Characterization and expression of the pseudorabies virus early gene UL54

A Recombinant Duck Plague Virus Containing the ICP27 Deletion Marker Provides Robust Protection in Ducks

Duck plague virus (DPV) is a member of Alphaherpesvirus genus and poses a major threat to waterfowl breeding. Genetic engineered vaccines that are capable of distinguishing naturally infected from vaccine-immunized animals are useful for eradicating duck plague. In this study, reverse genetics was used to develop an ICP27-deficient strain (CHv-ΔICP27), and its potential as a marker vaccination candidate was evaluated. The results showed that the CHv-ΔICP27 generated in this study exhibited good genetic stability in vitro and was highly attenuated both in vivo and in vitro. The level of neutralizing antibody generated by CHv-ΔICP27 was comparable to that induced by a commercial DPV vaccine, suggesting that it could protect ducks from virulent DPV attack. By using molecular identification techniques such as PCR, restriction fragment length polymorphism, immunofluorescence, Western blotting, and others, it is possible to differentiate the CHv-ΔICP27 from wild-type strains. Moreover, ICP27 can also be a potential target for the genetic engineering vaccine development of alphavirus or perhaps the entire herpesvirus family members due to the highly conservative of ICP27 protein in all herpesvirus family members. IMPORTANCE The development of distinguishable marker vaccines from natural infection is a key step toward eradicating duck plague. Here, we generated a recombinant DPV that carries an ICP27 deletion marker that could be easily distinguished from wild-type strain by molecular biological methods. It was highly attenuated in vitro and in vivo and could provide comparable protection to ducks after a single dose of immunizations, as commercial vaccines did. Our findings support the use of the ICP27-deficient virus as a marker vaccine for DPV control and future eradication.

Resveratrol Inhibits Pseudorabies Virus Replication by Targeting IE180 Protein

Resveratrol is a natural polyphenolic product in red wine and peanuts and has many pharmacological activities in humans. Our previous studies showed that resveratrol has good antiviral activity against the pseudorabies virus (PRV). However, little is known about the antiviral mechanism of resveratrol against PRV. In this study, we found that resveratrol inhibited the nuclear localization of IE180 protein, which is an important step for activating early/late genes transcription. Interestingly, the results show that resveratrol inhibited the activity of IE180 protein by dual-luciferase assay. Furthermore, molecular docking analysis shows that resveratrol could bind to the Thr601, Ser603, and Pro606 of IE180 protein. Point mutation assay confirmed that resveratrol lost its inhibition activity against the mutant IE180 protein. The results demonstrate that resveratrol exerts its antiviral activity against PRV by targeting the Thr601/Ser603/Pro606 sites of IE180 protein and inhibiting the transcriptional activation activity of IE180 protein. This study provides a novel insight into the antiviral mechanism of resveratrol against herpes viruses.

The antiviral activity of kaempferol against pseudorabies virus in mice

Background

Pseudorabies virus (PRV), a member of the Alphaherpesviruses, is one of the most important pathogens that harm the global pig industry. Accumulated evidence indicated that PRV could infect humans under certain circumstances, inducing severe clinical symptoms such as acute human encephalitis. Currently, there are no antiviral drugs to treat PRV infections, and vaccines available only for swine could not provide full protection. Thus, new control measures are urgently needed.

Results

In the present study, kaempferol exhibited anti-PRV activity in mice through improving survival rate by 22.22 %, which was higher than acyclovir (Positive control) with the survival rate of 16.67 % at 6 days post infection (dpi); meanwhile, the survival rate was 0 % at 6 dpi in the infected-untreated group. Kaempferol could inhibit the virus replication in the brain, lung, kidney, heart and spleen, especially the viral gene copies were reduced by over 700-fold in the brain, which was further confirmed by immunohistochemical examination. The pathogenic changes induced by PRV infection in these organs were also alleviated. The transcription of the only immediate-early gene IE180 in the brain was significantly inhibited by kaempferol, leading to the decreased transcriptional levels of the early genes (EPO and TK). The expression of latency-associated transcript (LAT) was also inhibited in the brain, which suggested that kaempferol could inhibit PRV latency. Kaempferol-treatment could induce higher levels of IL-1β, IL-4, IL-6, TNF-α and IFN-γ in the serum at 3 dpi which were then declined to normal levels at 5 dpi.

Conclusions

These results suggested that kaempferol was expected to be a new alternative control measure for PRV infection.

Microfluidic electrical cell lysis for high-throughput and continuous production of cell-free varicella-zoster virus

Varicella-zoster virus (VZV), the causative agent of varicella and herpes zoster, is highly cell-associated and spreads via cell-to-cell contact in tissue culture. The lack of cell-free VZV hampers studies on VZV biology as well as antiviral and vaccine development. In the present study, a poly(methylmethacrylate) microfluidic device integrated with arrays of microelectrode was fabricated to continuously electrolyse VZV-infected cells to produce cell-free viruses. By designing multiple constrictions and microelectrode arrays, a high electric field is focused on the constricted region of the microchannel to disrupt large numbers of virus-infected cells with high-throughput on a microfluidic platform. Plaque assay and scanning electron microscopy were conducted to quantify and characterize cell-free VZV produced using the microfluidic continuous-flow electrical cell lysis device. The process of microfluidic electrical cell lysis followed by subsequent filtration and virus concentration process yielded a 1.4-2.1 × 10⁴ plaque-forming units (PFUs) per mL of cell-free VZV from 7.0 × 10⁶ VZV-infected human foreskin fibroblasts (HFF) cells. The high electric field formed inside a microfluidic channel combined with the continuous-flow of virus-infected cells within the microchannel enabled the rapid and efficient production of high-titer cell-free virus in large quantities with relatively low input of the voltage.

Evaluation of the impact of ul54 gene-deletion on the global transcription and DNA replication of pseudorabies virus

Pseudorabies virus (PRV) is an animal alphaherpesvirus with a wide host range. PRV has 67 protein-coding genes and several non-coding RNA molecules, which can be classified into three temporal groups, immediate early, early and late classes. The ul54 gene of PRV and its homolog icp27 of herpes simplex virus have a multitude of functions, including the regulation of viral DNA synthesis and the control of the gene expression. Therefore, abrogation of PRV ul54 function was expected to exert a significant effect on the global transcriptome and on DNA replication. Real-time PCR and real-time RT-PCR platforms were used to investigate these presumed effects. Our analyses revealed a drastic impact of the ul54 mutation on the genome-wide expression of PRV genes, especially on the transcription of the true late genes. A more than two hour delay was observed in the onset of DNA replication, and the amount of synthesized DNA molecules was significantly decreased in comparison to the wild-type virus. Furthermore, in this work, we were able to successfully demonstrate the utility of long-read SMRT sequencing for genotyping of mutant viruses.

Duck enteritis virus UL54 is an IE protein primarily located in the nucleus

Background

The UL54 protein of Duck Enteritis Virus (DEV) is a homolog of herpes simplex virus-1 (HSV-1) immediate-early infectious cell protein 27 (ICP27), a multifunctional protein essential for viral infection. Nonetheless, there is little information on the UL54 protein of DEV.

Methods

The UL54 gene was cloned into the pPAL7 vector, and the recombinant protein, expressed in the E. coli Rosetta, was used to produce a specific antibody. Using this antibody, Western blotting and indirect immunofluorescence analysis (IFA) were used to analyze the expression level and intracellular localization, respectively, of UL54 in DEV-infected cells at different times. Real-time quantitative reverse transcription PCR (RT-PCR) and the pharmacological inhibition test were utilized to ascertain the kinetic class of the UL54 gene.

Results

UL54 was expressed as a fusion protein of approximately 66.0 kDa using the prokaryotic expression system, and this protein was used to generate the specific anti-UL54 antibody. The UL54 protein was initially diffusely distributed throughout the cytoplasmic region; then, after 2 h, it gradually distributed into the nucleus, peaking at 24 h, and complete localization to the nucleus was observed thereafter. The UL54 transcript was detected as early as 0.5 h, and peak expression was observed at 24 h. The UL54 gene was insensitive to the DNA polymerase inhibitor Ganciclovir (GCV) and the protein synthesis inhibitor Cycloheximide (CHX), both of which confirmed that UL54 was an immediate early gene.

Conclusions

The DEV UL54 gene was expressed in a prokaryotic expression system and characterized for expression level, intracellular localization and gene kinetic class. We propose that these results will provide the foundation for further functional analyses of this gene.

Identification of nuclear and nucleolar localization signals of pseudorabies virus (PRV) early protein UL54 reveals that its nuclear targeting is required for efficient production of PRV

The pseudorabies virus (PRV) early protein UL54 is a homologue of herpes simplex virus 1 (HSV-1) immediate-early protein ICP27, which is a multifunctional protein that is essential for HSV-1 infection. In this study, the subcellular localization and nuclear import signals of PRV UL54 were characterized. UL54 was shown to predominantly localize to the nucleolus in transfected cells. By constructing a series of mutants, a functional nuclear localization signal (NLS) and a genuine nucleolar localization signal (NoLS) of UL54 were for the first time identified and mapped to amino acids (61)RQRRR(65) and (45)RRRRGGRGGRAAR(57), respectively. Additionally, three recombinant viruses with mutations of the NLS and/or the NoLS in UL54 were constructed based on PRV bacterial artificial chromosome (BAC) pBecker2 to test the effect of UL54 nuclear targeting on viral replication. In comparison with the wild-type virus, a recombinant virus harboring an NLS or NoLS mutation of UL54 reduced viral production to different extents. However, mutations of both the NLS and NoLS targeted UL54 to the cytoplasm in recombinant virus-infected cells and significantly impaired viral replication, comparable to the UL54-null virus. In addition, a virus lacking the NLS or the NoLS displayed modest defects in viral gene expression and DNA synthesis. However, deletion of both the NLS and the NoLS resulted in severe defects in viral gene expression and DNA synthesis, as well as production of infectious progeny. Thus, we have identified a classical NLS and a genuine NoLS in UL54 and demonstrate that the nuclear targeting of UL54 is required for efficient production of PRV.

Characterization of molecular determinants for nucleocytoplasmic shuttling of PRV UL54

The pseudorabies virus (PRV) early protein UL54 is a homologue of the herpes simplex virus 1 (HSV-1) immediate-early protein ICP27, which is a multifunctional protein and essential for HSV-1 infection. To determine if UL54 might shuttle between the nucleus and cytoplasm, as has been shown for its homologues in human herpesviruses, the molecular determinants for its nucleocytoplasmic shuttling were investigated. Heterokaryon assays demonstrated that UL54 was a nucleocytoplasmic shuttling protein and this property could not be blocked by leptomycin B, an inhibitor of chromosome region maintenance 1 (CRM1). However, TAP/NXF1 promoted the nuclear export of UL54 and interacted with UL54, suggesting that UL54 shuttles between the nucleus and the cytoplasm via a TAP/NXF1, but not CRM1, dependent nuclear export pathway. Furthermore, UL54 was demonstrated to target to the nucleus through a classic Ran-, importin β1- and α5-dependent nuclear import mechanism.

Characterization of duck enteritis virus UL53 gene and glycoprotein K

Background

Most of the previous research work had focused on the epidemiology and prevention of duck enteritis virus (DEV). Whilst with the development of protocols in molecular biology, nowadays more and more information about the genes of DEV was reported. But little information about DEV UL53 gene and glycoprotein K(gK) was known except our reported data.

Results

In our paper, the fluorescent quantitative real-time PCR(FQ-RT-PCR) assay and nucleic acid inhibition test were used to study the transcription characteristic of the DEV UL53 gene. Except detecting the mRNA of DEV UL53 gene, the product gK encoded by UL53 gene was detected through the expression kinetics of UL53 gene by the purified rabbit anti-UL53 protein polyclonal antibodies. Western-blotting and indirect immunofluorescence assays were used to detect gK. From the results of these experiments, the UL53 gene and gK were respectively identified as a late gene and a really late protein. On the other hand, the indirect immunofluorescence assay provided another information that the intracellular localization of DEV gK was mainly distributed in cytoplasm.

Conclusions

By way of conclusions, we conceded that DEV UL53 gene is a really late gene, which is coincident with properties of UL53 homologs from other herpesvirus, such as ILTV(Infectious Laryngotracheitis virus) and HSV-1(Herpes simplex virus type 1). The properties of intracellular localization about gK protein provided a foundation for further functional analysis and further studies will be focused on constructing of the UL53 gene DEV mutant.

Whole-genome analysis of pseudorabies virus gene expression by real-time quantitative RT-PCR assay

Background

Pseudorabies virus (PRV), a neurotropic herpesvirus of pigs, serves as an excellent model system with which to investigate the herpesvirus life cycle both in cultured cells and in vivo. Real-time RT-PCR is a very sensitive, accurate and reproducible technique that can be used to detect very small amounts of RNA molecules, and it can therefore be applied for analysis of the expression of herpesvirus genes from the very early period of infection.

Results

In this study, we have developed and applied a quantitative reverse transcriptase-based real-time PCR technique in order to profile transcription from the whole genome of PRV after lytic infection in porcine kidney cells. We calculated the relative expression ratios in a novel way, which allowed us to compare different PRV genes with respect to their expression dynamics, and to divide the PRV genes into distinct kinetic classes. This is the first publication on the whole-genome analysis of the gene expression of an alpha-herpesvirus by qRT2-PCR. We additionally established the kinetic properties of uncharacterized PRV genes and revised or confirmed data on PRV genes earlier examined by traditional methods such as Northern blot analysis. Our investigations revealed that genes with the same expression properties form clusters on the PRV genome: nested overlapping genes belong in the same kinetic class, while most convergent genes belong in different kinetic classes. Further, we detected inverse relationships as concerns the expressions of EP0 and IE180 mRNAs and their antisense partners.

Conclusion

Most (if not all) PRV genes begin to be expressed from the onset of viral expression. No sharp boundary was found between the groups of early and late genes classified on the basis of their requirement for viral DNA synthesis. The expressions of the PRV genes were analyzed, categorized and compared by qRT2-PCR assay, with the average of the minimum cycle threshold used as a control for the calculation of a particular R value. In principle, this new calculation technique is applicable for the analysis of gene expression in all temporally changing genetic systems.

UL54-null pseudorabies virus is attenuated in mice but productively infects cells in culture

The pseudorabies virus (PRV) UL54 homologs are important multifunctional proteins with roles in shutoff of host protein synthesis, transactivation of virus and cellular genes, and regulation of splicing and translation. Here we describe the first genetic characterization of UL54. We constructed UL54 null mutations in a PRV bacterial artificial chromosome using sugar suicide and lambdaRed allele exchange systems. Surprisingly, UL54 is dispensable for growth in tissue culture but exhibits a small-plaque phenotype that can be complemented in trans by both the herpes simplex virus type 1 ICP27 and varicella-zoster virus open reading frame 4 proteins. Deletion of UL54 in the virus vJSdelta54 had no effect on the ability of the virus to shut off host cell protein synthesis but did affect virus gene expression. The glycoprotein gC accumulated to lower levels in cells infected with vJSdelta54 compared to those infected with wild-type virus, while gK levels were undetectable. Other late gene products, gB, gE, and Us9, accumulated to higher levels than those seen in cells infected with wild-type virus in a multiplicity-dependent manner. DNA replication is also reduced in cells infected with vJSdelta54. UL54 appears to regulate UL53 and UL52 at the transcriptional level as their respective RNAs are decreased in cells infected with vJSdelta54. Interestingly, vJSdelta54 is highly attenuated in a mouse model of PRV infection. Animals infected with vJSdelta54 survive twice as long as animals infected with wild-type virus, and this results in delayed accumulation of virus-specific antigens in skin, dorsal root ganglia, and spinal cord tissues.

Molecular biology of pseudorabies virus: impact on neurovirology and veterinary medicine

Pseudorabies virus (PRV) is a herpesvirus of swine, a member of the Alphaherpesvirinae subfamily, and the etiological agent of Aujeszky's disease. This review describes the contributions of PRV research to herpesvirus biology, neurobiology, and viral pathogenesis by focusing on (i) the molecular biology of PRV, (ii) model systems to study PRV pathogenesis and neurovirulence, (iii) PRV transsynaptic tracing of neuronal circuits, and (iv) veterinary aspects of pseudorabies disease. The structure of the enveloped infectious particle, the content of the viral DNA genome, and a step-by-step overview of the viral replication cycle are presented. PRV infection is initiated by binding to cellular receptors to allow penetration into the cell. After reaching the nucleus, the viral genome directs a regulated gene expression cascade that culminates with viral DNA replication and production of new virion constituents. Finally, progeny virions self-assemble and exit the host cells. Animal models and neuronal culture systems developed for the study of PRV pathogenesis and neurovirulence are discussed. PRV serves asa self-perpetuating transsynaptic tracer of neuronal circuitry, and we detail the original studies of PRV circuitry mapping, the biology underlying this application, and the development of the next generation of tracer viruses. The basic veterinary aspects of pseudorabies management and disease in swine are discussed. PRV infection progresses from acute infection of the respiratory epithelium to latent infection in the peripheral nervous system. Sporadic reactivation from latency can transmit PRV to new hosts. The successful management of PRV disease has relied on vaccination, prevention, and testing.

Mapping of functional regions conferring nuclear localization and RNA-binding activity of pseudorabies virus early protein UL54

Pseudorabies virus (PRV) is an alphaherpesvirus, and its gene organization and regulation are similar to the well-characterized human herpes simplex virus (HSV). The PRV early protein UL54 consists of 363 amino acids with homology to the HSV ICP27 immediate-early protein. Previously, we have demonstrated the nuclear accumulation and poly(G) RNA-binding activity of UL54 protein. In the present study, we have identified further the functional regions within UL54 conferring for nuclear localization and RNA-binding activity. Several recombinant expression plasmids containing various coding regions of UL54 gene were constructed for producing a series of C-terminally truncated or internally deleted forms of UL54 mutants in Escherichia coli or porcine kidney (PK-15) cells. RNA-binding activity of E. coli-expressed UL54 mutants was characterized by the binding ability to poly(G) RNA homopolymer in dot blot hybridization assay and the results have shown that the N-terminal 83 residues were responsible for RNA-binding, and the region of residues 35-82 containing an RGG box was necessary for its function. Furthermore, the region responsible for nuclear localization was investigated by transient expression of various deletion mutants in PK-15 cells followed by detection of their subcellular distribution. The results showed that C-terminal deletion beyond the amino acid residue 83 or internal deletion containing the RGG box sequence could restrict UL54 mutants in the cytoplasm. The ability of the N-terminal 83 residues to target the green fluorescence protein to the nucleus confirmed further its role as a functional nuclear localization signal (NLS). The utmost N-terminal 83 residues portion of UL54 contains two important functional domains, NLS and RNA-binding, and thus it would play an indispensable role in UL54 regulatory function.