Japanese Encephalitis Virus Utilizes the Canonical Pathway To Activate NF-κB but It Utilizes the Type I Interferon Pathway To Induce Major Histocompatibility Complex Class I Expression in Mouse Embryonic Fibroblasts

Abstract

ABSTRACT Flaviviruses have been shown to induce cell surface expression of major histocompatibility complex class I (MHC-I) through the activation of NF-κB. Using IKK1 −/− , IKK2 −/− , NEMO −/− , and IKK1 −/− IKK2 −/− double mutant as well as p50 −/− RelA −/− cRel −/− triple mutant mouse embryonic fibroblasts infected with Japanese encephalitis virus (JEV), we show that this flavivirus utilizes the canonical pathway to activate NF-κB in an IKK2- and NEMO-, but not IKK1-, dependent manner. NF-κB DNA binding activity induced upon virus infection was shown to be composed of RelA:p50 dimers in these fibroblasts. Type I interferon (IFN) production was significantly decreased but not completely abolished upon virus infection in cells defective in NF-κB activation. In contrast, induction of classical MHC-I (class 1a) genes and their cell surface expression remained unaffected in these NF-κB-defective cells. However, MHC-I induction was impaired in IFNAR −/− cells that lack the alpha/beta IFN receptor, indicating a dominant role of type I IFNs but not NF-κB for the induction of MHC-I molecules by Japanese encephalitis virus. Our further analysis revealed that the residual type I IFN signaling in NF-κB-deficient cells is sufficient to drive MHC-I gene expression upon virus infection in mouse embryonic fibroblasts. However, NF-κB could indirectly regulate MHC-I expression, since JEV-induced type I IFN expression was found to be critically dependent on it.