Characterization of a Unique Novel LORF3 Protein of Duck Plague Virus and Its Potential Pathogenesis

Duck enteritis virus LORF4 gene is a late gene and nonessential for virus replication in vitro

Duck enteritis virus (DEV) is an avian alpha-herpesvirus that primarily causes an acute and highly contagious infectious disease of ducks. The LORF4 gene is one of the specific genes of DEV, with limited reports on its biological characteristics and functions. This study investigates the basic biological properties of LORF4 protein (pLORF4). The results show that DEV LORF4 is a late gene mainly localized in the cytoplasm of DEV-infected DEF. To explore the role of pLORF4 in the DEV replication life cycle, a recombinant virus lacking pLORF4 expression was constructed. The results showed that pLORF4 is not essential for virus replication and does not affect virus adsorption, assembly and release, it plays a positive role in virus invasion and DNA replication. In summary, this study provides a foundation for further research on the function of the LORF4 gene.

Duck plague virus UL24 protein initiates K48/K63-linked IRF7 polyubiquitination to antagonize the innate immune response

Duck plague virus (DPV), which is the causative agent of duck viral enteritis, is highly infectious and can cause severe disease and death in ducks, geese and other waterfowl. Several tegument proteins of DPV have been shown to affect the cyclic GMP-AMP synthase (cGAS)-STING signaling pathway to modulate host innate immune responses. DPV UL24, an important DPV tegument protein, can inhibit the activity of the IFN-β promoter. However, the mechanism by which the DPV UL24 protein regulates the host innate immune response remains unclear. In this study, we found that the UL24 protein can significantly inhibit the activity of the interferon-β promoter induced by poly(I:C) and reduce the production of IFN-β, interferon-stimulated genes (OASL, Mx), and the cellular inflammatory factor IL-6. 2) The UL24 protein can widely inhibit the mRNA level of immune signaling molecules. The UL24 protein can also downregulate the protein expression of RIG-I, MDA5, MAVS, cGAS, STING, TBK1 and IRF7 in DEFs. RT-qPCR results revealed that UL24 significantly inhibited the mRNA accumulation for the immune signaling molecules cGAS, STING, TBK1 and IRF7. 3) The UL24 protein induced the degradation of IRF7 via ubiquitination. After the DEFs were treated with the ubiquitin proteasome inhibitor MG132, the degradation of IRF7 by the UL24 protein was alleviated. Coimmunoprecipitation results revealed that DPV UL24 induced the K48/K63-linked ubiquitination of IRF7, which promoted its degradation and thus antagonized the host innate immune response.

N-glycosylation of the envelope glycoprotein I is essential for the proliferation and virulence of the duck plague virus

Duck plague virus (DPV) causes the highly pathogenic duck plague, and the envelope glycoprotein I (gI), as one of the key virulence genes, has not yet had its critical virulence sites identified through screening. This study used reverse genetics technology to target the gI, specifically within the DPV genome. Four DPV mutants with gI N-glycosylation site mutations were designed and constructed, and these mutant strains were successfully rescued. Our results confirmed that three asparagine residues of gI (N69, N78, and N265) are N-glycosylation sites, and western blot analysis substantiated that glycosylation at each predicted N-glycosylation site was compromised. The deglycosylation of gI leads to the protein misfolding and subsequent retention in the endoplasmic reticulum (ER). The subsequent deglycosylated gI is carried into the Golgi apparatus (GM130) in the interaction of gE. Compared to the parental virus, the mutated virus shows a 66.3% reduction in intercellular transmission capability. In ducks, the deglycosylation of gI significantly reduces DPV replication in vivo, thereby weakening the virulence of DPV. This study represents the first successful creation of a weak DPV virus strain by specific mutation at the N-glycosylation site. The findings provide a foundational understanding of DPV pathogenesis and form the basis for developing live attenuated vaccines against the disease.

Multiple functions of the herpesvirus UL14 gene product in viral infection

Herpesviruses are a family of double-stranded DNA viruses with a tegument structure and a genome composed of a single sequence and terminal repeat (TR) sequences. The herpesvirus UL14 gene encodes the protein UL14 (pUL14), which has various subcellular localizations and plays a vital role in regulating immediate-early (IE) gene transcription and expression, influences the intracellular localization patterns of several proteins belonging to the capsid and the DNA packaging machinery, participates in secondary envelopment, and influences viral particle release. Additionally, pUL14 has roles in maintaining cellular homeostasis and preventing apoptosis. This review discusses how pUL14 engages in the life cycle of herpesviruses and provides new ideas for further research on pUL14's function in viral infection.

Duck plague virus Us3 regulates the expression of pUL48

Duck plague (DP) is one of the contagious diseases caused by Duck plague virus (DPV), which is a serious threat to the development of duck farming. Us3 is a PKA-like protein kinase in alphaherpesvirus, which can regulate the biological functions of many viral proteins, but whether Us3 regulates pUL48 protein has not been reported. In this paper, Western Blot, qRT-PCR, dual luciferase reporter system and Co-IP were used to investigate the relationship between pUL48 and Us3. The results showed that: 1) pUL48 interacted with Us3 at 138-256aa through its DBD region. 2) Us3 enhanced the protein expression of pUL48 in a dose-dependent manner. 3) Us3 promoted the mRNA level of pUL48 by activating its promoter activity. 4) Us3 inhibited the transcriptional activation function of pUL48. The results can provide scientific data for perfecting and supplementing the function of alpha herpesvirus Us3 and pUL48.

Mechanism of herpesvirus UL24 protein regulating viral immune escape and virulence

Herpesviruses have evolved a series of abilities involved in the process of host infection that are conducive to virus survival and adaptation to the host, such as immune escape, latent infection, and induction of programmed cell death for sustainable infection. The herpesvirus gene UL24 encodes a highly conserved core protein that plays an important role in effective viral infection. The UL24 protein can inhibit the innate immune response of the host by acting on multiple immune signaling pathways during virus infection, and it also plays a key role in the proliferation and pathogenicity of the virus in the later stage of infection. This article reviews the mechanism by which the UL24 protein mediates herpesvirus immune escape and its effects on viral proliferation and virulence by influencing syncytial formation, DNA damage and the cell cycle. Reviewing these studies will enhance our understanding of the pathogenesis of herpesvirus infection and provide evidence for new strategies to combat against viral infection.