Optineurin negatively regulates the induction of IFNbeta in response to RNA virus infection

"Without Ub I am nothing": NEMO as a multifunctional player in ubiquitin-mediated control of NF-kappaB activation

Ubiquitination has emerged over the years as the most sophisticated way to modify proteins to affect their fate and function. In particular, it has been reported to be instrumental in regulating several steps of the NF-kappaB signalling pathway which controls inflammation, immunity, adhesion and cell survival. Integrating ubiquitination into NF-kappaB activation requires the regulatory subunit of IKK, NEMO, which not only displays affinity for polyubiquitin chains, but is also posttranslationally modified by a complex set of reactions involving ubiquitin. Here, we examine how studies of the NEMO/ubiquitin relationship have provided novel insights into the IKK activation process and have uncovered molecular mechanisms that should represent in the future attractive targets for specifically modulating NF-kappaB function.

Combined agonist-antagonist genome-wide functional screening identifies broadly active antiviral microRNAs

Although the functional parameters of microRNAs (miRNAs) have been explored in some depth, the roles of these molecules in viral infections remain elusive. Here we report a general method for global analysis of miRNA function that compares the significance of both overexpressing and inhibiting each mouse miRNA on the growth properties of different viruses. Our comparative analysis of representatives of all three herpesvirus subfamilies identified host miRNAs with broad anti- and proviral properties which extend to a single-stranded RNA virus. Specifically, we demonstrate the broad antiviral capacity of miR-199a-3p and illustrate that this individual host-encoded miRNA regulates multiple pathways required and/or activated by viruses, including PI3K/AKT and ERK/MAPK signaling, oxidative stress signaling, and prostaglandin synthesis. Global miRNA expression analysis further demonstrated that the miR-199a/miR-214 cluster is down-regulated in both murine and human cytomegalovirus infection and manifests similar antiviral properties in mouse and human cells. Overall, we report a general strategy for examining the contributions of individual host miRNAs in viral infection and provide evidence that these molecules confer broad inhibitory potential against multiple viruses.

TAX1BP1 and A20 inhibit antiviral signaling by targeting TBK1-IKKi kinases

Induction of type I interferons by the transcription factor IRF3 is essential in the initiation of antiviral innate immunity. Activation of IRF3 requires C-terminal phosphorylation by the upstream kinases TBK1-IKKi, where IRF3 phosphorylation promotes dimerization, and subsequent nuclear translocation to the IFNbeta promoter. Recent studies have described the ubiquitin-editing enzyme A20 as a negative regulator of IRF3 signaling by associating with TBK1-IKKi; however, the regulatory mechanism of A20 inhibition remains unclear. Here we describe the adaptor protein, TAX1BP1, as a key regulator of A20 function in terminating signaling to IRF3. Murine embryonic fibroblasts (MEFs) deficient in TAX1BP1 displayed increased amounts of IFNbeta production upon viral challenge compared with WT MEFs. TAX1BP1 inhibited virus-mediated activation of IRF3 at the level of TBK1-IKKi. TAX1BP1 and A20 blocked antiviral signaling by disrupting Lys(63)-linked polyubiquitination of TBK1-IKKi independently of the A20 deubiquitination domain. Furthermore, TAX1BP1 was required for A20 effector function because A20 was defective for the targeting and inactivation of TBK1 and IKKi in Tax1bp1(-)(/)(-) MEFs. Additionally, we found the E3 ubiquitin ligase TRAF3 to play a critical role in promoting TBK1-IKKi ubiquitination. Collectively, our results demonstrate TBK1-IKKi to be novel substrates for A20 and further identify a novel mechanism whereby A20 and TAX1BP1 restrict antiviral signaling by disrupting a TRAF3-TBK1-IKKi signaling complex.