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Levin A, Hayouka Z, Friedler A, Loyter A. Nucleocytoplasmic shuttling of HIV-1 integrase is controlled by the viral Rev protein. Nucleus 2014. [DOI: 10.4161/nucl.11300] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
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2
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Kubo T, Yanagihara K, Sato Y, Morita Y, Seyama T. Enhancement of gene silencing effect and membrane permeability by Peptide-conjugated 27-nucleotide small interfering RNA. Molecules 2012; 17:11089-102. [PMID: 22983148 PMCID: PMC6268710 DOI: 10.3390/molecules170911089] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/29/2012] [Revised: 09/10/2012] [Accepted: 09/11/2012] [Indexed: 11/16/2022] Open
Abstract
Two different sizes of siRNAs, of which one type was 21-nucleotide (nt) siRNA containing 2-nt dangling ends and the other type was 27-nt siRNA with blunt ends, were conjugated with a nuclear export signal peptide of HIV-1 Rev at the 5'-sense end. Processing by Dicer enzyme, cell membrane permeability, and RNAi efficiency of the peptide-conjugated siRNAs were examined. Dicer cleaved the peptide-conjugated 27-nt siRNA leading to the release of 21-nt siRNA, whereas the peptide-conjugated 21-nt siRNA was not cleaved. High membrane permeability and cytoplasmic localization was found in the conjugates. Moreover, the peptide-conjugated 27-nt siRNA showed increased potency of RNAi in comparison with the nonmodified 21-nt and 27-nt siRNAs, whereas the peptide-conjugated 21-nt siRNA showed decreased RNAi efficacy. This potent RNAi efficacy is probably owing to acceleration of RISC through recognition by Dicer, as well as to the improvement of cell membrane permeability and intracellular accumulation.
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Affiliation(s)
- Takanori Kubo
- Faculty of Pharmacy, Yasuda Women’s University, 6-13-1 Yasuhigashi, Asaminami-ku, Hiroshima 731-0153, Japan; (Y.S.); (Y.M.); (T.S.)
- Author to whom correspondence should be addressed; ; Tel.: +81-82-878-9447; Fax: +81-82-878-9540
| | - Kazuyoshi Yanagihara
- Division of Genetics, National Cancer Center Research Institute, 5-1-1 Tsukiji, Chuo-ku, Tokyo 104-0045, Japan;
| | - Yuichiro Sato
- Faculty of Pharmacy, Yasuda Women’s University, 6-13-1 Yasuhigashi, Asaminami-ku, Hiroshima 731-0153, Japan; (Y.S.); (Y.M.); (T.S.)
| | - Yasuhiro Morita
- Faculty of Pharmacy, Yasuda Women’s University, 6-13-1 Yasuhigashi, Asaminami-ku, Hiroshima 731-0153, Japan; (Y.S.); (Y.M.); (T.S.)
| | - Toshio Seyama
- Faculty of Pharmacy, Yasuda Women’s University, 6-13-1 Yasuhigashi, Asaminami-ku, Hiroshima 731-0153, Japan; (Y.S.); (Y.M.); (T.S.)
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3
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Levin A, Hayouka Z, Friedler A, Loyter A. Nucleocytoplasmic shuttling of HIV-1 integrase is controlled by the viral Rev protein. Nucleus 2010; 1:190-201. [PMID: 21326951 PMCID: PMC3030695 DOI: 10.4161/nucl.1.2.11300] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/10/2009] [Revised: 01/13/2010] [Accepted: 01/14/2010] [Indexed: 01/21/2023] Open
Abstract
In the current study we show that the Rev protein of Human Immunodeficiency Virus type 1 (HIV-1) inhibits nuclear import and mediates nuclear export of the HIV-1 integrase (IN) protein, which catalyzes integration of the viral cDNA. Interaction between IN and Rev in virus infected cells, resulting in the formation of a Rev-IN complex, has been previously described by us. Here we show that nuclear import of the IN, is inhibited by early expressed Rev. No nuclear import of IN was observed when Rev-overexpressing cells were infected by wild-type HIV-1. Similarly, no translocation of IN into nuclei was observed in the presence of Rev-derived peptides. On the other hand, massive nuclear import was observed following infection by a ΔRev virus or in the presence of peptides that promote dissociation of the Rev-IN complex. Our results show that IN is only transiently present within the nuclei of infected cells. Treatment of infected cells with leptomycin B caused nuclear retention of the Rev-IN complex. Removal of the leptomycin from these treated cells resulted in nuclear export of both Rev and IN. On the other hand, disruption of the nuclear located Rev-IN complex resulted in export of only the Rev protein indicating Rev-mediated nuclear export of IN. Our results suggest the involvement of Rev in regulating the integration process by limiting the number of integration events per cell despite the presence of numerous copies of viral cDNA.
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Affiliation(s)
- Aviad Levin
- Department of Biological Chemistry; The Alexander Silberman Institute of Life Sciences
| | - Zvi Hayouka
- Institute of Chemistry; The Hebrew University of Jerusalem; Jerusalem, Israel
| | - Assaf Friedler
- Institute of Chemistry; The Hebrew University of Jerusalem; Jerusalem, Israel
| | - Abraham Loyter
- Department of Biological Chemistry; The Alexander Silberman Institute of Life Sciences
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4
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Dunn EF, Hammell CM, Hodge CA, Cole CN. Yeast poly(A)-binding protein, Pab1, and PAN, a poly(A) nuclease complex recruited by Pab1, connect mRNA biogenesis to export. Genes Dev 2005; 19:90-103. [PMID: 15630021 PMCID: PMC540228 DOI: 10.1101/gad.1267005] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2004] [Accepted: 11/02/2004] [Indexed: 11/25/2022]
Abstract
In eukaryotic cells, pre-mRNAs undergo extensive processing in the nucleus prior to export. Processing is subject to a quality-control mechanism that retains improperly processed transcripts at or near sites of transcription. A poly(A) tail added by the normal 3'-processing machinery is necessary but not sufficient for export. Retention depends on the exosome. In this study, we identify the poly(A)-binding protein, Pab1, and the poly(A) nuclease, PAN, as important factors that couple 3' processing to export. Pab1 contains a nonessential leucine-rich nuclear export signal and shuttles between the nucleus and the cytoplasm. It can exit the nucleus either as cargo of exportin 1 or bound to mRNA. Pab1 is essential but several bypass suppressors have been identified. Deletion of PAB1 from these bypass suppressor strains results in exosome-dependent retention at sites of transcription. Retention is also seen in cells lacking PAN, which Pab1 is thought to recruit and which may be responsible for the final step of mRNA biogenesis, trimming of the poly(A) tail to the length found on newly exported mRNAs. The studies presented here suggest that proper loading of Pab1 onto mRNAs and final trimming of the tail allows release from transcription sites and couples pre-mRNA processing to export.
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Affiliation(s)
- Ewan F Dunn
- Department of Biochemistry, the Norris Cotton Cancer Center, Dartmouth Medical School, Hanover, New Hampshire 03755, USA
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5
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Zhao J, Jin SB, Wieslander L. CRM1 and Ran are present but a NES-CRM1-RanGTP complex is not required in Balbiani ring mRNP particles from the gene to the cytoplasm. J Cell Sci 2004; 117:1553-66. [PMID: 15020682 DOI: 10.1242/jcs.00992] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Messenger RNA is formed from precursors known as pre-mRNA. These precursors associate with proteins to form pre-mRNA-protein (pre-mRNP) complexes. Processing machines cap, splice and polyadenylate the pre-mRNP and in this way build the mRNP. These processing machines also affect the export of the mRNP complexes from the nucleus to the cytoplasm. Export to the cytoplasm takes place through a structure in the nuclear membrane called the nuclear pore complex (NPC). Export involves adapter proteins in the mRNP and receptor proteins that bind to the adapter proteins and to components of the NPC. We show that the export receptor chromosomal region maintenance protein 1 (CRM1), belonging to a family of proteins known as importin-beta-like proteins, binds to gene-specific Balbiani ring (BR) pre-mRNP while transcription takes place. We also show that the GTPase known as Ran binds to BR pre-mRNP, and that it binds mainly in the interchromatin. However, we also show using leptomycin B treatment that a NES-CRM1-RanGTP complex is not essential for export, even though both CRM1 and Ran accompany the BR mRNP through the NPC. Our results therefore suggest that several export receptors associate with BR mRNP and that these receptors have redundant functions in the nuclear export of BR mRNP.
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Affiliation(s)
- Jian Zhao
- Department of Molecular Biology and Functional Genomics, Stockholm University, SE-106 91 Stockholm, Sweden
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6
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Thomas F, Kutay U. Biogenesis and nuclear export of ribosomal subunits in higher eukaryotes depend on the CRM1 export pathway. J Cell Sci 2003; 116:2409-19. [PMID: 12724356 DOI: 10.1242/jcs.00464] [Citation(s) in RCA: 137] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The production of ribosomes constitutes a major biosynthetic task for cells. Eukaryotic small and large ribosomal subunits are assembled in the nucleolus and independently exported to the cytoplasm. Most nuclear export pathways require RanGTP-binding export receptors. We analyzed the role of CRM1, the export receptor for leucine-rich nuclear export signals (NES), in the biogenesis of ribosomal subunits in vertebrate cells. Inhibition of the CRM1 export pathway led to a defect in nuclear export of both 40S and 60S subunits in HeLa cells. Moreover, the export of newly made ribosomal subunits in Xenopus oocytes was efficiently and specifically competed by BSA-NES conjugates. The CRM1 dependence of 60S subunit export suggested a conserved function for NMD3, a factor proposed to be a 60S subunit export adaptor in yeast. Indeed, we observed that nuclear export of human NMD3 (hNMD3) is sensitive to leptomycin B (LMB), which inactivates CRM1. It had, however, not yet been demonstrated that Nmd3 can interact with CRM1. Using purified recombinant proteins we have shown here that hNMD3 binds to CRM1 directly, in a RanGTP-dependent manner, by way of a C-terminal NES sequence. Our results suggest that the functions of CRM1 and NMD3 in ribosomal subunit export are conserved from yeast to higher eukaryotes.
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Affiliation(s)
- Franziska Thomas
- Swiss Federal Institute of Technology (ETH) Zürich, Institute of Biochemistry, HPM F11.1, Switzerland
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7
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Trotta CR, Lund E, Kahan L, Johnson AW, Dahlberg JE. Coordinated nuclear export of 60S ribosomal subunits and NMD3 in vertebrates. EMBO J 2003; 22:2841-51. [PMID: 12773398 PMCID: PMC156746 DOI: 10.1093/emboj/cdg249] [Citation(s) in RCA: 101] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2002] [Revised: 03/26/2003] [Accepted: 03/26/2003] [Indexed: 11/14/2022] Open
Abstract
60S and 40S ribosomal subunits are assembled in the nucleolus and exported from the nucleus to the cytoplasm independently of each other. We show that in vertebrate cells, transport of both subunits requires the export receptor CRM1 and Ran.GTP. Export of 60S subunits is coupled with that of the nucleo- cytoplasmic shuttling protein NMD3. Human NMD3 (hNMD3) contains a CRM-1-dependent leucine-rich nuclear export signal (NES) and a complex, dispersed nuclear localization signal (NLS), the basic region of which is also required for nucleolar accumulation. When present in Xenopus oocytes, both wild-type and export-defective mutant hNMD3 proteins bind to newly made nuclear 60S pre-export particles at a late step of subunit maturation. The export-defective hNMD3, but not the wild-type protein, inhibits export of 60S subunits from oocyte nuclei. These results indicate that the NES mutant protein competes with endogenous wild-type frog NMD3 for binding to nascent 60S subunits, thereby preventing their export. We propose that NMD3 acts as an adaptor for CRM1-Ran.GTP-mediated 60S subunit export, by a mechanism that is conserved from vertebrates to yeast.
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Affiliation(s)
- Christopher R Trotta
- Department of Biomolecular Chemistry, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA
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8
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Fornerod M, Ohno M. Exportin-mediated nuclear export of proteins and ribonucleoproteins. Results Probl Cell Differ 2002; 35:67-91. [PMID: 11791409 DOI: 10.1007/978-3-540-44603-3_4] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
Affiliation(s)
- Maarten Fornerod
- EMBL, Gene Expression Programme, Meyerhofstrasse 1, 69117 Heidelberg, Germany
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9
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Abstract
The transport of messenger RNAs (mRNAs) from the nucleus to the cytoplasm involves adapter proteins that bind the mRNA as well as receptor proteins that interact with the nuclear pore complex. We demonstrate the utility of cell-permeable peptides designed to interfere with interactions between potential adapter and receptor proteins to define the pathways accessed by particular mRNAs. We show that HuR, a protein implicated in the stabilization of short-lived mRNAs containing AU-rich elements (AREs), serves as an adapter for c-fos mRNA export through two pathways. One involves the HuR shuttling domain, HNS, which exhibits a heat shock-sensitive interaction with transportin 2 (Trn2); the other involves two protein ligands of HuR-pp32 and APRIL-which contain leucine-rich nuclear export signals (NES) recognized by the export receptor CRM1. Heterokaryon and in situ hybridization experiments reveal that the peptides selectively block the nucleocytoplasmic shuttling of their respective adapter proteins without perturbing the overall cellular distribution of polyadenylated mRNAs.
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Affiliation(s)
- I E Gallouzi
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, 295 Congress Avenue, New Haven, CT 06536, USA
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10
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Heger P, Lohmaier J, Schneider G, Schweimer K, Stauber RH. Qualitative highly divergent nuclear export signals can regulate export by the competition for transport cofactors in vivo. Traffic 2001; 2:544-55. [PMID: 11489212 DOI: 10.1034/j.1600-0854.2001.20804.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Nucleo-cytoplasmic transport of proteins is mediated by nuclear export signals, identified in various proteins executing heterologous biological functions. However, the molecular mechanism underlying the orchestration of export is only poorly understood. Using microinjection of defined recombinant export substrates, we now demonstrate that leucine-rich nuclear export signals varied dramatically in determining the kinetics of export in vivo. Thus, nuclear export signals could be kinetically classified which correlated with their affinities for CRM1-containing export complexes in vitro. Strikingly, cotransfection experiments revealed that proteins containing a fast nuclear export signal inhibited export and the biological activity of proteins harboring a slower nuclear export signal in vivo. The affinity for export complexes seems therefore predominantly controlled by the nuclear export signal itself, even in the context of the complete protein in vivo. Overexpression of FG-rich repeats of nucleoporins affected a medium nuclear export signal containing protein to the same extent as a fast nuclear export signal containing protein, indicating that nucleoporins appear not to contribute significantly to nuclear export signal-specific export regulation. Our results imply a novel mode for controlling the biological activity of shuttle proteins already by the composition of the nuclear export signal itself.
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Affiliation(s)
- P Heger
- Institute for Clinical and Molecular Virology, University of Erlangen-Nürnberg, Schlossgarten 4, D-91054 Erlangen, Germany
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11
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Mangos S, Vanderbeld B, Krawetz R, Sudol K, Kelly GM. Ran binding protein RanBP1 in zebrafish embryonic development. Mol Reprod Dev 2001; 59:235-48. [PMID: 11424209 DOI: 10.1002/mrd.1028] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Ran, which functions in nucleocytoplasmic transport and mitosis, binds to and is regulated in part by RanBP1. We have identified a zebrafish RanBP1 cDNA and report that it encodes for a polypeptide of 233 amino acids with considerable similarity to human and Xenopus RanBP1, despite the fact that it is 10% longer due to an extension at its carboxy terminus. RanBP1 mRNA is present as a maternal transcript and is expressed ubiquitously throughout the developing embryo. At the protein level, RanBP1 is present at all embryonic stages. Surprisingly, the ectopic overexpression of the protein had no obvious effect on embryogenesis. Attempts were also made to down-regulate RanBP1 activity by RNA interference. Injecting double-stranded RNA augmented both the mortality rate and the frequency of induced defects. Specific defects accompanied by changes in RanBP1 expression were not seen, leading us to propose that RNAi is not a reliable method for deregulating the activity of constitutively expressed genes, like RanBP1, in zebrafish. Mol. Reprod. Dev. 59:235-248, 2001.
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Affiliation(s)
- S Mangos
- Department of Zoology, Molecular Genetics Unit, University of Western Ontario, London, Ontario, Canada
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12
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Nappi F, Schneider R, Zolotukhin A, Smulevitch S, Michalowski D, Bear J, Felber BK, Pavlakis GN. Identification of a novel posttranscriptional regulatory element by using a rev- and RRE-mutated human immunodeficiency virus type 1 DNA proviral clone as a molecular trap. J Virol 2001; 75:4558-69. [PMID: 11312326 PMCID: PMC114209 DOI: 10.1128/jvi.75.10.4558-4569.2001] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2000] [Accepted: 02/20/2001] [Indexed: 01/28/2023] Open
Abstract
Human immunodeficiency virus (HIV) and all other lentiviruses utilize the essential viral protein Rev, which binds to RRE RNA, to export their unspliced and partially spliced mRNAs from the nucleus. We used a rev- and RRE-defective HIV type 1 (HIV-1) molecular clone in complementation experiments to establish a method for the rapid isolation of posttranscriptional regulatory elements from the mammalian genome by selecting for rescue of virus replication. Viruses rescued by this method contained a novel element with homology to rodent intracisternal A-particle (IAP) retroelements. A functional element was contained within a 247-nucleotide fragment named RNA transport element (RTE), which was able to promote replication of the Rev- and RRE-defective HIV-1 in both human lymphoid cell lines and primary lymphocytes, demonstrating its potent posttranscriptional function. RTE was functional in many cell types, indicating that the cellular factors that recognize RTE are widely expressed and evolutionarily conserved. RTE also promoted RNA export from Xenopus oocyte nuclei. RTE-mediated RNA transport was CRM1 independent, and RTE did not show high affinity for binding to mRNA export factor TAP/NXF1. Since CRM1 and TAP/NXF1 are critical export receptors associated with the two recognized mRNA export pathways, these results suggest that RTE functions via a distinct export mechanism. Taken together, our results identify a novel posttranscriptional control element that uses a conserved cellular export mechanism.
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MESH Headings
- Active Transport, Cell Nucleus
- Animals
- Base Sequence
- Carrier Proteins/metabolism
- Cloning, Molecular
- DNA, Viral
- Gene Products, rev/genetics
- Genes, Intracisternal A-Particle
- Genes, Regulator
- Genes, env/genetics
- HIV-1/genetics
- Humans
- Jurkat Cells
- Karyopherins
- Mice
- Molecular Sequence Data
- Mutagenesis
- Nuclear Proteins/metabolism
- Nucleocytoplasmic Transport Proteins
- Proviruses/genetics
- RNA/metabolism
- RNA Processing, Post-Transcriptional
- RNA, Messenger/metabolism
- RNA-Binding Proteins/metabolism
- Receptors, Cytoplasmic and Nuclear
- Regulatory Sequences, Nucleic Acid
- Xenopus laevis
- rev Gene Products, Human Immunodeficiency Virus
- Exportin 1 Protein
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Affiliation(s)
- F Nappi
- Human Retrovirus Section, Basic Research Laboratory, National Cancer Institute-Frederick, Frederick, Maryland 21702-1201, USA
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13
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Renault L, Kuhlmann J, Henkel A, Wittinghofer A. Structural basis for guanine nucleotide exchange on Ran by the regulator of chromosome condensation (RCC1). Cell 2001; 105:245-55. [PMID: 11336674 DOI: 10.1016/s0092-8674(01)00315-4] [Citation(s) in RCA: 197] [Impact Index Per Article: 8.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/17/2022]
Abstract
RCC1 (regulator of chromosome condensation), a beta propeller chromatin-bound protein, is the guanine nucleotide exchange factor (GEF) for the nuclear GTP binding protein Ran. We report here the 1.8 A crystal structure of a Ran*RCC1 complex in the absence of nucleotide, an intermediate in the multistep GEF reaction. In contrast to previous structures, the phosphate binding region of the nucleotide binding site is perturbed only marginally, possibly due to the presence of a polyvalent anion in the P loop. Biochemical experiments show that a sulfate ion stabilizes the Ran*RCC1 complex and inhibits dissociation by guanine nucleotides. Based on the available structural and biochemical evidence, we present a unified scenario for the GEF mechanism where interaction of the P loop lysine with an acidic residue is a crucial element for the overall reaction.
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Affiliation(s)
- L Renault
- Max-Planck-Institut für Molekulare Physiologie, Postfach 50 02 47, 44202, Dortmund, Germany
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14
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Abstract
mRNA export is mediated by RNA-binding proteins which shuttle between the nucleus and cytoplasm. Using an in vitro unidirectional export assay, we observe that the shuttling mRNA-binding protein, hnRNP A1, is exported only extremely slowly unless incubations are supplemented with snRNA-specific oligonucleotides which inhibit splicing. In vivo microinjection experiments support this conclusion. Like many examples of nucleocytoplasmic transport, export of hnRNP A1 requires energy and is sensitive to the presence of wheat germ agglutinin. It does not, however, require supplementation with cytoplasmic proteins. Although the exportin, Crm1, is needed for export of several varieties of RNA, both the in vitro assay and in vivo assays show that it is not required for export of hnRNP A1. In vitro and in vivo studies also show that inhibition of transcription allows continued shuttling of hnRNP A1 and in fact accelerates its export. Judging from the stimulatory effects of targeted destruction of snRNAs, this is likely to reflect completion of the covalent maturation of the RNAs with which hnRNP A1 associates. These observations therefore provide a simple explanation of why multiple RNA-binding proteins relocate to the cytoplasm upon inhibition of transcription in vivo.
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15
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Maurer P, Redd M, Solsbacher J, Bischoff FR, Greiner M, Podtelejnikov AV, Mann M, Stade K, Weis K, Schlenstedt G. The nuclear export receptor Xpo1p forms distinct complexes with NES transport substrates and the yeast Ran binding protein 1 (Yrb1p). Mol Biol Cell 2001; 12:539-49. [PMID: 11251069 PMCID: PMC30962 DOI: 10.1091/mbc.12.3.539] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2000] [Revised: 10/18/2000] [Accepted: 01/09/2001] [Indexed: 11/11/2022] Open
Abstract
Xpo1p (Crm1p) is the nuclear export receptor for proteins containing a leucine-rich nuclear export signal (NES). Xpo1p, the NES-containing protein, and GTP-bound Ran form a complex in the nucleus that translocates across the nuclear pore. We have identified Yrb1p as the major Xpo1p-binding protein in Saccharomyces cerevisiae extracts in the presence of GTP-bound Gsp1p (yeast Ran). Yrb1p is cytoplasmic at steady-state but shuttles continuously between the cytoplasm and the nucleus. Nuclear import of Yrb1p is mediated by two separate nuclear targeting signals. Export from the nucleus requires Xpo1p, but Yrb1p does not contain a leucine-rich NES. Instead, the interaction of Yrb1p with Xpo1p is mediated by Gsp1p-GTP. This novel type of export complex requires the acidic C-terminus of Gsp1p, which is dispensable for the binding to importin beta-like transport receptors. A similar complex with Xpo1p and Gsp1p-GTP can be formed by Yrb2p, a relative of Yrb1p predominantly located in the nucleus. Yrb1p also functions as a disassembly factor for NES/Xpo1p/Gsp1p-GTP complexes by displacing the NES protein from Xpo1p/Gsp1p. This Yrb1p/Xpo1p/Gsp1p complex is then completely dissociated after GTP hydrolysis catalyzed by the cytoplasmic GTPase activating protein Rna1p.
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Affiliation(s)
- P Maurer
- Medizinische Biochemie und Molekularbiologie, Universität des Saarlandes, 66421 Homburg, Germany
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16
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Abstract
All major nuclear export pathways so far examined follow a general paradigm. Specifically, a complex is formed in the nucleus, containing the export cargo, a member of the importin-beta family of transporters and RanGTP. This complex is translocated across the nuclear pore to the cytoplasm, where hydrolysis of the GTP on Ran is stimulated by the GTPase-activating protein RanGAP. The activity of RanGAP is increased by RanBP1, which also promotes disassembly of RanGTP-cargo-transporter complexes. Here we investigate the role of RanGTP in the export of mRNAs generated by splicing. We show that nuclear injection of a Ran mutant (RanT24N) or the normally cytoplasmic RanGAP potently inhibits the export of both tRNA and U1 snRNA, but not of spliced mRNAs. Moreover, nuclear injection of RanGAP together with RanBP1 blocks tRNA export but does not affect mRNA export. These and other data indicate that export of spliced mRNA is the first major cellular transport pathway that is independent of the export co-factor Ran.
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Affiliation(s)
- K N Clouse
- Department of Cell Biology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA
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17
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Tang H, Wong-Staal F. Specific interaction between RNA helicase A and Tap, two cellular proteins that bind to the constitutive transport element of type D retrovirus. J Biol Chem 2000; 275:32694-700. [PMID: 10924507 DOI: 10.1074/jbc.m003933200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Constitutive transport element (CTE) facilitates retroviral RNA export by interacting with the cellular RNA export machinery. Two cellular proteins, RNA helicase A (RHA) and Tip-associated protein (Tap) were identified as binding to CTE and were proposed to function as CTE co-factors (1,2). Here, we report that these two CTE-binding proteins interact with each other in vitro and in vivo. The in vitro binding of RHA to Tap is direct and independent of either CTE or the nuclear transport domain of RHA. The removal of the first 60 amino acids of Tap significantly diminishes the binding to RHA. The activity of this Tap mutant to enhance CTE-mediated gene expression is also markedly reduced. A transdominant mutant of Tap inhibited RHA-mediated up-regulation of CTE function in mammalian cells. The nuclear transport domain of RHA also interfered with Tap-mediated transactivation of the CTE function in quail cells, in which the function of CTE is dependent on the expression of a functional human Tap cDNA.
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Affiliation(s)
- H Tang
- Departments of Biology and Medicine, University of California, San Diego, La Jolla, California 92093-0665, USA
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18
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Brennan CM, Gallouzi IE, Steitz JA. Protein ligands to HuR modulate its interaction with target mRNAs in vivo. J Cell Biol 2000; 151:1-14. [PMID: 11018049 PMCID: PMC2189805 DOI: 10.1083/jcb.151.1.1] [Citation(s) in RCA: 300] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/19/2000] [Accepted: 08/15/2000] [Indexed: 02/08/2023] Open
Abstract
AU-rich elements (AREs) present in the 3' untranslated regions of many protooncogene, cytokine, and lymphokine messages target them for rapid degradation. HuR, a ubiquitously expressed member of the ELAV (embryonic lethal abnormal vision) family of RNA binding proteins, selectively binds AREs and stabilizes ARE-containing mRNAs in transiently transfected cells. Here, we identify four mammalian proteins that bind regions of HuR known to be essential for its ability to shuttle between the nucleus and the cytoplasm and to stabilize mRNA: SETalpha, SETbeta, pp32, and acidic protein rich in leucine (APRIL). Three have been reported to be protein phosphatase 2A inhibitors. All four ligands contain long, acidic COOH-terminal tails, while pp32 and APRIL share a second motif: rev-like leucine-rich repeats in their NH(2)-terminal regions. We show that pp32 and APRIL are nucleocytoplasmic shuttling proteins that interact with the nuclear export factor CRM1 (chromosomal region maintenance protein 1). The inhibition of CRM1 by leptomycin B leads to the nuclear retention of pp32 and APRIL, their increased association with HuR, and an increase in HuR's association with nuclear poly(A)+ RNA. Furthermore, transcripts from the ARE-containing c-fos gene are selectively retained in the nucleus, while the cytoplasmic distribution of total poly(A)+ RNA is not altered. These data provide evidence that interaction of its ligands with HuR modulate HuR's ability to bind its target mRNAs in vivo and suggest that CRM1 is instrumental in the export of at least some cellular mRNAs under certain conditions. We discuss the possible role of these ligands upstream of HuR in pathways that govern the stability of ARE-containing mRNAs.
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Affiliation(s)
- C M Brennan
- Department of Molecular Biophysics and Biochemistry, Howard Hughes Medical Institute, Yale University School of Medicine, New Haven, Connecticut 06536, USA
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19
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Vainberg IE, Dower K, Rosbash M. Nuclear export of heat shock and non-heat-shock mRNA occurs via similar pathways. Mol Cell Biol 2000; 20:3996-4005. [PMID: 10805742 PMCID: PMC85767 DOI: 10.1128/mcb.20.11.3996-4005.2000] [Citation(s) in RCA: 40] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/08/1999] [Accepted: 03/08/2000] [Indexed: 11/20/2022] Open
Abstract
Several studies of the yeast Saccharomyces cerevisiae support differential regulation of heat shock mRNA (hs mRNA) and non-hs mRNA nuclear export during stress. These include the finding that hs mRNA export at 42 degrees C is inhibited in the absence of the nucleoporinlike protein Rip1p (also called Nup42p) (C. A. Saavedra, C. M. Hammell, C. V. Heath, and C. N. Cole, Genes Dev. 11:2845-2856, 1997; F. Stutz, J. Kantor, D. Zhang, T. McCarthy, M. Neville, and M. Rosbash, Genes Dev. 11:2857-2868, 1997). However, the results reported in this paper provide little evidence for selective non-hs mRNA retention or selective hs mRNA export under heat shock conditions. First, we do not detect a block to non-hs mRNA export at 42 degrees C in a wild-type strain. Second, hs mRNA export appears to be mediated by the Ran system and several other factors previously reported to be important for general mRNA export. Third, the export of non-hs mRNA as well as hs mRNA is inhibited in the absence of Rip1p at 42 degrees C. As a corollary, we find no evidence for cis-acting hs mRNA sequences that promote transport during heat shock. Taken together, our data suggest that a shift to 42 degrees C in the absence of Rip1p impacts a late stage of transport affecting most if not all mRNA.
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Affiliation(s)
- I E Vainberg
- Department of Biology, Howard Hughes Medical Institute, MS008 Brandeis University, Waltham, Massachusetts 02454, USA
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20
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Künzler M, Gerstberger T, Stutz F, Bischoff FR, Hurt E. Yeast Ran-binding protein 1 (Yrb1) shuttles between the nucleus and cytoplasm and is exported from the nucleus via a CRM1 (XPO1)-dependent pathway. Mol Cell Biol 2000; 20:4295-308. [PMID: 10825193 PMCID: PMC85797 DOI: 10.1128/mcb.20.12.4295-4308.2000] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/01/1999] [Accepted: 03/29/2000] [Indexed: 11/20/2022] Open
Abstract
The RanGTP-binding protein RanBP1, which is located in the cytoplasm, has been implicated in release of nuclear export complexes from the cytoplasmic side of the nuclear pore complex. Here we show that Yrb1 (the yeast homolog of RanBP1) shuttles between the nucleus and the cytoplasm. Nuclear import of Yrb1 is a facilitated process that requires a short basic sequence within the Ran-binding domain (RBD). By contrast, nuclear export of Yrb1 requires an intact RBD, which forms a ternary complex with the Xpo1 (Crm1) NES receptor in the presence of RanGTP. Nuclear export of Yrb1, however, is insensitive towards leptomycin B, suggesting a novel type of substrate recognition between Yrb1 and Xpo1. Taken together, these data suggest that ongoing nuclear import and export is an important feature of Yrb1 function in vivo.
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Affiliation(s)
- M Künzler
- Ruprecht-Karls-Universität Heidelberg, Biochemie-Zentrum Heidelberg (BZH), Germany
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21
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Plafker K, Macara IG. Facilitated nucleocytoplasmic shuttling of the Ran binding protein RanBP1. Mol Cell Biol 2000; 20:3510-21. [PMID: 10779340 PMCID: PMC85643 DOI: 10.1128/mcb.20.10.3510-3521.2000] [Citation(s) in RCA: 63] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/1999] [Accepted: 02/21/2000] [Indexed: 12/19/2022] Open
Abstract
The Ran binding protein RanBP1 is localized to the cytosol of interphase cells. A leucine-rich nuclear export signal (NES) near the C terminus of RanBP1 is essential to maintain this distribution. We now show that RanBP1 accumulates in nuclei of cells treated with the export inhibitor, leptomycin B, and collapse of the nucleocytoplasmic Ran:GTP gradient leads to equilibration of RanBP1 across the nuclear envelope. Low temperature prevents nuclear accumulation of RanBP1, suggesting that import does not occur via simple diffusion. Glutathione S-transferase (GST)-RanBP1(1-161), which lacks the NES, accumulates in the nucleus after cytoplasmic microinjection. In permeabilized cells, nuclear accumulation of GST-RanBP1(1-161) requires nuclear Ran:GTP but is not inhibited by a dominant interfering G19V mutant of Ran. Nuclear accumulation is enhanced by addition of exogenous karyopherins/importins or RCC1, both of which also enhance nuclear Ran accumulation. Import correlates with Ran concentration. Remarkably, an E37K mutant of RanBP1 does not import into the nuclei under any conditions tested despite the fact that it can form a ternary complex with Ran and importin beta. These data indicate that RanBP1 translocates through the pores by an active, nonclassical mechanism and requires Ran:GTP for nuclear accumulation. Shuttling of RanBP1 may function to clear nuclear pores of Ran:GTP, to prevent premature release of import cargo from transport receptors.
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Affiliation(s)
- K Plafker
- Markey Center for Cell Signaling and Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908, USA
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22
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Luo MJ, Reed R. Splicing is required for rapid and efficient mRNA export in metazoans. Proc Natl Acad Sci U S A 1999; 96:14937-42. [PMID: 10611316 PMCID: PMC24751 DOI: 10.1073/pnas.96.26.14937] [Citation(s) in RCA: 296] [Impact Index Per Article: 11.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Pre-mRNA splicing is among the last known nuclear events before export of mature mRNA to the cytoplasm. At present, it is not known whether splicing and mRNA export are biochemically coupled processes. In this study, we have injected pre-mRNAs containing a single intron or the same mRNAs lacking an intron (Deltai-mRNAs) into Xenopus oocyte nuclei. We find that the spliced mRNAs are exported much more rapidly and efficiently than the identical Deltai-mRNAs. Moreover, competition studies using excess Deltai-mRNA indicate that different factor(s) are involved in the inefficient export of Deltai-mRNA vs. the efficient export of spliced mRNA. Consistent with this conclusion, spliced mRNA and Deltai-mRNA, though identical in sequence, are assembled into different messenger ribonucleoprotein particles (mRNP) in vitro. Strikingly, the mRNA in the spliced mRNP, but not in the Deltai-mRNP, is exported rapidly and efficiently. We conclude that splicing generates a specific nucleoprotein complex that targets mRNA for export. Our results, revealing a link between splicing and efficient mRNA export, may explain the reports that an intron is required for efficient expression of many protein-coding genes in metazoans.
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Affiliation(s)
- M J Luo
- Department of Cell Biology, Harvard Medical School, Boston, MA 02115, USA
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23
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Askjaer P, Bachi A, Wilm M, Bischoff FR, Weeks DL, Ogniewski V, Ohno M, Niehrs C, Kjems J, Mattaj IW, Fornerod M. RanGTP-regulated interactions of CRM1 with nucleoporins and a shuttling DEAD-box helicase. Mol Cell Biol 1999; 19:6276-85. [PMID: 10454574 PMCID: PMC84588 DOI: 10.1128/mcb.19.9.6276] [Citation(s) in RCA: 173] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/1999] [Accepted: 06/21/1999] [Indexed: 11/20/2022] Open
Abstract
CRM1 is an export receptor mediating rapid nuclear exit of proteins and RNAs to the cytoplasm. CRM1 export cargoes include proteins with a leucine-rich nuclear export signal (NES) that bind directly to CRM1 in a trimeric complex with RanGTP. Using a quantitative CRM1-NES cargo binding assay, significant differences in affinity for CRM1 among natural NESs are demonstrated, suggesting that the steady-state nucleocytoplasmic distribution of shuttling proteins could be determined by the relative strengths of their NESs. We also show that a trimeric CRM1-NES-RanGTP complex is disassembled by RanBP1 in the presence of RanGAP, even though RanBP1 itself contains a leucine-rich NES. Selection of CRM1-binding proteins from Xenopus egg extract leads to the identification of an NES-containing DEAD-box helicase, An3, that continuously shuttles between the nucleus and the cytoplasm. In addition, we identify the Xenopus homologue of the nucleoporin CAN/Nup214 as a RanGTP- and NES cargo-specific binding site for CRM1, suggesting that this nucleoporin plays a role in export complex disassembly and/or CRM1 recycling.
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Affiliation(s)
- P Askjaer
- Department of Gene Expression, Deutsches Krebsforschungszentrum, Heidelberg, Germany
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24
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Krebber H, Taura T, Lee MS, Silver PA. Uncoupling of the hnRNP Npl3p from mRNAs during the stress-induced block in mRNA export. Genes Dev 1999; 13:1994-2004. [PMID: 10444597 PMCID: PMC316916 DOI: 10.1101/gad.13.15.1994] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/1999] [Accepted: 06/10/1999] [Indexed: 11/24/2022]
Abstract
Npl3p, the major mRNA-binding protein of the yeast Saccharomyces cerevisiae shuttles between the nucleus and the cytoplasm. A single amino acid change in the carboxyl terminus of Npl3p (E409 --> K) renders the mutant protein largely cytoplasmic because of a delay in its import into the nucleus. This import defect can be reversed by increasing the intracellular concentration of Mtr10p, the nuclear import receptor for Npl3p. Conversely, using this mutant, we show that Npl3p and mRNA export out of the nucleus is significantly slowed in cells bearing mutations in XPO1/CRM1, which encodes the export receptor for NES-containing proteins and in RAT7, which encodes an essential nucleoporin. Interestingly, following induction of stress by heat shock, high salt, or ethanol, conditions under which most mRNA export is blocked, Npl3p is still exported from the nucleus. The stress-induced export of Npl3p is independent of both the activity of Xpo1p and the continued selective export of heat-shock mRNAs that occurs following stress. UV-cross-linking experiments show that Npl3p is bound to mRNA under normal conditions, but is no longer RNA associated in stressed cells. Taken together, we suggest that the uncoupling of Npl3p and possibly other mRNA-binding proteins from mRNAs in the nucleus provides a general switch that regulates mRNA export. By this model, under normal conditions Npl3p is a major component of an export-competent RNP complex. However, under conditions of stress, Npl3p no longer associates with the export complex, rendering it export incompetent and thus nuclear.
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Affiliation(s)
- H Krebber
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School and The Dana-Farber Cancer Institute, Boston, Massachusetts 02115, USA
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25
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Liu Y, Guo W, Tartakoff PY, Tartakoff AM. A Crm1p-independent nuclear export path for the mRNA-associated protein, Npl3p/Mtr13p. Proc Natl Acad Sci U S A 1999; 96:6739-44. [PMID: 10359782 PMCID: PMC21985 DOI: 10.1073/pnas.96.12.6739] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/04/1998] [Indexed: 11/18/2022] Open
Abstract
mRNA export involves association of mRNAs with nucleoplasmic proteins, delivery to the nuclear pore complex, translocation to the cytoplasm, and reimport of recycling components. Many yeast mutants inhibit mRNA export, but there is little information concerning the RNA carriers and steps of transport that they affect. The hnRNP/serine-arginine-rich-like protein, Npl3p/Mtr13p, binds poly(A)+ RNA and shuttles between the nucleus and cytoplasm. Its export accelerates on inhibition of RNA synthesis. In vivo tests show that its export requires two proteins with putative leucine-rich nuclear export signals: Gle1p, Mex67p, and several additional nuclear and nuclear pore complex-associated proteins. Surprisingly, a nonnuclear pool of an import factor (the importin alpha homologue, Srp1p) is also required. Changes in the methylation status of Npl3p do not correlate with its nucleocytoplasmic distribution. A crm1 mutant that inhibits export of proteins with leucine-rich nuclear export signals and mRNAs does not inhibit Npl3p export. Moreover, several proteins needed for Npl3p export are not needed for export of a typical Crm1p cargo. Thus, Npl3p export requires only a subset of proteins implicated in mRNA export, suggesting that more than one mRNA export path exists. A distinct group of mutants, including a mutation of a member of the importin beta superfamily, inhibits Npl3p reimport from the cytoplasm.
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Affiliation(s)
- Y Liu
- Pathology Department and Cell Biology Program, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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26
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Watanabe M, Fukuda M, Yoshida M, Yanagida M, Nishida E. Involvement of CRM1, a nuclear export receptor, in mRNA export in mammalian cells and fission yeast. Genes Cells 1999; 4:291-7. [PMID: 10421839 DOI: 10.1046/j.1365-2443.1999.00259.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
BACKGROUND CRM1, an evolutionarily conserved protein, was shown to be a receptor for leucine-rich nuclear export signal (NES)-dependent protein transport. In lower eukaryotes CRM1 is reported to be required for the export of mRNA, however, involvement of the NES-dependent transport pathway in mRNA export in higher eukaryotes has not been established. RESULTS We have found that treatment of mammalian cells with leptomycin B (LMB), a specific inhibitor of CRM1, induces the nuclear accumulation of endogenous mRNA, probably due to the inhibition of its export. In fission yeasts, the nuclear accumulation of mRNA also occurred in cells treated with LMB or in a temperature-sensitive crm1 mutant at a restrictive temperature. A synthetic mRNA that was injected into the nucleus of mammalian cultured cells was exported from the nucleus within 5 h. This export was inhibited by both wheat germ agglutinin and a temperature of 4 degrees C. Importantly, this mRNA export was inhibited by LMB or by an excess amount of the NES peptide-conjugates. LMB treatment, on the other hand, rapidly induced the nuclear entry of RanBP1, a factor involved in the active nucleocytoplasmic transport, although the treatment did not interfere with a nuclear localization signal-dependent transport system within 7 h. CONCLUSION These results suggest that CRM1 is involved in mRNA export in eukaryotic cells.
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Affiliation(s)
- M Watanabe
- Department of Biophysics, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto 606-8502, Japan
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27
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Paraskeva E, Izaurralde E, Bischoff FR, Huber J, Kutay U, Hartmann E, Lührmann R, Görlich D. CRM1-mediated recycling of snurportin 1 to the cytoplasm. J Cell Biol 1999; 145:255-64. [PMID: 10209022 PMCID: PMC2133107 DOI: 10.1083/jcb.145.2.255] [Citation(s) in RCA: 140] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/1998] [Revised: 03/05/1999] [Indexed: 11/22/2022] Open
Abstract
Importin beta is a major mediator of import into the cell nucleus. Importin beta binds cargo molecules either directly or via two types of adapter molecules, importin alpha, for import of proteins with a classical nuclear localization signal (NLS), or snurportin 1, for import of m3G-capped U snRNPs. Both adapters have an NH2-terminal importin beta-binding domain for binding to, and import by, importin beta, and both need to be returned to the cytoplasm after having delivered their cargoes to the nucleus. We have shown previously that CAS mediates export of importin alpha. Here we show that snurportin 1 is exported by CRM1, the receptor for leucine-rich nuclear export signals (NESs). However, the interaction of CRM1 with snurportin 1 differs from that with previously characterized NESs. First, CRM1 binds snurportin 1 50-fold stronger than the Rev protein and 5,000-fold stronger than the minimum Rev activation domain. Second, snurportin 1 interacts with CRM1 not through a short peptide but rather via a large domain that allows regulation of affinity. Strikingly, snurportin 1 has a low affinity for CRM1 when bound to its m3G-capped import substrate, and a high affinity when substrate-free. This mechanism appears crucial for productive import cycles as it can ensure that CRM1 only exports snurportin 1 that has already released its import substrate in the nucleus.
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Affiliation(s)
- E Paraskeva
- Zentrum für Molekulare Biologie der Universität Heidelberg, D-69120 Heidelberg, Germany
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28
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MacMorris MA, Zorio DA, Blumenthal T. An exon that prevents transport of a mature mRNA. Proc Natl Acad Sci U S A 1999; 96:3813-8. [PMID: 10097120 PMCID: PMC22377 DOI: 10.1073/pnas.96.7.3813] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In Caenorhabditis elegans, pre-mRNA for the essential splicing factor U2AF65 sometimes is spliced to produce an RNA that includes an extra 216-bp internal exon, exon 3. Inclusion of exon 3 inserts an in-frame stop codon, yet this RNA is not subject to SMG-mediated RNA surveillance. To test whether exon 3 causes RNA to remain nuclear and thereby escape decay, we inserted it into the 3' untranslated region of a gfp reporter gene. Although exon 3 did not affect accumulation or processing of the mRNA, it dramatically suppressed expression of green fluorescent protein (GFP). We showed by in situ hybridization that exon 3-containing gfp RNA is retained in the nucleus. Intriguingly, exon 3 contains 10 matches to the 8-bp 3' splice-site consensus. We hypothesized that U2AF might recognize this octamer and thereby prevent export. This idea is supported by RNA interference experiments in which reduced levels of U2AF resulted in a small burst of gfp expression.
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Affiliation(s)
- M A MacMorris
- Department of Biochemistry and Molecular Genetics, University of Colorado Health Sciences Center, Denver, CO 80262, USA
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29
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Ullman KS, Shah S, Powers MA, Forbes DJ. The nucleoporin nup153 plays a critical role in multiple types of nuclear export. Mol Biol Cell 1999; 10:649-64. [PMID: 10069809 PMCID: PMC25193 DOI: 10.1091/mbc.10.3.649] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The fundamental process of nucleocytoplasmic transport takes place through the nuclear pore. Peripheral pore structures are presumably poised to interact with transport receptors and their cargo as these receptor complexes first encounter the pore. One such peripheral structure likely to play an important role in nuclear export is the basket structure located on the nuclear side of the pore. At present, Nup153 is the only nucleoporin known to localize to the surface of this basket, suggesting that Nup153 is potentially one of the first pore components an RNA or protein encounters during export. In this study, anti-Nup153 antibodies were used to probe the role of Nup153 in nuclear export in Xenopus oocytes. We found that Nup153 antibodies block three major classes of RNA export, that of snRNA, mRNA, and 5S rRNA. Nup153 antibodies also block the NES protein export pathway, specifically the export of the HIV Rev protein, as well as Rev-dependent RNA export. Not all export was blocked; Nup153 antibodies did not impede the export of tRNA or the recycling of importin beta to the cytoplasm. The specific antibodies used here also did not affect nuclear import, whether mediated by importin alpha/beta or by transportin. Overall, the results indicate that Nup153 is crucial to multiple classes of RNA and protein export, being involved at a vital juncture point in their export pathways. This juncture point appears to be one that is bypassed by tRNA during its export. We asked whether a physical interaction between RNA and Nup153 could be observed, using homoribopolymers as sequence-independent probes for interaction. Nup153, unlike four other nucleoporins including Nup98, associated strongly with poly(G) and significantly with poly(U). Thus, Nup153 is unique among the nucleoporins tested in its ability to interact with RNA and must do so either directly or indirectly through an adaptor protein. These results suggest a unique mechanistic role for Nup153 in the export of multiple cargos.
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Affiliation(s)
- K S Ullman
- Department of Biology, University of California at San Diego, La Jolla, California 92093-0347, USA.
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30
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Shah S, Forbes DJ. Separate nuclear import pathways converge on the nucleoporin Nup153 and can be dissected with dominant-negative inhibitors. Curr Biol 1998; 8:1376-86. [PMID: 9889100 DOI: 10.1016/s0960-9822(98)00018-9] [Citation(s) in RCA: 110] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Proteins generally enter or exit the nucleus as cargo of one of a small family of import and export receptors. These receptors bear distant homology to importin beta, a subunit of the receptor for proteins with classical nuclear localisation sequences (NLSs). To understand the mechanism of nuclear transport, the next question involves identifying the nuclear pore proteins that interact with the different transport receptors as they dock at the pore and translocate through it. RESULTS Two pathways of nuclear import were found to intersect at a single nucleoporin, Nup153, localized on the intranuclear side of the nuclear pore. Nup153 contains separate binding sites for importin alpha/beta, which mediates classical NLS import, and for transportin, which mediates import of different nuclear proteins. Strikingly, a Nup153 fragment containing the importin beta binding site acted as a dominant-negative inhibitor of NLS import, with no effect on transportin-mediated import. Conversely, a Nup153 fragment containing the transportin binding site acted as a strong dominant-negative inhibitor of transportin import, with no effect on classical NLS import. The interaction of transportin with Nup153 could be disrupted by a non-hydrolyzable form of GTP or by a GTPase-deficient mutant of Ran, and was not observed if transportin carried cargo. Neither Nup153 fragment affected binding of the export receptor Crm1 at the nuclear rim. CONCLUSIONS Two nuclear import pathways, mediated by importin beta and transportin, converge on a single nucleoporin, Nup153. Dominant-negative fragments of Nup153 can now be used to distinguish different nuclear import pathways and, potentially, to dissect nuclear export.
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Affiliation(s)
- S Shah
- Department of Biology 0347, University of California at San Diego, La Jolla, California 92093-0347, USA
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31
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Yan C, Lee LH, Davis LI. Crm1p mediates regulated nuclear export of a yeast AP-1-like transcription factor. EMBO J 1998; 17:7416-29. [PMID: 9857197 PMCID: PMC1171086 DOI: 10.1093/emboj/17.24.7416] [Citation(s) in RCA: 210] [Impact Index Per Article: 8.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The yeast AP-1-like transcription factor, Yap1p, activates genes required for the response to oxidative stress. Yap1p is normally cytoplasmic and inactive, but will activate by nuclear translocation if cells are placed in an oxidative environment. Here we show that Yap1p is a target of the beta-karyopherin-like nuclear exporter, Crm1p. Yap1p is constitutively nuclear in a crm1 mutant, and Crm1p binds to a nuclear export sequence (NES)-like sequence in Yap1p in the presence of RanGTP. Recognition of Yap1p by Crm1p is inhibited by oxidation, and this inhibition requires at least one of the three cysteine residues flanking the NES. These results suggest that Yap1p localization is largely regulated at the level of nuclear export, and that the oxidation state affects the accessibility of the Yap1p NES to Crm1p directly. We also show that a mutation in RanGAP (rna1-1) is synthetically lethal with crm1 mutants. Yap1p export is inhibited in both rna1-1 and prp20 (RanGNRF) mutant strains, but Yap1p rapidly accumulates at the nuclear periphery after shifting rna1-1, but not other mutant cells to the non-permissive temperature. Thus, disassembly of export complexes in response to RanGTP hydrolysis may be required for release of substrate from a terminal binding site at the nuclear pore complex (NPC).
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Affiliation(s)
- C Yan
- W.M.Keck Institute for Cellular Visualization, Rosenstiel Center and Department of Biology, MS 029, Brandeis University, 415 South Street, Waltham, MA 02453, USA
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32
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Askjaer P, Jensen TH, Nilsson J, Englmeier L, Kjems J. The specificity of the CRM1-Rev nuclear export signal interaction is mediated by RanGTP. J Biol Chem 1998; 273:33414-22. [PMID: 9837918 DOI: 10.1074/jbc.273.50.33414] [Citation(s) in RCA: 169] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Nuclear export of intron-containing human immunodeficiency virus type 1 (HIV-1) RNA is mediated by the viral Rev protein that contains both an RNA binding domain specific for the viral Rev response element (RRE) and a nuclear export signal (NES). The cellular CRM1 (Exportin1) protein functions as a nuclear export receptor for proteins carrying a Rev-like NES in a process that also requires the GTP bound form of the Ran GTPase. Using purified recombinant factors, we show by co-precipitation, gel mobility shift and protein footprinting assays that full-length Rev protein interacts directly with CRM1 in vitro independently of both the integrity of the characteristic leucine residues of the NES and the presence of the cytotoxin leptomycin B (LMB). Addition of RanGTP induces the formation of an RRE-Rev-CRM1-RanGTP complex that is sensitive to LMB, NES mutations, and Ran being charged with GTP. Within this complex, CRM1 is readily cross-linked to Cys89 near the NES of Rev. By protein footprinting, we demonstrate that the NES of Rev and two regions in CRM1 become inaccessible to endoproteinases upon binding suggesting that these regions are involved in protein-protein interactions. Our data are consistent with a model in which CRM1 is the nuclear export receptor for the Rev-RRE ribonucleoprotein complex and that RanGTP binds to a preformed Rev-CRM1 complex and specifies a functional interaction with the NES.
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Affiliation(s)
- P Askjaer
- Department of Molecular and Structural Biology, University of Aarhus, C. F. Mollers Allé, Building 130, DK-8000 Aarhus C, Denmark
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Semmes OJ, Chen L, Sarisky RT, Gao Z, Zhong L, Hayward SD. Mta has properties of an RNA export protein and increases cytoplasmic accumulation of Epstein-Barr virus replication gene mRNA. J Virol 1998; 72:9526-34. [PMID: 9811685 PMCID: PMC110453 DOI: 10.1128/jvi.72.12.9526-9534.1998] [Citation(s) in RCA: 61] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/07/1998] [Accepted: 09/09/1998] [Indexed: 11/20/2022] Open
Abstract
The Epstein-Barr virus (EBV) Zta and Mta regulatory proteins were previously found to be required for efficient replication of oriLyt in cotransfection-replication assays, but the contribution of Mta to the replication process was unknown. We now demonstrate that Mta regulates replication gene expression. Using the polymerase processivity factor BMRF1 as an example, we found that in transfected cells, total BMRF1 mRNA levels were unaffected by Mta but that the amounts of cytoplasmic BMRF1 RNA and protein were greatly increased in the presence of Mta. Mta also increased cytoplasmic accumulation of the BALF2, BALF5, BSLF1, and BBLF4 replication gene mRNAs but did not affect cytoplasmic levels of BBLF2/3 mRNA. Thus, five of the six core replication genes require Mta for efficient accumulation of cytoplasmic RNA. The contribution of Mta to posttranscriptional RNA processing was examined. Examination of Mta localization in transfected cells by indirect immunofluorescence revealed that Mta colocalized with the splicing factor SC35. We also found that Mta has RNA binding activity. Glutathione S-transferase-Mta bound to BMRF1 and BMLF1 transcripts but not to a control cellular gene RNA. Mta contains a consensus leucine-rich nuclear export signal. Such signal sequences are characteristic of proteins that undergo nuclear export. Examination of Mta localization in a heterokaryon assay provided evidence that Mta shuttles between the nucleus and the cytoplasm. Our experiments indicate that Mta functions in RNA processing and transport and mediates cytoplasmic accumulation of a number of EBV early mRNAs.
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MESH Headings
- Amino Acid Sequence
- Animals
- Base Sequence
- Biological Transport, Active
- Cell Line
- Cell Nucleus/metabolism
- Cell Nucleus/virology
- Chlorocebus aethiops
- Cytoplasm/metabolism
- Cytoplasm/virology
- DNA Primers/genetics
- Genes, Viral
- Herpesvirus 4, Human/genetics
- Herpesvirus 4, Human/metabolism
- Herpesvirus 4, Human/physiology
- Humans
- RNA Processing, Post-Transcriptional
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Viral/genetics
- RNA, Viral/metabolism
- Trans-Activators/genetics
- Trans-Activators/metabolism
- Transfection
- Vero Cells
- Viral Proteins/genetics
- Viral Proteins/metabolism
- Virus Replication/genetics
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Affiliation(s)
- O J Semmes
- Molecular Virology Laboratories, Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
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Affiliation(s)
- F Stutz
- Institut de Microbiologie, Centre Hospitalier Universitaire Vaudois, 1011 Lausanne, Switzerland.
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35
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Hellmuth K, Lau DM, Bischoff FR, Künzler M, Hurt E, Simos G. Yeast Los1p has properties of an exportin-like nucleocytoplasmic transport factor for tRNA. Mol Cell Biol 1998; 18:6374-86. [PMID: 9774653 PMCID: PMC109223 DOI: 10.1128/mcb.18.11.6374] [Citation(s) in RCA: 204] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Saccharomyces cerevisiae Los1p, which is genetically linked to the nuclear pore protein Nsp1p and several tRNA biogenesis factors, was recently grouped into the family of importin/karyopherin-beta-like proteins on the basis of its sequence similarity. In a two-hybrid screen, we identified Nup2p as a nucleoporin interacting with Los1p. Subsequent purification of Los1p from yeast demonstrates its physical association not only with Nup2p but also with Nsp1p. By the use of the Gsp1p-G21V mutant, Los1p was shown to preferentially bind to the GTP-bound form of yeast Ran. Furthermore, overexpression of full-length or N-terminally truncated Los1p was shown to have dominant-negative effects on cell growth and different nuclear export pathways. Finally, Los1p could interact with Gsp1p-GTP, but only in the presence of tRNA, as revealed in an indirect in vitro binding assay. These data confirm the homology between Los1p and the recently identified human exportin for tRNA and reinforce the possibility of a role for Los1p in nuclear export of tRNA in yeast.
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Affiliation(s)
- K Hellmuth
- Biochemie-Zentrum Heidelberg, Deutsches Krebsforschungszentrum, 69120 Heidelberg, Germany
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36
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Otero GC, Harris ME, Donello JE, Hope TJ. Leptomycin B inhibits equine infectious anemia virus Rev and feline immunodeficiency virus rev function but not the function of the hepatitis B virus posttranscriptional regulatory element. J Virol 1998; 72:7593-7. [PMID: 9696859 PMCID: PMC110012 DOI: 10.1128/jvi.72.9.7593-7597.1998] [Citation(s) in RCA: 101] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/1998] [Accepted: 06/09/1998] [Indexed: 11/20/2022] Open
Abstract
Human immunodeficiency virus type 1 Rev export depends upon the presence of the nuclear export signal (NES), a leucine-rich stretch of hydrophobic amino acids. Recently, the nuclear NES-binding receptor has been identified as CRM1 or exportin 1. Rev export has been shown to be CRM1 dependent. The function of the atypical NES-containing Rev-like proteins of equine infectious anemia virus (EIAV) and feline immunodeficiency virus (FIV) is inhibited by leptomycin B, a drug that specifically blocks NES-CRM1 interactions. These data suggest that the function of atypical NES-containing proteins is CRM1 dependent. In contrast to the inhibition of EIAV Rev and FIV Rev, the cytoplasmic accumulation of hepatitis B virus (HBV) posttranscriptional regulatory element (PRE)-containing and Mason-Pfizer monkey virus (MPMV) constitutive transport element (CTE)-containing RNAs is not inhibited by leptomycin B treatment. We conclude that the HBV PRE, like the MPMV CTE, functions independently of an NES receptor-exportin 1 interaction.
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Affiliation(s)
- G C Otero
- Infectious Disease Laboratory, The Salk Institute for Biological Studies, La Jolla, California 92037, USA
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37
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Love DC, Sweitzer TD, Hanover JA. Reconstitution of HIV-1 rev nuclear export: independent requirements for nuclear import and export. Proc Natl Acad Sci U S A 1998; 95:10608-13. [PMID: 9724751 PMCID: PMC27942 DOI: 10.1073/pnas.95.18.10608] [Citation(s) in RCA: 88] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
Abstract
The Rev protein of HIV-1 actively shuttles between nucleus and cytoplasm and mediates the export of unspliced retroviral RNAs. The localization of shuttling proteins such as Rev is controlled by the relative rates of nuclear import and export. To study nuclear export in isolation, we generated cell lines expressing a green fluorescent protein-labeled chimeric protein consisting of HIV-1 Rev and a hormone-inducible nuclear localization sequence. Steroid removal switches off import thus allowing direct visualization of the Rev export pathway in living cells. After digitonin permeabilization of these cells, we found that a functional nuclear export sequence (NES), ATP, and fractionated cytosol were sufficient for nuclear export in vitro. Nuclear pore-specific lectins and leptomycin B were potent export inhibitors. Nuclear export was not inhibited by antagonists of calcium metabolism that block nuclear import. These data further suggest that nuclear pores do not functionally close when luminal calcium stores are depleted. The distinct requirements for nuclear import and export argue that these competing processes may be regulated independently. This system should have wide applicability for the analysis of nuclear import and export.
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Affiliation(s)
- D C Love
- Laboratory of Cell Biochemistry and Biology, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, MD 20892-0851, USA
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38
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Watkins JL, Murphy R, Emtage JL, Wente SR. The human homologue of Saccharomyces cerevisiae Gle1p is required for poly(A)+ RNA export. Proc Natl Acad Sci U S A 1998; 95:6779-84. [PMID: 9618489 PMCID: PMC22633 DOI: 10.1073/pnas.95.12.6779] [Citation(s) in RCA: 74] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/1997] [Indexed: 02/07/2023] Open
Abstract
The mechanism of mRNA export is a complex issue central to cellular physiology. We characterized previously yeast Gle1p, a protein with a leucine-rich (LR) nuclear export sequence (NES) that is essential for poly(A)+ RNA export in Saccharomyces cerevisiae. To characterize elements of the vertebrate mRNA export pathway, we identified a human homologue of yeast Gle1p and analyzed its function in mammalian cells. hGLE1 encodes a predicted 75-kDa polypeptide with high sequence homology to yeast Gle1p, but hGle1p does not contain a sequence motif matching any of the previously characterized NESs. hGLE1 can complement a yeast gle1 temperature-sensitive export mutant only if a LR-NES is inserted into it. To determine whether hGle1p played a role in nuclear export, anti-hGle1p antibodies were microinjected into HeLa cells. In situ hybridization of injected cells showed that poly(A)+ RNA export was inhibited. In contrast, there was no effect on the nuclear import of a glucocorticoid receptor reporter. We conclude that hGle1p functions in poly(A)+ RNA export, and that human cells facilitate such export with a factor similar to yeast but without a recognizable LR-NES. With hGle1p localized at the nuclear pore complexes, hGle1p is positioned to act at a terminal step in the export of mature RNA messages to the cytoplasm.
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Affiliation(s)
- J L Watkins
- Department of Cell Biology and Physiology, Washington University School of Medicine, 660 S. Euclid Ave., St. Louis, MO 63110, USA
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39
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Abstract
Significant and exciting advances in the field of RNA and protein export have been made recently, due in large part to discovery of the roles played by Ran, a small, soluble GTPase present in both the nucleus and cytoplasm of all eukaryotic cells. Ran is thought to be primarily bound to GTP in the nucleus and to GDP in the cytoplasm, as a result of the assymetric distribution of factors that interact with Ran to promote guanine nucleotide exchange (in the nucleus) and GTP hydrolysis (in the cytoplasm). A key function of the nuclear Ran.GTP is to support formation of complexes containing an export receptor (an exportin) and cargos such as RNAs, RNPs or proteins that are destined for export. In the cytoplasm, removal of the Ran.GTP from the complex results in its destabilization and release of the export cargo. Although Ran.GTP is required for formation of the export complex, GTP hydrolysis does not appear to be necessary for translocation through the nuclear pore complex or cytoplasmic release. Nevertheless, the GTPase of Ran does appear to be required in as yet unidentified intranuclear steps prior to export of some, but not all, RNAs.
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Affiliation(s)
- J E Dahlberg
- Department of Biomolecular Chemistry, University of Wisconsin-Madison, WI 53706, USA.
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40
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Abstract
Every minute, several million protein and RNA molecules must be transported between the cytoplasm and the nucleus of a eukaryotic cell. The characterization of mediators, receptors and accessory factors for different nuclear import and export pathways has provided a glimpse at the molecular machinery that is responsible for these trafficking events. It appears that both inbound and outbound traffic is mediated by a protein family of related transport factors that can be classified as importins and exportins.
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Affiliation(s)
- K Weis
- Dept of Biochemistry and Biophysics, UCSF 94143-0448, USA.
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41
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Abstract
The nuclear export of intron-containing HIV-1 RNA is critically dependent on the activity of Rev, a virally encoded sequence-specific RNA-binding protein. Rev shuttles between the nucleus and the cytoplasm and harbors both a nuclear localization signal and a nuclear export signal. These essential peptide motifs have now been shown to function by accessing cellular signal-mediated pathways for nuclear import and nuclear export. HIV-1 Rev therefore represents an excellent system with which to study aspects of transport across the nuclear envelope.
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MESH Headings
- Alternative Splicing
- Amino Acid Sequence
- Carrier Proteins/analysis
- Carrier Proteins/genetics
- Carrier Proteins/metabolism
- Carrier Proteins/physiology
- Cell Nucleus/metabolism
- Gene Expression Regulation, Viral
- Gene Products, rev/analysis
- Gene Products, rev/genetics
- Gene Products, rev/metabolism
- Gene Products, rev/physiology
- HIV Infections/therapy
- HIV-1/chemistry
- Humans
- Karyopherins
- Molecular Sequence Data
- RNA, Messenger/metabolism
- RNA, Viral/chemistry
- RNA, Viral/metabolism
- Receptors, Cytoplasmic and Nuclear
- Trans-Activators
- rev Gene Products, Human Immunodeficiency Virus
- Exportin 1 Protein
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Affiliation(s)
- V W Pollard
- Department of Microbiology, University of Pennsylvania School of Medicine, Philadelphia 19104-6148, USA.
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