Investigation of The Role of The Ubiquitin Proteasome Pathway in Dengue Virus Life Cycle

Abstract

The mosquito-borne dengue virus (DENV) is a cause of significant global health burden. However, no licensed vaccine or specific antiviral treatment for dengue is available. DENV interacts with host cell factors to complete its life cycle although this virus-host interplay remains to be fully elucidated. Many studies have identified the ubiquitin proteasome pathway (UPP) to be important for successful DENV production, but how the UPP contributes to DENV life cycle as host factors remain ill defined. We show here that a functional UPP is critical for virus egress in both Aedes aegypti mosquitoes and human monocytic cell lines. Using RNA inference studies, we show in vivo that knockdown of ubiquitin proteasome pathway-related genes, including proteasomal subunits, ?1, ?2 and ?5 decouples RNA replication from infectious titer production in the mosquito midgut. Mechanistically, inhibition of proteasome function prevented virus egress by exacerbating endoplasmic reticulum (ER) stress through the unfolded protein response (UPR). UPR-induced translational repression reduced overall protein levels of the exocyst components needed for exocytosis. This mechanism also appears to be amenable for clinical translation as inhibition of UPP in primary monocytes with the licensed proteasome inhibitor, bortezomib, inhibited DENV titers even at low nanomolar drug concentration. Furthermore, we show in vivo in a wild type mouse model that DENV replication and spread in the mouse spleen is exquisitely sensitive to proteasome inhibition. The mechanism of action suggests that such a therapeutic approach may apply to other viruses that rely on exocytosis for virus egress to complete their life cycle.