African swine fever virus pS273R antagonizes stress granule formation by cleaving the nucleating protein G3BP1 to facilitate viral replication

The Strategies Used by Animal Viruses to Antagonize Host Antiviral Innate Immunity: New Clues for Developing Live Attenuated Vaccines (LAVs)

As an essential type of vaccine, live attenuated vaccines (LAVs) play a crucial role in animal disease prevention and control. Nevertheless, developing LAVs faces the challenge of balancing safety and efficacy. Understanding the mechanisms animal viruses use to antagonize host antiviral innate immunity may help to precisely regulate vaccine strains and maintain strong immunogenicity while reducing their pathogenicity. It may improve the safety and efficacy of LAVs, as well as provide a more reliable means for the prevention and control of infectious livestock diseases. Therefore, exploring viral antagonistic mechanisms is a significant clue for developing LAVs, which helps to explore more viral virulence factors (as new vaccine targets) and provides a vital theoretical basis and technical support for vaccine development. Among animal viruses, ASFV, PRRSV, PRV, CSFV, FMDV, PCV, PPV, and AIV are some typical representatives. It is crucial to conduct in-depth research and summarize the antagonistic strategies of these typical animal viruses. Studies have indicated that animal viruses may antagonize the antiviral innate immunity by directly or indirectly blocking the antiviral signaling pathways. In addition, viruses also do this by antagonizing host restriction factors targeting the viral replication cycle. Beyond that, viruses may antagonize via regulating apoptosis, metabolic pathways, and stress granule formation. A summary of viral antagonistic mechanisms might provide a new theoretical basis for understanding the pathogenic mechanism of animal viruses and developing LAVs based on antagonistic mechanisms and viral virulence factors.

African swine fever virus enhances viral replication by increasing intracellular reduced glutathione levels, which suppresses stress granule formation

African swine fever virus (ASFV) is a DNA virus that has significantly impacted the global swine industry. Currently, there are no effective therapies or vaccines against ASFV. Stress granules (SGs), known for their antiviral properties, are not induced during ASFV infection, even though reactive oxygen species (ROS) are generated. The mechanism by which ASFV regulates SGs formation remains unclear. This study demonstrates that ASFV antagonises SGs formation and increases intracellular levels of reduced glutathione (GSH) levels. The use of the GSH inhibitor BSO and the activator NAC confirmed that the ASFV-induced increase in GSH helps to suppress SGs formation and influences viral replication. Additionally, this study revealed that ASFV enhances GSH by upregulating the antioxidant transcription factor NRF2, as well as factors involved in GSH synthesis and regeneration, such as GCLC, and those related to the ferroptosis pathway, such as SLC7A11. Furthermore, the study uncovered that ASFV manipulates intracellular GSH levels by activating the mitochondrial protein AIFM1. This regulatory mechanism helps the virus inhibit the formation of intracellular SGs, thereby creating an optimal environment for viral replication. These findings provide new insights into the molecular strategies employed by ASFV.

Application of stress granule core element G3BP1 in various diseases: A review

Ras-GTPase-activating protein-binding protein 1 (G3BP1) is a core component and crucial regulatory switch in stress granules (SGs). When the concentration of free RNA within cells increases, it can trigger RNA-dependent liquid-liquid phase separation (LLPS) with G3BP1 as the core, thereby forming SGs that affect cell survival or death. In addition, G3BP1 interacts with various host proteins to regulate the expression of SGs. As a multifunctional binding protein, G3BP1 has diverse biological functions, influencing cell proliferation, differentiation, apoptosis, and RNA metabolism and serving as a crucial regulator in signaling pathways such as Rac1-PAK1, TSC-mTORC1, NF-κB, and STAT3. Therefore, it plays a significant role in the regulation of neurodegenerative diseases, myocardial hypertrophy, and congenital immunity, and is involved in the proliferation, invasion, and metastasis of cancer cells. G3BP1 is an important antiviral factor that interacts with viral proteins, and regulates SG assembly to exert antiviral effects. This article focuses on the recent discoveries and progress of G3BP1 in biology, including its structure and function, regulation of SG formation and dissolution, and its relationships with non-neoplastic diseases, tumors, and viruses.

Specific Monoclonal Antibodies against African Swine Fever Virus Protease pS273R Revealed a Novel and Conserved Antigenic Epitope

The African swine fever virus (ASFV) is a large enveloped DNA virus that causes a highly pathogenic hemorrhagic disease in both domestic pigs and wild boars. The ASFV genome contains a double-stranded DNA encoding more than 150 proteins. The ASFV possesses only one protease, pS273R, which is important for virion assembly and host immune evasion. Therefore, the specific monoclonal antibody (mAb) against pS273R is useful for ASFV research. Here, we generated two specific anti-pS273R mAbs named 2F3 and 3C2, both of which were successfully applied for ELISA, Western blotting, and immunofluorescence assays. Further, we showed that both 2F3 and 3C2 mAbs recognize a new epitope of N terminal 1-25 amino acids of pS273R protein, which is highly conserved across different ASFV strains including all genotype I and II strains. Based on the recognized epitope, an indirect ELISA was established and was effective in detecting antibodies during ASFV infection. To conclude, the specific pS273R mAbs and corresponding epitope identified will strongly promote ASFV serological diagnosis and vaccine research.

Comprehensive Characterization of the Genetic Landscape of African Swine Fever Virus: Insights into Infection Dynamics, Immunomodulation, Virulence and Genes with Unknown Function

African Swine Fever (ASF) is a lethal contagious hemorrhagic viral disease affecting the swine population. The causative agent is African Swine Fever Virus (ASFV). There is no treatment or commercial vaccine available at present. This virus poses a significant threat to the global swine industry and economy, with 100% mortality rate in acute cases. ASFV transmission occurs through both direct and indirect contact, with control measures limited to early detection, isolation, and culling of infected pigs. ASFV exhibits a complex genomic structure and encodes for more than 50 structural and 100 non-structural proteins and has 150 to 167 open reading frames (ORFs). While many of the proteins are non-essential for viral replication, they play crucial roles in mediating with the host to ensure longevity and transmission of virus in the host. The dynamic nature of ASFV research necessitates constant updates, with ongoing exploration of various genes and their functions, vaccine development, and other ASF-related domains. This comprehensive review aims to elucidate the structural and functional roles of both newly discovered and previously recorded genes involved in distinct stages of ASFV infection and immunomodulation. Additionally, the review discusses the virulence genes and genes with unknown functions, and proposes future interventions.

African swine fever virus maintains de novo global cellular protein synthesis and inhibits stress granules formation via dephosphorylating eIF2α

African swine fever virus (ASFV) has caused enormous economic losses since its first reported detection, and there is still no effective vaccines or drug treatment. During infection, viruses may employ various strategies, such as regulating the host endoplasmic reticulum stress/unfolded protein response or the formation of stress granules (SGs), to form an optimal environment for virus replication. However, how ASFV infection regulates host endoplasmic reticulum stress, eIF2α-regulated protein synthesis, and the formation of SGs remains unclear. Here, we evaluated the activation of ER stress and its three downstream axes during ASFV infection and identified a powerful dephosphorylation of eIF2α by ASFV ex vivo. This strong dephosphorylation property could maintain the efficiency of eIF2α-mediated de novo global protein synthesis, thus ensuring efficient viral protein synthesis at early stage. In addition, the powerful dephosphorylation of eIF2α by ASFV upon infection could also inhibit the formation of SGs induced by sodium arsenite. In addition, a specific eIF2α dephosphorylation inhibitor, salubrinal, could partially counteract ASFV-mediated eIF2α dephosphorylation and inhibit viral replication. Our results provide new insights into the areas of ASFV`s escape from host immunity and hijacking of the host protein translation system.