| Ebola virus is a highly lethal pathogen capable of inducing severe hemorrhagic fever in humans and non-human primates. Although the complete pathogenic mechanisms contributing to the extreme virulence of Ebola virus are still unknown, several lines of evidence suggest that the viral envelope glycoprotein (GP) likely contributes to the pathogenicity of the virus due to its ability to induce the loss of cell adherence and vascular integrity in vitro. The cytotoxic effects of Ebola GP are dependent on a highly glycosylated region of GP, termed the mucin-like domain. The expression of a deletion mutant missing this region (GPDeltamuc) reverses the GP-induced phenotype. However the complete molecular mechanisms that lead to toxicity are unknown. In order to gain insights into the mechanisms involved in GP-induced cytotoxicity, we examined the consequences of GP expression on host cellular gene expression and intracellular signaling. We also studied the specific interactions between GP and cellular proteins since such interactions may mediate the changes induced by GP. Our results indicate that GP expression modifies normal cellular functions at many levels to lead to cell rounding and detachment. We found that Ebola GP induces alterations, both at the gene and protein level, in the ERK signaling cascade, an important mediator of cell growth and survival. We also identified an association between GP and the ER chaperone BiP. Significantly, the overexpression of BiP substantially reduced GP-induced cytotoxicity. Furthermore, the chaperone function of BiP was found to be required for the protective effect. These findings suggest that the cytotoxic phenotype is triggered by protein aggregation and retention within the ER. Taken together, our results demonstrate that GP-induced cytotoxicity results from a complex series of events that affect a multitude of cellular processes including cell adhesion, gene expression, intracellular trafficking and signaling. All of these events combine to induce the cytotoxic phenotype. Our findings not only elucidate the mechanisms of GP-induced cytotoxicity but also have the potential to facilitate the development of novel therapeutic targets against Ebola virus. |
