A novel IRAK1–IKKε signaling axis limits the activation of TAK1–IKKβ downstream of TLR3

D Bruni, J Sebastia, S Dunne, M Schröder… - The Journal of …, 2013 - journals.aai.org
D Bruni, J Sebastia, S Dunne, M Schröder, MP Butler
The Journal of Immunology, 2013journals.aai.org
IRAK1 is involved in the regulation of type I IFN production downstream of TLR3. Previous
work indicated that IRAK1 negatively regulates TRIF-mediated activation of IRF3 and IRF7.
We report that IRAK1 limits the activation of the TLR3–NF-κB pathway. Following TLR3
stimulation, IRAK1-deficient macrophages produced increased levels of IL-6 and IFN-β
compared with wild type macrophages. Pharmacological inhibition of TAK1 reduced this
increase in IFN-β, together with the heightened activation of IRF3 and p65 found in TLR3 …
Abstract
IRAK1 is involved in the regulation of type I IFN production downstream of TLR3. Previous work indicated that IRAK1 negatively regulates TRIF-mediated activation of IRF3 and IRF7. We report that IRAK1 limits the activation of the TLR3–NF-κB pathway. Following TLR3 stimulation, IRAK1-deficient macrophages produced increased levels of IL-6 and IFN-β compared with wild type macrophages. Pharmacological inhibition of TAK1 reduced this increase in IFN-β, together with the heightened activation of IRF3 and p65 found in TLR3-ligand stimulated IRAK1-deficient macrophages. Recently, IKKε and TANK-binding kinase 1 (TBK1) were reported to limit activation of the NF-κB pathway downstream of IL-1R, TNFR1, and TLRs. We show that TBK1 has a positive role in the TLR3–NF-κB pathway, because we detected reduced levels of IL-6 and reduced activation of p65 in TBK1-deficient macrophages. In contrast, we show that IKKε limits the activation of the TLR3–NF-κB pathway. Furthermore, we show that IRAK1 is required for the activation of IKKε downstream of TLR3. We report impaired activation of ERK1/2 in IRAK1–and IKKε-deficient macrophages, a novel finding for both kinases. Importantly, this work provides novel mechanistic insight into the regulation of the TLR3-signaling pathway, providing strong evidence that an IRAK1-IKKε–signaling axis acts to limit the production of both type I IFNs and proinflammatory cytokines by regulating TAK1 activity.
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