Less Is More: Ebola Virus Surface Glycoprotein Expression Levels Regulate Virus Production and Infectivity

Abstract

ABSTRACT The Ebola virus (EBOV) surface glycoprotein (GP 1,2 ) mediates host cell attachment and fusion and is the primary target for host neutralizing antibodies. Expression of GP 1,2 at high levels disrupts normal cell physiology, and EBOV uses an RNA-editing mechanism to regulate expression of the GP gene. In this study, we demonstrate that high levels of GP 1,2 expression impair production and release of EBOV virus-like particles (VLPs) as well as infectivity of GP 1,2 -pseudotyped viruses. We further show that this effect is mediated through two mechanisms. First, high levels of GP 1,2 expression reduce synthesis of other proteins needed for virus assembly. Second, viruses containing high levels of GP 1,2 are intrinsically less infectious, possibly due to impaired receptor binding or endosomal processing. Importantly, proteolysis can rescue the infectivity of high-GP 1,2 -containing viruses. Taken together, our findings indicate that GP 1,2 expression levels have a profound effect on factors that contribute to virus fitness and that RNA editing may be an important mechanism employed by EBOV to regulate GP 1,2 expression in order to optimize virus production and infectivity. IMPORTANCE The Ebola virus (EBOV), as well as other members of the Filoviridae family, causes severe hemorrhagic fever that is highly lethal, with up to 90% mortality. The EBOV surface glycoprotein (GP 1,2 ) plays important roles in virus infection and pathogenesis, and its expression is tightly regulated by an RNA-editing mechanism during virus replication. Our study demonstrates that the level of GP 1,2 expression profoundly affects virus particle production and release and uncovers a new mechanism by which Ebola virus infectivity is regulated by the level of GP 1,2 expression. These findings extend our understanding of EBOV infection and replication in adaptation of host environments, which will aid the development of countermeasures against EBOV infection.