Arenavirus Nucleoprotein Targets Interferon Regulatory Factor-Activating Kinase IKKε

Arenaviruses perturb innate antiviral defense by blocking induction of type I interferon (IFN) production. Accordingly, the arenavirus nucleoprotein (NP) was shown to block activation and nuclear translocation of interferon regulatory factor 3 (IRF3) in response to virus infection. Here, we sought to identify cellular factors involved in innate antiviral signaling targeted by arenavirus NP. Consistent with previous studies, infection with the prototypic arenavirus lymphocytic choriomeningitis virus (LCMV) prevented phosphorylation of IRF3 in response to infection with Sendai virus, a strong inducer of the retinoic acid-inducible gene I (RIG-I)/mitochondrial antiviral signaling (MAVS) pathway of innate antiviral signaling. Using a combination of coimmunoprecipitation and confocal microscopy, we found that LCMV NP associates with the I kappa B kinase (IKK)-related kinase IKK epsilon but that, rather unexpectedly, LCMV NP did not bind to the closely related TANK-binding kinase 1 (TBK-1). The NP-IKK epsilon interaction was highly conserved among arenaviruses from different clades. In LCMV-infected cells, IKK epsilon colocalized with NP but not with MAVS located on the outer membrane of mitochondria. LCMV NP bound the kinase domain (KD) of IKK epsilon (IKBKE) and blocked its autocatalytic activity and its ability to phosphorylate IRF3, without undergoing phosphorylation. Together, our data identify IKK epsilon as a novel target of arenavirus NP. Engagement of NP seems to sequester IKK epsilon in an inactive complex. Considering the important functions of IKK epsilon in innate antiviral immunity and other cellular processes, the NP-IKK epsilon interaction likely plays a crucial role in arenavirus-host interaction.