Abstract:
Rift Valley fever virus (RVFV) and Venezuelan equine encephalitis virus (VEEV) are two mosquito-borne, select agent viruses with severe effects on humans and livestock, and for which no FDA-approved vaccines or specific treatments exist. To identify potential therapeutic targets, this research focuses on viral interactions with host microRNA (miRNA), a class of small, non-coding RNA which bind to messenger RNA (mRNA) to regulate its endpoint proteins. This study demonstrates dependence of both RVFV and VEEV on the host miRNA pathway through different means. RVFV infection induces upregulation of miR-630 and miR-99a, which downregulate the anti-apoptotic protein IGF1R. Inhibition of these miRNA partially rescues IGF1R and decreases viral replication. Conversely, RVFV NSs protein inhibits the anti-apoptotic miR-17-92 cluster, revealing interplay between NSs and miRNA for control of host functions during infection, while overexpression of this cluster reduces viral replication. In contrast, VEEV replication depends heavily on miRNA processing enzymes including Drosha, Exportin 5, and Argonaute 2 (Ago2). Knockdown or inhibition of these enzymes leads to decreased replication and production of viral proteins. The Ago2 inhibitor acriflavine (ACF) reduces VEEV replication in both vaccine and virulent strains by approximately 6-log10 in culture, and is similarly effective against Eastern and Western equine encephalitis viruses. Taken together, these data show the importance of the miRNA pathway for several types of virus, suggesting a fine-tuning function for replication in RVFV and an active use of the pathway itself for VEEV and related Alphaviruses.
