Expression of proinflammatory cytokines as well as type I interferons (IFNs) in response to viral and microbial stimuli is regulated by a number of key transcription factors, including NF-κB and interferon regulatory factors (IRFs) [[14]]. Previous studies have established a cross-talk between the NF-κB BVD-523 purchase activation pathway and FOXO3: FOXO3 can antagonize NF-κB via yet-to-be-fully-understood mechanisms and thereby regulate cytokine production [[15]]. On the other hand, IKK-α and IKK-β, two important kinases involved in NF-κB activation, are able to phosphorylate and inactivate FOXO3 in response to stimulation with

TNF-α [[16]]. IKK-ε, an IKK-related kinase involved in Toll-like receptor (TLR) 3/4-mediated antiviral and antibacterial responses and key for type I IFN production [[17-19]], was recently identified as an oncogene in breast and prostate cancers [[20, 21]]. Interestingly, its overexpression in a breast cancer model system could functionally replace PI3K constitutive activation and prevent cell-cycle arrest and apoptosis see more [[20]], processes often mediated by FOXO3

target genes, such as Cyclin D, p27/KIP1, FasL, bim [[2]]. Based on the homology of IKK-ε and IKK-β, we hypothesized that IKK-ε may regulate FOXO3 protein activity and thereby influence the expression of cell-cycle arrest- and apoptosis-related genes. Here, Thalidomide we demonstrate that IKK-ε is indeed able to interact with and phosphorylate FOXO3, resulting in its inactivation and nuclear exclusion. Conversely, FOXO3 itself is able to antagonize the activity of NF-κB and IRFs, and thus its inactivation in response to microbial stimuli is essential for efficient IFN-β expression. These findings further our knowledge of cross-talks between immune

and cell survival signaling pathways and highlight a new role for FOXO3 in controlling the innate immune response. To test whether IKK-ε may influence the expression of FOXO3-target genes, we examined the effect of ectopically expressed IKK-ε on activity of a luciferase-reporter construct driven by the promoter of a known FOXO3 target gene p27, a member of the cyclin-dependent kinase inhibitor family [[22]]. As expected, the luciferase-reporter activity was strongly induced by FOXO3, but expression of IKK-ε resulted in its complete abrogation (Fig. 1A). The dominant negative mutant of IKK-ε bearing a mutation in the kinase domain (IKK-ε-KA) had no effect (Fig. 1A). AKT was recently demonstrated to be a direct target of the TBK1/IKK-ε complex [[23]].