IFITM3 promotes NiV envelope protein-mediated entry into MDCK cells and interacts with the fusion subunit of the F protein

IFITM proteins are a host restriction factor with broad-spectrum antiviral activity, but the role in the paramyxovirus entry remains unclear. Nipah virus (NiV) is a zoonotic virus of the paramyxoviridae with extremely high lethality. Here, we assessed the role of IFITM3 on NiV G and F glycoprotein-mediated virus entry. Using NiV pseudovirus bearing NiV G and F proteins to infect IFITM3-induced MDCK cells, we found that overexpression of IFITM3 promotes NiV G and F proteins-mediated virus entry. Mechanistically, the subcellular distribution showed that F protein completely co-localized with IFITM3, but G protein does not. Immunoprecipitation further indicated that IFITM3 strongly captures F protein rather than G protein. F protein truncation found that the F1 subunit completely co-localized and captures with IFITM3, but not the F2 subunit. Furthermore, IFITM3 strongly binds to F1 truncations containing fusion peptide (FP), and F1 strongly captures IFITM3 truncation with the intramembrane domain (IMD). Together, the results suggest that IFITM3 can promote NiV G and F proteins-mediated virus entry into MDCK cells, and IFITM3 directly interacts with the F1 subunit of NiV F protein dependent on the former's IMD and the latter's FP, which may occur after incorporation of fusion peptides into the cell membrane following virus fusion activation.