Lumpy Skin Disease Virus ORF137 Protein Inhibits Type I Interferon Production by Interacting with and Decreasing the Phosphorylation of IRF3.

Lumpy skin disease (LSD) is an invasive infectious disease caused by the lumpy skin disease virus (LSDV), which is detrimental to the production of cattle. LSDV encodes about 156 proteins, most of whose functions are still unknown. In this study, we found that the ORF137 protein was identified as one of the strongest inhibitors of IFN-β and ISG expression, determining LSDV ORF137 as a negative regulator of interferon (IFN) β signaling. Further evidence suggests that ORF137 interacts with the signal transduction factor IRF3 and inhibits the activation of IFN-β signaling by reducing Phospho-IRF3 (p-IRF3). Further investigation indicated that overexpression of ORF137 in BMEC could significantly inhibit the transcription of IFN-β and ISGs, thereby promoting the replication of LSDV. More importantly, through homologous recombination, we deleted the ORF137 gene from the LSDV/FJ/CHA/2021 strain and constructed the recombinant strain LSDV-ΔORF137-EGFP. Compared with the parental strain, LSDV-ΔORF137-EGFP showed a weakened effect on inhibiting the transcription of IFN-β and ISGs and a reduced replication level in infected MDBK cells. In summary, ORF137 facilitates LSDV replication by targeting IRF3 to inhibit IFN-β signaling. Our findings reveal a new mechanism by which LSDV suppresses the host antiviral response, which may facilitate the development of attenuated live vaccines for LSDV.