Deletion of MGF-110-9L gene from African swine fever virus weakens autophagic degradation of TBK1 as a mechanism for enhancing type I interferon production

Deletion of MGF505-2R Gene Activates the cGAS-STING Pathway Leading to Attenuation and Protection against Virulent African Swine Fever Virus

African swine fever virus (ASFV) is the etiological agent causing African swine fever (ASF), affecting domestic pigs and wild boar, which is currently the biggest animal epidemic in the world and a major threat to the swine sector. At present, some safety concerns about using LAVs against ASFV still exist despite a commercial vaccine licensed in Vietnam. Therefore, the efforts to identify virulence factors and their mechanisms, as well as to generate new vaccine prototypes, are of major interest. In this work, we have identified the MGF505-2R gene product as an inhibitor of the cGAS/STING pathway, specifically through its interaction with STING protein, controlling IFN-β production. In addition, immunization of a recombinant virus lacking this gene, Arm/07-ΔMGF505-2R, resulted in complete attenuation, demonstrating its involvement in ASFV virulence. Finally, immunization with Arm/07-ΔMGF505-2R induced the generation of antibodies and proved to be partially protective against virulent ASFV strains. These results identify MGF505-2R, as well as its mechanism of action, as a gene contributing to understanding the molecular mechanisms of ASFV virulence, which will be of great value in the design of future vaccine prototypes.

Adaptation of African swine fever virus to MA-104 cells: Implications of unique genetic variations

African swine fever virus (ASFV) is a large, double-stranded DNA virus that causes a fatal, contagious disease specifically in pigs. However, prevention and control of ASFV outbreaks have been hampered by the lack of an effective vaccine or antiviral treatment for ASFV. Although ASFV has been reported to adapt to a variety of continuous cell lines, the phenotypic and genetic changes associated with ASFV adaptation to MA-104 cells remain poorly understood. Here, we adapted ASFV field isolates to efficiently propagate through serial viral passages in MA-104 cells. The adapted ASFV strain developed a pronounced cytopathic effect and robust infection in MA-104 cells. Interestingly, the adapted variant maintained its tropism in primary porcine kidney macrophages. Whole genome analysis of the adapted virus revealed unique gene deletions in the left and right variable regions of the viral genome compared to other previously reported cell culture-adapted ASFV strains. Notably, gene duplications at the 5' and 3' ends of the viral genome were in reverse complementary alignment with their paralogs. Single point mutations in protein-coding genes and intergenic regions were also observed in the viral genome. Collectively, our results shed light on the significance of these unique genetic changes during adaptation, which facilitate the growth of ASFV in MA-104 cells.

SNX32 is a host restriction factor that degrades African swine fever virus CP204L via the RAB1B-dependent autophagy pathway

African swine fever virus (ASFV) causes a highly contagious and deadly disease in domestic pigs and European wild boars, posing a severe threat to the global pig industry. ASFV CP204L, a highly immunogenic protein, is produced during the early stages of ASFV infection. However, the impact of CP204L protein-interacting partners on the outcome of ASFV infection is poorly understood. To accomplish this, coimmunoprecipitation and mass spectrometry analysis were conducted in ASFV-infected porcine alveolar macrophages (PAMs). We have demonstrated that sorting nexin 32 (SNX32) is a CP204L-binding protein and that CP204L interacted and colocalized with SNX32 in ASFV-infected PAMs. ASFV growth and replication were promoted by silencing SNX32 and suppressed by overexpressing SNX32. SNX32 degraded CP204L by recruiting the autophagy-related protein Ras-related protein Rab-1b (RAB1B). RAB1B overexpression inhibited ASFV replication, while knockdown of RAB1B had the opposite effect. Additionally, RAB1B, SNX32, and CP204L formed a complex upon ASFV infection. Taken together, this study demonstrates that SNX32 antagonizes ASFV growth and replication by recruiting the autophagy-related protein RAB1B. This finding extends our understanding of the interaction between ASFV CP204L and its host and provides new insights into exploring the relationship between ASFV infection and autophagy.IMPORTANCEAfrican swine fever (ASF) is a highly contagious and acute hemorrhagic viral disease with a high mortality near 100% in domestic pigs. ASF virus (ASFV), which is the only member of the family Asfarviridae, is a dsDNA virus of great complexity and size, encoding more than 150 proteins. Currently, there are no available vaccines against ASFV. ASFV CP204L represents the most abundantly expressed viral protein early in infection and plays an important role in regulating ASFV replication. However, the mechanism by which the interaction between ASFV CP204L and host proteins affects ASFV replication remains unclear. In this study, we demonstrated that the cellular protein SNX32 interacted with CP204L and degraded CP204L by upregulating the autophagy-related protein RAB1B. In summary, this study will help us understand the interaction mechanism between CP204L and its host upon infection and provide new insights for the development of vaccines and antiviral drugs.