Indexed: 11/22/2022]
Abstract
Modification of proteins by the addition of poly(ADP-ribose) is carried out by poly(ADP-ribose) polymerases (PARPs). PARPs have been implicated in a wide range of biological processes in eukaryotes, but no universal function has been established. A study of the Aspergillus nidulans PARP ortholog (PrpA) revealed that the protein is essential and involved in DNA repair, reminiscent of findings using mammalian systems. We found that a Neurospora PARP orthologue (NPO) is dispensable for cell survival, DNA repair and epigenetic silencing but that replicative aging of mycelia is accelerated in an npo mutant strain. We propose that PARPs may control aging as proposed for Sirtuins, which also consume NAD+ and function either as mono(ADP-ribose) transferases or protein deacetylases. PARPs may regulate aging by impacting NAD+/NAM availability, thereby influencing Sirtuin activity, or they may function in alternative NAD+-dependent or NAD+-independent aging pathways.
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126
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Adams PD. Healing and hurting: molecular mechanisms, functions, and pathologies of cellular senescence. Mol Cell 2009; 36:2-14. [PMID: 19818705 DOI: 10.1016/j.molcel.2009.09.021] [Citation(s) in RCA: 257] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/10/2009] [Indexed: 01/07/2023]
Abstract
Cellular senescence is a proliferation arrest that is typically irreversible and caused by various cellular stresses, including excess rounds of cell division and cancer-causing genetic alterations. Senescence actively contributes to a tissue-level response to tissue wounding and incipient cancer, healing the tissue and suppressing tumor formation. However, in the long term, the same senescence program may hurt the tissue, thereby contributing to tissue aging. Tumor suppression, wound healing, and aging are each associated with inflammation, and here it is proposed that cellular senescence contributes to a "nonimmune cell" component of the tissue inflammatory response.
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Affiliation(s)
- Peter D Adams
- Cancer Research UK Beatson Labs, University of Glasgow, Glasgow G61 1BD, UK.
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127
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Reeves R. Nuclear functions of the HMG proteins. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2009; 1799:3-14. [PMID: 19748605 DOI: 10.1016/j.bbagrm.2009.09.001] [Citation(s) in RCA: 188] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/31/2009] [Accepted: 09/04/2009] [Indexed: 12/12/2022]
Abstract
Although the three families of mammalian HMG proteins (HMGA, HMGB and HMGN) participate in many of the same nuclear processes, each family plays its own unique role in modulating chromatin structure and regulating genomic function. This review focuses on the similarities and differences in the mechanisms by which the different HMG families impact chromatin structure and influence cellular phenotype. The biological implications of having three architectural transcription factor families with complementary, but partially overlapping, nuclear functions are discussed.
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Affiliation(s)
- Raymond Reeves
- School of Molecular Biosciences, Washington State University, Biotechnology/Life Sciences Bldg., Rm. 143, Pullman, WA 99164-7520, USA.
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128
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Longworth MS, Dyson NJ. pRb, a local chromatin organizer with global possibilities. Chromosoma 2009; 119:1-11. [PMID: 19714354 DOI: 10.1007/s00412-009-0238-0] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2009] [Revised: 08/12/2009] [Accepted: 08/14/2009] [Indexed: 12/22/2022]
Abstract
The retinoblastoma (pRb) family of proteins are well known for their tumor suppressor properties and for their ability to regulate transcription. The action of pRb family members correlates with the appearance of repressive chromatin marks at promoter regions of genes encoding key regulators of cell proliferation. Recent studies raise the possibility that pRb family members do not simply act by controlling the activity of individual promoters but that they may also function by promoting the more general organization of chromatin. In several contexts, pRb family members stimulate the compaction or condensation of chromatin and promote the formation of heterochromatin. In this review, we summarize studies that link pRb family members to the condensation or compaction of DNA.
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Affiliation(s)
- Michelle S Longworth
- Massachusetts General Hospital Cancer Center and Harvard Medical School, Building 149, 13th Street, Charlestown, MA, 02129, USA
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129
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HMGA1 levels influence mitochondrial function and mitochondrial DNA repair efficiency. Mol Cell Biol 2009; 29:5426-40. [PMID: 19687300 DOI: 10.1128/mcb.00105-09] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
HMGA chromatin proteins, a family of gene regulatory factors found at only low concentrations in normal cells, are almost universally overexpressed in cancer cells. HMGA proteins are located in the nuclei of normal cells except during the late S/G(2) phases of the cell cycle, when HMGA1, one of the members of the family, reversibly migrates to the mitochondria, where it binds to mitochondrial DNA (mtDNA). In many cancer cells, this controlled shuttling is lost and HMGA1 is found in mitochondria throughout the cell cycle. To investigate the effects of HMGA1 on mitochondria, we employed a genetically engineered line of human MCF-7 cells in which the levels of transgenic HMGA1 protein could be reversibly controlled. "Turn-ON" and "turn-OFF" time course experiments were performed with these cells to either increase or decrease intracellular HMGA1 levels, and various mitochondrial changes were monitored. Results demonstrated that changes in both mtDNA levels and mitochondrial mass inversely paralleled changes in HMGA1 concentrations, strongly implicating HMGA1 in the regulation of these parameters. Additionally, the level of cellular reactive oxygen species (ROS) increased and the efficiency of repair of oxidatively damaged mtDNA decreased as consequences of elevated HMGA1 expression. Increased ROS levels and reduced repair efficiency in HMGA1-overexpressing cells likely contribute to the increased occurrence of mutations in mtDNA frequently observed in cancer cells.
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130
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Fiorentino FP, Symonds CE, Macaluso M, Giordano A. Senescence and p130/Rbl2: a new beginning to the end. Cell Res 2009; 19:1044-51. [PMID: 19668264 DOI: 10.1038/cr.2009.96] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Senescence is the process of cellular aging dependent on the normal physiological functions of non-immortalized cells. With increasing data being uncovered in this field, the complex molecular web regulating senescence is gradually being unraveled. Recent studies have suggested two main phases of senescence, the triggering of senescence and the maintenance of senescence. Each has been supported by data implying precise roles for DNA methyltransferases, reactive oxygen species and other factors. We will first summarize the data supporting these claims and then highlight the specific role that we hypothesize that p130/Rbl2 plays in the modulation of the senescence process.
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Affiliation(s)
- Francesco P Fiorentino
- Section of Medical Oncology, Department of Oncology, Regional Reference Center for the Biomolecular Characterization and Genetic Screening of Hereditary Tumors, Università di Palermo, Via del Vespro 127, 90127, Palermo, Italy
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131
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Hwang ES, Yoon G, Kang HT. A comparative analysis of the cell biology of senescence and aging. Cell Mol Life Sci 2009; 66:2503-24. [PMID: 19421842 PMCID: PMC11115533 DOI: 10.1007/s00018-009-0034-2] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2009] [Revised: 04/02/2009] [Accepted: 04/15/2009] [Indexed: 01/10/2023]
Abstract
Various intracellular organelles, such as lysosomes, mitochondria, nuclei, and cytoskeletons, change during replicative senescence, but the utility of these changes as general markers of senescence and their significance with respect to functional alterations have not been comprehensively reviewed. Furthermore, the relevance of these alterations to cellular and functional changes in aging animals is poorly understood. In this paper, we review the studies that report these senescence-associated changes in various aging cells and their underlying mechanisms. Changes associated with lysosomes and mitochondria are found not only in cells undergoing replicative or induced senescence but also in postmitotic cells isolated from aged organisms. In contrast, other changes occur mainly in cells undergoing in vitro senescence. Comparison of age-related changes and their underlying mechanisms in in vitro senescent cells and aged postmitotic cells would reveal the relevance of replicative senescence to the physiological processes occurring in postmitotic cells as individuals age.
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Affiliation(s)
- Eun Seong Hwang
- Department of Life Science, University of Seoul, Dongdaemungu, Jeonnongdong 90, Seoul 130-743, Republic of Korea.
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132
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Pfannkuche K, Summer H, Li O, Hescheler J, Dröge P. The high mobility group protein HMGA2: a co-regulator of chromatin structure and pluripotency in stem cells? Stem Cell Rev Rep 2009; 5:224-30. [PMID: 19551524 DOI: 10.1007/s12015-009-9078-9] [Citation(s) in RCA: 84] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2009] [Accepted: 06/01/2009] [Indexed: 11/25/2022]
Abstract
The small, chromatin-associated HMGA proteins contain three separate DNA binding domains, so-called AT hooks, which bind preferentially to short AT-rich sequences. These proteins are abundant in pluripotent embryonic stem (ES) cells and most malignant human tumors, but are not detectable in normal somatic cells. They act both as activator and repressor of gene expression, and most likely facilitate DNA architectural changes during formation of specialized nucleoprotein structures at selected promoter regions. For example, HMGA2 is involved in transcriptional activation of certain cell proliferation genes, which likely contributes to its well-established oncogenic potential during tumor formation. However, surprisingly little is known about how HMGA proteins bind DNA packaged in chromatin and how this affects the chromatin structure at a larger scale. Experimental evidence suggests that HMGA2 competes with binding of histone H1 in the chromatin fiber. This could substantially alter chromatin domain structures in ES cells and contribute to the activation of certain transcription networks. HMGA2 also seems capable of recruiting enzymes directly involved in histone modifications to trigger gene expression. Furthermore, it was shown that multiple HMGA2 molecules bind stably to a single nucleosome core particle whose structure is known. How these features of HMGA2 impinge on chromatin organization inside a living cell is unknown. In this commentary, we propose that HMGA2, through the action of three independent DNA binding domains, substantially contributes to the plasticity of ES cell chromatin and is involved in the maintenance of a un-differentiated cell state.
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Affiliation(s)
- Kurt Pfannkuche
- Institute for Neurophysiology, University of Cologne, Robert Koch Str. 39, 50931, Cologne, Germany.
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133
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Li AYJ, Boo LM, Wang SY, Lin HH, Wang CCC, Yen Y, Chen BPC, Chen DJ, Ann DK. Suppression of nonhomologous end joining repair by overexpression of HMGA2. Cancer Res 2009; 69:5699-706. [PMID: 19549901 DOI: 10.1158/0008-5472.can-08-4833] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Understanding the molecular details associated with aberrant high mobility group A2 (HMGA2) gene expression is key to establishing the mechanism(s) underlying its oncogenic potential and effect on the development of therapeutic strategies. Here, we report the involvement of HMGA2 in impairing DNA-dependent protein kinase (DNA-PK) during the nonhomologous end joining (NHEJ) process. We showed that HMGA2-expressing cells displayed deficiency in overall and precise DNA end-joining repair and accumulated more endogenous DNA damage. Proper and timely activation of DNA-PK, consisting of Ku70, Ku80, and DNA-PKcs subunits, is essential for the repair of DNA double strand breaks (DSB) generated endogenously or by exposure to genotoxins. In cells overexpressing HMGA2, accumulation of histone 2A variant X phosphorylation at Ser-139 (gamma-H2AX) was associated with hyperphosphorylation of DNA-PKcs at Thr-2609 and Ser-2056 before and after the induction of DSBs. Also, the steady-state complex of Ku and DNA ends was altered by HMGA2. Microirradiation and real-time imaging in living cells revealed that HMGA2 delayed the release of DNA-PKcs from DSB sites, similar to observations found in DNA-PKcs mutants. Moreover, HMGA2 alone was sufficient to induce chromosomal aberrations, a hallmark of deficiency in NHEJ-mediated DNA repair. In summary, a novel role for HMGA2 to interfere with NHEJ processes was uncovered, implicating HMGA2 in the promotion of genome instability and tumorigenesis.
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Affiliation(s)
- Angela Y J Li
- Department of Clinical and Molecular Pharmacology, City of Hope National Medical Center, Duarte, California 91010-3000, USA
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134
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Orthaus S, Klement K, Happel N, Hoischen C, Diekmann S. Linker histone H1 is present in centromeric chromatin of living human cells next to inner kinetochore proteins. Nucleic Acids Res 2009; 37:3391-406. [PMID: 19336418 PMCID: PMC2691837 DOI: 10.1093/nar/gkp199] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Revised: 03/09/2009] [Accepted: 03/10/2009] [Indexed: 01/04/2023] Open
Abstract
The vertebrate kinetochore complex assembles at the centromere on alpha-satellite DNA. In humans, alpha-satellite DNA has a repeat length of 171 bp slightly longer than the DNA in the chromatosome containing the linker histone H1. The centromere-binding protein CENP-B binds specifically to alpha-satellite DNA with properties of a centromeric-linker histone. Here, we analysed if linker histone H1 is present at or excluded from centromeric chromatin by CENP-B. By immunostaining we detected the presence, but no enrichment or depletion of five different H1 subtypes at centromeric chromatin. The binding dynamics of H1 at centromeric sites were similar to that at other locations in the genome. These dynamics did not change in CENP-B depleted cells, suggesting that CENP-B and H1 co-exist in centromeric chromatin with no or little functional overlap. By bimolecular fluorescence complementation (BiFC) and Förster resonance energy transfer (FRET), we revealed that the linker histone H1 subtypes H1 degrees and H1.2 bind to centromeric chromatin in interphase nuclei in direct neighbourhood to inner kinetochore proteins.
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Affiliation(s)
- S. Orthaus
- Leibniz-Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena and Department of Molecular Biology, Institute for Biochemistry and Molecular Cell Biology, University Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany
| | - K. Klement
- Leibniz-Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena and Department of Molecular Biology, Institute for Biochemistry and Molecular Cell Biology, University Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany
| | - N. Happel
- Leibniz-Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena and Department of Molecular Biology, Institute for Biochemistry and Molecular Cell Biology, University Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany
| | - C. Hoischen
- Leibniz-Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena and Department of Molecular Biology, Institute for Biochemistry and Molecular Cell Biology, University Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany
| | - S. Diekmann
- Leibniz-Institute for Age Research - Fritz Lipmann Institute, Beutenbergstr. 11, D-07745 Jena and Department of Molecular Biology, Institute for Biochemistry and Molecular Cell Biology, University Goettingen, Humboldtallee 23, D-37073 Goettingen, Germany
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135
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Dimauro T, David G. Chromatin modifications: the driving force of senescence and aging? Aging (Albany NY) 2009; 1:182-90. [PMID: 20157508 PMCID: PMC2806002 DOI: 10.18632/aging.100023] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2009] [Accepted: 02/11/2009] [Indexed: 12/23/2022]
Abstract
An emerging field of
investigation in the search for treatment of human disease is the
modulation of chromatin modifications. Chromatin modifications impart
virtually all processes occurring in the mammalian nucleus, from regulation
of transcription to genomic stability and nuclear high order organization.
It has been well recognized that, as the mammalian cell ages, its chromatin
structure evolves, both at a global level and at specific loci. While these
observations are mostly correlative, recent technical developments allowing
loss-of-function experiments and genome-wide approaches have permitted the
identification of a causal relationship between specific changes in
chromatin structure and the aging phenotype. Here we review the evidence
pointing to the modulation of chromatin structure as a potential driving
force of cellular aging in mammals.
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Affiliation(s)
- Teresa Dimauro
- Department of Pharmacology, NYU Langone Medical Center, New York, NY 10016, USA
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136
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Zimmermann S, Biniossek ML, Pantic M, Pfeifer D, Veelken H, Martens UM. Proteomic profiling of tumor cells after induction of telomere dysfunction. Proteomics 2009; 9:521-34. [DOI: 10.1002/pmic.200800471] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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137
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CHD8 suppresses p53-mediated apoptosis through histone H1 recruitment during early embryogenesis. Nat Cell Biol 2009; 11:172-82. [PMID: 19151705 DOI: 10.1038/ncb1831] [Citation(s) in RCA: 148] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/29/2008] [Accepted: 10/28/2008] [Indexed: 12/16/2022]
Abstract
The chromodomain helicase DNA-binding (CHD) family of enzymes is thought to regulate gene expression, but their role in the regulation of specific genes has been unclear. Here we show that CHD8 is expressed at a high level during early embryogenesis and prevents apoptosis mediated by the tumour suppressor protein p53. CHD8 was found to bind to p53 and to suppress its transactivation activity. CHD8 promoted the association of p53 and histone H1, forming a trimeric complex on chromatin that was required for inhibition of p53-dependent transactivation and apoptosis. Depletion of CHD8 or histone H1 resulted in p53 activation and apoptosis. Furthermore, Chd8(-/-) mice died early during embryogenesis, manifesting widespread apoptosis, whereas deletion of p53 ameliorated this developmental arrest. These observations reveal a mode of p53 regulation mediated by CHD8, which may set a threshold for induction of apoptosis during early embryogenesis by counteracting p53 function through recruitment of histone H1.
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138
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Human UBN1 is an ortholog of yeast Hpc2p and has an essential role in the HIRA/ASF1a chromatin-remodeling pathway in senescent cells. Mol Cell Biol 2008; 29:758-70. [PMID: 19029251 DOI: 10.1128/mcb.01047-08] [Citation(s) in RCA: 92] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Cellular senescence is an irreversible proliferation arrest, tumor suppression process and likely contributor to tissue aging. Senescence is often characterized by domains of facultative heterochromatin, called senescence-associated heterochromatin foci (SAHF), which repress expression of proliferation-promoting genes. Given its likely contribution to tumor suppression and tissue aging, it is essential to identify all components of the SAHF assembly pathway. Formation of SAHF in human cells is driven by a complex of histone chaperones, namely, HIRA and ASF1a. In yeast, the complex orthologous to HIRA/ASF1a contains two additional proteins, Hpc2p and Hir3p. Using a sophisticated approach to search for remote orthologs conserved in multiple species through evolution, we identified the HIRA-associated proteins, UBN1 and UBN2, as candidate human orthologs of Hpc2p. We show that the Hpc2-related domain of UBN1, UBN2, and Hpc2p is an evolutionarily conserved HIRA/Hir-binding domain, which directly interacts with the N-terminal WD repeats of HIRA/Hir. UBN1 binds to proliferation-promoting genes that are repressed by SAHF and associates with histone methyltransferase activity that methylates lysine 9 of histone H3, a site that is methylated in SAHF. UBN1 is indispensable for formation of SAHF. We conclude that UBN1 is an ortholog of yeast Hpc2p and a novel regulator of senescence.
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139
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Naru E, Takanezawa Y, Kobayashi M, Misaki Y, Kaji K, Arakane K. Increased levels of a particular phosphatidylcholine species in senescent human dermal fibroblasts in vitro. Hum Cell 2008; 21:70-8. [PMID: 18667023 DOI: 10.1111/j.1749-0774.2008.00052.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Plasma membranes are essential components of living cells, and phospholipids are major components of cellular membranes. Here, we used liquid chromatography/mass spectrometry to investigate changes in the membrane phospholipid content that occur in association with aging. Our results indicate that the levels of a particular species of phosphatidylcholine comprised of stearic acid and arachidonic acid increased with age. To determine the reason for the increased levels of this particular phosphatidylcholine, we examined the effect of highly unsaturated fatty acids, such as arachidonic acid and eicosapentaenoic acid, on cellular aging. Applied arachidonic acid was incorporated into phosphatidylcholine molecules, but neither arachidonic acid nor other related unsaturated fatty acids had any effect. We conclude that increased levels of this distinctive phosphatidylcholine are a result of in vitro senescence.
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Affiliation(s)
- Eiji Naru
- Research and Development Division, KOSE Corporation, Tokyo, 114-0005, Japan.
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140
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Sancho M, Diani E, Beato M, Jordan A. Depletion of human histone H1 variants uncovers specific roles in gene expression and cell growth. PLoS Genet 2008; 4:e1000227. [PMID: 18927631 PMCID: PMC2563032 DOI: 10.1371/journal.pgen.1000227] [Citation(s) in RCA: 152] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2008] [Accepted: 09/15/2008] [Indexed: 11/19/2022] Open
Abstract
At least six histone H1 variants exist in somatic mammalian cells that bind to the linker DNA and stabilize the nucleosome particle contributing to higher order chromatin compaction. In addition, H1 seems to be actively involved in the regulation of gene expression. However, it is not well known whether the different variants have distinct roles or if they regulate specific promoters. We have explored this by inducible shRNA-mediated knock-down of each of the H1 variants in a human breast cancer cell line. Rapid inhibition of each H1 variant was not compensated for by changes of expression of other variants. Microarray experiments have shown a different subset of genes to be altered in each H1 knock-down. Interestingly, H1.2 depletion caused specific effects such as a cell cycle G1-phase arrest, the repressed expression of a number of cell cycle genes, and decreased global nucleosome spacing. On its side, H1.4 depletion caused cell death in T47D cells, providing the first evidence of the essential role of an H1 variant for survival in a human cell type. Thus, specific phenotypes are observed in breast cancer cells depleted of individual histone H1 variants, supporting the theory that distinct roles exist for the linker histone variants. Eukaryotic DNA is packaged into chromatin through its association with histone proteins. The linker histone H1 sits at the base of the nucleosome near the DNA entry and exit sites to stabilize two full turns of DNA. In particular, histone H1 participates in nucleosome spacing and formation of the higher-order chromatin structure. In addition, H1 seems to be actively involved in the regulation of gene expression. Histone H1 in mammals is a family of closely related, single-gene encoded proteins, including five somatic subtypes (from H1.1 to H1.5) and a terminally differentiated expressed isoform (H1.0). It is not well known whether the different variants have distinct roles or if they regulate specific promoters. We have explored this by inducible knock-down of each of the H1 variants in breast cancer cells. A different subset of genes is altered in each H1 knock-down, and depletion has different effects on cell survival. Interestingly, H1.2 and H1.4 depletion specifically caused arrest of cell proliferation. Concomitant with this, H1.2 depletion caused decreased global nucleosome spacing and repressed expression of a number of cell cycle genes. Thus, specific phenotypes are observed in breast cancer cells depleted of individual histone H1 variants.
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Affiliation(s)
- Mónica Sancho
- Centre de Regulació Genòmica (CRG-UPF), Barcelona, Spain
| | - Erika Diani
- Centre de Regulació Genòmica (CRG-UPF), Barcelona, Spain
| | - Miguel Beato
- Centre de Regulació Genòmica (CRG-UPF), Barcelona, Spain
| | - Albert Jordan
- Centre de Regulació Genòmica (CRG-UPF), Barcelona, Spain
- * E-mail:
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141
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Khidr L, Wu G, Davila A, Procaccio V, Wallace D, Lee WH. Role of SUV3 helicase in maintaining mitochondrial homeostasis in human cells. J Biol Chem 2008; 283:27064-73. [PMID: 18678873 PMCID: PMC2556002 DOI: 10.1074/jbc.m802991200] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 07/23/2008] [Indexed: 11/06/2022] Open
Abstract
In yeast mitochondria, RNA degradation takes place through the coordinated activities of ySuv3 helicase and yDss1 exoribonuclease (mtEXO), whereas in bacteria, RNA is degraded via RNaseE, RhlB, PNPase, and enolase. Yeast lacking the Suv3 component of the mtEXO form petits and undergo a toxic accumulation of omega intron RNAs. Mammalian mitochondria resemble their prokaryotic origins by harboring a polyadenylation-dependent RNA degradation mechanism, but whether SUV3 participates in regulating RNA turnover in mammalian mitochondria is unclear. We found that lack of hSUV3 in mammalian cells subsequently yielded an accumulation of shortened polyadenylated mtRNA species and impaired mitochondrial protein synthesis. This suggests that SUV3 may serve in part as a component of an RNA degradosome, resembling its yeast ancestor. Reduction in the expression levels of oxidative phosphorylation components correlated with an increase in reactive oxygen species generation, whereas membrane potential and ATP production were decreased. These cumulative defects led to pleiotropic effects in mitochondria such as decreased mtDNA copy number and a shift in mitochondrial morphology from tubular to granular, which eventually manifests in cellular senescence or cell death. Thus, our results suggest that SUV3 is essential for maintaining proper mitochondrial function, likely through a conserved role in mitochondrial RNA regulation.
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Affiliation(s)
- Lily Khidr
- Department of Biological Chemistry, School of Medicine, University of California, Irvine, California 92697, USA
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142
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Kawakami K, Nakamura A, Ishigami A, Goto S, Takahashi R. Age-related difference of site-specific histone modifications in rat liver. Biogerontology 2008; 10:415-21. [PMID: 18814051 DOI: 10.1007/s10522-008-9176-0] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2008] [Accepted: 09/01/2008] [Indexed: 11/26/2022]
Abstract
Aging is associated with decrease in activities of the transcription, replication and DNA repair that can result in deterioration of cellular and tissue functions. Changes of chromatin structures with age are likely major underling mechanisms for the functional decline. Chromatin consists of DNA and histones as well as non-histone proteins. While age-associated change of DNA methylation is well documented, little information is available on site-specific histone modifications in aging. We studied here age-related change of selected modifications of rat liver histone, i.e., histone H3 Lys9 acetylation (H3K9ac), H3 Lys9 methylation (H3K9me), H3 Ser10 phosphorylation (H3S10ph) and H3 Lys14 acetylation (H3K14ac). H3K9ac was decreased and H3S10ph was increased with age significantly. In view of reports indicating that decrease in acetylation and increase in phosphorylation of H3 histones can suppress gene activity, our findings suggest that a mechanism of decreased chromatin functions with age is due to such epigenetic changes.
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Affiliation(s)
- Kyojiro Kawakami
- Department of Biochemistry, Faculty of Pharmaceutical Sciences, Toho University, Funabashi, Chiba, Japan
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143
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Satoh D, Sato D, Tsuyama T, Saito M, Ohkura H, Rolls MM, Ishikawa F, Uemura T. Spatial control of branching within dendritic arbors by dynein-dependent transport of Rab5-endosomes. Nat Cell Biol 2008; 10:1164-71. [PMID: 18758452 DOI: 10.1038/ncb1776] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2008] [Accepted: 07/21/2008] [Indexed: 01/07/2023]
Abstract
Dendrites allow neurons to integrate sensory or synaptic inputs, and the spatial disposition and local density of branches within the dendritic arbor limit the number and type of inputs. Drosophila melanogaster dendritic arborization (da) neurons provide a model system to study the genetic programs underlying such geometry in vivo. Here we report that mutations of motor-protein genes, including a dynein subunit gene (dlic) and kinesin heavy chain (khc), caused not only downsizing of the overall arbor, but also a marked shift of branching activity to the proximal area within the arbor. This phenotype was suppressed when dominant-negative Rab5 was expressed in the mutant neurons, which deposited early endosomes in the cell body. We also showed that 1) in dendritic branches of the wild-type neurons, Rab5-containing early endosomes were dynamically transported and 2) when Rab5 function alone was abrogated, terminal branches were almost totally deleted. These results reveal an important link between microtubule motors and endosomes in dendrite morphogenesis.
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Affiliation(s)
- Daisuke Satoh
- Department of Biophysics, Graduate School of Science, Sakyo-ku, Kyoto 606-8507, Japan
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144
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Wu C, Bassett A, Travers A. A variable topology for the 30-nm chromatin fibre. EMBO Rep 2008; 8:1129-34. [PMID: 18059311 DOI: 10.1038/sj.embor.7401115] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/14/2007] [Accepted: 10/09/2007] [Indexed: 12/17/2022] Open
Abstract
The structure of the 30-nm chromatin fibre is an important determinant of the regulation of eukaryotic transcription. A fundamental issue is whether the stacking of nucleosomes in this fibre is organized as a one-start or two-start helix. We argue that all recent experimental data are compatible with a two-start helix and propose that the topology of the fibre, but not the mode of stacking the nucleosomes, is dependent on the length of the linker DNA. This arrangement conserves nucleosome stacking and thus the external morphology of the fibre, and also ensures that the fibre adopts the highest available packing density.
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Affiliation(s)
- Chenyi Wu
- Medical Research Council Laboratory of Molecular Biology, Hills Road, Cambridge CB2 0QH, UK
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145
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Jeyapalan JC, Sedivy JM. Cellular senescence and organismal aging. Mech Ageing Dev 2008; 129:467-74. [PMID: 18502472 DOI: 10.1016/j.mad.2008.04.001] [Citation(s) in RCA: 256] [Impact Index Per Article: 16.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2007] [Revised: 03/27/2008] [Accepted: 04/06/2008] [Indexed: 01/22/2023]
Abstract
Cellular senescence, first observed and defined using in vitro cell culture studies, is an irreversible cell cycle arrest which can be triggered by a variety of factors. Emerging evidence suggests that cellular senescence acts as an in vivo tumor suppression mechanism by limiting aberrant proliferation. It has also been postulated that cellular senescence can occur independently of cancer and contribute to the physiological processes of normal organismal aging. Recent data have demonstrated the in vivo accumulation of senescent cells with advancing age. Some characteristics of senescent cells, such as the ability to modify their extracellular environment, could play a role in aging and age-related pathology. In this review, we examine current evidence that links cellular senescence and organismal aging.
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Affiliation(s)
- Jessie C Jeyapalan
- Department of Molecular Biology, Cell Biology and Biochemistry, Brown University, Providence, RI 02912, USA
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146
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Modification of the ATM/ATR directed DNA damage response state with aging and long after hepatocyte senescence induction in vivo. Mech Ageing Dev 2008; 129:332-40. [PMID: 18440596 DOI: 10.1016/j.mad.2008.02.014] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/02/2007] [Revised: 02/26/2008] [Accepted: 02/29/2008] [Indexed: 01/24/2023]
Abstract
The cellular DNA damage response (DDR) entails the activation of ATM, ATR and/or DNA PK protein kinases that causes modifications of proteins including Chk1, Chk2 and 53BP1, aggregation of DDR proteins into foci, and activation of p53. The DDR is thought to be required for initiation and maintenance of cellular senescence. Potentially senescent cells with DNA damage foci occur in large numbers in vivo with many diseases, but, with the exception of mammalian dermis, there is little evidence for that with normal aging. After experimental induction of cellular senescence in the livers of juvenile mice, there was robust expression of DDR markers in hepatocytes at 1 week; however, by 7 weeks, activation of ATM/ATR kinase targets was limited, although cells with DNA damage foci were present. An analysis of hepatocytes of aged, 22-month-old mice, not experimentally exposed to genotoxins, showed limited activation of ATM/ATR targets, though high numbers of cells with DNA damage foci were found, similar to that seen many weeks after artificial senescence induction in young mice. Based on senescence heterochromatin and SA ss Gal assays of the 22-month-old mouse liver, more than 20% of hepatocytes were potentially senescent, though only some components of the DDR were enriched.
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147
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Aging by epigenetics--a consequence of chromatin damage? Exp Cell Res 2008; 314:1909-17. [PMID: 18423606 DOI: 10.1016/j.yexcr.2008.02.023] [Citation(s) in RCA: 120] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/19/2008] [Revised: 02/28/2008] [Accepted: 02/28/2008] [Indexed: 01/09/2023]
Abstract
Chromatin structure is not fixed. Instead, chromatin is dynamic and is subject to extensive developmental and age-associated remodeling. In some cases, this remodeling appears to counter the aging and age-associated diseases, such as cancer, and extend organismal lifespan. However, stochastic non-deterministic changes in chromatin structure might, over time, also contribute to the break down of nuclear, cell and tissue function, and consequently aging and age-associated diseases.
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148
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Kiyono T. Molecular mechanisms of cellular senescence and immortalization of human cells. Expert Opin Ther Targets 2008; 11:1623-37. [PMID: 18020982 DOI: 10.1517/14728222.11.12.1623] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
Cellular senescence was originally described as a phenomenon observed in cultured human cells. Accumulating lines of evidence now indicate that the same processes also take place in vivo, suggesting important implications for tumor development. Telomere shortening is the most well-established cause of cellular senescence that can be induced by many other intrinsic and extrinsic factors. The retinoblastoma susceptibility gene product is a convergent target that is downstream of these factors. p53, p38MAPK and cyclin-dependent kinase inhibitors p16INK4a (p16) and p21CIP1 (p21) are key mediators. As most stresses that induce cellular senescence are also known causes of cancer, a common strategy might be applied to the development of cancer chemopreventive agents and anti-ageing drugs.
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Affiliation(s)
- Tohru Kiyono
- National Cancer Center Research Institute, Virology Division, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan.
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149
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Downs JA. Chromatin structure and DNA double-strand break responses in cancer progression and therapy. Oncogene 2008; 26:7765-72. [PMID: 18066089 DOI: 10.1038/sj.onc.1210874] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Defects in the detection and repair of DNA double-strand breaks (DSBs) have been causatively linked to tumourigenesis. Moreover, inhibition of DNA damage responses (DDR) can increase the efficacy of cancer therapies that rely on generation of damaged DNA. DDR must occur within the context of chromatin, and there have been significant advances in recent years in understanding how the modulation and manipulation of chromatin contribute to this activity. One particular covalent modification of a histone variant--the phosphorylation of H2AX--has been investigated in great detail and has been shown to have important roles in DNA DSB responses and in preventing tumourigenesis. These studies are reviewed here in the context of their relevance to cancer therapy and diagnostics. In addition, there is emerging evidence for contributions by proteins involved in mediating higher order structure to DNA DSB responses. The contributions of a subset of these proteins--linker histones and high-mobility group box (HMGB) proteins--to DDR and their potential significance in tumourigenesis are discussed.
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Affiliation(s)
- J A Downs
- MRC Genome Damage and Stability Centre, University of Sussex, Falmer, Brighton, UK.
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150
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Kimura H, Hayashi-Takanaka Y, Goto Y, Takizawa N, Nozaki N. The Organization of Histone H3 Modifications as Revealed by a Panel of Specific Monoclonal Antibodies. Cell Struct Funct 2008; 33:61-73. [DOI: 10.1247/csf.07035] [Citation(s) in RCA: 246] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Affiliation(s)
- Hiroshi Kimura
- Nuclear Function and Dynamics Unit, HMRO, Graduate School of Medicine, Kyoto University
- Cell Biology Group, Kansai Advanced Research Center, National Institute of Information and Communications Technology
- Graduate School of Frontier Biosciences, Osaka University
| | - Yoko Hayashi-Takanaka
- Nuclear Function and Dynamics Unit, HMRO, Graduate School of Medicine, Kyoto University
- Cell Biology Group, Kansai Advanced Research Center, National Institute of Information and Communications Technology
| | - Yuji Goto
- Nuclear Function and Dynamics Unit, HMRO, Graduate School of Medicine, Kyoto University
- Present address: College of Life and Health Sciences, Chubu University
| | - Nanako Takizawa
- Nuclear Function and Dynamics Unit, HMRO, Graduate School of Medicine, Kyoto University
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