Arenavirus Nucleoprotein Targets Interferon Regulatory

Arenaviruses perturb innate antiviral defense by blocking induction of type I interferon (IFN) production. Accordingly, the are-navirus 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 arenavi-rus 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 coimmu-noprecipitation and confocal microscopy, we found that LCMVNP associates with the IB kinase (IKK)-related kinase IKK but that, rather unexpectedly, LCMVNP did not bind to the closely related TANK-binding kinase 1 (TBK-1). The NP-IKK interac-tion was highly conserved among arenaviruses from different clades. In LCMV-infected cells, IKK colocalized with NP but not withMAVS located on the outer membrane of mitochondria. LCMVNP bound the kinase domain (KD) of IKK (IKBKE) and blocked its autocatalytic activity and its ability to phosphorylate IRF3, without undergoing phosphorylation. Together, our data identify IKK as a novel target of arenavirus NP. Engagement of NP seems to sequester IKK in an inactive complex. Consider-ing the important functions of IKK in innate antiviral immunity and other cellular processes, the NP-IKK interaction likely plays a crucial role in arenavirus-host interaction. Arenaviruses are a large and diverse family of viruses of rele-vance as both powerfulmodel systems for experimental virol