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1.
PLoS Pathog ; 13(9): e1006555, 2017 Sep.
Article in English | MEDLINE | ID: mdl-28910389

ABSTRACT

Many pathogens, including Kaposi's sarcoma herpesvirus (KSHV), lack tractable small animal models. KSHV persists as a multi-copy, nuclear episome in latently infected cells. KSHV latency-associated nuclear antigen (kLANA) binds viral terminal repeat (kTR) DNA to mediate episome persistence. Model pathogen murine gammaherpesvirus 68 (MHV68) mLANA acts analogously on mTR DNA. kLANA and mLANA differ substantially in size and kTR and mTR show little sequence conservation. Here, we find kLANA and mLANA act reciprocally to mediate episome persistence of TR DNA. Further, kLANA rescued mLANA deficient MHV68, enabling a chimeric virus to establish latent infection in vivo in germinal center B cells. The level of chimeric virus in vivo latency was moderately reduced compared to WT infection, but WT or chimeric MHV68 infected cells had similar viral genome copy numbers as assessed by immunofluorescence of LANA intranuclear dots or qPCR. Thus, despite more than 60 Ma of evolutionary divergence, mLANA and kLANA act reciprocally on TR DNA, and kLANA functionally substitutes for mLANA, allowing kLANA investigation in vivo. Analogous chimeras may allow in vivo investigation of genes of other human pathogens.


Subject(s)
Antigens, Viral/metabolism , DNA, Viral/genetics , Genome, Viral/genetics , Germinal Center/metabolism , Herpesvirus 8, Human , Nuclear Proteins/metabolism , Plasmids/metabolism , Sarcoma, Kaposi/metabolism , Virus Latency/genetics , Animals , Antigens, Viral/genetics , B-Lymphocytes/metabolism , B-Lymphocytes/virology , Mice , Nuclear Proteins/genetics , Plasmids/genetics , Sarcoma, Kaposi/virology
2.
Sci Rep ; 6: 39144, 2016 12 22.
Article in English | MEDLINE | ID: mdl-28004818

ABSTRACT

Cancer cells have been increasingly grown in pharmaceutical research to understand tumorigenesis and develop new therapeutic drugs. Currently, cells are typically grown using two-dimensional (2-D) cell culture approaches, where the native tumor microenvironment is difficult to recapitulate. Thus, one of the main obstacles in oncology is the lack of proper infection models that recount main features present in tumors. In recent years, microtechnology-based platforms have been employed to generate three-dimensional (3-D) models that better mimic the native microenvironment in cell culture. Here, we present an innovative approach to culture Kaposi's sarcoma-associated herpesvirus (KSHV) infected human B cells in 3-D using a microwell array system. The results demonstrate that the KSHV-infected B cells can be grown up to 15 days in a 3-D culture. Compared with 2-D, cells grown in 3-D had increased numbers of KSHV latency-associated nuclear antigen (LANA) dots, as detected by immunofluorescence microscopy, indicating a higher viral genome copy number. Cells in 3-D also demonstrated a higher rate of lytic reactivation. The 3-D microwell array system has the potential to improve 3-D cell oncology models and allow for better-controlled studies for drug discovery.


Subject(s)
Antigens, Viral/genetics , B-Lymphocytes/virology , Cell Culture Techniques/instrumentation , Gene Expression Regulation, Viral , Herpesvirus 8, Human/physiology , Nuclear Proteins/genetics , Antigens, Viral/metabolism , Cell Line, Tumor , Humans , Nuclear Proteins/metabolism , Viral Load , Virus Activation , Virus Latency/genetics
3.
J Biomol Screen ; 19(6): 947-58, 2014 Jul.
Article in English | MEDLINE | ID: mdl-24518064

ABSTRACT

Kaposi's sarcoma-associated herpesvirus (KSHV) has a causative role in several human malignancies, especially in immunocompromised hosts. KSHV latently infects tumor cells and persists as an extrachromosomal episome (plasmid). KSHV latency-associated nuclear antigen (LANA) mediates KSHV episome persistence. LANA binds specific KSHV sequence to replicate viral DNA. In addition, LANA tethers KSHV genomes to mitotic chromosomes to efficiently segregate episomes to daughter nuclei after mitosis. N-terminal LANA (N-LANA) binds histones H2A and H2B to attach to chromosomes. Currently, there are no specific inhibitors of KSHV latent infection. To enable high-throughput screening (HTS) of inhibitors of N-LANA binding to nucleosomes, here we develop, miniaturize, and validate a fluorescence polarization (FP) assay that detects fluorophore-labeled N-LANA peptide binding to nucleosomes. We also miniaturize a counterscreen to identify DNA intercalators that nonspecifically inhibit N-LANA binding to nucleosomes, and also develop an enzyme-linked immunosorbent assay to assess N-LANA binding to nucleosomes in the absence of fluorescence. HTS of libraries containing more than 350,000 compounds identified multiple compounds that inhibited N-LANA binding to nucleosomes. No compounds survived all counterscreens, however. More complex small-molecule libraries will likely be necessary to identify specific inhibitors of N-LANA binding to histones H2A and H2B; these assays should prove useful for future screens.


Subject(s)
Antiviral Agents/chemistry , Herpesvirus 8, Human/drug effects , Nuclear Proteins/antagonists & inhibitors , Nucleosomes/chemistry , Animals , Antigens/chemistry , Antigens, Viral/chemistry , Cell Survival , Chickens , Drug Design , Enzyme-Linked Immunosorbent Assay , Erythrocytes/virology , Fluorescence Polarization , Fluorescent Dyes/chemistry , Glutathione Transferase/metabolism , HeLa Cells , High-Throughput Screening Assays , Histones/chemistry , Humans , Mitosis , Nuclear Proteins/chemistry , Plasmids/chemistry , Protein Domains , Spectrometry, Fluorescence
4.
PLoS Pathog ; 9(10): e1003673, 2013.
Article in English | MEDLINE | ID: mdl-24146618

ABSTRACT

Latency-associated nuclear antigen (LANA) mediates γ2-herpesvirus genome persistence and regulates transcription. We describe the crystal structure of the murine gammaherpesvirus-68 LANA C-terminal domain at 2.2 Šresolution. The structure reveals an alpha-beta fold that assembles as a dimer, reminiscent of Epstein-Barr virus EBNA1. A predicted DNA binding surface is present and opposite this interface is a positive electrostatic patch. Targeted DNA recognition substitutions eliminated DNA binding, while certain charged patch mutations reduced bromodomain protein, BRD4, binding. Virus containing LANA abolished for DNA binding was incapable of viable latent infection in mice. Virus with mutations at the charged patch periphery exhibited substantial deficiency in expansion of latent infection, while central region substitutions had little effect. This deficiency was independent of BRD4. These results elucidate the LANA DNA binding domain structure and reveal a unique charged region that exerts a critical role in viral latent infection, likely acting through a host cell protein(s).


Subject(s)
DNA, Viral/chemistry , Protein Folding , Rhadinovirus/chemistry , Viral Proteins/chemistry , Virus Latency , DNA, Viral/genetics , DNA, Viral/metabolism , Mutation , Protein Binding , Protein Structure, Tertiary , Rhadinovirus/physiology , Viral Proteins/genetics , Viral Proteins/metabolism
5.
J Virol ; 86(21): 11863-76, 2012 Nov.
Article in English | MEDLINE | ID: mdl-22915819

ABSTRACT

Murine gammaherpesvirus 68 (MHV68) ORF73 (mLANA) has sequence homology to Kaposi's sarcoma-associated herpesvirus (KSHV) latency-associated nuclear antigen (LANA). LANA acts on the KSHV terminal repeat (TR) elements to mediate KSHV episome maintenance. Disruption of mLANA expression severely reduces the ability of MHV68 to establish latent infection in mice, consistent with the possibility that mLANA mediates episome persistence. Here we assess the roles of mLANA and MHV68 TR (mTR) elements in episome persistence. mTR-associated DNA persisted as an episome in latently MHV68-infected tumor cells, demonstrating that the mTR elements can serve as a cis-acting element for MHV68 episome maintenance. In some cases, both control vector and mTR-associated DNAs integrated into MHV68 episomal genomes. Therefore, we also assessed the roles of mTRs as well as mLANA in the absence of infection. DNA containing both mLANA and mTRs in cis persisted as an episome in murine A20 or MEF cells. In contrast, mTR DNA never persisted as an episome in the absence of mLANA. mLANA levels were increased when mLANA was expressed from its native promoters, and episome maintenance was more efficient with higher mLANA levels. Increased numbers of mTRs conferred more efficient episome maintenance, since DNA containing mLANA and eight mTR elements persisted more efficiently in A20 cells than did DNA with mLANA and two or four mTRs. Similar to KSHV LANA, mLANA broadly associated with mitotic chromosomes but relocalized to concentrated dots in the presence of episomes. Therefore, mLANA acts on mTR elements to mediate MHV68 episome persistence.


Subject(s)
Antigens, Viral/metabolism , DNA, Viral/metabolism , Nuclear Proteins/metabolism , Plasmids , Rhadinovirus/physiology , Terminal Repeat Sequences , Virus Latency , Virus Replication , Animals , Cell Line , Mice , Protein Binding
6.
Virology ; 377(1): 216-25, 2008 Jul 20.
Article in English | MEDLINE | ID: mdl-18501944

ABSTRACT

Eukaryotic elongation factor 1-alpha (eEF1A) was identified as an interactor of Turnip mosaic virus (TuMV) RNA-dependent RNA polymerase (RdRp) and VPg-protease (VPg-Pro) using tandem affinity purification and/or in vitro assays. Subcellular fractionation experiments revealed that the level of eEF1A substantially increased in membrane fractions upon TuMV infection. Replication of TuMV occurs in cytoplasmic membrane vesicles, which are induced by 6K-VPg-Pro. Confocal microscopy indicated that eEF1A was included in these vesicles. To confirm that eEF1A was found in replication vesicles, we constructed an infectious recombinant TuMV that contains an additional copy of the 6K protein fused to the green fluorescent protein (GFP). In cells infected with this recombinant TuMV, fluorescence emitted by 6KGFP was associated with cytoplasmic membrane vesicles that contained VPg-Pro, the eukaryotic initiation factor (iso) 4E, the poly(A)-binding protein, the heat shock cognate 70-3 protein, and eEF1A. These results suggest that TuMV-induced membrane vesicles host at least three plant translation factors in addition to the viral replication proteins.


Subject(s)
Peptide Elongation Factor 1/physiology , Peptide Hydrolases/physiology , Potyvirus/physiology , RNA-Dependent RNA Polymerase/physiology , Arabidopsis/genetics , Arabidopsis/physiology , Arabidopsis/virology , Arabidopsis Proteins/genetics , Arabidopsis Proteins/physiology , Base Sequence , DNA Primers/genetics , Host-Pathogen Interactions , Peptide Elongation Factor 1/genetics , Peptide Hydrolases/genetics , Plants, Genetically Modified , Potyvirus/pathogenicity , Protein Binding , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Nicotiana/genetics , Nicotiana/physiology , Virus Replication
7.
Virology ; 374(1): 217-27, 2008 Apr 25.
Article in English | MEDLINE | ID: mdl-18222516

ABSTRACT

Tandem affinity purification was used in Arabidopsis thaliana to identify cellular interactors of Turnip mosaic virus (TuMV) RNA-dependent RNA polymerase (RdRp). The heat shock cognate 70-3 (Hsc70-3) and poly(A)-binding (PABP) host proteins were recovered and shown to interact with the RdRp in vitro. As previously shown for PABP, Hsc70-3 was redistributed to nuclear and membranous fractions in infected plants and both RdRp interactors were co-immunoprecipitated from a membrane-enriched extract using RdRp-specific antibodies. Fluorescently tagged RdRp and Hsc70-3 localized to the cytoplasm and the nucleus when expressed alone or in combination in Nicotiana benthamiana. However, they were redistributed to large perinuclear ER-derived vesicles when co-expressed with the membrane binding 6K-VPg-Pro protein of TuMV. The association of Hsc70-3 with the RdRp could possibly take place in membrane-derived replication complexes. Thus, Hsc70-3 and PABP2 are potentially integral components of the replicase complex and could have important roles to play in the regulation of potyviral RdRp functions.


Subject(s)
Arabidopsis/virology , HSC70 Heat-Shock Proteins/metabolism , Plant Proteins/metabolism , RNA-Dependent RNA Polymerase/metabolism , Transport Vesicles/virology , Tymovirus/metabolism , Viral Proteins/metabolism , Amino Acid Sequence , Cell Nucleus/chemistry , Cytoplasm/chemistry , Immunoprecipitation , Microscopy, Fluorescence , Molecular Sequence Data , Protein Binding , Protein Interaction Mapping , Nicotiana/virology
8.
J Virol ; 81(20): 10905-13, 2007 Oct.
Article in English | MEDLINE | ID: mdl-17670821

ABSTRACT

Poly(A) binding protein 2 (PABP2) of Arabidopsis thaliana was previously shown to interact with VPg-Pro of turnip mosaic virus (TuMV) and may consequently play an important role during infection. Subcellular fractionation experiments revealed that PABP2 was predominantly a cytoplasmic soluble protein in healthy plants. However, in TuMV-infected plants, a subpopulation of PABP2 was membrane associated or was localized in the nucleus. Confocal microscopy experiments indicated that PABP2 was partially retargeted to the nucleolus in the presence of TuMV VPg-Pro. In addition, the membrane association of PABP2 during TuMV infection resulted from the internalization of the host protein in 6K-VPg-Pro-induced vesicles, as shown by a combination of confocal microscopy and sucrose gradient fractionation experiments. This redistribution of an important translation initiation factor to the nucleolus and to membrane structure likely underlies two important processes of the TuMV replication cycle.


Subject(s)
Cell Nucleolus/virology , Plant Diseases/virology , Poly(A)-Binding Protein II/metabolism , Tymovirus/pathogenicity , Arabidopsis , Microscopy, Confocal , Plants/ultrastructure , Plants/virology , Protein Transport , Tymovirus/metabolism , Viral Proteins/metabolism , Virus Replication
9.
Transgenic Res ; 16(2): 213-22, 2007 Apr.
Article in English | MEDLINE | ID: mdl-17103245

ABSTRACT

We developed an inactivated DNA replicon of Turnip Mosaic Virus (TuMV), which was reactivated by a recombination event based on the Cre-loxP system. Viral replication was prevented by the insertion of a translation terminator sequence flanked by two loxP sites at the junction of the P1-HCPro-coding genes. In vitro recombination was tested with purified Cre, which excised the floxed sequence from the TuMV DNA, leaving a single loxP site in the reactivated viral genome, and restored the open reading frame of the replicon. Arabidopsis thaliana plants were made transgenic for the inactivated TuMV replicon. Removal of the translation terminator sequence was achieved by the controlled expression of Cre. Delivery of the Cre recombinase to the transgenic plants was obtained by three methods: agroinfiltration, PVX-based production, or transgenic chemical-inducible expression. In each case, reactivation of TuMV replication was observed.


Subject(s)
Arabidopsis/genetics , Gene Transfer Techniques , Genetic Vectors , Plants, Genetically Modified , Integrases/genetics , Potyvirus
10.
J Virol ; 81(2): 775-82, 2007 Jan.
Article in English | MEDLINE | ID: mdl-17079311

ABSTRACT

The RNA genome of Turnip mosaic virus is covalently linked at its 5' end to a viral protein known as VPg. This protein binds to the translation eukaryotic initiation factor iso 4E [eIF(iso)4E]. This interaction has been shown to be important for virus infection, although its exact biological function(s) has not been elucidated. In this study, we investigated the subcellular site of the VPg-eIF(iso)4E interaction using bimolecular fluorescence complementation (BiFC). As a first step, eIF(iso)4E, 6K-VPg-Pro, and VPg-Pro were expressed as full-length green fluorescent protein (GFP) fusions in Nicotiana benthamiana, and their subcellular localizations were visualized by confocal microscopy. eIF(iso)4E was predominantly associated with the endoplasmic reticulum (ER), and VPg-Pro was observed in the nucleus and possibly the nucleolus, while 6K-VPg-Pro-GFP induced the formation of cytoplasmic vesicles budding from the ER. In BiFC experiments, reconstituted green fluorescence was observed throughout the nucleus, with a preferential accumulation in subnuclear structures when the GFP split fragments were fused to VPg-Pro and eIF(iso)4E. On the other hand, the interaction of 6K-VPg-Pro with eIF(iso)4E was observed in cytoplasmic vesicles embedded in the ER. These data suggest that the association of VPg with the translation factor might be needed for two different functions, depending of the VPg precursor involved in the interaction. VPg-Pro interaction with eIF(iso)4E may be involved in perturbing normal cellular functions, while 6K-VPg-Pro interaction with the translation factor may be needed for viral RNA translation and/or replication.


Subject(s)
Brassica/metabolism , Eukaryotic Initiation Factor-4E/metabolism , Potyvirus/metabolism , Protein Precursors/metabolism , Ribonucleoproteins/metabolism , Viral Nonstructural Proteins/metabolism , Arabidopsis Proteins , Brassica/ultrastructure , Brassica/virology , Cytoplasmic Vesicles/metabolism , Cytoplasmic Vesicles/ultrastructure , Endoplasmic Reticulum/ultrastructure , Eukaryotic Initiation Factors , Green Fluorescent Proteins/genetics , Green Fluorescent Proteins/metabolism , Microscopy, Confocal , Plant Leaves/ultrastructure , Plant Leaves/virology , Potyvirus/genetics , Protein Precursors/genetics , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Ribonucleoproteins/genetics , Nicotiana/metabolism , Nicotiana/virology , Viral Nonstructural Proteins/genetics
11.
Virus Res ; 112(1-2): 1-8, 2005 Sep.
Article in English | MEDLINE | ID: mdl-16022896

ABSTRACT

With the aim of developing a biotechnological tool for the production of foreign proteins in plants, we first engineered an infectious turnip mosaic virus (TuMV) cDNA that contained the jellyfish green fluorescent protein (GFP) gene or the bacterial beta-glucuronidase (GUS) gene (uidA). Two insertion sites were assessed, either between P1 and HCPro cistrons or Pol and CP cistrons. In each construct, the junctions flanking the inserted gene coded for P1 and/or VPg-Pro cleavage recognition site sequences, to produce free GUS or GFP. After transfection by particle bombardment on Brassica perviridis, characteristic symptoms for TuMV infection appeared and Western blot analyses showed that GFP and GUS had been excised from the viral polyprotein. No significant differences in expression level were noticed between the two insertion sites. By RT-PCR, gfp was found to be stable over 30 days post-transfection (dpt) while uidA was gradually lost at 15 dpt. We also created two constructs containing either gene at each insertion sites on the same molecule. Attenuated systemic symptoms were observed after particle bombardment on B. perviridis and Western blot analyses showed that both foreign proteins were produced. Also, the same stability/instability as for the single-gene constructs were observed. These results indicate that it is possible to produce at least two foreign proteins simultaneously in a TuMV-based vector.


Subject(s)
Genetic Vectors , Glucuronidase/metabolism , Green Fluorescent Proteins/metabolism , Potyvirus/metabolism , Amino Acid Sequence , Base Sequence , Brassica/virology , Genetic Engineering/methods , Glucuronidase/genetics , Green Fluorescent Proteins/genetics , Molecular Sequence Data , Plant Diseases/virology , Polyproteins/chemistry , Polyproteins/genetics , Potyvirus/genetics , Transfection
12.
J Gen Virol ; 85(Pt 4): 1055-1063, 2004 Apr.
Article in English | MEDLINE | ID: mdl-15039548

ABSTRACT

The viral protein linked to the genome (VPg) of Turnip mosaic virus (TuMV) interacts in vitro with the translation eukaryotic initiation factor (eIF) 4E. In the present study, we investigated the consequence of TuMV infection on eIF4E expression. Two isomers are present in plants, namely eIF4E and eIF(iso)4E. Expression of the latter was detected in both TuMV-infected and mock-inoculated Brassica perviridis plants, but expression of eIF4E was found only in infected plants. Membranes from TuMV-infected or mock-inoculated tissues were separated by sucrose gradient centrifugation and fractions were collected. Immunoblot analyses showed that 6K(2)-VPg-Pro/VPg-Pro polyproteins were associated with endoplasmic reticulum membranes and were the viral forms likely to interact with eIF(iso)4E and eIF4E. In planta interaction between 6K(2)-VPg-Pro/VPg-Pro and eIF(iso)4E/eIF4E was confirmed by co-purification by metal chelation chromatography. The poly(A)-binding protein (PABP) was also found to co-purify with VPg-Pro. Direct interaction between VPg-Pro and PABP was shown by an ELISA-based binding assay. These experiments suggest that a multi-protein complex may form around VPg-Pro of TuMV.


Subject(s)
Brassica/virology , Eukaryotic Initiation Factor-4E/physiology , Poly(A)-Binding Proteins/physiology , Potyvirus/physiology , Viral Core Proteins/physiology , Base Sequence , Brassica/genetics , Brassica/physiology , Cell Membrane/physiology , Cell Membrane/virology , DNA, Plant/genetics , Eukaryotic Initiation Factor-4E/genetics , Macromolecular Substances , Plant Diseases/genetics , Plant Diseases/virology , Poly(A)-Binding Proteins/genetics , Potyvirus/genetics , Protein Biosynthesis , Protein Isoforms/genetics , Protein Isoforms/physiology , Viral Core Proteins/genetics
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