Viral Gene Expression In Cells Research Articles

Selective Inhibition of Murine Cytomegalovirus Viral Gene Expression by the Antiviral Peptide TAT-I24.

The effect of the antiviral peptide TAT-I24 on viral gene expression in cells infected with murine cytomegalovirus (MCMV) was investigated. The expression of immediate-early, early and late genes was highly induced upon infection with MCMV. In the presence of the peptide, the expression of all tested genes was sustainably reduced to a similar extent, independent of whether they were immediate-early, early or late genes. In contrast, the expression of host genes, such as NF-κB inhibitor alpha (Nfkbia), interferon-induced protein with tetratricopeptide repeats 1 (Ifit1), chemokine (C-X-C motif) ligand 10 (Cxcl10), chemokine (C-C motif) ligand 7 (Ccl7) and chemokine (C-C motif) ligand 5 (Ccl5), which are induced early upon virus infection, was only transiently suppressed in peptide-treated cells. The expression of other host genes which are affected by MCMV infection and play a role in endoplasmic reticulum stress or DNA-damage repair was not inhibited by the peptide. A combination of TAT-I24 with the nucleoside analogue cidofovir showed enhancement of the antiviral effect, demonstrating that viral replication can be more efficiently inhibited with a combination of drugs acting at different stages of the viral life-cycle.

Identification and analysis of differentially expressed microRNAs in rainbow trout (Oncorhynchus mykiss) responding to infectious hematopoietic necrosis virus infection

MicroRNAs (miRNAs) are a class of regulators essential for numerous biological processes. Infectious hematopoietic necrosis virus (IHNV) is one of the most important viral pathogens in salmon and trout. In this study, the miRNA expression profiles of rainbow trout upon IHNV infection were explored. In total, 392 known miRNAs and 936 novel miRNAs were identified. Twelve known and 13 novel miRNAs were differentially expressed between infected and uninfected fish. Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analyses revealed that certain miRNA target genes were associated with biological regulation, the immune system, and signal transduction. In addition, over- and suppressed expression of miR-146a-3p, miR-155–5p, miR-216a-5p, and miR-499b-5p could respectively increase and decrease viral gene expression in cells and viral titers. MiR-146a-3p and miR-216a-5p inhibited the expression of type-I IFN and the Mx1 gene induced by IHNV. These results provide preliminary insights into the IHNV–host interactions mediated by miRNAs.

Transcriptional Reprogramming during Effector-to-Memory Transition Renders CD4+ T Cells Permissive for Latent HIV-1 Infection

The latent reservoir for HIV-1 in resting memory CD4+ Tcells is the major barrier to curing HIV-1 infection. Studies of HIV-1 latency have focused on regulation of viral gene expression in cells in which latent infection is established. However, it remains unclear how infection initially becomes latent. Here we described a unique set of properties of CD4+ Tcells undergoing effector-to-memory transition including temporary upregulation of CCR5 expression and rapid downregulation of cellular gene transcription. These cells allowed completion of steps in the HIV-1 life cycle through integration but suppressed HIV-1 gene transcription, thus allowing the establishment of latency. CD4+ Tcells in this stage were substantially more permissive for HIV-1 latent infection than other CD4+ Tcells. Establishment of latent HIV-1 infection in CD4+ T could be inhibited by viral-specific CD8+ Tcells, a result with implications for elimination of latent HIV-1 infection by Tcell-based vaccines.

The Product of the Herpes Simplex Virus 2 UL16 Gene Is Critical for the Egress of Capsids from the Nuclei of Infected Cells.

The herpes simplex virus (HSV) UL16 gene is conserved throughout the Herpesviridae and encodes a poorly understood tegument protein. The HSV-1 UL16 protein forms complexes with several viral proteins, including UL11, gE, VP22, and UL21. We previously demonstrated that HSV-2 UL21 was essential for virus propagation due to the failure of DNA-containing capsids (C capsids) to exit the nucleus. We hypothesized that if a UL16/UL21 complex was required for nuclear egress, HSV-2 lacking UL16 would have a phenotype similar to that of HSV-2 lacking UL21. Deletion of HSV-2 UL16 (Δ16) resulted in a 950-fold reduction in virus propagation in mouse L cell fibroblasts and a 200-fold reduction in virus propagation in Vero cells that was fully reversed upon the repair of Δ16 (Δ16R) and partially reversed by infecting UL16-expressing cells with Δ16. The kinetics of viral gene expression in cells infected with Δ16 were indistinguishable from those of cells infected with Δ16R or the parental virus. Additionally, similar numbers of capsids were isolated from the nuclei of cells infected with Δ16 and the parental virus. However, transmission electron microscopy, fluorescence in situ hybridization experiments, and fluorescent capsid localization assays all indicated a reduction in the ability of Δ16 C capsids to exit the nucleus of infected cells. Taken together, these data indicate that, like UL21, UL16 is critical for HSV-2 propagation and suggest that the UL16 and UL21 proteins may function together to facilitate the nuclear egress of capsids.IMPORTANCE HSV-2 is a highly prevalent sexually transmitted human pathogen that is the main cause of genital herpes infections and is fueling the epidemic transmission of HIV in sub-Saharan Africa. Despite important differences in the pathological features of HSV-1 and HSV-2 infections, HSV-2 is understudied compared to HSV-1. Here we demonstrate that a deletion of the HSV-2 UL16 gene results in a substantial inhibition of virus replication due to a reduction in the ability of DNA-containing capsids to exit the nucleus of infected cells. The phenotype of this UL16 mutant resembles that of an HSV-2 UL21 mutant described previously by our laboratory. Because UL16 and UL21 interact, these findings suggest that a complex containing both proteins may function together in nuclear egress.

Pharmacokinetics and tolerability of ABX464, a novel first-in-class compound to treat HIV infection, in healthy HIV-uninfected subjects.

An anti-HIV compound (ABX464) has been developed with a novel mechanism of activity in that it blocks viral gene expression in cells that are already infected. A first-in-man study was conducted to determine the pharmacokinetic and safety profiles of ABX464. This was carried out as an open label, parallel group, single ascending dose, exploratory study. Twenty-four male subjects in good health without HIV infection, aged from 18 to 55 years old, with BMIs of 18-27 kg/m 2 were included. A single oral dose of ABX464 (50, 100, 150 or 200 mg) was administered on the morning of day 0 after overnight fasting, with follow-up for 45 days. Safety assessments consisted of vital signs, electrocardiogram, physical examination, laboratory tests and urinalysis. Pharmacokinetic parameters were calculated for ABX464 and its main metabolite ABX-464- N -glucuronide (ABX464-NGlc). The study was registered at https://www.clinicaltrials (trial number NCT02792686). ABX464 was well tolerated; the most frequent related treatment-emergent adverse events were headaches, nausea and vomiting; they were not considered as treatment-limiting effects. ABX464's C max was observed approximately 2 h after administration in all groups. ABX464 was rapidly and substantially metabolized into ABX464-NGlc. The C max of ABX464-NGlc was observed approximately 4 h post-dose and was about 160-fold higher than that of the parent with a much longer t 1/2 (90-110 h). The ratio of metabolite to parent drug was consistent across the complete dose range. These studies confirmed that ABX464 is well tolerated and rapidly and substantially metabolized into ABX464-NGlc in human subjects.

Transcription factor Spi-B binds unique sequences present in the tandem repeat promoter/enhancer of JC virus and supports viral activity

Progressive multifocal leukoencephalopathy (PML) is an often fatal demyelinating disease caused by lytic infection of oligodendrocytes with JC virus (JCV). The development of PML in non-immunosuppressed individuals is a growing concern with reports of mortality in patients treated with mAb therapies. JCV can persist in the kidneys, lymphoid tissue and bone marrow. JCV gene expression is restricted by non-coding viral regulatory region sequence variation and cellular transcription factors. Because JCV latency has been associated with cells undergoing haematopoietic development, transcription factors previously reported as lymphoid specific may regulate JCV gene expression. This study demonstrates that one such transcription factor, Spi-B, binds to sequences present in the JCV promoter/enhancer and may affect early virus gene expression in cells obtained from human brain tissue. We identified four potential Spi-B-binding sites present in the promoter/enhancer elements of JCV sequences from PML variants and the non-pathogenic archetype. Spi-B sites present in the promoter/enhancers of PML variants alone bound protein expressed in JCV susceptible brain and lymphoid-derived cell lines by electromobility shift assays. Expression of exogenous Spi-B in semi- and non-permissive cells increased early viral gene expression. Strikingly, mutation of the Spi-B core in a binding site unique to the Mad-4 variant was sufficient to abrogate viral activity in progenitor-derived astrocytes. These results suggest that Spi-B could regulate JCV gene expression in susceptible cells, and may play an important role in JCV activity in the immune and nervous systems.

Deletion of AcMNPV AC16 and AC17 results in delayed viral gene expression in budded virus infected cells but not transfected cells

This study investigated the combined function of the Autographa californica multiple nucleopolyhedrovirus overlapping genes ac16 (BV/ODV-E26, DA26) and ac17. Ac17 is a late gene and the promoter is within the ac16 open reading frame. A double ac16 – ac17 knockout virus was generated to assess the function of each gene independently or together. Loss of ac17 did not affect viral DNA synthesis but budded virus (BV) production was reduced. Deletion of both ac16 – ac17 resulted in reduced viral DNA synthesis and a further reduction in BV production. In BV infected Sf9 cells, viral gene expression was delayed up to 12 h in the absence of both AC16 and AC17 but not if either gene was present. Cells infected by transfecting viral DNA, by-passing the BV particle, exhibited no delay in gene expression from the double knockout virus. AC16 and AC17 are therefore required for rapid viral gene expression in cells infected by BV.

Kinetic Analysis of Human T-Cell Leukemia Virus Type 1 Gene Expression in Cell Culture and Infected Animals

Human T-cell leukemia virus type 1 (HTLV-1) infection causes adult T-cell leukemia and is associated with a variety of lymphocyte-mediated disorders. It has been hypothesized that a highly regulated pattern of HTLV-1 gene expression is critical for virus survival and disease pathogenesis. In this study, real-time reverse transcriptase PCR was used to determine the kinetics of viral gene expression in cells transiently transfected with an HTLV-1 proviral plasmid, in newly infected human peripheral blood mononuclear cells (PBMCs), and in PBMCs from newly infected rabbits. The HTLV-1 gene expression profiles in transiently transfected and infected cells were similar; over time, all transcripts increased and then maintained stable levels. gag/pol, tax/rex, and env mRNA were detected first and at the highest levels, whereas the expression levels of the accessory genes, including the antisense Hbz, were significantly lower than the tax/rex levels (ranging from 1 to 4 logs depending on the specific mRNA). In infected rabbits, tax/rex and gag/pol mRNA levels peaked early after inoculation and progressively decreased, which correlated inversely with the proviral load and host antibody response against viral proteins. Interestingly, Hbz mRNA was detectable at 1 week postinfection and increased and stabilized. The expression levels of all other HTLV-1 genes in infected rabbit PBMCs were at or below our limit of detection. This analysis provides insight into viral gene expression under various in vitro and in vivo experimental conditions. Our in vivo data indicate that in infected rabbits, Hbz mRNA expression over time directly correlates with the proviral load, which provides the first evidence linking Hbz expression to proviral load and the survival of the virus-infected cell in the host.

Varicella-Zoster Virus IE63, a Major Viral Latency Protein, Is Required To Inhibit the Alpha Interferon-Induced Antiviral Response

Varicella-zoster virus (VZV) open reading frame 63 (ORF63) is the most abundant transcript expressed during latency in human sensory ganglia. VZV with ORF63 deleted is impaired for replication in melanoma cells and fibroblasts and for latency in rodents. We found that replication of the ORF63 deletion mutant is fully complemented in U2OS cells, which have been shown to complement the growth of herpes simplex virus type 1 (HSV-1) ICP0 mutants. Since HSV-1 ICP0 mutants are hypersensitive to alpha interferon (IFN-alpha), we examined the effect of IFN-alpha on VZV replication. Replication of the ORF63 mutant in melanoma cells was severely inhibited in the presence of IFN-alpha, in contrast to other VZV mutants that were similarly impaired for replication or to parental virus. The VZV ORF63 mutant was not hypersensitive to IFN-gamma. IFN-alpha inhibited viral-gene expression in cells infected with the ORF63 mutant at a posttranscriptional level. Since IFN-alpha stimulates gene products that can phosphorylate the alpha subunit of eukaryotic initiation factor 2 (eIF-2alpha) and inhibit translation, we determined whether cells infected with the ORF63 mutant had increased phosphorylation of eIF-2alpha compared with cells infected with parental virus. While phosphorylated eIF-2alpha was undetectable in uninfected cells or cells infected with parental virus, it was present in cells infected with the ORF63 mutant. Conversely, expression of IE63 (encoded by ORF63) in the absence of other viral proteins inhibited phosphorylation of eIF-2alpha. Since IFN-alpha has been shown to limit VZV replication in human skin xenografts, the ability of VZV IE63 to block the effects of the cytokine may play a critical role in VZV pathogenesis.

Vesicular Stomatitis Viruses Resistant to the Methylase Inhibitor Sinefungin Upregulate RNA Synthesis and Reveal Mutations That Affect mRNA Cap Methylation

Sinefungin (SIN), a natural S-adenosyl-L-methionine analog produced by Streptomyces griseolus, is a potent inhibitor of methyltransferases. We evaluated the effect of SIN on replication of vesicular stomatitis virus (VSV), a prototype of the nonsegmented negative-strand RNA viruses. The 241-kDa large polymerase (L) protein of VSV methylates viral mRNA cap structures at the guanine-N-7 (G-N-7) and ribose-2'-O (2'-O) positions. By performing transcription reactions in vitro, we show that both methylations are inhibited by SIN and that methylation was more sensitive at the G-N-7 than at 2'-O position. We further show that SIN inhibited growth of VSV in cell culture, reducing viral yield by 50-fold and diminishing plaque size. We isolated eight mutants that were resistant to SIN as judged by their growth characteristics. The SIN-resistant (SINR) viruses contained mutations in the L gene, the promoter for L gene expression provided by the conserved sequence elements of the G-L gene junction and the M gene. Five mutations resulted in amino acid substitutions to conserved regions II/III and VI of the L protein. For each mutant, we examined viral gene expression in cells and cap methylation in vitro. SINR mutants upregulated RNA synthesis in the presence of SIN, which may be responsible for their resistance. We also found that some SINR viruses with L gene mutations were defective in cap methylation in vitro, yet their methylases were less sensitive to SIN inhibition than those of the wild-type parent. These studies show that the VSV methylases are inhibited by SIN, and they define new regions of L protein that affect cap methylation. These studies also provide experimental evidence that inhibition of cap methylases is a potential strategy for development of antiviral therapeutics against nonsegmented negative-strand RNA viruses.

Engineered RNase P Ribozymes Increase Their Cleavage Activities and Efficacies in Inhibiting Viral Gene Expression in Cells by Enhancing the Rate of Cleavage and Binding of the Target mRNA

Engineered RNase P ribozymes are promising gene-targeting agents that can be used in both basic research and clinical applications. We have previously selected ribozyme variants for their activity in cleaving an mRNA substrate from a pool of ribozymes containing randomized sequences. In this study, one of the variants was used to target the mRNA encoding thymidine kinase (TK) of herpes simplex virus 1 (HSV-1). The variant exhibited enhanced cleavage and substrate binding and was at least 30 times more efficient in cleaving TK mRNA in vitro than the ribozyme derived from the wild type sequence. Our results provide the first direct evidence to suggest that a point mutation at nucleotide 95 of RNase P catalytic RNA from Escherichia coli (G(95) --> U(95)) increases the rate of cleavage, whereas another mutation at nucleotide 200 (A(200) --> C(200)) enhances substrate binding of the ribozyme. A reduction of about 99% in TK expression was observed in cells expressing the variant, whereas a 70% reduction was found in cells expressing the ribozyme derived from the wild type sequence. Thus, the RNase P ribozyme variant is highly effective in inhibiting HSV-1 gene expression. Our study demonstrates that ribozyme variants increase their cleavage activity and efficacy in blocking gene expression in cells through enhanced substrate binding and rate of cleavage. These results also provide insights into the mechanism of how RNase P ribozymes efficiently cleave an mRNA substrate and, furthermore, facilitate the development of highly active RNase P ribozymes for gene-targeting applications.

Role of Bovine Adenovirus-3 33K protein in viral replication*1

The L6 region of bovine adenovirus type (BAdV)-3 encodes a nonstructural protein named 33K. To identify and characterize the 33K protein, rabbit polyclonal antiserum was raised against a 33K-GST fusion protein expressed in bacteria. Anti-33K serum immunoprecipitated a protein of 42 kDa in in vitro translated and transcribed mRNA of 33K. However, three proteins of 42, 38, and 33 kDa were detected in BAdV-3 infected cells. To determine the role of this protein in virus replication, a recombinant BAV-33S1 containing insertional inactivation of 33K (a stop codon created at the seventh amino acid of 33K ORF) was constructed. Although BAV-33S1 could be isolated, the mutant showed a severe defect in the production of progeny virus. Inactivation of the 33K gene showed no effect on early and late viral gene expression in cells infected with BAV-33S1. However, formation of mature virions was significantly reduced in cells infected with BAV-33S1. Surprisingly, insertional inactivation of 33K at amino acid 97 (pFBAV-33.KS2) proved lethal for virus production. Although expression of early or late genes was not affected, no capsid formation could be observed in mutant DNA-transfected cells. These results suggest that 33K is required for capsid assembly and efficient DNA capsid interaction.

Role of Bovine Adenovirus-3 33K protein in viral replication

The L6 region of bovine adenovirus type (BAdV)-3 encodes a nonstructural protein named 33K. To identify and characterize the 33K protein, rabbit polyclonal antiserum was raised against a 33K-GST fusion protein expressed in bacteria. Anti-33K serum immunoprecipitated a protein of 42 kDa in in vitro translated and transcribed mRNA of 33K. However, three proteins of 42, 38, and 33 kDa were detected in BAdV-3 infected cells. To determine the role of this protein in virus replication, a recombinant BAV-33S1 containing insertional inactivation of 33K (a stop codon created at the seventh amino acid of 33K ORF) was constructed. Although BAV-33S1 could be isolated, the mutant showed a severe defect in the production of progeny virus. Inactivation of the 33K gene showed no effect on early and late viral gene expression in cells infected with BAV-33S1. However, formation of mature virions was significantly reduced in cells infected with BAV-33S1. Surprisingly, insertional inactivation of 33K at amino acid 97 (pFBAV-33.KS2) proved lethal for virus production. Although expression of early or late genes was not affected, no capsid formation could be observed in mutant DNA-transfected cells. These results suggest that 33K is required for capsid assembly and efficient DNA capsid interaction.

An early regulatory function required in a cell type-dependent manner is expressed by the genomic but not the cDNA copy of the herpes simplex virus 1 gene encoding infected cell protein 0.

The alpha 0 genes of herpes simplex virus 1 (HSV-1) contain three exons. Earlier studies have shown that the substitution of genomic sequences with a cDNA copy does not alter the capacity of the virus to replicate or establish latent infection. Other studies have demonstrated that HSV-1 may express alternatively spliced forms of alpha 0 transcripts. The studies reported here centered on a mutant HSV-1(vCPc0) strain in which the genomic copies of the alpha 0 gene were replaced with cDNA copies. From our research, we report the following observations. (i) In contrast to events transpiring in cells infected with wild-type virus, the expression of HSV-1(vCPc0) genes was delayed or restricted to alpha genes for many hours in rabbit skin cells and to a lesser extent in HEp-2 cells but not in Vero cells. This delay in the expression of HSV-1(vCPc0) beta or gamma genes was also multiplicity of infection dependent. (ii) Exposure to MG132, a proteasomal inhibitor, before infection with wild-type virus had no significant effect on the accumulation of viral proteins in Vero cells and caused an only slight delay in viral gene expression in rabbit skin cells in a multiplicity of infection-dependent fashion. The drug had no effect when it was added to the medium 3 h after infection. (iii) Rabbit skin or HEp-2 cells exposed to MG132 3 h after infection with the HSV-1(vCPc0) mutant accumulated only alpha proteins. This restriction was cell type dependent but not multiplicity of infection dependent. (iv) Both the delay in the expression of beta and gamma genes and the effect of MG132 added to the medium 3 h after infection were rescued by restoration of the intron 1 sequences in the HSV-1(vCPc0) mutant. However, cells transduced by baculoviruses expressing intron 1 RNA did not complement the HSV-1(vCPc0) mutant, suggesting that the function of intron 1 is in cis rather than in trans. We came to the following conclusions as a result. (i) Post-alpha gene expression requires the involvement of the proteasomal pathway in a cell type-dependent manner. Consistent with this requirement, the proapoptotic functions of MG132 are blocked in cells infected before exposure to the drug but not after exposure. (ii) A function encoded by the alpha 0 gene that is absent from the cDNA copy is required for viral gene expression in a cell type- and multiplicity of infection-dependent fashion. The absence of this master function delays but does not ultimately block viral gene expression in the cell lines tested here.

Antibody-dependent transcriptional regulation of measles virus in persistently infected neural cells.

Application of neutralizing anti-hemagglutinin antibodies to mouse neuroblastoma cells (NS20Y/MS) persistently infected with measles virus (MV) leads to a significant reduction of viral structural proteins within 6 days. While the transcriptional gradient for MV-specific mRNAs remained unaffected upon antibody treatment, the total amount of MV-specific transcripts dropped by 80% after 24 h. The expression of genomic RNA was affected similarly, with slightly slower time kinetics. Both transcription and expression of the viral structural proteins could be completely reactivated when viral antibodies were removed from the tissue culture. The same findings could be obtained in rat glioma cells persistently infected with subacute sclerosing panencephalitis virus (C6/SSPE) but not in cells of nonneural origin. The data indicate that antibody-induced antigenic modulation affects the early stages of viral transcription within a few hours after the addition of antibodies and leads to an almost complete repression of viral gene expression in cells of neural origin.

Helical polymers of the REV protein of human immunodeficiency virus 1

The pattern of viral gene expression in cells infected with HIV-1 is orchestrated by several regulatory proteins. One such viral gene product is Rev (regulator of expression of virus), a 13 kDa basic protein that plays a crucial role in determining whether full-length transcripts coding for the major structural proteins of HIV-1 are exported intact from the nucleus into the cytoplasm, so that active proliferation of the virus can ensue. Purified Rov has been shown to polymerize in vitro into long filamentous polymers. Based on this and other observations, it has been hypothesized that Rev functions rather like the nucleocapsid protein of a filamentous RNA virus, and that coating of the transcripts in question by Rev is the mechanism whereby they are protected from splicing. To explore this hypothesis further, we have studied the structure of these Rev polymers in greater detail.