Inhibitors of signal peptide peptidase and subtilisin/kexin-isozyme 1 inhibit Ebola virus glycoprotein-driven cell entry by interfering with activity and cellular localization of endosomal cathepsins

Martin Spiegel,Teresa Plegge,Nadine Krüger,Michael Winkler,Inga Nehlmeier,Mariana González Hernández,Stefan Pöhlmann

doi:10.1371/journal.pone.0214968

Martin Spiegel, Teresa Plegge + Show 5 more

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https://doi.org/10.1371/journal.pone.0214968

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Abstract

Emerging viruses such as severe fever and thrombocytopenia syndrome virus (SFTSV) and Ebola virus (EBOV) are responsible for significant morbidity and mortality. Host cell proteases that process the glycoproteins of these viruses are potential targets for antiviral intervention. The aspartyl protease signal peptide peptidase (SPP) has recently been shown to be required for processing of the glycoprotein precursor, Gn/Gc, of Bunyamwera virus and for viral infectivity. Here, we investigated whether SPP is also required for infectivity of particles bearing SFTSV-Gn/Gc. Entry driven by the EBOV glycoprotein (GP) and the Lassa virus glycoprotein (LASV-GPC) depends on the cysteine proteases cathepsin B and L (CatB/CatL) and the serine protease subtilisin/kexin-isozyme 1 (SKI-1), respectively, and was examined in parallel for control purposes. We found that inhibition of SPP and SKI-1 did not interfere with SFTSV Gn + Gc-driven entry but, unexpectedly, blocked entry mediated by EBOV-GP. The inhibition occurred at the stage of proteolytic activation and the SPP inhibitor was found to block CatL/CatB activity. In contrast, the SKI-1 inhibitor did not interfere with CatB/CatL activity but disrupted CatB localization in endo/lysosomes, the site of EBOV-GP processing. These results underline the potential of protease inhibitors for antiviral therapy but also show that previously characterized compounds might exert broader specificity than initially appreciated and might block viral entry via diverse mechanisms.

Highlights

Our results show that inhibitors of the host cell proteases signal peptide peptidase (SPP) and subtilisin/kexin-isozyme 1 (SKI-1) do not impact severe fever and thrombocytopenia syndrome virus (SFTSV) Gn + Gc-driven entry but block entry mediated by Ebola virus (EBOV)-GP
We demonstrate that the SPP inhibitor blocks the enzymatic activity of the Ebola virus glycoprotein (EBOV-GP) processing host cell proteases CatB/CatL while the SKI-1 inhibitor interferes with localization of CatB in late endosomes/ lysosomes, the site of EBOV-GP processing
Our results show that inhibition of SKI-1 blocks EBOV-GP-driven entry and indicate that inhibitors of viral glycoprotein processing host cell proteases can interfere with viral entry in a direct and an indirect manner

Summary

Introduction

Anthropogenic drivers including climate change, exploitation of natural resources and global travel promote the constant emergence of novel pathogens in the human population [1,2,3]. Viral glycoproteins are synthesized as inactive precursors and depend on priming by host cell proteases to transit into an active form [10, 11]. Priming can occur at different cellular localizations, for instance the constitutive secretory pathway, the plasma membrane and the extracellular space, and can proceed during different stages of viral spread, including glycoprotein biogenesis in infected cells, particle release from infected cells and entry into new target cells [10, 11]. The activity of host cell proteases is required for priming of viral glycoproteins and for viral infectivity and the responsible enzymes constitute potential targets for antiviral intervention. We report that inhibition of SPP and SKI-1 activity did not interfere with SFTSV Gn + Gcdriven host cell entry but, counterintuitively, blocked entry driven by the EBOV glycoprotein (GP). We show that the SPP inhibitor blocks EBOV-GP-driven entry by interfering with CatB activity while the SKI-1 inhibitor blocks entry by altering the cellular localization of CatB

Results

Discussion

Material and methods