Niemann-Pick C1 Is Essential for Ebola Virus Infection and a Target of Small Molecule Inhibitors

Abstract

Ebolavirus (EboV) is a highly pathogenic enveloped virus that causes outbreaks of zoonotic infection in Africa. The clinical symptoms are manifestations of the massive production of pro-inflammatory cytokines in response to infection and in many outbreaks, case fatality rate exceeds 75%. The unpredictable onset, ease of transmission, rapid progression of disease, high mortality and lack of effective vaccine or therapy have created a high level of public concern about EboV. Here we report the properties of a benzylpiperazine adamantane diamide-derived compound identified in a screen for inhibitors of EboV infection. We found that the inhibitor is specific, reversible, and that the target(s) for inhibition are present in cells and not in virus particles. The compound is not an inhibitor of acid pH-dependent endosome protease activity, which is required for EboV infection. Treatment of cells with this compound causes accumulation of cholesterol in late endosomes and lysosomes (LE/LY), suggesting it inhibits one or more proteins involved in regulation of cholesterol uptake into cells. Using mutant cell lines and informative derivatives of the inhibitor, we found the inhibitor target is the endosomal membrane protein Niemann-Pick C1 (NPC1). NPC1 is a polytopic LE/LY membrane protein that mediates uptake of lipoprotein-derived cholesterol into cells. We find that NPC1 is essential for EboV infection, that NPC1 binds to the protease-cleaved GP1 subunit of the EboV glycoprotein, and that the anti-viral compound inhibits infection by targeting NPC1 and interfering with binding to GP1. Furthermore, analysis of viral variants resistant to the anti-viral compound revealed that the residues which confer resistance are located on the surface of the receptor binding domain of GP1. Combined with the results of previous studies of GP structure and function, our findings support a model of EboV infection in which cleavage of the GP1 subunit by endosomal cathepsin proteases removes heavily glycosylated domains to expose the N-terminal domain, which is a ligand for NPC1 and regulates membrane fusion by the GP2 subunit. Thus, NPC1 is essential for EboV entry and a target for anti-viral therapy.