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RNA-Binding Proteins as Regulators of Internal Initiation of Viral mRNA Translation. Viruses 2022; 14:v14020188. [PMID: 35215780 PMCID: PMC8879377 DOI: 10.3390/v14020188] [Citation(s) in RCA: 6] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2021] [Revised: 01/03/2022] [Accepted: 01/14/2022] [Indexed: 12/17/2022] Open
Abstract
Viruses are obligate intracellular parasites that depend on the host’s protein synthesis machinery for translating their mRNAs. The viral mRNA (vRNA) competes with the host mRNA to recruit the translational machinery, including ribosomes, tRNAs, and the limited eukaryotic translation initiation factor (eIFs) pool. Many viruses utilize non-canonical strategies such as targeting host eIFs and RNA elements known as internal ribosome entry sites (IRESs) to reprogram cellular gene expression, ensuring preferential translation of vRNAs. In this review, we discuss vRNA IRES-mediated translation initiation, highlighting the role of RNA-binding proteins (RBPs), other than the canonical translation initiation factors, in regulating their activity.
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2
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Torma G, Tombácz D, Csabai Z, Göbhardter D, Deim Z, Snyder M, Boldogkői Z. An Integrated Sequencing Approach for Updating the Pseudorabies Virus Transcriptome. Pathogens 2021; 10:pathogens10020242. [PMID: 33672563 PMCID: PMC7924054 DOI: 10.3390/pathogens10020242] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Revised: 02/17/2021] [Accepted: 02/18/2021] [Indexed: 01/06/2023] Open
Abstract
In the last couple of years, the implementation of long-read sequencing (LRS) technologies for transcriptome profiling has uncovered an extreme complexity of viral gene expression. In this study, we carried out a systematic analysis on the pseudorabies virus transcriptome by combining our current data obtained by using Pacific Biosciences Sequel and Oxford Nanopore Technologies MinION sequencing with our earlier data generated by other LRS and short-read sequencing techniques. As a result, we identified a number of novel genes, transcripts, and transcript isoforms, including splice and length variants, and also confirmed earlier annotated RNA molecules. One of the major findings of this study is the discovery of a large number of 5′-truncations of larger putative mRNAs being 3′-co-terminal with canonical mRNAs of PRV. A large fraction of these putative RNAs contain in-frame ATGs, which might initiate translation of N-terminally truncated polypeptides. Our analyses indicate that CTO-S, a replication origin-associated RNA molecule is expressed at an extremely high level. This study demonstrates that the PRV transcriptome is much more complex than previously appreciated.
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Affiliation(s)
- Gábor Torma
- Department of Medical Biology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary; (G.T.); (D.T.); (Z.C.); (D.G.)
| | - Dóra Tombácz
- Department of Medical Biology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary; (G.T.); (D.T.); (Z.C.); (D.G.)
- Department of Genetics, School of Medicine, Stanford University, Stanford, CA 94304, USA;
| | - Zsolt Csabai
- Department of Medical Biology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary; (G.T.); (D.T.); (Z.C.); (D.G.)
| | - Dániel Göbhardter
- Department of Medical Biology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary; (G.T.); (D.T.); (Z.C.); (D.G.)
| | - Zoltán Deim
- Department of Biotechnology, Faculty of Science and Informatics, University of Szeged, 6726 Szeged, Hungary;
| | - Michael Snyder
- Department of Genetics, School of Medicine, Stanford University, Stanford, CA 94304, USA;
| | - Zsolt Boldogkői
- Department of Medical Biology, Faculty of Medicine, University of Szeged, 6720 Szeged, Hungary; (G.T.); (D.T.); (Z.C.); (D.G.)
- Correspondence:
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3
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Moodad S, El Hajj R, Hleihel R, Hajjar L, Tawil N, Karam M, Hamie M, Abou Merhi R, El Sabban M, El Hajj H. Lenalidomide in Combination with Arsenic Trioxide: an Effective Therapy for Primary Effusion Lymphoma. Cancers (Basel) 2020; 12:E2483. [PMID: 32883022 PMCID: PMC7563318 DOI: 10.3390/cancers12092483] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2020] [Revised: 07/22/2020] [Accepted: 07/23/2020] [Indexed: 12/15/2022] Open
Abstract
Primary effusion lymphoma (PEL) is a rare aggressive subset of non-Hodgkin B cell lymphoma. PEL is secondary to Kaposi sarcoma herpes virus (KSHV) and predominantly develops in serous cavities. Conventional chemotherapy remains the treatment of choice for PEL and yields high response rates with no significant comorbidities. Yet, chemotherapy often fails in achieving or maintaining long-term remission. Lenalidomide (Lena), an immunomodulatory drug, displayed some efficacy in the treatment of PEL. On the other hand, arsenic trioxide (ATO) in combination with other agents effectively treated a number of blood malignancies, including PEL. In this study, we present evidence that the combination of ATO/Lena significantly enhanced survival of PEL mice, decreased the volume of exacerbated ascites in the peritoneum, and reduced tumor infiltration in organs of treated animals. In ex vivo treated PEL cells, ATO/Lena decreased the proliferation and downregulated the expression of KSHV latent viral proteins. This was associated with decreased NF-κB activation, resulting in reactivation of viral replication, downregulation of interleukin-6 (IL-6) and IL-10, inhibition of vascular endothelial growth factor, and apoptosis. Our results elucidate the mechanism of action of ATO/Lena and present it as a promising targeted therapeutic modality in PEL management, which warrants further clinical investigation.
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Affiliation(s)
- Sara Moodad
- Department of Internal Medicine, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (S.M.); (R.H.); (M.H.)
| | - Rana El Hajj
- Department of Pathology and Laboratory Medicine, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon;
| | - Rita Hleihel
- Department of Internal Medicine, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (S.M.); (R.H.); (M.H.)
- Department of Anatomy, Cell Biology, and Physiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (L.H.); (M.E.S.)
| | - Layal Hajjar
- Department of Anatomy, Cell Biology, and Physiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (L.H.); (M.E.S.)
| | - Nadim Tawil
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (N.T.); (M.K.)
| | - Martin Karam
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (N.T.); (M.K.)
| | - Maguy Hamie
- Department of Internal Medicine, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (S.M.); (R.H.); (M.H.)
| | - Raghida Abou Merhi
- Department of Biology, Faculty of Sciences, GSBT laboratory, Lebanese University, Hadath 31143, Lebanon;
| | - Marwan El Sabban
- Department of Anatomy, Cell Biology, and Physiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (L.H.); (M.E.S.)
| | - Hiba El Hajj
- Department of Experimental Pathology, Immunology, and Microbiology, Faculty of Medicine, American University of Beirut, Beirut 202627, Lebanon; (N.T.); (M.K.)
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4
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Boldogkői Z, Moldován N, Balázs Z, Snyder M, Tombácz D. Long-Read Sequencing – A Powerful Tool in Viral Transcriptome Research. Trends Microbiol 2019; 27:578-592. [DOI: 10.1016/j.tim.2019.01.010] [Citation(s) in RCA: 49] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2018] [Revised: 01/21/2019] [Accepted: 01/30/2019] [Indexed: 12/16/2022]
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5
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Ullah H, Hou W, Dakshanamurthy S, Tang Q. Host targeted antiviral (HTA): functional inhibitor compounds of scaffold protein RACK1 inhibit herpes simplex virus proliferation. Oncotarget 2019; 10:3209-3226. [PMID: 31143369 PMCID: PMC6524932 DOI: 10.18632/oncotarget.26907] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2018] [Accepted: 04/21/2019] [Indexed: 12/11/2022] Open
Abstract
Due to the small number of molecular targets in viruses and the rapid evolution of viral genes, it is very challenging to develop specific antiviral drugs. Viruses require host factors to translate their transcripts, and targeting the host factor(s) offers a unique opportunity to develop broad antiviral drugs. It is well documented that some viruses utilize a host protein, Receptor for Activated C Kinase 1 (RACK1), to translate their mRNAs using a viral mRNA secondary structure known as the Internal Ribosomal Entry Site (IRES). RACK1 is essential for the translation of many viruses including hepatitis C (HCV), polio, Drosophila C (DCV), Dengue, Cricket Paralysis (CrpV), and vaccinia viruses. In addition, HIV-1 and Herpes Simplex virus (HSV-1) are known to use IRES as well. Therefore, host RACK1 protein is an attractive target for developing broad antiviral drugs. Depletion of the host's RACK1 will potentially inhibit virus replication. This background study has led us to the development of novel antiviral therapeutics, such as RACK1 inhibitors. By utilizing the crystal structure of the RACK1A protein from the model plant Arabidopsis and using a structure based drug design method, dozens of small compounds were identified that could potentially bind to the experimentally determined functional site of the RACK1A protein. The SPR assays showed that the small compounds bound strongly to recombinant RACK1A protein. Here we provide evidence that the drugs show high efficacy in inhibition of HSV-1 proliferation in a HEp-2 cell line. The drug showed similar efficacy as the available anti-herpes drug acyclovir and showed supralinear effect when applied in a combinatorial manner. As an increasing number of viruses are reported to use host RACK1 proteins, and more than 100 diverse animals and plant disease-causing viruses are known to use IRES-based translation, these drugs can be established as host-targeted broad antiviral drugs.
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Affiliation(s)
- Hemayet Ullah
- Department of Biology, Howard University, Washington, DC 20059, USA
| | - Wangheng Hou
- Department of Microbiology, Howard University College of Medicine, Washington, DC 20059, USA
| | - Sivanesan Dakshanamurthy
- Department of Oncology, Clinical and Experimental Therapeutics Program, Lombardi Comprehensive Cancer Center, Georgetown University Medical Center, Washington, DC 20057, USA
| | - Qiyi Tang
- Department of Microbiology, Howard University College of Medicine, Washington, DC 20059, USA
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6
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Development of an ORF45-Derived Peptide To Inhibit the Sustained RSK Activation and Lytic Replication of Kaposi's Sarcoma-Associated Herpesvirus. J Virol 2019; 93:JVI.02154-18. [PMID: 30842327 DOI: 10.1128/jvi.02154-18] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2018] [Accepted: 02/27/2019] [Indexed: 01/03/2023] Open
Abstract
The lytic replication of Kaposi's sarcoma-associated herpesvirus (KSHV) requires sustained extracellular signal-regulated kinase (ERK)-p90 ribosomal S6 kinase (RSK) activation, which is induced by an immediate early (IE) gene-encoded tegument protein called ORF45, to promote the late transcription and translation of viral lytic genes. An ORF45-null or single-point F66A mutation in ORF45 abolishes ORF45-RSK interaction and sustained ERK-RSK activation during lytic reactivation and subsequently results in a significant decrease in late lytic gene expression and virion production, indicating that ORF45-mediated RSK activation plays a critical role in KSHV lytic replication. Here, we demonstrate that a short ORF45-derived peptide in the RSK-binding region is sufficient for disrupting ORF45-RSK interaction, consequently suppressing lytic gene expression and virion production. We designed a nontoxic cell-permeable peptide derived from ORF45, TAT-10F10, which is composed of the ORF45 56 to 76 amino acid (aa) region and the HIV Tat protein transduction domain, and this peptide markedly inhibits KSHV lytic replication in iSLK.219 and BCBL1 cells. Importantly, this peptide enhances the inhibitory effect of rapamycin on KSHV-infected cells and decreases spontaneous and hypoxia-induced lytic replication in KSHV-positive lymphoma cells. These findings suggest that a small peptide that disrupts ORF45-RSK interaction might be a promising agent for controlling KSHV lytic infection and pathogenesis.IMPORTANCE ORF45-induced RSK activation plays an essential role in KSHV lytic replication, and ORF45-null or ORF45 F66A mutagenesis that abolishes sustained RSK activation and RSK inhibitors significantly decreases lytic replication, indicating that the ORF45-RSK association is a unique target for KSHV-related diseases. However, the side effects, low affinity, and poor efficacy of RSK modulators limit their clinical application. In this study, we developed a nontoxic cell-permeable ORF45-derived peptide from the RSK-binding region to disrupt ORF45-RSK associations and block ORF45-induced RSK activation without interfering with S6K1 activation. This peptide effectively suppresses spontaneous, hypoxia-induced, or chemically induced KSHV lytic replication and enhances the inhibitory effect of rapamycin on lytic replication and sensitivity to rapamycin in lytic KSHV-infected cells. Our results reveal that the ORF45-RSK signaling axis and KSHV lytic replication can be effectively targeted by a short peptide and provide a specific approach for treating KSHV lytic and persistent infection.
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7
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Butnaru M, Gaglia MM. Transcriptional and post-transcriptional regulation of viral gene expression in the gamma-herpesvirus Kaposi's sarcoma-associated herpesvirus. CURRENT CLINICAL MICROBIOLOGY REPORTS 2019; 5:219-228. [PMID: 30854283 DOI: 10.1007/s40588-018-0102-1] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022]
Abstract
Purpose of review Kaposi's sarcoma-associated herpesvirus (KSHV), the etiological agent of the AIDS-associated tumor Kaposi's sarcoma, is a complex virus that expresses ~90 proteins in a regulated temporal cascade during its replication cycle. Although KSHV relies on cellular machinery for gene expression, it also uses specialized regulators to control nearly every step of the process. In this review we discuss the current understanding of KSHV gene regulation. Recent findings High-throughput sequencing and a new robust system to mutate KSHV have paved the way for comprehensive studies of KSHV gene expression, leading to the characterization of new viral factors that control late gene expression and post-transcriptional steps of gene regulation. They have also revealed key aspects of chromatin-based control of gene expression in the latent and lytic cycle. Summary The combination of mutant analysis and high-throughput sequencing will continue to expand our model of KSHV gene regulation and point to potential new targets for anti-KSHV drugs.
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Affiliation(s)
- Matthew Butnaru
- Graduate Program in Biochemistry, Sackler School of Biomedical Sciences, Tufts University, Boston, MA, USA
- Department of Molecular Biology and Microbiology, School of Medicine, Tufts University, Boston, MA, USA
| | - Marta M Gaglia
- Department of Molecular Biology and Microbiology, School of Medicine, Tufts University, Boston, MA, USA
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Ueda K. KSHV Genome Replication and Maintenance in Latency. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2018; 1045:299-320. [DOI: 10.1007/978-981-10-7230-7_14] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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9
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Zaghloul HAH, Hice R, Arensburger P, Federici BA. Transcriptome Analysis of the Spodoptera frugiperda Ascovirus In Vivo Provides Insights into How Its Apoptosis Inhibitors and Caspase Promote Increased Synthesis of Viral Vesicles and Virion Progeny. J Virol 2017; 91:e00874-17. [PMID: 28956762 PMCID: PMC5686725 DOI: 10.1128/jvi.00874-17] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2017] [Accepted: 08/31/2017] [Indexed: 11/20/2022] Open
Abstract
Ascoviruses are double-stranded DNA (dsDNA) viruses that attack caterpillars and differ from all other viruses by inducing nuclear lysis followed by cleavage of host cells into numerous anucleate vesicles in which virus replication continues as these grow in the blood. Ascoviruses are also unusual in that most encode a caspase or caspase-like proteins. A robust cell line to study the novel molecular biology of ascovirus replication in vitro is lacking. Therefore, we used strand-specific transcriptome sequencing (RNA-Seq) to study transcription in vivo in third instars of Spodoptera frugiperda infected with the type species, Spodoptera frugiperda ascovirus1a (SfAV-1a), sampling transcripts at different time points after infection. We targeted transcription of two types of SfAV-1a genes; first, 44 core genes that occur in several ascovirus species, and second, 26 genes predicted in silico to have metabolic functions likely involved in synthesizing viral vesicle membranes. Gene cluster analysis showed differences in temporal expression of SfAV-1a genes, enabling their assignment to three temporal classes: early, late, and very late. Inhibitors of apoptosis (IAP-like proteins; ORF016, ORF025, and ORF074) were expressed early, whereas its caspase (ORF073) was expressed very late, which correlated with apoptotic events leading to viral vesicle formation. Expression analysis revealed that a Diedel gene homolog (ORF121), the only known "virokine," was highly expressed, implying that this ascovirus protein helps evade innate host immunity. Lastly, single-nucleotide resolution of RNA-Seq data revealed 15 bicistronic and tricistronic messages along the genome, an unusual occurrence for large dsDNA viruses.IMPORTANCE Unlike all other DNA viruses, ascoviruses code for an executioner caspase, apparently involved in a novel cytopathology in which viral replication induces nuclear lysis followed by cell cleavage, yielding numerous large anucleate viral vesicles that continue to produce virions. Our transcriptome analysis of genome expression in vivo by the Spodoptera frugiperda ascovirus shows that inhibitors of apoptosis are expressed first, enabling viral replication to proceed, after which the SfAV-1a caspase is synthesized, leading to viral vesicle synthesis and subsequent extensive production of progeny virions. Moreover, we detected numerous bicistronic and tricistronic mRNA messages in the ascovirus transcriptome, implying that ascoviruses use other noncanonical translational mechanisms, such as internal ribosome entry sites (IRESs). These results provide the first insights into the molecular biology of a unique coordinated gene expression pattern in which cell architecture is markedly modified, more than in any other known eukaryotic virus, to promote viral reproduction and transmission.
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Affiliation(s)
- Heba A H Zaghloul
- Interdepartmental Graduate Program in Microbiology and Institute for Integrative Genome Biology, University of California, Riverside, Riverside, California, USA
- Department of Botany and Microbiology, Faculty of Science, Alexandria University, Alexandria, Egypt
| | - Robert Hice
- Interdepartmental Graduate Program in Microbiology and Institute for Integrative Genome Biology, University of California, Riverside, Riverside, California, USA
| | - Peter Arensburger
- California State Polytechnic University, Pomona, Department of Biological Sciences, Pomona, California, USA
| | - Brian A Federici
- Interdepartmental Graduate Program in Microbiology and Institute for Integrative Genome Biology, University of California, Riverside, Riverside, California, USA
- Department of Entomology, University of California, Riverside, Riverside, California, USA
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10
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Terenin IM, Smirnova VV, Andreev DE, Dmitriev SE, Shatsky IN. A researcher's guide to the galaxy of IRESs. Cell Mol Life Sci 2017; 74:1431-1455. [PMID: 27853833 PMCID: PMC11107752 DOI: 10.1007/s00018-016-2409-5] [Citation(s) in RCA: 38] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2016] [Revised: 11/01/2016] [Accepted: 11/02/2016] [Indexed: 12/25/2022]
Abstract
The idea of internal initiation is frequently exploited to explain the peculiar translation properties or unusual features of some eukaryotic mRNAs. In this review, we summarize the methods and arguments most commonly used to address cases of translation governed by internal ribosome entry sites (IRESs). Frequent mistakes are revealed. We explain why "cap-independent" does not readily mean "IRES-dependent" and why the presence of a long and highly structured 5' untranslated region (5'UTR) or translation under stress conditions cannot be regarded as an argument for appealing to internal initiation. We carefully describe the known pitfalls and limitations of the bicistronic assay and artefacts of some commercially available in vitro translation systems. We explain why plasmid DNA transfection should not be used in IRES studies and which control experiments are unavoidable if someone decides to use it anyway. Finally, we propose a workflow for the validation of IRES activity, including fast and simple experiments based on a single genetic construct with a sequence of interest.
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Affiliation(s)
- Ilya M Terenin
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia.
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119334, Russia.
| | - Victoria V Smirnova
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia
- Department of Bioengineering and Bioinformatics, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - Dmitri E Andreev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - Sergey E Dmitriev
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia
- Engelhardt Institute of Molecular Biology, Russian Academy of Sciences, Moscow, 119334, Russia
- Department of Biochemistry, Biological Faculty, Lomonosov Moscow State University, Moscow, 119234, Russia
| | - Ivan N Shatsky
- Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow, 119234, Russia.
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11
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Hermann T. Small molecules targeting viral RNA. WILEY INTERDISCIPLINARY REVIEWS-RNA 2016; 7:726-743. [PMID: 27307213 PMCID: PMC7169885 DOI: 10.1002/wrna.1373] [Citation(s) in RCA: 105] [Impact Index Per Article: 13.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Revised: 04/29/2016] [Accepted: 05/23/2016] [Indexed: 02/06/2023]
Abstract
Highly conserved noncoding RNA (ncRNA) elements in viral genomes and transcripts offer new opportunities to expand the repertoire of drug targets for the development of antiinfective therapy. Ligands binding to ncRNA architectures are able to affect interactions, structural stability or conformational changes and thereby block processes essential for viral replication. Proof of concept for targeting functional RNA by small molecule inhibitors has been demonstrated for multiple viruses with RNA genomes. Strategies to identify antiviral compounds as inhibitors of ncRNA are increasingly emphasizing consideration of drug‐like properties of candidate molecules emerging from screening and ligand design. Recent efforts of antiviral lead discovery for RNA targets have provided drug‐like small molecules that inhibit viral replication and include inhibitors of human immunodeficiency virus (HIV), hepatitis C virus (HCV), severe respiratory syndrome coronavirus (SARS CoV), and influenza A virus. While target selectivity remains a challenge for the discovery of useful RNA‐binding compounds, a better understanding is emerging of properties that define RNA targets amenable for inhibition by small molecule ligands. Insight from successful approaches of targeting viral ncRNA in HIV, HCV, SARS CoV, and influenza A will provide a basis for the future exploration of RNA targets for therapeutic intervention in other viral pathogens which create urgent, unmet medical needs. Viruses for which targeting ncRNA components in the genome or transcripts may be promising include insect‐borne flaviviruses (Dengue, Zika, and West Nile) and filoviruses (Ebola and Marburg). WIREs RNA 2016, 7:726–743. doi: 10.1002/wrna.1373 This article is categorized under:
RNA Structure and Dynamics > Influence of RNA Structure in Biological Systems RNA Interactions with Proteins and Other Molecules > Small Molecule–RNA Interactions Regulatory RNAs/RNAi/Riboswitches > Regulatory RNAs
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Affiliation(s)
- Thomas Hermann
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, CA, USA. .,Center for Drug Discovery Innovation, University of California, San Diego, La Jolla, CA, USA.
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12
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Abstract
Herpesviral mRNAs are produced and translated by cellular machinery, rendering them susceptible to the network of regulatory events that impact translation. In response, these viruses have evolved to infiltrate and hijack translational control pathways as well as to integrate specialized host translation strategies into their own repertoire. They are robust systems to dissect mechanisms of mammalian translational regulation and continue to offer insight into cis-acting mRNA features that impact assembly and activity of the translation apparatus. Here, I discuss recent advances revealing the extent to which the three herpesvirus subfamilies regulate both host and viral translation, thereby dramatically impacting the landscape of protein synthesis in infected cells.
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Affiliation(s)
- Britt A Glaunsinger
- Department of Plant and Microbial Biology, University of California, Berkeley, California 94720;
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13
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Inefficient Codon Usage Impairs mRNA Accumulation: the Case of the v-FLIP Gene of Kaposi's Sarcoma-Associated Herpesvirus. J Virol 2015; 89:7097-107. [PMID: 25926644 DOI: 10.1128/jvi.03390-14] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2014] [Accepted: 04/21/2015] [Indexed: 01/02/2023] Open
Abstract
UNLABELLED Latent Kaposi's sarcoma-associated herpesvirus (KSHV) genomes encode a homolog of cellular FLICE-inhibitory proteins (termed v-FLIP) that activates NF-κB and can trigger important proinflammatory and antiapoptotic changes in latently infected cells. The protein is present at very low levels in infection and has generally been difficult to efficiently express in recombinant vectors. Here we show that codon usage in the v-FLIP gene is strikingly suboptimal. Optimization of codon use in expression vectors, as expected, restores efficient protein expression. Surprisingly, however, it also dramatically increases the steady-state level of v-FLIP mRNA, at least in part by increasing mRNA stability. When codon-optimized v-FLIP sequences are reintroduced into intact KSHV genomes, the resulting virus expresses readily detectable monocistronic v-FLIP mRNAs that are undetectable in wild-type (WT) infection by blot hybridization, suggesting that such RNAs are in fact transcribed in WT infection but fail to accumulate. The overexpression of v-FLIP by codon-optimized latent genomes results in a 5- to 7-fold decrement in virus production following lytic induction, indicating that maximizing NF-κB signaling is deleterious to induction. These studies provide a clear explanation for the evolution of inefficient codon usage in this gene and point to a strong connection between translational efficiency and RNA accumulation in mammalian cells. IMPORTANCE This study reports that inefficient codon usage in a herpesviral gene is strikingly correlated with the inability of its mRNA to accumulate in cells; correction of efficient translatability restores RNA abundance. A similar correlation has been reported in yeast species, but the mechanisms operating in mammalian cells appear substantially different.
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14
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Deforges J, Locker N, Sargueil B. mRNAs that specifically interact with eukaryotic ribosomal subunits. Biochimie 2014; 114:48-57. [PMID: 25530261 DOI: 10.1016/j.biochi.2014.12.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2014] [Accepted: 12/11/2014] [Indexed: 12/25/2022]
Abstract
The accuracy of start codon selection is determined by the translation initiation process. In prokaryotes the initiation step on most mRNAs relies on recruitment of the small ribosomal subunit onto the initiation codon by base pairing between the mRNA and the 16S rRNA. Eukaryotes have evolved a complex molecular machinery involving at least 11 initiation factors, and mRNAs do not directly recruit the small ribosomal subunit. Instead the initiation complex is recruited to the 5' end of the mRNA through a complex protein network including eIF4E that interacts with the 5' cap structure and poly-A binding protein that interacts with the 3'end. However, some viral and cellular mRNAs are able to escape this pathway by internal recruitment of one or several components of the translation machinery. Here we review those eukaryotic mRNAs that have been reported to directly recruit the 40S ribosomal subunit internally. In the well characterized cases of viral IRESes, a specific RNA structure is involved in this process, and in addition to recruitment of the ribosome, the mRNA also manipulates the ribosome structure to stimulate the first translocation step. We also review recently described IRES/ribosome interactions in cases where the molecular mechanism leading to translation initiation has yet to be described. Finally we evaluate the possibility that mRNA may recruit the 40S ribosomal subunit through base pairing with the 18S rRNA.
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Affiliation(s)
- Jules Deforges
- CNRS UMR8015, laboratoire de cristallographie et RMN biologiques, France; Université Paris Descartes, 4 avenue de l'observatoire, Paris Cedex 06, 75270, France
| | - Nicolas Locker
- University of Surrey, Faculty of Health and Medical Sciences, School of Biosciences and Medicine, Guildford, United Kingdom
| | - Bruno Sargueil
- CNRS UMR8015, laboratoire de cristallographie et RMN biologiques, France; Université Paris Descartes, 4 avenue de l'observatoire, Paris Cedex 06, 75270, France.
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15
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Othman Z, Sulaiman MK, Willcocks MM, Ulryck N, Blackbourn DJ, Sargueil B, Roberts LO, Locker N. Functional analysis of Kaposi's sarcoma-associated herpesvirus vFLIP expression reveals a new mode of IRES-mediated translation. RNA (NEW YORK, N.Y.) 2014; 20:1803-1814. [PMID: 25246653 PMCID: PMC4201831 DOI: 10.1261/rna.045328.114] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 08/26/2014] [Indexed: 06/03/2023]
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus, the etiological agent of Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). One of the key viral proteins that contributes to tumorigenesis is vFLIP, a viral homolog of the FLICE inhibitory protein. This KSHV protein interacts with the NFκB pathway to trigger the expression of antiapoptotic and proinflammatory genes and ultimately leads to tumor formation. The expression of vFLIP is regulated at the translational level by an internal ribosomal entry site (IRES) element. However, the precise mechanism by which ribosomes are recruited internally and the exact location of the IRES has remained elusive. Here we show that a 252-nt fragment directly upstream of vFLIP, within a coding region, directs translation. We have established its RNA structure and demonstrate that IRES activity requires the presence of eIF4A and an intact eIF4G. Furthermore, and unusually for an IRES, eIF4E is part of the complex assembled onto the vFLIP IRES to direct translation. These molecular interactions define a new paradigm for IRES-mediated translation.
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Affiliation(s)
- Zulkefley Othman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Mariam K Sulaiman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Margaret M Willcocks
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nathalie Ulryck
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - David J Blackbourn
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Bruno Sargueil
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - Lisa O Roberts
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nicolas Locker
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
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16
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Zhu Y, Huang Y, Jung JU, Lu C, Gao SJ. Viral miRNA targeting of bicistronic and polycistronic transcripts. Curr Opin Virol 2014; 7:66-72. [PMID: 24821460 DOI: 10.1016/j.coviro.2014.04.004] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/10/2014] [Revised: 04/05/2014] [Accepted: 04/12/2014] [Indexed: 11/19/2022]
Abstract
Successful viral infection entails a choreographic regulation of viral gene expression program. Kaposi's sarcoma-associated herpesvirus (KSHV) encodes numerous miRNAs that regulate viral life cycle. However, few viral targets have been identified due to the lack of information on KSHV 3' untranslated regions (3'UTRs). Recent genome-wide mapping of KSHV transcripts and 3'UTRs has revealed abundant bicistronic and polycistronic transcripts. The extended 3'UTRs of the 5' proximal genes of bicistronic and polycistronic transcripts offer additional regulatory targets. Indeed, a genome-wide screening of KSHV 3'UTRs has identified several bicistronic and polycistronic transcripts as the novel targets of viral miRNAs. Together, these works have expanded our knowledge of the unique features of KSHV gene regulation program and provided valuable resources for the research community.
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Affiliation(s)
- Ying Zhu
- Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA 90033, USA
| | - Yufei Huang
- Department of Electrical and Computer Engineering, University of Texas at San Antonio, San Antonio, TX 78249, USA
| | - Jae U Jung
- Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA 90033, USA
| | - Chun Lu
- Department of Immunology and Microbiology, Nanjing Medical University, Nanjing 210029, China
| | - Shou-Jiang Gao
- Department of Molecular Microbiology and Immunology, University of Southern California, Keck School of Medicine, Los Angeles, CA 90033, USA.
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17
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Zhi H, Zahoor MA, Shudofsky AMD, Giam CZ. KSHV vCyclin counters the senescence/G1 arrest response triggered by NF-κB hyperactivation. Oncogene 2014; 34:496-505. [PMID: 24469036 PMCID: PMC4112183 DOI: 10.1038/onc.2013.567] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2013] [Revised: 11/20/2013] [Accepted: 11/29/2013] [Indexed: 12/19/2022]
Abstract
Many oncogenic viruses activate NF-κB as a part of their replicative cycles. We have shown recently that persistent and potentially oncogenic activation of NF-κB by the human T-lymphotropic virus 1 (HTLV-1) oncoprotein Tax immediately triggers a host senescence response mediated by cyclin-dependent kinase inhibitors: p21CIP1/WAF1 (p21) and p27Kip1 (p27) Here we demonstrate that RelA/NF-κB activation by Kaposi sarcoma herpesvirus (KSHV) latency protein vFLIP also leads to p21/p27 up-regulation and G1 cell cycle arrest. Remarkably, KSHV vCyclin, another latency protein co-expressed with vFLIP from a bicistronic latency-specific mRNA, was found to prevent the senescence and G1 arrest induced by HTLV-1 Tax and vFLIP respectively. This is due to the known ability of vCyclin/CDK6 complex to resist p21 and p27 inhibition and cause p27 degradation23. In KSHV-transformed BCBL-1 cells, sustained vFLIP expression with shRNA-mediated vCyclin depletion resulted in G1 arrest. The functional interdependence of vFLIP and vCyclin explains why they are co-translated from the same viral mRNA. Importantly, deregulation of the G1 cyclin-dependent kinase can facilitate chronic IKK/NF-κB activation.
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Affiliation(s)
- H Zhi
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - M A Zahoor
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - A M D Shudofsky
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
| | - C-Z Giam
- Department of Microbiology and Immunology, Uniformed Services University of the Health Sciences, Bethesda, MD, USA
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18
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Macdonald DC, Singh H, Whelan MA, Escors D, Arce F, Bottoms SE, Barclay WS, Maini M, Collins MK, Rosenberg WMC. Harnessing alveolar macrophages for sustained mucosal T-cell recall confers long-term protection to mice against lethal influenza challenge without clinical disease. Mucosal Immunol 2014; 7:89-100. [PMID: 23715172 DOI: 10.1038/mi.2013.27] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/12/2012] [Accepted: 04/01/2013] [Indexed: 02/04/2023]
Abstract
Vaccines that induce T cells, which recognize conserved viral proteins, could confer universal protection against seasonal and pandemic influenza strains. An effective vaccine should generate sufficient mucosal T cells to ensure rapid viral control before clinical disease. However, T cells may also cause lung injury in influenza, so this approach carries inherent risks. Here we describe intranasal immunization of mice with a lentiviral vector expressing influenza nucleoprotein (NP), together with an NFκB activator, which transduces over 75% of alveolar macrophages (AM). This strategy recalls and expands NP-specific CD8+ T cells in the lung and airway of mice that have been immunized subcutaneously, or previously exposed to influenza. Granzyme B-high, lung-resident T-cell populations persist for at least 4 months and can control a lethal influenza challenge without harmful cytokine responses, weight loss, or lung injury. These data demonstrate that AM can be harnessed as effective antigen-presenting cells for influenza vaccination.
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Affiliation(s)
- D C Macdonald
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
| | - H Singh
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
| | - M A Whelan
- Division of Medicine, University College London, London, UK
| | - D Escors
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
| | - F Arce
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
| | - S E Bottoms
- Division of Medicine, University College London, London, UK
| | - W S Barclay
- Division of Virology, Imperial College London, St Mary's Campus, London, UK
| | - M Maini
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
| | - M K Collins
- Division of Infection and Immunity and MRC Centre for Medical Molecular Virology, University College London, London, UK
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19
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El Hajj H, Ali J, Ghantous A, Hodroj D, Daher A, Zibara K, Journo C, Otrock Z, Zaatari G, Mahieux R, El Sabban M, Bazarbachi A, Abou Merhi R. Combination of arsenic and interferon-α inhibits expression of KSHV latent transcripts and synergistically improves survival of mice with primary effusion lymphomas. PLoS One 2013; 8:e79474. [PMID: 24250827 PMCID: PMC3826709 DOI: 10.1371/journal.pone.0079474] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/23/2013] [Accepted: 09/23/2013] [Indexed: 01/08/2023] Open
Abstract
Background Kaposi sarcoma-associated herpesvirus (KSHV) is the etiologic agent of primary effusion lymphomas (PEL). PEL cell lines infected with KSHV, but negative for Epstein-Barr virus have a tumorigenic potential in non-obese diabetic/severe combined immunodeficient mice and result in efficient engraftment and formation of malignant ascites with notable abdominal distension, consistent with the clinical manifestations of PEL in humans. Methodology/Principal Findings Using this preclinical mouse model, we demonstrate that the combination of arsenic trioxide and interferon-alpha (IFN) inhibits proliferation, induces apoptosis and downregulates the latent viral transcripts LANA-1, v-FLIP and v-Cyc in PEL cells derived from malignant ascites. Furthermore, this combination decreases the peritoneal volume and synergistically increases survival of PEL mice. Conclusion/Significance These results provide a promising rationale for the therapeutic use of arsenic/IFN in PEL patients.
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Affiliation(s)
- Hiba El Hajj
- Department of Internal Medicine, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Jihane Ali
- Lebanese University, Rafik Hariri Campus, Faculty of Sciences, Biology Department, Hadath, Lebanon
| | - Akram Ghantous
- International Agency for Research on Cancer, Lyon, France
| | - Dana Hodroj
- Lebanese University, Rafik Hariri Campus, Faculty of Sciences, Biology Department, Hadath, Lebanon
| | - Ahmad Daher
- Lebanese University, Rafik Hariri Campus, Faculty of Sciences, Biology Department, Hadath, Lebanon
| | - Kazem Zibara
- Lebanese University, Faculty of Sciences, Biology Department, fifth section, Nabatieh, Lebanon
| | - Chloé Journo
- Equipe Oncogenèse Rétrovirale, Equipe labelisée “Ligue Nationale Contre le Cancer” INSERM U1111 - CNRS UMR5308, CIRI - International Center for Infectiology Research, Biology Department, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Zaher Otrock
- Leukemia Program, Cleveland Clinic Taussig Cancer Institute, Cleveland, Ohio, United States of America
| | - Ghazi Zaatari
- Department of Pathology and Laboratory Medicine, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Renaud Mahieux
- Equipe Oncogenèse Rétrovirale, Equipe labelisée “Ligue Nationale Contre le Cancer” INSERM U1111 - CNRS UMR5308, CIRI - International Center for Infectiology Research, Biology Department, Ecole Normale Supérieure de Lyon, Lyon, France
| | - Marwan El Sabban
- Department of Anatomy, Cell Biology and Physiology, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
| | - Ali Bazarbachi
- Department of Internal Medicine, Faculty of Medicine, American University of Beirut, Beirut, Lebanon
- * E-mail: (AB); (RAM)
| | - Raghida Abou Merhi
- Lebanese University, Rafik Hariri Campus, Faculty of Sciences, Biology Department, Hadath, Lebanon
- * E-mail: (AB); (RAM)
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20
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The DNA virus white spot syndrome virus uses an internal ribosome entry site for translation of the highly expressed nonstructural protein ICP35. J Virol 2013; 87:13263-78. [PMID: 24089551 DOI: 10.1128/jvi.01732-13] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Although shrimp white spot syndrome virus (WSSV) is a large double-stranded DNA virus (∼300 kbp), it expresses many polycistronic mRNAs that are likely to use internal ribosome entry site (IRES) elements for translation. A polycistronic mRNA encodes the gene of the highly expressed nonstructural protein ICP35, and here we use a dual-luciferase assay to demonstrate that this protein is translated cap independently by an IRES element located in the 5' untranslated region of icp35. A deletion analysis of this region showed that IRES activity was due to stem-loops VII and VIII. A promoterless assay, a reverse transcription-PCR together with quantitative real-time PCR analysis, and a stable stem-loop insertion upstream of the Renilla luciferase open reading frame were used, respectively, to rule out the possibility that cryptic promoter activity, abnormal splicing, or read-through was contributing to the IRES activity. In addition, a Northern blot analysis was used to confirm that only a single bicistronic mRNA was expressed. The importance of ICP35 to viral replication was demonstrated in a double-stranded RNA (dsRNA) interference knockdown experiment in which the mortality of the icp35 dsRNA group was significantly reduced. Tunicamycin was used to show that the α subunit of eukaryotic initiation factor 2 is required for icp35 IRES activity. We also found that the intercalating drug quinacrine significantly inhibited icp35 IRES activity in vitro and reduced the mortality rate and viral copy number in WSSV-challenged shrimp. Lastly, in Sf9 insect cells, we found that knockdown of the gene for the Spodoptera frugiperda 40S ribosomal protein RPS10 decreased icp35 IRES-regulated firefly luciferase activity but had no effect on cap-dependent translation.
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21
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Abstract
Glycoprotein D (gD) and glycoprotein I (gI) genes of bovine herpes virus 1 (BHV1) are contiguous genes with 141 bp region between the two open reading frames (ORFs). Expression of gD and gI from a bicistronic construct containing complete gD and gI gene has been reported either through internal ribosome entry site (IRES)-like element or through the scanning and leakage model (Mukhopadhyay 2000). We here show by computational and experimental means that gD is expressed solely as bicistronic transcript comprising gD and gI coding region in BHV1-infected cells. gI ORF was also shown to express separately. An IRES-like element was also predicted by IRES predicting software in the middle of the gD coding region; within that region a putative promoter was also identified by promoterscan. The intergenic region between the two ORF showed extensive secondary structure which brings the stop codon of gD very close to start codon of gI gene. gD gene transcript in BHV1-infected cells was solely bicistronic. gI transcript was also present in the BHV1-infected cells but in low copy number. The results indicate that gI is probably transcribed from its own transcript in BHV1-infected cells.
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22
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Dual short upstream open reading frames control translation of a herpesviral polycistronic mRNA. PLoS Pathog 2013; 9:e1003156. [PMID: 23382684 PMCID: PMC3561293 DOI: 10.1371/journal.ppat.1003156] [Citation(s) in RCA: 36] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2012] [Accepted: 12/11/2012] [Indexed: 12/21/2022] Open
Abstract
The Kaposi's sarcoma-associated herpesvirus (KSHV) protein kinase, encoded by ORF36, functions to phosphorylate cellular and viral targets important in the KSHV lifecycle and to activate the anti-viral prodrug ganciclovir. Unlike the vast majority of mapped KSHV genes, no viral transcript has been identified with ORF36 positioned as the 5′-proximal gene. Here we report that ORF36 is robustly translated as a downstream cistron from the ORF35–37 polycistronic transcript in a cap-dependent manner. We identified two short, upstream open reading frames (uORFs) within the 5′ UTR of the polycistronic mRNA. While both uORFs function as negative regulators of ORF35, unexpectedly, the second allows for the translation of the downstream ORF36 gene by a termination-reinitiation mechanism. Positional conservation of uORFs within a number of related viruses suggests that this may be a common γ-herpesviral adaptation of a host translational regulatory mechanism. Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent of multicentric Castleman's disease, primary effusion lymphoma and Kaposi's sarcoma. KSHV expresses a number of transcripts with the potential to generate multiple proteins, yet relies on the cellular translation machinery that is primed to synthesize only one protein per mRNA. Here we report that the viral transcript encompassing ORF35–37 is able to direct synthesis of two proteins and that the translational switch is regulated by two short upstream open reading frames (uORFs) in the native 5′ untranslated region. uORFs are elements commonly found upstream of mammalian genes that function to interfere with unrestrained ribosomal scanning and thus repress translation of the major ORF. The sequence of the viral uORF appears unimportant, and instead functions to position the translation machinery in a location that favors translation of the downstream major ORF, via a reinitiation mechanism. Thus, KSHV uses a host strategy generally reserved to repress translation to instead allow for the expression of an internal gene.
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23
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Walsh D, Mathews MB, Mohr I. Tinkering with translation: protein synthesis in virus-infected cells. Cold Spring Harb Perspect Biol 2013; 5:a012351. [PMID: 23209131 DOI: 10.1101/cshperspect.a012351] [Citation(s) in RCA: 178] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022]
Abstract
Viruses are obligate intracellular parasites, and their replication requires host cell functions. Although the size, composition, complexity, and functions encoded by their genomes are remarkably diverse, all viruses rely absolutely on the protein synthesis machinery of their host cells. Lacking their own translational apparatus, they must recruit cellular ribosomes in order to translate viral mRNAs and produce the protein products required for their replication. In addition, there are other constraints on viral protein production. Crucially, host innate defenses and stress responses capable of inactivating the translation machinery must be effectively neutralized. Furthermore, the limited coding capacity of the viral genome needs to be used optimally. These demands have resulted in complex interactions between virus and host that exploit ostensibly virus-specific mechanisms and, at the same time, illuminate the functioning of the cellular protein synthesis apparatus.
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Affiliation(s)
- Derek Walsh
- Department of Microbiology, New York University School of Medicine, New York, NY 10016, USA.
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24
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Leidal AM, Pringle ES, McCormick C. Evasion of oncogene-induced senescence by gammaherpesviruses. Curr Opin Virol 2012; 2:748-54. [PMID: 23064053 DOI: 10.1016/j.coviro.2012.09.009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2012] [Revised: 09/17/2012] [Accepted: 09/20/2012] [Indexed: 12/15/2022]
Abstract
A common feature of herpesvirus infection is activation of DNA damage responses (DDRs) that are essential for efficient lytic replication. Latent infection with Epstein-Barr virus (EBV) and Kaposi's sarcoma-associated herpesvirus (KSHV) also elicit DDRs via the action of latent viral oncoproteins that deregulate cell proliferation and initiate a host anti-proliferative defense known as oncogene-induced senescence (OIS). These viruses encode auxiliary latent proteins that undermine OIS to allow the ongoing proliferation of infected cells despite robust DDR signaling. Persistent DDRs have also been linked to the aberrant secretion of pathogenetically important inflammatory mediators from infected cells. The accumulating evidence indicates that herpesviruses have evolved ways to co-opt DDR signaling to manage both latent and lytic phases of infection, and that DDR subversion may contribute to herpesvirus-associated disease states.
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Affiliation(s)
- Andrew M Leidal
- Department of Microbiology and Immunology, Dalhousie University, 5850 College Street, PO Box 15000, Halifax, NS, Canada B3H 4R2
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25
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Abstract
Viruses have adapted a broad range of unique mechanisms to modulate the cellular translational machinery to ensure viral translation at the expense of cellular protein synthesis. Many of these promote virus-specific translation by use of molecular tags on viral mRNA such as internal ribosome entry sites (IRES) and genome-linked viral proteins (VPg) that bind translation machinery components in unusual ways and promote RNA circularization. This review describes recent advances in understanding some of the mechanisms in which animal virus mRNAs gain an advantage over cellular transcripts, including new structural and biochemical insights into IRES function and novel proteins that function as alternate met-tRNAimet carriers in translation initiation. Comparisons between animal and plant virus mechanisms that promote translation of viral mRNAs are discussed.
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Affiliation(s)
- Lucas C Reineke
- Department of Molecular Virology and Microbiology, Baylor College of Medicine, Houston, TX 77030, USA
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26
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Deletion of Kaposi's sarcoma-associated herpesvirus FLICE inhibitory protein, vFLIP, from the viral genome compromises the activation of STAT1-responsive cellular genes and spindle cell formation in endothelial cells. J Virol 2011; 85:10375-88. [PMID: 21795355 DOI: 10.1128/jvi.00226-11] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023] Open
Abstract
Kaposi's sarcoma herpesvirus (KSHV) Fas-associated death domain (FADD)-like interleukin-1 beta-converting enzyme (FLICE)-inhibitory protein, vFLIP, has antiapoptotic properties, is a potent activator of the NF-κB pathway, and induces the formation of endothelial spindle cells, the hallmark of Kaposi's sarcoma, when overexpressed in primary endothelial cells. We used a reverse genetics approach to study several functions of KSHV vFLIP in the context of the whole viral genome. Deletion of the gene encoding vFLIP from a KSHV genome cloned in a bacterial artificial chromosome (BAC) reduced the ability of the virus to persist and induce spindle cell formation in primary human umbilical vein endothelial cells (HUVECs). Only a few, mainly interferon (IFN)-responsive, genes were expressed in wild-type KSHV (KSHV-wt)-infected endothelial cells at levels higher than those in KSHV-ΔFLIP-infected endothelial cells, in contrast to the plethora of cellular genes induced by overexpressed vFLIP. In keeping with this observation, vFLIP induces the phosphorylation of STAT1 and STAT2 in an NF-κB-dependent manner in endothelial cells. vFLIP-dependent phosphorylation of STAT1 and STAT2 could be demonstrated after endothelial cells were infected with KSHV-wt, KSHV-ΔFLIP, and a KSHV-vFLIP revertant virus. These findings document the impact of KSHV vFLIP on the transcriptome of primary endothelial cells during viral persistence and highlight the role of vFLIP in the activation of STAT1/STAT2 and STAT-responsive cellular genes by KSHV.
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27
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Lee HR, Lee S, Chaudhary PM, Gill P, Jung JU. Immune evasion by Kaposi's sarcoma-associated herpesvirus. Future Microbiol 2011; 5:1349-65. [PMID: 20860481 DOI: 10.2217/fmb.10.105] [Citation(s) in RCA: 41] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Persistent viral infections are often associated with serious diseases, primarily by altering functions of the host immune system. The hallmark of Kaposi's sarcoma-associated herpesvirus (KSHV) infection is the establishment of a life-long persistent infection, which leads to several clinical, epidemiological and infectious diseases, such as Kaposi's sarcoma, a plasmablastic variant of multicentric Castleman's disease, and primary effusion lymphoma. To sustain an efficient life-long persistency, KSHV dedicates a large portion of its genome to encoding immunomodulatory proteins that antagonize the immune system of its host. In this article, we highlight the strategies KSHV uses to evade, escape and survive its battle against the host's immune system.
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Affiliation(s)
- Hye-Ra Lee
- Department of Molecular Microbiology & Immunology, University of Southern California, Los Angeles, CA 90033, USA.
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28
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Luan SL, Boulanger E, Ye H, Chanudet E, Johnson N, Hamoudi RA, Bacon CM, Liu H, Huang Y, Said J, Chu P, Clemen CS, Cesarman E, Chadburn A, Isaacson PG, Du MQ. Primary effusion lymphoma: genomic profiling revealed amplification of SELPLG and CORO1C encoding for proteins important for cell migration. J Pathol 2010; 222:166-79. [PMID: 20690162 DOI: 10.1002/path.2752] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Primary effusion lymphoma (PEL) is associated with Kaposi sarcoma herpesvirus (KSHV) but its pathogenesis is poorly understood. Many KSHV-associated products can deregulate cellular pathways commonly targeted in cancer. However, KSHV infection alone is insufficient for malignant transformation. PEL also lacks the chromosomal translocations seen in other lymphoma subtypes. We investigated 28 PELs and ten PEL cell lines by 1 Mb resolution array comparative genomic hybridization (CGH) and found frequent gains of 1q21-41 (47%), 4q28.3-35 (29%), 7q (58%), 8q (63%), 11 (32%), 12 (61%), 17q (29%), 19p (34%), and 20q (34%), and losses of 4q (32%), 11q25 (29%), and 14q32 (63%). Recurrent focal amplification was seen at several regions on chromosomes 7, 8, and 12. High-resolution chromosome-specific tile-path array CGH confirmed these findings, and identified selectin-P ligand (SELPLG) and coronin-1C (CORO1C) as the targets of a cryptic amplification at 12q24.11. Interphase FISH and quantitative PCR showed SELPLG/CORO1C amplification (>4 extra copies) and low levels of copy number gain (1-4 extra copies) in 23% of PELs, respectively. Immunohistochemistry revealed strong expression of both SELPLG and coronin-1C in the majority of PELs, irrespective of their gene dosage. SELPLG is critical for cell migration and chemotaxis, while CORO1C regulates actin-dependent processes, thus important for cell motility. Their overexpression in PEL is expected to play an important role in its pathogenesis.
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Affiliation(s)
- Shi-Lu Luan
- Department of Pathology, University of Cambridge, Cambridge, CB2 0QQ, UK
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29
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Stress-inducible alternative translation initiation of human cytomegalovirus latency protein pUL138. J Virol 2010; 84:9472-86. [PMID: 20592073 DOI: 10.1128/jvi.00855-10] [Citation(s) in RCA: 57] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
We have previously characterized a 21-kDa protein encoded by UL138 (pUL138) as a viral factor inherent to low-passage strains of human cytomegalovirus (HCMV) that is required for latent infection in vitro. pUL138 is encoded on 3.6-, 2.7-, and 1.4-kb 3' coterminal transcripts that are produced during productive and latent infections. pUL138 is encoded at the 3' end of each transcript and is preceded by an extensive 5' sequence (approximately 0.5 to 2.5 kb) containing several putative open reading frames (ORFs). We determined that three putative ORFs upstream of UL138 (UL133, UL135, and UL136) encode proteins. The UL138 transcripts are polycistronic, such that each transcript expresses pUL138 in addition to the most-5' ORF. The upstream coding sequences (CDS) present a significant challenge for the translation of pUL138 in mammalian cells. We hypothesized that sequences 5' of UL138 mediate translation initiation of pUL138 by alternative strategies. Accordingly, a 663-nucloetide (nt) sequence overlapping the UL136 CDS supported expression of a downstream cistron in a bicistronic reporter system. We did not detect cryptic promoter activity or RNA splicing events that could account for downstream cistron expression. These data are consistent with the sequence element functioning as an internal ribosome entry site (IRES). Interestingly, pUL138 expression from the 3.6- and 2.7-kb transcripts was induced by serum stress, which concomitantly inhibited normal cap-dependent translation. Our work suggests that an alternative and stress-inducible strategy of translation initiation ensures expression of pUL138 under a variety of cellular contexts. The UL138 polycistronic transcripts serve to coordinate the expression of multiple proteins, including a viral determinant of HCMV latency.
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Understanding pathogenetic aspects and clinical presentation of primary effusion lymphoma through its derived cell lines. AIDS 2010; 24:479-90. [PMID: 20051807 DOI: 10.1097/qad.0b013e3283365395] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Primary effusion lymphoma (PEL) is a very rare subgroup of B-cell lymphomas presenting as pleural, peritoneal and pericardial neoplastic effusions in the absence of a solid tumor mass or recognizable nodal involvement. There is strong evidence that Kaposi's sarcoma-associated herpesvirus (KSHV) is a causal agent of PEL. PEL tumor cells are latently infected by KSHV with consistent expression of several viral proteins and microRNAs that can affect cellular proliferation, differentiation and survival. The most relevant data on pathogenesis and biology of KSHV have been provided by studies on PEL-derived cell lines. Fourteen continuous cell lines have been established from the malignant effusions of patients with AIDS-associated and non-AIDS-associated PEL. These KSHV+ EBV+/- cell lines are well characterized, authenticated and mostly available from public biological resource centers. The PEL cell lines display unique features and are clearly distinct from other lymphoma cell lines. PEL cell lines represent an indispensable tool for the understanding of KSHV biology and its impact on the clinical manifestation of PEL. Studies on PEL cell lines have shown that a number of viral genes, expressed during latency or lytic life cycle, have effects on cell binding, proliferation, angiogenesis and inflammation. Also, PEL cell lines are important model systems for the study of the disorder of PEL including the lack of invasive or destructive growth patterns and the peculiar propensity of PEL to involve body cavity surfaces.
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Wen KW, Damania B. Kaposi sarcoma-associated herpesvirus (KSHV): molecular biology and oncogenesis. Cancer Lett 2009; 289:140-50. [PMID: 19651473 DOI: 10.1016/j.canlet.2009.07.004] [Citation(s) in RCA: 153] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2008] [Revised: 07/10/2009] [Accepted: 07/13/2009] [Indexed: 11/17/2022]
Abstract
Kaposi sarcoma-associated herpesvirus (KSHV) is a double-stranded DNA herpesvirus belonging to the gamma-herpesvirinae subfamily. KSHV has been associated with the development of three neoplastic diseases: Kaposi sarcoma (KS), primary effusion lymphoma (PEL), and multicentric Castleman disease (MCD). In this review, we discuss the three KSHV-associated malignancies, KSHV genome, latent and lytic aspects of the viral lifecycle, putative viral oncogenes, as well as therapeutic regimens used for the treatment of KS, PEL, and MCD.
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Affiliation(s)
- Kwun Wah Wen
- Lineberger Comprehensive Cancer Center, University of North Carolina, Chapel Hill, NC 27599, USA
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Deniz N, Lenarcic EM, Landry DM, Thompson SR. Translation initiation factors are not required for Dicistroviridae IRES function in vivo. RNA (NEW YORK, N.Y.) 2009; 15:932-46. [PMID: 19299549 PMCID: PMC2673076 DOI: 10.1261/rna.1315109] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/13/2008] [Accepted: 01/27/2009] [Indexed: 05/22/2023]
Abstract
The cricket paralysis virus (CrPV) intergenic region (IGR) internal ribosome entry site (IRES) uses an unusual mechanism of initiating translation, whereby the IRES occupies the P-site of the ribosome and the initiating tRNA enters the A-site. In vitro experiments have demonstrated that the CrPV IGR IRES is able to bind purified ribosomes and form 80S complexes capable of synthesizing small peptides in the absence of any translation initiation factors. These results suggest that initiation by this IRES is factor-independent. To determine whether the IGR IRES functions in the absence of initiation factors in vivo, we assayed IGR IRES activity in various yeast strains harboring mutations in canonical translation initiation factors. We used a dicistronic reporter assay in yeast to determine whether the CrPV IGR IRES is able to promote translation sufficient to support growth in the presence of various deletions or mutations in translation initiation factors. Using this assay, we have previously shown that the CrPV IGR IRES functions efficiently in yeast when ternary complexes (eIF2*GTP*initiator tRNA(met)) are reduced. Here, we demonstrate that the CrPV IGR IRES activity does not require the eukaryotic initiation factors eIF4G1 or eIF5B, and it is enhanced when eIF2B, the eIF3b subunit of eIF3, or eIF4E are impaired. Taken together, these data support a model in which the CrPV IGR IRES is capable of initiating protein synthesis in the absence of any initiation factors in vivo, and suggests that the CrPV IGR IRES initiates translation by directly recruiting the ribosomal subunits in vivo.
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Affiliation(s)
- Nilsa Deniz
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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Kang ST, Leu JH, Wang HC, Chen LL, Kou GH, Lo CF. Polycistronic mRNAs and internal ribosome entry site elements (IRES) are widely used by white spot syndrome virus (WSSV) structural protein genes. Virology 2009; 387:353-63. [PMID: 19285701 DOI: 10.1016/j.virol.2009.02.012] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2008] [Revised: 01/06/2009] [Accepted: 02/06/2009] [Indexed: 11/19/2022]
Abstract
The genome of the white spot syndrome virus (WSSV) Taiwan isolate has many structural and non-structural genes that are arranged in clusters. Screening with Northern blots showed that at least four of these clusters produce polycistronic mRNA, and one of these (vp31/vp39b/vp11) was studied in detail. The vp31/vp39b/vp11 cluster produces two transcripts, including a large 3.4-kb polycistronic transcript of all three genes. No monocistronic vp39b mRNA was detected. TNT and in vitro translation assays showed that vp39b translation was independent of vp31 translation, and that ribosomal reinitiation was not a possible mechanism for vp39b. An unusually located IRES (internal ribosome entry site) element was identified in the vp31/vp39b coding region, and this region was able to promote the expression of a downstream firefly luciferase reporter. We show that vp31/vp39b/vp11 is representative of many other WSSV structural/non-structural gene clusters, and argue that these are also likely to produce polycistronic mRNAs and that use an IRES mechanism to regulate their translation.
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Affiliation(s)
- Shih-Ting Kang
- Institute of Zoology, National Taiwan University, Taipei, Taiwan
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Expression of vFLIP in a lentiviral vaccine vector activates NF-{kappa}B, matures dendritic cells, and increases CD8+ T-cell responses. J Virol 2008; 83:1555-62. [PMID: 19036811 PMCID: PMC2643792 DOI: 10.1128/jvi.00709-08] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Lentiviral vectors deliver antigens to dendritic cells (DCs) in vivo, but they do not trigger DC maturation. We therefore expressed a viral protein that constitutively activates NF-kappaB, vFLIP from Kaposi's sarcoma-associated herpesvirus (KSHV), in a lentivector to mature DCs. vFLIP activated NF-kappaB in mouse bone marrow-derived DCs in vitro and matured these DCs to a similar extent as lipopolysaccharide; costimulatory markers CD80, CD86, CD40, and ICAM-1 were upregulated and tumor necrosis factor alpha and interleukin-12 secreted. The vFLIP-expressing lentivector also matured DCs in vivo. When we coexpressed vFLIP in a lentivector with ovalbumin (Ova), we found an increased immune response to Ova; up to 10 times more Ova-specific CD8(+) T cells secreting gamma interferon were detected in the spleens of vFLIP_Ova-immunized mice than in the spleens of mice immunized with GFP_Ova. Furthermore, this increased CD8(+) T-cell response correlated with improved tumor-free survival in a tumor therapy model. A single immunization with vFLIP_Ova also reduced the parasite load when mice were challenged with OVA-Leishmania donovani. In conclusion, vFLIP from KSHV is a DC activator, maturing DCs in vitro and in vivo. This demonstrates that NF-kappaB activation is sufficient to induce many aspects of DC maturation and that expression of a constitutive NF-kappaB activator can improve the efficacy of a vaccine vector.
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35
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Ganem D. KSHV infection and the pathogenesis of Kaposi's sarcoma. ANNUAL REVIEW OF PATHOLOGY-MECHANISMS OF DISEASE 2007; 1:273-96. [PMID: 18039116 DOI: 10.1146/annurev.pathol.1.110304.100133] [Citation(s) in RCA: 217] [Impact Index Per Article: 12.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Kaposi's sarcoma (KS) has long been suspected of having an infectious etiology on the basis of its unusual epidemiology, histopathology, and natural history. Nearly a decade ago, a novel herpesviral genome was discovered in KS biopsies, and since that time strong epidemiologic evidence has accumulated correlating infection with this KS-associated herpesvirus (KSHV, also known as human herpesvirus 8) with the development of the disease. Here we review the evidence linking KSHV infection to KS risk and discuss current notions of how KSHV gene expression promotes the development of this remarkable neoplasm. These studies show that both latent and lytic viral replicative cycles contribute significantly-but differently-to KS development. The studies also highlight mechanistic differences between oncogenesis caused by KSHV and that caused by its distant relative Epstein-Barr virus.
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Affiliation(s)
- Don Ganem
- Howard Hughes Medical Institute, Department of Microbiology and Immunology, University of California, San Francisco, California 94143, USA.
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Du MQ, Bacon CM, Isaacson PG. Kaposi sarcoma-associated herpesvirus/human herpesvirus 8 and lymphoproliferative disorders. J Clin Pathol 2007; 60:1350-7. [PMID: 18042691 PMCID: PMC2095558 DOI: 10.1136/jcp.2007.047969] [Citation(s) in RCA: 70] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/03/2007] [Indexed: 12/29/2022]
Abstract
Kaposi sarcoma-associated herpesvirus (KSHV), also known as human herpesvirus 8 (HHV8), is a recent addition to the list of human viruses that are directly associated with lymphoproliferative disorders. KSHV was first shown to be involved in multicentric Castleman disease and primary effusion lymphoma (PEL). Subsequently, the virus was identified in solid lymphomas, often of extranodal sites, with morphological and immunophenotypic characteristics similar to those of PEL, and in other lymphoproliferative disorders with heterogeneous clinicopathological presentations. The recent advances in our understanding of the histology, immunophenotype and pathogenesis of these KSHV-associated lymphoproliferative disorders are reviewed.
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Affiliation(s)
- M-Q Du
- Department of Pathology, University of Cambridge, Cambridge, UK.
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Xuan C, Qiao W, Li J, Peng G, Liu M, Chen Q, Zhou J, Geng Y. BTat, a trans-acting regulatory protein, contributes to bovine immunodeficiency virus-induced apoptosis. Cell Microbiol 2007; 10:31-40. [PMID: 17645750 DOI: 10.1111/j.1462-5822.2007.01011.x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Bovine immunodeficiency virus (BIV) is a member of the lentivirus subfamily of retroviruses highly related to human immunodeficiency virus in morphologic, antigenic and genomic features. BIV is known to induce chronic pathological changes in infected hosts, which are often associated with the development of immune-mediated lesions. However, the molecular events underlying the cytopathic effect of BIV remain poorly understood. In this study, BIV was found to induce apoptotic cell death, and a small trans-acting regulatory protein encoded by BIV, BTat, was found to participate in the pro-apoptotic action of BIV. Introduction of exogenous BTat to cells triggered apoptosis dramatically, as revealed by assays such as terminal deoxynucleotidyl transferase-mediated dUTP nick-end labelling, nuclear morphology analysis, flow cytometry, and cleavages of caspases and poly(ADP-ribose)polymerase. Interestingly, the pro-apoptotic effect of BTat was found to be mediated through its interaction with cellular microtubules and its interference with microtubule dynamics. These results provide the first evidence that induction of apoptosis may contribute to the cytopathic effect of BIV. In addition, these results uncover a novel role for BTat in regulating microtubule dynamics in addition to its conventional role in regulating gene transcription.
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Affiliation(s)
- Chenghao Xuan
- Key Laboratory of Microbial Functional Genomics (Tianjin), College of Life Sciences, Nankai University, Tianjin 300071, China
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Isaksson A, Berggren M, Ekeland-Sjöberg K, Samuelsson T, Ricksten A. Cell specific internal translation efficiency of Epstein-Barr virus present in solid organ transplant patients. J Med Virol 2007; 79:573-81. [PMID: 17385682 DOI: 10.1002/jmv.20854] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The U leader exon in the 5' untranslated region of the Epstein-Barr virus nuclear antigen 1 (EBNA1) gene contains an internal ribosome entry site, the EBNA internal ribosome entry segment (IRES), which promotes cap-independent translation and increases the expression level of the EBNA1 protein. It was previously reported that immunosuppressed organ transplanted patients showed an alternatively spliced EBNA1 transcript, excluding the EBNA IRES element. To further investigate the function of the EBNA IRES, sequence analysis of the EBNA IRES mRNA was performed in samples from seven organ transplant patients. Two nucleotide changes, G --> A at position 67531 and C --> U at position 67585 were found in the EBNA IRES mRNA, relative to the corresponding genomic Epstein-Barr virus (EBV) sequence in all patients. Moreover, the patient derived EBNA IRES mRNA was shown to differ from the IRES mRNA derived from the cell line B95.8 at position 67531 and from the cell lines Rael and P3HR1 at positions 67531 and 67585. cDNA from the various EBNA IRES sequences were cloned into bicistronic vectors, respectively, and used in transient transfection experiments in six human cell lines. The patient specific sequence significantly decreased the IRES activity in T-cells, while the base changes had no significant impact on the activity in B- or in epithelial cells. The genetic mechanisms behind EBV-associated diseases are complex, involving gene regulation by alternative promoters, alternative splicing, and translational control. The nucleotide changes in the patient specific EBNA IRES transcript and its influence on the translational activity, might illustrate new strategies utilised by the EBV to adapt to the immune control in patients with EBV associated diseases.
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Affiliation(s)
- Asa Isaksson
- Institute of Biomedicine, Department of Clinical Chemistry and Transfusion Medicine, Sahlgrenska University Hospital, Göteborg University, Gothenburg, Sweden
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Greene W, Kuhne K, Ye F, Chen J, Zhou F, Lei X, Gao SJ. Molecular biology of KSHV in relation to AIDS-associated oncogenesis. Cancer Treat Res 2007; 133:69-127. [PMID: 17672038 PMCID: PMC2798888 DOI: 10.1007/978-0-387-46816-7_3] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
KSHV has been established as the causative agent of KS, PEL, and MCD, malignancies occurring more frequently in AIDS patients. The aggressive nature of KSHV in the context of HIV infection suggests that interactions between the two viruses enhance pathogenesis. KSHV latent infection and lytic reactivation are characterized by distinct gene expression profiles, and both latency and lytic reactivation seem to be required for malignant progression. As a sophisticated oncogenic virus, KSHV has evolved to possess a formidable repertoire of potent mechanisms that enable it to target and manipulate host cell pathways, leading to increased cell proliferation, increased cell survival, dysregulated angiogenesis, evasion of immunity, and malignant progression in the immunocompromised host. Worldwide, approximately 40.3 million people are currently living with HIV infection. Of these, a significant number are coinfected with KSHV. The complex interplay between the two viruses dramatically elevates the risk for development of KSHV-induced malignancies, KS, PEL, and MCD. Although HAART significantly reduces HIV viral load, the entire T-cell repertoire and immune function may not be completely restored. In fact, clinically significant immune deficiency is not necessary for the induction of KSHV-related malignancy. Because of variables such as lack of access to therapy noncompliance with prescribed treatment, failure to respond to treatment and the development of drug-resistant strains of HIV, KSHV-induced malignancies will continue to present as major health concerns.
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Affiliation(s)
- Whitney Greene
- Tiumor Virology Program, Children's Cancer Research Institute, Department of Pediatrics, The University of Texas Health Science Center at San Antonio, San Antonio, TX, USA
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40
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Cesarman E, Mesri EA. Kaposi sarcoma-associated herpesvirus and other viruses in human lymphomagenesis. Curr Top Microbiol Immunol 2006; 312:263-87. [PMID: 17089801 DOI: 10.1007/978-3-540-34344-8_10] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Kaposi sarcoma-associated herpesvirus (KSHV), also called human herpesvirus 8 (HHV-8), is associated with a specific subset of lymphoproliferative disorders. These include two main categories. The first is primary effusion lymphomas and related solid variants. The second is multicentric Castleman disease, from which KSHV-positive plasmablastic lymphomas can arise. KSHV contributes to lymphomagenesis by subverting the host cell molecular signaling machinery to deregulate cell growth and survival. KSHV expresses a selected set of genes in the lymphoma cells, encoding viral proteins that play important roles in KSHV lymphomagenesis. Deregulation of the NF-kappaB pathway is an important strategy used by KSHV to promote lymphoma cell survival, and the viral protein vFLIP is essential for this process. Two other viruses that are well documented to be causally associated with lymphoid neoplasia in humans are Epstein-Barr virus (EBV/HHV-4) and human T-cell lymphotropic virus (HTLV-1). Both of these are similar to KSHV in their use of viral proteins to promote cell survival by deregulating the NF-kappaB pathway. Here we review the basic information and recent developments that have contributed to our knowledge of lymphomas caused by KSHV and other viruses. The understanding of the mechanisms of viral lymphomagenesis should lead to the identification of novel therapeutic targets and to the development of rationally designed therapies.
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Affiliation(s)
- E Cesarman
- Department of Pathology and Laboratory Medicine, Weill Medical College of Cornell University, New York, NY 10021, USA.
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41
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Verma SC, Lan K, Robertson E. Structure and function of latency-associated nuclear antigen. Curr Top Microbiol Immunol 2006; 312:101-36. [PMID: 17089795 PMCID: PMC3142369 DOI: 10.1007/978-3-540-34344-8_4] [Citation(s) in RCA: 89] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Latency-associated nuclear antigen (LANA) encoded by open reading frame 73 (ORF73) is the major latent protein expressed in all forms of KSHV-associated malignancies. LANA is a large (222-234 kDa) nuclear protein that interacts with various cellular as well as viral proteins. LANA has been classified as an oncogenic protein as it dysregulates various cellular pathways including tumor suppressor pathways associated with pRb and p53 and can transform primary rat embryo fibroblasts in cooperation with the cellular oncogene Hras. It associates with GSK-3beta, an important modulator of Wnt signaling pathway leading to the accumulation of cytoplasmic beta-catenin, which upregulates Tcf/Lef regulated genes after entering into the nucleus. LANA also blocks the expression of RTA, the reactivation transcriptional activator, which is critical for the latency to lytic switch, and thus helps in maintaining viral latency. LANA tethers the viral episomal DNA to the host chromosomes by directly binding to its cognate binding sequence within the TR region of the genome through its C terminus and to the nucleosomes through the N terminus of the molecule. Tethering to the host chromosomes helps in efficient partitioning of the viral episomes in the dividing cells. Disruptions of LANA expression led to reduction in the episomal copies of the viral DNA, supporting its role in persistence of the viral DNA. The functions known so far suggest that LANA is a key player in KSHV-mediated pathogenesis.
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Affiliation(s)
- S C Verma
- Department of Microbiology and Tumor Virology Program of the Abramson Comprehensive Cancer Center, University of Pennsylvania School of Medicine, 201E Johnson Pavilion, 3610 Hamilton Walk, Philadelphia, PA 19104, USA.
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Abstract
The cell has many ways to regulate the production of proteins. One mechanism is through the changes to the machinery of translation initiation. These alterations favor the translation of one subset of mRNAs over another. It was first shown that internal ribosome entry sites (IRESes) within viral RNA genomes allowed the production of viral proteins more efficiently than most of the host proteins. The RNA secondary structure of viral IRESes has sometimes been conserved between viral species even though the primary sequences differ. These structures are important for IRES function, but no similar structure conservation has yet to be shown in cellular IRES. With the advances in mathematical modeling and computational approaches to complex biological problems, is there a way to predict an IRES in a data set of unknown sequences? This review examines what is known about cellular IRES structures, as well as the data sets and tools available to examine this question. We find that the lengths, number of upstream AUGs, and %GC content of 5'-UTRs of the human transcriptome have a similar distribution to those of published IRES-containing UTRs. Although the UTRs containing IRESes are on the average longer, almost half of all 5'-UTRs are long enough to contain an IRES. Examination of the available RNA structure prediction software and RNA motif searching programs indicates that while these programs are useful tools to fine tune the empirically determined RNA secondary structure, the accuracy of de novo secondary structure prediction of large RNA molecules and subsequent identification of new IRES elements by computational approaches, is still not possible.
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Affiliation(s)
- Stephen D Baird
- Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ontario K1H 8M5, Canada
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Haque M, Wang V, Davis DA, Zheng ZM, Yarchoan R. Genetic organization and hypoxic activation of the Kaposi's sarcoma-associated herpesvirus ORF34-37 gene cluster. J Virol 2006; 80:7037-51. [PMID: 16809309 PMCID: PMC1489055 DOI: 10.1128/jvi.00553-06] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is the etiologic agent for Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). We previously reported that hypoxia activates KSHV lytic replication and that the promoter for open reading frame 34 (ORF34) contains a functional hypoxia-responsive element (HRE). ORF34 is part of a cluster of lytic genes (ORF34-37) that includes ORF36, a phosphotransferase, and ORF37, a shutoff exonuclease. Rapid amplification of cDNA ends analysis revealed that they share a common polyadenylation signal but have two start sites. Two transcripts were identified, one 3.4 kb encoding ORF35-37, and the other 4.2 kb encoding ORF34 and also having coding potential for ORF35-37. Exposure of PEL cell lines to hypoxia induced messages of lengths consistent with those of these transcripts. Reporter assays with Hep3B cells showed activation of both transcripts by hypoxia. The ORF34-37 promoter region has six consensus HREs. Sequential deletion, site-directed mutagenesis experiments, and Northern blot analysis of RNA produced by constructs indicated that the second HRE (HRE-2) plays a critical role in the hypoxic activation of both RNA transcripts. The ORF35-37 transcript was upregulated by cotransfected hypoxia-inducible factor (HIF). Electrophoretic mobility shift assays demonstrated that HRE-2 and ancillary sequences bind and compete for HIF with hypoxic Hep3B nuclear extract. The activation of this gene cluster by hypoxia may have implications for the pathogenesis of PEL and KS. Moreover, the activation of ORF36 by hypoxia might be exploited to develop targeted therapy for PEL, which arises in a hypoxic environment (pleural effusions).
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Affiliation(s)
- Muzammel Haque
- HIV and AIDS Malignancy Branch, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892-1868, USA
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Allen RD, Dickerson S, Speck SH. Identification of spliced gammaherpesvirus 68 LANA and v-cyclin transcripts and analysis of their expression in vivo during latent infection. J Virol 2006; 80:2055-62. [PMID: 16439562 PMCID: PMC1367133 DOI: 10.1128/jvi.80.4.2055-2062.2006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Regulation of orf73 (LANA) gene expression is critical to the establishment and maintenance of latency following infection by members of the gamma-2 herpesvirus (rhadinovirus) family. Previous studies of murine gammaherpesvirus 68 (gammaHV68) have demonstrated that loss of LANA function results in a complete failure to establish virus latency in the spleens of laboratory mice. Here we report the characterization of alternatively spliced LANA and v-cyclin (orf72) transcripts encoded by gammaHV68. Similar to other rhadinoviruses, alternative splicing, coupled with alternative 3' processing, of a ca. 16-kb transcriptional unit can lead to expression of either LANA or v-cyclin during gammaHV68 infection. Spliced LANA and v-cyclin transcripts were initially identified from an analysis of the gammaHV68 latently infected B-cell lymphoma cell line S11E, but were also detected during lytic infection of NIH 3T12 fibroblasts. 5' Random amplification of cDNA ends (RACE) analyses identified two distinct promoters, p1 and p2, that drive expression of spliced LANA transcripts. Analysis of p1 and p2, using transiently transfected reporter constructs, mapped the minimal sequences required for promoter activity and demonstrated that both promoters are active in the absence of any viral antigens. Analysis of spliced LANA and v-cyclin transcripts in spleens recovered from latently infected mice at days 16 and 42 postinfection revealed that spliced v-cyclin transcripts can only be detected sporadically, suggesting that these may be associated with cells reactivating from latency. In contrast, spliced LANA transcripts were detected in ca. 1 in 4,000 splenocytes harvested at day 16 postinfection. Notably, based on the frequency of viral genome-positive splenocytes at day 16 postinfection (ca. 1 in 200), only 5 to 10% of viral genome-positive splenocytes express LANA. The failure of the majority of infected splenocytes at day 16 postinfection to express LANA may contribute to the contraction in the frequency of latently infected splenocytes as chronic infection is established, due to failure to maintain the viral episome in proliferating B cells.
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Affiliation(s)
- Robert D Allen
- Center for Emerging Infectious Diseases, Yerkes National Primate Research Center, Emory University School of Medicine, 954 Gatewood Rd., NE, Atlanta, GA 30329, USA.
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45
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Pearce M, Matsumura S, Wilson AC. Transcripts encoding K12, v-FLIP, v-cyclin, and the microRNA cluster of Kaposi's sarcoma-associated herpesvirus originate from a common promoter. J Virol 2006; 79:14457-64. [PMID: 16254382 PMCID: PMC1280212 DOI: 10.1128/jvi.79.22.14457-14464.2005] [Citation(s) in RCA: 86] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is the causative agent of three malignancies associated with AIDS and immunosuppression. Tumor cells harbor latent virus and express kaposin (open reading frame [ORF] K12), v-FLIP (ORF 71), v-Cyclin (ORF 72), and latency-associated nuclear antigen (LANA; ORF 73). ORFs 71 to 73 are transcribed as multicistronic RNAs initiating from adjacent constitutive and inducible promoters upstream of ORF 73. Here we characterize a third promoter embedded within the ORF 71-to-73 transcription unit specifying transcripts that encode ORF 71/72 or K12. These transcripts may also be the source of 11 microRNAs arranged as a cluster between K12 and ORF 71. Our studies reveal a complex arrangement of interlaced transcription units, incorporating four important protein-encoding genes required for latency and pathogenesis and the entire KSHV microRNA repertoire.
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Affiliation(s)
- Michael Pearce
- Department of Microbiology and NYU Cancer Institute, New York University School of Medicine, New York, New York 10016, USA
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Matsumura S, Fujita Y, Gomez E, Tanese N, Wilson AC. Activation of the Kaposi's sarcoma-associated herpesvirus major latency locus by the lytic switch protein RTA (ORF50). J Virol 2005; 79:8493-505. [PMID: 15956592 PMCID: PMC1143749 DOI: 10.1128/jvi.79.13.8493-8505.2005] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) maintains a latent infection in primary effusion lymphoma cells but can be induced to enter full lytic replication by exposure to a variety of chemical inducing agents or by expression of the KSHV-encoded replication and transcription activator (RTA) protein. During latency, only a few viral genes are expressed, and these include the three genes of the so-called latency transcript (LT) cluster: v-FLIP (open reading frame 71 [ORF71]), v-cyclin (ORF72), and latency-associated nuclear antigen (ORF73). During latency, all three open reading frames are transcribed from a common promoter as part of a multicistronic mRNA. Subsequent alternative mRNA splicing and internal ribosome entry allows for the expression of each protein. Here, we show that transcription of LT cassette mRNA can be induced by RTA through the activation of a second promoter (LT(i)) immediately downstream of the constitutively active promoter (LT(c)). We identified a minimal cis-regulatory region, which overlaps with the promoter for the bicistronic K14/v-GPCR delayed early gene that is transcribed in the opposite direction. In addition to a TATA box at -30 relative to the LT(i) mRNA start sites, we identified three separate RTA response elements that are also utilized by the K14/v-GPCR promoter. Interestingly, LT(i) is unresponsive to sodium butyrate, a potent inducer of lytic replication. This suggests there is a previously unrecognized class of RTA-responsive promoters that respond to direct, but not indirect, induction of RTA. These studies highlight the fact that induction method can influence the precise program of viral gene expression during early events in reactivation and also suggest a mechanism by which RTA contributes to establishment of latency during de novo infections.
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Affiliation(s)
- Satoko Matsumura
- Department of Microbiology and NYU Cancer Institute, New York, New York 10016, USA
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Zhang X, Wang JF, Chandran B, Persaud K, Pytowski B, Fingeroth J, Groopman JE. Kaposi's Sarcoma-associated Herpesvirus Activation of Vascular Endothelial Growth Factor Receptor 3 Alters Endothelial Function and Enhances Infection. J Biol Chem 2005; 280:26216-24. [PMID: 15878864 DOI: 10.1074/jbc.m411392200] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV; also known as human herpesvirus 8) is the etiologic agent of Kaposi's sarcoma, an endothelial neoplasm. This gamma-herpesvirus encodes for several unique proteins that alter target cell function, including the virion envelope-associated glycoprotein B (gB). Glycoprotein B has an RGD (Arg-Gly-Asp) motif at the extracellular amino terminus region and binds to the alpha3beta1 surface integrin, which enhances virus entry. We now report that gB can activate the vascular endothelial growth factor receptor 3 (VEGFR-3) on the surface of microvascular endothelial cells and trigger receptor signaling, which can modulate endothelial migration and proliferation. Furthermore, we observed that VEGFR-3 expression and activation enhance KSHV infection and participate in KSHV-mediated transformation. These functional changes in the endothelium may contribute to the pathogenesis of Kaposi's sarcoma and suggest that interventions that inhibit gB activation of VEGFR-3 could be useful in the treatment of this neoplasm.
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Affiliation(s)
- Xuefeng Zhang
- Division of Experimental Medicine, Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts 02115, USA
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48
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Griffiths A, Coen DM. An unusual internal ribosome entry site in the herpes simplex virus thymidine kinase gene. Proc Natl Acad Sci U S A 2005; 102:9667-72. [PMID: 15972803 PMCID: PMC1172279 DOI: 10.1073/pnas.0504132102] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
We have investigated a herpes simplex virus mutant that expresses low levels of thymidine kinase (TK), a phenotype associated with drug resistance and pathogenicity, despite a single-base deletion in the gene. Using a dual-reporter system, a 39-nt sequence including the mutation was shown to direct expression of the downstream reporter gene in reticulocyte lysate. Translation of the downstream reporter was not impaired when the mRNA lacked a 5' cap or had a stable stem loop 5' of the upstream reporter and was relatively resistant to edeine, an antibiotic that prevents AUG codon recognition by the 40S-eIF2-GTP/Met-tRNAi complex. Twelve nucleotides were as active as the original sequence for translation of the downstream reporter. Surprisingly, this sequence lacks an AUG codon. Analysis of point mutations showed that a CUG codon in the sequence was important. However, many single-base changes had only limited effects, and introduction of AUG codons did not increase translation. A mutant virus containing both the single-base deletion and a mutation that reduced downstream translation in vitro had significantly less TK activity than a virus with the single-base deletion alone. Thus, a remarkably short internal ribosome entry site (IRES) that lacks an AUG codon resides in the viral tk gene. The IRES appears to be responsible for TK expression from a drug-resistant mutant that would otherwise express no TK, which may contribute to pathogenicity. Because we found numerous short sequences with IRES activity, there might be many hitherto unrecognized polypeptides expressed at low levels from eukaryotic mRNAs.
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Affiliation(s)
- Anthony Griffiths
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 250 Longwood Avenue, Boston, MA 02115, USA
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Curreli F, Friedman-Kien AE, Flore O. Glycyrrhizic acid alters Kaposi sarcoma-associated herpesvirus latency, triggering p53-mediated apoptosis in transformed B lymphocytes. J Clin Invest 2005; 115:642-52. [PMID: 15765147 PMCID: PMC1051998 DOI: 10.1172/jci23334] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/13/2004] [Accepted: 12/21/2004] [Indexed: 01/13/2023] Open
Abstract
Kaposi sarcoma-associated herpesvirus (KSHV) is linked with all clinical forms of Kaposi sarcoma and several lymphoproliferative disorders. Like other herpesviruses, KSHV becomes latent in the infected cells, expressing only a few genes that are essential for the establishment and maintenance of its latency and for the survival of the infected cells. Inhibiting the expression of these latent genes should lead to eradication of herpesvirus infection. All currently available drugs are ineffective against latent infection. Here we show, for the first time to our knowledge, that latent infection with KSHV in B lymphocytes can be terminated by glycyrrhizic acid (GA), a triterpenoid compound earlier shown to inhibit the lytic replication of other herpesviruses. We demonstrate that GA disrupts latent KSHV infection by downregulating the expression of latency-associated nuclear antigen (LANA) and upregulating the expression of viral cyclin and selectively induces cell death of KSHV-infected cells. We show that reduced levels of LANA lead to p53 reactivation, an increase in ROS, and mitochondrial dysfunction, which result in G1 cell cycle arrest, DNA fragmentation, and oxidative stress-mediated apoptosis. Latent genes are involved in KSHV-induced oncogenesis, and strategies to interfere with their expression might prove useful for eradicating latent KSHV infection and have future therapeutic implications.
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Affiliation(s)
- Francesca Curreli
- Department of Microbiology, New York University School of Medicine, New York, New York 10016, USA
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50
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Coleman HM, Efstathiou S, Stevenson PG. Transcription of the murine gammaherpesvirus 68 ORF73 from promoters in the viral terminal repeats. J Gen Virol 2005; 86:561-574. [PMID: 15722515 DOI: 10.1099/vir.0.80565-0] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Gammaherpesviruses persist as latent episomes in a dynamic lymphocyte pool. The regulated production of an episome maintenance protein is therefore crucial to their survival. The transcription initiation site of the murine gammaherpesvirus 68 episome maintenance protein, ORF73, was mapped to the viral terminal repeats, more than 10 kb distant from the open reading frame (ORF) itself. A 5' non-coding exon in the terminal repeats was spliced to the right end of the viral unique sequence, and then across ORFs 75a, 75b, 75c and 74 to ORF73. The right-hand portion of a single repeat unit was sufficient for constitutive promoter activity. The unique left end of the viral genome further enhanced ORF73 transcription. This, together with the large size of the predominant ORF73 mRNA, suggested that transcription initiates in distal repeat units and then splices between repeats to generate an extensive 5' untranslated region. A second promoter in the left-hand portion of the proximal terminal repeat unit generated a transcript which overlapped that of ORF73, but failed to splice to the ORF73 coding exon and so transcribed ORF75a. In distal repeat copies, however, transcription from this promoter would enter the next repeat unit to become an ORF73 mRNA. There was a third promoter just upstream of ORF73 itself. These data indicate that ORF73 transcription is highly complex, and support the idea that the terminal repeats of gamma-2-herpesviruses constitute a vital component of episomal persistence.
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Affiliation(s)
- Heather M Coleman
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Stacey Efstathiou
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
| | - Philip G Stevenson
- Division of Virology, Department of Pathology, University of Cambridge, Tennis Court Road, Cambridge CB2 1QP, UK
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