Polyubiquitin Binding to Optineurin Is Required for Optimal Activation of TANK-binding Kinase 1 and Production of Interferon β

TANK-binding kinase (TBK1) is essential for transcription of the interferon (IFN) beta gene in response to lipopolysaccharide (LPS) and double-stranded RNA, but the molecular mechanisms that underlie the activation of TBK1 are incompletely understood. Previously, we identified the NF-kappa B essential modulator (NEMO)-related polyubiquitin-binding protein, optineurin (OPTN), as a novel binding partner of TBK1. To determine whether the ubiquitin-binding function of OPTN is involved in regulating TBK1 and IFN beta production, we generated a mouse in which wild-type optineurin was replaced by the polyubiquitin binding-defective mutant, OPTND477N/D477N. In this study, we found that LPS or poly(I:C)-induced TBK1 activity was significantly reduced in bone marrow-derived macrophage (BMDM) from OPTND477N/D477N mice. Consistent with this, the phosphorylation of IFN regulatory factor 3 (IRF3) and the production of IFN beta mRNA and secretion were reduced. Stimulation of BMDMs with LPS triggered the phosphorylation of OPTN, which was reversed by phosphatase treatment and prevented by pharmacological inhibition of both the canonical I kappa B kinases (IKK alpha/beta) and the IKK-related kinases (TBK1/IKK epsilon). In contrast, LPS-stimulated phosphorylation of OPTN(D477N) was markedly reduced in BMDMs from OPTND477N/D477N mice, and inhibition of the canonical IKKs alone prevented phosphorylation, providing further evidence that ubiquitin binding to OPTN contributes to LPS-induced TBK1 activation. TBK1 and IKK beta phosphorylated OPTN preferentially at Ser-177 and Ser-513, respectively, in vitro. In conclusion, our results suggest that OPTN binds to polyubiquity-lated species formed in response to LPS and poly(I:C), enhancing the activation of TBK1 that is required for optimal phosphorylation of IRF3 and production of IFN beta.