Interferon-induced transmembrane protein 3 blocks fusion of sensitive but not resistant viruses by partitioning into virus-carrying endosomes

Suddala, Krishna C.; Lee, Christine C.; Meraner, Paul; Marin, Mariana; Markosyan, Ruben M.; Desai, Tanay M.; Cohen, Fredric S.; Brass, Abraham L.; Melikyan, Gregory B.

Analysis of single IAVpp and LASVpp co-trafficking with IFITM3-imTFP1 endosomes in the context of fusion (Figs 3-6) suggests that IAVpp would be trapped in IFITM3-positive endosomes/multivesicular bodies, while LASVpp would not. To test this notion, we followed the bulk virus uptake and transport in live A549 cells expressing IFITM3-imNG. Cells were incubated in the cold for 1.5 hr with IAVpp or LASVpp labeled with an internal fluorescent marker, Gag-mCherry, to allow virus binding. Cells were then incubated for indicated times (0, 15, 30, and 60 min) at 37ËšC, fixed and imaged at high spatial resolution. Representative images of IAVpp and LASVpp co-localization with IFITM3 containing vesicles at different time points are shown in Fig 7A. Quantification of virus colocalization with IFITM3-imNG over time shows that IAVpp increasingly co-localizes with IFITM3-imNG compartments, while LASVpp does not show a significant increase in colocalization up to 1 hr post-infection ( Fig 7B) . These data support the hypothesis that restriction-sensitive viruses (as is the case for IAV) co-traffic with IFITM3, while resistant viruses (like LASV) are transported through distinct endosomal compartments devoid of this restriction factor.