Constitutive activation of the transcription factor NF-kappa B results in impaired Borna disease virus replication

The inducible transcription factor NF-kappa B is commonly activated upon RNA virus infection and is a key player in the induction and regulation of the innate immune response. Borna disease virus (BDV) is a neurotropic negative-strand RNA virus, which replicates in the nucleus of the infected cell and causes a persistent infection that can lead to severe neurological disorders. To investigate the activation and function of NF-kappa B in BDV-infected cells, we stably transfected the highly susceptible neuronal guinea pig cell line CRL with a constitutively active (IKK EE) or dominant-negative (IKK KD) regulator of the IKK/NF-kappa B signaling pathway. While BDV titers were not affected in cells with impaired NF-kappa B signaling, the expression of an activated mutant Of I kappa B kinase (IKK) resulted in a strong reduction in the intracellular viral titer in CRL cells. Electrophoretic mobility shift assays and luciferase reporter gene assays revealed that neither NF-kappa B nor interferon regulatory factors (IRFs) were activated upon acute BDV infection of wild-type or vector-transfected CRL cells. However, when IKK EE-transfected cells were used as target cells for BDV infection, DNA binding to an IRF3/7-responsive DNA element was detectable. Since IRF3/7 is a key player in the antiviral interferon response, our data indicate that enhanced NF-kappa B activity in the presence of BDV leads to the induction of antiviral pathways resulting in reduced virus titers. Consistent with this observation, the anti-BDV activity of NF-kappa B preferentially spread to areas of the brains of infected rats where activated NF-kappa B was not detectable