Nucleophosmin 1 (NPM1)
The NPM1(B23.1) protein derived from the main transcription form and the longest transcript of the NPM gene, is mainly located in the granular region of nucleolus. It has several functional domains responsible for various actions, such as oligomerization, chaperone activity, histone binding, ribonuclease activity (H. K, A, & MO, 2000). As a nuclear shuttle protein, NPM1 plays multiple roles in the nucleolus including centrosome duplication, ribosome biogenesis, intracellular transport, apoptosis and mRNA splicing (MS, 2011). Importantly, a series of evidence have demonstrated the interaction/interplay of the PEDV N protein with the NPM1 protein, as well as their contribution to PEDV infection. Firstly, the interaction and co-localization of those two proteins has been confirmed by both immunoprecipitation (IP) and GST-pull down assay, as well as confocal microscopy, respectively. Moreover, the region of aa147-294 of the PEDV N protein and the region of aa189-294 of NPM1 was verified to be essential for their interaction. Secondly, the infection of PEDV was found to cause considerable upregulation of the NPM1 expression. Especially, the NPM1 overexpression of could promote the expression of the N protein and the proliferation of PEDV, while its downregulation led to converse consequences. Thirdly, mechanically the interaction between the N and NPM1 proteins could prevent the cells from being cut off, increase the cell resistance to apoptosis, avoid premature cell death, thus enhancing virus replication (Shi D et al., 2017).