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Cai J, Wang N, Lin G, Zhang H, Xie W, Zhang Y, Xu N. MBNL2 Regulates DNA Damage Response via Stabilizing p21. Int J Mol Sci 2021; 22:ijms22020783. [PMID: 33466733 PMCID: PMC7829980 DOI: 10.3390/ijms22020783] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2020] [Revised: 12/31/2020] [Accepted: 01/12/2021] [Indexed: 12/14/2022] Open
Abstract
RNA-binding proteins are frequently dysregulated in human cancer and able to modulate tumor cell proliferation as well as tumor metastasis through post-transcriptional regulation on target genes. Abnormal DNA damage response and repair mechanism are closely related to genome instability and cell transformation. Here, we explore the function of the RNA-binding protein muscleblind-like splicing regulator 2 (MBNL2) on tumor cell proliferation and DNA damage response. Transcriptome and gene expression analysis show that the PI3K/AKT pathway is enriched in MBNL2-depleted cells, and the expression of cyclin-dependent kinase inhibitor 1A (p21CDKN1A) is significantly affected after MBNL2 depletion. MBNL2 modulates the mRNA and protein levels of p21, which is independent of its canonical transcription factor p53. Moreover, depletion of MBNL2 increases the phosphorylation levels of checkpoint kinase 1 (Chk1) serine 345 (S345) and DNA damage response, and the effect of MBNL2 on DNA damage response is p21-dependent. MBNL2 would further alter tumor cell fate after DNA damage, MBNL2 knockdown inhibiting DNA damage repair and DNA damage-induced senescence, but promoting DNA damage-induced apoptosis.
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Affiliation(s)
- Jin Cai
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Open FIESTA Center, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Ningchao Wang
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Open FIESTA Center, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Guanglan Lin
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Open FIESTA Center, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Haowei Zhang
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Weidong Xie
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Yaou Zhang
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
| | - Naihan Xu
- State Key Laboratory of Chemical Oncogenomics, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China; (J.C.); (N.W.); (G.L.); (H.Z.); (W.X.); (Y.Z.)
- Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
- Correspondence:
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Taylor K, Sznajder LJ, Cywoniuk P, Thomas JD, Swanson MS, Sobczak K. MBNL splicing activity depends on RNA binding site structural context. Nucleic Acids Res 2019; 46:9119-9133. [PMID: 29955876 PMCID: PMC6158504 DOI: 10.1093/nar/gky565] [Citation(s) in RCA: 23] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2018] [Accepted: 06/16/2018] [Indexed: 02/02/2023] Open
Abstract
Muscleblind-like (MBNL) proteins are conserved RNA-binding factors involved in alternative splicing (AS) regulation during development. While AS is controlled by distribution of MBNL paralogs and isoforms, the affinity of these proteins for specific RNA-binding regions and their location within transcripts, it is currently unclear how RNA structure impacts MBNL-mediated AS regulation. Here, we defined the RNA structural determinants affecting MBNL-dependent AS activity using both cellular and biochemical assays. While enhanced inclusion of MBNL-regulated alternative exons is controlled by the arrangement and number of MBNL binding sites within unstructured RNA, when these sites are embedded in a RNA hairpin MBNL binds preferentially to one side of stem region. Surprisingly, binding of MBNL proteins to RNA targets did not entirely correlate with AS efficiency. Moreover, comparison of MBNL proteins revealed structure-dependent competitive behavior between the paralogs. Our results showed that the structure of targeted RNAs is a prevalent component of the mechanism of alternative splicing regulation by MBNLs.
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Affiliation(s)
- Katarzyna Taylor
- Laboratory of Gene Therapy, Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland
| | - Lukasz J Sznajder
- Center for NeuroGenetics and the Genetics Institute, Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, 2033 Mowry Road, Gainesville, FL 32610, USA
| | - Piotr Cywoniuk
- Laboratory of Gene Therapy, Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland
| | - James D Thomas
- Center for NeuroGenetics and the Genetics Institute, Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, 2033 Mowry Road, Gainesville, FL 32610, USA.,Computational Biology Program, Public Health Sciences Division, Fred Hutchinson Cancer Research Center, Seattle, WA 98109, USA
| | - Maurice S Swanson
- Center for NeuroGenetics and the Genetics Institute, Department of Molecular Genetics and Microbiology, University of Florida College of Medicine, 2033 Mowry Road, Gainesville, FL 32610, USA
| | - Krzysztof Sobczak
- Laboratory of Gene Therapy, Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznan, Poland
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Park S, Phukan PD, Zeeb M, Martinez-Yamout MA, Dyson HJ, Wright PE. Structural Basis for Interaction of the Tandem Zinc Finger Domains of Human Muscleblind with Cognate RNA from Human Cardiac Troponin T. Biochemistry 2017; 56:4154-4168. [PMID: 28718627 PMCID: PMC5560242 DOI: 10.1021/acs.biochem.7b00484] [Citation(s) in RCA: 22] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
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The human muscleblind-like
proteins (MBNL) regulate tissue-specific
splicing by targeting cardiac troponin T and other pre-mRNAs; aberrant
targeting of CUG and CCUG repeat expansions frequently accompanies
the neuromuscular disease myotonic dystrophy. We show, using biolayer
interferometry (Octet) and NMR spectroscopy, that the zinc finger
domains of MBNL isoform 1 (MBNL1) are necessary and sufficient for
binding CGCU sequences within the pre-mRNA of human cardiac troponin
T. Protein constructs containing zinc fingers 1 and 2 (zf12) and zinc
fingers 3 and 4 (zf34) of MBNL1 each fold into a compact globular
tandem zinc finger structure that participates in RNA binding. NMR
spectra show that the stoichiometry of the interaction between zf12
or zf34 and the CGCU sequence is 1:1, and that the RNA is single-stranded
in the complex. The individual zinc fingers within zf12 or zf34 are
nonequivalent: the primary RNA binding surface is formed in each pair
by the second zinc finger (zf2 or zf4), which interacts with the CGCU
RNA sequence. The NMR structure of the complex between zf12 and a
15-base RNA of sequence 95GUCUCGCUUUUCCCC109, containing a single
CGCU element, shows the single-stranded RNA wrapped around zf2 and
extending to bind to the C-terminal helix. Bases C101, U102, and U103
make well-defined and highly ordered contacts with the protein, whereas
neighboring bases are less well-ordered in the complex. Binding of
the MBNL zinc fingers to cardiac troponin T pre-mRNA is specific and
relatively simple, unlike the complex multiple dimer–trimer
stoichiometries postulated in some previous studies.
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Affiliation(s)
- Sangho Park
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Priti Deka Phukan
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Markus Zeeb
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Maria A Martinez-Yamout
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - H Jane Dyson
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
| | - Peter E Wright
- Department of Integrative Structural and Computational Biology and Skaggs Institute of Chemical Biology, The Scripps Research Institute , 10550 North Torrey Pines Road, La Jolla, California 92037, United States
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Sznajder ŁJ, Michalak M, Taylor K, Cywoniuk P, Kabza M, Wojtkowiak-Szlachcic A, Matłoka M, Konieczny P, Sobczak K. Mechanistic determinants of MBNL activity. Nucleic Acids Res 2016; 44:10326-10342. [PMID: 27733504 PMCID: PMC5137450 DOI: 10.1093/nar/gkw915] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Accepted: 10/05/2016] [Indexed: 11/13/2022] Open
Abstract
Muscleblind-like (MBNL) proteins are critical RNA processing factors in development. MBNL activity is disrupted in the neuromuscular disease myotonic dystrophy type 1 (DM1), due to the instability of a non-coding microsatellite in the DMPK gene and the expression of CUG expansion (CUGexp) RNAs. Pathogenic interactions between MBNL and CUGexp RNA lead to the formation of nuclear complexes termed foci and prevent MBNL function in pre-mRNA processing. The existence of multiple MBNL genes, as well as multiple protein isoforms, raises the question of whether different MBNL proteins possess unique or redundant functions. To address this question, we coexpressed three MBNL paralogs in cells at equivalent levels and characterized both specific and redundant roles of these proteins in alternative splicing and RNA foci dynamics. When coexpressed in the same cells, MBNL1, MBNL2 and MBNL3 bind the same RNA motifs with different affinities. While MBNL1 demonstrated the highest splicing activity, MBNL3 showed the lowest. When forming RNA foci, MBNL1 is the most mobile paralog, while MBNL3 is rather static and the most densely packed on CUGexp RNA. Therefore, our results demonstrate that MBNL paralogs and gene-specific isoforms possess inherent functional differences, an outcome that could be enlisted to improve therapeutic strategies for DM1.
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Affiliation(s)
- Łukasz J Sznajder
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Michał Michalak
- Department of Molecular and Cellular Biology, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Katarzyna Taylor
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Piotr Cywoniuk
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Michał Kabza
- Department of Bioinformatics, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Agnieszka Wojtkowiak-Szlachcic
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Magdalena Matłoka
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Patryk Konieczny
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
| | - Krzysztof Sobczak
- Department of Gene Expression, Institute of Molecular Biology and Biotechnology, Faculty of Biology, Adam Mickiewicz University, Umultowska 89, 61-614 Poznań, Poland
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Hartley SW, Mullikin JC, Klein DC, Park M, Coon SL. Alternative Isoform Analysis of Ttc8 Expression in the Rat Pineal Gland Using a Multi-Platform Sequencing Approach Reveals Neural Regulation. PLoS One 2016; 11:e0163590. [PMID: 27684375 PMCID: PMC5042479 DOI: 10.1371/journal.pone.0163590] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2016] [Accepted: 09/12/2016] [Indexed: 01/23/2023] Open
Abstract
Alternative isoform regulation (AIR) vastly increases transcriptome diversity and plays an important role in numerous biological processes and pathologies. However, the detection and analysis of isoform-level differential regulation is difficult, particularly in the face of complex and incompletely-annotated transcriptomes. Here we have used Illumina short-read/high-throughput RNA-Seq to identify 55 genes that exhibit neurally-regulated AIR in the pineal gland, and then used two other complementary experimental platforms to further study and characterize the Ttc8 gene, which is involved in Bardet-Biedl syndrome and non-syndromic retinitis pigmentosa. Use of the JunctionSeq analysis tool led to the detection of several novel exons and splice junctions in this gene, including two novel alternative transcription start sites which were found to display disproportionately strong neurally-regulated differential expression in several independent experiments. These high-throughput sequencing results were validated and augmented via targeted qPCR and long-read Pacific Biosciences SMRT sequencing. We confirmed the existence of numerous novel splice junctions and the selective upregulation of the two novel start sites. In addition, we identified more than 20 novel isoforms of the Ttc8 gene that are co-expressed in this tissue. By using information from multiple independent platforms we not only greatly reduce the risk of errors, biases, and artifacts influencing our results, we also are able to characterize the regulation and splicing of the Ttc8 gene more deeply and more precisely than would be possible via any single platform. The hybrid method outlined here represents a powerful strategy in the study of the transcriptome.
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Affiliation(s)
- Stephen W. Hartley
- Comparative Genomics Analysis Unit, Cancer Genetics and Comparative Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, 20892, United States of America
- * E-mail:
| | - James C. Mullikin
- Comparative Genomics Analysis Unit, Cancer Genetics and Comparative Genomics Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, 20892, United States of America
| | - David C. Klein
- Section on Neuroendocrinology, Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, 20892, United States of America
| | - Morgan Park
- National Institutes of Health Intramural Sequencing Center, National Human Genome Research Institute, National Institutes of Health, Rockville, Maryland, 20852, United States of America
| | - NISC Comparative Sequencing Program
- National Institutes of Health Intramural Sequencing Center, National Human Genome Research Institute, National Institutes of Health, Rockville, Maryland, 20852, United States of America
| | - Steven L. Coon
- Section on Neuroendocrinology, Program in Developmental Endocrinology and Genetics, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, 20892, United States of America
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6
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Sun X, Li PP, Zhu S, Cohen R, Marque LO, Ross CA, Pulst SM, Chan HYE, Margolis RL, Rudnicki DD. Nuclear retention of full-length HTT RNA is mediated by splicing factors MBNL1 and U2AF65. Sci Rep 2015. [PMID: 26218986 PMCID: PMC4517393 DOI: 10.1038/srep12521] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Huntington's disease (HD) is caused by a CAG repeat expansion in the huntingtin (HTT) gene. Recent evidence suggests that HD is a consequence of multimodal, non-mutually exclusive mechanisms of pathogenesis that involve both HTT protein- and HTT RNA-triggered mechanisms. Here we provide further evidence for the role of expanded HTT (expHTT) RNA in HD by demonstrating that a fragment of expHTT is cytotoxic in the absence of any translation and that the extent of cytotoxicity is similar to the cytotoxicity of an expHTT protein fragment encoded by a transcript of similar length and with a similar repeat size. In addition, full-length (FL) expHTT is retained in the nucleus. Overexpression of the splicing factor muscleblind-like 1 (MBNL1) increases nuclear retention of expHTT and decreases the expression of expHTT protein in the cytosol. The splicing and nuclear export factor U2AF65 has the opposite effect, decreasing expHTT nuclear retention and increasing expression of expHTT protein. This suggests that MBNL1 and U2AF65 play a role in nuclear export of expHTT RNA.
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Affiliation(s)
- Xin Sun
- 1] Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [2] Guangdong-Hong Kong-Macau Institute of CNS Regeneration, Jinan University, Guangzhou, Guangdong, China
| | - Pan P Li
- Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Shanshan Zhu
- Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Rachael Cohen
- Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Leonard O Marque
- Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Christopher A Ross
- 1] Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [2] Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [3] Department of Neuroscience, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [4] Program of Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Stefan M Pulst
- Department of Neurology, University of Utah, Salt Lake City, Utah, USA
| | - Ho Yin Edwin Chan
- Laboratory of Drosophila Research, School of Life Sciences, Faculty of Science, The Chinese University of Hong Kong, Shatin, N.T., Hong Kong SAR, China
| | - Russell L Margolis
- 1] Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [2] Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [3] Program of Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
| | - Dobrila D Rudnicki
- 1] Department of Psychiatry and Behavioral Sciences, Division of Neurobiology, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA [2] Program of Cellular and Molecular Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA
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7
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Simionescu-Bankston A, Pichavant C, Canner JP, Apponi LH, Wang Y, Steeds C, Olthoff JT, Belanto JJ, Ervasti JM, Pavlath GK. Creatine kinase B is necessary to limit myoblast fusion during myogenesis. Am J Physiol Cell Physiol 2015; 308:C919-31. [PMID: 25810257 DOI: 10.1152/ajpcell.00029.2015] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Accepted: 03/19/2015] [Indexed: 11/22/2022]
Abstract
Myoblast fusion is critical for proper muscle growth and regeneration. During myoblast fusion, the localization of some molecules is spatially restricted; however, the exact reason for such localization is unknown. Creatine kinase B (CKB), which replenishes local ATP pools, localizes near the ends of cultured primary mouse myotubes. To gain insights into the function of CKB, we performed a yeast two-hybrid screen to identify CKB-interacting proteins. We identified molecules with a broad diversity of roles, including actin polymerization, intracellular protein trafficking, and alternative splicing, as well as sarcomeric components. In-depth studies of α-skeletal actin and α-cardiac actin, two predominant muscle actin isoforms, demonstrated their biochemical interaction and partial colocalization with CKB near the ends of myotubes in vitro. In contrast to other cell types, specific knockdown of CKB did not grossly affect actin polymerization in myotubes, suggesting other muscle-specific roles for CKB. Interestingly, knockdown of CKB resulted in significantly increased myoblast fusion and myotube size in vitro, whereas knockdown of creatine kinase M had no effect on these myogenic parameters. Our results suggest that localized CKB plays a key role in myotube formation by limiting myoblast fusion during myogenesis.
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Affiliation(s)
- Adriana Simionescu-Bankston
- Graduate Program in Biochemistry, Cell and Developmental Biology, Emory University School of Medicine, Atlanta, Georgia; Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - Christophe Pichavant
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - James P Canner
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - Luciano H Apponi
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - Yanru Wang
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - Craig Steeds
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
| | - John T Olthoff
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - Joseph J Belanto
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - James M Ervasti
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, Minnesota
| | - Grace K Pavlath
- Department of Pharmacology, Emory University School of Medicine, Atlanta, Georgia; and
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8
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Edge C, Gooding C, Smith CWJ. Dissecting domains necessary for activation and repression of splicing by Muscleblind-like protein 1. BMC Mol Biol 2013; 14:29. [PMID: 24373687 PMCID: PMC3880588 DOI: 10.1186/1471-2199-14-29] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2013] [Accepted: 12/16/2013] [Indexed: 01/06/2023] Open
Abstract
Background Alternative splicing contributes to the diversity of the proteome, and provides the cell with an important additional layer of regulation of gene expression. Among the many RNA binding proteins that regulate alternative splicing pathways are the Muscleblind-like (MBNL) proteins. MBNL proteins bind YGCY motifs in RNA via four CCCH zinc fingers arranged in two tandem arrays, and play a crucial role in the transition from embryonic to adult muscle splicing patterns, deregulation of which leads to Myotonic Dystrophy. Like many other RNA binding proteins, MBNL proteins can act as both activators or repressors of different splicing events. Results We used targeted point mutations to interfere with the RNA binding of MBNL1 zinc fingers individually and in combination. The effects of the mutations were tested in assays for splicing repression and activation, including overexpression, complementation of siRNA-mediated knockdown, and artificial tethering using MS2 coat protein. Mutations were tested in the context of both full length MBNL1 as well as a series of truncation mutants. Individual mutations within full length MBNL1 had little effect, but mutations in ZF1 and 2 combined were more detrimental than those in ZF 3 and 4, upon splicing activation, repression and RNA binding. Activation and repression both required linker sequences between ZF2 and 3, but activation was more sensitive to loss of linker sequences. Conclusions Our results highlight the importance of RNA binding by MBNL ZF domains 1 and 2 for splicing regulatory activity, even when the protein is artificially recruited to its regulatory location on target RNAs. However, RNA binding is not sufficient for activity; additional regions between ZF 2 and 3 are also essential. Activation and repression show differential sensitivity to truncation of this linker region, suggesting interactions with different sets of cofactors for the two types of activity.
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Affiliation(s)
| | | | - Christopher W J Smith
- Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge CB2 1QW, UK.
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9
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Andres SF, Simmons JG, Mah AT, Santoro MA, Van Landeghem L, Lund PK. Insulin receptor isoform switching in intestinal stem cells, progenitors, differentiated lineages and tumors: evidence that IR-B limits proliferation. J Cell Sci 2013; 126:5645-56. [PMID: 24127567 DOI: 10.1242/jcs.132985] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
Despite evidence for the impact of insulin on intestinal epithelial physiology and pathophysiology, the expression patterns, roles, and regulation of insulin receptor (IR) and IR isoforms in the intestinal epithelium are not well characterized. IR-A is thought to mediate the proliferative effects of insulin or insulin growth factors (IGFs) in fetal or cancer cells. IR-B is considered to be the metabolic receptor for insulin in specialized tissues. This study used a novel Sox9-EGFP reporter mouse that permits isolation of intestinal epithelial stem cells (IESCs), progenitors, enteroendocrine cells and differentiated lineages, the Apc(Min/+) mouse model of precancerous adenoma and normal human intestinal and colorectal cancer (CRC) cell lines. We tested the hypothesis that there is differential expression of IR-A or IR-B in stem and tumor cells versus differentiated intestinal epithelial cells (IECs) and that IR-B impacts cell proliferation. Our findings provide evidence that IR-B expression is significantly lower in highly proliferative IESCs and progenitor cells versus post-mitotic, differentiated IECs and in subconfluent and undifferentiated versus differentiated Caco-2 cells. IR-B is also reduced in Apc(Min/+) tumors and highly tumorigenic CRC cells. These differences in IR-B were accompanied by altered levels of mRNAs encoding muscleblind-like 2 (MBNL2), a known regulator of IR alternative splicing. Forced IR-B expression in subconfluent and undifferentiated Caco-2 cells reduced proliferation and increased biomarkers of differentiation. Our findings indicate that the impact of insulin on different cell types in the intestinal epithelium might differ depending on relative IR-B IR-A expression levels and provide new evidence for the roles of IR-B to limit proliferation of CRC cells.
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Affiliation(s)
- Sarah F Andres
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA
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10
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Gooding C, Edge C, Lorenz M, Coelho MB, Winters M, Kaminski CF, Cherny D, Eperon IC, Smith CWJ. MBNL1 and PTB cooperate to repress splicing of Tpm1 exon 3. Nucleic Acids Res 2013; 41:4765-82. [PMID: 23511971 PMCID: PMC3643581 DOI: 10.1093/nar/gkt168] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Exon 3 of the rat α-tropomyosin (Tpm1) gene is repressed in smooth muscle cells, allowing inclusion of the mutually exclusive partner exon 2. Two key types of elements affect repression of exon 3 splicing: binding sites for polypyrimidine tract-binding protein (PTB) and additional negative regulatory elements consisting of clusters of UGC or CUG motifs. Here, we show that the UGC clusters are bound by muscleblind-like proteins (MBNL), which act as repressors of Tpm1 exon 3. We show that the N-terminal region of MBNL1, containing its four CCCH zinc-finger domains, is sufficient to mediate repression. The same region of MBNL1 can make a direct protein-to-protein interaction with PTB, and RNA binding by MBNL promotes this interaction, apparently by inducing a conformational change in MBNL. Moreover, single molecule analysis showed that MBNL-binding sites increase the binding of PTB to its own sites. Our data suggest that the smooth muscle splicing of Tpm1 is mediated by allosteric assembly of an RNA–protein complex minimally comprising PTB, MBNL and their cognate RNA-binding sites.
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Affiliation(s)
- Clare Gooding
- Department of Biochemistry, University of Cambridge, CB2 1QW, UK
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Deng H, Liu H, Li X, Xiao J, Wang S. A CCCH-type zinc finger nucleic acid-binding protein quantitatively confers resistance against rice bacterial blight disease. PLANT PHYSIOLOGY 2012; 158:876-89. [PMID: 22158700 PMCID: PMC3271775 DOI: 10.1104/pp.111.191379] [Citation(s) in RCA: 89] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/12/2023]
Abstract
Bacterial blight is a devastating disease of rice (Oryza sativa) caused by Xanthomonas oryzae pv oryzae (Xoo). Zinc finger proteins harboring the motif with three conserved cysteine residues and one histidine residue (CCCH) belong to a large family. Although at least 67 CCCH-type zinc finger protein genes have been identified in the rice genome, their functions are poorly understood. Here, we report that one of the rice CCCH-type zinc finger proteins, C3H12, containing five typical CX(8)-CX(5)-CX(3)-H zinc finger motifs, is involved in the rice-Xoo interaction. Activation of C3H12 partially enhanced resistance to Xoo, accompanied by the accumulation of jasmonic acid (JA) and induced expression of JA signaling genes in rice. In contrast, knockout or suppression of C3H12 resulted in partially increased susceptibility to Xoo, accompanied by decreased levels of JA and expression of JA signaling genes in rice. C3H12 colocalized with a minor disease resistance quantitative trait locus to Xoo, and the enhanced resistance of randomly chosen plants in the quantitative trait locus mapping population correlated with an increased expression level of C3H12. The C3H12 protein localized in the nucleus and possessed nucleic acid-binding activity in vitro. These results suggest that C3H12, as a nucleic acid-binding protein, positively and quantitatively regulates rice resistance to Xoo and that its function is likely associated with the JA-dependent pathway.
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Cass D, Hotchko R, Barber P, Jones K, Gates DP, Berglund JA. The four Zn fingers of MBNL1 provide a flexible platform for recognition of its RNA binding elements. BMC Mol Biol 2011; 12:20. [PMID: 21548961 PMCID: PMC3103431 DOI: 10.1186/1471-2199-12-20] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Accepted: 05/06/2011] [Indexed: 01/01/2023] Open
Abstract
Background Muscleblind-like 1 (MBNL1) is an alternative splicing factor containing four CCCH Zinc fingers (ZnFs). The sequestration of MBNL1 by expanded CUG and CCUG repeats is a major component in causing myotonic dystrophy. In addition to binding the structured expanded CUG and CCUG repeats; previous results suggested that MBNL1 binds single-stranded RNAs containing GC dinucleotides. Results We performed a systematic analysis of MBNL1 binding to single-stranded RNAs. These studies revealed that a single GC dinucleotide in poly-uridine is sufficient for MBNL1 binding and that a second GC dinucleotide confers higher affinity MBNL1 binding. However additional GC dinucleotides do not enhance RNA binding. We also showed that the RNA sequences adjacent to the GC dinucleotides play an important role in MBNL1 binding with the following preference: uridines >cytidines >adenosines >guanosines. For high affinity binding by MBNL1, the distance between the two GC dinucleotides can vary from 1 to 17 nucleotides. Conclusions These results suggest that MBNL1 is highly flexible and able to adopt different conformations to recognize RNAs with varying sequence configurations. Although MBNL1 contains four ZnFs, only two ZnF - GC dinucleotide interactions are necessary for high affinity binding.
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Affiliation(s)
- Danielle Cass
- Department of Chemistry, Reed College, Portland, OR 97202, USA
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Grammatikakis I, Goo YH, Echeverria GV, Cooper TA. Identification of MBNL1 and MBNL3 domains required for splicing activation and repression. Nucleic Acids Res 2010; 39:2769-80. [PMID: 21109529 PMCID: PMC3074124 DOI: 10.1093/nar/gkq1155] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Muscleblind-like 1 (MBNL1) is a splicing regulator that controls developmentally regulated alternative splicing of a large number of exons including exon 11 of the Insulin Receptor (IR) gene and exon 5 of the cardiac Troponin T (cTNT) gene. There are three paralogs of MBNL in humans, all of which promote IR exon 11 inclusion and cTNT exon 5 skipping. Here, we identify a cluster of three binding sequences located downstream of IR exon 11 that constitute the MBNL1 response element and a weaker response element in the upstream intron. In addition, we used sequential deletions to define the functional domains of MBNL1 and MBNL3. We demonstrate that the regions required for splicing regulation are separate from the two pairs of zinc-finger RNA-binding domains. MBNL1 and MBNL3 contain core regulatory regions for both activation and repression located within an 80-amino-acid segment located downstream of the N-terminal zinc-finger pair. Deletions of these regions abolished regulation without preventing RNA binding. These domains have common features with the CUG-BP and ETR3-like Factor (CELF) family of splicing regulators. These results have identified protein domains required for splicing repression and activation and provide insight into the mechanism of splicing regulation by MBNL proteins.
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Affiliation(s)
- Ioannis Grammatikakis
- Department of Pathology and Immunology, Baylor College of Medicine, Houston, TX 77030, USA
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Lee KS, Cao Y, Witwicka HE, Tom S, Tapscott SJ, Wang EH. RNA-binding protein Muscleblind-like 3 (MBNL3) disrupts myocyte enhancer factor 2 (Mef2) {beta}-exon splicing. J Biol Chem 2010; 285:33779-87. [PMID: 20709755 DOI: 10.1074/jbc.m110.124255] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Mammalian MBNL (muscleblind-like) proteins are regulators of alternative splicing and have been implicated in myotonic dystrophy, the most common form of adult onset muscular dystrophy. MBNL3 functions as an inhibitor of muscle differentiation and is expressed in proliferating muscle precursor cells but not in differentiated skeletal muscle. Here we demonstrate that MBNL3 regulates the splicing pattern of the muscle transcription factor myocyte enhancer factor 2 (Mef2) by promoting exclusion of the alternatively spliced β-exon. Expression of the transcriptionally more active (+)β isoform of Mef2D was sufficient to overcome the inhibitory effects of MBNL3 on muscle differentiation. These data suggest that MBNL3 antagonizes muscle differentiation by disrupting Mef2 β-exon splicing. MBNL3 regulates Mef2D splicing by directly binding to intron 7 downstream of the alternatively spliced exon in the pre-mRNA. The RNA binding activity of MBNL3 requires the CX(7)CX(4-6)CX(3)H zinc finger domains. Using a cell culture model of myotonic dystrophy and myotonic dystrophy patient tissue, we have evidence that expression of CUG expanded RNAs can lead to an increase in MBNL3 expression and a decrease in Mef2D β-exon splicing. These studies suggest that elevating MBNL3 activity in myogenic cells could lead to muscle degeneration disorders such as myotonic dystrophy.
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Affiliation(s)
- Kyung-Soon Lee
- Department of Pharmacology, University of Washington, Seattle, Washington 98195-2780, USA
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Du H, Cline MS, Osborne RJ, Tuttle DL, Clark TA, Donohue JP, Hall MP, Shiue L, Swanson MS, Thornton CA, Ares M. Aberrant alternative splicing and extracellular matrix gene expression in mouse models of myotonic dystrophy. Nat Struct Mol Biol 2010; 17:187-93. [PMID: 20098426 DOI: 10.1038/nsmb.1720] [Citation(s) in RCA: 250] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2009] [Accepted: 10/14/2009] [Indexed: 01/08/2023]
Abstract
The common form of myotonic dystrophy (DM1) is associated with the expression of expanded CTG DNA repeats as RNA (CUG(exp) RNA). To test whether CUG(exp) RNA creates a global splicing defect, we compared the skeletal muscle of two mouse models of DM1, one expressing a CTG(exp) transgene and another homozygous for a defective muscleblind 1 (Mbnl1) gene. Strong correlation in splicing changes for approximately 100 new Mbnl1-regulated exons indicates that loss of Mbnl1 explains >80% of the splicing pathology due to CUG(exp) RNA. In contrast, only about half of mRNA-level changes can be attributed to loss of Mbnl1, indicating that CUG(exp) RNA has Mbnl1-independent effects, particularly on mRNAs for extracellular matrix proteins. We propose that CUG(exp) RNA causes two separate effects: loss of Mbnl1 function (disrupting splicing) and loss of another function that disrupts extracellular matrix mRNA regulation, possibly mediated by Mbnl2. These findings reveal unanticipated similarities between DM1 and other muscular dystrophies.
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Affiliation(s)
- Hongqing Du
- RNA Center, Department of Molecular, Cell and Developmental Biology, Sinsheimer Labs, University of California, Santa Cruz, California, USA
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Mercante J, Edwards AN, Dubey AK, Babitzke P, Romeo T. Molecular geometry of CsrA (RsmA) binding to RNA and its implications for regulated expression. J Mol Biol 2009; 392:511-28. [PMID: 19619561 DOI: 10.1016/j.jmb.2009.07.034] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/22/2009] [Revised: 07/10/2009] [Accepted: 07/13/2009] [Indexed: 12/12/2022]
Abstract
The global regulatory protein CsrA binds to the 5'-untranslated leader of target transcripts and alters their translation and/or stability. CsrA is a symmetrical homodimer containing two identical RNA-binding surfaces. Gel shift assays with model RNA substrates now show that CsrA can bind simultaneously at two target sites within a transcript (bridging or dual-site binding). An intersite distance of approximately 18 nucleotides (nt) was optimal, although bridging occurred with an intersite distance of 10 to >or=63 nt. The close 10-nt spacing reduced the stability of dual-site binding, as competition for one site by a second CsrA dimer readily occurred. Both RNA-binding surfaces of a single CsrA protein were essential for efficient in vitro repression of a glgC'-'lacZ translational fusion that contains four CsrA target sites within the untranslated leader. Heterodimeric CsrA (HD-CsrA) containing a single R44A replacement, which was defective for binding at its mutant surface but bound RNA normally at its wild-type (WT) surface, was approximately 14-fold less effective at repression than homodimeric WT-CsrA. Furthermore, deletion of a CsrA target site of glgC that lies upstream from the Shine-Dalgarno sequence did not affect regulation by HD-CsrA but decreased regulation by WT-CsrA, confirming a regulatory role of dual-site binding. Finally, we propose a mechanism whereby a globular ribonucleoprotein complex is formed between CsrA and its noncoding RNA antagonist, CsrB. Because many target sites of CsrB are located closer together than is optimal for bridging, binding to nonadjacent sites should be energetically favored, causing multiple CsrA dimers to tether CsrB into the observed globular form rather than an extended CsrA-CsrB complex.
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Affiliation(s)
- Jeffrey Mercante
- Department of Microbiology and Immunology, Emory University School of Medicine, Atlanta, GA 30322, USA
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Kim JS, Coon SL, Weller JL, Blackshaw S, Rath MF, Møller M, Klein DC. Muscleblind-like 2: circadian expression in the mammalian pineal gland is controlled by an adrenergic-cAMP mechanism. J Neurochem 2009; 110:756-64. [PMID: 19457059 DOI: 10.1111/j.1471-4159.2009.06184.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
Muscleblind-like 2 (Mbnl2) is a zinc finger protein first identified in Drosophila. It appears to be essential for photoreceptor development and to be involved in RNA splicing. Here we report that Mbnl2 is strongly expressed in the rat pineal gland. The abundance of pineal Mbnl2 transcripts follows a marked circadian rhythm with peak levels approximately sevenfold higher at night than day levels. Mbnl2 protein exhibits a similar rhythm. In vitro studies indicate that the abundance of Mbnl2 transcripts and protein are controlled by an adrenergic/cAMP mechanism.
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Affiliation(s)
- Jong-So Kim
- Program on Developmental Endocrinology and Genetics, Section on Neuroendocrinology, The Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, Maryland, USA
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