NUDT2 Disruption Elevates Diadenosine Tetraphosphate (Ap(4)A) and Down-Regulates Immune Response and Cancer Promotion Genes

Marriott, Andrew S.; Vasieva, Olga; Fang, Yongxiang; Copeland, Nikki A.; McLennan, Alexander G.; Jones, Nigel J.

The canonical pathway in Fig 5 highlights the roles of the three RIG-1-like helicase PRRs of the innate immune response, RIG-1 (DDX58), MDA5 (IFIH1) and LGP2 (DHX58) in the activation of IFNB following stimulation by viral double-stranded RNAs and the feedback provided by IFNβ on the expression of these PRRs. All three receptor genes are down-regulated (3.1-, 2.3-and 3.0-fold respectively) (S3 Table) in NuKO cells. In addition, IFITM2 and IFITM3, whose products restrict the entry of many viruses [53] , and all four antiviral IFIT family members that bind viral components (IFIT1, 2, 3 and 5) [54] are down-regulated between 1.6-and 6.8-fold. Other down-regulated anti-viral genes include PKR, GBP1 and TLR10 [55-58] (S3 Table) . Cytokine signaling, inflammation and NF-κB. Interleukin-1 (IL-1) signaling is flagged by IPA 1 as a top down-regulated pathway (Table 4 ) with reduced expression of important pro-inflammatory members of the IL-1 superfamily [59] . For example, the mRNAs for IL-1β, its receptor IL-1R1 and accessory protein IL-1RAP are decreased 1.5-, 11.7-and 1.2-fold respectively while IL-18, IL-18R1 and IL-18RAP are down 2.3-, 3.0-and 4.0-fold respectively. Expression of pro-inflammatory IL32 is also reduced 5-fold, while the expression of Tumor Necrosis Factor (TNF or TNFα), which can activate both Type I IFNs and the inflammatory mediator NF-κB, is down-regulated 30-fold (S3 Table) . The canonical pathway leading to transcriptional activation by NF-κB through IL-1, TNFα and other ligands is shown in Fig 6. The NF-κB complex is an important mediator of inflammatory and immune responses and responds to PRRs and pro-inflammatory cytokines [60] . It can synergize with STAT signaling with the increased induction of target genes resulting from coordinate binding of STATs and NF-κB to GAS and NF-κB promoters. The p50 and p52 components of the NF-κB complex and the RELB transactivator are all down-regulated as are many components of signaling pathways that lead to NF-κB activation.