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Sengar AS, Kumar M, Rai C, Chakraborti S, Kumar D, Kumar P, Mukherjee S, Mondal K, Stewart A, Maity B. RGS6 drives cardiomyocyte death following nucleolar stress by suppressing Nucleolin/miRNA-21. J Transl Med 2024; 22:204. [PMID: 38409136 PMCID: PMC10895901 DOI: 10.1186/s12967-024-04985-3] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2023] [Accepted: 02/12/2024] [Indexed: 02/28/2024] Open
Abstract
BACKGROUND Prior evidence demonstrated that Regulator of G protein Signaling 6 (RGS6) translocates to the nucleolus in response to cytotoxic stress though the functional significance of this phenomenon remains unknown. METHODS Utilizing in vivo gene manipulations in mice, primary murine cardiac cells, human cell lines and human patient samples we dissect the participation of a RGS6-nucleolin complex in chemotherapy-dependent cardiotoxicity. RESULTS Here we demonstrate that RGS6 binds to a key nucleolar protein, Nucleolin, and controls its expression and activity in cardiomyocytes. In the human myocyte AC-16 cell line, induced pluripotent stem cell derived cardiomyocytes, primary murine cardiomyocytes, and the intact murine myocardium tuning RGS6 levels via overexpression or knockdown resulted in diametrically opposed impacts on Nucleolin mRNA, protein, and phosphorylation.RGS6 depletion provided marked protection against nucleolar stress-mediated cell death in vitro, and, conversely, RGS6 overexpression suppressed ribosomal RNA production, a key output of the nucleolus, and triggered death of myocytes. Importantly, overexpression of either Nucleolin or Nucleolin effector miRNA-21 counteracted the pro-apoptotic effects of RGS6. In both human and murine heart tissue, exposure to the genotoxic stressor doxorubicin was associated with an increase in the ratio of RGS6/Nucleolin. Preventing RGS6 induction via introduction of RGS6-directed shRNA via intracardiac injection proved cardioprotective in mice and was accompanied by restored Nucleolin/miRNA-21 expression, decreased nucleolar stress, and decreased expression of pro-apoptotic, hypertrophy, and oxidative stress markers in heart. CONCLUSION Together, these data implicate RGS6 as a driver of nucleolar stress-dependent cell death in cardiomyocytes via its ability to modulate Nucleolin. This work represents the first demonstration of a functional role for an RGS protein in the nucleolus and identifies the RGS6/Nucleolin interaction as a possible new therapeutic target in the prevention of cardiotoxicity.
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Affiliation(s)
- Abhishek Singh Sengar
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India
| | - Manish Kumar
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India
| | - Chetna Rai
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India
| | - Sreemoyee Chakraborti
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India
- Forensic Science Laboratory, Department of Home and Hill Affairs, Kolkata, West Bengal, 700037, India
| | - Dinesh Kumar
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India
| | - Pranesh Kumar
- Institute of Pharmaceutical Science, University of Lucknow, Lucknow, Uttar Pradesh, 226007, India
| | - Sukhes Mukherjee
- Biochemistry, AIIMS Bhopal, Saket Nagar, Bhopal, Madhya Pradesh, 462026, India
| | - Kausik Mondal
- Zoology, University of Kalyani, Nadia, West Bengal, 741235, India
| | - Adele Stewart
- Biomedical Science, Florida Atlantic University, Jupiter, FL, 33458, USA
| | - Biswanath Maity
- Centre of Biomedical Research (CBMR), SGPGI Campus, Raebareli Road, Lucknow, Uttar Pradesh, 226014, India.
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JAZF1, A Novel p400/TIP60/NuA4 Complex Member, Regulates H2A.Z Acetylation at Regulatory Regions. Int J Mol Sci 2021; 22:ijms22020678. [PMID: 33445503 PMCID: PMC7826843 DOI: 10.3390/ijms22020678] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 01/07/2021] [Accepted: 01/09/2021] [Indexed: 12/22/2022] Open
Abstract
Histone variants differ in amino acid sequence, expression timing and genomic localization sites from canonical histones and convey unique functions to eukaryotic cells. Their tightly controlled spatial and temporal deposition into specific chromatin regions is accomplished by dedicated chaperone and/or remodeling complexes. While quantitatively identifying the chaperone complexes of many human H2A variants by using mass spectrometry, we also found additional members of the known H2A.Z chaperone complexes p400/TIP60/NuA4 and SRCAP. We discovered JAZF1, a nuclear/nucleolar protein, as a member of a p400 sub-complex containing MBTD1 but excluding ANP32E. Depletion of JAZF1 results in transcriptome changes that affect, among other pathways, ribosome biogenesis. To identify the underlying molecular mechanism contributing to JAZF1's function in gene regulation, we performed genome-wide ChIP-seq analyses. Interestingly, depletion of JAZF1 leads to reduced H2A.Z acetylation levels at > 1000 regulatory sites without affecting H2A.Z nucleosome positioning. Since JAZF1 associates with the histone acetyltransferase TIP60, whose depletion causes a correlated H2A.Z deacetylation of several JAZF1-targeted enhancer regions, we speculate that JAZF1 acts as chromatin modulator by recruiting TIP60's enzymatic activity. Altogether, this study uncovers JAZF1 as a member of a TIP60-containing p400 chaperone complex orchestrating H2A.Z acetylation at regulatory regions controlling the expression of genes, many of which are involved in ribosome biogenesis.
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O-GlcNAc modified-TIP60/KAT5 is required for PCK1 deficiency-induced HCC metastasis. Oncogene 2021; 40:6707-6719. [PMID: 34650217 PMCID: PMC8677624 DOI: 10.1038/s41388-021-02058-z] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Revised: 09/22/2021] [Accepted: 10/01/2021] [Indexed: 02/04/2023]
Abstract
Aberrant glucose metabolism and elevated O-linked β-N-acetylglucosamine modification (O-GlcNAcylation) are hallmarks of hepatocellular carcinoma (HCC). Loss of phosphoenolpyruvate carboxykinase 1 (PCK1), the major rate-limiting enzyme of hepatic gluconeogenesis, increases hexosamine biosynthetic pathway (HBP)-mediated protein O-GlcNAcylation in hepatoma cell and promotes cell growth and proliferation. However, whether PCK1 deficiency and hyper O-GlcNAcylation can induce HCC metastasis is largely unknown. Here, gain- and loss-of-function studies demonstrate that PCK1 suppresses HCC metastasis in vitro and in vivo. Specifically, lysine acetyltransferase 5 (KAT5), belonging to the MYST family of histone acetyltransferases (HAT), is highly modified by O-GlcNAcylation in PCK1 knockout hepatoma cells. Mechanistically, PCK1 depletion suppressed KAT5 ubiquitination by increasing its O-GlcNAcylation, thereby stabilizing KAT5. KAT5 O-GlcNAcylation epigenetically activates TWIST1 expression via histone H4 acetylation, and enhances MMP9 and MMP14 expression via c-Myc acetylation, thus promoting epithelial-mesenchymal transition (EMT) in HCC. In addition, targeting HBP-mediated O-GlcNAcylation of KAT5 inhibits lung metastasis of HCC in hepatospecific Pck1-deletion mice. Collectively, our findings demonstrate that PCK1 depletion increases O-GlcNAcylation of KAT5, epigenetically induces TWIST1 expression and promotes HCC metastasis, and link metabolic enzyme, post-translational modification (PTM) with epigenetic regulation.
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4
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Farley-Barnes KI, McCann KL, Ogawa LM, Merkel J, Surovtseva YV, Baserga SJ. Diverse Regulators of Human Ribosome Biogenesis Discovered by Changes in Nucleolar Number. Cell Rep 2019; 22:1923-1934. [PMID: 29444442 PMCID: PMC5828527 DOI: 10.1016/j.celrep.2018.01.056] [Citation(s) in RCA: 71] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2017] [Revised: 11/09/2017] [Accepted: 11/19/2017] [Indexed: 12/31/2022] Open
Abstract
Ribosome biogenesis is a highly regulated, essential cellular process. Although studies in yeast have established some of the biological principles of ribosome biogenesis, many of the intricacies of its regulation in higher eukaryotes remain unknown. To understand how ribosome biogenesis is globally integrated in human cells, we conducted a genome-wide siRNA screen for regulators of nucleolar number. We found 139 proteins whose depletion changed the number of nucleoli per nucleus from 2–3 to only 1 in human MCF10A cells. Follow-up analyses on 20 hits found many (90%) to be essential for the nucleolar functions of rDNA transcription (7), pre-ribosomal RNA (pre-rRNA) processing (16), and/or global protein synthesis (14). This genome-wide analysis exploits the relationship between nucleolar number and function to discover diverse cellular pathways that regulate the making of ribosomes and paves the way for further exploration of the links between ribosome biogenesis and human disease.
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Affiliation(s)
- Katherine I Farley-Barnes
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Kathleen L McCann
- Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA; Epigenetics and Stem Cell Biology Laboratory, National Institute of Environmental Health Sciences, NIH, PO Box 12233 MD F3-05, Research Triangle Park, NC 27709, USA
| | - Lisa M Ogawa
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA
| | - Janie Merkel
- Yale Center for Molecular Discovery, Yale University, 600 West Campus Drive, West Haven, CT 06516, USA
| | - Yulia V Surovtseva
- Yale Center for Molecular Discovery, Yale University, 600 West Campus Drive, West Haven, CT 06516, USA
| | - Susan J Baserga
- Department of Molecular Biophysics and Biochemistry, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Genetics, Yale University School of Medicine, New Haven, CT 06520, USA; Department of Therapeutic Radiology, Yale University School of Medicine, New Haven, CT 06520, USA.
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5
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Sokpor G, Castro-Hernandez R, Rosenbusch J, Staiger JF, Tuoc T. ATP-Dependent Chromatin Remodeling During Cortical Neurogenesis. Front Neurosci 2018; 12:226. [PMID: 29686607 PMCID: PMC5900035 DOI: 10.3389/fnins.2018.00226] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Accepted: 03/22/2018] [Indexed: 12/20/2022] Open
Abstract
The generation of individual neurons (neurogenesis) during cortical development occurs in discrete steps that are subtly regulated and orchestrated to ensure normal histogenesis and function of the cortex. Notably, various gene expression programs are known to critically drive many facets of neurogenesis with a high level of specificity during brain development. Typically, precise regulation of gene expression patterns ensures that key events like proliferation and differentiation of neural progenitors, specification of neuronal subtypes, as well as migration and maturation of neurons in the developing cortex occur properly. ATP-dependent chromatin remodeling complexes regulate gene expression through utilization of energy from ATP hydrolysis to reorganize chromatin structure. These chromatin remodeling complexes are characteristically multimeric, with some capable of adopting functionally distinct conformations via subunit reconstitution to perform specific roles in major aspects of cortical neurogenesis. In this review, we highlight the functions of such chromatin remodelers during cortical development. We also bring together various proposed mechanisms by which ATP-dependent chromatin remodelers function individually or in concert, to specifically modulate vital steps in cortical neurogenesis.
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Affiliation(s)
- Godwin Sokpor
- Institute for Neuroanatomy, University Medical Center, Georg-August-University Goettingen, Goettingen, Germany
| | - Ricardo Castro-Hernandez
- Institute for Neuroanatomy, University Medical Center, Georg-August-University Goettingen, Goettingen, Germany
| | - Joachim Rosenbusch
- Institute for Neuroanatomy, University Medical Center, Georg-August-University Goettingen, Goettingen, Germany
| | - Jochen F Staiger
- Institute for Neuroanatomy, University Medical Center, Georg-August-University Goettingen, Goettingen, Germany.,DFG Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Goettingen, Germany
| | - Tran Tuoc
- Institute for Neuroanatomy, University Medical Center, Georg-August-University Goettingen, Goettingen, Germany.,DFG Center for Nanoscale Microscopy and Molecular Physiology of the Brain, Goettingen, Germany
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6
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Feng L, Shi Z, Chen X. Enhancer of polycomb coordinates multiple signaling pathways to promote both cyst and germline stem cell differentiation in the Drosophila adult testis. PLoS Genet 2017; 13:e1006571. [PMID: 28196077 PMCID: PMC5308785 DOI: 10.1371/journal.pgen.1006571] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 01/04/2017] [Indexed: 12/31/2022] Open
Abstract
Stem cells reside in a particular microenvironment known as a niche. The interaction between extrinsic cues originating from the niche and intrinsic factors in stem cells determines their identity and activity. Maintenance of stem cell identity and stem cell self-renewal are known to be controlled by chromatin factors. Herein, we use the Drosophila adult testis which has two adult stem cell lineages, the germline stem cell (GSC) lineage and the cyst stem cell (CySC) lineage, to study how chromatin factors regulate stem cell differentiation. We find that the chromatin factor Enhancer of Polycomb [E(Pc)] acts in the CySC lineage to negatively control transcription of genes associated with multiple signaling pathways, including JAK-STAT and EGF, to promote cellular differentiation in the CySC lineage. E(Pc) also has a non-cell-autonomous role in regulating GSC lineage differentiation. When E(Pc) is specifically inactivated in the CySC lineage, defects occur in both germ cell differentiation and maintenance of germline identity. Furthermore, compromising Tip60 histone acetyltransferase activity in the CySC lineage recapitulates loss-of-function phenotypes of E(Pc), suggesting that Tip60 and E(Pc) act together, consistent with published biochemical data. In summary, our results demonstrate that E(Pc) plays a central role in coordinating differentiation between the two adult stem cell lineages in Drosophila testes. Tissue maintenance and repair rely on adult stem cells, which can divide to generate new stem cells as well as cells committed for becoming specific cell types. Stem cell activity needs to be tightly controlled because insufficient or unlimited stem cell division may lead to tissue degeneration or tumorigenesis. This control depends not only on stem cells themselves, but also on the microenvironment where stem cells reside. The chromatin structure of stem cells is crucial to determine their activities. The signaling pathways connecting stem cells with their microenvironment is also important. Here we ask how chromatin factors interact with signaling pathways in determining stem cell activity. We use Drosophila adult testis as a model system, in which two types of stem cells co-exist and interact: germline stem cells and somatic stem cells. We find that a chromatin regulator called Enhancer of Polycomb [E(Pc)] acts in somatic cells to promote germ cell differentiation and maintain germ cell fate. This regulation is mediated by several signaling pathways, such as EGF and JAK-STAT pathways. E(Pc) also works with another chromatin regulator, the histone acetyltransferase Tip60, in somatic cells. Insufficient activity of the E(Pc) homolog in human leads to cancers. Our studies of E(Pc) may help understanding its roles as a tumor suppressor.
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Affiliation(s)
- Lijuan Feng
- Department of Biology, The Johns Hopkins University, Baltimore, MD, United States of America
| | - Zhen Shi
- Department of Biology, The Johns Hopkins University, Baltimore, MD, United States of America
| | - Xin Chen
- Department of Biology, The Johns Hopkins University, Baltimore, MD, United States of America
- * E-mail:
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7
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Abstract
Heterochromatin is the transcriptionally repressed portion of eukaryotic chromatin that maintains a condensed appearance throughout the cell cycle. At sites of ribosomal DNA (rDNA) heterochromatin, epigenetic states contribute to gene silencing and genome stability, which are required for proper chromosome segregation and a normal life span. Here, we focus on recent advances in the epigenetic regulation of rDNA silencing in Saccharomyces cerevisiae and in mammals, including regulation by several histone modifications and several protein components associated with the inner nuclear membrane within the nucleolus. Finally, we discuss the perturbations of rDNA epigenetic pathways in regulating cellular aging and in causing various types of diseases.
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8
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Xu Y, Wan W, Shou X, Huang R, You Z, Shou Y, Wang L, Zhou T, Liu W. TP53INP2/DOR, a mediator of cell autophagy, promotes rDNA transcription via facilitating the assembly of the POLR1/RNA polymerase I preinitiation complex at rDNA promoters. Autophagy 2016; 12:1118-28. [PMID: 27172002 DOI: 10.1080/15548627.2016.1175693] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Cells control their metabolism through modulating the anabolic and catabolic pathways. TP53INP2/DOR (tumor protein p53 inducible nuclear protein 2), participates in cell catabolism by serving as a promoter of autophagy. Here we uncover a novel function of TP53INP2 in protein synthesis, a major biosynthetic and energy-consuming anabolic process. TP53INP2 localizes to the nucleolus through its nucleolar localization signal (NoLS) located at the C-terminal domain. Chromatin immunoprecipitation (ChIP) assays detected an association of TP53INP2 with the ribosomal DNA (rDNA), when exclusion of TP53INP2 from the nucleolus repressed rDNA promoter activity and the production of ribosomal RNA (rRNA) and proteins. The removal of TP53INP2 also impaired the association of the POLR1/RNA polymerase I preinitiation complex (PIC) with rDNA. Further, TP53INP2 interacts directly with POLR1 PIC, and is required for the assembly of the complex. These data indicate that TP53INP2 promotes ribosome biogenesis through facilitating rRNA synthesis at the nucleolus, suggesting a dual role of TP53INP2 in cell metabolism, assisting anabolism on the nucleolus, and stimulating catabolism off the nucleolus.
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Affiliation(s)
- Yinfeng Xu
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Wei Wan
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Xin Shou
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Rui Huang
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Zhiyuan You
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Yanhong Shou
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Lingling Wang
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China
| | - Tianhua Zhou
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China.,b Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease, First Affiliated Hospital, Zhejiang University School of Medicine , Hangzhou , China
| | - Wei Liu
- a Department of Biochemistry and Molecular Biology , Program in Molecular and Cell Biology, Zhejiang University School of Medicine , Hangzhou , China.,b Collaborative Innovation Center for Diagnosis and Treatment of Infectious Disease, First Affiliated Hospital, Zhejiang University School of Medicine , Hangzhou , China
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Sun X, Chen H, Deng Z, Hu B, Luo H, Zeng X, Han L, Cai G, Ma L. The Warsaw breakage syndrome-related protein DDX11 is required for ribosomal RNA synthesis and embryonic development. Hum Mol Genet 2015; 24:4901-15. [PMID: 26089203 DOI: 10.1093/hmg/ddv213] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/07/2015] [Accepted: 06/04/2015] [Indexed: 12/20/2022] Open
Abstract
DDX11 was recently identified as a cause of Warsaw breakage syndrome (WABS). However, the functional mechanism of DDX11 and the contribution of clinically described mutations to the pathogenesis of WABS are elusive. Here, we show that DDX11 is a novel nucleolar protein that preferentially binds to hypomethylated active ribosomal DNA (rDNA) gene loci, where it interacts with upstream binding factor (UBF) and the RNA polymerase I (Pol I). DDX11 knockdown changed the epigenetic state of rDNA loci from euchromatic structures to more heterochromatic structures, reduced the activity of UBF, decreased the recruitment of UBF and RPA194 (a subunit of Pol I) to rDNA promoter, suppressed rRNA transcription and thereby inhibited growth and proliferation of HeLa cells. Importantly, two indentified WABS-derived mutants, R263Q and K897del, and a Fe-S deletion construct demonstrated significantly reduced binding abilities to rDNA promoters and lowered DNA-dependent ATPase activities compared with wild-type DDX11. Knockdown of the zebrafish ortholog of human DDX11 by morpholinos resulted in growth retardation and vertebral and craniofacial malformations in zebrafish, concomitant with the changes in histone epigenetic modifications at rDNA loci, the reduction of Pol I recruitment to the rDNA promoter and a significant decrease in nascent pre-RNA levels. These growth disruptions in zebrafish in response to DDX11 reduction showed similarities to the clinically described developmental abnormalities found in WABS patients for the first time in any vertebrate. Thus, our results indicate that DDX11 functions as a positive regulator of rRNA transcription and provides a novel insight into the pathogenesis of WABS.
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Affiliation(s)
- Xinliang Sun
- School of Life Sciences, Tsinghua University, Beijing, China, Division of Life Science and Health, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Hongbo Chen
- School of Life Sciences, Tsinghua University, Beijing, China, Division of Life Science and Health, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China,
| | - Zaian Deng
- School of Life Sciences, Tsinghua University, Beijing, China, Division of Life Science and Health, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China
| | - Bo Hu
- Department of Laboratory Medicine, The Third Affiliated Hospital of Sun Yat-sen University, Guangdong, China
| | - Hui Luo
- Department of Pharmacology, Guangdong Medical College, Zhanjiang 524023, Guangdong, China and and
| | - Xiaobin Zeng
- Department of Pharmacology, Guangdong Medical College, Zhanjiang 524023, Guangdong, China and and
| | - Liqiao Han
- Department of Laboratory Science, The Second Affiliated Hospital of Guangzhou University of Chinese Medicine, Guangdong, China
| | - Guoping Cai
- School of Life Sciences, Tsinghua University, Beijing, China, Division of Life Science and Health, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China,
| | - Lan Ma
- School of Life Sciences, Tsinghua University, Beijing, China, Division of Life Science and Health, Graduate School at Shenzhen, Tsinghua University, Shenzhen, China,
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van Sluis M, McStay B. A localized nucleolar DNA damage response facilitates recruitment of the homology-directed repair machinery independent of cell cycle stage. Genes Dev 2015; 29:1151-63. [PMID: 26019174 PMCID: PMC4470283 DOI: 10.1101/gad.260703.115] [Citation(s) in RCA: 159] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/2015] [Accepted: 05/11/2015] [Indexed: 12/13/2022]
Abstract
DNA double-strand breaks (DSBs) are repaired by two main pathways: nonhomologous end-joining and homologous recombination (HR). Repair pathway choice is thought to be determined by cell cycle timing and chromatin context. Nucleoli, prominent nuclear subdomains and sites of ribosome biogenesis, form around nucleolar organizer regions (NORs) that contain rDNA arrays located on human acrocentric chromosome p-arms. Actively transcribed rDNA repeats are positioned within the interior of the nucleolus, whereas sequences proximal and distal to NORs are packaged as heterochromatin located at the nucleolar periphery. NORs provide an opportunity to investigate the DSB response at highly transcribed, repetitive, and essential loci. Targeted introduction of DSBs into rDNA, but not abutting sequences, results in ATM-dependent inhibition of their transcription by RNA polymerase I. This is coupled with movement of rDNA from the nucleolar interior to anchoring points at the periphery. Reorganization renders rDNA accessible to repair factors normally excluded from nucleoli. Importantly, DSBs within rDNA recruit the HR machinery throughout the cell cycle. Additionally, unscheduled DNA synthesis, consistent with HR at damaged NORs, can be observed in G1 cells. These results suggest that HR can be templated in cis and suggest a role for chromosomal context in the maintenance of NOR genomic stability.
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Affiliation(s)
- Marjolein van Sluis
- Centre for Chromosome Biology, School of Natural Sciences, National University of Ireland, Galway, Ireland
| | - Brian McStay
- Centre for Chromosome Biology, School of Natural Sciences, National University of Ireland, Galway, Ireland
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A Neuronal Activity-Dependent Dual Function Chromatin-Modifying Complex Regulates Arc Expression. eNeuro 2015; 2:eN-NWR-0020-14. [PMID: 26464965 PMCID: PMC4586916 DOI: 10.1523/eneuro.0020-14.2015] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2014] [Revised: 01/18/2015] [Accepted: 01/22/2015] [Indexed: 11/21/2022] Open
Abstract
Chromatin modification is an important epigenetic mechanism underlying neuroplasticity. Histone methylation and acetylation have both been shown to modulate gene expression, but the machinery responsible for mediating these changes in neurons has remained elusive. Here we identify a chromatin-modifying complex containing the histone demethylase PHF8 and the acetyltransferase TIP60 as a key regulator of the activity-induced expression of Arc, an important mediator of synaptic plasticity. Clinically, mutations in PHF8 cause X-linked mental retardation while TIP60 has been implicated in the pathogenesis of Alzheimer's disease. Within minutes of increased synaptic activity, this dual function complex is rapidly recruited to the Arc promoter, where it specifically counteracts the transcriptionally repressive histone mark H3K9me2 to facilitate the formation of the transcriptionally permissive H3K9acS10P, thereby favoring transcriptional activation. Consequently, gain-of-function of the PHF8-TIP60 complex in primary rat hippocampal neurons has a positive effect on early activity-induced Arc gene expression, whereas interfering with the function of this complex abrogates it. A global proteomics screen revealed that the majority of common interactors of PHF8 and TIP60 were involved in mRNA processing, including PSF, an important molecule involved in neuronal gene regulation. Finally, we proceeded to show, using super-resolution microscopy, that PHF8 and TIP60 interact at the single molecule level with PSF, thereby situating this chromatin modifying complex at the crossroads of transcriptional activation. These findings point toward a mechanism by which an epigenetic pathway can regulate neuronal activity-dependent gene transcription, which has implications in the development of novel therapeutics for disorders of learning and memory.
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12
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Regulation of STAT signaling by acetylation. Cell Signal 2013; 25:1924-31. [PMID: 23707527 DOI: 10.1016/j.cellsig.2013.05.007] [Citation(s) in RCA: 137] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/25/2013] [Revised: 05/03/2013] [Accepted: 05/06/2013] [Indexed: 01/12/2023]
Abstract
Signal transducers and activators of transcription (STAT) belong to a family of latent cytoplasmic factors that can be activated by tyrosine phosphorylation by the members of the Jak tyrosine kinase family in response to a variety of cytokines and growth factors. Activated STATs form dimers and translocate into nucleus to induce expression of critical genes essential for normal cellular events. In the past several years, significant progress has been made in the characterization of STAT acetylation, which is dependent on the balance between histone deacetylases (HDACs) and histone acetyltransferases (HATs) such as CBP/p300. Acetylation of STAT1, STAT2, STAT3, STAT5b and STAT6 has been identified. This review will highlight acetylation on the modulation of STAT activation.
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13
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Goodfellow SJ, Zomerdijk JCBM. Basic mechanisms in RNA polymerase I transcription of the ribosomal RNA genes. Subcell Biochem 2013; 61:211-36. [PMID: 23150253 PMCID: PMC3855190 DOI: 10.1007/978-94-007-4525-4_10] [Citation(s) in RCA: 119] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
RNA Polymerase (Pol) I produces ribosomal (r)RNA, an essential component of the cellular protein synthetic machinery that drives cell growth, underlying many fundamental cellular processes. Extensive research into the mechanisms governing transcription by Pol I has revealed an intricate set of control mechanisms impinging upon rRNA production. Pol I-specific transcription factors guide Pol I to the rDNA promoter and contribute to multiple rounds of transcription initiation, promoter escape, elongation and termination. In addition, many accessory factors are now known to assist at each stage of this transcription cycle, some of which allow the integration of transcriptional activity with metabolic demands. The organisation and accessibility of rDNA chromatin also impinge upon Pol I output, and complex mechanisms ensure the appropriate maintenance of the epigenetic state of the nucleolar genome and its effective transcription by Pol I. The following review presents our current understanding of the components of the Pol I transcription machinery, their functions and regulation by associated factors, and the mechanisms operating to ensure the proper transcription of rDNA chromatin. The importance of such stringent control is demonstrated by the fact that deregulated Pol I transcription is a feature of cancer and other disorders characterised by abnormal translational capacity.
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Affiliation(s)
- Sarah J. Goodfellow
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee , Dundee DD1 5EH , UK
| | - Joost C. B. M. Zomerdijk
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee , Dundee DD1 5EH , UK
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14
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Yang C, Wu J, Zheng YG. Function of the active site lysine autoacetylation in Tip60 catalysis. PLoS One 2012; 7:e32886. [PMID: 22470428 PMCID: PMC3314657 DOI: 10.1371/journal.pone.0032886] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2011] [Accepted: 02/01/2012] [Indexed: 01/01/2023] Open
Abstract
The 60-kDa HIV-Tat interactive protein (Tip60) is a key member of the MYST family of histone acetyltransferases (HATs) that plays critical roles in multiple cellular processes. We report here that Tip60 undergoes autoacetylation at several lysine residues, including a key lysine residue (i.e. Lys-327) in the active site of the MYST domain. The mutation of K327 to arginine led to loss of both the autoacetylation activity and the cognate HAT activity. Interestingly, deacetylated Tip60 still kept a substantial degree of HAT activity. We also investigated the effect of cysteine 369 and glutamate 403 in Tip60 autoacetylation in order to understand the molecular pathway of the autoacetylation at K327. Together, we conclude that the acetylation of K327 which is located in the active site of Tip60 regulates but is not obligatory for the catalytic activity of Tip60. Since acetylation at this key residue appears to be evolutionarily conserved amongst all MYST proteins, our findings provide an interesting insight into the regulatory mechanism of MYST activities.
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Affiliation(s)
| | | | - Y. George Zheng
- Department of Chemistry, Georgia State University, Atlanta, Georgia, United States of America
- * E-mail:
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15
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Zhang SM, Song M, Yang TY, Fan R, Liu XD, Zhou PK. HIV-1 Tat impairs cell cycle control by targeting the Tip60, Plk1 and cyclin B1 ternary complex. Cell Cycle 2012; 11:1217-34. [PMID: 22391203 DOI: 10.4161/cc.11.6.19664] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
HIV-1 Tat triggers intrinsic and extrinsic apoptosis pathways in both infected and uninfected cells and plays an important role in the pathogenesis of AIDS. Knocking down Tip60, an interactive protein of Tat, leads to the impairment of cell cycle progression, indicating a key role of Tip60 in cell cycle control. We found that Tip60 interacts with Plk1 through its ZnFMYST domain, and that this interaction is enhanced in the G 2/M phase. In addition, cyclin B1 was confirmed to interact with the ZnF domain of Tip60. Immunofluorescence imaging showed that Tip60 co-localizes with both Plk1 and cyclin B1 at the centrosome during the mitotic phase and to the mid-body during cytokinesis. Further experiments revealed that Tip60 forms a ternary complex with Plk1 and cyclin B1 and acetylates Plk1 but not cyclin B1. HIV-1 Tat likely forms a quaternary complex with Tip60, cyclin B1 and Plk1. Fluorescent microscopy showed that Tat causes an unscheduled nuclear translocation of both cyclin B1 and Plk1, causing their co-localization with Tip60 in the nucleus. Tat, Tip60, cyclin B1 and Plk1 interactions provide new a mechanistic explanation for Tat-mediated cell cycle dysregulation and apoptosis.
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Affiliation(s)
- Shi-Meng Zhang
- Department of Radiation Toxicology and Oncology, Beijing Institute of Radiation Medicine, Beijing, China
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16
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Sapountzi V, Côté J. MYST-family histone acetyltransferases: beyond chromatin. Cell Mol Life Sci 2011; 68:1147-56. [PMID: 21132344 PMCID: PMC11114825 DOI: 10.1007/s00018-010-0599-9] [Citation(s) in RCA: 136] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2010] [Revised: 11/12/2010] [Indexed: 12/01/2022]
Abstract
Covalently modifying a protein has proven to be a powerful mechanism of functional regulation. N-epsilon acetylation of lysine residues was initially discovered on histones and has been studied extensively in the context of chromatin and DNA metabolism, such as transcription, replication and repair. However, recent research shows that acetylation is more widespread than initially thought and that it regulates various nuclear as well as cytoplasmic and mitochondrial processes. In this review, we present the multitude of non-histone proteins targeted by lysine acetyltransferases of the large and conserved MYST family, and known functional consequences of this acetylation. Substrates of MYST enzymes include factors involved in transcription, heterochromatin formation and cell cycle, DNA repair proteins, gluconeogenesis enzymes and finally subunits of MYST protein complexes themselves. Discovering novel substrates of MYST proteins is pivotal for the understanding of the diverse functions of these essential acetyltransferases in nuclear processes, signaling, stress response and metabolism.
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Affiliation(s)
- Vasileia Sapountzi
- Laval University Cancer Research Center, Hôtel-Dieu de Québec (CHUQ), 9 McMahon Street, Quebec City, QC G1R 2J6 Canada
| | - Jacques Côté
- Laval University Cancer Research Center, Hôtel-Dieu de Québec (CHUQ), 9 McMahon Street, Quebec City, QC G1R 2J6 Canada
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17
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Kong R, Zhang L, Hu L, Peng Q, Han W, Du X, Ke Y. hALP, a novel transcriptional U three protein (t-UTP), activates RNA polymerase I transcription by binding and acetylating the upstream binding factor (UBF). J Biol Chem 2010; 286:7139-48. [PMID: 21177859 PMCID: PMC3044971 DOI: 10.1074/jbc.m110.173393] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Transcription of ribosome RNA precursor (pre-rRNA) and pre-rRNA processing are coordinated by a subset of U three proteins (UTPs) known as transcriptional UTPs (t-UTPs), which participate in pre-rRNA transcription in addition to participation in 18 S rRNA processing. However, the mechanism by which t-UTPs function in pre-rRNA transcription remains undetermined. In the present study, we identified hALP, a histone acetyl-transferase as a novel t-UTP. We first showed that hALP is nucleolar, and is associated with U3 snoRNA and required for 18 S rRNA processing. Moreover, depletion of hALP resulted in a decreased level of 47 S pre-rRNA. Ectopic expression of hALP activated the rDNA promoter luciferase reporter and knockdown of hALP inhibited the reporter. In addition, hALP bound rDNA. Taken together these data identify hALP as a novel t-UTP. Immunoprecipitation and GST pulldown experiments showed that hALP binds the upstream binding factor (UBF) in vivo and in vitro. It is of importance that hALP acetylated UBF depending on HAT in vivo, and hALP but not hALP (ΔHAT) facilitated the nuclear translocation of the RNA polymerase I (Pol I)-associated factor 53 (PAF53) from the cytoplasm and promoted the association of UBF with PAF53. Thus, we provide a mechanism in which a novel t-UTP activates Pol I transcription by binding and acetylating UBF.
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Affiliation(s)
- Ruirui Kong
- Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Peking University School of Oncology, Beijing Cancer Hospital & Institute, Beijing 100142, China
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18
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PDCD5 interacts with Tip60 and functions as a cooperator in acetyltransferase activity and DNA damage-induced apoptosis. Neoplasia 2009; 11:345-54. [PMID: 19308289 DOI: 10.1593/neo.81524] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2008] [Revised: 02/01/2009] [Accepted: 02/03/2009] [Indexed: 12/21/2022] Open
Abstract
Tip60 is a histone acetyltransferase (HAT) involved in the acetyltransferase activity and the cellular response to DNA damage. Here, we show that programmed cell death 5 (PDCD5), a human apoptosis-related protein, binds to Tip60 and enhances the stability of Tip60 protein in unstressed conditions. The binding amount of PDCD5 and Tip60 is significantly increased after UV irradiation. Further, PDCD5 enhances HAT activity of Tip60 and Tip60-dependent histone acetylation in both basal and UV-induced levels. We also find that PDCD5 increases Tip60-dependent K120 acetylation of p53 and participates in the p53-dependent expression of apoptosis-related genes, such as Bax. Moreover, we demonstrate the biological significance of the PDCD5-Tip60 interaction; that is, they function in cooperation to accelerate DNA damage-induced apoptosis and knockdown of PDCD5 or Tip60 impairs their apoptosis-accelerating activity, mutually. Consistent with this, PDCD5 levels increase significantly on DNA damage in U2OS cells, as does Tip60. Together, our findings indicate that PDCD5 may play a dual role in the Tip60 pathway. Specifically, under normal growth conditions, PDCD5 contributes to maintaining a basal pool of Tip60 and its HAT activity. After DNA damage, PDCD5 functions as a Tip60 coactivator to promote apoptosis.
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19
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Birch JL, Tan BCM, Panov KI, Panova TB, Andersen JS, Owen-Hughes TA, Russell J, Lee SC, Zomerdijk JCBM. FACT facilitates chromatin transcription by RNA polymerases I and III. EMBO J 2009; 28:854-65. [PMID: 19214185 PMCID: PMC2647773 DOI: 10.1038/emboj.2009.33] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Accepted: 01/21/2009] [Indexed: 01/23/2023] Open
Abstract
Efficient transcription elongation from a chromatin template requires RNA polymerases (Pols) to negotiate nucleosomes. Our biochemical analyses demonstrate that RNA Pol I can transcribe through nucleosome templates and that this requires structural rearrangement of the nucleosomal core particle. The subunits of the histone chaperone FACT (facilitates chromatin transcription), SSRP1 and Spt16, co-purify and co-immunoprecipitate with mammalian Pol I complexes. In cells, SSRP1 is detectable at the rRNA gene repeats. Crucially, siRNA-mediated repression of FACT subunit expression in cells results in a significant reduction in 47S pre-rRNA levels, whereas synthesis of the first 40 nt of the rRNA is not affected, implying that FACT is important for Pol I transcription elongation through chromatin. FACT also associates with RNA Pol III complexes, is present at the chromatin of genes transcribed by Pol III and facilitates their transcription in cells. Our findings indicate that, beyond the established role in Pol II transcription, FACT has physiological functions in chromatin transcription by all three nuclear RNA Pols. Our data also imply that local chromatin dynamics influence transcription of the active rRNA genes by Pol I and of Pol III-transcribed genes.
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Affiliation(s)
- Joanna L Birch
- Wellcome Trust Centre for Gene Regulation and Expression, College of Life Sciences, University of Dundee, Dundee, UK
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20
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Wu J, Xie N, Wu Z, Zhang Y, Zheng YG. Bisubstrate Inhibitors of the MYST HATs Esa1 and Tip60. Bioorg Med Chem 2008; 17:1381-6. [PMID: 19114310 DOI: 10.1016/j.bmc.2008.12.014] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2008] [Revised: 11/30/2008] [Accepted: 12/07/2008] [Indexed: 01/03/2023]
Abstract
Esa1 (essential Sas2-related acetyltransferase 1) and Tip60 (HIV-1 TAT-interactive protein, 60 kDa) are key members of the MYST family of histone acetyltransferases (HATs) and play important functions in many cellular processes. In this work, we designed, synthesized and evaluated a series of substrate-based analogs for the inhibition of Esa1 and Tip60. The structures of these analogs feature that coenzyme A is covalently linked to the side chain amino group of the acetyl lysine residues in the histone peptide substrates. These bisubstrate analogs exhibit stronger potency in the inhibition of Esa1 and Tip60 compared to the small molecules curcumin and anacardic acid. In particular, H4K16CoA was tested as one of the most potent inhibitors for both Esa1 and Tip60. These substrate-based analog inhibitors will be useful mechanistic tools for analyzing biochemical mechanisms of Esa1 and Tip60, defining their functional roles in particular biological pathways, and facilitating protein crystallization and structural determination.
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Affiliation(s)
- Jiang Wu
- Department of Chemistry, Georgia State University, PO Box 4098, Atlanta, GA 30302, USA
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21
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Chromatin: linking structure and function in the nucleolus. Chromosoma 2008; 118:11-23. [PMID: 18925405 DOI: 10.1007/s00412-008-0184-2] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 09/17/2008] [Accepted: 09/18/2008] [Indexed: 01/07/2023]
Abstract
The nucleolus is an informative model structure for studying how chromatin-regulated transcription relates to nuclear organisation. In this review, we describe how chromatin controls nucleolar structure through both the modulation of rDNA activity by convergently-evolved remodelling complexes and by direct effects upon rDNA packaging. This packaging not only regulates transcription but may also be important for suppressing internal recombination between tandem rDNA repeats. The identification of nucleolar histone chaperones and novel chromatin proteins by mass spectrometry suggests that structure-specific chromatin components remain to be characterised and may regulate the nucleolus in novel ways. However, it also suggests that there is considerable overlap between nucleolar and non-nucleolar-chromatin components. We conclude that a fuller understanding of nucleolar chromatin will be essential for understanding how gene organisation is linked with nuclear architecture.
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22
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Hobbs CA, Wei G, DeFeo K, Paul B, Hayes CS, Gilmour SK. Tip60 protein isoforms and altered function in skin and tumors that overexpress ornithine decarboxylase. Cancer Res 2007; 66:8116-22. [PMID: 16912189 DOI: 10.1158/0008-5472.can-06-0359] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Elevated expression of ornithine decarboxylase (ODC) and increased synthesis of polyamines are hallmarks of epithelial tumorigenesis. The skin and tumors of K6/ODC and ODC/Ras transgenic mice, in which overexpression of ODC has been targeted to hair follicles, were found to exhibit intrinsically high histone acetyltransferase (HAT) activity. We identified Tip60 as a candidate enzyme for contributing significantly to this abnormally high HAT activity. Compared with normal littermate controls, the levels of Tip60 protein and an alternative splice variant Tip53 were found to be greater in K6/ODC mouse skin. Furthermore, skin tumors that spontaneously develop in ODC/Ras bigenic mice typically have substantially more Tip60 protein than adjacent non-tumor-bearing skin and exhibit a unique pattern of Tip60 size variants and chemically modified protein isoforms. Steady-state Tip60 and Tip53 mRNA levels were not affected in ODC-overexpressing skin and tumors, implying novel posttranscriptional regulation by polyamines. Given the diverse roles of Tip60, the overabundance of Tip60 protein is predicted to have biological consequences. Compared with normal littermate skin, we detected altered association of Tip60 with E2F1 and a subset of newly identified Tip60-interacting transcription factors in ODC transgenic mouse skin and tumors. E2F1 was shown to be bound in greater amounts to up-regulated target genes in ODC-overexpressing skin. Thus, up-regulation of Tip60 protein, influencing the expression of Tip60-regulated genes, could play a contributing role in polyamine-mediated tumor promotion. (
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Affiliation(s)
- Cheryl A Hobbs
- Lankenau Institute for Medical Research, Wynnewood, PA 19096, USA
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23
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Wang J, Liu N, Liu Z, Li Y, Song C, Yuan H, Li YY, Zhao X, Lu H. The orphan nuclear receptor Rev-erbbeta recruits Tip60 and HDAC1 to regulate apolipoprotein CIII promoter. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1783:224-36. [PMID: 17996965 DOI: 10.1016/j.bbamcr.2007.09.004] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/30/2007] [Revised: 08/21/2007] [Accepted: 09/20/2007] [Indexed: 11/19/2022]
Abstract
Nuclear hormone receptors function as ligand activated transcription factors. Ligand binding and modification such as acetylation have been reported to regulate nuclear hormone receptors. The orphan receptors, Rev-erbalpha and Rev-erbbeta, are members of the nuclear receptor superfamily and act as transcriptional repressors. In this study, the role of recruitment of co-factors by Rev-erbbeta and acetylation of Rev-erbbeta in modulating apolipoprotein CIII (apoCIII) transcription were investigated. Rev-erbbeta was found to transcriptionally repress apoCIII after binding to the apoCIII promoter. Tip60, a histone acetyl-transferase (HAT), was a novel binding partner for Rev-erbbeta and recruited to the apoCIII promoter by Rev-erbbeta. Tip60 was able to acetylate Rev-erbbeta and relieve the apoCIII repression mediated by Rev-erbbeta. This de-repression effect depended on acetylation of Rev-erbbeta at its RXKK motif by Tip60. In addition, histone deacetylase 1 (HDAC1) interacted with Rev-erbbeta and was recruited to the apoCIII promoter by Rev-erbbeta to antagonize Tip60's activity. Taken together, we have provided evidence that Rev-erbbeta modulates the apoCIII gene expression by recruiting different transcription co-activator or co-repressor.
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Affiliation(s)
- Jiadong Wang
- State Key Laboratory of Genetic Engineering, Institute of Genetics, Fudan University, Shanghai 200433, China
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24
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Kenneth NS, Ramsbottom BA, Gomez-Roman N, Marshall L, Cole PA, White RJ. TRRAP and GCN5 are used by c-Myc to activate RNA polymerase III transcription. Proc Natl Acad Sci U S A 2007; 104:14917-22. [PMID: 17848523 PMCID: PMC1986588 DOI: 10.1073/pnas.0702909104] [Citation(s) in RCA: 91] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Activation of RNA polymerase (pol) II transcription by c-Myc generally involves recruitment of histone acetyltransferases and acetylation of histones H3 and H4. Here, we describe the mechanism used by c-Myc to activate pol III transcription of tRNA and 5S rRNA genes. Within 2 h of its induction, c-Myc appears at these genes along with the histone acetyltransferase GCN5 and the cofactor TRRAP. At the same time, occupancy of the pol III-specific factor TFIIIB increases and histone H3 becomes hyperacetylated, but increased histone H4 acetylation is not detected at these genes. The rapid acetylation of histone H3 and promoter assembly of TFIIIB, c-Myc, GCN5, and TRRAP are followed by recruitment of pol III and transcriptional induction. The selective acetylation of histone H3 distinguishes pol III activation by c-Myc from mechanisms observed in other systems.
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Affiliation(s)
- Niall S. Kenneth
- *Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Ben A. Ramsbottom
- *Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Natividad Gomez-Roman
- *Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
| | - Lynne Marshall
- *Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
- Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, United Kingdom; and
| | - Philip A. Cole
- Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205
| | - Robert J. White
- *Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom
- Beatson Institute for Cancer Research, Garscube Estate, Switchback Road, Bearsden, Glasgow G61 1BD, United Kingdom; and
- To whom correspondence should be addressed. E-mail:
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25
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Sapountzi V, Logan IR, Nelson G, Cook S, Robson CN. Phosphorylation of Tat-interactive protein 60 kDa by protein kinase C epsilon is important for its subcellular localisation. Int J Biochem Cell Biol 2007; 40:236-44. [PMID: 17851107 DOI: 10.1016/j.biocel.2007.07.017] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2007] [Revised: 07/24/2007] [Accepted: 07/26/2007] [Indexed: 11/24/2022]
Abstract
Tat-interactive protein 60 kDa is a nuclear acetyltransferase that both coactivates and corepresses transcription factors and has a definitive function in the DNA damage response. Here, we provide evidence that Tat-interactive protein 60 kDa is phosphorylated by protein kinase C epsilon. In vitro, protein kinase C epsilon phosphorylates Tat-interactive protein 60 kDa on at least two sites within the acetyltransferase domain. In whole cells, activation of protein kinase C increases the levels of phosphorylated Tat-interactive protein 60 kDa and the interaction of Tat-interactive protein 60 kDa with protein kinase C epsilon. A phosphomimetic mutant Tat-interactive protein 60 kDa has distinct subcellular localisation compared to the wild-type protein in whole cells. Taken together, these findings suggest that the protein kinase C epsilon phosphorylation sites on Tat-interactive protein 60 kDa are important for its subcellular localisation. Regulation of the subcellular localisation of Tat-interactive protein 60 kDa via phosphorylation provides a novel means of controlling Tat-interactive protein 60 kDa function.
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Affiliation(s)
- Vasileia Sapountzi
- Surgical Oncology Laboratory, Northern Institute for Cancer Research, Paul O'Gorman Building, Framlington Place, Newcastle University, Newcastle upon Tyne NE2 4HH, UK
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26
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Li B, Samanta A, Song X, Iacono KT, Bembas K, Tao R, Basu S, Riley JL, Hancock WW, Shen Y, Saouaf SJ, Greene MI. FOXP3 interactions with histone acetyltransferase and class II histone deacetylases are required for repression. Proc Natl Acad Sci U S A 2007; 104:4571-6. [PMID: 17360565 PMCID: PMC1838642 DOI: 10.1073/pnas.0700298104] [Citation(s) in RCA: 315] [Impact Index Per Article: 18.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2006] [Indexed: 01/08/2023] Open
Abstract
The forkhead family protein FOXP3 acts as a repressor of transcription and is both an essential and sufficient regulator of the development and function of regulatory T cells. The molecular mechanism by which FOXP3-mediated transcriptional repression occurs remains unclear. Here, we report that transcriptional repression by FOXP3 involves a histone acetyltransferase-deacetylase complex that includes histone acetyltransferase TIP60 (Tat-interactive protein, 60 kDa) and class II histone deacetylases HDAC7 and HDAC9. The N-terminal 106-190 aa of FOXP3 are required for TIP60-FOXP3, HDAC7-FOXP3 association, as well as for the transcriptional repression of FOXP3 via its forkhead domain. FOXP3 can be acetylated in primary human regulatory T cells, and TIP60 promotes FOXP3 acetylation in vivo. Overexpression of TIP60 but not its histone acetyltransferase-deficient mutant promotes, whereas knockdown of endogenous TIP60 relieved, FOXP3-mediated transcriptional repression. A minimum FOXP3 ensemble containing native TIP60 and HDAC7 is necessary for IL-2 production regulation in T cells. Moreover, FOXP3 association with HDAC9 is antagonized by T cell stimulation and can be restored by the protein deacetylation inhibitor trichostatin A, indicating a complex dynamic aspect of T suppressor cell regulation. These findings identify a previously uncharacterized complex-based mechanism by which FOXP3 actively mediates transcriptional repression.
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Affiliation(s)
- Bin Li
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Arabinda Samanta
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Xiaomin Song
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Kathryn T. Iacono
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Kathryn Bembas
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Ran Tao
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Samik Basu
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - James L. Riley
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Wayne W. Hancock
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Yuan Shen
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Sandra J. Saouaf
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
| | - Mark I. Greene
- Department of Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, PA 19104-6082
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27
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Zhu X, Singh N, Donnelly C, Boimel P, Elefant F. The cloning and characterization of the histone acetyltransferase human homolog Dmel\TIP60 in Drosophila melanogaster: Dmel\TIP60 is essential for multicellular development. Genetics 2007; 175:1229-40. [PMID: 17179074 PMCID: PMC1840084 DOI: 10.1534/genetics.106.063685] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/18/2006] [Accepted: 12/14/2006] [Indexed: 11/18/2022] Open
Abstract
Chromatin packaging directly influences gene programming as it permits only certain portions of the genome to be activated in any given developmental stage, cell, and tissue type. Histone acetyltransferases (HATs) are a key class of chromatin regulatory proteins that mediate such developmental chromatin control; however, their specific roles during multicellular development remain unclear. Here, we report the first isolation and developmental characterization of a Drosophila HAT gene (Dmel\TIP60) that is the homolog of the human HAT gene TIP60. We show that Dmel\TIP60 is differentially expressed during Drosophila development, with transcript levels significantly peaking during embryogenesis. We further demonstrate that reducing endogenous Dmel\TIP60 expression in Drosophila embryonic cells by RNAi results in cellular defects and lethality. Finally, using a GAL4-targeted RNAi system in Drosophila, we show that ubiquitous or mesoderm/muscle-specific reduction of Dmel\TIP60 expression results in lethality during fly development. Our results suggest a mechanism for HAT regulation involving developmental control of HAT expression profiles and show that Dmel\TIP60 is essential for multicellular development. Significantly, our inducible and targeted HAT knockdown system in Drosophila now provides a powerful tool for effectively studying the roles of TIP60 in specific tissues and cell types during development.
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Affiliation(s)
- Xianmin Zhu
- Department of Bioscience and Biotechnology, Drexel University, Philadelphia, Pennsylvania 19104
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28
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Wei G, Hobbs CA, Defeo K, Hayes CS, Gilmour SK. Polyamine-mediated regulation of protein acetylation in murine skin and tumors. Mol Carcinog 2007; 46:611-7. [PMID: 17570504 DOI: 10.1002/mc.20350] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Overexpression of ornithine decarboxylase (ODC), resulting in increased polyamine metabolism, is a common feature of epithelial tumors. Polyamines play a complex role in promoting tumor development, affecting diverse cellular processes, including gene expression. One way polyamines may affect gene expression is to modulate the multiprotein complexes comprised of transcription factors and coregulatory factors that alter chromatin structure by acetylating/deacetylating nearby histones. We have capitalized on ODC-overexpressing cultured cells and K6/ODC and ODC/Ras transgenic mouse models, in which ODC overexpression is targeted to hair follicles, to evaluate the influence of polyamines on the acetylation of histones and other proteins. ODC overexpression was found to alter intrinsic histone acetyltransferase (HAT) and deacetylase activities and histone acetylation patterns. The high HAT activity exhibited by ODC transgenic mouse skin and tumors might be partly attributed to enhanced p300/creb-binding protein (CBP)-associated HAT activity and increased levels of Tat interactive protein, 60 kDa (Tip60) HAT protein isoforms. Altered association of Tip60 with E2F1 and a subset of newly identified Tip60-interacting transcription factors was detected in ODC mouse skin and tumors, implying novel polyamine modulation of Tip60-regulated gene expression. Polyamine effects on HAT enzymes also influence the acetylation status of nonhistone proteins. Overexpression of ODC in skin serves as a novel stimulus for acetylation of the tumor suppressor protein, p53--a target of both p300/CBP and Tip60--with concomitant increased binding to, and increased transcription of, a downstream target gene. The future challenge will be to elucidate the multiple mechanisms by which polyamines influence enzymes that regulate protein acetylation and gene transcription to promote cancer.
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Affiliation(s)
- Gang Wei
- Lankenau Institute for Medical Research, Wynnewood, Pennsylvania 19096, USA
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Squatrito M, Gorrini C, Amati B. Tip60 in DNA damage response and growth control: many tricks in one HAT. Trends Cell Biol 2006; 16:433-42. [PMID: 16904321 DOI: 10.1016/j.tcb.2006.07.007] [Citation(s) in RCA: 232] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Revised: 07/05/2006] [Accepted: 07/27/2006] [Indexed: 02/02/2023]
Abstract
The Tip60 histone acetyltransferase is part of an evolutionarily conserved multisubunit complex, NuA4, which is recruited by many transcription factors to their target promoters, where it is thought to participate in histone acetylation and transcriptional activation. These transcription factors include tumor promoters and also tumor suppressors, such as p53, which links Tip60 to DNA damage responses. Tip60 also has transcription-independent roles in DNA damage responses. First, independently from NuA4, Tip60 binds the kinases ataxia-telangiectasia mutated (ATM) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) and participates in their activation by DNA double-strand breaks. Second, NuA4 is recruited to the chromatin surrounding the breaks and, through a series of chromatin modifications, contributes to the dynamics of DNA repair. These molecular activities might endow Tip60 with multiple and potentially antagonistic biological functions.
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Affiliation(s)
- Massimo Squatrito
- Department of Experimental Oncology, European Institute of Oncology (IEO), IFOM-IEO Campus, Milan 20139, Italy
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Meraner J, Lechner M, Loidl A, Goralik-Schramel M, Voit R, Grummt I, Loidl P. Acetylation of UBF changes during the cell cycle and regulates the interaction of UBF with RNA polymerase I. Nucleic Acids Res 2006; 34:1798-806. [PMID: 16582105 PMCID: PMC1421502 DOI: 10.1093/nar/gkl101] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The upstream binding factor UBF, an activator of RNA polymerase I transcription, is posttranslationally modified by phosphorylation and acetylation. We found that in NIH3T3 cells, UBF is acetylated in S-phase but not in G1-phase. To assess the role of acetylation in regulation of UBF activity, we have established an NIH3T3 cell line that inducibly overexpresses HDAC1. Both in vivo and in vitro, HDAC1 efficiently hypoacetylates UBF. Immunoprecipitation with antibodies against the Pol I-associated factor PAF53 co-precipitated UBF in mock cells but not in cells overexpressing HDAC1. Pull-down experiments showed that acetylation of UBF augments the interaction with Pol I. Consistent with acetylation of UBF being important for association of PAF53 and recruitment of Pol I, the level of Pol I associated with rDNA and pre-rRNA synthesis were reduced in cells overexpressing HDAC1. The results suggest that acetylation and deacetylation of UBF regulate rRNA synthesis during cell cycle progression.
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Affiliation(s)
| | | | | | | | - Renate Voit
- Division of Molecular Biology of the Cell II, German Cancer Research CenterD-69120 Heidelberg, Germany
| | - Ingrid Grummt
- Division of Molecular Biology of the Cell II, German Cancer Research CenterD-69120 Heidelberg, Germany
| | - Peter Loidl
- To whom correspondence should be addressed. +43 512 507 3600; Fax: +43 512 507 9880;
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Sapountzi V, Logan IR, Robson CN. Cellular functions of TIP60. Int J Biochem Cell Biol 2006; 38:1496-509. [PMID: 16698308 DOI: 10.1016/j.biocel.2006.03.003] [Citation(s) in RCA: 192] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2006] [Revised: 03/09/2006] [Accepted: 03/09/2006] [Indexed: 11/20/2022]
Abstract
TIP60 was originally identified as a cellular acetyltransferase protein that interacts with HIV-1 Tat. As a consequence, the role of TIP60 in transcriptional regulation has been investigated intensively. Recent data suggest that TIP60 has more divergent functions than originally thought and roles for TIP60 in many processes, such as cellular signalling, DNA damage repair, cell cycle and checkpoint control and apoptosis are emerging. TIP60 is a tightly regulated transcriptional coregulator, acting in a large multiprotein complex for a range of transcription factors including androgen receptor, Myc, STAT3, NF-kappaB, E2F1 and p53. This usually involves recruitment of TIP60 acetyltransferase activities to chromatin. Additionally, in response to DNA double strand breaks, TIP60 is recruited to DNA lesions where it participates both in the initial as well as the final stages of repair. Here, we describe how TIP60 is a multifunctional enzyme involved in multiple nuclear transactions.
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Affiliation(s)
- Vasileia Sapountzi
- Northern Institute for Cancer Research, Paul O'Gorman Building, Medical School, Framlington Place, University of Newcastle Upon Tyne, Newcastle Upon Tyne NE2 4HH, United Kingdom
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Doyon Y, Cayrou C, Ullah M, Landry AJ, Côté V, Selleck W, Lane WS, Tan S, Yang XJ, Côté J. ING tumor suppressor proteins are critical regulators of chromatin acetylation required for genome expression and perpetuation. Mol Cell 2006; 21:51-64. [PMID: 16387653 DOI: 10.1016/j.molcel.2005.12.007] [Citation(s) in RCA: 508] [Impact Index Per Article: 28.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/19/2005] [Revised: 10/31/2005] [Accepted: 12/07/2005] [Indexed: 10/25/2022]
Abstract
Members of the ING family of tumor suppressors regulate cell cycle progression, apoptosis, and DNA repair as important cofactors of p53. ING1 and ING3 are stable components of the mSin3A HDAC and Tip60/NuA4 HAT complexes, respectively. We now report the purification of the three remaining human ING proteins. While ING2 is in an HDAC complex similar to ING1, ING4 associates with the HBO1 HAT required for normal progression through S phase and the majority of histone H4 acetylation in vivo. ING5 fractionates with two distinct complexes containing HBO1 or nucleosomal H3-specific MOZ/MORF HATs. These ING5 HAT complexes interact with the MCM helicase and are essential for DNA replication to occur during S phase. Our data also indicate that ING subunits are crucial for acetylation of chromatin substrates. Since INGs, HBO1, and MOZ/MORF contribute to oncogenic transformation, the multisubunit assemblies characterized here underscore the critical role of epigenetic regulation in cancer development.
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Affiliation(s)
- Yannick Doyon
- Laval University Cancer Research Center, Hôtel-Dieu de Québec (CHUQ), Québec City, Québec G1R 2J6, Canada
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Shimono K, Shimono Y, Shimokata K, Ishiguro N, Takahashi M. Microspherule protein 1, Mi-2beta, and RET finger protein associate in the nucleolus and up-regulate ribosomal gene transcription. J Biol Chem 2005; 280:39436-47. [PMID: 16186106 DOI: 10.1074/jbc.m507356200] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
The nucleolus is the site of ribosomal DNA (rDNA) transcription and ribosome production. In exploring the role of nucleolar protein MCRS1 (microspherule protein1)/MSP58 (58-kDa microspherule protein), we found that Mi-2beta, a component of a nucleosome remodeling and deacetylase (NuRD) complex, RET finger protein (RFP), and upstream binding factor (UBF) were associated with MCRS1. Yeast two-hybrid assays revealed that MCRS1 bound to the ATPase/helicase region of Mi-2beta and the coiled-coil region of RFP. Interestingly, confocal microscopic analyses revealed the co-localization of MCRS1, Mi-2beta, RFP, and the rRNA transcription factor UBF in the nucleoli. We also found that MCRS1, Mi-2beta, and RFP were associated with rDNA using a chromatin immunoprecipitation assay. Finally, we showed that MCRS1, Mi-2beta, and RFP up-regulated transcriptional activity of the rDNA promoter and that ribosomal RNA transcription was repressed when MCRS1, Mi-2beta, and RFP expression was reduced using siRNA. These results indicated that Mi-2beta and RFP, known to be involved in transcriptional repression in the nucleus, co-localize with MCRS1 in the nucleolus and appear to activate the rRNA transcription.
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Affiliation(s)
- Keiko Shimono
- Department of Pathology, Center for Neurological Diseases and Cancer, Nagoya University Graduate School of Medicine, 65 Tsurumai-cho, Showa-ku, Nagoya 466-8550, Japan
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Abstract
In the extensive network of interdependent biochemical processes required for cell growth and division, there is mounting evidence that ribosomal DNA transcription by RNA polymerase I (pol I) not only drives cell growth via its direct role in production of the ribosomal RNA (rRNA) component of the protein-synthesis machinery, but that it is also crucial in determining the fate of the cell. Considerable progress has been made in recent years towards understanding both the function of components of the pol I transcription machinery and how cells accomplish the tight control of pol I transcription, balancing the supply of rRNA with demand under different growth conditions.
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Affiliation(s)
- Jackie Russell
- Division of Gene Regulation and Expression, Wellcome Trust Biocentre, University of Dundee, Dundee DD1 5EH, Scotland, UK
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Arabi A, Wu S, Ridderstråle K, Bierhoff H, Shiue C, Fatyol K, Fahlén S, Hydbring P, Söderberg O, Grummt I, Larsson LG, Wright APH. c-Myc associates with ribosomal DNA and activates RNA polymerase I transcription. Nat Cell Biol 2005; 7:303-10. [PMID: 15723053 DOI: 10.1038/ncb1225] [Citation(s) in RCA: 358] [Impact Index Per Article: 18.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2004] [Accepted: 01/13/2005] [Indexed: 11/08/2022]
Abstract
The c-Myc oncoprotein regulates transcription of genes that are associated with cell growth, proliferation and apoptosis. c-Myc levels are modulated by ubiquitin/proteasome-mediated degradation. Proteasome inhibition leads to c-Myc accumulation within nucleoli, indicating that c-Myc might have a nucleolar function. Here we show that the proteins c-Myc and Max interact in nucleoli and are associated with ribosomal DNA. This association is increased upon activation of quiescent cells and is followed by recruitment of the Myc cofactor TRRAP, enhanced histone acetylation, recruitment of RNA polymerase I (Pol I), and activation of rDNA transcription. Using small interfering RNAs (siRNAs) against c-Myc and an inhibitor of Myc-Max interactions, we demonstrate that c-Myc is required for activating rDNA transcription in response to mitogenic signals. Furthermore, using the ligand-activated MycER (ER, oestrogen receptor) system, we show that c-Myc can activate Pol I transcription in the absence of Pol II transcription. These results suggest that c-Myc coordinates the activity of all three nuclear RNA polymerases, and thereby plays a key role in regulating ribosome biogenesis and cell growth.
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