Emodin inhibits Newcastle disease virus replication via regulating the phosphorylation levels of eEF2K/eEF2 and targeting viral N protein to reduce viral protein production.

Newcastle disease (ND) caused by Newcastle disease virus (NDV) infection is a highly contagious avian disease that causes substantial threat to the global poultry industry. Emodin (EMO), a member of the free anthraquinone compounds derived from traditional Chinese medicines, is known for its antibacterial, antiviral, antitumor, and antioxidant activity. However, the anti-NDV activity and potential mechanism of action of EMO remains unknown. In this study, EMO was found to exert a remarkable anti-NDV activity in a dose- and phase-dependent manner. In addition, EMO restricted NDV replication mainly by affecting the production of viral proteins, but not by inhibiting the viral RNA synthesis and transcription. Moreover, the EMO treatment-induced reduction of viral proteins was correlated well with the increased phosphorylation level of eukaryotic elongation factor 2 (eEF2) in NDV-infected cells, which was further confirmed by inhibition of eEF2 kinase (eEF2K) activity with pharmacological inhibitors NH125 and A-484954, respectively. Meanwhile, multiple signaling cascades, including p38 MAPK, mTORC1/p70 S6K, and ERK1/2/p90 RSK1, were found to regulate the phosphorylation levels and activities of eEF2K and eEF2 by which EMO reduced viral protein production and inhibited NDV replication. Furthermore, molecular docking combined with protein-protein interaction analysis showed that EMO could form stable hydrogen bond structures with the NDV N protein at the Lys32 and Leu225 residues, and attenuate its interaction with eIF4E to decrease the production of viral proteins. These findings reveal the anti-NDV effect and the underlying mechanism of EMO, offering a potential natural compound for the development of antiviral strategies against NDV.