Endosomal Proteolysis of the Ebola Virus Glycoprotein Is Necessary for Infection

Abstract

Ebola virus (EboV) causes rapidly fatal hemorrhagic fever in humans and there is currently no effective treatment. We found that the infection of African green monkey kidney (Vero) cells by vesicular stomatitis viruses bearing the EboV glycoprotein (GP) requires the activity of endosomal cysteine proteases. Using selective protease inhibitors and protease-deficient cell lines, we identified an essential role for cathepsin B (CatB) and an accessory role for cathepsin L (CatL) in EboV GP-dependent entry. Biochemical studies demonstrate that CatB and CatL mediate entry by carrying out proteolysis of the EboV GP subunit GP1 and support a multistep mechanism that explains the relative contributions of these enzymes to infection. CatB and CatB/CatL inhibitors diminish the multiplication of infectious EboV-Zaire in cultured cells and may merit investigation as anti-EboV drugs.

How Ebola and Marburg viruses battle the immune system

“…2). By affecting either viral entry 31,32 or exit 33,34 , these and other proteases could influence viral cellular tropisms and perhaps interactions between glycoprotein domains and antibodies (FIGS 2,3). Moreover, Barrientos and Rollin reported recently that endosomal proteolytic enzymes, including cathepsins, were released from EBOV-infected cells, that this release was more pronounced in cells infected with a more lytic variant of EBOV and that cytopathicity was diminished by the cathepsin inhibitor E64 (REF.…”

A Synthetic Serine Protease Inhibitor, Nafamostat Mesilate, Is a Drug Potentially Applicable to the Treatment of Ebola Virus Disease

“…Chandran et al (2005) performed in vitro experiments in the Vero cell line derived from the African green monkey kidney using recombinant vesicular stomatitis viruses expressing EBOV GP and showed that cysteine proteases are important for the proteolytic processing of the EBOV GP in the endosome, which facilitate EBOV entry into the cells, and CatB plays an essential role in this process. It was demonstrated that a synthetic CatB inhibitor, CA074, suppressed the proteolysis and viral replication following infection with the Zaire strain of EBOV (ZEBOV) (Chandran et al 2005). These findings presented that protease inhibitors that can effectively suppress CatB may be beneficial for treatment of EVD.…”

“…The processing is considered to prime the fusion as shown in Fig. 1 (Chandran et al 2005). In brief, a substantial portion of GP 1 is initially removed by CatL, which is then trimmed into a smaller form by CatL and/or CatB and is cleaved to a still smaller form by CatB.…”

“…Considering the effect of NM on CatB (Manabe et al 1992), we propose that NM might present a candidate drug to inhibit EBOV infection. Indeed, CatB is thought to be a major protease required for the proteolytic processing of EBOV GP (Chandran et al 2005).…”

“…This processing, particularly that by CatB and CatL, has suggested that interfering with cathepsin activity could represent a possible therapeutic strategy against EBOV infection (Chandran et al 2005;Hunt et al 2012). Nafamostat mesilate (NM), (6-amidinonaphthalen-2-yl 4-guanidinobenzoate bis (methanesulfonate)) is a synthetic serine protease inhibitor (Fujii and Hitomi 1981).…”