The NP protein of Newcastle disease virus dictates its oncolytic activity by regulating viral mRNA translation efficiency

Newcastle disease virus (NDV) has been extensively studied as a promising oncolytic virus for killing tumor cells in vitro and in vivo in clinical trials. However, the viral components that regulate the oncolytic activity of NDV remain incompletely understood. In this study, we systematically compared the replication ability of different NDV genotypes in various tumor cells and identified NP protein determines the oncolytic activity of NDV. On the one hand, NDV strains with phenylalanine (F) at the 450th amino acid position of the NP protein (450th-F-NP) exhibit a loss of oncolytic activity. This phenotype is predominantly associated with genotype VII NDVs. In contrast, the NP protein with a leucine amino acid at this site in other genotypes (450th-L-NP) can facilitate the loading of viral mRNA onto ribosomes more effectively than 450th-F-NP. On the other hand, the NP protein from NDV strains that exhibit strong oncogenicity interacts with eIF4A1 within its 366-489 amino acid region, leading to the inhibition of cellular mRNA translation with a complex 5' UTR structure. Our study provide mechanistic insights into how highly oncolytic NDV strains selectively promote the translation of viral mRNA and will also facilitate the screening of oncolytic strains for oncolytic therapy. The oncolytic potential of NDV has gained significant attention in the context of clinical trials. Therefore, it is crucial to systematically compare the oncolytic activities of different NDV subtypes and understand their underlying mechanisms. Our previous investigations revealed that genotype VII NDVs, predominant during the fourth epidemic, exhibit heightened avian pathogenicity compared to other subtypes. Interestingly, in tumor cells, NDV strains of varying virulence and genotypes possess some oncolytic capacity. However, in several genotype VII strains, the NP protein fails to facilitate the efficient loading of viral mRNA onto ribosomes. This is primarily attributed to the presence of phenylalanine at the 450th amino acid position of the NP protein. Additionally, it loses its ability to inhibit the eIF4A1-relative cellular mRNA translation through interaction with eIF4A1, mainly because of differences in its non-conserved region (366-489aa) of NP protein compared to other genotypes. These significantly hinder its ability to establish effective infections in tumor cells. Our study provides valuable insights for oncolytic NDV strain screening and enhances understanding of the functional role of NP protein.