Here, we report a novel role in immune response control via modulation of the IKK-ε/IRF/IFN-β

pathway. We demonstrate that FOXO3 is capable of inhibiting the LPS-induced production of IFN-β by Veliparib order blocking the activity of NF-κB and/or IRF transcription factors at its promoter. However, in human MDDCs, IFN-β is released of this inhibition by a mechanism which at least partially depends on IKK-ε, which interacts with, phosphorylates and inactivates FOXO3. Thus, our results provide new insight into the role of FOXO3 in inflammation by its effects on DC functions. DCs are key immune cells that control both the initiation and regulation of the immune response. In response to various stimuli, including TLR induction by microbial and viral pathogen, DCs produce proinflammatory cytokines and type I IFNs [[30]]. FOXO3 was previously reported to participate in the regulation of proinflammatory cytokine production in DCs and endothelial cells [10, 29, 31]. Here, we discover that FOXO3 also has the ability to inhibit IFN-β production in human MDDCs. Seen as a “danger” molecule to signal the presence of a wide range of pathogen, IFN-β is particularly well described for its antiviral Doramapimod in vivo activities [[30]]. In addition, our data suggest that FOXO3 could also inhibit IFN-λ1 transcription, a type III IFN also involved in innate antiviral immunity [[32]]. Thus, it is possible that FOXO3 may play a larger role

in controlling antiviral activity of DCs than originally suspected, but the physiological relevance of this inhibitory effect remains to be demonstrated. IFN-β production in response to TLR3/4 stimulation is initiated through the coordinated activation of a set of transcription factors including NF-κB and IRFs [[30, 33]]. Our results suggest that FOXO3 may affect expression of IFN-β via inhibition of both transcription factors.

FOXO3 was previously reported to inhibit NF-κB activation, but mechanism responsible for this effect remains unclear. One of the suggested mechanisms of NF-κB inhibition is upregulation of IκB expression directly or indirectly Urease [[15, 29]], but this is believed to be cell-type-dependent mechanism [[10, 11]]. Another direct physical interaction, which could prevent NF-κB from either entering the nucleus or, as demonstrated for FOXO4, or its binding to the DNA [[11, 15]]. Our data do not support the hypothesis that FOXO3 blocks nuclear translocation of NF-κB (Supporting Information Fig. 7A), but we confirm that FOXO3 can physically interact with p65/RelA, as well as with IRF3 (Supporting Information Fig. 7B). Of interest, most of the genes involved in proliferation and the cell-cycle regulation that are downregulated by FOXO3, are not dependent on FOXO3 interactions with DNA but rather on its protein–protein interaction [[31]] with transcription factors like p53 and β-catenin [[34]].