Ovine herpesvirus-2-encoded microRNAs target virus genes involved in virus latency

Abstract

The Roslin Institute & Royal (Dick) School of Veterinary Studies, University of Edinburgh, Easter Bush Veterinary Campus, Roslin, Midlothian EH25 9RG, UK Herpesviruses encode microRNAs (miRNAs) that target both virus and host genes; however, their role in herpesvirus biology is understood poorly. We identified previously eight miRNAs encoded by ovine herpesvirus-2 (OvHV-2), the causative agent of malignant catarrhal fever (MCF), and have now investigated the role of these miRNAs in regulating expression of OvHV-2 genes that play important roles in virus biology. ORF20 (cell cycle inhibition), ORF50 (reactivation) and ORF73 (latency maintenance) each contain predicted targets for several OvHV-2 miRNAs. Cotransfection of miRNA mimics with luciferase reporter constructs containing the predicted targets showed the 59 UTRs of ORF20 and ORF73 contain functional targets for ovhv-miR-2 and ovhv2-miR-8, respectively, and the 39 UTR of ORF50 contains a functional target for ovhv2-miR-5. Transfection of BJ1035 cells (an OvHV-2-infected bovine T-cell line) with the relevant miRNA mimic resulted in a significant decrease in ORF50 and a smaller but non-significant decrease in ORF20. However, we were unable to demonstrate a decrease in ORF73. MCF is a disease of dysregulated lymphocyte proliferation; miRNA inhibition of ORF20 expression may play a role in this aberrant lymphocyte proliferation. The proteins encoded by ORF50 and ORF73 play opposing roles in latency. It has been hypothesized that miRNA-induced inhibition of virus genes acts to ensure that fluctuations in virus mRNA levels do not result in reactivation under conditions that are unfavourable for viral replication and our data supported this hypothesis.

MicroRNAs in large herpesvirus DNA genomes: recent advances

“…Indeed, some of these miRNAs are able to target several immediate-early transactivators to lytic replication. Examples include EBV miR BART20-5p (46), ovine herpesvirus 2 (OvHV-2) miR-5 (47), and KSHV miRNAs miR-K1 (48), miR-K9* (49), miR-K5 (50) and miR-K7-5p (51), which have been shown to target reactivation transactivator (RTA) transcripts and thus promote latency. Similarly, herpesvirus simplex 1 (HSV-1) miR-H2 has been shown to target the HSV-1 functional equivalent of RTA, called ICP0, thus preventing reactivation (52).…”

Viruses and miRNAs: More Friends than Foes

“…Likewise, the ovine herpesvirus v-miRNA, OvHV-2-miR-5, targets ORF50 mRNA and maintains latency (Riaz et al, 2014). A v-miRNA-dependent strategy is also employed by HSV-1, which encodes miR-H2-3p that directly targets latency-associated transcripts, including the viral immediate early gene transactivator (Umbach et al, 2008).…”

Viral and Host Strategies for Regulation of Latency and Reactivation in Equid Herpesviruses

“…Authors demonstrated that inhibition of miRNA K12-9 causes reactivation from latent infection. The control of lytic-latent infection by miRNA has been found evolutionary conserved among all the herpesvirus subfamilies (Riaz et al, 2014). Together with restricting acute replication, regulation of cellular gene expression is equally important for establishment and maintenance of latency.…”