Cathepsins B and L activate Ebola but not Marburg virus glycoproteins for efficient entry into cell lines and macrophages independent of TMPRSS2 expression.

Ebola (EBOV) and Marburg virus (MARV) cause severe hemorrhagic fever. The host cell proteases cathepsin B and L activate the Zaire ebolavirus glycoprotein (GP) for cellular entry and constitute potential targets for antiviral intervention. However, it is unclear if different EBOV species and MARV equally depend on cathepsin B/L activity for infection of cell lines and macrophages, important viral target cells. Here, we show that cathepsin B/L inhibitors markedly reduce 293T cell infection driven by the GPs of all EBOV species, independent of the type II transmembrane serine protease TMPRSS2, which cleaved but failed to activate EBOV-GPs. Similarly, a cathepsin B/L inhibitor blocked macrophage infection mediated by different EBOV-GPs. In contrast, MARV-GP-driven entry exhibited little dependence on cathepsin B/L activity. Still, MARV-GP-mediated entry was efficiently blocked by leupeptin. These results suggest that cathepsins B/L promote entry of EBOV while MARV might employ so far unidentified proteases for GP activation.