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Kuss SK, Mata MA, Zhang L, Fontoura BMA. Nuclear imprisonment: viral strategies to arrest host mRNA nuclear export. Viruses 2013; 5:1824-49. [PMID: 23872491 PMCID: PMC3738964 DOI: 10.3390/v5071824] [Citation(s) in RCA: 45] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/10/2013] [Revised: 06/27/2013] [Accepted: 07/11/2013] [Indexed: 12/15/2022] Open
Abstract
Viruses possess many strategies to impair host cellular responses to infection. Nuclear export of host messenger RNAs (mRNA) that encode antiviral factors is critical for antiviral protein production and control of viral infections. Several viruses have evolved sophisticated strategies to inhibit nuclear export of host mRNAs, including targeting mRNA export factors and nucleoporins to compromise their roles in nucleo-cytoplasmic trafficking of cellular mRNA. Here, we present a review of research focused on suppression of host mRNA nuclear export by viruses, including influenza A virus and vesicular stomatitis virus, and the impact of this viral suppression on host antiviral responses.
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Affiliation(s)
- Sharon K Kuss
- Department of Cell Biology, University of Texas Southwestern Medical Center, Dallas, TX 75390, USA.
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2
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Shuen M, Avvakumov N, Torchia J, Mymryk JS. The E1A proteins of all six human adenovirus subgroups target the p300/CBP acetyltransferases and the SAGA transcriptional regulatory complex. Virology 2003; 316:75-83. [PMID: 14599792 DOI: 10.1016/j.virol.2003.08.005] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The N-terminal/conserved region 1 (CR1) portion of the human adenovirus (Ad) 5 E1A protein was previously shown to inhibit growth in the simple eukaryote Saccharomyces cerevisiae. We now demonstrate that the corresponding regions of the E1A proteins of Ad3,-4,-9,-12, and -40, which represent the remaining five Ad subgroups, also inhibit yeast growth. These results suggest that the E1A proteins of all six human Ad subgroups share a common cellular target(s) conserved in yeast. Growth inhibition induced by either full-length or the N-terminal/CR1 portion of Ad5 E1A was relieved by coexpression of the E1A binding portions of the mammalian p300, CBP, and pCAF acetyltransferases. Similarly, growth inhibition by the N-terminal/CR1 portions of the other Ad E1A proteins was suppressed by expression of the same regions of CBP or pCAF known to bind Ad5 E1A. The physical interaction of each of the different Ad E1A proteins with CBP, p300, and pCAF was confirmed in vitro. Furthermore, deletion of the gene encoding yGcn5, the yeast homolog of pCAF and a subunit of the SAGA transcriptional regulatory complex, restored growth in yeast expressing each of the different Ad E1A proteins. This indicates that the SAGA complex is a conserved target of all Ad E1A proteins. Our results demonstrate for the first time that the p300, CBP, and pCAF acetyltransferases are common targets for the E1A proteins of all six human Ad subgroups, highlighting the importance of these interactions for E1A function.
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Affiliation(s)
- Michael Shuen
- Department of Microbiology and Immunology, The University of Western Ontario, London, Regional Cancer Centre, 790 Commissioners Road East, N6A 4L6, London, Ontario, Canada
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Shuen M, Avvakumov N, Walfish PG, Brandl CJ, Mymryk JS. The adenovirus E1A protein targets the SAGA but not the ADA transcriptional regulatory complex through multiple independent domains. J Biol Chem 2002; 277:30844-51. [PMID: 12070146 DOI: 10.1074/jbc.m201877200] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Expression of the adenovirus E1A protein in the simple eukaryote Saccharomyces cerevisiae inhibits growth. We tested four regions of E1A that alter growth and transcription in mammalian cells for their effects in yeast when expressed as fusions to the Gal4p DNA binding domain. Expression of the N-terminal/conserved region (CR) 1 or CR3, but not of the CR2 or the C-terminal portion of E1A, inhibited yeast growth. Growth inhibition was relieved by deletion of the genes encoding the yGcn5p, Ngg1p, or Spt7p components of the SAGA transcriptional regulatory complex, but not the Ahc1p component of the related ADA complex, indicating that the N-terminal/CR1 and CR3 regions of E1A target the SAGA complex independently. Expression of the pCAF acetyltransferase, a mammalian homologue of yGcn5p, also suppressed growth inhibition by either portion of E1A. Furthermore, the N-terminal 29 residues and the CR3 portion of E1A interacted independently with yGcn5p and pCAF in vitro. Thus, two separate regions of E1A target the yGcn5p component of the SAGA transcriptional activation complex. A subregion of the N-terminal/CR1 fragment spanning residues 30-69 within CR1 also inhibited yeast growth in a SAGA-dependent fashion. However, this region did not interact with yGcn5p or pCAF, suggesting that it makes a third contact with another SAGA component. Our results provide a new model system to elucidate mechanisms by which E1A and the SAGA complex regulate transcription and growth.
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Affiliation(s)
- Michael Shuen
- Department of Microbiology and Immunology, London Regional Cancer Centre, The University of Western Ontario, 709 Commissioners Road E., London, Ontario N6A 4L6, Canada
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4
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Affiliation(s)
- T Dobner
- Institut für Medizinische Mikrobiologie und Hygiene, Universität Regensburg, Franz-Josef-Strauss-Allee 11, 93053 Regensburg, Germany
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5
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Punga T, Akusjärvi G. The adenovirus-2 E1B-55K protein interacts with a mSin3A/histone deacetylase 1 complex. FEBS Lett 2000; 476:248-52. [PMID: 10913622 DOI: 10.1016/s0014-5793(00)01739-7] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The adenovirus E1B-55K protein is a multifunctional phosphoprotein that regulates nuclear to cytoplasmic export of host cell and viral mRNAs during lytic viral growth. E1B-55K also blocks apoptosis by binding and functionally inactivating the human tumor suppressor protein p53. Here, we show that E1B-55K interacts with histone deacetylase 1 (HDAC1) and the transcriptional corepressor protein mSin3A, both in the adenovirus-transformed 293 cell line and during a lytic adenovirus infection. Furthermore, we show that the central amino acids 156-261 in E1B-55K are necessary for efficient HDAC1 interaction. Importantly, the E1B-55K/mSin3A/HDAC1 complex is also enzymatically active, catalyzing deacetylation of a histone substrate peptide. Collectively, our results suggest that E1B-55K interaction with mSin3A/HDAC1 containing complexes may be significant for one or several of the multiple activities ascribed to this protein.
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Affiliation(s)
- T Punga
- Department of Medical Biochemistry and Microbiology, Uppsala University, BMC, Box 582, 751 23, Uppsala, Sweden
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6
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Tartakoff AM, Lichtenstein M, Nanduri J, Tsao HM. Review: dynamic stability of the interphase nucleus in health and disease. J Struct Biol 2000; 129:144-58. [PMID: 10806065 DOI: 10.1006/jsbi.2000.4225] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
Ongoing export of newly synthesized RNAs, as well as control of transcriptional activity, involves dynamic nucleocytoplasmic transport of proteins. Some proteins that shuttle reside primarily in the nucleus while others are concentrated in the cytoplasm. Moreover, some proteins shuttle continuously, while others shuttle only once. A third group is stimulated to relocate either into or out of the nucleus as a result of interruption of shuttling. In addition to these protein-specific events, several physiological stimuli have global effects on nucleocytoplasmic transport. In related events, selected proteins move between distinct sites in the nucleoplasm, others enter and leave the nucleolus, and still others transit between the nuclear envelope and cytoplasmic membranes. These multiple dynamic distributions provide numerous opportunities for precise communication between spatially distant sites in the cell.
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Affiliation(s)
- A M Tartakoff
- Pathology Department, Cell Biology Program, Case Western Reserve University School of Medicine, 2085 Adelbert Road, Cleveland, Ohio, 44106, USA
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7
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Weigel S, Dobbelstein M. The nuclear export signal within the E4orf6 protein of adenovirus type 5 supports virus replication and cytoplasmic accumulation of viral mRNA. J Virol 2000; 74:764-72. [PMID: 10623738 PMCID: PMC111596 DOI: 10.1128/jvi.74.2.764-772.2000] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During the late phase of adenovirus infection, viral mRNA is efficiently transported from the nucleus to the cytoplasm while most cellular mRNA species are retained in the nucleus. Two viral proteins, E1B-55 kDa and E4orf6, are both necessary for these effects. The E4orf6 protein of adenovirus type 5 binds and relocalizes E1B-55 kDa, and the complex of the two proteins was previously shown to shuttle continuously between the nucleus and cytoplasm. Nucleocytoplasmic transport of the complex is achieved by a nuclear export signal (NES) within E4orf6. Mutation of this signal sequence severely reduces the ability of the E1B-55 kDa-E4orf6 complex to leave the nucleus. Here, we examined the role of functional domains within E4orf6 during virus infection. E4orf6 or mutants derived from it were transiently expressed, followed by infection with recombinant adenovirus lacking the E4 region and determination of virus yield. An arginine-rich putative alpha helix near the carboxy terminus of E4orf6 contributes to E1B-55 kDa binding and relocalization as well as to the synthesis of viral DNA, mRNA, and proteins. Further mutational analysis revealed that mutation of the NES within E4orf6 considerably reduces its ability to support virus production. The same effect was observed when nuclear export was blocked with a competitor. Further, a functional NES within E4orf6 contributed to the efficiency of late virus protein synthesis and viral DNA replication, as well as total and cytoplasmic accumulation of viral late mRNA. Our data support the view that NES-mediated nucleocytoplasmic shuttling strongly enhances most, if not all, intracellular activities of E4orf6 during the late phase of adenovirus infection.
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Affiliation(s)
- S Weigel
- Institut für Virologie, Zentrum für Mikrobiologie und Hygiene, Philipps-Universität Marburg, 35037 Marburg, Germany
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Ward BM, Lazarowitz SG. Nuclear export in plants. Use of geminivirus movement proteins for a cell-based export assay. THE PLANT CELL 1999; 11:1267-76. [PMID: 10402428 PMCID: PMC144272 DOI: 10.1105/tpc.11.7.1267] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/17/2023]
Abstract
The nuclear export of proteins and RNAs has been studied in heterokaryons or by microinjecting test substrates into nuclei of HeLa cells or Xenopus oocytes. We have previously shown that the two movement proteins BR1 and BL1 encoded by the plant pathogenic squash leaf curl virus act in a coordinated manner to facilitate virus cell-to-cell movement and that one of these (BR1) is a nuclear shuttle protein. By using a novel in vivo cell-based assay for nuclear export in which nuclear-localized BR1 is trapped by BL1 and redirected to the cortical cytoplasm, we demonstrate that residues 177 to 198 of BR1 contain a leucine-rich nuclear export signal (NES) of the type found in the Rev protein encoded by the human immunodeficiency virus and in Xenopus TFIIIA. We further show that the TFIIIA NES can functionally replace the NES of BR1 in both nuclear export and viral infectivity. These findings suggest that this basic pathway for nuclear export is highly conserved among plant and animal cells and in yeast.
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Affiliation(s)
- B M Ward
- Department of Microbiology, University of Illinois, Urbana, Illinois 61801, USA
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9
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Gabler S, Schütt H, Groitl P, Wolf H, Shenk T, Dobner T. E1B 55-kilodalton-associated protein: a cellular protein with RNA-binding activity implicated in nucleocytoplasmic transport of adenovirus and cellular mRNAs. J Virol 1998; 72:7960-71. [PMID: 9733834 PMCID: PMC110131 DOI: 10.1128/jvi.72.10.7960-7971.1998] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/12/1998] [Accepted: 07/01/1998] [Indexed: 11/20/2022] Open
Abstract
The adenovirus type 5 (Ad5) early 1B 55-kDa protein (E1B-55kDa) is a multifunctional phosphoprotein that regulates viral DNA replication and nucleocytoplasmic RNA transport in lytically infected cells. In addition, E1B-55kDa provides functions required for complete oncogenic transformation of rodent cells in cooperation with the E1A proteins. Using the far-Western technique, we have isolated human genes encoding E1B-55kDa-associated proteins (E1B-APs). The E1B-AP5 gene encodes a novel nuclear RNA-binding protein of the heterogeneous nuclear ribonucleoprotein (hnRNP) family that is highly related to hnRNP-U/SAF-A. Immunoprecipitation experiments indicate that two distinct segments in the 55-kDa polypeptide which partly overlap regions responsible for p53 binding are required for complex formation with E1B-AP5 in Ad-infected cells and that this protein interaction is modulated by the adenovirus E4orf6 protein. Expression of E1B-AP5 efficiently interferes with Ad5 E1A/E1B-mediated transformation of primary rat cells. Furthermore, stable expression of E1B-AP5 in Ad-infected cells overcomes the E1B-dependent inhibition of cytoplasmic host mRNA accumulation. These data suggest that E1B-AP5 might play a role in RNA transport and that this function is modulated by E1B-55kDa in Ad-infected cells.
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Affiliation(s)
- S Gabler
- Institut für Medizinische Mikrobiologie und Hygiene, Universität Regensburg, D-93053 Regensburg, Germany
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10
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Leppard KN. Regulated RNA Processing and RNA Transport during Adenovirus Infection. ACTA ACUST UNITED AC 1998. [DOI: 10.1006/smvy.1997.0132] [Citation(s) in RCA: 21] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
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11
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Roth J, Dobbelstein M, Freedman DA, Shenk T, Levine AJ. Nucleo-cytoplasmic shuttling of the hdm2 oncoprotein regulates the levels of the p53 protein via a pathway used by the human immunodeficiency virus rev protein. EMBO J 1998; 17:554-64. [PMID: 9430646 PMCID: PMC1170405 DOI: 10.1093/emboj/17.2.554] [Citation(s) in RCA: 478] [Impact Index Per Article: 18.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The hdm2 gene is overexpressed in a variety of human tumors. Its gene product localizes predominantly to the nucleus, where it acts as an inhibitor of the p53 tumor suppressor gene product. It is shown here that the hdm2 oncoprotein constantly shuttles between the nucleus and the cytoplasm. Shuttling of hdm2 does not depend on its interaction with p53. Nuclear export of hdm2 is mediated by a signal sequence similar to the nuclear export signal of the rev protein from human immunodeficiency virus and other lentiviruses. Mutation of this signal sequence abolishes detectable nucleo-cytoplasmic shuttling. When fused to a carrier protein, the hdm2 signal sequence can mediate nuclear export after intranuclear microinjection into HeLa cells. The export of hdm2 can be blocked by a competitive inhibitor of rev export, arguing that the export pathways for hdm2 and rev are either overlapping or identical. Inhibition of its export modifies the ability of hdm2 to block p53-mediated transcriptional activation, and hdm2's export function is required to accelerate the degradation of p53. Thus the rev nuclear export pathway may be used to regulate an oncogene product's activity and modulate cellular growth.
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Affiliation(s)
- J Roth
- Department of Molecular Biology, Princeton University, Lewis Thomas Laboratory, NJ 08544-1014, USA
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12
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Dobbelstein M, Roth J, Kimberly WT, Levine AJ, Shenk T. Nuclear export of the E1B 55-kDa and E4 34-kDa adenoviral oncoproteins mediated by a rev-like signal sequence. EMBO J 1997; 16:4276-84. [PMID: 9250671 PMCID: PMC1170053 DOI: 10.1093/emboj/16.14.4276] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The E1B 55-kDa and E4 34-kDa oncoproteins of adenovirus type 5 (abbreviated here as E1B-55kD and E4-34kD) promote the export of viral mRNA and inhibit the export of most cellular mRNA species. We show that the intracellular complex containing E1B-55kD and E4-34kD continuously shuttles between the nucleus and the cytoplasm, and may thus serve as a nucleocytoplasmic transporter for viral mRNA. We present evidence that within this complex, it is the E4-34kD protein that directs both nuclear import and nuclear export. E4-34kD contains a functional nuclear export signal similar to corresponding sequences found in the retroviral proteins rev and rex. This sequence element is required for nuclear export of the complex, and it can function autonomously when fused to a carrier protein and microinjected in HeLa cell nuclei. When E4-34kD is expressed alone, a portion of the protein that contains a predicted arginine-rich amphipathic alpha-helical structure mediates nuclear retention of the protein. This retention, however, can be abolished by the association with E1B-55kD or by a specific point mutation within the arginine-rich motif. The export of E4-34kD can be blocked by an HTLV-rex derived competitive inhibitor and overexpressed E4-34kD inhibits rev-mediated transport, suggesting that the export pathways accessed by the adenoviral and retroviral proteins share components. The interplay between two polypeptides as well as the involvement of a dominant nuclear retention domain are novel features that might contribute to the efficiency and regulation of the adenovirus export system.
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Affiliation(s)
- M Dobbelstein
- Howard Hughes Medical Institute, Princeton University, NJ 08544-1014, USA
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Rubenwolf S, Schütt H, Nevels M, Wolf H, Dobner T. Structural analysis of the adenovirus type 5 E1B 55-kilodalton-E4orf6 protein complex. J Virol 1997; 71:1115-23. [PMID: 8995632 PMCID: PMC191163 DOI: 10.1128/jvi.71.2.1115-1123.1997] [Citation(s) in RCA: 84] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The adenovirus type 5 (Ad5) early 1B (E1B) 55-kDa (E1B-55kDa)-E4orf6 protein complex has been implicated in the selective modulation of nucleocytoplasmic mRNA transport at late times after infection. Using a combined immunoprecipitation-immunoblotting assay, we mapped the domains in E1B-55kDa required for the interaction with the E4orf6 protein in lytically infected A549 cells. Several domains in the 496-residue 55-kDa polypeptide contributed to a stable association with the E4orf6 protein in E1B mutant virus-infected cells. Linker insertion mutations at amino acids 180 and 224 caused reduced binding of the E4orf6 protein, whereas linker insertion mutations at amino acid 143 and in the central domain of E1B-55kDa eliminated the binding of the E4orf6 protein. Earlier work showing that the central domain of E1B-55kDa is required for binding to p53 and the recent observation that the E4orf6 protein also interacts with the tumor suppressor protein led us to suspect that p53 might play a role in the E1B-E4 protein interaction. However, coimmunoprecipitation assays with extracts prepared from infected p53-negative H1299 cells established that p53 is not needed for the E1B-E4 protein interaction in adenovirus-infected cells. Using two different protein-protein interaction assays, we also mapped the region in the E4orf6 protein required for E1B-55kDa interaction to the amino-terminal 55 amino acid residues. Interestingly, both binding assays established that the same region in the E4orf6/7 protein can potentially interact with E1B-55kDa. Our results demonstrate that two distinct segments in the 55-kDa protein encoding the transformation and late lytic functions independently interact with p53 and the E4orf6 protein in vivo and provide further insight by which the multifunctional 55-kDa EIB protein can exert its multiple activities in lytically infected cells and in adenovirus transformation.
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Affiliation(s)
- S Rubenwolf
- Institut für Medizinische Mikrobiologie und Hygiene, Universität Regensburg, Germany
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14
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Liu Y, Liang S, Tartakoff AM. Heat shock disassembles the nucleolus and inhibits nuclear protein import and poly(A)+ RNA export. EMBO J 1996; 15:6750-7. [PMID: 8978700 PMCID: PMC452498] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Heat shock causes major positive and negative changes in gene expression, drastically alters the appearance of the nucleolus and inhibits rRNA synthesis. We here show that it causes many yeast nucleolar proteins, including the fibrillarin homolog Nop1p, to relocate to the cytoplasm. Relocation depends on several proteins implicated in mRNA transport (Mtrps) and is reversible. Two observations indicate, surprisingly, that disassembly results from a reduction in Ssa protein (Hsp70) levels: (i) selective depletion of Ssa1p leads to disassembly of the nucleolus; (ii) preincubation at 37 degrees C protects the nucleolus against disassembly by heat shock, unless expression of Ssa proteins is specifically inhibited. We observed that heat shock or reduction of Ssa1p levels inhibits protein import into the nucleus and therefore we propose that inhibition of import leads to disassembly of the nucleolus. These observations provide a simple explanation of the effects of heat shock on the anatomy of the nucleolus and rRNA transcription. They also extend understanding of the path of nuclear export. Since a number of nucleoplasmic proteins also relocate upon heat shock, these observations can provide a general mechanism for regulation of gene expression. Relocation of the hnRNP-like protein Mtr13p (= Npl3p, Nop3p), explains the heat shock sensitivity of export of average poly(A)+ RNA. Strikingly, Hsp mRNA export appears not to be affected.
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Affiliation(s)
- Y Liu
- Department of Pathology and Cell Biology Program, Case Western Reserve University School of Medicine, Cleveland, OH 44106, USA
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15
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Goodrum FD, Shenk T, Ornelles DA. Adenovirus early region 4 34-kilodalton protein directs the nuclear localization of the early region 1B 55-kilodalton protein in primate cells. J Virol 1996; 70:6323-35. [PMID: 8709260 PMCID: PMC190658 DOI: 10.1128/jvi.70.9.6323-6335.1996] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The localization of the adenovirus type 5 34-kDa E4 and 55-kDa E1B proteins was determined in the absence of other adenovirus proteins. When expressed by transfection in human, monkey, hamster, rat, and mouse cell lines, the E1B protein was predominantly cytoplasmic and typically was excluded from the nucleus. When expressed by transfection, the E4 protein accumulated in the nucleus. Strikingly, when coexpressed by transfection in human, monkey, or baby hamster kidney cells, the E1B protein colocalized in the nucleus with the E4 protein. A complex of the E4 and E1B proteins was identified by coimmunoprecipitation in transfected HeLa cells. By contrast to the interaction observed in primate and baby hamster kidney cells, the E4 protein failed to direct the E1B protein to the nucleus in rat and mouse cell lines as well as CHO and V79 hamster cell lines. This failure of the E4 protein to direct the nuclear localization of the E1B protein in REF-52 rat cells was overcome by fusion with HeLa cells. Within 4 h of heterokaryon formation and with protein synthesis inhibited, a portion of the E4 protein present in the REF-52 nuclei migrated to the HeLa nuclei. Simultaneously, the previously cytoplasmic E1B protein colocalized with the E4 protein in both human and rat cell nuclei. These results suggest that a primate cell-specific factor mediates the functional interaction of the E1B and E4 proteins of adenovirus.
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Affiliation(s)
- F D Goodrum
- Molecular Genetics Program, Bowman Gray School of Medicine, Wake Forest University, Winston-Salem, North Carolina 27157-1064, USA
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