Duck Enteritis Virus Inhibits the cGAS-STING DNA-Sensing Pathway To Evade the Innate Immune Response

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.

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.

Development and immunogenicity evaluation of a quadruple-gene-deleted pseudorabies virus strain

Since 2011, the emergence of Pseudorabies virus (PRV) variants has led to significant vaccine failures, resulting in severe economic losses in China's swine industry. Conventional PRV vaccines have shown limited efficacy against these emergent variants, underscoring the urgent need for novel immunization strategies. This study aimed to develop and evaluate a novel recombinant PRV vaccine candidate with improved safety and immunogenicity profiles. Utilizing the homology-directed repair (HDR)-CRISPR/Cas9 system, we generated a recombinant PRV strain, designated PRV SX-10ΔgI/gE/TK/UL24, with deletions in the gI, gE, TK, and UL24 genes. In vitro analyses demonstrated that the recombinant virus exhibited similar replication kinetics and growth curves comparable to the parental strain. The immunological properties of the recombinant PRV were assessed in murine and porcine models. All animals inoculated with PRV SX-10ΔgI/gE/TK/UL24 survived without exhibiting significant clinical signs or pathological alterations. Immunological assays revealed that PRV SX-10ΔgI/gE/TK/UL24 elicited significantly higher levels of gB-specific antibodies, neutralizing antibodies, and cytokines (including IFN-γ, IL-2, and IL-4) compared to both the Bartha-K61 and PRV SX-10ΔgI/gE/TK strains. Notably, both murine and porcine subjects immunized with PRV SX-10ΔgI/gE/TK/UL24 demonstrated enhanced protection against challenges with the variant PRV SX-10 strain, compared to other vaccine strains. These findings suggest that PRV SX-10ΔgI/gE/TK/UL24 represents a promising PRV vaccine candidate strain, offering valuable insights for the prevention and control of PRV in clinical applications.

The precise function of alphaherpesvirus tegument proteins and their interactions during the viral life cycle

Alphaherpesvirus is a widespread pathogen that causes diverse diseases in humans and animals and can severely damage host health. Alphaherpesvirus particles comprise a DNA core, capsid, tegument and envelope; the tegument is located between the nuclear capsid and envelope. According to biochemical and proteomic analyses of alphaherpesvirus particles, the tegument contains at least 24 viral proteins and plays an important role in the alphaherpesvirus life cycle. This article reviews the important role of tegument proteins and their interactions during the viral life cycle to provide a reference and inspiration for understanding alphaherpesvirus infection pathogenesis and identifying new antiviral strategies.

The role of the cGAS-STING pathway in metabolic diseases

The cyclic GMP-AMP synthase (cGAS)-stimulator of interferon genes (STING) pathway is a critical innate immune pathway primarily due to its vital DNA sensing mechanism in pathogen defence. Recent research advances have shown that excessive activation or damage to the cGAS-STING pathway can exacerbate chronic inflammatory responses, playing a significant role in metabolic dysfunction and aging, leading to the development of related diseases such as obesity, osteoporosis, and neurodegenerative diseases. This article reviews the structure and biological functions of the cGAS-STING signaling pathway and discusses in detail how this pathway regulates the occurrence and development of metabolic and age-related diseases. Additionally, this article introduces potential small molecule drugs targeting cGAS and STING, aiming to provide new research perspectives for studying the pathogenesis and treatment of metabolic-related diseases.

An alpha-herpesvirus employs host HEXIM1 to promote viral transcription

Although it is widely accepted that herpesviruses utilize host RNA polymerase II (RNAPII) to transcribe viral genes, the mechanism of utilization varies significantly among herpesviruses. With the exception of herpes simplex virus 1 (HSV-1) in alpha-herpesviruses, the mechanism by which RNAPII transcribes viral genes in the remaining alpha-herpesviruses has not been reported. In this study, we investigated the transcriptional mechanism of an avian alpha-herpesvirus, Anatid herpesvirus 1 (AnHV-1). We discovered for the first time that hexamethylene-bis-acetamide-inducing protein 1 (HEXIM1), a major inhibitor of positive elongation factor B (P-TEFb), was significantly upregulated during AnHV-1 infection, and its expression was dynamically regulated throughout the progression of the disease. However, the expression level of HEXIM1 remained stable before and after HSV-1 infection. Excessive HEXIM1 assists AnHV-1 in progeny virus production, gene expression, and RNA polymerase II recruitment by promoting the formation of more inactive P-TEFb and the loss of RNAPII S2 phosphorylation. Conversely, the expression of some host survival-related genes, such as SOX8, CDK1, MYC, and ID2, was suppressed by HEXIM1 overexpression. Further investigation revealed that the C-terminus of the AnHV-1 US1 gene is responsible for the upregulation of HEXIM1 by activating its promoter but not by interacting with P-TEFb, which is the mechanism adopted by its homologs, HSV-1 ICP22. Additionally, the virus proliferation deficiency caused by US1 deletion during the early infection stage could be partially rescued by HEXIM1 overexpression, suggesting that HEXIM1 is responsible for AnHV-1 gaining transcription advantages when competing with cells. Taken together, this study revealed a novel HEXIM1-dependent AnHV-1 transcription mechanism, which has not been previously reported in herpesvirus or even DNA virus studies.IMPORTANCEHexamethylene-bis-acetamide-inducing protein 1 (HEXIM1) has been identified as an inhibitor of positive transcriptional elongation factor b associated with cancer, AIDS, myocardial hypertrophy, and inflammation. Surprisingly, no previous reports have explored the role of HEXIM1 in herpesvirus transcription. This study reveals a mechanism distinct from the currently known herpesvirus utilization of RNA polymerase II, highlighting the dependence on high HEXIM1 expression, which may be a previously unrecognized facet of the host shutoff manifested by many DNA viruses. Moreover, this discovery expands the significance of HEXIM1 in pathogen infection. It raises intriguing questions about whether other herpesviruses employ similar mechanisms to manipulate HEXIM1 and if this molecular target can be exploited to limit productive replication. Thus, this discovery not only contributes to our understanding of herpesvirus infection regulation but also holds implications for broader research on other herpesviruses, even DNA viruses.

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.

IRF7: role and regulation in immunity and autoimmunity

Interferon regulatory factor (IRF) 7 was originally identified as master transcriptional factor that produced IFN-I and regulated innate immune response, subsequent studies have revealed that IRF7 performs a multifaceted and versatile functions in multiple biological processes. In this review, we provide a comprehensive overview on the current knowledge of the role of IRF7 in immunity and autoimmunity. We focus on the latest regulatory mechanisms of IRF7 in IFN-I, including signaling pathways, transcription, translation, and post-translational levels, the dimerization and nuclear translocation, and the role of IRF7 in IFN-III and COVID-19. In addition to antiviral immunity, we also discuss the role and mechanism of IRF7 in autoimmunity, and the further research will expand our understanding of IRF7.

Molecular mechanisms and cellular functions of liquid-liquid phase separation during antiviral immune responses

Spatiotemporal separation of cellular components is vital to ensure biochemical processes. Membrane-bound organelles such as mitochondria and nuclei play a major role in isolating intracellular components, while membraneless organelles (MLOs) are accumulatively uncovered via liquid-liquid phase separation (LLPS) to mediate cellular spatiotemporal organization. MLOs orchestrate various key cellular processes, including protein localization, supramolecular assembly, gene expression, and signal transduction. During viral infection, LLPS not only participates in viral replication but also contributes to host antiviral immune responses. Therefore, a more comprehensive understanding of the roles of LLPS in virus infection may open up new avenues for treating viral infectious diseases. In this review, we focus on the antiviral defense mechanisms of LLPS in innate immunity and discuss the involvement of LLPS during viral replication and immune evasion escape, as well as the strategy of targeting LLPS to treat viral infectious diseases.