The pseudorabies virus vhs protein cleaves RNA containing an IRES sequence

Pseudorabies virus VHS protein abrogates interferon responses by blocking NF-κB and IRF3 nuclear translocation

Herpesviruses antagonize host antiviral responses through a myriad of molecular strategies culminating in the death of the host cells. Pseudorabies virus (PRV) is a significant veterinary pathogen in pigs, causing neurological sequalae that ultimately lead to the animal's demise. PRV is known to trigger apoptotic cell death during the late stages of infection. The virion host shutdown protein (VHS) encoded by UL41 plays a crucial role in the PRV infection process. In this study, we demonstrate that UL41 inhibits PRV-induced activation of inflammatory cytokine and negatively regulates the cGAS-STING-mediated antiviral activity by targeting IRF3, thereby inhibiting the translocation and phosphorylation of IRF3. Notably, mutating the conserved amino acid sites (E192, D194, and D195) in the RNase domain of UL41 or knocking down UL41 inhibits the immune evasion of PRV, suggesting that UL41 may play a crucial role in PRV's evasion of the host immune response during infection. These results enhance our understanding of how PRV structural proteins assist the virus in evading the host immune response.

The Role of Viral RNA Degrading Factors in Shutoff of Host Gene Expression

Many viruses induce shutoff of host gene expression (host shutoff) as a strategy to take over cellular machinery and evade host immunity. Without host shutoff activity, these viruses generally replicate poorly in vivo, attesting to the importance of this antiviral strategy. In this review, we discuss one particularly advantageous way for viruses to induce host shutoff: triggering widespread host messenger RNA (mRNA) decay. Viruses can trigger increased mRNA destruction either directly, by encoding RNA cleaving or decapping enzymes, or indirectly, by activating cellular RNA degradation pathways. We review what is known about the mechanism of action of several viral RNA degradation factors. We then discuss the consequences of widespread RNA degradation on host gene expression and on the mechanisms of immune evasion, highlighting open questions. Answering these questions is critical to understanding how viral RNA degradation factors regulate host gene expression and how this process helps viruses evade host responses and replicate.

Pseudorabies Virus: From Pathogenesis to Prevention Strategies

Pseudorabies (PR), also called Aujeszky’s disease (AD), is a highly infectious viral disease which is caused by pseudorabies virus (PRV). It has been nearly 200 years since the first PR case occurred. Currently, the virus can infect human beings and various mammals, including pigs, sheep, dogs, rabbits, rodents, cattle and cats, and among them, pigs are the only natural host of PRV infection. PRV is characterized by reproductive failure in pregnant sows, nervous disorders in newborn piglets, and respiratory distress in growing pigs, resulting in serious economic losses to the pig industry worldwide. Due to the extensive application of the attenuated vaccine containing the Bartha-K61 strain, PR was well controlled. With the variation of PRV strain, PR re-emerged and rapidly spread in some countries, especially China. Although researchers have been committed to the design of diagnostic methods and the development of vaccines in recent years, PR is still an important infectious disease and is widely prevalent in the global pig industry. In this review, we introduce the structural composition and life cycle of PRV virions and then discuss the latest findings on PRV pathogenesis, following the molecular characteristic of PRV and the summary of existing diagnosis methods. Subsequently, we also focus on the latest clinical progress in the prevention and control of PRV infection via the development of vaccines, traditional herbal medicines and novel small RNAs. Lastly, we provide an outlook on PRV eradication.

Construction of BHV-1 UL41 Defective Virus Using the CRISPR/Cas9 System and Analysis of Viral Replication Properties

Bovine herpesvirus type 1 (BHV-1) is a neurotropic herpesvirus that causes infectious rhinotracheitis and vulvovaginitis in cattle. The virion host shutoff protein encoded by the BHV-1 UL41 gene is highly conserved in the Alphaherpesvirinae subfamily. This protein can degrade viral and host messenger RNA (mRNA) to interrupt host defense and facilitate the rapid proliferation of BHV-1. However, studies on the BHV-1 UL41 gene are limited, and BHV-1 defective virus construction using the CRISPR/Cas9 system is somewhat challenging. In this study, we rapidly constructed a BHV-1 UL41-deficient strain using the CRISPR/Cas9 system in BL primary bovine-derived cells. BHV-1 UL41-defective mutants were screened by Western blot analysis using specific polyclonal antibodies as the primary antibodies. During the isolation and purification of the defective strain, a mixed virus pool edited by an efficient single-guide RNA (sgRNA) showed a plaque number reduction. Viral growth property assessment showed that BHV-1 UL41 was dispensable for replication, but the UL41-defective strain exhibited early and slowed viral replication. Furthermore, the BHV-1 UL41-deficient strain exhibited enhanced sensitivity to temperature and acidic environments. The BHV-1 UL41-deficient strain regulated viral and host mRNA levels to affect viral replication.

PCV2 and PRV Coinfection Induces Endoplasmic Reticulum Stress via PERK-eIF2α-ATF4-CHOP and IRE1-XBP1-EDEM Pathways

Porcine circovirus 2 (PCV2) and pseudorabies virus (PRV) are two important pathogens in the pig industry. PCV2 or PRV infection can induce endoplasmic reticulum stress (ERS) and unfolded protein response (UPR). However, the effect of PCV2 and PRV coinfection on the ERS and UPR pathways remains unclear. In this study, we found that PRV inhibited the proliferation of PCV2 mainly at 36 to 72 hpi, while PCV2 enhanced the proliferation of PRV in the middle stage of the infection. Notably, PRV is the main factor during coinfection. The results of the transcriptomic analysis showed that coinfection with PCV2 and PRV activated cellular ERS, and upregulated expressions of the ERS pathway-related proteins, including GRP78, eIF2α, and ATF4. Further research indicated that PRV played a dominant role in the sequential infection and coinfection of PCV2 and PRV. PCV2 and PRV coinfection induced the ERS activation via the PERK-eIF2α-ATF4-CHOP axis and IRE1-XBP1-EDEM pathway, and thus may enhance cell apoptosis and exacerbate the diseases.

A conserved region of nonstructural protein 1 from alphacoronaviruses inhibits host gene expression and is critical for viral virulence

Coronaviruses are enveloped, single-stranded RNA viruses that are distributed worldwide. They include transmissible gastroenteritis virus (TGEV), porcine epidemic diarrhea virus (PEDV), and the human coronaviruses severe acute respiratory syndrome coronavirus (SARS-CoV) and Middle East respiratory syndrome coronavirus (MERS-CoV), many of which seriously endanger human health and well-being. Only alphacoronaviruses and betacoronaviruses harbor nonstructural protein 1 (nsp1), which performs multiple functions in inhibiting antiviral host responses. The role of the C terminus of betacoronavirus nsp1 in virulence has been characterized, but the location of the alphacoronavirus nsp1 region that is important for virulence remains unclear. Here, using TGEV nsp1 as a model to explore the function of this protein in alphacoronaviruses, we demonstrate that alphacoronavirus nsp1 inhibits host gene expression. Solving the crystal structure of full-length TGEV at 1.85-Å resolution and conducting several biochemical analyses, we observed that a specific motif (amino acids 91-95) of alphacoronavirus nsp1 is a conserved region that inhibits host protein synthesis. Using a reverse-genetics system based on CRISPR/Cas9 technology to construct a recombinant TGEV in which this specific nsp1 motif was altered, we found that this mutation does not affect virus replication in cell culture but significantly reduces TGEV pathogenicity in pigs. Taken together, our findings suggest that alphacoronavirus nsp1 is an essential virulence determinant, providing a potential paradigm for the development of a new attenuated vaccine based on modified nsp1.

Molecular characterization of duck enteritis virus UL41 protein

BACKGROUND

Duck enteritis virus (DEV) belongs to the subfamily Alphaherpesvirinae, and information on the DEV UL41 gene is limited.

METHODS

The DEV UL41 gene was cloned into the pET32a(+) vector and expressed in a prokaryotic expression system. Antiserum was raised against a bacterially expressed UL41-His fusion protein for further experiments. Transcription was quantified and UL41 protein expression levels were determined in DEV-infected cells at different time points by RT-qPCR and western blotting, respectively. DEV virions were purified by sucrose gradient centrifugation and analyzed by mass spectrometry to identify protein content. We confirmed the DEV UL41 gene kinetic class using a pharmacological test. IFA was used to analyze the intracellular localization of pUL41.

RESULTS

The recombinant expression plasmid, pET-32a(+)-UL41, which highly expresses a 76.0 kDa fusion protein, was constructed and expressed in E. coli BL21 (DE3) after induction with 0.2 mM IPTG at 30 °C for 10 h, generating a specific mouse anti-UL41 protein polyclonal antibody. RT-qPCR and western blot analyses revealed that the UL41 transcript number peaked at 36 hpi, and peak protein expression occurred at 48 hpi. The pharmacological test showed that UL41 was a γ2 gene. Mass spectrometry analysis showed that pUL41 was a virion component. IFA results revealed that pUL41 was localized throughout DEV-infected cells but only localized to the cytoplasm of transfected cells. DEV pUL47 translocated pUL41 to the nuclei of DEF cells; this translocation was dependent on predicted pUL47 NLS signals (40-50 aa and 768-777 aa).

CONCLUSIONS

DEV UL41 is a γ2 gene that encodes a virion structural protein, pUL41 localizes throughout DEV-infected cells but only localizes to the cytoplasm of transfected cells. pUL41 cannot autonomously localize to the nucleus, as this nuclear localization is dependent on predicted DEV pUL47 NLS signals (40-50 aa and 768-777 aa).