Novel Function of African Swine Fever Virus pE66L in Inhibition of Host Translation by the PKR/eIF2α Pathway

African swine fever virus (ASFV) is one of the most contagious and lethal viruses infecting pigs. This virus is endemic in many countries and has very recently spread to China, but no licensed vaccines or treatments are currently available. Despite extensive research, the basic question remains of how ASFV-encoded proteins inhibit host translation. Here, we examined how ASFV interferes with host translation and optimizes viral gene expression. We found that 14 ASFV proteins inhibited Renilla luciferase (Rluc) activity greater than 5-fold, and the protein with the strongest inhibitory effect was pE66L, which was not previously reported. Combined with bioinformatic analysis and biochemical experiments, we determined that the transmembrane (TM) domain (amino acids 13 to 34) of pE66L was required for the inhibition of host gene expression. Notably, we constructed a recombinant plasmid with the TM domain linked to enhanced green fluorescent protein (EGFP) and further demonstrated that this domain broadly inhibited protein synthesis. Confocal and biochemical analyses indicated the TM domain might help proteins locate to the endoplasmic reticulum (ER) to suppress translation though the PKR/eIF2 alpha pathway. Deletion of the E66L gene had little effect on virus replication in macrophages, but significantly recovered host gene expression. Taken together, our findings complement studies on the host translation of ASFV proteins and suggest that ASFV pE66L induces host translation shutoff, which is dependent on activation of the PKR/eIF2 alpha pathway. IMPORTANCE African swine fever virus (ASFV) is a member of the nucleocytoplasmic large DNA virus superfamily that predominantly replicates in the cytoplasm of infected cells. The ASFV double-stranded DNA genome varies in length from approximately 170 to 193 kbp depending on the isolate and contains between 150 and 167 open reading frames (ORF5), of which half the encoded proteins have not been explored. Our study showed that 14 proteins had an obvious in-hibitory effect on Renilla luciferase (Rluc) protein synthesis, with pE66L showing the most significant effect. Furthermore, the transmembrane (TM) domain of pE66L broadly inhibited host protein synthesis in a PKR/eIF2 alpha pathway-dependent manner. Loss of pE66L during ASFV infection had little effect on virus replication, but significantly recovered host protein synthetic. Based on the above results, our findings expand our view of ASFV in determining the fate of host-pathogen interactions.

Automated summary

African swine fever virus (ASFV) is highly contagious and lethal in pigs, and understanding how ASFV proteins inhibit host translation through the transmembrane domain of pE66L sheds light on the mechanism of host translation shut-off induced by ASFV. This study provides important insights into the interaction between ASFV and its host cells, suggesting that ASFV pE66L plays a key role in modulating host gene expression.