TBK1 and IKKε prevent TNF-induced cell death by RIPK1 phosphorylation

Abstract

LUBAC modulates signalling by various immune receptors. In TNF signalling, linear (also known as M1) ubiquitin enables full gene-activation and prevents cell death. However, the mechanisms underlying cell-death prevention remain ill-defined. We show that LUBAC activity enables TBK1 and IKKε recruitment to and activation at the TNFR1-signalling complex (TNFR1-SC). Whilst exerting only limited effects on TNF-induced gene-activation, TBK1/IKKε are essential to prevent TNF-induced cell death. Mechanistically, TBK1/IKKε phosphorylate RIPK1 in the TNFR1-SC, thereby preventing RIPK1-kinase-activity-dependent cell death. This activity is essential in vivo , as it prevents TNF-induced lethal shock. Strikingly, NEMO/IKKγ, which mostly, but not exclusively, binds to the TNFR1-SC via M1-ubiquitin, mediates recruitment of the adaptors TANK and NAP1/AZI2 which are constitutively associated with TBK1/IKKε and TBK1, respectively. We here discover a previously unrecognised TBK1/IKKε-mediated cell-death checkpoint and uncover an essential survival function for NEMO by enabling recruitment and activation of these noncanonical IKKs to prevent TNF-induced cell death.

3‐O‐acetylrubianol C (3AR‐C) induces RIPK1‐dependent programmed cell death by selective inhibition of IKKβ

“…In complex‐I, ligation of TNFR1 induces various types of RIPK1 ubiquitination, which plays an essential role in recruiting the IKKs (IKKα/β/NEMO) and subsequent transcriptional induction of NF‐κB‐dependent pro‐survival genes including c‐FLIP, A20, and cIAP2 . In addition, transient phosphorylation of RIPK1 at Ser 25 by IKKs prevents its dissociation from complex‐I, and suppresses its Ser 166 ‐autophosphorylation‐dependent association with FADD to initiate formation of complex‐II/necrosome which functions as transcription‐independent players in TNF‐induced cell death . The kinase activity of RIPK1 is required for activation of RIPK3 that plays an essential role in necroptosis induction .…”

“…[6][7][8]48 In addition, transient phosphorylation of RIPK1 at Ser 25 by IKKs prevents its dissociation from complex-I, and suppresses its Ser 166 -autophosphorylationdependent association with FADD to initiate formation of complex-II/necrosome which functions as transcription-independent players in TNF-induced cell death. 18,22,49,50 The kinase activity of RIPK1 is required for activation of RIPK3 that plays an essential role in necroptosis induction. 14,15 Thus, discovery of small molecules regulating RIPK1 phosphorylation provides a basic research tool and substantiates the overall importance of early cell death checkpoint controlling apoptosis and necroptosis.…”

Dual TBK1/IKKɛ inhibitor amlexanox attenuates the severity of hepatotoxin‐induced liver fibrosis and biliary fibrosis in mice

“…Based on a previous study showing that 100 mg/kg amlexanox was no side effect to experimental mouse, 22 different doses of amlexanox (25,50, and 100 mg/kg) were used in our in vivo experiments. To induce hepatotoxin-mediated liver fibrosis, CCl 4 (Sigma-Aldrich; CCl 4 , 2:5 v/v in corn oil) or same volume of corn oil (Sigma-Aldrich) were administered intraperitoneally (i.p.)…”

“…46,47 In line with these findings, treatment of amlexanox sig- On the contrary, STAT3 in hepatocyte exerts hepatoprotective effects through enhancing proliferation of hepatocytes in livers with persistent damage and fibrosis. 50 Therefore, cell type-specific role of TBK1 and IKKε needs to be further determined the relationship between these two kinases and liver fibrosis. 50 Therefore, cell type-specific role of TBK1 and IKKε needs to be further determined the relationship between these two kinases and liver fibrosis.…”

“…Meanwhile, these mice were orally administered with vehicle or amlexanox(25,50, and 100 mg/kg) daily. Mice were i.p.…”