Overexpression of TMPRSS12 enhances cleavage level and fusogenic activity of aMPV/B F protein. (A) The effect of hepsin, TMPRSS2, and TMPRSS12 expression on the extent of aMPV/B F protein cleavage. The cleavage of aMPV/B F protein was analyzed by biotinylation and Western blot assay. (B) Effect of TMPRSS12 expression on syncytium formation in Vero cells. Syncytium formation in Vero cells was observed and photographed (magnification, ×100; 8.5 cm by 9.1 cm, as shown). (C to J) The effect of TMPRSS12, hepsin, and TMPRSS2 expression on aMPV/B F protein fusogenic activity was analyzed by syncytium formation (C, E, G, and I) and reporter gene assays (D, F, H, and J).