A novel role of classical swine fever virus E(rns) glycoprotein in counteracting the newcastle disease virus (NDV)-mediated IFN-beta Induction

E(rns) is an envelope glycoprotein of classical swine fever virus (CSFV) and has an unusual feature of RNase activity. In the present study, we demonstrate that E(rns) counteracts Newcastle disease virus (NDV)-mediated induction of IFN-beta. For this purpose, E(rns) fused to the enhanced green fluorescent protein (EGFP) was transiently expressed in porcine kidney 15 (PK15) cells. In luciferase activity assay, E(rns)-EGFP was found to prevent IFN-beta promoter-driven luciferase expression and block the induction of IFN-beta promoter mediated by NDV in a dosedependent manner. Through IFN-specific semi-quantitative RT-PCR detection, obvious decrease of IFN-beta mRNA in NDV-infected PK15 cells was observed in the presence of E(rns)-EGFP. In contrast, EGFP alone showed none of this block capacity. In addition, E(rns)-EGFP mutations with RNase inactivation were also found to block NDV-mediated induction of IFN-beta. These evidences establish a novel function for CSFV E(rns) glycoprotein in counteraction of the IFN-beta induction pathway.