The CRM1-dependent NES257−266 motif in the matrix protein: another factor influencing Newcastle disease virus propagation and virulence

As an important structural protein of Newcastle disease virus (NDV), the M protein plays a crucial role in the assembly and budding of the virus. In previous reports, we confirmed the existence of a classical nuclear export signal (NES) sequence on the M protein (i.e., amino acids 257 to 266), which plays an important role in the nuclear export of the protein. In this study, we found that the NES^257-266 motif is associated with the evolutionary history of NDV, and found that the NES-mediated nuclear export efficiency of M proteins varies among different genotypes. Further research on the LaSota-NES and JSD0812-NES variants showed that the NES both affects the nuclear-cytoplasmic trafficking efficiency of M protein and influences the formation of virus-like particles (VLPs). The NES^257-266 conforms to the chromosome region maintenance 1 (CRM1)-associated consensus leucine/isoleucine-rich NES motif, and our results confirm that the NES-mediated nuclear-cytoplasmic trafficking of M protein is dependent on the CRM1 pathway. At last, several recombinant LaSota strains were rescued using reverse genetics, with their NES sequence replaced by either a potent NES motif, or an R247K mutation, or both. The rescued rLaSota-QMS and rLaSota-FM strains showed elevated hemagglutination (HA) titers, increased 50% egg infective dose (EID₅₀) values, along with marginally higher mean death time (MDT) and intracerebral pathogenicity index (ICPI) values, all of which are attributable to their enhanced proliferation rates when compared to the wild-type (wt) rLaSota strain. Our findings contribute to a better understanding of the molecular mechanisms of replication and pathogenicity in NDV and, by extension, in other paramyxoviruses.