Overexpression of microRNA gga-miR-21 in chicken fibroblasts suppresses replication of infectious bursal disease virus through inhibiting VP1 translation.

Previously we have identified a series of cellular miRNA molecules up- or down-regulated in infectious bursal disease virus (IBDV) infected chicken embryo fibroblasts and Bursa of Fabricius with gene microarray analysis. Here we studied in detail a relatively well studied miRNA, gga-miR-21, for better understanding miRNAs involvement in IBDV-host interactions. Chicken pri-gga-miRNA-21 and a control miRNA Caenorhabditis elegans pri-cel-lin-4 gene were cloned into a lentiviral vector, respectively. The resulting recombinant lentiviruses were used to infect chicken fibroblast cell line DF-1, and two stable cell lines, DF-miR-21 (overexpressing gga-miR-21) and DF-lin-4 (overexpressing cel-lin-4), were selected. Replication of IBDV in DF-miR-21, DF-lin-4 and DF-1 cells were compared and molecular mechanism of IBDV replication alteration was explored using bioinformatics, reporter gene system, qRT-PCR and Western blot analysis. IBDV replication was markedly lower in DF-miR-21 than in DF-lin-4 or DF-1 cells. A gga-miR-21 target sequence was identified within IBDV VP1 gene (1713-1734bp). Fusion of a 520nt long partial IBDV VP1 gene containing the target with a luciferase gene resulted in significantly lower transient luciferase activity in DF-miR-21 cells as compared to that in DF-lin-4 or DF-1 cell. Following IBDV infection of the cell lines, VP1 protein level in DF-miR-21 cells was dramatically lower than that in DF-lin-4 or DF-1 cells but VP1 mRNA level was not different. The finding indicated that gga-miR-21 could suppress IBDV replication through down regulating IBDV VP1 expression at translational level.