1
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Palma FR, Coelho DR, Pulakanti K, Sakiyama MJ, Huang Y, Ogata FT, Danes JM, Meyer A, Furdui CM, Spitz DR, Gomes AP, Gantner BN, Rao S, Backman V, Bonini MG. Histone H3.1 is a chromatin-embedded redox sensor triggered by tumor cells developing adaptive phenotypic plasticity and multidrug resistance. Cell Rep 2024; 43:113897. [PMID: 38493478 DOI: 10.1016/j.celrep.2024.113897] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2023] [Revised: 01/08/2024] [Accepted: 02/16/2024] [Indexed: 03/19/2024] Open
Abstract
Chromatin structure is regulated through posttranslational modifications of histone variants that modulate transcription. Although highly homologous, histone variants display unique amino acid sequences associated with specific functions. Abnormal incorporation of histone variants contributes to cancer initiation, therapy resistance, and metastasis. This study reports that, among its biologic functions, histone H3.1 serves as a chromatin redox sensor that is engaged by mitochondrial H2O2. In breast cancer cells, the oxidation of H3.1Cys96 promotes its eviction and replacement by H3.3 in specific promoters. We also report that this process facilitates the opening of silenced chromatin domains and transcriptional activation of epithelial-to-mesenchymal genes associated with cell plasticity. Scavenging nuclear H2O2 or amino acid substitution of H3.1(C96S) suppresses plasticity, restores sensitivity to chemotherapy, and induces remission of metastatic lesions. Hence, it appears that increased levels of H2O2 produced by mitochondria of breast cancer cells directly promote redox-regulated H3.1-dependent chromatin remodeling involved in chemoresistance and metastasis.
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Affiliation(s)
- Flavio R Palma
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Diego R Coelho
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Kirthi Pulakanti
- Versiti Blood Research Institute of Wisconsin, and Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Marcelo J Sakiyama
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Yunping Huang
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Fernando T Ogata
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Jeanne M Danes
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA
| | - Alison Meyer
- Versiti Blood Research Institute of Wisconsin, and Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Cristina M Furdui
- Department of Internal Medicine, Section on Molecular Medicine, Wake Forest School of Medicine, Winston-Salem, NC 27157, USA
| | - Douglas R Spitz
- Free Radical and Radiation Biology Program, Department of Radiation Oncology, Holden Comprehensive Cancer Center, University of Iowa, Iowa City, IA 52245, USA
| | - Ana P Gomes
- Molecular Oncology Program, H. Lee Moffitt Cancer Center, Tampa, FL 33612, USA
| | - Benjamin N Gantner
- Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Sridhar Rao
- Versiti Blood Research Institute of Wisconsin, and Department of Cell Biology, Neurobiology, and Anatomy, Medical College of Wisconsin, Milwaukee, WI 53226, USA; Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, USA
| | - Vadim Backman
- Department of Biomedical Engineering, Northwestern University McCormick School of Engineering, Evanston, IL 60208, USA
| | - Marcelo G Bonini
- Department of Medicine, Division of Hematology Oncology, Northwestern University Feinberg School of Medicine and the Robert H. Lurie Comprehensive Cancer Center of Chicago, Chicago, IL 60611, USA; Department of Biochemistry and Molecular Genetics, Northwestern University Feinberg School of Medicine, Chicago, IL 60611, USA.
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2
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Choi J, Kim T, Cho EJ. HIRA vs. DAXX: the two axes shaping the histone H3.3 landscape. Exp Mol Med 2024; 56:251-263. [PMID: 38297159 PMCID: PMC10907377 DOI: 10.1038/s12276-023-01145-3] [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: 09/27/2023] [Revised: 11/20/2023] [Accepted: 11/23/2023] [Indexed: 02/02/2024] Open
Abstract
H3.3, the most common replacement variant for histone H3, has emerged as an important player in chromatin dynamics for controlling gene expression and genome integrity. While replicative variants H3.1 and H3.2 are primarily incorporated into nucleosomes during DNA synthesis, H3.3 is under the control of H3.3-specific histone chaperones for spatiotemporal incorporation throughout the cell cycle. Over the years, there has been progress in understanding the mechanisms by which H3.3 affects domain structure and function. Furthermore, H3.3 distribution and relative abundance profoundly impact cellular identity and plasticity during normal development and pathogenesis. Recurrent mutations in H3.3 and its chaperones have been identified in neoplastic transformation and developmental disorders, providing new insights into chromatin biology and disease. Here, we review recent findings emphasizing how two distinct histone chaperones, HIRA and DAXX, take part in the spatial and temporal distribution of H3.3 in different chromatin domains and ultimately achieve dynamic control of chromatin organization and function. Elucidating the H3.3 deposition pathways from the available histone pool will open new avenues for understanding the mechanisms by which H3.3 epigenetically regulates gene expression and its impact on cellular integrity and pathogenesis.
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Affiliation(s)
- Jinmi Choi
- Sungkyunkwan University School of Pharmacy, Seoburo 2066, Jangan-gu Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Taewan Kim
- Sungkyunkwan University School of Pharmacy, Seoburo 2066, Jangan-gu Suwon, Gyeonggi-do, 16419, Republic of Korea
| | - Eun-Jung Cho
- Sungkyunkwan University School of Pharmacy, Seoburo 2066, Jangan-gu Suwon, Gyeonggi-do, 16419, Republic of Korea.
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3
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Hao H, Ren C, Lian Y, Zhao M, Bo T, Xu J, Wang W. Independent and Complementary Functions of Caf1b and Hir1 for Chromatin Assembly in Tetrahymena thermophila. Cells 2023; 12:2828. [PMID: 38132148 PMCID: PMC10741905 DOI: 10.3390/cells12242828] [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: 11/17/2023] [Revised: 12/09/2023] [Accepted: 12/11/2023] [Indexed: 12/23/2023] Open
Abstract
Histones and DNA associate to form the nucleosomes of eukaryotic chromatin. Chromatin assembly factor 1 (CAF-1) complex and histone regulatory protein A (HIRA) complex mediate replication-couple (RC) and replication-independent (RI) nucleosome assembly, respectively. CHAF1B and HIRA share a similar domain but play different roles in nucleosome assembly by binding to the different interactors. At present, there is limited understanding for the similarities and differences in their respective functions. Tetrahymena thermophila contains transcriptionally active polyploid macronuclei (MAC) and transcriptionally silent diploid micronuclei (MIC). Here, the distribution patterns of Caf1b and Hir1 exhibited both similarities and distinctions. Both proteins localized to the MAC and MIC during growth, and to the MIC during conjugation. However, Hir1 exhibited additional signaling on parental MAC and new MAC during sexual reproduction and displayed a punctate signal on developing anlagen. Caf1b and Hir1 only co-localized in the MIC with Pcna1 during conjugation. Knockdown of CAF1B impeded cellular growth and arrested sexual reproductive development. Loss of HIR1 led to MIC chromosome defects and aborted sexual development. Co-interference of CAF1B and HIR1 led to a more severe phenotype. Moreover, CAF1B knockdown led to the up-regulation of HIR1 expression, while knockdown of HIR1 also led to an increase in CAF1B expression. Furthermore, Caf1b and Hir1 interacted with different interactors. These results showed that CAF-1 and Hir1 have independent and complementary functions for chromatin assembly in T. thermophila.
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Affiliation(s)
- Huijuan Hao
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Chenhui Ren
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Yinjie Lian
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Min Zhao
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Tao Bo
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
| | - Jing Xu
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
- School of Life Science, Shanxi University, Taiyuan 030006, China
| | - Wei Wang
- Key Laboratory of Chemical Biology and Molecular Engineering of Ministry of Education, Institute of Biotechnology, Shanxi University, Taiyuan 030006, China; (H.H.); (C.R.); (Y.L.); (M.Z.); (T.B.)
- Shanxi Key Laboratory of Biotechnology, Taiyuan 030006, China
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4
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Zhang M, Zhao X, Feng X, Hu X, Zhao X, Lu W, Lu X. Histone chaperone HIRA complex regulates retrotransposons in embryonic stem cells. Stem Cell Res Ther 2022; 13:137. [PMID: 35365225 PMCID: PMC8973876 DOI: 10.1186/s13287-022-02814-2] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2021] [Accepted: 03/11/2022] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Histone cell cycle regulator (HIRA) complex is an important histone chaperone that mediates the deposition of the H3.3 histone variant onto chromatin independently from DNA synthesis. However, it is still unknown whether it participates in the expression control of retrotransposons and cell fate determination. METHODS We screened the role of HIRA complex members in repressing the expression of retrotransposons by shRNA depletion in embryonic stem cells (ESCs) followed by RT-qPCR. RNA-seq was used to study the expression profiles after depletion of individual HIRA member. RT-qPCR and western blot were used to determine overexpression of HIRA complex members. Chromatin immunoprecipitation (ChIP)-qPCR was used to find the binding of H3.3, HIRA members to chromatin. Co-immunoprecipitation was used to identify the interaction between Hira mutant and Ubn2. ChIP-qPCR was used to identify H3.3 deposition change and western blot of chromatin extract was used to validate the epigenetic change. Bioinformatics analysis was applied for the analysis of available ChIP-seq data. RESULTS We revealed that Hira, Ubn2, and Ubn1 were the main repressors of 2-cell marker retrotransposon MERVL among HIRA complex members. Surprisingly, Ubn2 and Hira targeted different groups of retrotransposons and retrotransposon-derived long noncoding RNAs (lncRNAs), despite that they partially shared target genes. Furthermore, Ubn2 prevented ESCs to gain a 2-cell like state or activate trophectodermal genes upon differentiation. Mechanistically, Ubn2 and Hira suppressed retrotransposons by regulating the deposition of histone H3.3. Decreased H3.3 deposition, that was associated with the loss of Ubn2 or Hira, caused the reduction of H3K9me2 and H3K9me3, which are known repressive marks of retrotransposons. CONCLUSIONS Overall, our findings shed light on the distinct roles of HIRA complex members in controlling retrotransposons and cell fate conversion in ESCs.
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Affiliation(s)
- Miao Zhang
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, 300350, People's Republic of China
| | - Xin Zhao
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, 300350, People's Republic of China
| | - Xiao Feng
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, 300350, People's Republic of China
| | | | - Xuan Zhao
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, 300350, People's Republic of China
| | - Wange Lu
- State Key Laboratory of Medicinal Chemical Biology, College of Life Sciences, Nankai University, Tianjin, 300071, People's Republic of China
| | - Xinyi Lu
- State Key Laboratory of Medicinal Chemical Biology, Nankai University, Tianjin, 300350, People's Republic of China.
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5
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Nakatsukasa H, Oda M, Yin J, Chikuma S, Ito M, Koga-Iizuka M, Someya K, Kitagawa Y, Ohkura N, Sakaguchi S, Koya I, Sanosaka T, Kohyama J, Tsukada YI, Yamanaka S, Takamura-Enya T, Lu Q, Yoshimura A. Loss of TET proteins in regulatory T cells promotes abnormal proliferation, Foxp3 destabilization and IL-17 expression. Int Immunol 2019; 31:335-347. [DOI: 10.1093/intimm/dxz008] [Citation(s) in RCA: 36] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/05/2018] [Accepted: 01/26/2019] [Indexed: 12/17/2022] Open
Affiliation(s)
| | - Mayumi Oda
- Department of Systems Medicine, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Jinghua Yin
- Department of Dermatology, Second Xiangya Hospital, Central South University, Hunan Key Laboratory of Medical Epigenomics, Changsha, Hunan 410011, China
| | | | - Minako Ito
- Department of Microbiology and Immunology
| | | | | | - Yohko Kitagawa
- Department of Experimental Immunology, Immunology Frontier Research Center, Osaka University, 3-1 Yamada-oka, Suita 565-0871, Japan
| | - Naganari Ohkura
- Department of Experimental Immunology, Immunology Frontier Research Center, Osaka University, 3-1 Yamada-oka, Suita 565-0871, Japan
| | - Shimon Sakaguchi
- Department of Experimental Immunology, Immunology Frontier Research Center, Osaka University, 3-1 Yamada-oka, Suita 565-0871, Japan
| | - Ikuko Koya
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Tsukasa Sanosaka
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Jun Kohyama
- Department of Physiology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Yu-ichi Tsukada
- Advanced Biological Information Research Division, INAMORI Frontier Research Center, Kyushu University, Fukuoka, Fukuoka 819-0395, Japan
| | - Soichiro Yamanaka
- Department of Molecular Biology, Keio University School of Medicine, 35 Shinanomachi, Shinjuku-ku, Tokyo 160-8582, Japan
| | - Takeji Takamura-Enya
- Department of Applied Chemistry, Kanagawa Institute of Technology, Shimo-Ogino 1030, Atsugi-shi 243-0292, Japan
| | - Qianjin Lu
- Department of Dermatology, Second Xiangya Hospital, Central South University, Hunan Key Laboratory of Medical Epigenomics, Changsha, Hunan 410011, China
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6
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Park J, Lee H, Han N, Kwak S, Lee HT, Kim JH, Kang K, Youn BH, Yang JH, Jeong HJ, Kang JS, Kim SY, Han JW, Youn HD, Cho EJ. Long non-coding RNA ChRO1 facilitates ATRX/DAXX-dependent H3.3 deposition for transcription-associated heterochromatin reorganization. Nucleic Acids Res 2018; 46:11759-11775. [PMID: 30335163 PMCID: PMC6294499 DOI: 10.1093/nar/gky923] [Citation(s) in RCA: 31] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/14/2018] [Revised: 09/20/2018] [Accepted: 10/05/2018] [Indexed: 12/23/2022] Open
Abstract
Constitutive heterochromatin undergoes a dynamic clustering and spatial reorganization during myogenic differentiation. However the detailed mechanisms and its role in cell differentiation remain largely elusive. Here, we report the identification of a muscle-specific long non-coding RNA, ChRO1, involved in constitutive heterochromatin reorganization. ChRO1 is induced during terminal differentiation of myoblasts, and is specifically localized to the chromocenters in myotubes. ChRO1 is required for efficient cell differentiation, with global impacts on gene expression. It influences DNA methylation and chromatin compaction at peri/centromeric regions. Inhibition of ChRO1 leads to defects in the spatial fusion of chromocenters, and mislocalization of H4K20 trimethylation, Suv420H2, HP1, MeCP2 and cohesin. In particular, ChRO1 specifically associates with ATRX/DAXX/H3.3 complex at chromocenters to promote H3.3 incorporation and transcriptional induction of satellite repeats, which is essential for chromocenter clustering. Thus, our results unveil a mechanism involving a lncRNA that plays a role in large-scale heterochromatin reorganization and cell differentiation.
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MESH Headings
- Animals
- CRISPR-Cas Systems
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Cell Cycle Proteins/genetics
- Cell Cycle Proteins/metabolism
- Cell Differentiation
- Chromosomal Proteins, Non-Histone/genetics
- Chromosomal Proteins, Non-Histone/metabolism
- Co-Repressor Proteins
- Female
- Gene Editing
- Gene Expression Regulation, Developmental
- HEK293 Cells
- Heterochromatin/chemistry
- Heterochromatin/metabolism
- Histone-Lysine N-Methyltransferase/genetics
- Histone-Lysine N-Methyltransferase/metabolism
- Histones/genetics
- Histones/metabolism
- Humans
- Intracellular Signaling Peptides and Proteins/genetics
- Intracellular Signaling Peptides and Proteins/metabolism
- Male
- Methyl-CpG-Binding Protein 2/genetics
- Methyl-CpG-Binding Protein 2/metabolism
- Mice
- Mice, Inbred C57BL
- Molecular Chaperones
- Muscle Development/genetics
- Muscle, Skeletal/cytology
- Muscle, Skeletal/growth & development
- Muscle, Skeletal/metabolism
- NIH 3T3 Cells
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- RNA, Long Noncoding/antagonists & inhibitors
- RNA, Long Noncoding/genetics
- RNA, Long Noncoding/metabolism
- RNA, Small Interfering/genetics
- RNA, Small Interfering/metabolism
- Transcription, Genetic
- X-linked Nuclear Protein/genetics
- X-linked Nuclear Protein/metabolism
- Cohesins
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Affiliation(s)
- Jinyoung Park
- School of Pharmacy, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea
| | - Hongmin Lee
- School of Pharmacy, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea
| | - Namshik Han
- Milner Therapeutics Institute, University of Cambridge, Cambridge CB2 1QN, UK
| | - Sojung Kwak
- Department of Biomedical Sciences,National Creative Research Center for Epigenome Reprogramming Network, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul 03080, Republic of Korea
| | - Han-Teo Lee
- Department of Molecular Medicine & Biopharmaceutical Sciences, Graduate School of Convergence Science and technology, Seoul National University, Seoul 03080, Republic of Korea
| | - Jae-Hwan Kim
- Department of Biomedical Sciences,National Creative Research Center for Epigenome Reprogramming Network, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul 03080, Republic of Korea
| | - Keonjin Kang
- School of Pharmacy, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea
| | - Byoung Ha Youn
- Medical Genome Research Center, KRIBB, Daejeon 34141, Republic of Korea
| | - Jae-Hyun Yang
- Department of Genetics, Paul F. Glenn Center for the Biology of Aging, Harvard Medical School, Boston, MA 02115, USA
| | - Hyeon-Ju Jeong
- College of Medicine, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Republic of Korea
| | - Jong-Sun Kang
- College of Medicine, Sungkyunkwan University, Suwon, Gyeonggi-do 440-746, Republic of Korea
| | - Seon-Young Kim
- Medical Genome Research Center, KRIBB, Daejeon 34141, Republic of Korea
| | - Jeung-Whan Han
- School of Pharmacy, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea
| | - Hong-Duk Youn
- Department of Biomedical Sciences,National Creative Research Center for Epigenome Reprogramming Network, Ischemic/Hypoxic Disease Institute, Seoul National University College of Medicine, Seoul 03080, Republic of Korea
- Department of Molecular Medicine & Biopharmaceutical Sciences, Graduate School of Convergence Science and technology, Seoul National University, Seoul 03080, Republic of Korea
| | - Eun-Jung Cho
- School of Pharmacy, Sungkyunkwan University, Suwon, Gyeonggi-do 16419, Republic of Korea
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7
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A Molecular Prospective for HIRA Complex Assembly and H3.3-Specific Histone Chaperone Function. J Mol Biol 2016; 429:1924-1933. [PMID: 27871933 DOI: 10.1016/j.jmb.2016.11.010] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2016] [Revised: 11/14/2016] [Accepted: 11/15/2016] [Indexed: 11/24/2022]
Abstract
Incorporation of variant histone sequences, in addition to post-translational modification of histones, serves to modulate the chromatin environment. Different histone chaperone proteins mediate the storage and chromatin deposition of variant histones. Although the two non-centromeric histone H3 variants, H3.1 and H3.3, differ by only 5 aa, replacement of histone H3.1 with H3.3 can modulate the transcription for highly expressed and developmentally required genes, lead to the formation of repressive heterochromatin, or aid in DNA and chromatin repair. The human histone cell cycle regulator (HIRA) complex composed of HIRA, ubinuclein-1, CABIN1, and transiently anti-silencing function 1, forms one of the two complexes that bind and deposit H3.3/H4 into chromatin. A number of recent biochemical and structural studies have revealed important details underlying how these proteins assemble and function together as a multiprotein H3.3-specific histone chaperone complex. Here, we present a review of existing data and present a new model for the assembly of the HIRA complex and for the HIRA-mediated incorporation of H3.3/H4 into chromatin.
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8
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Paul PK, Rabaglia ME, Wang CY, Stapleton DS, Leng N, Kendziorski C, Lewis PW, Keller MP, Attie AD. Histone chaperone ASF1B promotes human β-cell proliferation via recruitment of histone H3.3. Cell Cycle 2016; 15:3191-3202. [PMID: 27753532 DOI: 10.1080/15384101.2016.1241914] [Citation(s) in RCA: 34] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Anti-silencing function 1 (ASF1) is a histone H3-H4 chaperone involved in DNA replication and repair, and transcriptional regulation. Here, we identify ASF1B, the mammalian paralog to ASF1, as a proliferation-inducing histone chaperone in human β-cells. Overexpression of ASF1B led to distinct transcriptional signatures consistent with increased cellular proliferation and reduced cellular death. Using multiple methods of monitoring proliferation and mitotic progression, we show that overexpression of ASF1B is sufficient to induce human β-cell proliferation. Co-expression of histone H3.3 further augmented β-cell proliferation, whereas suppression of endogenous H3.3 attenuated the stimulatory effect of ASF1B. Using the histone binding-deficient mutant of ASF1B (V94R), we show that histone binding to ASF1B is required for the induction of β-cell proliferation. In contrast to H3.3, overexpression of histone H3 variants H3.1 and H3.2 did not have an impact on ASF1B-mediated induction of proliferation. Our findings reveal a novel role of ASF1B in human β-cell replication and show that ASF1B and histone H3.3A synergistically stimulate human β-cell proliferation.
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Affiliation(s)
- Pradyut K Paul
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
| | - Mary E Rabaglia
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
| | - Chen-Yu Wang
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
| | - Donald S Stapleton
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
| | - Ning Leng
- b Department of Statistics , University of Wisconsin , Madison , WI , USA
| | - Christina Kendziorski
- c Department of Biostatistics and Medical Informatics , University of Wisconsin , Madison , WI , USA
| | - Peter W Lewis
- d Department of Biomolecular Chemistry , University of Wisconsin , Madison , WI , USA
| | - Mark P Keller
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
| | - Alan D Attie
- a Department of Biochemistry , University of Wisconsin , Madison , WI , USA
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9
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Seol JH, Song TY, Oh SE, Jo C, Choi A, Kim B, Park J, Hong S, Song I, Jung KY, Yang JH, Park H, Ahn JH, Han JW, Cho EJ. Identification of small molecules that inhibit the histone chaperone Asf1 and its chromatin function. BMB Rep 2016; 48:685-90. [PMID: 26058396 PMCID: PMC4791324 DOI: 10.5483/bmbrep.2015.48.12.063] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2015] [Indexed: 12/01/2022] Open
Abstract
The eukaryotic genome is packed into chromatin, which is important for the genomic integrity and gene regulation. Chromatin structures are maintained through assembly and disassembly of nucleosomes catalyzed by histone chaperones. Asf1 (anti-silencing function 1) is a highly conserved histone chaperone that mediates histone transfer on/off DNA and promotes histone H3 lysine 56 acetylation at globular core domain of histone H3. To elucidate the role of Asf1 in the modulation of chromatin structure, we screened and identified small molecules that inhibit Asf1 and H3K56 acetylation without affecting other histone modifications. These pyrimidine-2,4,6-trione derivative molecules inhibited the nucleosome assembly mediated by Asf1 in vitro, and reduced the H3K56 acetylation in HeLa cells. Furthermore, production of HSV viral particles was reduced by these compounds. As Asf1 is implicated in genome integrity, cell proliferation, and cancer, current Asf1 inhibitor molecules may offer an opportunity for the therapeutic development for treatment of diseases. [BMB Reports 2015; 48(12): 685-690]
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Affiliation(s)
- Ja-Hwan Seol
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Tae-Yang Song
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Se Eun Oh
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Chanhee Jo
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Ahreum Choi
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Byungho Kim
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Jinyoung Park
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Suji Hong
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Ilrang Song
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Kwan Young Jung
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Jae-Hyun Yang
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Hwangseo Park
- Department of Bioscience and Biotechnology, Sejong University, Seoul 05006, Korea
| | - Jin-Hyun Ahn
- Department of Molecular Cell Biology, Sungkyunkwan University School of Medicine, Suwon 16419, Korea
| | - Jeung-Whan Han
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
| | - Eun-Jung Cho
- School of Pharmacy, Sungkyunkwan University, Suwon 16419, Korea
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10
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Xu W, Li Y, Cheng Z, Xia G, Wang M. A wheat histone variant gene TaH2A.7 enhances drought tolerance and promotes stomatal closure in Arabidopsis. PLANT CELL REPORTS 2016; 35:1853-62. [PMID: 27215438 DOI: 10.1007/s00299-016-1999-6] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/06/2016] [Accepted: 05/12/2016] [Indexed: 05/22/2023]
Abstract
We found a histone variant enhances drought tolerance partially via promoting stomatal closure other than osmotic stress resistance, indicating the crucial and complicated contribution of epigenetic regulation to abiotic stress response. Histone variants epigenetically regulate gene transcription through remodeling chromatin. They have been implicated in modulating plant abiotic stress response, however, the role(s) is not well documented. Here, we identified an abiotic stress responsive H2A variant gene TaH2A.7 from wheat. TaH2A.7 shared high identity with H2A homologs and localized to the nucleus. TaH2A.7 overexpression in Arabidopsis significantly enhanced drought tolerance, but had no effect on the response to saline, osmotic and oxidative stresses. TaH2A.7 lowered water loss rate, and promoted ABA-induced stomatal closure. In TaH2A.7 overexpression plants, the mRNA levels of numerous genes involved in the ABA pathway and stomatal movement signaling pathway were elevated, H2O2 level in guard cells was increased, as well. Together, TaH2A.7 can enhance drought tolerance via, at least in part, promoting stomatal closure, and appears to be a promising target for molecular breeding.
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Affiliation(s)
- Wenjing Xu
- Key Laboratory of Cellular Engineering and Germplasm Innovation, School of Life Science, Ministry of Education, Shandong University, 27 Shandanan Road, Jinan, 250100, China
| | - Yongchao Li
- Key Laboratory of Cellular Engineering and Germplasm Innovation, School of Life Science, Ministry of Education, Shandong University, 27 Shandanan Road, Jinan, 250100, China
| | - Zhaohui Cheng
- Key Laboratory of Cellular Engineering and Germplasm Innovation, School of Life Science, Ministry of Education, Shandong University, 27 Shandanan Road, Jinan, 250100, China
| | - Guangmin Xia
- Key Laboratory of Cellular Engineering and Germplasm Innovation, School of Life Science, Ministry of Education, Shandong University, 27 Shandanan Road, Jinan, 250100, China
| | - Mengcheng Wang
- Key Laboratory of Cellular Engineering and Germplasm Innovation, School of Life Science, Ministry of Education, Shandong University, 27 Shandanan Road, Jinan, 250100, China.
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11
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Divergent Residues Within Histone H3 Dictate a Unique Chromatin Structure in Saccharomyces cerevisiae. Genetics 2015; 202:341-9. [PMID: 26534951 DOI: 10.1534/genetics.115.180810] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 10/21/2015] [Indexed: 11/18/2022] Open
Abstract
Histones are among the most conserved proteins known, but organismal differences do exist. In this study, we examined the contribution that divergent amino acids within histone H3 make to cell growth and chromatin structure in Saccharomyces cerevisiae. We show that, while amino acids that define histone H3.3 are dispensable for yeast growth, substitution of residues within the histone H3 α3 helix with human counterparts results in a severe growth defect. Mutations within this domain also result in altered nucleosome positioning, both in vivo and in vitro, which is accompanied by increased preference for nucleosome-favoring sequences. These results suggest that divergent amino acids within the histone H3 α3 helix play organismal roles in defining chromatin structure.
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12
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Tissue-specific expression of histone H3 variants diversified after species separation. Epigenetics Chromatin 2015; 8:35. [PMID: 26388943 PMCID: PMC4574566 DOI: 10.1186/s13072-015-0027-3] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/13/2015] [Accepted: 07/27/2015] [Indexed: 12/02/2022] Open
Abstract
Background The selective incorporation of appropriate histone variants into chromatin is critical for the regulation of genome function. Although many histone variants have been identified, a complete list has not been compiled. Results We screened mouse, rat and human genomes by in silico hybridization using canonical histone sequences. In the mouse genome, we identified 14 uncharacterized H3 genes, among which 13 are similar to H3.3 and do not have human or rat counterparts, and one is similar to human testis-specific H3 variant, H3T/H3.4, and had a rat paralog. Although some of these genes were previously annotated as pseudogenes, their tissue-specific expression was confirmed by sequencing the 3′-UTR regions of the transcripts. Certain new variants were also detected at the protein level by mass spectrometry. When expressed as GFP-tagged versions in mouse C2C12 cells, some variants were stably incorporated into chromatin and the genome-wide distributions of most variants were similar to that of H3.3. Moreover, forced expression of H3 variants in chromatin resulted in alternate gene expression patterns after cell differentiation. Conclusions We comprehensively identified and characterized novel mouse H3 variant genes that encoded highly conserved amino acid sequences compared to known histone H3. We speculated that the diversity of H3 variants acquired after species separation played a role in regulating tissue-specific gene expression in individual species. Their biological relevance and evolutionary aspect involving pseudogene diversification will be addressed by further functional analysis. Electronic supplementary material The online version of this article (doi:10.1186/s13072-015-0027-3) contains supplementary material, which is available to authorized users.
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13
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Ricketts MD, Frederick B, Hoff H, Tang Y, Schultz DC, Singh Rai T, Grazia Vizioli M, Adams PD, Marmorstein R. Ubinuclein-1 confers histone H3.3-specific-binding by the HIRA histone chaperone complex. Nat Commun 2015; 6:7711. [PMID: 26159857 PMCID: PMC4510971 DOI: 10.1038/ncomms8711] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2015] [Accepted: 06/01/2015] [Indexed: 01/01/2023] Open
Abstract
Histone chaperones bind specific histones to mediate their storage, eviction or deposition from/or into chromatin. The HIRA histone chaperone complex, composed of HIRA, ubinuclein-1 (UBN1) and CABIN1, cooperates with the histone chaperone ASF1a to mediate H3.3-specific binding and chromatin deposition. Here we demonstrate that the conserved UBN1 Hpc2-related domain (HRD) is a novel H3.3-specific-binding domain. Biochemical and biophysical studies show the UBN1-HRD preferentially binds H3.3/H4 over H3.1/H4. X-ray crystallographic and mutational studies reveal that conserved residues within the UBN1-HRD and H3.3 G90 as key determinants of UBN1–H3.3-binding specificity. Comparison of the structure with the unrelated H3.3-specific chaperone DAXX reveals nearly identical points of contact between the chaperone and histone in the proximity of H3.3 G90, although the mechanism for H3.3 G90 recognition appears to be distinct. This study points to UBN1 as the determinant of H3.3-specific binding and deposition by the HIRA complex. Ubinuclein-1 (UBN1) is a subunit of the HIRA histone chaperone complex that deposits histone H3.3 into chromatin. Here the authors use structural and biochemical studies to show that a conserved domain in UBN1 mediates H3.3-specific binding by the HIRA complex.
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Affiliation(s)
- M Daniel Ricketts
- 1] Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA [2] Graduate Group in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
| | - Brian Frederick
- The Wistar Institute, Philadelphia, Pennsylvania, 19104, USA
| | - Henry Hoff
- The Wistar Institute, Philadelphia, Pennsylvania, 19104, USA
| | - Yong Tang
- The Wistar Institute, Philadelphia, Pennsylvania, 19104, USA
| | - David C Schultz
- The Wistar Institute, Philadelphia, Pennsylvania, 19104, USA
| | - Taranjit Singh Rai
- 1] Institute of Cancer Sciences, CR-UK Beatson Labs, University of Glasgow, Glasgow G61 1BD, UK [2] Institute of Biomedical and Environmental Health Research, University of West of Scotland, Paisley PA1 2BE, UK
| | - Maria Grazia Vizioli
- Institute of Cancer Sciences, CR-UK Beatson Labs, University of Glasgow, Glasgow G61 1BD, UK
| | - Peter D Adams
- Institute of Cancer Sciences, CR-UK Beatson Labs, University of Glasgow, Glasgow G61 1BD, UK
| | - Ronen Marmorstein
- 1] Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA [2] Graduate Group in Biochemistry and Molecular Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA [3] Abramson Family Cancer Research Institute, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA
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14
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Duc C, Benoit M, Le Goff S, Simon L, Poulet A, Cotterell S, Tatout C, Probst AV. The histone chaperone complex HIR maintains nucleosome occupancy and counterbalances impaired histone deposition in CAF-1 complex mutants. THE PLANT JOURNAL : FOR CELL AND MOLECULAR BIOLOGY 2015; 81:707-22. [PMID: 25600486 DOI: 10.1111/tpj.12758] [Citation(s) in RCA: 37] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/03/2014] [Revised: 11/21/2014] [Accepted: 12/23/2014] [Indexed: 05/09/2023]
Abstract
Chromatin organization is essential for coordinated gene expression, genome stability, and inheritance of epigenetic information. The main components involved in chromatin assembly are specific complexes such as Chromatin Assembly Factor 1 (CAF-1) and Histone Regulator (HIR), which deposit histones in a DNA synthesis-dependent or -independent manner, respectively. Here, we characterize the role of the plant orthologs Histone Regulator A (HIRA), Ubinuclein (UBN) and Calcineurin Binding protein 1 (CABIN1), which constitute the HIR complex. Arabidopsis loss-of-function mutants for the various subunits of the complex are viable, but hira mutants show reduced fertility. We show that loss of HIRA reduces extractable histone H3 protein levels and decreases nucleosome occupancy at both actively transcribed genes and heterochromatic regions. Concomitantly, HIRA contributes to maintenance of silencing of pericentromeric repeats and certain transposons. A genetic analysis based on crosses between mutants deficient in subunits of the CAF-1 and HIR complexes showed that simultaneous loss of both the CAF-1 and HIR histone H3 chaperone complexes severely affects plant survival, growth and reproductive development. Our results suggest that HIRA partially rescues impaired histone deposition in fas mutants to preserve nucleosome occupancy, implying plasticity in histone variant interaction and deposition.
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Affiliation(s)
- Céline Duc
- Génétique, Reproduction et Développement, CNRS UMR 6293, Clermont Université, INSERM U1103, 24 Avenue des Landais, BP 80026, Aubière Cedex, 63171, France
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15
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Harada A, Maehara K, Sato Y, Konno D, Tachibana T, Kimura H, Ohkawa Y. Incorporation of histone H3.1 suppresses the lineage potential of skeletal muscle. Nucleic Acids Res 2014; 43:775-86. [PMID: 25539924 PMCID: PMC4333396 DOI: 10.1093/nar/gku1346] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Lineage potential is triggered by lineage-specific transcription factors in association with changes in the chromatin structure. Histone H3.3 variant is thought to play an important role in the regulation of lineage-specific genes. To elucidate the function of H3.3 in myogenic differentiation, we forced the expression of GFP-H3.1 to alter the balance between H3.1 and H3.3 in mouse C2C12 cells that could be differentiated into myotubes. GFP-H3.1 replaced H3.3 in the regulatory regions of skeletal muscle (SKM) genes and induced a decrease of H3K4 trimethylation (H3K4me3) and increase of H3K27 trimethylation (H3K27me3). Similar results were obtained by H3.3 knockdown. In contrast, MyoD-dependent H3.3 incorporation into SKM genes in fibroblasts induced an increase of H3K4me3 and H3K27me3. In mouse embryos, a bivalent modification of H3K4me3 and H3K27me3 was formed on H3.3-incorporated SKM genes before embryonic skeletal muscle differentiation. These results suggest that lineage potential is established through a selective incorporation of specific H3 variants that governs the balance of histone modifications.
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Affiliation(s)
- Akihito Harada
- Department of Advanced Medical Initiatives, Faculty of Medicine, Kyushu University, Fukuoka 812-8582, Japan
| | - Kazumitsu Maehara
- Department of Advanced Medical Initiatives, Faculty of Medicine, Kyushu University, Fukuoka 812-8582, Japan
| | - Yuko Sato
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0021, Japan
| | - Daijiro Konno
- Laboratory for Cell Asymmetry, Center for Developmental Biology, RIKEN, Kobe 650-0047, Japan
| | - Taro Tachibana
- Department Bioengineering, Graduate School of Engineering, Osaka City University, Osaka 558-8585, Japan
| | - Hiroshi Kimura
- Graduate School of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0021, Japan
| | - Yasuyuki Ohkawa
- Department of Advanced Medical Initiatives, Faculty of Medicine, Kyushu University, Fukuoka 812-8582, Japan CREST, JST, 4-1-8 Honcho, Kawaguchi, Saitama, 332-0021, Japan
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16
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Otero S, Desvoyes B, Gutierrez C. Histone H3 dynamics in plant cell cycle and development. Cytogenet Genome Res 2014; 143:114-24. [PMID: 25060842 DOI: 10.1159/000365264] [Citation(s) in RCA: 30] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Chromatin is a macromolecular complex where DNA associates with histone proteins and a variety of non-histone proteins. Among the 4 histone types present in nucleosomes, histone H3 is encoded by a large number of genes in most eukaryotic species and is the histone that contains the largest variety of potential post-translational modifications in the N-terminal amino acid residues. In addition to centromeric histone H3, 2 major types of histone H3 exist, namely the canonical H3.1 and the variant H3.3. In this article, we review the most recent observations on the distinctive features of plant H3 proteins in terms of their expression and dynamics during the cell cycle and at various developmental stages. We also include a discussion on the histone H3 chaperones that actively participate in H3 deposition, in particular CAF-1, HIRA and ASF1, and on the putative plant homologs of human ATRX and DEK chaperones. Accumulating evidence confirms that the balanced deposition of H3.1 and H3.3 is of primary relevance for cell differentiation during plant organogenesis.
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Affiliation(s)
- Sofía Otero
- Department of Genome Dynamics and Function, Centro de Biologia Molecular Severo Ochoa, CSIC-UAM, Madrid, Spain
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17
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Nabeel-Shah S, Ashraf K, Pearlman RE, Fillingham J. Molecular evolution of NASP and conserved histone H3/H4 transport pathway. BMC Evol Biol 2014; 14:139. [PMID: 24951090 PMCID: PMC4082323 DOI: 10.1186/1471-2148-14-139] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2014] [Accepted: 06/12/2014] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND NASP is an essential protein in mammals that functions in histone transport pathways and maintenance of a soluble reservoir of histones H3/H4. NASP has been studied exclusively in Opisthokonta lineages where some functional diversity has been reported. In humans, growing evidence implicates NASP miss-regulation in the development of a variety of cancers. Although a comprehensive phylogenetic analysis is lacking, NASP-family proteins that possess four TPR motifs are thought to be widely distributed across eukaryotes. RESULTS We characterize the molecular evolution of NASP by systematically identifying putative NASP orthologs across diverse eukaryotic lineages ranging from excavata to those of the crown group. We detect extensive silent divergence at the nucleotide level suggesting the presence of strong purifying selection acting at the protein level. We also observe a selection bias for high frequencies of acidic residues which we hypothesize is a consequence of their critical function(s), further indicating the role of functional constraints operating on NASP evolution. Our data indicate that TPR1 and TPR4 constitute the most rapidly evolving functional units of NASP and may account for the functional diversity observed among well characterized family members. We also show that NASP paralogs in ray-finned fish have different genomic environments with clear differences in their GC content and have undergone significant changes at the protein level suggesting functional diversification. CONCLUSION We draw four main conclusions from this study. First, wide distribution of NASP throughout eukaryotes suggests that it was likely present in the last eukaryotic common ancestor (LECA) possibly as an important innovation in the transport of H3/H4. Second, strong purifying selection operating at the protein level has influenced the nucleotide composition of NASP genes. Further, we show that selection has acted to maintain a high frequency of functionally relevant acidic amino acids in the region that interrupts TPR2. Third, functional diversity reported among several well characterized NASP family members can be explained in terms of quickly evolving TPR1 and TPR4 motifs. Fourth, NASP fish specific paralogs have significantly diverged at the protein level with NASP2 acquiring a NNR domain.
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Affiliation(s)
| | | | | | - Jeffrey Fillingham
- Department of Chemistry and Biology, Ryerson University, 350 Victoria St,, Toronto M5B 2K3, Canada.
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