RIPK1 and allies in the battle against hepatocyte apoptosis and liver cancer (original) (raw)
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RIPK1 Suppresses a TRAF2-Dependent Pathway to Liver Cancer
Cancer cell, 2016
Receptor-interacting protein kinase 1 (RIPK1) represents an essential signaling node in cell death and inflammation. Ablation of Ripk1 in liver parenchymal cells (LPC) did not cause a spontaneous phenotype, but led to tumor necrosis factor (TNF)-dependent hepatocyte apoptosis and liver injury without affecting inducible nuclear factor κB (NF-κB) activation. Loss of Ripk1 induced the TNF-dependent proteasomal degradation of the E3-ligase, TNF receptor-associated factor 2 (TRAF2), in a kinase-independent manner, thereby activating caspase-8. Moreover, loss of both Ripk1 and Traf2 in LPC not only resulted in caspase-8 hyperactivation but also impaired NF-κB activation, promoting the spontaneous development of hepatocellular carcinoma. In line, low RIPK1 and TRAF2 expression in human HCCs was associated with an unfavorable prognosis, suggesting that RIPK1 collaborates with TRAF2 to inhibit murine and human hepatocarcinogenesis.
TBK1 and IKKε prevent TNF-induced cell death by RIPK1 phosphorylation
Nature Cell Biology
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-kinaseactivity-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 celldeath checkpoint and uncover an essential survival function for NEMO by enabling recruitment and activation of these noncanonical IKKs to prevent TNF-induced cell death.
F1000 - Post-publication peer review of the biomedical literature, 2019
Stimulation of TNFR1 by TNFα can promote three distinct alternative mechanisms of cell death: necroptosis, RIPK1-independent and-dependent apoptosis. How cells decide which way to die is unclear. Here, we report that TNFα-induced phosphorylation of RIPK1 in the intermediate domain by TAK1 plays a key role in regulating this critical decision. Using phospho-Ser321 as a marker, we show that the transient phosphorylation of RIPK1 intermediate domain induced by TNFα leads to RIPK1-independent apoptosis when NF-κB activation is inhibited by cycloheximide. On the other hand, blocking Ser321 phosphorylation promotes RIPK1 activation and its interaction with FADD to mediate RIPK1-dependent apoptosis (RDA). Finally, sustained phosphorylation of RIPK1 intermediate domain at multiple sites by TAK1 promotes its interaction with RIPK3 and necroptosis. Thus, absent, transient and sustained levels of TAK1-mediated RIPK1 phosphorylation may represent distinct states in TNF-RSC to dictate the activation of three alternative cell death mechanisms, RDA, RIPK1independent apoptosis and necroptosis.
Impaired RIPK1 ubiquitination sensitizes mice to TNF toxicity and inflammatory cell death
Cell Death & Differentiation, 2020
Receptor-interacting protein 1 (RIP1; RIPK1) is a key regulator of multiple signaling pathways that mediate inflammatory responses and cell death. TNF-TNFR1 triggered signaling complex formation, subsequent NF-κB and MAPK activation and induction of cell death involve RIPK1 ubiquitination at several lysine residues including Lys376 and Lys115. Here we show that mutating the ubiquitination site K376 of RIPK1 (K376R) in mice activates cell death resulting in embryonic lethality. In contrast to Ripk1K376R/K376R mice, Ripk1K115R/K115R mice reached adulthood and showed slightly higher responsiveness to TNF-induced death. Cell death observed in Ripk1K376R/K376R embryos relied on RIPK1 kinase activity as administration of RIPK1 inhibitor GNE684 to pregnant heterozygous mice effectively blocked cell death and prolonged survival. Embryonic lethality of Ripk1K376R/K376R mice was prevented by the loss of TNFR1, or by simultaneous deletion of caspase-8 and RIPK3. Interestingly, elimination of t...
Journal of Biological Chemistry, 2004
The death domain kinase Rip1 is recruited to the tumor necrosis factor receptor type 1 and mediates the IB kinase and p38 MAP kinase pathways. In response to tumor necrosis factor-␣ (TNF-␣), we find Rip1 phosphorylated and ubiquitinated, suggesting that Rip1 phosphorylation may stimulate its ubiquitination. To address the contribution of the kinase activity of Rip1 to its ubiquitination and to TNF-␣ signaling, we introduced wild type Rip1 and a kinase-inactive form of Rip1, Rip1D138N, into rip1؊/؊ murine embryonic fibroblast cells by retroviral infection. TNF-␣-induced ubiquitination of Rip1 is observed in Rip1D138N cells, supporting the argument that Rip1 autophosphorylation is not required for Rip1 ubiquitination. TNF-␣-induced Ikk and p38 MAP kinase activation is normal, and the Rip1D138N cells are resistant to TNF-␣-induced cell death, indicating that the kinase activity of Rip1 is not required to mediate its antiapoptotic functions. In the absence of Traf2, TNF-␣-induced ubiquitination of Rip1 is impaired, suggesting that Traf2 may be the E3 ubiquitin ligase responsible for the TNF-␣-dependent, ubiquitination of Rip1. Finally, recruitment of the ubiquitinated Tak1 complex is dependent on the presence of Rip1, suggesting that Rip1 ubiquitination rather than its phosphorylation is critical in signaling.
Holding RIPK1 on the Ubiquitin Leash in TNFR1 Signaling
Trends in Cell Biology, 2016
The Linear Ubiquitin chain Assembly Complex (LUBAC) is required for optimal gene activation and prevention of cell death upon activation of immune receptors, including TNFR1 1. Deficiency in the LUBAC components SHARPIN or HOIP in mice results in severe inflammation in adulthood or embryonic lethality, respectively, due to deregulation of TNFR1-mediated cell death 2-8. In humans, deficiency in the third LUBAC component, HOIL-1, causes autoimmunity and inflammatory disease, similar to HOIP deficiency, whereas HOIL-1 deficiency in mice was reported to cause no overt phenotype 9-11. By creating HOIL-1-deficient mice, we here show that HOIL-1 is, however, as essential for LUBAC function as HOIP, albeit for different reasons: whereas HOIP is LUBAC's catalytically active component, HOIL-1 is required for LUBAC assembly, stability and optimal retention in the TNFR1-signalling complex (TNFR1-SC), thereby preventing aberrant cell death. Both, HOIL-1 and HOIP prevent embryonic lethality at midgestation by interfering with aberrant TNFR1-mediated endothelial cell death, which only partially depends on RIPK1 kinase activity. Co-deletion of Caspase-8 with RIPK3 or MLKL prevents cell death in Hoil-1-/embryos, yet only combined loss of Caspase-8 with MLKL results in viable HOIL-1-deficient mice. Interestingly, Ripk3-/-Caspase-8-/-Hoil-1-/embryos die at lategestation due to haematopoietic defects that are rescued by co-deletion of RIPK1 but not MLKL. Collectively, these results demonstrate that both, HOIP and HOIL-1 are essential LUBAC components and are required for embryogenesis by preventing aberrant cell death. Furthermore, they unveil that, when LUBAC and Caspase-8 are absent, RIPK3 prevents RIPK1 from inducing embryonic lethality by causing defects in foetal haematopoiesis.
RIPK1 protects from TNF-α-mediated liver damage during hepatitis
Cell death & disease, 2016
Cell death of hepatocytes is a prominent characteristic in the pathogenesis of liver disease, while hepatolysis is a starting point of inflammation in hepatitis and loss of hepatic function. However, the precise molecular mechanisms of hepatocyte cell death, the role of the cytokines of hepatic microenvironment and the involvement of intracellular kinases, remain unclear. Tumor necrosis factor alpha (TNF-α) is a key cytokine involved in cell death or survival pathways and the role of RIPK1 has been associated to the TNF-α-dependent signaling pathway. We took advantage of two different deficient mouse lines, the RIPK1 kinase dead knock-in mice (Ripk1(K45A)) and the conditional knockout mice lacking RIPK1 only in liver parenchymal cells (Ripk1(LPC-KO)), to characterize the role of RIPK1 and TNF-α in hepatitis induced by concanavalin A (ConA). Our results show that RIPK1 is dispensable for liver homeostasis under steady-state conditions but in contrast, RIPK1 kinase activity contribute...