Type I interferons such as interferon-beta (IFN-β) play essential roles in the host innate immune response to herpes simplex virus type I (HSV-1) infection. The transcription of type I interferon genes is controlled by nuclear factor-κB (NF-κB) and interferon regulatory factor (IRF) family members including IRF3. NF-κB activation depends on the phosphorylation of inhibitor of κB (IκB), which triggers its ubiqitination and degradation. It has been reported that neddylation inhibition by a pharmacological agent MLN4924 potently suppresses lipopolysaccharide (LPS)-induced proinflammatory cytokine production with the accumulation of phosphorylated IκBα. However, the role of neddylation in type I interferon expression remains unknown. Here, we report that neddylation inhibition with MLN4924 or upon UBA3 deficiency led to accumulation of phosphorylated IκBα, impaired IκBα degradation, and impaired NF-κB nuclear translocation in the early phase of HSV-1 infection even though phosphorylation and nuclear translocation of IRF3 were not affected. The blockade of NF-κB nuclear translocation by neddylation inhibition becomes less efficient at the later time points of HSV-1 infection. Consequently, HSV-1-induced early phase IFN-β production significantly decreased upon MLN4924 treatment and UBA3 deficiency. NF-κB inhibitor JSH-23 mimicked the effects of neddylation inhibition in the early phase of HSV-1 infection. Moreover, the effects of neddylation inhibition on HSV-1-induced early phase IFN-β production diminished in the presence of NF-κB inhibitor JSH-23. Thus, neddylation contributes to HSV-1-induced early phase IFN-β production through, at least partially, promoting NF-κB activation.

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Neddylation, an important type of post-translational modification, has been implicated in innate and adapted immunity. But the role of neddylation in innate immune response against RNA viruses remains elusive. Here we report that neddylation promotes RNA virus-induced type I IFN production, especially IFN-α. More importantly, myeloid deficiency of UBA3 or NEDD8 renders mice less resistant to RNA virus infection. Neddylation is essential for RNA virus-triggered activation of Ifna gene promoters. Further exploration has revealed that mammalian IRF7undergoes neddylation, which is enhanced after RNA virus infection. Even though neddylation blockade does not hinder RNA virus-triggered IRF7 expression, IRF7 mutant defective in neddylation exhibits reduced ability to activate Ifna gene promoters. Neddylation blockade impedes RNA virus-induced IRF7 nuclear translocation without hindering its phosphorylation and dimerization with IRF3. By contrast, IRF7 mutant defective in neddylation shows enhanced dimerization with IRF5, an Ifna repressor when interacting with IRF7. In conclusion, our data demonstrate that myeloid neddylation contributes to host anti-viral innate immunity through targeting IRF7 and promoting its transcriptional activity.

Abstract. Neddylation is a ubiquitination-like pathway. It has been reported that neddylation inhibition with the pharmacological agent MLN4924 potently uppresses lipopolysaccharide (LPS)-induced proinflammatory cytokine production, including tumor necrosis factor (TNF)-α and interleukin (IL)-6, by preventing the degradation of phosphorylated inhibitor of κB (p-IκB) in macrophages. However, whether neddylation serves a similar role in neutrophils remains unknown. In the present study MLN4924 treatment led to the accumulation of P-IκBα in neutrophils as well as the decreased production of TNF-α, IL-6 and IL-1β in response to LPS, in a dose-dependent manner. The viability of neutrophils was only marginally affected in the same conditions, without statistical significance. Furthermore, the nuclear factor (NF)-κB inhibitor JSH-23 mimicked the effects of MLN4924 in neutrophils, and the inhibitory effects of MLN4924 on LPS-induced proinflammatory cytokine production diminished in the presence of JSH-23. Thus, the results of the present study suggest that neddylation inhibition suppresses neutrophil function by suppressing the NF-κB signaling pathway. IntroductionNeutrophils serve crucial roles in the anti-bacterial and anti-fungal innate immune response and produce cytokines to initiate inflammatory responses; however, their inappropriate or excessive activation contributes to tissue damage during autoimmune and inflammatory diseases (1). Furthermore, the activity of neutrophils is associated with tumor progression, as demonstrated in colitis-associated cancer and glioblastoma (2,3).Previous studies have revealed that in order to protect the human body from invading pathogens and endogenous damage-associated molecules, neutrophils sense these threats through innate immune receptors, such as toll-like receptors (TLRs) and other pattern recognition receptors, to upregulate the secretion of inflammatory cytokines (4,5). The recognition of lipopolysaccharide (LPS) from gram-negative bacteria by TLR4 is a well-characterized example with the initiation of proinflammatory gene transcription through multiple signaling pathways, including nuclear factor (NF)-κB) (6,7). The exposure of neutrophils to bacterial LPS may contribute to tissue damage, under certain conditions, including endotoxic shock and infection-induced adult respiratory distress syndrome (8).Neddylation is a novel-type protein post-translational modification, a multistep enzymatic process that adds the ubiquitin-like molecule neural precursor cell expressed developmentally downregulated protein 8 (Nedd8) to target proteins in an ATP-dependent manner. Neddylation is vital for a range of processes, including cell viability, growth and development (9-12). To the best of our knowledge, the only known E1 for neddylation is a heterodimer comprised of the amyloid precursor protein-binding protein and ubiquitin-like modifier activating enzyme 3 (9-12). A previous study identified the ubiquitin-conjugating enzymes Ube2M and Ube2F as Nedd8 E2s (13). Several targets for N...

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