Ebolavirus Entry: Cell Adhesion-dependent Control of Viral Tropism

Ebolavirus is an enveloped, RNA virus that causes severe hemorrhagic fever disease for which there are currently no approved vaccines or antivirals. The first stage of ebolavirus infection is viral entry, which consists of host cell binding, internalization, and fusion of the viral and cellular membranes. The sole envelope glycoprotein (GP) of ebolavirus is both necessary and sufficient for virus binding and entry and as such, represents an important focus of ebolavirus study. Our laboratory previously showed that GP directs virus particles to the endocytic pathway, where endosomal cathepsins cleave full length GP into a 19 kDa fusion primed form, a necessary event for productive infection. Together with other lab members, I first determined the molecular identity of 19 kDa GP. Using Fc-conjugated truncation variants, we identified the receptor binding region (RBR) within 19 kDa GP and then demonstrated the importance of four conserved lysine residues within the RBR for cell binding. Further, RBR-specific Fab fragments inhibited both RBR binding and GP-mediated pseudovirion infection, supporting the importance of the RBR for ebolavirus infection. Employing the RBR construct, we next examined the cellular aspects of ebolavirus binding. We found that cellular adhesion increases the amount of an RBR receptor at the cell surface resulting in enhanced susceptibility to GPmediated infection. Additionally, non-permissive suspension cells including lymphocytes, which do not bind RBR at the cell surface and were previously considered to lack an ebolavirus receptor, were found to sequester an RBR receptor intracellularly. This intracellular pool of RBR receptor is closely associated with the trans-golgi network and traffics to the cell surface upon cellular adhesion in a microtubule-dependent manner. ii Importantly, we showed that two adherent B lymphocyte cell lines bind RBR at the cell surface and are susceptible to GP-mediated entry and infection. These findings represent a novel mode of regulating viral tropism that may play an important role in the often fatal disease progression of ebolavirus.

Note: Abstract extracted from PDF text