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Rathbun MM, Shipley MM, Bowen CD, Selke S, Wald A, Johnston C, Szpara ML. Comparison of herpes simplex virus 1 genomic diversity between adult sexual transmission partners with genital infection. PLoS Pathog 2022; 18:e1010437. [PMID: 35587470 PMCID: PMC9119503 DOI: 10.1371/journal.ppat.1010437] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/16/2021] [Accepted: 03/11/2022] [Indexed: 01/15/2023] Open
Abstract
Herpes simplex virus (HSV) causes chronic infection in the human host, characterized by self-limited episodes of mucosal shedding and lesional disease, with latent infection of neuronal ganglia. The epidemiology of genital herpes has undergone a significant transformation over the past two decades, with the emergence of HSV-1 as a leading cause of first-episode genital herpes in many countries. Though dsDNA viruses are not expected to mutate quickly, it is not yet known to what degree the HSV-1 viral population in a natural host adapts over time, or how often viral population variants are transmitted between hosts. This study provides a comparative genomics analysis for 33 temporally-sampled oral and genital HSV-1 genomes derived from five adult sexual transmission pairs. We found that transmission pairs harbored consensus-level viral genomes with near-complete conservation of nucleotide identity. Examination of within-host minor variants in the viral population revealed both shared and unique patterns of genetic diversity between partners, and between anatomical niches. Additionally, genetic drift was detected from spatiotemporally separated samples in as little as three days. These data expand our prior understanding of the complex interaction between HSV-1 genomics and population dynamics after transmission to new infected persons.
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Affiliation(s)
- Molly M. Rathbun
- Department of Biochemistry and Molecular Biology, Department of Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Mackenzie M. Shipley
- Department of Biochemistry and Molecular Biology, Department of Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Christopher D. Bowen
- Department of Biochemistry and Molecular Biology, Department of Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Stacy Selke
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, United States of America
| | - Anna Wald
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, United States of America
- Department of Epidemiology, University of Washington, Seattle, Washington, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
| | - Christine Johnston
- Department of Laboratory Medicine and Pathology, University of Washington, Seattle, United States of America
- Department of Medicine, University of Washington, Seattle, Washington, United States of America
- Vaccine and Infectious Disease Division, Fred Hutchinson Cancer Research Center, Seattle, Washington, United States of America
| | - Moriah L. Szpara
- Department of Biochemistry and Molecular Biology, Department of Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, United States of America
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2
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Abstract
Alphaherpesviruses, as large double-stranded DNA viruses, were long considered to be genetically stable and to exist in a homogeneous state. Recently, the proliferation of high-throughput sequencing (HTS) and bioinformatics analysis has expanded our understanding of herpesvirus genomes and the variations found therein. Recent data indicate that herpesviruses exist as diverse populations, both in culture and in vivo, in a manner reminiscent of RNA viruses. In this review, we discuss the past, present, and potential future of alphaherpesvirus genomics, including the technical challenges that face the field. We also review how recent data has enabled genome-wide comparisons of sequence diversity, recombination, allele frequency, and selective pressures, including those introduced by cell culture. While we focus on the human alphaherpesviruses, we draw key insights from related veterinary species and from the beta- and gamma-subfamilies of herpesviruses. Promising technologies and potential future directions for herpesvirus genomics are highlighted as well, including the potential to link viral genetic differences to phenotypic and disease outcomes.
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Affiliation(s)
- Chad V. Kuny
- Departments of Biology, and Biochemistry and Molecular Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
| | - Moriah L. Szpara
- Departments of Biology, and Biochemistry and Molecular Biology, Center for Infectious Disease Dynamics, and the Huck Institutes of the Life Sciences, Pennsylvania State University, University Park, Pennsylvania, 16802, USA
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3
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Korniy N, Goyal A, Hoffmann M, Samatova E, Peske F, Pöhlmann S, Rodnina MV. Modulation of HIV-1 Gag/Gag-Pol frameshifting by tRNA abundance. Nucleic Acids Res 2019; 47:5210-5222. [PMID: 30968122 PMCID: PMC6547452 DOI: 10.1093/nar/gkz202] [Citation(s) in RCA: 28] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Revised: 03/12/2019] [Accepted: 04/08/2019] [Indexed: 12/16/2022] Open
Abstract
A hallmark of translation in human immunodeficiency virus type 1 (HIV-1) is a –1 programmed ribosome frameshifting event that produces the Gag-Pol fusion polyprotein. The constant Gag to Gag-Pol ratio is essential for the virion structure and infectivity. Here we show that the frameshifting efficiency is modulated by Leu-tRNALeu that reads the UUA codon at the mRNA slippery site. This tRNALeu isoacceptor is particularly rare in human cell lines derived from T-lymphocytes, the cells that are targeted by HIV-1. When UUA decoding is delayed, the frameshifting follows an alternative route, which maintains the Gag to Gag-Pol ratio constant. A second potential slippery site downstream of the first one is normally inefficient but can also support –1-frameshifting when altered by a compensatory resistance mutation in response to current antiviral drug therapy. Together these different regimes allow the virus to maintain a constant –1-frameshifting efficiency to ensure successful virus propagation.
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Affiliation(s)
- Natalia Korniy
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Akanksha Goyal
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Markus Hoffmann
- Infection Biology Unit, German Primate Center, Kellnerweg 4, 37077 Göttingen, Germany
| | - Ekaterina Samatova
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Frank Peske
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
| | - Stefan Pöhlmann
- Infection Biology Unit, German Primate Center, Kellnerweg 4, 37077 Göttingen, Germany.,Faculty of Biology and Psychology, University of Göttingen, Wilhelm-Weber-Str. 2, 37073 Göttingen, Germany
| | - Marina V Rodnina
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, 37077 Göttingen, Germany
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Korniy N, Samatova E, Anokhina MM, Peske F, Rodnina MV. Mechanisms and biomedical implications of -1 programmed ribosome frameshifting on viral and bacterial mRNAs. FEBS Lett 2019; 593:1468-1482. [PMID: 31222875 PMCID: PMC6771820 DOI: 10.1002/1873-3468.13478] [Citation(s) in RCA: 35] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2019] [Revised: 05/14/2019] [Accepted: 05/26/2019] [Indexed: 12/11/2022]
Abstract
Some proteins are expressed as a result of a ribosome frameshifting event that is facilitated by a slippery site and downstream secondary structure elements in the mRNA. This review summarizes recent progress in understanding mechanisms of –1 frameshifting in several viral genes, including IBV 1a/1b, HIV‐1 gag‐pol, and SFV 6K, and in Escherichia coli dnaX. The exact frameshifting route depends on the availability of aminoacyl‐tRNAs: the ribosome normally slips into the –1‐frame during tRNA translocation, but can also frameshift during decoding at condition when aminoacyl‐tRNA is in limited supply. Different frameshifting routes and additional slippery sites allow viruses to maintain a constant production of their key proteins. The emerging idea that tRNA pools are important for frameshifting provides new direction for developing antiviral therapies.
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Affiliation(s)
- Natalia Korniy
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Ekaterina Samatova
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Maria M Anokhina
- Institute of Pathology, University Hospital of Cologne, Cologne, Germany
| | - Frank Peske
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
| | - Marina V Rodnina
- Department of Physical Biochemistry, Max Planck Institute for Biophysical Chemistry, Göttingen, Germany
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5
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Atkins JF, Loughran G, Bhatt PR, Firth AE, Baranov PV. Ribosomal frameshifting and transcriptional slippage: From genetic steganography and cryptography to adventitious use. Nucleic Acids Res 2016; 44:7007-78. [PMID: 27436286 PMCID: PMC5009743 DOI: 10.1093/nar/gkw530] [Citation(s) in RCA: 161] [Impact Index Per Article: 20.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/21/2016] [Accepted: 05/26/2016] [Indexed: 12/15/2022] Open
Abstract
Genetic decoding is not ‘frozen’ as was earlier thought, but dynamic. One facet of this is frameshifting that often results in synthesis of a C-terminal region encoded by a new frame. Ribosomal frameshifting is utilized for the synthesis of additional products, for regulatory purposes and for translational ‘correction’ of problem or ‘savior’ indels. Utilization for synthesis of additional products occurs prominently in the decoding of mobile chromosomal element and viral genomes. One class of regulatory frameshifting of stable chromosomal genes governs cellular polyamine levels from yeasts to humans. In many cases of productively utilized frameshifting, the proportion of ribosomes that frameshift at a shift-prone site is enhanced by specific nascent peptide or mRNA context features. Such mRNA signals, which can be 5′ or 3′ of the shift site or both, can act by pairing with ribosomal RNA or as stem loops or pseudoknots even with one component being 4 kb 3′ from the shift site. Transcriptional realignment at slippage-prone sequences also generates productively utilized products encoded trans-frame with respect to the genomic sequence. This too can be enhanced by nucleic acid structure. Together with dynamic codon redefinition, frameshifting is one of the forms of recoding that enriches gene expression.
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Affiliation(s)
- John F Atkins
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland School of Microbiology, University College Cork, Cork, Ireland Department of Human Genetics, University of Utah, Salt Lake City, UT 84112, USA
| | - Gary Loughran
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland
| | - Pramod R Bhatt
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland
| | - Andrew E Firth
- Division of Virology, Department of Pathology, University of Cambridge, Hills Road, Cambridge CB2 0QQ, UK
| | - Pavel V Baranov
- School of Biochemistry and Cell Biology, University College Cork, Cork, Ireland
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6
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Abstract
Antiviral drug resistance is a matter of great clinical importance that, historically, has been investigated mostly from a virological perspective. Although the proximate mechanisms of resistance can be readily uncovered using these methods, larger evolutionary trends often remain elusive. Recent interest by population geneticists in studies of antiviral resistance has spurred new metrics for evaluating mutation and recombination rates, demographic histories of transmission and compartmentalization, and selective forces incurred during viral adaptation to antiviral drug treatment. We present up-to-date summaries on antiviral resistance for a range of drugs and viral types, and review recent advances for studying their evolutionary histories. We conclude that information imparted by demographic and selective histories, as revealed through population genomic inference, is integral to assessing the evolution of antiviral resistance as it pertains to human health.
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Affiliation(s)
- Kristen K Irwin
- School of Life Sciences, École Polytechnique Fédéral de Lausanne (EPFL), Lausanne, Switzerland.,Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
| | - Nicholas Renzette
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| | - Timothy F Kowalik
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, Massachusetts, USA
| | - Jeffrey D Jensen
- School of Life Sciences, École Polytechnique Fédéral de Lausanne (EPFL), Lausanne, Switzerland.,Swiss Institute of Bioinformatics (SIB), Lausanne, Switzerland
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7
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Lian Z, Wu Q, Wang T. Identification and characterization of a -1 reading frameshift in the heavy chain constant region of an IgG1 recombinant monoclonal antibody produced in CHO cells. MAbs 2015; 8:358-70. [PMID: 26652198 PMCID: PMC4966638 DOI: 10.1080/19420862.2015.1116658] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2015] [Revised: 10/27/2015] [Accepted: 11/01/2015] [Indexed: 01/16/2023] Open
Abstract
Frameshifts lead to complete alteration of the intended amino acid sequences, and therefore may affect the biological activities of protein therapeutics and pose potential immunogenicity risks. We report here the identification and characterization of a novel -1 frameshift variant in a recombinant IgG1 therapeutic monoclonal antibody (mAb) produced in Chinese hamster ovary cells during the cell line selection studies. The variant was initially observed as an atypical post-monomer fragment peak in size exclusion chromatography. Characterization of the fragment peak using intact and reduced liquid chromatography-mass spectrometry (LC-MS) analyses determined that the fragment consisted of a normal light chain disulfide-linked to an aberrant 26 kDa fragment that could not be assigned to any HC fragment even after considering common modifications. Further analysis using LC-MS/MS peptide mapping revealed that the aberrant fragment contained the expected HC amino acid sequence (1-232) followed by a 20-mer novel sequence corresponding to expression of heavy chain DNA sequence in the -1 reading frame. Examination of the DNA sequence around the frameshift initiation site revealed that a mononucleotide repeat GGGGGG located in the IgG1 HC constant region was most likely the structural root cause of the frameshift. Rapid identification of the frameshift allowed us to avoid use of a problematic cell line containing the frameshift as the production cell line. The frameshift reported here may be observed in other mAb products and the hypothesis-driven analytical approaches employed here may be valuable for rapid identification and characterization of frameshift variants in other recombinant proteins.
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Affiliation(s)
- Zhirui Lian
- Bioproduct Research and Development, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA
| | - Qindong Wu
- Bioproduct Research and Development, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA
| | - Tongtong Wang
- Bioproduct Research and Development, Eli Lilly and Company, Lilly Corporate Center, Indianapolis, IN 46285, USA
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Zhao M, Zheng R, Jiang J, Dickinson D, Fu B, Chu TC, Lee LH, Pearl H, Hsu S. Topical lipophilic epigallocatechin-3-gallate on herpes labialis: a phase II clinical trial of AverTeaX formula. Oral Surg Oral Med Oral Pathol Oral Radiol 2015; 120:717-24. [DOI: 10.1016/j.oooo.2015.08.018] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2015] [Revised: 08/21/2015] [Accepted: 08/24/2015] [Indexed: 01/27/2023]
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9
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Phenotypic and genotypic characterization of induced acyclovir-resistant clinical isolates of herpes simplex virus type 1. Antiviral Res 2013; 100:306-13. [DOI: 10.1016/j.antiviral.2013.09.008] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 09/03/2013] [Accepted: 09/10/2013] [Indexed: 11/24/2022]
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10
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Pan D, Kaye SB, Hopkins M, Kirwan R, Hart IJ, Coen DM. Common and new acyclovir resistant herpes simplex virus-1 mutants causing bilateral recurrent herpetic keratitis in an immunocompetent patient. J Infect Dis 2013; 209:345-9. [PMID: 23945375 DOI: 10.1093/infdis/jit437] [Citation(s) in RCA: 33] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
We investigated thymidine kinase (tk) mutants isolated during multiple episodes of recurrent bilateral acyclovir resistant herpes simplex keratitis in an immunocompetent patient. From one eye, we found a single guanine insertion, previously shown to greatly reduce TK expression, and from the other, a previously unidentified substitution, which genetic experiments confirmed confers drug resistance. The substitution, although distant from substrate binding sites, reduced thymidine phosphorylation 10-20-fold, and acyclovir phosphorylation >100-fold. This phenotype should permit reactivation from latency to cause recurrent disease. The results may have implications for the prevalence and prevention of acyclovir resistance in patients with herpes simplex keratitis.
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Affiliation(s)
- Dongli Pan
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts
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11
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Firth AE, Jagger BW, Wise HM, Nelson CC, Parsawar K, Wills NM, Napthine S, Taubenberger JK, Digard P, Atkins JF. Ribosomal frameshifting used in influenza A virus expression occurs within the sequence UCC_UUU_CGU and is in the +1 direction. Open Biol 2013; 2:120109. [PMID: 23155484 PMCID: PMC3498833 DOI: 10.1098/rsob.120109] [Citation(s) in RCA: 64] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2012] [Accepted: 10/04/2012] [Indexed: 01/13/2023] Open
Abstract
Programmed ribosomal frameshifting is used in the expression of many virus genes and some cellular genes. In eukaryotic systems, the most well-characterized mechanism involves -1 tandem tRNA slippage on an X_XXY_YYZ motif. By contrast, the mechanisms involved in programmed +1 (or -2) slippage are more varied and often poorly characterized. Recently, a novel gene, PA-X, was discovered in influenza A virus and found to be expressed via a shift to the +1 reading frame. Here, we identify, by mass spectrometric analysis, both the site (UCC_UUU_CGU) and direction (+1) of the frameshifting that is involved in PA-X expression. Related sites are identified in other virus genes that have previously been proposed to be expressed via +1 frameshifting. As these viruses infect insects (chronic bee paralysis virus), plants (fijiviruses and amalgamaviruses) and vertebrates (influenza A virus), such motifs may form a new class of +1 frameshift-inducing sequences that are active in diverse eukaryotes.
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Affiliation(s)
- A E Firth
- Division of Virology, Department of Pathology, University of Cambridge, Cambridge CB2 1QP, UK
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12
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Glass M, Everett RD. Components of promyelocytic leukemia nuclear bodies (ND10) act cooperatively to repress herpesvirus infection. J Virol 2013; 87:2174-85. [PMID: 23221561 PMCID: PMC3571464 DOI: 10.1128/jvi.02950-12] [Citation(s) in RCA: 90] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/19/2012] [Accepted: 11/28/2012] [Indexed: 01/12/2023] Open
Abstract
Upon the entry of the viral genome into the nucleus, herpes simplex virus type 1 (HSV-1) gene expression is rapidly repressed by constitutively expressed cellular proteins. This intrinsic antiviral defense is normally counteracted by ICP0, which allows virus infection to proceed efficiently. Replication of ICP0-null mutant HSV-1, however, is severely repressed by mechanisms that are conferred, at least in part, by nuclear domain 10 (ND10) components, including hDaxx, the promyelocytic leukemia (PML) protein, and Sp100. To investigate if these ND10 components repress viral gene expression in a cooperative manner, we simultaneously depleted host cells for hDaxx, PML, and Sp100 by multiple short hairpin RNA (shRNA) knockdown from a single lentivirus vector. We found that replication and gene expression of ICP0-null mutant HSV-1 were cooperatively repressed by hDaxx, PML, and Sp100 immediately upon infection, and all stages of virus replication were inhibited. Plaque-forming efficiency was enhanced at least 50-fold in the triple-depleted cells, a much larger increase than achieved by depletion of any single ND10 protein. Similar effects were also observed during infection of triple-depleted cells with human cytomegalovirus (HCMV). Moreover, using a cell culture model of quiescent infection, we found that triple depletion resulted in a much larger number of viral genomes escaping repression. However, triple depletion was unable to fully overcome the ICP0-null phenotype, implying the presence of additional repressive host factors, possibly components of the SUMO modification or DNA repair pathways. We conclude that several ND10 components cooperate in an additive manner to regulate HSV-1 and HCMV infection.
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Affiliation(s)
- Mandy Glass
- MRC-University of Glasgow Centre for Virus Research, Glasgow, Scotland, United Kingdom
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Lazniewska J, Milowska K, Gabryelak T. Dendrimers--revolutionary drugs for infectious diseases. WILEY INTERDISCIPLINARY REVIEWS-NANOMEDICINE AND NANOBIOTECHNOLOGY 2012; 4:469-91. [PMID: 22761054 DOI: 10.1002/wnan.1181] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
Abstract
Over recent years innovative nanomolecules in a form of dendrimers have been gaining increasing interest. These compounds can be designed and modified in many ways giving a molecule which meets required expectations. For this reason dendrimers are the object of intensive studies in many fields of nanoscience including one of the most thriving--biomedicine. Numerous studies provide evidence that some dendrimers exhibit activities against many species/strains of viruses, bacteria, fungi, and prions. These types of dendritic nanostructures which are distinguished by antipathogenic properties and low cytotoxicity to eukaryotic cells may be potentially applied in medicine as novel drugs for various infectious diseases, especially those which are persistent, marked by high mortality rate, or untreatable. Dendrimers can exert their effect via different mechanisms of action, which are, in most cases, related to multivalency of the nanomolecule. The application of dendrimers is likely to be a breakthrough in prevention and treatment of infectious diseases which still beset humanity and may significantly improve the quality of people's life.
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Quantification and analysis of thymidine kinase expression from acyclovir-resistant G-string insertion and deletion mutants in herpes simplex virus-infected cells. J Virol 2012; 86:4518-26. [PMID: 22301158 DOI: 10.1128/jvi.06995-11] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To be clinically relevant, drug-resistant mutants must both evade drug action and retain pathogenicity. Many acyclovir-resistant herpes simplex virus mutants from clinical isolates have one or two base insertions (G8 and G9) or one base deletion (G6) in a homopolymeric run of seven guanines (G string) in the gene encoding thymidine kinase (TK). Nevertheless, G8 and G9 mutants express detectable TK activity and can reactivate from latency in mice, a pathogenicity marker. On the basis of studies using cell-free systems, ribosomal frameshifting can explain this ability to express TK. To investigate frameshifting in infected cells, we constructed viruses that express epitope-tagged versions of wild-type and mutant TKs. We measured TK activity by plaque autoradiography and expression of frameshifted and unframeshifted TK polypeptides using a very sensitive immunoprecipitation-Western blotting method. The G6 mutant expressed ∼0.01% of wild-type levels of TK polypeptide. For the G9 mutant, consistent with previous results, much TK expression could be ascribed to reversion. For the G8 mutant, from these assays and pulse-labeling studies, we determined the ratio of synthesis of frameshifted to unframeshifted polypeptides to be 1:100. The effects of stop codons before or after the G string argue that frameshifting can initiate within the first six guanines. However, frameshifting efficiency was altered by stop codons downstream of the string in the 0 frame. The G8 mutant expressed only 0.1% of the wild-type level of full-length TK, considerably lower than estimated previously. Thus, remarkably low levels of TK are sufficient for reactivation from latency in mice.
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