Functional analysis of the UL24 protein of suid herpesvirus 1

Comparative Review of the Conserved UL24 Protein Family in Herpesviruses

The UL24 protein family, conserved across all subfamilies of Orthoherpesviridae, plays diverse and significant roles in viral replication, host-virus interactions and pathogenesis. Understanding the molecular mechanisms and interactions of UL24 proteins is key to unraveling the complex interplay between herpesviruses and their hosts. This review provides a comparative and comprehensive overview of current knowledge on UL24 family members, including their conservation, expression patterns, cellular localization, and functional roles upon their expression and during viral infection, highlighting their significance in herpesvirus biology and their potential functions.

Host Zinc-finger CCHC-type containing protein 3 inhibits pseudorabies virus proliferation by regulating type I interferon signaling

Zinc finger CCHC-type containing protein 3 (ZCCHC3) acts as an antiviral factor that interacts with RIG-I and cGAS to modulate innate signaling against viral infections. Here, we investigated the role of porcine ZCCHC3 during pseudorabies virus (PRV) proliferation. We found that porcine ZCCHC3 plays an inhibitory role in the proliferation of PRV by regulating cellular innate immune responses. Further, overexpression of ZCCHC3 inhibited gB protein levels and viral titers, whereas knockdown of ZCCHC3 promoted viral growth. ZCCHC3 overexpression increased IFN-β expression to upregulate downstream gene expression, thus leading to the suppression of viral replication. However, PRV infection reduced the endogenous expression of ZCCHC3 in permissive cells. Importantly, PRV-encoded UL13 and UL24 proteins were identified to inhibit the expression of ZCCHC3, thus antagonizing its antiviral effect. Collectively, our data underscore the important role of ZCCHC3 against PRV infection and promote understandings of viral proteins in PRV pathogenesis.

Tk-deleted pseudorabies virus retains high pathogenicity in rats

Introduction

The pseudorabies virus (PRV) gene encoding thymidine kinase (tk) is an important virulence-associated factor. Attenuation of PRV in susceptible animals is a frequent result of tk deletion. The aim of the study was to assess the pathogenicity of tk-deleted PRV in rats.

Material and Methods

Sprague Dawley rats were infected with the tk-deleted PRV strain SuHV-1 ΔTK:247via intranasal or intramuscular inoculation. PRV loads in ten tissues from dead and euthanised rats were determined using real-time PCR.

Results

Infection with SuHV-1 ΔTK:247 could cause death in rats. The 50% lethal dose (LD₅₀) of SuHV-1 ΔTK:247 via intranasal inoculation was 10^3.16 TCID₅₀ in rats. Intramuscular inoculation required a higher dose of SuHV-1 ΔTK:247 (10^5.0 TCID₅₀). A high SuHV-1 ΔTK:247 titre was observed in the trigeminal ganglia or spinal cord of dead rats.

Conclusion

The results of this study show that rats are highly susceptible to PRV infection, and tk deletion did not completely diminish the pathogenicity of PRV in rats.

Application of CRISPR-Cas9 Editing for Virus Engineering and the Development of Recombinant Viral Vaccines

CRISPR-Cas technology, discovered originally as a bacterial defense system, has been extensively repurposed as a powerful tool for genome editing for multiple applications in biology. In the field of virology, CRISPR-Cas9 technology has been widely applied on genetic recombination and engineering of genomes of various viruses to ask some fundamental questions about virus-host interactions. Its high efficiency, specificity, versatility, and low cost have also provided great inspiration and hope in the field of vaccinology to solve a series of bottleneck problems in the development of recombinant viral vaccines. This review highlights the applications of CRISPR editing in the technological advances compared to the traditional approaches used for the construction of recombinant viral vaccines and vectors, the main factors affecting their application, and the challenges that need to be overcome for further streamlining their effective usage in the prevention and control of diseases. Factors affecting efficiency, target specificity, and fidelity of CRISPR-Cas editing in the context of viral genome editing and development of recombinant vaccines are also discussed.

Inhibition of the DNA-Sensing pathway by pseudorabies virus UL24 protein via degradation of interferon regulatory factor 7

The cyclic guanosine monophosphate-adenosine monophosphate synthase (cGAS)-stimulator of interferon genes (STING) signaling pathway plays an important role in the innate immune response by the production of type I interferon (IFN) against DNA virus infection. However, viruses have evolved a variety of strategies to antagonize the host antiviral response to facilitate infection and replication. Pseudorabies virus (PRV), a DNA virus that causes great economic losses to the swine industry, encodes approximate 70 proteins, including some that are involved in evasion of host immunity. However, the mechanism employed by PRV to regulate type I IFN remains unclear. The results of the present study showed that the transcription levels of type I IFN were significantly upregulated by a UL24-deleted PRV strain. Furthermore, IFN-β activation induced by poly(dA:dT) or stimulated by cGAS-STING was inhibited by UL24 overexpression in PK15 cells. Co-immunoprecipitation analysis demonstrated that UL24 interacts with and can degrade interferon regulatory factor 7 (IRF7) through the proteasome pathway in a dose-dependent manner. Together, these results showed that PRV UL24 interacted with IRF7 via the proteasome pathway and antagonized cGAS-STING-mediated activation of IFN-β.

Pseudorabies virus UL24 antagonizes OASL-mediated antiviral effect

Oligoadenylate synthetases-like (OASL) protein exerts various effects on DNA and RNA viruses by inhibiting cGAS-mediated IFN production and by enhancing RIG-I-mediated IFN induction, respectively. In this study, we aimed to examine the role of OASL in pseudorabies virus (PRV) proliferation and investigate the function of the PRV UL24 protein in cellular innate immunity. We found that OASL regulates PRV proliferation by enhancing RIG-I signaling. PRV infection decreased the expression of OASL at both the mRNA and protein levels in PK15 and HeLa cells. OASL expression suppressed the proliferation of PRV in a RIG-I-dependent manner and boosted RIG-I-mediated IFN expression as well as IFN-stimulated gene (ISG) induction. In contrast, knockdown of OASL enhanced PRV proliferation and reduced RIG-I signaling. However, the PRV UL24 protein was found to impair RIG-I signaling, thus inhibiting transcription of IFN and ISGs. In addition, the UL24 protein reduced RIG-I-induced expression of endogenous OASL in an IRF3-dependent manner, thereby antagonizing the OASL antiviral effect. Taken together, our findings characterize the role of OASL in PRV proliferation and provide new insights into the role of UL24 in PRV pathogenesis.