African swine fever virus pNP419L inhibits host translation and increases viral replication through the PERK/eIF2α pathway.

Abstract

African swine fever (ASF) is a highly contagious disease caused by African swine fever virus (ASFV), which poses a significant threat to pig farming worldwide. Although ASFV encodes many self-sustaining proteins, its mRNA translation relies on the host's translation machinery. However, the mechanisms by which ASFV-encoded proteins regulate the host's translation process in infected cells remain largely unexplored. In this study, we investigated how ASFV-encoded proteins affect the translation of host cells. We identified 21 ASFV genes, excluding those from multigene families, that significantly inhibited Renilla luciferase (Rluc) activity. Among these genes, only NP419L, which is known as an early-expressed gene, demonstrated a strong inhibitory effect. We showed that NP419L significantly suppressed host protein synthesis, independent of its enzymatic activity. Our study, which utilized confocal microscopy and biochemical assays, revealed significant implications for ASFV infection. We found that ASFV pNP419L localized to the endoplasmic reticulum (ER), induced ER stress and activated the PERK/eIF2α pathway, resulting in the inhibition of host translation. Furthermore, viral assays demonstrated that knockdown of NP419L effectively reduced viral replication and significantly restored host gene expression. Overall, our findings improve the understanding of how the ASFV protein inhibits host translation and reveal a novel function of ASFV pNP419L beyond its DNA ligase activity for the first time, providing critical insights into translational regulation during ASFV infection.