Lipopolysaccharide-mediated interferon regulatory factor activation involves TBK1-IKKε-dependent lys63-linked polyubiquitination and phosphorylation of TANK/I-TRAF

Abstract

Type I interferon gene induction relies on IKK-related kinase TBK1 and IKKε-mediated phosphorylations of IRF3/7 through the Toll-like receptor-dependent signaling pathways. The scaffold proteins that assemble these kinase complexes are poorly characterized. We show here that TANK/ITRAF is required for the TBK1- and IKKε-mediated IRF3/7 phosphorylations through some Toll-like receptor-dependent pathways and is part of a TRAF3-containing complex. Moreover, TANK is dispensable for the early phase of double-stranded RNA-mediated IRF3 phosphorylation. Interestingly, TANK is heavily phosphorylated by TBK1-IKKε upon lipopolysaccharide stimulation and is also subject to lipopolysaccharide-and TBK1-IKKε-mediated Lys63-linked polyubiquitination, a mechanism that does not require TBK1-IKKε kinase activity. Thus, we have identified TANK as a scaffold protein that assembles some but not all IRF3/7-phosphorylating TBK1-IKKε complexes and demonstrated that these kinases possess two functions, namely the phosphorylation of both IRF3/7 and TANK as well as the recruitment of an E3 ligase for Lys63-linked polyubiquitination of their scaffold protein, TANK.