Figure 6. Mutation of the human IFITM3 endocytosis motif converts IFITM3 into an enhancer of SARS‐CoV‐2 Spike‐mediated cell‐to‐cell membrane fusion.

U2OS cells transfected with EGFP and the indicated IFITM3 constructs or vector control were mixed with Calu‐3 cells transfected with mCherry and SARS‐CoV‐2 Spike (S) or vector control. Cells were co‐cultured for 24 h and imaged by fluorescent microscopy to visualize EGFP and mCherry as well as nuclei via Hoechst dye.

1. Representative example fluorescent imaging of the indicated co‐cultures showing the presence of EGFP/mCherry double‐positive cell syncytia dependent upon S expression as well as varying effects of the IFITM3 constructs. Scale bar indicates 50 µm.
2. Quantification of nuclei per EGFP/mCherry double‐positive cell syncytia in co‐cultures involving the indicated IFITM3 constructs as compared to vector control. Bars depict averages of three independent experiments with circles representing the individual data points. For each condition, nuclei within 50–75 individual syncytia were counted. Error bars represent SD. ^# P < 0.05 compared to vector control by ANOVA followed by Tukey’s multiple comparisons test.

Source data are available online for this figure.