Effect of mdv1-miR-M4 and Related MicroRNAs On Expression of Innate Immune Response Genes In Chicken Embryo Fibroblasts

Abstract

MicroRNAs (miRNAs) have been shown to post-transcriptionally regulate gene expression. Past studies have shown that Marek’s disease virus (MDV) has multiple miRNAs in its genome. MDV1-miR-M4 is a particularly important miRNA found in MDV serotype 1 and this miRNA has been implicated in T cell lymphoma formation caused by MDV. MDV1-miR-M4 shares a seed sequence with miR-155, which is another oncogenic miRNA. MiR-155 is found across phylogeny. We inserted mdv1-miR-M4, the meq miRNA cluster, as well as miR-155 into the genome of herpesvirus of turkeys (HVT) in order to study the functions of these miRNAs since the non-recombinant parent HVT does not express them. The expression levels of interferons (IFNs), including IFN-alpha, IFN-beta, and IFN-lambda were examined post-infection. IFN-alpha and IFN-beta were not induced under the experimental conditions, and IFN-lambda was induced at approximately 48 hours post-infection. We also examined expression of IFN-inducible genes. Expression of the IFNinducible genes MX-1 and OAS-3 was elevated in some instances under the experimental conditions. Expression of MX-1 and OAS-3 is typically type I IFN dependent, but in this case elevation was observed in the absence of induction of IFNalpha and/or IFN-beta. Inhibition of MX-1 and OAS-3 induction by meq miRNAs and miR-155 when compared to infection with parent HVT was seen at 30 minutes, and at 3, 6, 15, 24, and 48 hours post-infection The results suggest that meq miRNAs, including MDV1-miR-M4 and the MDV1-miR-M4 analog, oncogenic miR-155, contribute to inhibition of innate immune responses.