Identification of TBK1 complexes required for the phosphorylation of IRF3 and the production of interferon β

The double-stranded RNA mimetic poly(I:C) and LPS activate Toll-like Receptor 3 (TLR3) and TLR4, respectively, triggering the activation of TANK- Binding Kinase 1 (TBK1) complexes, the phosphorylation of Interferon Regulatory Factor 3 (IRF3) and transcription of the Interferon β (IFNβ) gene. Here, we demonstrate that the TANK-TBK1 and Optineurin (OPTN)-TBK1 complexes control this pathway. The poly(I:C)- or LPS-stimulated phosphorylation of IRF3 at Ser396 and production of IFNβ were greatly reduced in bone-marrow-derived macrophages (BMDM) from TANK knock-out (KO) mice crossed to knock-in mice-expressing the ubiquitin-binding-defective OPTN[D477N] mutant. In contrast, IRF3 phosphorylation and IFN production were not reduced significantly in BMDM from OPTN[D477N] knock-in mice and only reduced partially in TANK KO BMDM. The TLR3/TLR4-dependent phosphorylation of IRF3 and IFNβ gene transcription was not decreased in macrophages from OPTN[D477N] crossed to mice deficient in IκB kinase ε (IKKε), a TANK-binding kinase related to TBK1. In contrast to the OPTN-TBK1 complex, TBK1 associated with OPTN[D477N] did not undergo phosphorylation at Ser172 in response to poly(I:C) or LPS, indicating that the interaction of ubiquitin chains with OPTN is required to activate OPTN-TBK1 in BMDM. The phosphorylation of IRF3 and IFNβ production induced by Sendai virus infection was unimpaired in BMDM from TANK KO x OPTN[D477N] mice, suggesting that other/additional TBK1 complexes control the RIG-I-Like Receptor-dependent production of IFNβ. Finally, we present evidence that in human HACAT cells the poly(I:C)-dependentphosphorylation of TBK1 at Ser172 involves a novel TBK1-activating kinase(s).