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Wang J, Hsu Y, Lee Y, Lin N. Importin α2 participates in RNA interference against bamboo mosaic virus accumulation in Nicotiana benthamiana via NbAGO10a-mediated small RNA clearance. Mol Plant Pathol 2024; 25:e13422. [PMID: 38279848 PMCID: PMC10799208 DOI: 10.1111/mpp.13422] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/27/2023] [Revised: 12/20/2023] [Accepted: 12/21/2023] [Indexed: 01/29/2024]
Abstract
Karyopherins, the nucleocytoplasmic transporters, participate in multiple RNA silencing stages by transporting associated proteins into the nucleus. Importin α is a member of karyopherins and has been reported to facilitate virus infection via nuclear import of viral proteins. Unlike other RNA viruses, silencing of importin α2 (α2i) by virus-induced gene silencing (VIGS) boosted the titre of bamboo mosaic virus (BaMV) in protoplasts, and inoculated and systemic leaves of Nicotiana benthamiana. The enhanced BaMV accumulation in importin α2i plants was linked to reduced levels of RDR6-dependent secondary virus-derived small-interfering RNAs (vsiRNAs). Small RNA-seq revealed importin α2 silencing did not affect the abundance of siRNAs derived from host mRNAs but significantly reduced the 21 and 22 nucleotide vsiRNAs in BaMV-infected plants. Deletion of BaMV TGBp1, an RNA silencing suppressor, compromised importin α2i-mediated BaMV enhancement. Moreover, silencing of importin α2 upregulated NbAGO10a, a proviral protein recruited by TGBp1 for BaMV vsiRNAs clearance, but hindered the nuclear import of NbAGO10a. Taken together, these results indicate that importin α2 acts as a negative regulator of BaMV invasion by controlling the expression and nucleocytoplasmic shuttling of NbAGO10a, which removes vsiRNAs via the TGBp1-NbAGO10a-SDN1 pathway. Our findings reveal the hidden antiviral mechanism of importin α2 in countering BaMV infection in N. benthamiana.
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Affiliation(s)
- Jiun‐Da Wang
- Institute of Plant and Microbial BiologyAcademia SinicaTaipeiTaiwan
| | - Yau‐Heiu Hsu
- Graduate Institute of BiotechnologyNational Chung Hsing UniversityTaichungTaiwan
| | - Yun‐Shien Lee
- Department of BiotechnologyMing Chuan UniversityTaipeiTaiwan
| | - Na‐Sheng Lin
- Institute of Plant and Microbial BiologyAcademia SinicaTaipeiTaiwan
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2
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Liu Z, Jin D, Wei X, Gao Y, Gao X, Li X, Wang X, Wei P, Liu T. ZBTB34 is a hepatocellular carcinoma-associated protein with a monopartite nuclear localization signal. Aging (Albany NY) 2023; 15:8487-8500. [PMID: 37650557 PMCID: PMC10496988 DOI: 10.18632/aging.204987] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2023] [Accepted: 07/18/2023] [Indexed: 09/01/2023]
Abstract
ZBTB34 is a novel zinc finger protein with an unknown function. In this study, the gene expression and survival prognosis of ZBTB34 were analyzed across tumors based on the TCGA datasets. According to the bioinformatics analysis and qPCR results, liver hepatocellular carcinomas exhibit a high level of ZBTB34 expression. Additionally, the experiment supported the bioinformatics analysis findings that ZBTB34 expression was regulated by miR-125b-5p and that ZBTB34 affected ZBTB10, POLR1B, and AUH expression in HepG2 cells. Biological software analysis further revealed that ZBTB34 contains a monopartite nuclear localization signal (NLS). Arginine and lysine inside the putative NLS were substituted using the alanine-scanning mutagenesis method. The findings showed that the ability of ZBTB34 to enter the nucleus was abolished by the alanine substitution of the sequence 320RGGRARQKRA329 and the mutation of Lys327 and Arg328 residues. ZBTB34 was co-immunoprecipitated with importin α1, importin α3, importin α4, and importin β1, according to the results of the co-immunoprecipitation assay. In conclusion, ZBTB34 is a hepatocellular carcinoma-associated protein with a monopartite NLS. The nuclear import of ZBTB34 is mediated by importin α1, importin α3, importin α4, and importin β1. ZBTB34 performs its biological functions via a putative miR-125b-5p/ZBTB34/(ZBTB10, POLR1B, and AUH) signaling axis in HepG2 cells.
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Affiliation(s)
- Zheng Liu
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
- Guihang Guiyang Hospital Affiliated to Zunyi Medical University, Guiyang 550027, Guizhou, China
| | - Di Jin
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Xinran Wei
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Yue Gao
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Xiaodie Gao
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Xia Li
- Clinical Laboratory, Hospital Affiliated to Guilin Medical University, Guilin 541001, Guangxi, China
| | - Xiujuan Wang
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Pingying Wei
- College of Medical Laboratory Science, Guilin Medical University, Guilin 541004, Guangxi, China
| | - Tao Liu
- Guihang Guiyang Hospital Affiliated to Zunyi Medical University, Guiyang 550027, Guizhou, China
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3
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Doll SG, Meshkin H, Bryer AJ, Li F, Ko YH, Lokareddy RK, Gillilan RE, Gupta K, Perilla JR, Cingolani G. Recognition of the TDP-43 nuclear localization signal by importin α1/β. Cell Rep 2022; 39:111007. [PMID: 35767952 PMCID: PMC9290431 DOI: 10.1016/j.celrep.2022.111007] [Citation(s) in RCA: 23] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2021] [Revised: 03/31/2022] [Accepted: 06/06/2022] [Indexed: 11/27/2022] Open
Abstract
Cytoplasmic mislocalization of the TAR-DNA binding protein of 43 kDa (TDP-43) leads to large, insoluble aggregates that are a hallmark of amyotrophic lateral sclerosis and frontotemporal dementia. Here, we study how importin α1/β recognizes TDP-43 bipartite nuclear localization signal (NLS). We find that the NLS makes extensive contacts with importin α1, especially at the minor NLS-binding site. NLS binding results in steric clashes with the C terminus of importin α1 that disrupts the TDP-43 N-terminal domain (NTD) dimerization interface. A putative phosphorylation site in the proximity of TDP-43 R83 at the minor NLS site destabilizes binding to importins by reducing the NLS backbone dynamics. Based on these data, we explain the pathogenic role of several post-translational modifications and mutations in the proximity of TDP-43 minor NLS site that are linked to disease and shed light on the chaperone activity of importin α1/β.
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Affiliation(s)
- Steven G Doll
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA
| | - Hamed Meshkin
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
| | - Alexander J Bryer
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
| | - Fenglin Li
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA
| | - Ying-Hui Ko
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA
| | - Ravi K Lokareddy
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA
| | - Richard E Gillilan
- Macromolecular Diffraction Facility, Cornell High Energy Synchrotron Source (MacCHESS), Cornell University, 161 Synchrotron Drive, Ithaca, NY 14853, USA
| | - Kushol Gupta
- Department of Biochemistry and Biophysics, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, USA
| | - Juan R Perilla
- Department of Chemistry and Biochemistry, University of Delaware, Newark, DE 19716, USA
| | - Gino Cingolani
- Department of Biochemistry and Molecular Biology, Thomas Jefferson University, 1020 Locust St., Philadelphia, PA 19107, USA.
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4
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Zheng H, Ma L, Gui R, Lin X, Ke X, Jian X, Ye C, Chen Q. G Protein Subunit β1 Facilitates Influenza A Virus Replication by Promoting the Nuclear Import of PB2. J Virol 2022;:e0049422. [PMID: 35604143 DOI: 10.1128/jvi.00494-22] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
G protein subunit β1 (GNB1), the beta subunit of the G protein family, plays an important role in regulating transmembrane signal transduction. Although a recent study has demonstrated that GNB1 can bind the matrix protein 1 (M1) to facilitate M1 transport to budding sites and promote the release of progeny influenza A virus (IAV), whether the GNB1 protein has other functions in IAV replication requires further study. Here, we found that GNB1 promoted IAV replication, as virus yield decreased in GNB1 knockdown or knockout cells. GNB1 interacted with polymerase subunits PB2, PB1, and PA. Overexpressed GNB1 facilitated PB2 binding to importin α3, α5, and α7 promoting the nuclear import of PB2, enhancing viral RNA synthesis and polymerase activity. Altogether, our results demonstrated that GNB1 positively regulates virus replication by interacting with polymerase subunits and facilitating the nuclear import of PB2, which provide novel insights into the molecular mechanism of IAV. IMPORTANCE Until now, there has been only one article on the role of GNB1 in IAV budding. No study has investigated the role of GNB1 in IAV replication. In this study, our research demonstrated that GNB1 could increase the interaction between PB2 and the importin α isoform and mediate the nuclear import of PB2. Therefore, GNB1 could promote viral replication and transcription. Our results provide a better understanding of the molecular mechanisms of viral replication and provide potential antiviral drug targets.
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Jibiki K, Kodama TS, Suenaga A, Kawase Y, Shibazaki N, Nomoto S, Nagasawa S, Nagashima M, Shimodan S, Kikuchi R, Okayasu M, Takashita R, Mehmood R, Saitoh N, Yoneda Y, Akagi KI, Yasuhara N. Importin α2 association with chromatin: Direct DNA binding via a novel DNA-binding domain. Genes Cells 2021; 26:945-966. [PMID: 34519142 DOI: 10.1111/gtc.12896] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2021] [Revised: 09/10/2021] [Accepted: 09/11/2021] [Indexed: 12/18/2022]
Abstract
The nuclear transport of proteins is important for facilitating appropriate nuclear functions. The importin α family proteins play key roles in nuclear transport as transport receptors for copious nuclear proteins. Additionally, these proteins possess other functions, including chromatin association and gene regulation. However, these nontransport functions of importin α are not yet fully understood, especially their molecular-level mechanisms and consequences for functioning with chromatin. Here, we report the novel molecular characteristics of importin α binding to diverse DNA sequences in chromatin. We newly identified and characterized a DNA-binding domain-the Nucleic Acid Associating Trolley pole domain (NAAT domain)-in the N-terminal region of importin α within the conventional importin β binding (IBB) domain that is necessary for nuclear transport of cargo proteins. Furthermore, we found that the DNA binding of importin α synergistically coupled the recruitment of its cargo protein to DNA. This is the first study to delineate the interaction between importin α and chromatin DNA via the NAAT domain, indicating the bifunctionality of the importin α N-terminal region for nuclear transport and chromatin association.
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Affiliation(s)
- Kazuya Jibiki
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan
| | - Takashi S Kodama
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), Osaka, Japan
| | - Atsushi Suenaga
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan.,Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Yota Kawase
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan
| | - Noriko Shibazaki
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Shin Nomoto
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan
| | - Seiya Nagasawa
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Misaki Nagashima
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Shieri Shimodan
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Renan Kikuchi
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Mina Okayasu
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Ruka Takashita
- Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
| | - Rashid Mehmood
- Department of Life Sciences, College of Science and General Studies, Alfaisal University, Riyadh, Saudi Arabia
| | - Noriko Saitoh
- Division of Cancer Biology, The Cancer Institute of JFCR, Tokyo, Japan
| | - Yoshihiro Yoneda
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), Osaka, Japan
| | - Ken-Ichi Akagi
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), Osaka, Japan.,Environmental Metabolic Analysis Research Team, RIKEN Center for Sustainable Resource Science, Yokohama, Japan
| | - Noriko Yasuhara
- Graduate School of Integrated Basic Sciences, Nihon University, Tokyo, Japan.,Department of Biosciences, College of Humanities and Sciences, Nihon University, Tokyo, Japan
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Ma Y, Lu H, Wang W, Zhu J, Zhao W, Cui F. Membrane association of importin α facilitates viral entry into salivary gland cells of vector insects. Proc Natl Acad Sci U S A 2021; 118:e2103393118. [PMID: 34290144 DOI: 10.1073/pnas.2103393118] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The importin α family belongs to the conserved nuclear transport pathway in eukaryotes. However, the biological functions of importin α in the plasma membrane are still elusive. Here, we report that importin α, as a plasma membrane-associated protein, is exploited by the rice stripe virus (RSV) to enter vector insect cells, especially salivary gland cells. When the expression of three importin α genes was simultaneously knocked down, few virions entered the salivary glands of the small brown planthopper, Laodelphax striatellus Through hemocoel inoculation of virions, only importin α2 was found to efficiently regulate viral entry into insect salivary-gland cells. Importin α2 bound the nucleocapsid protein of RSV with a relatively high affinity through its importin β-binding (IBB) domain, with a dissociation constant K D of 9.1 μM. Furthermore, importin α2 and its IBB domain showed a distinct distribution in the plasma membrane through binding to heparin in heparan sulfate proteoglycan. When the expression of importin α2 was knocked down in viruliferous planthoppers or in nonviruliferous planthoppers before they acquired virions, the viral transmission efficiency of the vector insects in terms of the viral amount and disease incidence in rice was dramatically decreased. These findings not only reveal the specific function of the importin α family in the plasma membrane utilized by viruses, but also provide a promising target gene in vector insects for manipulation to efficiently control outbreaks of rice stripe disease.
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7
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Zhao W, Zhu J, Lu H, Zhu J, Jiang F, Wang W, Luo L, Kang L, Cui F. The nucleocapsid protein of rice stripe virus in cell nuclei of vector insect regulates viral replication. Protein Cell 2021; 13:360-378. [PMID: 33675514 PMCID: PMC7936609 DOI: 10.1007/s13238-021-00822-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2020] [Accepted: 01/08/2021] [Indexed: 01/05/2023] Open
Abstract
Rice stripe virus (RSV) transmitted by the small brown planthopper causes severe rice yield losses in Asian countries. Although viral nuclear entry promotes viral replication in host cells, whether this phenomenon occurs in vector cells remains unknown. Therefore, in this study, we systematically evaluated the presence and roles of RSV in the nuclei of vector insect cells. We observed that the nucleocapsid protein (NP) and viral genomic RNAs were partially transported into vector cell nuclei by utilizing the importin α nuclear transport system. When blocking NP nuclear localization, cytoplasmic RSV accumulation significantly increased. In the vector cell nuclei, NP bound the transcription factor YY1 and affected its positive regulation to FAIM. Subsequently, decreased FAIM expression triggered an antiviral caspase-dependent apoptotic reaction. Our results reveal that viral nuclear entry induces completely different immune effects in vector and host cells, providing new insights into the balance between viral load and the immunity pressure in vector insects.
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Affiliation(s)
- Wan Zhao
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Junjie Zhu
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Hong Lu
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Jiaming Zhu
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Fei Jiang
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Wei Wang
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Lan Luo
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Le Kang
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China
| | - Feng Cui
- State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing, 100101, China.
- CAS Center for Excellence in Biotic Interactions, University of Chinese Academy of Sciences, Beijing, 100049, China.
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8
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Liu Y, Wang Y, Wang F, Pan J, Xu J, Li J, Zhou C, Ding G, Wu Y, Liu X, Sheng J, Huang H. Mechanism underlying the retarded nuclear translocation of androgen receptor splice variants. Sci China Life Sci 2019; 62:257-67. [PMID: 30267260 DOI: 10.1007/s11427-018-9379-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/14/2018] [Accepted: 08/14/2018] [Indexed: 12/25/2022]
Abstract
As shown in our previous study, two alternatively spliced androgen receptor (AR) variants, which are exclusively expressed in the granulosa cells of patients with polycystic ovary syndrome, exhibit retarded nuclear translocation compared with wild-type AR. However, researchers have not yet determined whether these abnormalities correlate with heat shock protein 90 (HSP90) and importin α (the former is a generally accepted co-chaperone of AR, and the latter is a component of classical nuclear import complexes). Here, these two variants were mainly retained in cytoplasm with HSP90 and importin α in the presence of dihydrotestosterone (DHT), and their levels in nucleus were significantly reduced, according to the immunofluorescence staining. The binding affinity of two AR variants for importin α was consistently decreased, while it was increased in WT-AR following DHT stimulation, leading to reduced nuclear import, particularly for the insertion-AR (Ins-AR). However, the binding affinities of two AR variants for HSP90 were increased in the absence of DHT compared with WT-AR, which functioned to maintain spatial structural stability, particularly for the deletion-AR (Del-AR). Therefore, the retarded nuclear translocation of two AR variants is associated with HSP90 and importin α, and the abnormal binding affinities for them play critical roles in this process.
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Kirby TW, Pedersen LC, Gabel SA, Gassman NR, London RE. Variations in nuclear localization strategies among pol X family enzymes. Traffic 2018; 19:10.1111/tra.12600. [PMID: 29931796 PMCID: PMC6684861 DOI: 10.1111/tra.12600] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/17/2017] [Revised: 06/19/2018] [Accepted: 06/20/2018] [Indexed: 12/22/2022]
Abstract
Despite the essential roles of pol X family enzymes in DNA repair, information about the structural basis of their nuclear import is limited. Recent studies revealed the unexpected presence of a functional nuclear localization signal (NLS) in DNA polymerase β, indicating the importance of active nuclear targeting, even for enzymes likely to leak into and out of the nucleus. The current studies further explore the active nuclear transport of these enzymes by identifying and structurally characterizing the functional NLS sequences in the three remaining human pol X enzymes: terminal deoxynucleotidyl transferase (TdT), DNA polymerase mu (pol μ) and DNA polymerase lambda (pol λ). NLS identifications are based on Importin α (Impα) binding affinity determined by fluorescence polarization of fluorescein-labeled NLS peptides, X-ray crystallographic analysis of the Impα∆IBB•NLS complexes and fluorescence-based subcellular localization studies. All three polymerases use NLS sequences located near their N-terminus; TdT and pol μ utilize monopartite NLS sequences, while pol λ utilizes a bipartite sequence, unique among the pol X family members. The pol μ NLS has relatively weak measured affinity for Impα, due in part to its proximity to the N-terminus that limits non-specific interactions of flanking residues preceding the NLS. However, this effect is partially mitigated by an N-terminal sequence unsupportive of Met1 removal by methionine aminopeptidase, leading to a 3-fold increase in affinity when the N-terminal methionine is present. Nuclear targeting is unique to each pol X family enzyme with variations dependent on the structure and unique functional role of each polymerase.
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Affiliation(s)
- Thomas W Kirby
- National Institute of Environmental Health Sciences, Genome Integrity and Structural Biology Laboratory, National Institutes of Health, Research Triangle Park, North Carolina
| | - Lars C Pedersen
- National Institute of Environmental Health Sciences, Genome Integrity and Structural Biology Laboratory, National Institutes of Health, Research Triangle Park, North Carolina
| | - Scott A Gabel
- National Institute of Environmental Health Sciences, Genome Integrity and Structural Biology Laboratory, National Institutes of Health, Research Triangle Park, North Carolina
| | - Natalie R Gassman
- Molecular & Metabolic Oncology, University of South Alabama Mitchell Cancer Institute, Mobile, Alabama
| | - Robert E London
- National Institute of Environmental Health Sciences, Genome Integrity and Structural Biology Laboratory, National Institutes of Health, Research Triangle Park, North Carolina
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Abstract
Nucleocytoplasmic transport is an essential process in eukaryotes. The molecular mechanisms underlying nuclear transport that involve the nuclear transport receptor, small GTPase Ran, and the nuclear pore complex are highly conserved from yeast to humans. On the other hand, it has become clear that the nuclear transport system diverged during evolution to achieve various physiological functions in multicellular eukaryotes. In this review, we first summarize the molecular mechanisms of nuclear transport and how these were elucidated. Then, we focus on the diverse functions of importin α, which acts not merely an import factor but also as a multi-functional protein contributing to a variety of cellular functions in higher eukaryotes.
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Affiliation(s)
- Masahiro OKA
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), Osaka, Japan
| | - Yoshihiro YONEDA
- National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), Osaka, Japan
- Correspondence should be addressed: Y. Yoneda, National Institutes of Biomedical Innovation, Health and Nutrition (NIBIOHN), 7-6-8 Saito-Asagi, Ibaraki, Osaka 567-0085, Japan (e-mail: )
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11
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Okuyama T, Yamagishi R, Shimada J, Ikeda M, Maruoka Y, Kaneko H. Structural and mechanistic insights into nuclear transport and delivery of the critical pluripotency factor Oct4 to DNA. J Biomol Struct Dyn 2017; 36:767-778. [PMID: 28166455 DOI: 10.1080/07391102.2017.1289124] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/20/2022]
Abstract
Oct4 is a master regulator of the induction and maintenance of cellular pluripotency, and has crucial roles in early stages of differentiation. It is the only factor that cannot be substituted by other members of the same protein family to induce pluripotency. However, although Oct4 nuclear transport and delivery to target DNA are critical events for reprogramming to pluripotency, little is known about the molecular mechanism. Oct4 is imported to the nucleus by the classical nuclear transport mechanism, which requires importin α as an adaptor to bind the nuclear localization signal (NLS). Although there are structures of complexes of the NLS of transcription factors (TFs) in complex with importin α, there are no structures available for complexes involving intact TFs. We have therefore modeled the structure of the complex of the whole Oct4 POU domain and importin α2 using protein-protein docking and molecular dynamics. The model explains how the Ebola virus VP24 protein has a negative effect on the nuclear import of STAT1 by importin α but not on Oct4, and how Nup 50 facilitates cargo release from importin α. The model demonstrates the structural differences between the Oct4 importin α bound and DNA bound crystal states. We propose that the 'expanded linker' between the two DNA-binding domains of Oct4 is an intrinsically disordered region and that its conformational changes have a key role in the recognition/binding to both DNA and importin α. Moreover, we propose that this structural change enables efficient delivery to DNA after release from importin α.
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Affiliation(s)
- Takahide Okuyama
- a Graduate School of Integrated Basic Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550 , Japan
| | - Ryosuke Yamagishi
- b Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya, Tokyo 156-8550 , Japan.,c National Institutes of Biomedical Innovation, Health and Nutrition , 7-6-8 Saito-Asagi, Ibaraki, Osaka 675-0085 , Japan
| | - Jiro Shimada
- b Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya, Tokyo 156-8550 , Japan
| | - Masaaki Ikeda
- b Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya, Tokyo 156-8550 , Japan
| | - Yayoi Maruoka
- b Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya, Tokyo 156-8550 , Japan
| | - Hiroki Kaneko
- a Graduate School of Integrated Basic Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya-ku, Tokyo 156-8550 , Japan.,b Department of Integrated Sciences in Physics and Biology, College of Humanities and Sciences , Nihon University , 3-25-40 Sakurajousui, Setagaya, Tokyo 156-8550 , Japan.,c National Institutes of Biomedical Innovation, Health and Nutrition , 7-6-8 Saito-Asagi, Ibaraki, Osaka 675-0085 , Japan
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Sankhala RS, Lokareddy RK, Cingolani G. Divergent Evolution of Nuclear Localization Signal Sequences in Herpesvirus Terminase Subunits. J Biol Chem 2016; 291:11420-33. [PMID: 27033706 DOI: 10.1074/jbc.m116.724393] [Citation(s) in RCA: 21] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2016] [Indexed: 11/06/2022] Open
Abstract
The tripartite terminase complex of herpesviruses assembles in the cytoplasm of infected cells and exploits the host nuclear import machinery to gain access to the nucleus, where capsid assembly and genome-packaging occur. Here we analyzed the structure and conservation of nuclear localization signal (NLS) sequences previously identified in herpes simplex virus 1 (HSV-1) large terminase and human cytomegalovirus (HCMV) small terminase. We found a monopartite NLS at the N terminus of large terminase, flanking the ATPase domain, that is conserved only in α-herpesviruses. In contrast, small terminase exposes a classical NLS at the far C terminus of its helical structure that is conserved only in two genera of the β-subfamily and absent in α- and γ-herpesviruses. In addition, we predicted a classical NLS in the third terminase subunit that is partially conserved among herpesviruses. Bioinformatic analysis revealed that both location and potency of NLSs in terminase subunits evolved more rapidly than the rest of the amino acid sequence despite the selective pressure to keep terminase gene products active and localized in the nucleus. We propose that swapping NLSs among terminase subunits is a regulatory mechanism that allows different herpesviruses to regulate the kinetics of terminase nuclear import, reflecting a mechanism of virus:host adaptation.
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Affiliation(s)
- Rajeshwer S Sankhala
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 and
| | - Ravi K Lokareddy
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 and
| | - Gino Cingolani
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107 and Institute of Biomembranes and Bioenergetics, National Research Council, Via Amendola 165/A, 70126 Bari, Italy
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Tsujii A, Miyamoto Y, Moriyama T, Tsuchiya Y, Obuse C, Mizuguchi K, Oka M, Yoneda Y. Retinoblastoma-binding Protein 4-regulated Classical Nuclear Transport Is Involved in Cellular Senescence. J Biol Chem 2015; 290:29375-88. [PMID: 26491019 DOI: 10.1074/jbc.m115.681908] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/28/2015] [Indexed: 12/19/2022] Open
Abstract
Nucleocytoplasmic trafficking is a fundamental cellular process in eukaryotic cells. Here, we demonstrated that retinoblastoma-binding protein 4 (RBBP4) functions as a novel regulatory factor to increase the efficiency of importin α/β-mediated nuclear import. RBBP4 accelerates the release of importin β1 from importin α via competitive binding to the importin β-binding domain of importin α in the presence of RanGTP. Therefore, it facilitates importin α/β-mediated nuclear import. We showed that the importin α/β pathway is down-regulated in replicative senescent cells, concomitant with a decrease in RBBP4 level. Knockdown of RBBP4 caused both suppression of nuclear transport and induction of cellular senescence. This is the first report to identify a factor that competes with importin β1 to bind to importin α, and it demonstrates that the loss of this factor can trigger cellular senescence.
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Affiliation(s)
- Akira Tsujii
- From the Graduate School of Medicine and the Laboratories of Nuclear Transport Dynamics and
| | | | | | | | - Chikashi Obuse
- the Graduate School of Life Science, Hokkaido University, Sapporo, Hokkaido 001-0021, Japan
| | | | - Masahiro Oka
- the Laboratories of Nuclear Transport Dynamics and Laboratory of Biomedical Innovation, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565-0871,
| | - Yoshihiro Yoneda
- Laboratory of Biomedical Innovation, Graduate School of Pharmaceutical Sciences, Osaka University, Suita, Osaka 565-0871, National Institutes of Biomedical Innovation, Health and Nutrition, Ibaraki, Osaka 567-0085, and
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14
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Deng S, Zhou Y, Ouyang D, Xiong J, Zhang L, Tu C, Zhang K, Song Z, Zhang F. The effect of dexamethasone on lentiviral vector infection is associated with importin α. Biomed Rep 2013; 2:137-141. [PMID: 24649085 DOI: 10.3892/br.2013.194] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2013] [Accepted: 10/30/2013] [Indexed: 02/02/2023] Open
Abstract
Importin α (Imα) plays an important role during the shuttling of the HIV-1 preintegration complex (PIC) from the cytoplasm to the nucleus. Imα may bind to the glucocorticoid receptor (GR), which is localized to nucleus following hormone binding. However, it remains unclear whether the binding of dexamethasone (Dex) to GR affects the Imα redistribution and, thus, alters PIC import. In our study, 293T cells were transfected with the lentiviral vector (LV) carrying the luciferase (Luci) gene following Dex or RU486 pretreatment. The Luci activity (LucA) in the Dex or RU486 group was significantly higher compared to that in the control group (P≤0.01). The effects of Dex and RU486 were inhibited by the Imα inhibitor Bimax1 (P≤0.01), although the inhibitory effect of Bimax1 was alleviated by increasing the Dex dose. Furthermore, it was observed that the LucA in the 30-min Dex treatment group was lower compared to that in the 30-min Dex pretreatment group (P≤0.01). These results suggested that Dex may improve PIC import via increasing the cytoplasmic Imα levels. Kunming mice were transfected in vivo with the LV, either 30 min or 15 h following an intraperitoneal injection of Dex. The LucA in the liver of the 30-min group mice was significantly lower compared to that of the 15-h group mice (P≤0.01), suggesting that the effect of Dex on LV infection depends mainly on the suppression of immune and inflammatory responses in vivo. Taken together, our data indicated that the effect of Dex on LV infection may be associated with Imα, constituting a novel signaling pathway mediating the effects of Dex on HIV-1 infection.
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Affiliation(s)
- Shengchang Deng
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Ying Zhou
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Dong Ouyang
- Jiangxi Police College, Nanchang, Jiangxi 330103, P.R. China
| | - Junping Xiong
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Lei Zhang
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Changchun Tu
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Keping Zhang
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
| | - Zengliang Song
- Department of Neurosurgery, The Third People's Hospital of Nanchang, Nanchang, Jiangxi 330009, P.R. China
| | - Fanglin Zhang
- School of Medicine, Nanchang University, Nanchang, Jiangxi 330006, P.R. China
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15
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Liang P, Zhang H, Wang G, Li S, Cong S, Luo Y, Zhang B. KPNB1, XPO7 and IPO8 mediate the translocation ofNF-κB/p65 into the nucleus. Traffic 2013; 14:1132-43. [PMID: 23906023 DOI: 10.1111/tra.12097] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2012] [Revised: 07/30/2013] [Accepted: 08/01/2013] [Indexed: 12/25/2022]
Abstract
NF-κB/p65 is retained in the cytoplasm until it is activated in response to stress. Nuclear import of p65 is regulated by importin α in a nuclear localization signal (NLS)-dependent manner. However, the role of importin β family members in the nuclear translocation of p65 is largely unclear. In this study, using high-content siRNA screening, we identified three of 17 importin β family members that are involved in the nuclear import of p65. Our data showed that knockdown of KPNB1, XPO7 and IPO8 reduced the amount of nuclear p65 following tumor necrosis factor-α (TNF-α) stimulation, resulting in lower NF-κB activity. KPNB1 was the major importin β receptor for p65 import, and this import was dependent on the NLS of p65. However, NLS-mutated p65 still entered the nucleus and bound to XPO7 and IPO8. Interestingly, among the six members of the importin α family, KPNA2 was most important for p65 import. Taken together, our results show that the import of p65 mainly relies on the canonical KPNA2/KPNB1 pathway; however, p65 is also imported by an alternative pathway that is independent of its NLS. Redundant importin receptors are likely to maintain the important function of p65 according to need.
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Affiliation(s)
- Peizhou Liang
- State Key Laboratory of Respiratory Diseases, Guangzhou Institutes of Biomedicine and Health, Chinese Academy of Sciences, 190 Kaiyuan Avenue, Guangzhou , 510530, China
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16
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Luo Y, Wang Z, Tian L, Li X. The function of importin β1 is conserved in eukaryotes but the substrates may vary in organisms. Plant Signal Behav 2013; 8:25106. [PMID: 23733071 PMCID: PMC3999071 DOI: 10.4161/psb.25106] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Accepted: 05/21/2013] [Indexed: 06/02/2023]
Abstract
Importin β1 is the nuclear-cytoplasmic transport receptor in eukaryotic cells. Its main function is to transport NLS (nuclear localization signal)-containing proteins from cytoplasm to nucleus. Our recent study found that AtKPNB1, a homolog of the human KPNB1, is an essential component of the classical nuclear import of the NLS-containing proteins in Arabidopsis and modulates plant development and ABA-mediated stress response. Human KPNB1 can also directly transport the nuclear proteins, such as ribosomal protein RPS7e, without the intervention of importin α proteins. However, we found that AtKPNB1 does not directly recognize and import the human RPS7e homologous proteins AtRPS7A, AtRPS7B and AtRPS7C into the nucleus like human KPNB1. These findings suggest that the importin β1 protein has the conserved function in translocating nuclear proteins to the nucleus, but their specific cargos may vary in different organisms.
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Affiliation(s)
- Yanjie Luo
- The State Key Laboratory of Plant Cell & Chromosome Engineering; Center of Agricultural Research Resources; Institute of Genetics and Developmental Biology
- Gradulate University of Chinese Academy of Sciences; Beijing, PR China
| | - Zhijuan Wang
- The State Key Laboratory of Plant Cell & Chromosome Engineering; Center of Agricultural Research Resources; Institute of Genetics and Developmental Biology
| | - Lining Tian
- Southern Crop Protection and Food Research Centre; Agriculture and Agri-Food Canada; London, ON Canada
- Department of Biology; Western University; London, ON Canada
| | - Xia Li
- The State Key Laboratory of Plant Cell & Chromosome Engineering; Center of Agricultural Research Resources; Institute of Genetics and Developmental Biology
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Abstract
Importin α is recognized as a classical nuclear localization signal (cNLS) receptor which mediates nucleocytoplasmic transport. However, it rapidly accumulates in the nucleus in response to cellular stresses, including oxidative stress, causing a blockade of the classical nuclear import pathway. We set out to determine whether importin α performs roles in the nucleus after cellular exposure to stresses and discovered that it can act directly to modulate gene expression. With remarkable selectivity, importin α2 can access the promoter of Serine/threonine kinase 35 (STK35) and increase the levels of this transcript without requirement for importin β1. The nuclear accumulation of importin α occurred following exposure to stresses which decreased intracellular ATP levels and was followed by non-apoptotic cell death. Hence the gene regulatory function of nuclear importin α can direct cell fate. There are now several reports of nuclear-localized importin α proteins in diverse cellular states, including cancer. Here we discuss the physiological significance of this novel functional capacity of nuclear importin α relationship to a variety of cellular states and fates.
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Wang X, Zhang Y, Xu J, Shi L, Fan H, Han C, Li D, Yu J. The R-rich motif of Beet black scorch virus P7a movement protein is important for the nuclear localization, nucleolar targeting and viral infectivity. Virus Res 2012; 167:207-18. [PMID: 22626884 PMCID: PMC7172424 DOI: 10.1016/j.virusres.2012.05.001] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/04/2011] [Revised: 05/01/2012] [Accepted: 05/06/2012] [Indexed: 01/07/2023]
Abstract
Beet black scorch virus (BBSV) encodes three movement proteins (P7a, P7b and P5') that facilitate its cell-to-cell movement. An arginine-rich motif of P7a N-terminus was found to determine nuclear and nucleolar localization. Amino acids substitution or deletion of the R-rich motif interfered with P7a nuclear and nucleolar localization. Bimolecular fluorescence complementation (BiFC) assays revealed that P7a protein interacted with Nicotiana benthamiana nuclear import factor importin α, suggesting that P7a is translocated into the nucleus by the classical importin α/β-dependent pathway. Moreover, P7a also interacted with the nucleolar protein fibrillarin. Mutations in the R-rich motif of P7a diminished P7a interactions with importin α and fibrillarin, influenced viral replication in Nicotiana benthamiana protoplasts and altered the symptom phenotype and viral RNA accumulation in Chenopodium amaranticolor plants. These results demonstrate that the R-rich motif of P7a is correlated with nuclear and nucleolar localization, viral replication and virus infection.
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Affiliation(s)
- Xiaohui Wang
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Yanjing Zhang
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Jin Xu
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Lindan Shi
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Huiyan Fan
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Chenggui Han
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Dawei Li
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
| | - Jialin Yu
- State Key Laboratory of Agro-Biotechnology, College of Biological Sciences, China Agricultural University, Beijing 100193, PR China
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19
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Lott K, Bhardwaj A, Sims PJ, Cingolani G. A minimal nuclear localization signal (NLS) in human phospholipid scramblase 4 that binds only the minor NLS-binding site of importin alpha1. J Biol Chem 2011; 286:28160-9. [PMID: 21690087 PMCID: PMC3151061 DOI: 10.1074/jbc.m111.228007] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2011] [Revised: 06/10/2011] [Indexed: 12/16/2022] Open
Abstract
Importin α1 can bind classical nuclear localization signals (NLSs) in two NLS-binding sites, known as "major" and "minor." The major site is located between ARM repeats 2-4, whereas the minor site spans ARM 7-8. In this study, we have characterized the cellular localization of human phospholipid scramblase 4 (hPLSCR4), a member of the phospholipid scramblase protein family. We identified a minimal NLS in hPLSCR4 ((273)GSIIRKWN(280)) that contains only two basic amino acids. This NLS is both necessary for nuclear localization of hPLSCR4 in transfected HeLa cells and sufficient for nuclear import of a non-diffusible cargo in permeabilized cells. Mutation of only one of the two basic residues, Arg(277), correlates with loss of nuclear localization, suggesting this amino acid plays a key role in nuclear transport. Crystallographic analysis of mammalian importin α1 in complex with the hPLSCR4-NLS reveals this minimal NLS binds specifically and exclusively to the minor binding site of importin α. These data provide the first structural and functional evidence of a novel NLS-binding mode in importin α1 that uses only the minor groove as the exclusive site for nuclear import of nonclassical cargos.
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Affiliation(s)
- Kaylen Lott
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
- the Department of Biochemistry and Molecular Biology, SUNY Upstate Medical University, Syracuse, New York 13210, and
| | - Anshul Bhardwaj
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
| | - Peter J. Sims
- the Department of Pathology and Laboratory Medicine, University of Rochester Medical Center, Rochester, New York 14642-8626
| | - Gino Cingolani
- From the Department of Biochemistry and Molecular Biology, Thomas Jefferson University, Philadelphia, Pennsylvania 19107
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20
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Kotera I, Sekimoto T, Miyamoto Y, Saiwaki T, Nagoshi E, Sakagami H, Kondo H, Yoneda Y. Importin alpha transports CaMKIV to the nucleus without utilizing importin beta. EMBO J 2005; 24:942-51. [PMID: 15719015 PMCID: PMC554133 DOI: 10.1038/sj.emboj.7600587] [Citation(s) in RCA: 75] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2004] [Accepted: 01/27/2005] [Indexed: 12/20/2022] Open
Abstract
Ca(2+)/calmodulin-dependent protein kinase type IV (CaMKIV) plays an essential role in the transcriptional activation of cAMP response element-binding protein-mediated signaling pathways. Although CaMKIV is localized predominantly in the nucleus, the molecular mechanism of the nuclear import of CaMKIV has not been elucidated. We report here that importin alpha is able to carry CaMKIV into the nucleus without the need for importin beta or any other soluble proteins in digitonin-permeabilized cells. An importin beta binding-deficient mutant (DeltaIBB) of importin alpha also carried CaMKIV into the nucleus, which strongly suggests that CaMKIV is transported in an importin beta-independent manner. While CaMKIV directly interacted with the C-terminal region of importin alpha, the CaMKIV/importin alpha complex did not form a ternary complex with importin beta, which explains the nonrequirement of importin beta for the nuclear transport of CaMKIV. The cytoplasmic microinjection of importin alpha-DeltaIBB enhanced the rate of nuclear translocation of CaMKIV in vivo. This is the first report to demonstrate definitely that mammalian importin alpha solely carries a cargo protein into the nucleus without utilizing the classical importin beta-dependent transport system.
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Affiliation(s)
- Ippei Kotera
- Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Toshihiro Sekimoto
- Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Yoichi Miyamoto
- Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
| | - Takuya Saiwaki
- Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Emi Nagoshi
- Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
| | - Hiroyuki Sakagami
- Department of Cell Biology, Graduate School of Medicine, Tohoku University, Aoba-ku, Sendai, Japan
| | - Hisatake Kondo
- Department of Cell Biology, Graduate School of Medicine, Tohoku University, Aoba-ku, Sendai, Japan
| | - Yoshihiro Yoneda
- Department of Cell Biology and Neuroscience, Graduate School of Medicine, Osaka University, Suita, Osaka, Japan
- Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, Suita, Osaka, Japan
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Herold A, Truant R, Wiegand H, Cullen BR. Determination of the functional domain organization of the importin alpha nuclear import factor. J Cell Biol 1998; 143:309-18. [PMID: 9786944 PMCID: PMC2132842 DOI: 10.1083/jcb.143.2.309] [Citation(s) in RCA: 108] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/1998] [Revised: 09/09/1998] [Indexed: 12/22/2022] Open
Abstract
Although importin alpha (Imp alpha) has been shown to act as the receptor for basic nuclear localization signals (NLSs) and to mediate their recruitment to the importin beta nuclear import factor, little is known about the functional domains present in Imp alpha, with the exception that importin beta binding is known to map close to the Imp alpha NH2 terminus. Here, we demonstrate that sequences essential for binding to the CAS nuclear export factor are located near the Imp alpha COOH terminus and include a critical acidic motif. Although point mutations introduced into this acidic motif inactivated both CAS binding and Imp alpha nuclear export, a putative leucine-rich nuclear export signal proved to be neither necessary nor sufficient for Imp alpha nuclear export. Analysis of sequences within Imp alpha that bind to the SV-40 T antigen NLS or to the similar LEF-1 NLS revealed that both NLSs interact with a subset of the eight degenerate armadillo (Arm) repeats that form the central part of Imp alpha. However, these two NLS-binding sites showed only minimal overlap, thus suggesting that the degeneracy of the Arm repeat region of Imp alpha may serve to facilitate binding to similar but nonidentical basic NLSs. Importantly, the SV-40 T NLS proved able to specifically inhibit the interaction of Imp alpha with CAS in vitro, thus explaining why the SV-40 T NLS is unable to also function as a nuclear export signal.
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Affiliation(s)
- A Herold
- Department of Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA
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