关键词: 非洲猪瘟病毒, MGF110-5L-6L蛋白, eIF2α磷酸化, 翻译阻滞, 应激颗粒

Abstract:

【Background】 African swine fever (ASF) is an acute, highly contagious, and deadly infectious disease of pigs caused by ASF virus (ASFV), which is currently considered the biggest killer in global swine industry. To date, there is no effective vaccines or antiviral drugs for the prevention or treatment of ASF. As obligate intracellular parasites, the viruses are fully reliant on the host translation machinery to produce the polypeptides that are essential for viral replication. A central mechanism regulating translation initiation involves phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α), which directs host translational control and adaptation to cellular stress. The regulation of eIF2α phosphorylation has been regarded as a critical step for viral infection, with important effects on virulence, tissue tropism, pathogenicity, and immunoevasion. However, the molecular mechanisms by which most of the ASFV-encoded proteins affecting eIF2α phosphorylation have not been well studied. 【Objective】 The aim of this study was to explore the mechanism of ASFV MGF110-5L-6L protein on the host cell translation block and promote the formation of stress particles, so as to provide a scientific basis for further revealing the pathogenic mechanism of African swine fever virus.【Method】 The preliminary screening by luciferase reporter assays identified that ectopic expression of ASFV MGF110-5L-6L, a previously uncharacterized member of the multigene family 110, significantly increased eIF2α phosphorylation levels. To confirm and clarify the potential role of MGF110-5L-6L expression in mediating eIF2α phosphorylation and downstream of translation control, two continuous porcine cell lines, including 3D4/21 (porcine alveolar macrophage) and PK-15 (porcine kidney), were used for the plasmid transfection and/or drug treatment and subjected to immunoblotting or confocal immunofluorescence analysis. To investigate how the ectopic expression of MGF110-5L-6L triggers cellular stress, the structure, subcellular localization and function of the MGF110-5L-6L protein were further characterized by a combination of bioinformatic prediction, immunofluorescence and immunoblotting analysis.【Result】 Here, it was confirmed that ectopic expression of MGF110-5L-6L remarkably promoted eIF2α phosphorylation and the expression of ATF4, indicating that it functions in the integrated stress response. The subsequent analyses revealed that MGF110-5L-6L expression could trigger the ER stress and activate the unfolded protein response, and the phosphorylation of eIF2α was mediated via PERK and PKR, resulting in the suppression of host translation and stress granule formation. It was further observed that MGF110-5L-6L protein had two highly conserved central cysteine-rich domains and was mainly retained in the endoplasmic reticulum (ER), and also caused a significant reorganization of the subcellular distribution and morphological characteristics of the Golgi and peroxisome, suggesting that it might interfere with ER redox homeostasis, secretory pathway, and other membrane-bound organelles to trigger cellular stress.【Conclusion】 Together, these results demonstrated a previously uncharacterized role of ASFV MGF110-5L-6L and further defined several molecular interfaces by which ASFV MGF110-5L-6L hijacks the host cell translation, which expanded the view of ASFV in determining the fate of host-pathogen interactions.

Key words: African swine fever virus, MGF110-5L-6L protein, eIF2α phosphorylation, translation arrest, stress granules