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Huang X, Huang Y, Qin L, Xiao Q, Wang Q, Wang J, Wang W, Lu X, Wu Y. Maize DDK1 encoding an Importin-4 β protein is essential for seed development and grain filling by mediating nuclear exporting of eIF1A. THE NEW PHYTOLOGIST 2024; 241:2075-2089. [PMID: 38095260 DOI: 10.1111/nph.19475] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/01/2023] [Accepted: 11/27/2023] [Indexed: 02/09/2024]
Abstract
Nuclear-cytoplasmic trafficking is crucial for protein synthesis in eukaryotic cells due to the spatial separation of transcription and translation by the nuclear envelope. However, the mechanism underlying this process remains largely unknown in plants. In this study, we isolated a maize (Zea mays) mutant designated developmentally delayed kernel 1 (ddk1), which exhibits delayed seed development and slower filling. Ddk1 encodes a plant-specific protein known as Importin-4 β, and its mutation results in reduced 80S monosomes and suppressed protein synthesis. Through our investigations, we found that DDK1 interacts with eIF1A proteins in vivo. However, in vitro experiments revealed that this interaction exhibits low affinity in the absence of RanGTP. Additionally, while the eIF1A protein primarily localizes to the cytoplasm in the wild-type, it remains significantly retained within the nuclei of ddk1 mutants. These observations suggest that DDK1 functions as an exportin and collaborates with RanGTP to facilitate the nuclear export of eIF1A, consequently regulating endosperm development at the translational level. Importantly, both DDK1 and eIF1A are conserved among various plant species, implying the preservation of this regulatory module across diverse plants.
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Affiliation(s)
- Xing Huang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
- University of the Chinese Academy of Sciences, Beijing, 100049, China
| | - Yongcai Huang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
| | - Li Qin
- Institute of Molecular Breeding for Maize, Qilu Normal University, Jinan, 250200, China
| | - Qiao Xiao
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
- University of the Chinese Academy of Sciences, Beijing, 100049, China
| | - Qiong Wang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
| | - Jiechen Wang
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
| | - Wenqin Wang
- College of Life Science, Shanghai Normal University, 100 Guilin Road, Shanghai, 200233, China
| | - Xiaoduo Lu
- Institute of Molecular Breeding for Maize, Qilu Normal University, Jinan, 250200, China
| | - Yongrui Wu
- National Key Laboratory of Plant Molecular Genetics, CAS Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology & Ecology, Chinese Academy of Sciences, Shanghai, 200032, China
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2
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Bin JM, Suminaite D, Benito-Kwiecinski SK, Kegel L, Rubio-Brotons M, Early JJ, Soong D, Livesey MR, Poole RJ, Lyons DA. Importin 13-dependent axon diameter growth regulates conduction speeds along myelinated CNS axons. Nat Commun 2024; 15:1790. [PMID: 38413580 PMCID: PMC10899189 DOI: 10.1038/s41467-024-45908-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2023] [Accepted: 02/06/2024] [Indexed: 02/29/2024] Open
Abstract
Axon diameter influences the conduction properties of myelinated axons, both directly, and indirectly through effects on myelin. However, we have limited understanding of mechanisms controlling axon diameter growth in the central nervous system, preventing systematic dissection of how manipulating diameter affects myelination and conduction along individual axons. Here we establish zebrafish to study axon diameter. We find that importin 13b is required for axon diameter growth, but does not affect cell body size or axon length. Using neuron-specific ipo13b mutants, we assess how reduced axon diameter affects myelination and conduction, and find no changes to myelin thickness, precision of action potential propagation, or ability to sustain high frequency firing. However, increases in conduction speed that occur along single myelinated axons with development are tightly linked to their growth in diameter. This suggests that axon diameter growth is a major driver of increases in conduction speeds along myelinated axons over time.
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Affiliation(s)
- Jenea M Bin
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK.
| | - Daumante Suminaite
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | | | - Linde Kegel
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Maria Rubio-Brotons
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Jason J Early
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Daniel Soong
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
| | - Matthew R Livesey
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK
- Sheffield Institute for Translational Neuroscience, University of Sheffield, Sheffield, S10 2HQ, UK
- Neuroscience Institute, University of Sheffield, Sheffield, S10 2TN, UK
| | - Richard J Poole
- Department of Cell and Developmental Biology, University College London, London, WC1E 6BT, UK
| | - David A Lyons
- Centre for Discovery Brain Sciences, University of Edinburgh, Edinburgh, EH16 4SB, UK.
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3
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Shaffer JM, Jiou J, Tripathi K, Olaluwoye OS, Fung HYJ, Chook YM, D'Arcy S. Molecular basis of RanGTP-activated release of Histones H2A-H2B from Importin-9. Structure 2023; 31:903-911.e3. [PMID: 37379840 PMCID: PMC10527638 DOI: 10.1016/j.str.2023.06.001] [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: 04/06/2023] [Revised: 05/22/2023] [Accepted: 06/02/2023] [Indexed: 06/30/2023]
Abstract
Imp9 is the primary importin for shuttling H2A-H2B from the cytoplasm to the nucleus. It employs an unusual mechanism where the binding of RanGTP is insufficient to release H2A-H2B. The resulting stable RanGTP·Imp9·H2A-H2B complex gains nucleosome assembly activity with H2A-H2B able to be deposited into an assembling nucleosome in vitro. Using hydrogen-deuterium exchange coupled with mass spectrometry (HDX), we show that Imp9 stabilizes H2A-H2B beyond the direct-binding site, like other histone chaperones. HDX also shows that binding of RanGTP releases H2A-H2B contacts at Imp9 HEAT repeats 4-5, but not 18-19. DNA- and histone-binding surfaces of H2A-H2B are exposed in the ternary complex, facilitating nucleosome assembly. We also reveal that RanGTP has a weaker affinity for Imp9 when H2A-H2B is bound. Imp9 thus provides a connection between the nuclear import of H2A-H2B and its deposition into chromatin.
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Affiliation(s)
- Joy M Shaffer
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson 75080, USA
| | - Jenny Jiou
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75390, USA
| | - Kiran Tripathi
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson 75080, USA
| | - Oladimeji S Olaluwoye
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson 75080, USA
| | - Ho Yee Joyce Fung
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75390, USA
| | - Yuh Min Chook
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas 75390, USA
| | - Sheena D'Arcy
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson 75080, USA.
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4
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Shaffer JM, Jiou J, Tripathi K, Olaluwoye OS, Fung HYJ, Chook YM, D’Arcy S. Molecular basis of RanGTP-activated nucleosome assembly with Histones H2A-H2B bound to Importin-9. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.01.27.525896. [PMID: 36747879 PMCID: PMC9901172 DOI: 10.1101/2023.01.27.525896] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
Padavannil et al. 2019 show that Importin-9 (Imp9) transports Histones H2A-H2B from the cytoplasm to the nucleus using a non-canonical mechanism whereby binding of a GTP-bound Ran GTPase (RanGTP) fails to evict the H2A-H2B cargo. Instead, a stable complex forms, comprised of equimolar RanGTP, Imp9, and H2A-H2B. Unlike the binary Imp9•H2A-H2B complex, this RanGTP•Imp9•H2A-H2B ternary complex can release H2A-H2B to an assembling nucleosome. Here, we define the molecular basis for this RanGTP-activated nucleosome assembly by Imp9. We use hydrogen-deuterium exchange coupled with mass spectrometry and compare the dynamics and interfaces of the RanGTP•Imp9•H2A-H2B ternary complex to those in the Imp9•H2A-H2B or Imp9•RanGTP binary complexes. Our data are consistent with the Imp9•H2A-H2B structure by Padavannil et al. 2019 showing that Imp9 HEAT repeats 4-5 and 18-19 contact H2A-H2B, as well as many homologous importin•RanGTP structures showing that importin HEAT repeats 1 and 3, and the h8 loop, contact RanGTP. We show that Imp9 stabilizes H2A-H2B beyond the direct binding site, similar to other histone chaperones. Importantly, we reveal that binding of RanGTP releases H2A-H2B interaction at Imp9 HEAT repeats 4-5, but not 18-19. This exposes DNA- and histone-binding surfaces of H2A-H2B, thereby facilitating nucleosome assembly. We also reveal that RanGTP has a weaker affinity for Imp9 when H2A-H2B is bound. This may ensure that H2A-H2B is only released in high RanGTP concentrations near chromatin. We delineate the molecular link between the nuclear import of H2A-H2B and its deposition into chromatin by Imp9. Significance Imp9 is the primary importin for shuttling H2A-H2B from the cytoplasm to the nucleus. It employs an unusual mechanism where the binding of RanGTP alone is insufficient to release H2A-H2B. The resulting stable RanGTP•Imp9•H2A-H2B complex gains nucleosome assembly activity as H2A-H2B can be deposited onto an assembling nucleosome. We show that H2A-H2B is allosterically stabilized via interactions with both N- and C-terminal portions of Imp9, reinforcing its chaperone-like behavior. RanGTP binding causes H2A-H2B release from the N-terminal portion of Imp9 only. The newly-exposed H2A-H2B surfaces can interact with DNA or H3-H4 in nucleosome assembly. Imp9 thus plays a multi-faceted role in histone import, storage, and deposition regulated by RanGTP, controlling histone supply in the nucleus and to chromatin.
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Affiliation(s)
- Joy M. Shaffer
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, United States, 75080
| | - Jenny Jiou
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States, 75390
| | - Kiran Tripathi
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, United States, 75080
| | - Oladimeji S. Olaluwoye
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, United States, 75080
| | - Ho Yee Joyce Fung
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States, 75390
| | - Yuh Min Chook
- Department of Pharmacology, University of Texas Southwestern Medical Center, Dallas, United States, 75390
| | - Sheena D’Arcy
- Department of Chemistry and Biochemistry, The University of Texas at Dallas, Richardson, United States, 75080
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5
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V M DD, Sivaramakrishnan V, Arvind Kumar K. Structural systems biology approach delineate the functional implications of SNPs in exon junction complex interaction network. J Biomol Struct Dyn 2023; 41:11969-11986. [PMID: 36617892 DOI: 10.1080/07391102.2022.2164355] [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: 02/03/2022] [Accepted: 12/26/2022] [Indexed: 01/10/2023]
Abstract
In eukaryotes, transcripts that carry premature termination codons (PTC) leading to truncated proteins are degraded by the Nonsense Mediated Decay (NMD) machinery. Missense and nonsense Single Nucleotide Polymorphisms (SNPs) in proteins belonging to Exon junction complex (EJC) and up-frameshift protein (UPF) will compromise NMD leading to the accumulation of truncated proteins in various diseases. The EJC and UPF which are involved in NMD is a good model system to study the effect of SNPs at a system level. Despite the availability of crystal structures, computational tools, and data on mutational and deletion studies, with functional implications, an integrated effort to understand the impact of SNPs at the systems level is lacking. To study the functional consequences of missense SNPs, sequence-based techniques like SIFT and PolyPhen which classify SNPs as deleterious or non-deleterious and structure-based methods like FoldX which calculate the Delta Delta G, (ddGs, ∆∆G) are used. Using FoldX, the ddG for mutations with experimentally validated functional effects is calculated and compared with those calculated for SNPs in the same protein-protein interaction interface. Further, a model is conceived to explain the functional implications of SNPs based on the effects observed for known mutants. The results are visualized in a network format. The effects of nonsense mutations are discerned by comparing with deletion mutation studies and loss of interaction in the crystal structure. The present work not only integrates genomics, proteomics, and classical genetics with 'Structural Biology' but also helps to integrate it into a 'systems-level functional network'.Communicated by Ramaswamy H. Sarma.
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Affiliation(s)
- Datta Darshan V M
- Disease Biology Lab, Department of Biosciences, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Anantapur, Andhra Pradesh, India
| | - Venketesh Sivaramakrishnan
- Disease Biology Lab, Department of Biosciences, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Anantapur, Andhra Pradesh, India
| | - K Arvind Kumar
- Disease Biology Lab, Department of Biosciences, Sri Sathya Sai Institute of Higher Learning, Prasanthi Nilayam, Anantapur, Andhra Pradesh, India
- Department of Physiology and Biophysics, School of Medicine, Case Western Reserve University, Cleveland, OH, USA
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6
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Martin H, Rupkey J, Asthana S, Yoon J, Patel S, Mott J, Pei Z, Mao Y. Diverse Roles of the Exon Junction Complex Factors in the Cell Cycle, Cancer, and Neurodevelopmental Disorders-Potential for Therapeutic Targeting. Int J Mol Sci 2022; 23:ijms231810375. [PMID: 36142288 PMCID: PMC9499366 DOI: 10.3390/ijms231810375] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Revised: 09/01/2022] [Accepted: 09/05/2022] [Indexed: 12/04/2022] Open
Abstract
The exon junction complex (EJC) plays a crucial role in regulating gene expression at the levels of alternative splicing, translation, mRNA localization, and nonsense-mediated decay (NMD). The EJC is comprised of three core proteins: RNA-binding motif 8A (RBM8A), Mago homolog (MAGOH), eukaryotic initiation factor 4A3 (eIF4A3), and a peripheral EJC factor, metastatic lymph node 51 (MLN51), in addition to other peripheral factors whose structural integration is activity-dependent. The physiological and mechanistic roles of the EJC in contribution to molecular, cellular, and organismal level function continue to be explored for potential insights into genetic or pathological dysfunction. The EJC’s specific role in the cell cycle and its implications in cancer and neurodevelopmental disorders prompt enhanced investigation of the EJC as a potential target for these diseases. In this review, we highlight the current understanding of the EJC’s position in the cell cycle, its relation to cancer and developmental diseases, and potential avenues for therapeutic targeting.
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Affiliation(s)
- Hannah Martin
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Julian Rupkey
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Shravan Asthana
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
- Feinberg School of Medicine, Northwestern University, 303 East Superior Street, Chicago, IL 60611, USA
| | - Joy Yoon
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Shray Patel
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Jennifer Mott
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Zifei Pei
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
| | - Yingwei Mao
- Department of Biology, Pennsylvania State University, University Park, State College, PA 16802, USA
- Correspondence:
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7
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Nsengimana B, Khan FA, Ngowi EE, Zhou X, Jin Y, Jia Y, Wei W, Ji S. Processing body (P-body) and its mediators in cancer. Mol Cell Biochem 2022; 477:1217-1238. [PMID: 35089528 DOI: 10.1007/s11010-022-04359-7] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2021] [Accepted: 01/11/2022] [Indexed: 12/24/2022]
Abstract
In recent years, processing bodies (P-bodies) formed by liquid-liquid phase separation, have attracted growing scientific attention due to their involvement in numerous cellular activities, including the regulation of mRNAs decay or storage. These cytoplasmic dynamic membraneless granules contain mRNA storage and decay components such as deadenylase and decapping factors. In addition, different mRNA metabolic regulators, including m6A readers and gene-mediated miRNA-silencing, are also associated with such P-bodies. Cancerous cells may profit from these mRNA decay shredders by up-regulating the expression level of oncogenes and down-regulating tumor suppressor genes. The main challenges of cancer treatment are drug resistance, metastasis, and cancer relapse likely associated with cancer stem cells, heterogeneity, and plasticity features of different tumors. The mRNA metabolic regulators based on P-bodies play a great role in cancer development and progression. The dysregulation of P-bodies mediators affects mRNA metabolism. However, less is known about the relationship between P-bodies mediators and cancerous behavior. The current review summarizes the recent studies on P-bodies mediators, their contribution to tumor development, and their potential in the clinical setting, particularly highlighting the P-bodies as potential drug-carriers such as exosomes to anticancer in the future.
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Affiliation(s)
- Bernard Nsengimana
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China
| | - Faiz Ali Khan
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China
| | - Ebenezeri Erasto Ngowi
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China
| | - Xuefeng Zhou
- Department of Oncology, Dongtai Affiliated Hospital of Nantong University, Dongtai, 224200, Jiangsu, People's Republic of China
| | - Yu Jin
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China
| | - Yuting Jia
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China
| | - Wenqiang Wei
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China.
| | - Shaoping Ji
- Laboratory of Cell Signal Transduction, Department of Biochemistry and Molecular Biology, School of Basic Medical Sciences, Henan University, Henan, 475004, People's Republic of China.
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8
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Wing CE, Fung HYJ, Chook YM. Karyopherin-mediated nucleocytoplasmic transport. Nat Rev Mol Cell Biol 2022; 23:307-328. [PMID: 35058649 PMCID: PMC10101760 DOI: 10.1038/s41580-021-00446-7] [Citation(s) in RCA: 107] [Impact Index Per Article: 53.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 12/09/2021] [Indexed: 12/25/2022]
Abstract
Efficient and regulated nucleocytoplasmic trafficking of macromolecules to the correct subcellular compartment is critical for proper functions of the eukaryotic cell. The majority of the macromolecular traffic across the nuclear pores is mediated by the Karyopherin-β (or Kap) family of nuclear transport receptors. Work over more than two decades has shed considerable light on how the different Kap family members bring their respective cargoes into the nucleus or the cytoplasm in efficient and highly regulated manners. In this Review, we overview the main features and established functions of Kap family members, describe how Kaps recognize their cargoes and discuss the different ways in which these Kap-cargo interactions can be regulated, highlighting new findings and open questions. We also describe current knowledge of the import and export of the components of three large gene expression machines - the core replisome, RNA polymerase II and the ribosome - pointing out the questions that persist about how such large macromolecular complexes are trafficked to serve their function in a designated subcellular location.
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9
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Nuclear import of histones. Biochem Soc Trans 2021; 48:2753-2767. [PMID: 33300986 PMCID: PMC7752055 DOI: 10.1042/bst20200572] [Citation(s) in RCA: 23] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2020] [Revised: 10/30/2020] [Accepted: 11/13/2020] [Indexed: 12/14/2022]
Abstract
The transport of histones from the cytoplasm to the nucleus of the cell, through the nuclear membrane, is a cellular process that regulates the supply of new histones in the nucleus and is key for DNA replication and transcription. Nuclear import of histones is mediated by proteins of the karyopherin family of nuclear transport receptors. Karyopherins recognize their cargos through linear motifs known as nuclear localization/export sequences or through folded domains in the cargos. Karyopherins interact with nucleoporins, proteins that form the nuclear pore complex, to promote the translocation of their cargos into the nucleus. When binding to histones, karyopherins not only function as nuclear import receptors but also as chaperones, protecting histones from non-specific interactions in the cytoplasm, in the nuclear pore and possibly in the nucleus. Studies have also suggested that karyopherins might participate in histones deposition into nucleosomes. In this review we describe structural and biochemical studies from the last two decades on how karyopherins recognize and transport the core histone proteins H3, H4, H2A and H2B and the linker histone H1 from the cytoplasm to the nucleus, which karyopherin is the major nuclear import receptor for each of these histones, the oligomeric state of histones during nuclear import and the roles of post-translational modifications, histone-chaperones and RanGTP in regulating these nuclear import pathways.
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10
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Kimura M, Imai K, Morinaka Y, Hosono-Sakuma Y, Horton P, Imamoto N. Distinct mutations in importin-β family nucleocytoplasmic transport receptors transportin-SR and importin-13 affect specific cargo binding. Sci Rep 2021; 11:15649. [PMID: 34341383 PMCID: PMC8329185 DOI: 10.1038/s41598-021-94948-1] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2020] [Accepted: 07/20/2021] [Indexed: 01/25/2023] Open
Abstract
Importin-(Imp)β family nucleocytoplasmic transport receptors (NTRs) are supposed to bind to their cargoes through interaction between a confined interface on an NTR and a nuclear localization or export signal (NLS/NES) on a cargo. Although consensus NLS/NES sequence motifs have been defined for cargoes of some NTRs, many experimentally identified cargoes of those NTRs lack those motifs, and consensus NLSs/NESs have been reported for only a few NTRs. Crystal structures of NTR-cargo complexes have exemplified 3D structure-dependent binding of cargoes lacking a consensus NLS/NES to different sites on an NTR. Since only a limited number of NTR-cargo interactions have been studied, whether most cargoes lacking a consensus NLS/NES bind to the same confined interface or to various sites on an NTR is still unclear. Addressing this issue, we generated four mutants of transportin-(Trn)SR, of which many cargoes lack a consensus NLS, and eight mutants of Imp13, where no consensus NLS has been defined, and we analyzed their binding to as many as 40 cargo candidates that we previously identified by a nuclear import reaction-based method. The cargoes bind differently to the NTR mutants, suggesting that positions on an NTR contribute differently to the binding of respective cargoes.
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Affiliation(s)
- Makoto Kimura
- Cellular Dynamics Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama, Japan.
| | - Kenichiro Imai
- Cellular and Molecular Biotechnology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo, Japan.
- Molecular Profiling Research Center for Drug Discovery, National Institute of Advanced Industrial Science and Technology (AIST), Tokyo, Japan.
| | - Yuriko Morinaka
- Cellular Dynamics Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama, Japan
| | - Yoshiko Hosono-Sakuma
- Cellular Dynamics Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama, Japan
| | - Paul Horton
- Department of Computer Science and Information Engineering, National Cheng Kung University, Tainan City, Taiwan
| | - Naoko Imamoto
- Cellular Dynamics Laboratory, RIKEN Cluster for Pioneering Research, Wako, Saitama, Japan.
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11
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Brandi V, Polticelli F. In Silico Analysis of Huntingtin Homologs in Lower Eukaryotes. Int J Mol Sci 2021; 22:3214. [PMID: 33809947 PMCID: PMC8004120 DOI: 10.3390/ijms22063214] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/08/2021] [Revised: 03/09/2021] [Accepted: 03/17/2021] [Indexed: 12/11/2022] Open
Abstract
Huntington's disease is a rare neurodegenerative and autosomal dominant disorder. HD is caused by a mutation in the gene coding for huntingtin (Htt). The result is the production of a mutant Htt with an abnormally long polyglutamine repeat that leads to pathological Htt aggregates. Although the structure of human Htt has been determined, albeit at low resolution, its functions and how they are performed are largely unknown. Moreover, there is little information on the structure and function of Htt in other organisms. The comparison of Htt homologs can help to understand if there is a functional conservation of domains in the evolution of Htt in eukaryotes. In this work, through a computational approach, Htt homologs from lower eukaryotes have been analysed, identifying ordered domains and modelling their structure. Based on the structural models, a putative function for most of the domains has been predicted. A putative C. elegans Htt-like protein has also been analysed following the same approach. The results obtained support the notion that this protein is a orthologue of human Htt.
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Affiliation(s)
| | - Fabio Polticelli
- Department of Sciences, Roma Tre University, 00146 Rome, Italy;
- National Institute of Nuclear Physics, Roma Tre Section, 00146 Rome, Italy
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12
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Paci G, Caria J, Lemke EA. Cargo transport through the nuclear pore complex at a glance. J Cell Sci 2021; 134:237315. [PMID: 33495357 DOI: 10.1242/jcs.247874] [Citation(s) in RCA: 45] [Impact Index Per Article: 15.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Bidirectional transport of macromolecules across the nuclear envelope is a hallmark of eukaryotic cells, in which the genetic material is compartmentalized inside the nucleus. The nuclear pore complex (NPC) is the major gateway to the nucleus and it regulates nucleocytoplasmic transport, which is key to processes including transcriptional regulation and cell cycle control. Accordingly, components of the nuclear transport machinery are often found to be dysregulated or hijacked in diseases. In this Cell Science at a Glance article and accompanying poster, we provide an overview of our current understanding of cargo transport through the NPC, from the basic transport signals and machinery to more emerging aspects, all from a 'cargo perspective'. Among these, we discuss the transport of large cargoes (>15 nm), as well as the roles of different cargo properties to nuclear transport, from size and number of bound nuclear transport receptors (NTRs), to surface and mechanical properties.
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Affiliation(s)
- Giulia Paci
- Biocentre, Johannes Gutenberg-University Mainz, Hans-Dieter-Hüsch-Weg 15, 555128 Mainz, Germany.,Institute of Molecular Biology, Ackermannweg 4, 55128 Mainz, Germany.,European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Joana Caria
- Biocentre, Johannes Gutenberg-University Mainz, Hans-Dieter-Hüsch-Weg 15, 555128 Mainz, Germany.,Institute of Molecular Biology, Ackermannweg 4, 55128 Mainz, Germany.,European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
| | - Edward A Lemke
- Biocentre, Johannes Gutenberg-University Mainz, Hans-Dieter-Hüsch-Weg 15, 555128 Mainz, Germany .,Institute of Molecular Biology, Ackermannweg 4, 55128 Mainz, Germany.,European Molecular Biology Laboratory, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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13
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Hu J, Li P, Shi B, Tie J. Importin β1 mediates nuclear import of the factors associated with nonsense-mediated RNA decay. Biochem Biophys Res Commun 2021; 542:34-39. [PMID: 33486189 DOI: 10.1016/j.bbrc.2021.01.034] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/08/2021] [Accepted: 01/11/2021] [Indexed: 12/15/2022]
Abstract
In eukaryotic cells, nonsense-mediated RNA decay (NMD) is an essential physiological mechanism coupled to translation, regulating the stability of abnormal RNA containing premature termination codon (PTC) and a significant fraction of normal transcriptomes. So far, the molecular regulation mechanism of NMD pathway is far from fully elucidated. Previously, we observed the interaction between importin β1 (Impβ1) and UPF1, a core factor of NMD. Here, we demonstrated that Impβ1 knockdown stabilized NMD reporters, and Impβ1 and UPF1 interacted and co-regulated an extensive number of target transcripts. Furthermore, Impβ1 affected the interaction between UPF1 and SMG5 or MAGOH, and the nuclear distributions of UPF1, SMG1, SMG5 and MAGOH. Besides, Ran knockdown extremely promoted the dissociation of UPF1 from SMG5 or MAGOH. Our findings provide molecular insight into the potential function of Impβ1in nonsense-mediated RNA decay.
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Affiliation(s)
- Jianran Hu
- Department of Biological Science and Technology, Changzhi University, Changzhi, 046011, China.
| | - Ping Li
- Department of Biological Science and Technology, Changzhi University, Changzhi, 046011, China
| | - Baozhong Shi
- Department of Biological Science and Technology, Changzhi University, Changzhi, 046011, China
| | - Jun Tie
- Department of Biological Science and Technology, Changzhi University, Changzhi, 046011, China
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14
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Pechmann S. Programmed Trade-offs in Protein Folding Networks. Structure 2020; 28:1361-1375.e4. [PMID: 33053320 DOI: 10.1016/j.str.2020.09.009] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/05/2020] [Revised: 07/25/2020] [Accepted: 09/23/2020] [Indexed: 12/14/2022]
Abstract
Molecular chaperones as specialized protein quality control enzymes form the core of cellular protein homeostasis. How chaperones selectively interact with their substrate proteins thus allocate their overall limited capacity remains poorly understood. Here, I present an integrated analysis of sequence and structural determinants that define interactions of protein domains as the basic protein folding unit with the Saccharomyces cerevisiae Hsp70 Ssb. Structural homologs of single-domain proteins that differentially interact with Ssb for de novo folding were found to systematically differ in complexity of their folding landscapes, selective use of nonoptimal codons, and presence of short discriminative sequences, thus highlighting pervasive trade-offs in chaperone-assisted protein folding landscapes. However, short discriminative sequences were found to contribute by far the strongest signal toward explaining Ssb interactions. This observation suggested that some chaperone interactions may be directly programmed in the amino acid sequences rather than responding to folding challenges, possibly for regulatory advantages.
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Affiliation(s)
- Sebastian Pechmann
- Département de biochimie, Université de Montréal, 2900 Boulevard Edouard-Montpetit, Montréal, QC H3T 1J4, Canada.
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15
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Differential Behaviours and Preferential Bindings of Influenza Nucleoproteins on Importins-α. Viruses 2020; 12:v12080834. [PMID: 32751671 PMCID: PMC7472415 DOI: 10.3390/v12080834] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2020] [Revised: 07/23/2020] [Accepted: 07/27/2020] [Indexed: 12/20/2022] Open
Abstract
Influenza viruses are negative single-stranded RNA viruses with nuclear transcription and replication. They enter the nucleus by using the cellular importin-α/-β nuclear import machinery. Influenza nucleoproteins from influenza A, B, C and D viruses possess a nuclear localization signal (NLS) localized on an intrinsically disordered extremity (NPTAIL). In this paper, using size exclusion chromatography (SEC), SEC-multi-angle laser light scattering (SEC-MALLS) analysis, surface plasmon resonance (SPR) and fluorescence anisotropy, we provide the first comparative study designed to dissect the interaction between the four NPTAILs and four importins-α identified as partners. All interactions between NPTAILs and importins-α have high association and dissociation rates and present a distinct and specific behaviour. D/NPTAIL interacts strongly with all importins-α while B/NPTAIL shows weak affinity for importins-α. A/NPTAIL and C/NPTAIL present preferential importin-α partners. Mutations in B/NPTAIL and D/NPTAIL show a loss of importin-α binding, confirming key NLS residues. Taken together, our results provide essential highlights of this complex translocation mechanism.
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16
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A Day in the Life of the Exon Junction Complex. Biomolecules 2020; 10:biom10060866. [PMID: 32517083 PMCID: PMC7355637 DOI: 10.3390/biom10060866] [Citation(s) in RCA: 49] [Impact Index Per Article: 12.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2020] [Revised: 05/29/2020] [Accepted: 06/02/2020] [Indexed: 12/12/2022] Open
Abstract
The exon junction complex (EJC) is an abundant messenger ribonucleoprotein (mRNP) component that is assembled during splicing and binds to mRNAs upstream of exon-exon junctions. EJCs accompany the mRNA during its entire life in the nucleus and the cytoplasm and communicate the information about the splicing process and the position of introns. Specifically, the EJC’s core components and its associated proteins regulate different steps of gene expression, including pre-mRNA splicing, mRNA export, translation, and nonsense-mediated mRNA decay (NMD). This review summarizes the most important functions and main protagonists in the life of the EJC. It also provides an overview of the latest findings on the assembly, composition and molecular activities of the EJC and presents them in the chronological order, in which they play a role in the EJC’s life cycle.
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17
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Swale C, Da Costa B, Sedano L, Garzoni F, McCarthy AA, Berger I, Bieniossek C, Ruigrok RWH, Delmas B, Crépin T. X-ray Structure of the Human Karyopherin RanBP5, an Essential Factor for Influenza Polymerase Nuclear Trafficking. J Mol Biol 2020; 432:3353-3359. [PMID: 32222384 DOI: 10.1016/j.jmb.2020.03.021] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2020] [Revised: 03/16/2020] [Accepted: 03/22/2020] [Indexed: 12/15/2022]
Abstract
Here, we describe the crystal structures of two distinct isoforms of ligand-free human karyopherin RanBP5 and investigate its global propensity to interact with influenza A virus polymerase. Our results confirm the general architecture and mechanism of the IMB3 karyopherin-β subfamily whilst also highlighting differences with the yeast orthologue Kap121p. Moreover, our results provide insight into the structural flexibility of β-importins in the unbound state. Based on docking of a nuclear localisation sequence, point mutations were designed, which suppress influenza PA-PB1 subcomplex binding to RanBP5 in a binary protein complementation assay.
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Affiliation(s)
- Christopher Swale
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38044 Grenoble, France; EMBL Grenoble Outstation, 71 Avenue des Martyrs, BP181, F-38042 Grenoble Cedex 9, France
| | - Bruno Da Costa
- Virologie et Immunologie Moléculaires, INRA, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Laura Sedano
- Virologie et Immunologie Moléculaires, INRA, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Frédéric Garzoni
- EMBL Grenoble Outstation, 71 Avenue des Martyrs, BP181, F-38042 Grenoble Cedex 9, France
| | - Andrew A McCarthy
- EMBL Grenoble Outstation, 71 Avenue des Martyrs, BP181, F-38042 Grenoble Cedex 9, France
| | - Imre Berger
- EMBL Grenoble Outstation, 71 Avenue des Martyrs, BP181, F-38042 Grenoble Cedex 9, France; Max Planck Centre for Minimal Biology, University of Bristol, Clifton BS8 1TD, United Kingdom
| | - Christoph Bieniossek
- Roche Innovation Centre, Basel, Switzerland F. Hoffmann-La Roche AG, Grenzacherstrasse 124, CH-4070 Basel, Switzerland
| | - Rob W H Ruigrok
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38044 Grenoble, France
| | - Bernard Delmas
- Virologie et Immunologie Moléculaires, INRA, Université Paris-Saclay, 78350 Jouy-en-Josas, France
| | - Thibaut Crépin
- Institut de Biologie Structurale (IBS), University Grenoble Alpes, CEA, CNRS, 38044 Grenoble, France.
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18
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Aksu M, Trakhanov S, Vera Rodriguez A, Görlich D. Structural basis for the nuclear import and export functions of the biportin Pdr6/Kap122. J Cell Biol 2019; 218:1839-1852. [PMID: 31023722 PMCID: PMC6548137 DOI: 10.1083/jcb.201812093] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2018] [Revised: 03/26/2019] [Accepted: 03/28/2019] [Indexed: 12/26/2022] Open
Abstract
Importins ferry proteins into nuclei while exportins carry cargoes to the cytoplasm. In the accompanying paper in this issue (Vera Rodriguez et al. 2019. J. Cell Biol. https://doi.org/10.1083/jcb.201812091), we discovered that Pdr6 is a biportin that imports, e.g., the SUMO E2 ligase Ubc9 while depleting the translation factor eIF5A from the nuclear compartment. In this paper, we report the structures of key transport intermediates, namely, of the Ubc9•Pdr6 import complex, of the RanGTP•Pdr6 heterodimer, and of the trimeric RanGTP•Pdr6•eIF5A export complex. These revealed nonlinear transport signals, chaperone-like interactions, and how the RanGTPase system drives Pdr6 to transport Ubc9 and eIF5A in opposite directions. The structures also provide unexpected insights into the evolution of transport selectivity. Specifically, they show that recognition of Ubc9 by Pdr6 differs fundamentally from that of the human Ubc9-importer Importin 13. Likewise, Pdr6 recognizes eIF5A in a nonhomologous manner compared with the mammalian eIF5A-exporter Exportin 4. This suggests that the import of Ubc9 and active nuclear exclusion of eIF5A evolved in different eukaryotic lineages more than once and independently from each other.
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Affiliation(s)
- Metin Aksu
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Sergei Trakhanov
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Arturo Vera Rodriguez
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Dirk Görlich
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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19
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Abstract
The nuclear pore complex (NPC) serves as the sole bidirectional gateway of macromolecules in and out of the nucleus. Owing to its size and complexity (∼1,000 protein subunits, ∼110 MDa in humans), the NPC has remained one of the foremost challenges for structure determination. Structural studies have now provided atomic-resolution crystal structures of most nucleoporins. The acquisition of these structures, combined with biochemical reconstitution experiments, cross-linking mass spectrometry, and cryo-electron tomography, has facilitated the determination of the near-atomic overall architecture of the symmetric core of the human, fungal, and algal NPCs. Here, we discuss the insights gained from these new advances and outstanding issues regarding NPC structure and function. The powerful combination of bottom-up and top-down approaches toward determining the structure of the NPC offers a paradigm for uncovering the architectures of other complex biological machines to near-atomic resolution.
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Affiliation(s)
- Daniel H Lin
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA;
| | - André Hoelz
- Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, California 91125, USA;
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20
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Padavannil A, Sarkar P, Kim SJ, Cagatay T, Jiou J, Brautigam CA, Tomchick DR, Sali A, D'Arcy S, Chook YM. Importin-9 wraps around the H2A-H2B core to act as nuclear importer and histone chaperone. eLife 2019; 8:e43630. [PMID: 30855230 PMCID: PMC6453568 DOI: 10.7554/elife.43630] [Citation(s) in RCA: 38] [Impact Index Per Article: 7.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2018] [Accepted: 03/09/2019] [Indexed: 01/29/2023] Open
Abstract
We report the crystal structure of nuclear import receptor Importin-9 bound to its cargo, the histones H2A-H2B. Importin-9 wraps around the core, globular region of H2A-H2B to form an extensive interface. The nature of this interface coupled with quantitative analysis of deletion mutants of H2A-H2B suggests that the NLS-like sequences in the H2A-H2B tails play a minor role in import. Importin-9•H2A-H2B is reminiscent of interactions between histones and histone chaperones in that it precludes H2A-H2B interactions with DNA and H3-H4 as seen in the nucleosome. Like many histone chaperones, which prevent inappropriate non-nucleosomal interactions, Importin-9 also sequesters H2A-H2B from DNA. Importin-9 appears to act as a storage chaperone for H2A-H2B while escorting it to the nucleus. Surprisingly, RanGTP does not dissociate Importin-9•H2A-H2B but assembles into a RanGTP•Importin-9•H2A-H2B complex. The presence of Ran in the complex, however, modulates Imp9-H2A-H2B interactions to facilitate its dissociation by DNA and assembly into a nucleosome.
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Affiliation(s)
- Abhilash Padavannil
- Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasUnited States
| | - Prithwijit Sarkar
- Department of Biological SciencesUniversity of Texas at DallasRichardsonUnited States
| | - Seung Joong Kim
- Department of PhysicsKorea Advanced Institute of Science and Technology (KAIST)DaejeonKorea
| | - Tolga Cagatay
- Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasUnited States
| | - Jenny Jiou
- Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasUnited States
| | - Chad A Brautigam
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasUnited States
| | - Diana R Tomchick
- Department of BiophysicsUniversity of Texas Southwestern Medical CenterDallasUnited States
| | - Andrej Sali
- Department of Bioengineering and Therapeutic Sciences, California Institute for Quantitative BiosciencesUniversity of California, San FranciscoSan FranciscoUnited States
- Department of Pharmaceutical Chemistry, California Institute for Quantitative BiosciencesUniversity of California, San FranciscoSan FranciscoUnited states
| | - Sheena D'Arcy
- Department of Chemistry and BiochemistryUniversity of Texas at DallasRichardsonUnited States
| | - Yuh Min Chook
- Department of PharmacologyUniversity of Texas Southwestern Medical CenterDallasUnited States
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21
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Ma Q, Tatsuno T, Nakamura Y, Izumi S, Tomosugi N, Ishigaki Y. Immuno‐detection of mRNA‐binding protein complex in human cells under transmission electron microscopy. Microsc Res Tech 2019; 82:680-688. [DOI: 10.1002/jemt.23214] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2018] [Revised: 12/13/2018] [Accepted: 12/15/2018] [Indexed: 11/06/2022]
Affiliation(s)
- Qingfeng Ma
- Medical Research InstituteKanazawa Medical University Uchinada Kahoku Japan
- Department of Clinical Laboratory, Liyuan Hospital, Tongji Medical CollegeHuazhong University of Science and Technology Wuhan China
| | - Takanori Tatsuno
- Medical Research InstituteKanazawa Medical University Uchinada Kahoku Japan
| | - Yuka Nakamura
- Medical Research InstituteKanazawa Medical University Uchinada Kahoku Japan
| | - Shin‐Ichi Izumi
- Department of Cell Biology, Unit of Biomedical SciencesNagasaki University Graduate School of Biomedical Sciences Sakamoto Nagasaki Japan
| | - Naohisa Tomosugi
- Medical Research InstituteKanazawa Medical University Uchinada Kahoku Japan
- Medical Care Proteomics Biotechnology Co., Ltd. Uchinada Kahoku Japan
| | - Yasuhito Ishigaki
- Medical Research InstituteKanazawa Medical University Uchinada Kahoku Japan
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22
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Higher-Order Organization Principles of Pre-translational mRNPs. Mol Cell 2018; 72:715-726.e3. [PMID: 30415953 DOI: 10.1016/j.molcel.2018.09.012] [Citation(s) in RCA: 48] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 06/20/2018] [Accepted: 09/12/2018] [Indexed: 11/21/2022]
Abstract
Compared to noncoding RNAs (ncRNAs), such as rRNAs and ribozymes, for which high-resolution structures abound, little is known about the tertiary structures of mRNAs. In eukaryotic cells, newly made mRNAs are packaged with proteins in highly compacted mRNA particles (mRNPs), but the manner of this mRNA compaction is unknown. Here, we developed and implemented RIPPLiT (RNA immunoprecipitation and proximity ligation in tandem), a transcriptome-wide method for probing the 3D conformations of RNAs stably associated with defined proteins, in this case, exon junction complex (EJC) core factors. EJCs multimerize with other mRNP components to form megadalton-sized complexes that protect large swaths of newly synthesized mRNAs from endonuclease digestion. Unlike ncRNPs, wherein strong locus-specific structures predominate, mRNPs behave more like flexible polymers. Polymer analysis of proximity ligation data for hundreds of mRNA species demonstrates that nascent and pre-translational mammalian mRNAs are compacted by their associated proteins into linear rod-like structures.
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23
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PKA-site phosphorylation of importin13 regulates its subcellular localization and nuclear transport function. Biochem J 2018; 475:2699-2712. [PMID: 30045875 DOI: 10.1042/bcj20180082] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 07/12/2018] [Accepted: 07/16/2018] [Indexed: 01/25/2023]
Abstract
Importin 13 (IPO13) is a key member of the importin β superfamily, which can transport cargoes both into and out of the nucleus to contribute to a variety of important cellular processes. IPO13 is known to undergo phosphorylation, but the impact of this on function has not been investigated. Here, we show for the first time that IPO13 is phosphorylated by cAMP-dependent protein kinase A specifically at serine 193. Results from fluorescence recovery after photobleaching and fluorescence loss in photobleaching approaches establish that negative charge at serine 193 through phosphorylation or point mutation both reduces IPO13 nuclear import and increases its nuclear export. Importantly, phosphorylation also appears to enhance cargo interaction on the part of IPO13, with significant impact on localization, as shown for the Pax6 homeobox-containing transcription partner. This is the first report that IPO13 can be phosphorylated at Ser193 and that this modification regulates IPO13 subcellular localization and nucleocytoplasmic transport function, with important implications for IPO13's role in development and other processes.
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24
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Aksu M, Pleiner T, Karaca S, Kappert C, Dehne HJ, Seibel K, Urlaub H, Bohnsack MT, Görlich D. Xpo7 is a broad-spectrum exportin and a nuclear import receptor. J Cell Biol 2018; 217:2329-2340. [PMID: 29748336 PMCID: PMC6028547 DOI: 10.1083/jcb.201712013] [Citation(s) in RCA: 29] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2017] [Revised: 04/09/2018] [Accepted: 04/24/2018] [Indexed: 11/28/2022] Open
Abstract
Exportins bind cargo molecules in a RanGTP-dependent manner inside nuclei and transport them through nuclear pores to the cytoplasm. CRM1/Xpo1 is the best-characterized exportin because specific inhibitors such as leptomycin B allow straightforward cargo validations in vivo. The analysis of other exportins lagged far behind, foremost because no such inhibitors had been available for them. In this study, we explored the cargo spectrum of exportin 7/Xpo7 in depth and identified not only ∼200 potential export cargoes but also, surprisingly, ∼30 nuclear import substrates. Moreover, we developed anti-Xpo7 nanobodies that acutely block Xpo7 function when transfected into cultured cells. The inhibition is pathway specific, mislocalizes export cargoes of Xpo7 to the nucleus and import substrates to the cytoplasm, and allowed validation of numerous tested cargo candidates. This establishes Xpo7 as a broad-spectrum bidirectional transporter and paves the way for a much deeper analysis of exportin and importin function in the future.
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Affiliation(s)
- Metin Aksu
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Tino Pleiner
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Samir Karaca
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Christin Kappert
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Heinz-Jürgen Dehne
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Katharina Seibel
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Henning Urlaub
- Bioanalytical Mass Spectrometry Group, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
- Institute for Clinical Chemistry, University Medical Center Göttingen, Göttingen, Germany
| | - Markus T Bohnsack
- Institute for Molecular Biology, University Medical Center Göttingen, Göttingen, Germany
| | - Dirk Görlich
- Department of Cellular Logistics, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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25
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Baade I, Spillner C, Schmitt K, Valerius O, Kehlenbach RH. Extensive Identification and In-depth Validation of Importin 13 Cargoes. Mol Cell Proteomics 2018; 17:1337-1353. [PMID: 29666159 PMCID: PMC6030721 DOI: 10.1074/mcp.ra118.000623] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2018] [Revised: 04/09/2018] [Indexed: 11/06/2022] Open
Abstract
Importin 13 is a member of the importin β family of transport receptors. Unlike most family members, importin 13 mediates both, nuclear protein import and export. To search for novel importin 13 cargoes, we used stable isotope labeling of amino acids in cell culture (SILAC) and mass spectrometry. Using stringent criteria, we identified 255 importin 13 substrates, including the known cargoes Ubc9, Mago and eIF1A, and validate many of them as transport cargoes by extensive biochemical and cell biological characterization. Several novel cargoes can also be transported by the export receptor CRM1, demonstrating a clear redundancy in receptor choice. Using importin 13 mutants, we show that many of the novel substrates contact regions on the transport receptor that are not used by Ubc9, Mago or eIF1A. Together, this study significantly expands the repertoire of importin 13 cargoes and sets the basis for a more detailed characterization of this extremely versatile transport receptor.
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Affiliation(s)
- Imke Baade
- From the ‡Department of Molecular Biology, Faculty of Medicine, Göttingen Center of Biosciences (GZMB), Georg-August-University Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Christiane Spillner
- From the ‡Department of Molecular Biology, Faculty of Medicine, Göttingen Center of Biosciences (GZMB), Georg-August-University Göttingen, Humboldtallee 23, 37073 Göttingen, Germany
| | - Kerstin Schmitt
- §Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, Grisebachstr 8, 37077 Göttingen, Germany
| | - Oliver Valerius
- §Department of Molecular Microbiology and Genetics, Institute of Microbiology and Genetics, GZMB, Georg-August-University Göttingen, Grisebachstr 8, 37077 Göttingen, Germany
| | - Ralph H Kehlenbach
- From the ‡Department of Molecular Biology, Faculty of Medicine, Göttingen Center of Biosciences (GZMB), Georg-August-University Göttingen, Humboldtallee 23, 37073 Göttingen, Germany;
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26
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Tsirkone VG, Blokken J, De Wit F, Breemans J, De Houwer S, Debyser Z, Christ F, Strelkov SV. N-terminal half of transportin SR2 interacts with HIV integrase. J Biol Chem 2017; 292:9699-9710. [PMID: 28356354 PMCID: PMC5465493 DOI: 10.1074/jbc.m117.777029] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2017] [Revised: 03/14/2017] [Indexed: 11/06/2022] Open
Abstract
The karyopherin transportin SR2 (TRN-SR2, TNPO3) is responsible for shuttling specific cargoes such as serine/arginine-rich splicing factors from the cytoplasm to the nucleus. This protein plays a key role in HIV infection by facilitating the nuclear import of the pre-integration complex (PIC) that contains the viral DNA as well as several cellular and HIV proteins, including the integrase. The process of nuclear import is considered to be the bottleneck of the viral replication cycle and therefore represents a promising target for anti-HIV drug design. Previous studies have demonstrated that the direct interaction between TRN-SR2 and HIV integrase predominantly involves the catalytic core domain (CCD) and the C-terminal domain (CTD) of the integrase. We aimed at providing a detailed molecular view of this interaction through a biochemical characterization of the respective protein complex. Size-exclusion chromatography was used to characterize the interaction of TRN-SR2 with a truncated variant of the HIV-1 integrase, including both the CCD and CTD. These experiments indicate that one TRN-SR2 molecule can specifically bind one CCD-CTD dimer. Next, the regions of the solenoid-like TRN-SR2 molecule that are involved in the interaction with integrase were identified using AlphaScreen binding assays, revealing that the integrase interacts with the N-terminal half of TRN-SR2 principally through the HEAT repeats 4, 10, and 11. Combining these results with small-angle X-ray scattering data for the complex of TRN-SR2 with truncated integrase, we propose a molecular model of the complex. We speculate that nuclear import of the PIC may proceed concurrently with the normal nuclear transport.
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Affiliation(s)
| | - Jolien Blokken
- the Laboratory for Molecular Virology and Gene Therapy, KU Leuven, 3000 Leuven, Belgium
| | - Flore De Wit
- the Laboratory for Molecular Virology and Gene Therapy, KU Leuven, 3000 Leuven, Belgium
| | | | - Stéphanie De Houwer
- the Laboratory for Molecular Virology and Gene Therapy, KU Leuven, 3000 Leuven, Belgium
| | - Zeger Debyser
- the Laboratory for Molecular Virology and Gene Therapy, KU Leuven, 3000 Leuven, Belgium
| | - Frauke Christ
- the Laboratory for Molecular Virology and Gene Therapy, KU Leuven, 3000 Leuven, Belgium
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Fatima S, Wagstaff KM, Lieu KG, Davies RG, Tanaka SS, Yamaguchi YL, Loveland KL, Tam PP, Jans DA. Interactome of the inhibitory isoform of the nuclear transporter Importin 13. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2017; 1864:546-561. [DOI: 10.1016/j.bbamcr.2016.12.017] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/08/2016] [Revised: 11/11/2016] [Accepted: 12/15/2016] [Indexed: 10/20/2022]
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Woodward LA, Mabin JW, Gangras P, Singh G. The exon junction complex: a lifelong guardian of mRNA fate. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 8. [PMID: 28008720 DOI: 10.1002/wrna.1411] [Citation(s) in RCA: 59] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Subscribe] [Scholar Register] [Received: 08/03/2016] [Revised: 10/27/2016] [Accepted: 11/09/2016] [Indexed: 12/28/2022]
Abstract
During messenger RNA (mRNA) biogenesis and processing in the nucleus, many proteins are imprinted on mRNAs assembling them into messenger ribonucleoproteins (mRNPs). Some of these proteins remain stably bound within mRNPs and have a long-lasting impact on their fate. One of the best-studied examples is the exon junction complex (EJC), a multiprotein complex deposited primarily 24 nucleotides upstream of exon-exon junctions as a consequence of pre-mRNA splicing. The EJC maintains a stable, sequence-independent, hold on the mRNA until its removal during translation in the cytoplasm. Acting as a molecular shepherd, the EJC travels with mRNA across the cellular landscape coupling pre-mRNA splicing to downstream, posttranscriptional processes such as mRNA export, mRNA localization, translation, and nonsense-mediated mRNA decay (NMD). In this review, we discuss our current understanding of the EJC's functions during these processes, and expound its newly discovered functions (e.g., pre-mRNA splicing). Another focal point is the recently unveiled in vivo EJC interactome, which has shed new light on the EJC's location on the spliced RNAs and its intimate relationship with other mRNP components. We summarize new strides being made in connecting the EJC's molecular function with phenotypes, informed by studies of human disorders and model organisms. The progress toward understanding EJC functions has revealed, in its wake, even more questions, which are discussed throughout. WIREs RNA 2017, 8:e1411. doi: 10.1002/wrna.1411 For further resources related to this article, please visit the WIREs website.
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Affiliation(s)
- Lauren A Woodward
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Justin W Mabin
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Pooja Gangras
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
| | - Guramrit Singh
- Department of Molecular Genetics, The Ohio State University, Columbus, OH, USA
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Hir HL, Saulière J, Wang Z. The exon junction complex as a node of post-transcriptional networks. Nat Rev Mol Cell Biol 2015; 17:41-54. [DOI: 10.1038/nrm.2015.7] [Citation(s) in RCA: 167] [Impact Index Per Article: 18.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
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Christie M, Chang CW, Róna G, Smith KM, Stewart AG, Takeda AAS, Fontes MRM, Stewart M, Vértessy BG, Forwood JK, Kobe B. Structural Biology and Regulation of Protein Import into the Nucleus. J Mol Biol 2015; 428:2060-90. [PMID: 26523678 DOI: 10.1016/j.jmb.2015.10.023] [Citation(s) in RCA: 181] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2015] [Revised: 10/16/2015] [Accepted: 10/24/2015] [Indexed: 11/28/2022]
Abstract
Proteins are translated in the cytoplasm, but many need to access the nucleus to perform their functions. Understanding how these nuclear proteins are transported through the nuclear envelope and how the import processes are regulated is therefore an important aspect of understanding cell function. Structural biology has played a key role in understanding the molecular events during the transport processes and their regulation, including the recognition of nuclear targeting signals by the corresponding receptors. Here, we review the structural basis of the principal nuclear import pathways and the molecular basis of their regulation. The pathways involve transport factors that are members of the β-karyopherin family, which can bind cargo directly (e.g., importin-β, transportin-1, transportin-3, importin-13) or through adaptor proteins (e.g., importin-α, snurportin-1, symportin-1), as well as unrelated transport factors such as Hikeshi, involved in the transport of heat-shock proteins, and NTF2, involved in the transport of RanGDP. Solenoid proteins feature prominently in these pathways. Nuclear transport factors recognize nuclear targeting signals on the cargo proteins, including the classical nuclear localization signals, recognized by the adaptor importin-α, and the PY nuclear localization signals, recognized by transportin-1. Post-translational modifications, particularly phosphorylation, constitute key regulatory mechanisms operating in these pathways.
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Affiliation(s)
- Mary Christie
- The Garvan Institute of Medical Research, 384 Victoria Street, Darlinghurst, NSW 2010, Australia; St Vincent's Clinical School, University of New South Wales Faculty of Medicine, Darlinghurst, NSW 2010, Australia
| | - Chiung-Wen Chang
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; Verna and Marrs McLean Department of Biochemistry and Molecular Biology, Baylor College of Medicine, Houston, TX 77030, USA
| | - Gergely Róna
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest H-1117, Hungary; Department of Applied Biotechnology and Food Sciences, Budapest University of Technology and Economics, Budapest H-1111, Hungary
| | - Kate M Smith
- School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW 2650, Australia
| | - Alastair G Stewart
- School of Molecular Bioscience, The University of Sydney, Sydney, NSW 2006, Australia
| | - Agnes A S Takeda
- Department of Physics and Biophysics, Institute of Biosciences, Universidade Estadual Paulista, Botucatu, São Paulo 18618-000, Brazil
| | - Marcos R M Fontes
- Department of Physics and Biophysics, Institute of Biosciences, Universidade Estadual Paulista, Botucatu, São Paulo 18618-000, Brazil
| | - Murray Stewart
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia; MRC Laboratory of Molecular Biology, Francis Crick Avenue, Cambridge Biomedical Campus, Cambridge CB2 0QH, United Kingdom
| | - Beáta G Vértessy
- Institute of Enzymology, Research Centre for Natural Sciences, Hungarian Academy of Sciences, Budapest H-1117, Hungary; Department of Applied Biotechnology and Food Sciences, Budapest University of Technology and Economics, Budapest H-1111, Hungary
| | - Jade K Forwood
- School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, NSW 2650, Australia
| | - Bostjan Kobe
- School of Chemistry and Molecular Biosciences, Institute for Molecular Bioscience and Australian Infectious Diseases Research Centre, University of Queensland, Brisbane, QLD 4072, Australia.
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Abstract
The Karyopherin-β family of proteins mediates nuclear transport of macromolecules. Nuclear versus cytoplasmic localization of proteins is often suggested by the presence of NLSs (nuclear localization signals) or NESs (nuclear export signals). Import-Karyopherin-βs or Importins bind to NLSs in their protein cargos to transport them through nuclear pore complexes into the nucleus. Until recently, only two classes of NLS had been biochemically and structurally characterized: the classical NLS, which is recognized by the Importin-α/β heterodimer and the PY-NLS (proline-tyrosine NLS), which is recognized by Karyopherin-β2 or Transportin-1. Structures of two other Karyopherin-βs, Kap121 and Transportin-SR2, in complex with their respective cargos were reported for the first time recently, revealing two new distinct classes of NLSs. The present paper briefly describes the classical NLS, reviews recent literature on the PY-NLS and provides in-depth reviews of the two newly discovered classes of NLSs that bind Kap121p and Transportin-SR respectively.
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32
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Zou D, McSweeney C, Sebastian A, Reynolds DJ, Dong F, Zhou Y, Deng D, Wang Y, Liu L, Zhu J, Zou J, Shi Y, Albert I, Mao Y. A critical role of RBM8a in proliferation and differentiation of embryonic neural progenitors. Neural Dev 2015; 10:18. [PMID: 26094033 PMCID: PMC4479087 DOI: 10.1186/s13064-015-0045-7] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2015] [Accepted: 06/17/2015] [Indexed: 02/04/2023] Open
Abstract
Background Nonsense mediated mRNA decay (NMD) is an RNA surveillance mechanism that controls RNA stability and ensures the speedy degradation of erroneous and unnecessary transcripts. This mechanism depends on several core factors in the exon junction complex (EJC), eIF4A3, RBM8a, Magoh, and BTZ, as well as peripheral factors to distinguish premature stop codons (PTCs) from normal stop codons in transcripts. Recently, emerging evidence has indicated that NMD factors are associated with neurodevelopmental disorders such as autism spectrum disorder (ASD) and intellectual disability (ID). However, the mechanism in which these factors control embryonic brain development is not clear. Result We found that RBM8a is critical for proliferation and differentiation in cortical neural progenitor cells (NPCs). RBM8a is highly expressed in the subventricular zone (SVZ) of the early embryonic cortex, suggesting that RBM8a may play a role in regulating NPCs. RBM8a overexpression stimulates embryonic NPC proliferation and suppresses neuronal differentiation. Conversely, knockdown of RBM8a in the neocortex reduces NPC proliferation and promotes premature neuronal differentiation. Moreover, overexpression of RBM8a suppresses cell cycle exit and keeps cortical NPCs in a proliferative state. To uncover the underlying mechanisms of this phenotype, genome-wide RNAseq was used to identify potential downstream genes of RBM8a in the brain, which have been implicated in autism and neurodevelopmental disorders. Interestingly, autism and schizophrenia risk genes are highly represented in downstream transcripts of RBM8a. In addition, RBM8a regulates multiple alternative splicing genes and NMD targets that are implicated in ASD. Taken together, this data suggests a novel role of RBM8a in the regulation of neurodevelopment. Conclusions Our studies provide some insight into causes of mental illnesses and will facilitate the development of new therapeutic strategies for neurodevelopmental illnesses. Electronic supplementary material The online version of this article (doi:10.1186/s13064-015-0045-7) contains supplementary material, which is available to authorized users.
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Affiliation(s)
- Donghua Zou
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi Province, 530021, China. .,Department of Geriatrics, The 303 Hospital of Chinese People's Liberation Army, Nanning, Guangxi Province, 530021, China. .,Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Colleen McSweeney
- Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Aswathy Sebastian
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Derrick James Reynolds
- Department of Microbiology & Molecular Genetics School of Medicine, University of California, Irvine, CA, 92697, USA.
| | - Fengping Dong
- Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Yijing Zhou
- Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Dazhi Deng
- Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA. .,Department of Emergency, Guangxi Zhuang Autonomous Region People's Hospital, Nanning, Guangxi Province, 530021, China.
| | - Yonggang Wang
- Department of Neurology, School of Medicine, Renji Hospital, Shanghai Jiaotong University, Shanghai, 200127, China.
| | - Long Liu
- Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA. .,Department of Chemistry and Biology, College of Science, National University of Defense Technology, Changsha, 410073, China.
| | - Jun Zhu
- Systems Biology Center, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD, 20892, USA.
| | - Jizhong Zou
- Center for Molecular Medicine, National Heart, Lung, and Blood Institute, NIH, Bethesda, MD, 20892, USA.
| | - Yongsheng Shi
- Department of Microbiology & Molecular Genetics School of Medicine, University of California, Irvine, CA, 92697, USA.
| | - Istvan Albert
- Department of Biochemistry and Molecular Biology, Pennsylvania State University, University Park, PA, 16802, USA.
| | - Yingwei Mao
- Department of Neurology, The First Affiliated Hospital of Guangxi Medical University, Nanning, Guangxi Province, 530021, China. .,Department of Biology, Pennsylvania State University, University Park, PA, 16802, USA.
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Cautain B, Hill R, de Pedro N, Link W. Components and regulation of nuclear transport processes. FEBS J 2014; 282:445-62. [PMID: 25429850 PMCID: PMC7163960 DOI: 10.1111/febs.13163] [Citation(s) in RCA: 177] [Impact Index Per Article: 17.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Revised: 11/11/2014] [Accepted: 11/12/2014] [Indexed: 12/27/2022]
Abstract
The spatial separation of DNA replication and gene transcription in the nucleus and protein translation in the cytoplasm is a uniform principle of eukaryotic cells. This compartmentalization imposes a requirement for a transport network of macromolecules to shuttle these components in and out of the nucleus. This nucleo‐cytoplasmic transport of macromolecules is critical for both cell physiology and pathology. Consequently, investigating its regulation and disease‐associated alterations can reveal novel therapeutic approaches to fight human diseases, such as cancer or viral infection. The characterization of the nuclear pore complex, the identification of transport signals and transport receptors, as well as the characterization of the Ran system (providing the energy source for efficient cargo transport) has greatly facilitated our understanding of the components, mechanisms and regulation of the nucleo‐cytoplasmic transport of proteins in our cells. Here we review this knowledge with a specific emphasis on the selection of disease‐relevant molecular targets for potential therapeutic intervention.
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Affiliation(s)
- Bastien Cautain
- Fundacion MEDINA Parque tecnológico ciencias de la salud, Granada, Spain
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34
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Tsirkone VG, Beutels KG, Demeulemeester J, Debyser Z, Christ F, Strelkov SV. Structure of transportin SR2, a karyopherin involved in human disease, in complex with Ran. Acta Crystallogr F Struct Biol Commun 2014; 70:723-9. [PMID: 24915079 PMCID: PMC4051523 DOI: 10.1107/s2053230x14009492] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2014] [Accepted: 04/28/2014] [Indexed: 11/10/2022] Open
Abstract
Transportin SR2 (TRN-SR2) is a β-type karyopherin responsible for the nuclear import of specific cargoes, including serine/arginine-rich splicing factors. The protein has been implicated in a variety of human diseases, including HIV infection, primary biliary cirrhosis and limb-girdle muscular dystrophy 1F. Towards understanding its molecular mechanism, a 2.9 Å resolution crystal structure of human TRN-SR2 complexed with the small GTPase Ran has been determined. TRN-SR2 is composed of 20 α-helical HEAT repeats forming a solenoid-like fold. The first nine repeats form a `cradle' for the binding of RanGTP, revealing similarities but also differences with respect to the related importin 13 complex.
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Affiliation(s)
- Vicky G. Tsirkone
- Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
| | - Katrien G. Beutels
- Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
| | - Jonas Demeulemeester
- Laboratory of Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
| | - Zeger Debyser
- Laboratory of Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
| | - Frauke Christ
- Laboratory of Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
| | - Sergei V. Strelkov
- Laboratory for Biocrystallography, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Herestraat 49 bus 822, 3000 Leuven, Belgium
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35
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Structural basis for nuclear import of splicing factors by human Transportin 3. Proc Natl Acad Sci U S A 2014; 111:2728-33. [PMID: 24449914 DOI: 10.1073/pnas.1320755111] [Citation(s) in RCA: 103] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Transportin 3 (Tnpo3, Transportin-SR2) is implicated in nuclear import of splicing factors and HIV-1 replication. Herein, we show that the majority of cellular Tnpo3 binding partners contain arginine-serine (RS) repeat domains and present crystal structures of human Tnpo3 in its free as well as GTPase Ran- and alternative splicing factor/splicing factor 2 (ASF/SF2)-bound forms. The flexible β-karyopherin fold of Tnpo3 embraces the RNA recognition motif and RS domains of the cargo. A constellation of charged residues on and around the arginine-rich helix of Tnpo3 HEAT repeat 15 engage the phosphorylated RS domain and are critical for the recognition and nuclear import of ASF/SF2. Mutations in the same region of Tnpo3 impair its interaction with the cleavage and polyadenylation specificity factor 6 (CPSF6) and its ability to support HIV-1 replication. Steric incompatibility of the RS domain and RanGTP engagement by Tnpo3 provides the mechanism for cargo release in the nucleus. Our results elucidate the structural bases for nuclear import of splicing factors and the Tnpo3-CPSF6 nexus in HIV-1 biology.
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36
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Abstract
Classic nuclear shuttling is mediated by an importin-α∙β heterodimer that binds to cargoes containing a nuclear localization signal, and shuttles most nuclear proteins immediately after their translation. Aside from this canonical mechanism, kariopheryn-βs or β-like importins operate by binding to non-canonical nuclear localization signals to mediate translocation without the assistance of importin-α. The mechanism by which these components operate is much less understood and is currently under investigation. Recently, several β-like importins have been implicated in the stimulated nuclear translocation of signaling proteins. Here, we propose that this group of importins might be responsible for the swift nuclear shuttling of many proteins following various stimuli.
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37
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Taltynov O, Demeulemeester J, Christ F, De Houwer S, Tsirkone VG, Gerard M, Weeks SD, Strelkov SV, Debyser Z. Interaction of transportin-SR2 with Ras-related nuclear protein (Ran) GTPase. J Biol Chem 2013; 288:25603-25613. [PMID: 23878195 DOI: 10.1074/jbc.m113.484345] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The human immunodeficiency virus type 1 (HIV-1) and other lentiviruses are capable of infecting non-dividing cells and, therefore, need to be imported into the nucleus before integration into the host cell chromatin. Transportin-SR2 (TRN-SR2, Transportin-3, TNPO3) is a cellular karyopherin implicated in nuclear import of HIV-1. A model in which TRN-SR2 imports the viral preintegration complex into the nucleus is supported by direct interaction between TRN-SR2 and HIV-1 integrase (IN). Residues in the C-terminal domain of HIV-1 IN that mediate binding to TRN-SR2 were recently delineated. As for most nuclear import cargoes, the driving force behind HIV-1 preintegration complex import is likely a gradient of the GDP- and GTP-bound forms of Ran, a small GTPase. In this study we offer biochemical and structural characterization of the interaction between TRN-SR2 and Ran. By size exclusion chromatography we demonstrate stable complex formation of TRN-SR2 and RanGTP in solution. Consistent with the behavior of normal nuclear import cargoes, HIV-1 IN is released from the complex with TRN-SR2 by RanGTP. Although in concentrated solutions TRN-SR2 by itself was predominantly present as a dimer, the TRN-SR2-RanGTP complex was significantly more compact. Further analysis supported a model wherein one monomer of TRN-SR2 is bound to one monomer of RanGTP. Finally, we present a homology model of the TRN-SR2-RanGTP complex that is in excellent agreement with the experimental small angle x-ray scattering data.
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Affiliation(s)
- Oliver Taltynov
- From the Laboratory for Molecular Virology and Gene Therapy and
| | | | - Frauke Christ
- From the Laboratory for Molecular Virology and Gene Therapy and
| | | | - Vicky G Tsirkone
- Laboratory for Biocrystallography, KU Leuven, B-3000 Leuven, Belgium
| | - Melanie Gerard
- From the Laboratory for Molecular Virology and Gene Therapy and
| | - Stephen D Weeks
- Laboratory for Biocrystallography, KU Leuven, B-3000 Leuven, Belgium
| | - Sergei V Strelkov
- Laboratory for Biocrystallography, KU Leuven, B-3000 Leuven, Belgium
| | - Zeger Debyser
- From the Laboratory for Molecular Virology and Gene Therapy and.
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Shaharuddin B, Ahmad S, Ali S, Meeson A. Limbal side population cells: a future treatment for limbal stem cell deficiency. Regen Med 2013; 8:319-31. [DOI: 10.2217/rme.13.18] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
Corneal blindness carries a morbidity that affects quality of life and is often associated with an increased economic burden. In this review, we focus on the severe and painful condition of limbal stem cell deficiency, an important cause of corneal blindness. Conventional corneal transplantation usually results in graft failure and is contraindicated in this condition. Ex vivo-expanded limbal epithelial transplantation has been used as a cellular-based therapy to regenerate and reconstruct the ocular surface as a mode of treatment. Enrichment methods for stem cells are a strategy to improve the outcome of limbal stem cell transplantation. Here we discuss the side population assay as a functional assay to enrich for stem cells as an important source of limbal stem cells. The challenges in ex vivo-expanded limbal stem cell transplantation are wide and varied and will be addressed in this review with regard to improving the clinical outcomes of cultivated limbal stem cell transplantation.
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Affiliation(s)
- Bakiah Shaharuddin
- Advanced Medical & Dental Institute, Universiti Sains Malaysia, 13200 Pulau Pinang, Malaysia
| | - Sajjad Ahmad
- St Paul’s Eye Unit, Royal Liverpool University Hospital, Prescot Street, Liverpool, L7 8XP, UK
- Department of Eye & Vision Sciences, Institute of Ageing & Chronic Disease, University of Liverpool, 4th Floor UCD Building, Daulby Street, Liverpool, L69 3GA, UK
| | - Simi Ali
- Institute of Cellular Medicine, William-Leech Building, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK
| | - Annette Meeson
- Institute of Genetic Medicine, Newcastle University, International Centre for Life, Newcastle upon Tyne, NE1 3BZ, UK
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Wang R, Shen J, Huang P, Zhu X. CCCTC-binding factor controls its own nuclear transport via regulating the expression of importin 13. Mol Cells 2013; 35:388-95. [PMID: 23620300 PMCID: PMC3887860 DOI: 10.1007/s10059-013-2283-z] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2012] [Revised: 03/07/2013] [Accepted: 03/15/2013] [Indexed: 11/25/2022] Open
Abstract
CCCTC-binding factor (CTCF), a multivalent zinc-finger protein, is involved in different aspects of regulation including promoter activation or repression, gene silencing, chromatin insulation, gene imprinting, X-chromosome inactivation, cell growth or differentiation and tumor genesis. However, the molecular mechanisms of CTCF nuclear import remains unclear. In this study, we showed that the expression of CTCF influenced the intracellular distribution of itself, which might go through transport receptor - import 13 (IPO13). We further confirmed that there is a CTCF target site in ipo13 -774∼-573 bp promoter region and CTCF regulates the expression of IPO13. Besides, GST pull-down and Co-IP experiments demonstrated that CTCF interacts with IPO13. Immunofluorescence staining showed that IPO13 influenced intracellular distribution of CTCF. In all, we conclude that CTCF regulates the expression of IPO13, which, in turn, mediates the nuclear import of CTCF.
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Affiliation(s)
- Rong Wang
- Laboratory of Protein Engineering, Beijing Institute of Biotechnology, Beijing,
China
| | - Jingjing Shen
- Laboratory of Protein Engineering, Beijing Institute of Biotechnology, Beijing,
China
| | - Peitang Huang
- Laboratory of Protein Engineering, Beijing Institute of Biotechnology, Beijing,
China
| | - Xudong Zhu
- Laboratory of Protein Engineering, Beijing Institute of Biotechnology, Beijing,
China
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40
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Structural basis for the nuclear export activity of Importin13. EMBO J 2013; 32:899-913. [PMID: 23435562 DOI: 10.1038/emboj.2013.29] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2012] [Accepted: 01/28/2013] [Indexed: 02/05/2023] Open
Abstract
Importin13 (Imp13) is a bidirectional karyopherin that can mediate both import and export of cargoes. Imp13 recognizes several import cargoes, which include the exon junction complex components Mago-Y14 and the E2 SUMO-conjugating enzyme Ubc9, and one known export cargo, the translation initiation factor 1A (eIF1A). To understand how Imp13 can perform double duty, we determined the 3.6-Å crystal structure of Imp13 in complex with RanGTP and with eIF1A. eIF1A binds at the inner surface of the Imp13 C-terminal arch adjacent and concomitantly to RanGTP illustrating how eIF1A can be exported by Imp13. Moreover, the 3.0-Å structure of Imp13 in its unbound state reveals the existence of an open conformation in the cytoplasm that explains export cargo release and completes the export branch of the Imp13 pathway. Finally, we demonstrate that Imp13 is able to bind and export eIF1A in vivo and that its function is essential.
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Llorca O. Structural insights into nonsense-mediated mRNA decay (NMD) by electron microscopy. Curr Opin Struct Biol 2012; 23:161-7. [PMID: 23102542 DOI: 10.1016/j.sbi.2012.10.004] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Revised: 10/03/2012] [Accepted: 10/05/2012] [Indexed: 10/27/2022]
Affiliation(s)
- Oscar Llorca
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, Ramiro de Maetzu 9, 28040 Madrid, Spain.
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42
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Larue R, Gupta K, Wuensch C, Shkriabai N, Kessl JJ, Danhart E, Feng L, Taltynov O, Christ F, Van Duyne GD, Debyser Z, Foster MP, Kvaratskhelia M. Interaction of the HIV-1 intasome with transportin 3 protein (TNPO3 or TRN-SR2). J Biol Chem 2012; 287:34044-58. [PMID: 22872640 PMCID: PMC3464514 DOI: 10.1074/jbc.m112.384669] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2012] [Revised: 08/01/2012] [Indexed: 01/14/2023] Open
Abstract
Transportin 3 (TNPO3 or TRN-SR2) has been shown to be an important cellular factor for early steps of lentiviral replication. However, separate studies have implicated distinct mechanisms for TNPO3 either through its interaction with HIV-1 integrase or capsid. Here we have carried out a detailed biophysical characterization of TNPO3 and investigated its interactions with viral proteins. Biophysical analyses including circular dichroism, analytical ultracentrifugation, small-angle x-ray scattering, and homology modeling provide insight into TNPO3 architecture and indicate that it is highly structured and exists in a monomer-dimer equilibrium in solution. In vitro biochemical binding assays argued against meaningful direct interaction between TNPO3 and the capsid cores. Instead, TNPO3 effectively bound to the functional intasome but not to naked viral DNA, suggesting that TNPO3 can directly engage the HIV-1 IN tetramer prebound to the cognate DNA. Mass spectrometry-based protein footprinting and site-directed mutagenesis studies have enabled us to map several interacting amino acids in the HIV-1 IN C-terminal domain and the cargo binding domain of TNPO3. Our findings provide important information for future genetic analysis to better understand the role of TNPO3 and its interacting partners for HIV-1 replication.
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Affiliation(s)
- Ross Larue
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
| | - Kushol Gupta
- the Department of Biochemistry and Biophysics and The Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, and
| | - Christiane Wuensch
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
| | - Nikolozi Shkriabai
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
| | - Jacques J. Kessl
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
| | - Eric Danhart
- the Department of Chemistry,The Ohio State University, Columbus, Ohio 43210
| | - Lei Feng
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
| | - Oliver Taltynov
- the Division of Molecular Medicine, Katholieke Universiteit Leuven, Leuven, Flanders 3000, Belgium
| | - Frauke Christ
- the Division of Molecular Medicine, Katholieke Universiteit Leuven, Leuven, Flanders 3000, Belgium
| | - Gregory D. Van Duyne
- the Department of Biochemistry and Biophysics and The Howard Hughes Medical Institute, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104, and
| | - Zeger Debyser
- the Division of Molecular Medicine, Katholieke Universiteit Leuven, Leuven, Flanders 3000, Belgium
| | - Mark P. Foster
- the Department of Chemistry,The Ohio State University, Columbus, Ohio 43210
| | - Mamuka Kvaratskhelia
- From the Center for Retrovirus Research and Comprehensive Cancer Center, College of Pharmacy and
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43
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Kataoka N, Diem MD, Yoshida M, Hatai C, Dobashi I, Dreyfuss G, Hagiwara M, Ohno M. Specific Y14 domains mediate its nucleo-cytoplasmic shuttling and association with spliced mRNA. Sci Rep 2011; 1:92. [PMID: 22355610 PMCID: PMC3216578 DOI: 10.1038/srep00092] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2011] [Accepted: 08/26/2011] [Indexed: 11/09/2022] Open
Abstract
Pre-mRNA splicing deposits multi-protein complexes, termed exon junction complexes (EJCs), on mRNAs near exon-exon junctions. The core of EJC consists of four proteins, eIF4AIII, MLN51, Y14 and Magoh. Y14 is a nuclear protein that can shuttle between the nucleus and the cytoplasm, and binds specifically to Magoh. Here we delineate a Y14 nuclear localization signal that also confers its nuclear export, which we name YNS. We further identified a 12-amino-acid peptide near Y14's carboxyl terminus that is required for its association with spliced mRNAs, as well as for Magoh binding. Furthermore, the Y14 mutants, which are deficient in binding to Magoh, could still be localized to the nucleus, suggesting the existence of both the nuclear import pathway and function for Y14 unaccompanied by Magoh.
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Affiliation(s)
- Naoyuki Kataoka
- Medical Top Track Program, Medical Research Institute, Tokyo Dental and Medical University, Tokyo 113-8510, Japan.
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44
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Ran-dependent nuclear export mediators: a structural perspective. EMBO J 2011; 30:3457-74. [PMID: 21878989 DOI: 10.1038/emboj.2011.287] [Citation(s) in RCA: 159] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 07/22/2011] [Indexed: 12/25/2022] Open
Abstract
Nuclear export is an essential eukaryotic activity. It proceeds through nuclear pore complexes (NPCs) and is mediated by soluble receptors that shuttle between nucleus and cytoplasm. RanGTPase-dependent export mediators (exportins) constitute the largest class of these carriers and are functionally highly versatile. All of these exportins load their substrates in response to RanGTP binding in the nucleus and traverse NPCs as ternary RanGTP-exportin-cargo complexes to the cytoplasm, where GTP hydrolysis leads to export complex disassembly. The different exportins vary greatly in their substrate range. Recent structural studies of both protein- and RNA-specific exporters have illuminated how exportins bind their cargoes, how Ran triggers cargo loading and how export complexes are disassembled in the cytoplasm. Here, we review the current state of knowledge and highlight emerging principles as well as prevailing questions.
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45
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Diebold ML, Fribourg S, Koch M, Metzger T, Romier C. Deciphering correct strategies for multiprotein complex assembly by co-expression: Application to complexes as large as the histone octamer. J Struct Biol 2011; 175:178-88. [DOI: 10.1016/j.jsb.2011.02.001] [Citation(s) in RCA: 83] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/14/2010] [Revised: 02/08/2011] [Accepted: 02/08/2011] [Indexed: 10/18/2022]
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46
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Arias-Palomo E, Yamashita A, Fernández IS, Núñez-Ramírez R, Bamba Y, Izumi N, Ohno S, Llorca O. The nonsense-mediated mRNA decay SMG-1 kinase is regulated by large-scale conformational changes controlled by SMG-8. Genes Dev 2011; 25:153-64. [PMID: 21245168 DOI: 10.1101/gad.606911] [Citation(s) in RCA: 69] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Nonsense-mediated mRNA decay (NMD) is a eukaryotic surveillance pathway that regulates the degradation of mRNAs harboring premature translation termination codons. NMD also influences the expression of many physiological transcripts. SMG-1 is a large kinase essential to NMD that phosphorylates Upf1, which seems to be the definitive signal triggering mRNA decay. However, the regulation of the kinase activity of SMG-1 remains poorly understood. Here, we reveal the three-dimensional architecture of SMG-1 in complex with SMG-8 and SMG-9, and the structural mechanisms regulating SMG-1 kinase. A bent arm comprising a long region of HEAT (huntington, elongation factor 3, a subunit of PP2A and TOR1) repeats at the N terminus of SMG-1 functions as a scaffold for SMG-8 and SMG-9, and projects from the C-terminal core containing the phosphatidylinositol 3-kinase domain. SMG-9 seems to control the activity of SMG-1 indirectly through the recruitment of SMG-8 to the N-terminal HEAT repeat region of SMG-1. Notably, SMG-8 binding to the SMG-1:SMG-9 complex specifically down-regulates the kinase activity of SMG-1 on Upf1 without contacting the catalytic domain. Assembly of the SMG-1:SMG-8:SMG-9 complex induces a significant motion of the HEAT repeats that is signaled to the kinase domain. Thus, large-scale conformational changes induced by SMG-8 after SMG-9-mediated recruitment tune SMG-1 kinase activity to modulate NMD.
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Affiliation(s)
- Ernesto Arias-Palomo
- Centro de Investigaciones Biológicas (CIB), Spanish National Research Council (Consejo Superior de Investigaciones Científicas, CSIC), 28040 Madrid, Spain
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47
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Chuang TW, Peng PJ, Tarn WY. The exon junction complex component Y14 modulates the activity of the methylosome in biogenesis of spliceosomal small nuclear ribonucleoproteins. J Biol Chem 2011; 286:8722-8. [PMID: 21209085 DOI: 10.1074/jbc.m110.190587] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The RNA-binding protein Y14 heterodimerizes with Mago as the core of the exon junction complex during precursor mRNA splicing and plays a role in mRNA surveillance in the cytoplasm. Using the Y14/Magoh heterodimer as bait in a screening for its interacting partners, we identified the protein-arginine methyltransferase PRMT5 as a candidate. We show that Y14 and Magoh, but not other factors of the exon junction complex, interact with the cytoplasmic PRMT5-containing methylosome. We further provide evidence that Y14 promoted the activity of PRMT5 in methylation of Sm proteins of the small nuclear ribonucleoprotein core, whereas knockdown of Y14 reduced their methylation level. Moreover, Y14 overexpression induced the formation of a large, active, and small nuclear ribonucleoprotein (snRNP)-associated methylosome complex. However, Y14 may only transiently associate with the snRNP assembly complex in the cytoplasm. Together, our results suggest that Y14 facilitates Sm protein methylation probably by its activity in promoting the formation or stability of the methylosome-containing complex. We hypothesize that Y14 provides a regulatory link between pre-mRNA splicing and snRNP biogenesis.
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Affiliation(s)
- Tzu-Wei Chuang
- Institute of Biomedical Sciences, Academia Sinica, Taipei 11529, Taiwan
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48
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Kaláb P, Solc P, Motlík J. The role of RanGTP gradient in vertebrate oocyte maturation. Results Probl Cell Differ 2011; 53:235-67. [PMID: 21630149 DOI: 10.1007/978-3-642-19065-0_12] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The maturation of vertebrate oocyte into haploid gamete, the egg, consists of two specialized asymmetric cell divisions with no intervening S-phase. Ran GTPase has an essential role in relaying the active role of chromosomes in their own segregation by the meiotic process. In addition to its conserved role as a key regulator of macromolecular transport between nucleus and cytoplasm, Ran has important functions during cell division, including in mitotic spindle assembly and in the assembly of nuclear envelope at the exit from mitosis. The cellular functions of Ran are mediated by RanGTP interactions with nuclear transport receptors (NTRs) related to importin β and depend on the existence of chromosome-centered RanGTP gradient. Live imaging with FRET biosensors indeed revealed the existence of RanGTP gradient throughout mouse oocyte maturation. NTR-dependent transport of cell cycle regulators including cyclin B1, Wee2, and Cdc25B between the oocyte cytoplasm and germinal vesicle (GV) is required for normal resumption of meiosis. After GVBD in mouse oocytes, RanGTP gradient is required for timely meiosis I (MI) spindle assembly and provides long-range signal directing egg cortex differentiation. However, RanGTP gradient is not required for MI spindle migration and may be dispensable for MI spindle function in chromosome segregation. In contrast, MII spindle assembly and function in maturing mouse and Xenopus laevis eggs depend on RanGTP gradient, similar to X. laevis MII-derived egg extracts.
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Affiliation(s)
- Petr Kaláb
- Laboratory of Cellular and Molecular Biology, National Cancer Institute, NIH, Bethesda, MD 20892-4256, USA.
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49
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Bono F, Gehring NH. Assembly, disassembly and recycling: the dynamics of exon junction complexes. RNA Biol 2011; 8:24-9. [PMID: 21289489 DOI: 10.4161/rna.8.1.13618] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Efficient gene expression requires that, during their lifetime, mRNAs associate with different sets of RNA binding proteins to form messenger ribonucleoprotein particles (mRNPs). The protein components of mRNPs are essential for the correct post-transcriptional function and regulation of mRNAs. mRNPs are constitutively remodeled during the maturation of the mRNA in the nucleus and downstream steps in the cytoplasm, and can also change depending on the cellular environment. Here we review the current understanding of the biochemical and structural aspects of a central mRNP component and regulator, the exon junction complex (EJC).
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Affiliation(s)
- Fulvia Bono
- Max-Planck-Institute for Developmental Biology, Tübingen, Germany.
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50
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Structure of Importin13-Ubc9 complex: nuclear import and release of a key regulator of sumoylation. EMBO J 2010; 30:427-38. [PMID: 21139563 DOI: 10.1038/emboj.2010.320] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2010] [Accepted: 11/10/2010] [Indexed: 01/09/2023] Open
Abstract
Importin13 (Imp13) is an unusual β-karyopherin that is able to both import and export cargoes in and out of the nucleus. In the cytoplasm, Imp13 associates with different cargoes such as Mago-Y14 and Ubc9, and facilitates their import into the nucleus where RanGTP binding promotes the release of the cargo. In this study, we present the 2.8 Å resolution crystal structure of Imp13 in complex with the SUMO E2-conjugating enzyme, Ubc9. The structure shows an uncommon mode of cargo-karyopherin recognition with Ubc9 binding at the N-terminal portion of Imp13, occupying the entire RanGTP-binding site. Comparison of the Imp13-Ubc9 complex with Imp13-Mago-Y14 shows the remarkable plasticity of Imp13, whose conformation changes from a closed ring to an open superhelix when bound to the two different cargoes. The structure also shows that the binding mode is compatible with the sumoylated states of Ubc9. Indeed, we find that Imp13 is able to bind sumoylated Ubc9 in vitro and suppresses autosumoylation activity in the complex.
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