[The nuclear import of Newcastle disease virus matrix protein depends on KPNB1 and Ran protein].

Objective: The aim of this study was to identify the transport proteins that mediates the nuclear import of Newcastle disease virus (NDV) matrix (M) protein.

Methods: Chicken KPNA1 to KPNA6 gene and KPNB1 gene were cloned from DF-1 cells and then inserted into eukaryotic expression vectors. The constructed recombinant plasmids with a combination of grouping were transfected into HEK-293T cells to identify the transport proteins interacting with NDV M protein by co-immunoprecipitation (Co-IP) assay. Moreover, fluorescent co-localization assay was used to verify the transport proteins by co-expressing M and Ran protein mutant or M and its interactive protein deletant.

Results: The recombinant proteins could normally express in plasmid-transfected HEK-293T cells. Indirect immunofluorescence detection showed that the recombinant proteins except for Myc-KPNA2 displayed the same nuclear localization as NDV M protein. The results of Co-IP revealed that M protein could interact with KPNA1 and KPNB1. Further fluorescent co-localization indicated that co-expression of M and DN-KPNA1 did not change the nuclear localization of M, whereas co-expression of M and DN-KPNB1 or M and Ran-Q69L disrupted the nuclear localization of M, demonstrating that the nuclear import of M protein was dependent on KPNB1 and Ran protein.

Conclusion: KPNB1 and Ran protein jointly mediated the nuclear import of NDV M protein, showing that KPNB1 protein interacted with NDV M protein to form binary complex and then entered into the nucleus with the assistance of Ran protein.