Myeloid TAKI [corrected] acts as a negative regulator of the LPS response and mediates resistance to endotoxemia

IL-1β turnover by the UBE2L3 ubiquitin conjugating enzyme and HECT E3 ligases limits inflammation

The cytokine interleukin-1β (IL-1β) has pivotal roles in antimicrobial immunity, but also incites inflammatory disease. Bioactive IL-1β is released following proteolytic maturation of the pro-IL-1β precursor by caspase-1. UBE2L3, a ubiquitin conjugating enzyme, promotes pro-IL-1β ubiquitylation and proteasomal disposal. However, actions of UBE2L3 in vivo and its ubiquitin ligase partners in this process are unknown. Here we report that deletion of Ube2l3 in mice reduces pro-IL-1β turnover in macrophages, leading to excessive mature IL-1β production, neutrophilic inflammation and disease following inflammasome activation. An unbiased RNAi screen identified TRIP12 and AREL1 E3 ligases of the Homologous to E6 C-terminus (HECT) family in adding destabilising K27-, K29- and K33- poly-ubiquitin chains on pro-IL-1β. We show that precursor abundance determines mature IL-1β production, and UBE2L3, TRIP12 and AREL1 limit inflammation by shrinking the cellular pool of pro-IL-1β. Our study uncovers fundamental processes governing IL-1β homeostasis and provides molecular insights that could be exploited to mitigate its adverse actions in disease.

TAK1 protein kinase activity is required for TLR signalling and cytokine production in myeloid cells

A conditional knock-in mouse was generated in which the TAK1 catalytic subunit was largely replaced by the kinase-inactive TAK1[D175A] mutant in immune cells. The activation of p38α MAP kinase, c-Jun N-terminal kinases 1 and 2 (JNK1/2) and the canonical IKK complex induced by stimulation with several TLR-activating ligands was reduced in bone marrow-derived macrophages (BMDM) from TAK1[D175A] mice. TLR signalling in TAK1[D175A] BMDM was catalysed by the residual wild-type TAK1 in these cells because it was abolished by either of two structurally unrelated TAK1 inhibitors (NG25 and 5Z-7-oxozeaenol) whose off-target effects do not overlap. The secretion of inflammatory mediators and production of the mRNAs encoding these cytokines induced by TLR ligation was greatly reduced in peritoneal neutrophils or BMDM from TAK1[D175A] mice. The Pam3CSK4- or LPS-stimulated activation of MAP kinases and the canonical IKK complex, as well as cytokine secretion, was also abolished in TAK1 knock-out human THP1 monocytes or macrophages. The results establish that TAK1 protein kinase activity is required for TLR-dependent signalling and cytokine secretion in myeloid cells from mice. We discuss possible reasons why other investigators, studying myeloid mice with a conditional knock-out of TAK1 or a different conditional kinase-inactive knock-in of TAK1, reported TAK1 to be a negative regulator of LPS-signalling and cytokine production in mouse macrophages and neutrophils.

ZBP1 and TAK1: Master Regulators of NLRP3 Inflammasome/Pyroptosis, Apoptosis, and Necroptosis (PAN-optosis)

Cell death is central to development, organismal homeostasis, and immune responses. The cell death field has experienced tremendous progress by delineating the molecular programs specific to each of the apoptotic and inflammatory cell death pathways. Moreover, the discovery of the inflammasomes and pyroptosis and necroptosis pathway regulators have provided the genetic basis for the programmed inflammatory cell death pathways. Earlier research highlighted the unique regulation of each of these pathways, but emerging studies discovered co-regulation and crosstalk between these seemingly different cell death complexes. The progress in this area has led to an idea that master regulators play central roles in orchestrating multiple cell death pathways. Here, we provide a brief review of the master regulators, the innate immune sensor ZBP1 and the essential cell survival kinase TAK1, that play vital roles in the regulation of RIPK1/RIPK3-FADD-caspase-8 cell death complex assembly and its versatility in executing Pyroptosis, Apoptosis, and Necroptosis, which we dubbed here as PAN-optosis. Furthermore, we discuss the implications and therapeutic potential of targeting these master regulators in health and disease.

One Sentence Summary

ZBP1 and TAK1 regulate PAN-optosis.

RIPK1 and death receptor signaling drive biliary damage and early liver tumorigenesis in mice with chronic hepatobiliary injury

Hepatocyte apoptosis is intrinsically linked to chronic liver disease and hepatocarcinogenesis. Conversely, necroptosis of hepatocytes and other liver cell types and its relevance for liver disease is debated. Using liver parenchymal cell (LPC)-specific TGF-beta-activated kinase 1 (TAK1)-deficient (TAK1^LPC-KO) mice, which exhibit spontaneous hepatocellular and biliary damage, hepatitis, and early hepatocarcinogenesis, we have investigated the contribution of apoptosis and necroptosis in hepatocyte and cholangiocyte death and their impact on liver disease progression. Here, we provide in vivo evidence showing that TAK1-deficient cholangiocytes undergo spontaneous necroptosis induced primarily by TNFR1 and dependent on RIPK1 kinase activity, RIPK3, and NEMO. In contrast, TAK1-deficient hepatocytes die by FADD-dependent apoptosis, which is not significantly inhibited by LPC-specific RIPK1 deficiency, inhibition of RIPK1 kinase activity, RIPK3 deficiency or combined LPC-specific deletion of TNFR1, TRAILR, and Fas. Accordingly, normal mouse cholangiocytes can undergo necroptosis, while primary hepatocytes are resistant to it and die exclusively by apoptosis upon treatment with cell death-inducing stimuli in vitro, likely due to the differential expression of RIPK3. Interestingly, the genetic modifications that conferred protection from biliary damage also prevented the spontaneous lethality that was often observed in TAK1^LPC-KO mice. In the presence of chronic hepatocyte apoptosis, preventing biliary damage delayed but did not avert hepatocarcinogenesis. On the contrary, inhibition of hepatocyte apoptosis fully prevented liver tumorigenesis even in mice with extensive biliary damage. Altogether, our results suggest that using RIPK1 kinase activity inhibitors could be therapeutically useful for cholestatic liver disease patients.

Synthetic Lethal and Convergent Biological Effects of Cancer-Associated Spliceosomal Gene Mutations

Mutations affecting RNA splicing factors are the most common genetic alterations in myelodysplastic syndrome (MDS) patients and occur in a mutually exclusive manner. The basis for the mutual exclusivity of these mutations and how they contribute to MDS is not well understood. Here we report that although different spliceosome gene mutations impart distinct effects on splicing, they are negatively selected for when co-expressed due to aberrant splicing and downregulation of regulators of hematopoietic stem cell survival and quiescence. In addition to this synthetic lethal interaction, mutations in the splicing factors SF3B1 and SRSF2 share convergent effects on aberrant splicing of mRNAs that promote nuclear factor κB signaling. These data identify shared consequences of splicing-factor mutations and the basis for their mutual exclusivity.

Myeloid-specific TAK1 deletion results in reduced brain monocyte infiltration and improved outcomes after stroke

Background

Activation of transforming growth factor-β-activated kinase 1 (TAK1) occurs after stroke and leads to an exacerbation of brain injury. TAK1 is involved in innate and adaptive immune responses, but it has divergent inflammatory effects that are dependent on the cell type in which it is activated. There is a robust infiltration of myeloid cells after stroke; however, the contribution of myeloid TAK1 to cerebral ischemia is currently unknown. We hypothesized that myeloid-specific deletion of TAK1 would protect against ischemic brain injury.

Methods

Myeloid TAK1^ΔM and wild-type (WT) mice were subjected to middle cerebral artery occlusion (MCAo). Brain-infiltrating and splenic immune cells were evaluated at 3 days after stroke. Assessment of infarct size and behavioral deficits were performed on days 3 and 7 post-stroke.

Results

Infarcts were significantly smaller in TAK1^ΔM mice (p < 0.01), and behavioral deficits were less severe despite equivalent reduction in cerebral blood flow. Flow cytometry demonstrated an increase in the frequency of splenic monocytes and neutrophils (p < 0.05) and a decrease in splenic CD3⁺ T (p < 0.01) and CD19⁺ B (p = 0.06) cells in TAK1^ΔM mice compared to WT at baseline. Three days after stroke, a significant increase in the number of brain-infiltrating immune cell was observed in both TAK1^ΔM (p < 0.05) and WT (p < 0.001) mice compared to their respective shams. However, there was a significant decrease in the infiltrating CD45^hi immune cell counts (p < 0.05), with a pronounced reduction in infiltrating monocytes (p < 0.001) in TAK1^ΔM after stroke compared to WT stroke mice. Additionally, a significant reduction in CD49d⁺ monocytes was seen in the brains of TAK1^ΔM stroke mice compared to wild-type mice. Importantly, TAK1^ΔM MCAo mice had smaller infarcts and improved behavioral outcomes at day 7 post-stroke.

Conclusion

Our results showed that deletion of myeloid TAK1 resulted in smaller infarcts and improved functional outcomes at the peak of inflammation (day 3) and a reduction in brain-infiltrating immune cells that were primarily monocytes. Myeloid TAK1 deletion was also protective at 7 days post MCAo, reflecting a detrimental role of myeloid TAK1 in the progression of ischemic injury.

Electronic supplementary material

The online version of this article (10.1186/s12974-018-1188-3) contains supplementary material, which is available to authorized users.

Adenovirus-Mediated Small Interfering RNA Targeting TAK1 Ameliorates Joint Inflammation with Collagen-Induced Arthritis in Mice

Transforming growth factor β-activated kinase-1 (TAK1) is a key upstream kinase in cell signaling during inflammation, which regulates the expression of inflammatory mediators. Small interfering RNA (siRNA) against TAK1 offers promise as a potential therapeutic strategy in immune-mediated inflammatory disorder including rheumatoid arthritis. Here, we are to evaluate the therapeutic effects of intra-articular administration of adenoviral-mediated siRNA against TAK1 (ad-siRNA-TAK1) on collagen-induced arthritis (CIA) in mice. Ad-siRNA-TAK1 was constructed. The murine RAW 264.7 macrophages were infected with ad-siRNA-TAK1, and the silencing specificity of TAK1 was assessed by quantitative polymerase chain reaction (PCR) and western blot. DBA/1 mice were injected intra-articularly with ad-siRNA-TAK1. Development and severity of arthritis was assessed histologically. Synovial inflammation and bone destruction were determined by hematoxylin and eosin (HE) staining. Articular and serum concentrations of tumor necrosis factor-α, interleukin-1, and interleukin-6 were determined using enzyme-linked immunosorbent assay. Levels of phosphorylated p38, c-Jun N-terminal kinase (JNK), and extracellular-signal-regulated kinase (ERK) were detected by western blot. In vitro, ad--siRNA-TAK1 efficiently inhibited the expression of TAK1 at both mRNA and protein levels. In vivo, intra-articular injection of ad-siRNA-TAK1 efficiently alleviated joint inflammation, decreased the expression of pro-inflammatory mediators, and suppressed JNK pathways. Our results demonstrate the efficiency of ad--siRNA-TAK1 in controlling joint inflammation of CIA, which is associated with the suppression of the expression of pro-inflammatory cytokines and JNK activation.

Negative role of TAK1 in marginal zone B-cell development incidental to NF-κB noncanonical pathway activation

The transcription factor nuclear factor-κB (NF-κB) signaling pathway is crucial in B-cell physiology. One key molecule regulating this pathway is the serine/threonine kinase TAK1 (MAP3K7). TAK1 is responsible for positive feedback mechanisms in B-cell receptor signaling that serve as an NF-κB activation threshold. This study aimed to better understand the correlation between TAK1-mediated signaling and B-cell development and humoral immune responses. Here we showed that a B-cell conditional deletion of TAK1 using mb1-cre resulted in a dramatic elimination of the humoral immune response, consistent with the absence of the B-1 B-cell subset. When monitoring the self-reactive B-cell system (the immunoglobulin hen egg lysozyme/soluble hen egg lysozyme double-transgenic mouse model), we found that TAK1-deficient B cells exhibited an enhanced susceptibility to cell death that might explain the disappearance of the B1 subset. In contrast, these mice gained numerous marginal zone (MZ) B cells. We consequently examined the basal and B-cell receptor-induced activity of NF-κB2 that is reported to regulate MZ B-cell development, and demonstrated that the activity of NF-κB2 increased in TAK1-deficient B cells. Thus, our results present a novel in vivo function, the negative role of TAK1 in MZ B-cell development that is likely associated with NF-κB2 activation.

Activated macrophage survival is coordinated by TAK1 binding proteins

Macrophages play diverse roles in tissue homeostasis and immunity, and canonically activated macrophages are critically associated with acute inflammatory responses. It is known that activated macrophages undergo cell death after transient activation in some settings, and the viability of macrophages impacts on inflammatory status. Here we report that TGFβ- activated kinase (TAK1) activators, TAK1-binding protein 1 (TAB1) and TAK1-binding protein 2 (TAB2), are critical molecules in the regulation of activated macrophage survival. While deletion of Tak1 induced cell death in bone marrow derived macrophages even without activation, Tab1 or Tab2 deletion alone did not profoundly affect survival of naïve macrophages. However, in lipopolysaccharide (LPS)-activated macrophages, even single deletion of Tab1 or Tab2 resulted in macrophage death with both necrotic and apoptotic features. We show that TAB1 and TAB2 were redundantly involved in LPS-induced TAK1 activation in macrophages. These results demonstrate that TAK1 activity is the key to activated macrophage survival. Finally, in an in vivo setting, Tab1 deficiency impaired increase of peritoneal macrophages upon LPS challenge, suggesting that TAK1 complex regulation of macrophages may participate in in vivo macrophage homeostasis. Our results demonstrate that TAB1 and TAB2 are required for activated macrophages, making TAB1 and TAB2 effective targets to control inflammation by modulating macrophage survival.

TNF and MAP kinase signalling pathways

The binding of tumour necrosis factor α (TNFα) to cell surface receptors engages multiple signal transduction pathways, including three groups of mitogen-activated protein (MAP) kinases: extracellular-signal-regulated kinases (ERKs); the cJun NH2-terminal kinases (JNKs); and the p38 MAP kinases. These MAP kinase signalling pathways induce a secondary response by increasing the expression of several inflammatory cytokines (including TNFα) that contribute to the biological activity of TNFα. MAP kinases therefore function both upstream and down-stream of signalling by TNFα receptors. Here we review mechanisms that mediate these actions of MAP kinases during the response to TNFα.

Inhibitory Fcγ receptor is required for the maintenance of tolerance through distinct mechanisms

The inhibitory FcγR FcγRIIB is widely expressed on B cells, dendritic cells (DCs), and myeloid effector cells and modulates a variety of Ab-driven in vivo functions. Although it has been established that FcγRIIB plays an important role in the maintenance of peripheral tolerance, the responsible cell-specific FcγRIIB expression remains to be determined. In this study, we generated mice with selective deletion of FcγRIIB in B cells, DCs, and myeloid effector cells and evaluated these novel strains in models of tolerance and autoimmune diseases. Our results demonstrate that mice with selective deletion of FcγRIIB expression in B cells and DCs have increased Ab and T cell responses, respectively, and display enhanced susceptibility to disease in distinct models, suggesting that FcγRIIB expression in distinct cellular populations contributes to the maintenance of peripheral tolerance through different mechanisms.

TAK1 regulates hepatic cell survival and carcinogenesis

TGF-β-activated kinase 1 (TAK1 or MAP3K7) is an intracellular hub molecule that regulates both nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways that play key roles in development, cell survival, immune response, metabolism, and carcinogenesis. TAK1 activity is tightly regulated by its binding proteins, TAB1 and TAB2/TAB3, as well as by post-translational modification including ubiquitination and phosphorylation. Accumulating evidence demonstrates that TAK1 plays a role in tumor initiation, progression, and metastasis as a tumor prompter or tumor suppressor. An understanding of the role of TAK1 in liver physiology and diseases is required for the development of therapeutic agencies targeting TAK1. In this review, we highlight the activation mechanism and pathophysiological roles of TAK1 in the liver.

Protein kinase networks that limit TLR signalling

TLRs (Toll-like receptors) detect invading micro-organisms which triggers the production of pro-inflammatory mediators needed to combat infection. Although these signalling networks are required to protect the host against invading pathogens, dysregulation of TLR pathways contributes to the development of chronic inflammatory diseases and autoimmune disorders. Molecular mechanisms have therefore evolved to restrict the strength of TLR signalling. In the present review, I highlight recent advances in our understanding of the protein kinase networks required to suppress the innate immune response by negatively regulating TLR signalling and/or promoting the secretion of anti-inflammatory cytokines. I present my discoveries on the key roles of the IKK (inhibitor of nuclear factor κB kinase)-related kinases and the SIKs (salt-inducible kinases) in limiting innate immunity within the greater context of the field.

Mitogen-activated protein kinases in innate immunity

Following pathogen infection or tissue damage, the stimulation of pattern recognition receptors on the cell surface and in the cytoplasm of innate immune cells activates members of each of the major mitogen-activated protein kinase (MAPK) subfamilies--the extracellular signal-regulated kinase (ERK), p38 and Jun N-terminal kinase (JNK) subfamilies. In conjunction with the activation of nuclear factor-κB and interferon-regulatory factor transcription factors, MAPK activation induces the expression of multiple genes that together regulate the inflammatory response. In this Review, we discuss our current knowledge about the regulation and the function of MAPKs in innate immunity, as well as the importance of negative feedback loops in limiting MAPK activity to prevent host tissue damage. We also examine how pathogens have evolved complex mechanisms to manipulate MAPK activation to increase their virulence. Finally, we consider the potential of the pharmacological targeting of MAPK pathways to treat autoimmune and inflammatory diseases.

Cell type-specific function of TAK1 in innate immune signaling

Transforming growth factor β-activated kinase 1 (TAK1 or MAP3K7) is a key signaling component of nuclear factor-κB (NF-κB) and mitogen-activated protein kinase (MAPK) signaling pathways. Activation of TAK1 is tightly regulated through its binding partners and protein modifications. Although TAK1 functions as an essential and positive regulator of innate immune signaling and apoptosis in mouse embryonic fibroblasts (MEFs), T cells, and other cells, it negatively regulates cell development and activation of proinflammatory signaling pathways in neutrophils. However, the molecular mechanisms responsible for the opposite roles of TAK1 in different cell types remain to be addressed. In this article, we discuss the latest progresses in our understanding of TAK1 regulation, function, and mechanisms in a cell-type specific manner.

Intravenous delivery of HIV-based lentiviral vectors preferentially transduces F4/80+ and Ly-6C+ cells in spleen, important target cells in autoimmune arthritis

Antigen presenting cells (APCs) play an important role in arthritis and APC specific gene therapeutic targeting will enable intracellular modulation of cell activity. Viral mediated overexpression is a potent approach to achieve adequate transgene expression levels and lentivirus (LV) is useful for sustained expression in target cells. Therefore, we studied the feasibility of lentiviral mediated targeting of APCs in experimental arthritis. Third generation VSV-G pseudotyped self-inactivating (SIN)-LV were injected intravenously and spleen cells were analyzed with flow cytometry for green fluorescent protein (GFP) transgene expression and cell surface markers. Collagen-induced arthritis (CIA) was induced by immunization with bovine collagen type II in complete Freund's adjuvant. Effect on inflammation was monitored macroscopically and T-cell subsets in spleen were analyzed by flow cytometry. Synovium from arthritic knee joints were analyzed for proinflammatory cytokine expression. Lentiviruses injected via the tail vein preferentially infected the spleen and transduction peaks at day 10. A dose escalating study showed that 8% of all spleen cells were targeted and further analysis showed that predominantly Ly6C+ and F4/80+ cells in spleen were targeted by the LV. To study the feasibility of blocking TAK1-dependent pathways by this approach, a catalytically inactive mutant of TAK1 (TAK1-K63W) was overexpressed during CIA. LV-TAK1-K63W significantly reduced incidence and arthritis severity macroscopically. Further histological analysis showed a significant decrease in bone erosion in LV-TAK1-K63W treated animals. Moreover, systemic Th17 levels were decreased by LV-TAK1-K63W treatment in addition to diminished IL-6 and KC production in inflamed synovium. In conclusion, systemically delivered LV efficiently targets monocytes and macrophages in spleen that are involved in autoimmune arthritis. Moreover, this study confirms efficacy of TAK1 targeting in arthritis. This approach may provide a valuable tool in targeting splenic APCs, to unravel their role in autoimmune arthritis and to identify and validate APC specific therapeutic targets.

Deletion of TAK1 in the myeloid lineage results in the spontaneous development of myelomonocytic leukemia in mice

Previous studies of the conditional ablation of TGF-β activated kinase 1 (TAK1) in mice indicate that TAK1 has an obligatory role in the survival and/or development of hematopoietic stem cells, B cells, T cells, hepatocytes, intestinal epithelial cells, keratinocytes, and various tissues, primarily because of these cells’ increased apoptotic sensitivity, and have implicated TAK1 as a critical regulator of the NF-κB and stress kinase pathways and thus a key intermediary in cellular survival. Contrary to this understanding of TAK1’s role, we report a mouse model in which TAK1 deletion in the myeloid compartment that evoked a clonal myelomonocytic cell expansion, splenomegaly, multi-organ infiltration, genomic instability, and aggressive, fatal myelomonocytic leukemia. Unlike in previous reports, simultaneous deletion of TNF receptor 1 (TNFR1) failed to rescue this severe phenotype. We found that the features of the disease in our mouse model resemble those of human chronic myelomonocytic leukemia (CMML) in its transformation to acute myeloid leukemia (AML). Consequently, we found TAK1 deletion in 13 of 30 AML patients (43%), thus providing direct genetic evidence of TAK1’s role in leukemogenesis.

TAK1 is essential for osteoclast differentiation and is an important modulator of cell death by apoptosis and necroptosis

Transforming growth factor β (TGF-β)-activated kinase 1 (TAK1), a mitogen-activated protein 3 (MAP3) kinase, plays an essential role in inflammation by activating the IκB kinase (IKK)/nuclear factor κB (NF-κB) and stress kinase (p38 and c-Jun N-terminal kinase [JNK]) pathways in response to many stimuli. The tumor necrosis factor (TNF) superfamily member receptor activator of NF-κB ligand (RANKL) regulates osteoclastogenesis through its receptor, RANK, and the signaling adaptor TRAF6. Because TAK1 activation is mediated through TRAF6 in the interleukin 1 receptor (IL-1R) and toll-like receptor (TLR) pathways, we sought to investigate the consequence of TAK1 deletion in RANKL-mediated osteoclastogenesis. We generated macrophage colony-stimulating factor (M-CSF)-derived monocytes from the bone marrow of mice with TAK1 deletion in the myeloid lineage. Unexpectedly, TAK1-deficient monocytes in culture died rapidly but could be rescued by retroviral expression of TAK1, inhibition of receptor-interacting protein 1 (RIP1) kinase activity with necrostatin-1, or simultaneous genetic deletion of TNF receptor 1 (TNFR1). Further investigation using TAK1-deficient mouse embryonic fibroblasts revealed that TNF-α-induced cell death was abrogated by the simultaneous inhibition of caspases and knockdown of RIP3, suggesting that TAK1 is an important modulator of both apoptosis and necroptosis. Moreover, TAK1-deficient monocytes rescued from programmed cell death did not form mature osteoclasts in response to RANKL, indicating that TAK1 is indispensable to RANKL-induced osteoclastogenesis. To our knowledge, we are the first to report that mice in which TAK1 has been conditionally deleted in osteoclasts develop osteopetrosis.

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFβ-activated kinase 1 (TAK1) play essential roles in the C-type lectin receptor signaling in response to Candida albicans infection

Tumor necrosis factor receptor-associated factor 6 (TRAF6) and TGFβ-activated kinase 1 (TAK1) are considered as key intermediates in Toll-like receptor (TLR) signaling. However, the role of TRAF6 and TAK1 in C-type lectin receptors (CLRs) in response to fungal infection has not been studied. In this study, we have utilized macrophages derived from TRAF6 knock-out mice and myeloid-specific TAK1-deficient mice and determined the role of TRAF6 and TAK1 in CLR-induced signal transduction events. We demonstrate that TRAF6 and TAK1 are required for NF-κB and JNK activation, and expression of proinflammatory cytokines in response to Candida albicans infection. Our results highlight TRAF6 and TAK1 as key components in the signaling cascade downstream of C-type lectin receptors and as critical mediators of the anti-fungal immune response. Therefore, our studies provide a mechanistic understanding of the host immune response to C. albicans, which has a significant impact for the development of anti-fungal therapeutics and in understanding risk-factors and determining susceptibility to C. albicans infection.

Inactivation of the deubiquitinase CYLD in hepatocytes causes apoptosis, inflammation, fibrosis, and cancer

The tumor suppressor cylindromatosis (CYLD) inhibits the NFκB and mitogen-activated protein kinase (MAPK) activation pathways by deubiquitinating upstream regulatory factors. Here we show that liver-specific disruption of CYLD triggers hepatocyte cell death in the periportal area via spontaneous and chronic activation of TGF-β activated kinase 1 (TAK1) and c-Jun N-terminal kinase (JNK). This is followed by hepatic stellate cell and Kupffer cell activation, which promotes progressive fibrosis, inflammation, tumor necrosis factor (TNF) production, and expansion of hepatocyte apoptosis toward the central veins. At later stages, compensatory proliferation results in the development of cancer foci featuring re-expression of oncofetal hepatic and stem cell-specific genes. The results demonstrate that, in the liver, CYLD acts as an important regulator of hepatocyte homeostasis, protecting cells from spontaneous apoptosis by preventing uncontrolled TAK1 and JNK activation.