Explore the vast range of titles available.

Ubiquitylation of the TNFR1 signalling complex (TNF-RSC) controls the activation of RIPK1, a kinase critically involved in mediating multiple TNFα-activated deleterious events. However, the molecular mechanism that coordinates different types of ubiquitylation modification to regulate the activation of RIPK1 kinase remains unclear. Here, we show that ABIN-1/NAF-1, a ubiquitin-binding protein, is recruited rapidly into TNF-RSC in a manner dependent on the Met1-ubiquitylating complex LUBAC to regulate the recruitment of A20 to control Lys63 deubiquitylation of RIPK1. ABIN-1 deficiency reduces the recruitment of A20 and licenses cells to die through necroptosis by promoting Lys63 ubiquitylation and activation of RIPK1 with TNFα stimulation under conditions that would otherwise exclusively activate apoptosis in wild-type cells. Inhibition of RIPK1 kinase and RIPK3 deficiency block the embryonic lethality of Abin-1 –/– mice. We propose that ABIN-1 provides a critical link between Met1 ubiquitylation mediated by the LUBAC complex and Lys63 deubiquitylation by phospho-A20 to modulate the activation of RIPK1. Dziedzic et al. show that the ubiquitin-binding protein ABIN-1 is recruited into TNFR1 signalling complex in a manner dependent on Met1 -ubiquitinating complex LUBAC to regulate K63 de-ubiquitination to activate RIPK1.

Intestinal epithelial cell (IEC) death is a common feature of inflammatory bowel disease (IBD) that triggers inflammation by compromising barrier integrity. In many patients with IBD, epithelial damage and inflammation are TNF-dependent. Elevated TNF production in IBD is accompanied by increased expression of the TNFAIP3 gene, which encodes A20, a negative feedback regulator of NF-κB. A20 in intestinal epithelium from patients with IBD coincided with the presence of cleaved caspase-3, and A20 transgenic (Tg) mice, in which A20 is expressed from an IEC-specific promoter, were highly susceptible to TNF-induced IEC death, intestinal damage, and shock. A20-expressing intestinal organoids were also susceptible to TNF-induced death, demonstrating that enhanced TNF-induced apoptosis was a cell-autonomous property of A20. This effect was dependent on Receptor Interacting Protein Kinase 1 (RIPK1) activity, and A20 was found to associate with the Ripoptosome complex, potentiating its ability to activate caspase-8. A20-potentiated RIPK1-dependent apoptosis did not require the A20 deubiquitinase (DUB) domain and zinc finger 4 (ZnF4), which mediate NF-κB inhibition in fibroblasts, but was strictly dependent on ZnF7 and A20 dimerization. We suggest that A20 dimers bind linear ubiquitin to stabilize the Ripoptosome and potentiate its apoptosis-inducing activity.

Genome-wide studies reveal that transcription by RNA polymerase II (Pol II) is dynamically regulated. To obtain a comprehensive view of a single transcription cycle, we switched on transcription of five long human genes (>100 kbp) with tumor necrosis factor-α (TNFα) and monitored (using microarrays, RNA fluorescence in situ hybridization, and chromatin immunoprecipitation) the appearance of nascent RNA, changes in binding of Pol II and two insulators (the cohesin subunit RAD21 and the CCCTC-binding factor CTCF), and modifications of histone H3. Activation triggers a wave of transcription that sweeps along the genes at ≈3.1 kbp/min; splicing occurs cotranscriptionally, a major checkpoint acts several kilobases downstream of the transcription start site to regulate polymerase transit, and Pol II tends to stall at cohesin/CTCF binding sites.

TNFα is a pleiotropic cytokine which fuels tumor cell growth, invasion, and metastasis in some malignancies, while in others it induces cytotoxic cell death. However, the molecular mechanism by which TNFα exerts its diverse effects on breast cancer subtypes remains elusive. Using in vitro assays and mouse xenografts, we show here that TNFα contributes to the aggressive properties of triple negative breast cancer (TNBC) cell lines via upregulation of TNFAIP3(A20). In a striking contrast, TNFα induces a potent cytotoxic cell death in luminal (ER+) breast cancer cell lines which fail to upregulate A20 expression. Overexpression of A20 not only protects luminal breast cancer cell lines from TNFα-induced cell death via inducing HSP70-mediated anti-apoptotic pathway but also promotes a robust EMT/CSC phenotype by activating the pStat3-mediated inflammatory signaling. Furthermore, A20 overexpression in luminal breast cancer cells induces aggressive metastatic properties in mouse xenografts via generating a permissive inflammatory microenvironment constituted by granulocytic-MDSCs. Collectively, our results reveal a mechanism by which A20 mediates pleiotropic effects of TNFα playing role in aggressive behaviors of TNBC subtype while its deficiency results in TNFα-induced apoptotic cell death in luminal breast cancer subtype.

Inflammatory bowel disease (IBD) is an important etiologic factor in the development of colorectal cancer. However, the mechanism underlying carcinogenesis through chronic inflammation is still unknown. Activation-induced cytidine deaminase (AID) is induced by the inflammation and involved in various human carcinogenesis via its mutagenic activity. In the current study, we investigated whether the inflammation/AID axis plays an integral role in the development of colitis-associated cancers. Inflammation in the cecum was more severe than that in other colonic regions, and endogenous AID expression was enhanced most prominently in the inflamed cecal mucosa of interleukin (IL)-10 −/− mice. Blockade of tumor necrosis factor (TNF)-α and IL-12 significantly suppressed AID expression. Although proinflammatory cytokine expression was comparable between IL-10 −/− AID +/+ and IL-10 −/− AID −/− mice, sequencing analyses revealed a significantly lower incidence of somatic mutations in Trp53 gene in the colonic mucosa of IL-10 −/− AID −/− than IL-10 −/− AID +/+ mice. Colon cancers spontaneously developed in the cecum in 6 of 22 (27.2%) IL-10 −/− AID +/+ mice. In contrast, none of the IL-10 −/− AID −/− mice developed cancers except only one case of neoplasia in the distal colon. These findings suggest that the proinflammatory cytokine-induced aberrant production of AID links colonic inflammation to an enhanced genetic susceptibility to oncogenic mutagenesis. Targeting AID could be a novel strategy to prevent colitis-associated colon carcinogenesis irrespective of ongoing colonic inflammation.

Key Points TNF is a pleiotropic cytokine that exerts homeostatic and pathogenic bioactivities A new concept in therapeutics of TNF-mediated diseases is the selective inhibition of the pathogenic effects of TNF with preservation of its homeostatic functions TNF-induced necroptosis is a new pathway potentially implicated in TNF-mediated pathologies TNF induces cellular priming, tolerization, and short-term transcriptional memory in a context-dependent manner Combining TNF-blockade with drugs that target pathogenic pathways or cells not implicated in host defence is an attractive approach to improve effectiveness without compromising safety Despite the clinical success of therapeutics that inhibit TNF, gaps remain about the biology of this pleiotropic cytokine. This Review explores the latest discoveries related to TNF signalling pathways, TNF-induced gene expression, and the homeostatic and pathogenic functions of TNF, as well as the implications of these findings for therapeutics for TNF-mediated diseases. TNF is a pleiotropic cytokine with important functions in homeostasis and disease pathogenesis. Recent discoveries have provided insights into TNF biology that introduce new concepts for the development of therapeutics for TNF-mediated diseases. The model of TNF receptor signalling has been extended to include linear ubiquitination and the formation of distinct signalling complexes that are linked with different functional outcomes, such as inflammation, apoptosis and necroptosis. Our understanding of TNF-induced gene expression has been enriched by the discovery of epigenetic mechanisms and concepts related to cellular priming, tolerization and induction of 'short-term transcriptional memory'. Identification of distinct homeostatic or pathogenic TNF-induced signalling pathways has introduced the concept of selectively inhibiting the deleterious effects of TNF while preserving its homeostatic bioactivities for therapeutic purposes. In this Review, we present molecular mechanisms underlying the roles of TNF in homeostasis and inflammatory disease pathogenesis, and discuss novel strategies to advance therapeutic paradigms for the treatment of TNF-mediated diseases.

The development of effective therapies against brain metastasis is currently hindered by limitations in our understanding of the molecular mechanisms driving it. Here we define the contributions of tumour-secreted exosomes to brain metastatic colonization and demonstrate that pre-conditioning the brain microenvironment with exosomes from brain metastatic cells enhances cancer cell outgrowth. Proteomic analysis identified cell migration-inducing and hyaluronan-binding protein (CEMIP) as elevated in exosomes from brain metastatic but not lung or bone metastatic cells. CEMIP depletion in tumour cells impaired brain metastasis, disrupting invasion and tumour cell association with the brain vasculature, phenotypes rescued by pre-conditioning the brain microenvironment with CEMIP + exosomes. Moreover, uptake of CEMIP + exosomes by brain endothelial and microglial cells induced endothelial cell branching and inflammation in the perivascular niche by upregulating the pro-inflammatory cytokines encoded by Ptgs2 , Tnf and Ccl/Cxcl , known to promote brain vascular remodelling and metastasis. CEMIP was elevated in tumour tissues and exosomes from patients with brain metastasis and predicted brain metastasis progression and patient survival. Collectively, our findings suggest that targeting exosomal CEMIP could constitute a future avenue for the prevention and treatment of brain metastasis. Rodrigues et al. show that exosomal CEMIP derived from brain metastatic cells elicits vascular remodelling and inflammation and supports subsequent metastatic colonization in the brain microenvironment.

TNF, an inflammatory cytokine that is enriched in the tumor microenvironment, promotes tumor growth and subverts innate immune responses to cancer cells. We previously reported that tumors implanted in TNF receptor-deficient (Tnfr-/-) mice are spontaneously rejected; however, the molecular mechanisms underlying this rejection are unclear. Here we report that TNF signaling drives the peripheral accumulation of myeloid-derived suppressor cells (MDSCs). MDSCs expand extensively during inflammation and tumor progression in mice and humans and can enhance tumor growth by repressing T cell-mediated antitumor responses. Peripheral accumulation of MDSCs was drastically impaired in Tnfr-/- mice. Signaling of TNFR-2, but not TNFR-1, promoted MDSC survival through upregulation of cellular FLICE-inhibitory protein (c-FLIP) and inhibition of caspase-8 activity. Loss of TNFRs impaired the induction of MDSCs from bone marrow cells, but this could be reversed by treatment with caspase inhibitors. These results demonstrate that TNFR-2 signaling promotes MDSC survival and accumulation and helps tumor cells evade the immune system.

Necroptosis and ferroptosis are two distinct necrotic cell death modalities with no known common molecular mechanisms. Necroptosis is activated by ligands of death receptors such as tumor necrosis factor-α (TNF-α) under caspase-deficient conditions, whereas ferroptosis is mediated by the accumulation of lipid peroxides upon the depletion/or inhibition of glutathione peroxidase 4 (GPX4). The molecular mechanism that mediates the execution of ferroptosis remains unclear. In this study, we identified 2-amino-5-chloro-N,3-dimethylbenzamide (CDDO), a compound known to inhibit heat shock protein 90 (HSP90), as an inhibitor of necroptosis that could also inhibit ferroptosis. We found that HSP90 defined a common regulatory nodal between necroptosis and ferroptosis. We showed that inhibition of HSP90 by CDDO blocked necroptosis by inhibiting the activation of RIPK1 kinase. Furthermore, we showed that the activation of ferroptosis by erastin increased the levels of lysosome-associated membrane protein 2a to promote chaperone-mediated autophagy (CMA), which, in turn, promoted the degradation of GPX4. Importantly, inhibition of CMA stabilized GPX4 and reduced ferroptosis. Our results suggest that activation of CMA is involved in the execution of ferroptosis.

Necroptosis, a form of regulated necrotic cell death, is governed by RIP1/RIP3-mediated activation of MLKL. However, the signaling process leading to necroptotic death remains to be elucidated. In this study, we found that PUMA, a proapoptotic BH3-only Bcl-2 family member, is transcriptionally activated in an RIP3/MLKL-dependent manner following induction of necroptosis. The induction of PUMA, which is mediated by autocrine TNF-α and enhanced NF-κB activity, contributes to necroptotic death in RIP3-expressing cells with caspases inhibited. On induction, PUMA promotes the cytosolic release of mitochondrial DNA and activation of the DNA sensors DAI/Zbp1 and STING, leading to enhanced RIP3 and MLKL phosphorylation in a positive feedback loop. Furthermore, deletion of PUMA partially rescues necroptosis-mediated developmental defects in FADD-deficient embryos. Collectively, our results reveal a signal amplification mechanism mediated by PUMA and cytosolic DNA sensors that is involved in TNF-driven necroptotic death in vitro and in vivo.