Mechanisms of Ebola Virus Entry

Ebola virus (EBOV) is an enveloped RNA virus belonging to the family Filoviridae. It occurs episodically in sub-Saharan Africa, and is noted for the severe and highly lethal hemorrhagic fever it causes in humans as well as nonhuman primates. There are currently no clinically approved therapies or vaccines, and many mysteries remain concerning its path of entry into the cell. After binding to and being internalized from the cell surface, it traffics to a late endocytic compartment, where the viral glycoprotein is proteolytically primed and triggered to fuse. Fusion enables genome egress to the cytoplasm and subsequent replication. While much has been learned in recent years about its method of entry into host cells, many mysteries remain about EBOV entry and fusion. To address, some of these questions, I developed a novel preparation of filamentous virus-like-particles (VLPs) as surrogates for EBOV. These VLPs enabled me to dissect different steps of EBOV penetration into the host cell, particularly internalization from the cell surface and cytoplasmic entry. Using these multi-purpose VLPs, I found that EBOV VLP entry is slow relative to particle internalization. I further showed that this delayed entry was not the result of cathepsin priming of GP. Subsequently, we used this VLP system to characterize the method of action of several compounds that had been shown to inhibit EBOV infection. We showed that these compounds blocked a late stage of EBOV entry. In a concurrent study, we found that these drugs belonged to a chemical class known as cationic amphiphiles, and that they cause cholesterol accumulation in endosomes, a hallmark of Niemann-Pick C1 disease. All of the ii robust EBOV entry inhibitors identified in this study also caused this phenotype, and furthermore appeared to be acting through an NPC1-dependent pathway distinct from that previously described by other groups. These studies have therefore revealed a possible additional critical role for NPC1 in supporting successful EBOV entry, and further validate NPC1 as a target for anti-EBOV therapy. Lastly, these studies have identified a large class of chemical compounds which may hold potential for combating filoviral, and especially ebolavirus infection.

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