Apoptotic cell death is essential for maintaining liver homeostasis, and its dysregulation contributes to liver diseases, which can lead to fibrosis and end-stage liver failure. Tumour Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) signalling is a key regulator of hepatobiliary apoptosis, yet the mechanisms that govern TRAIL sensitivity remain poorly defined. Here, we identify the Abscission/NoCut Checkpoint Regulator (ANCHR) and its interacting E3 ubiquitin ligase Mind Bomb 2 (MIB2) as novel modulators of death receptor-mediated apoptosis, with a particular emphasis on TRAIL signalling. Specifically, we show that ANCHR protects cancer cells from TRAIL-induced apoptosis by limiting mitochondrial engagement of the apoptotic cascade. Loss of ANCHR promotes Mcl-1 depletion, enhances caspase-8 and BID processing, and sensitises otherwise TRAIL-resistant cancer cells to apoptosis. In vivo, ANCHR-deficient mice exhibit increased TRAIL/DR5-induced liver injury suggesting that ANCHR contributes to liver tissue integrity and immune homeostasis. These findings provide mechanistic insights into death receptor-mediated apoptosis regulation and highlight ANCHR as a key modulator of cell survival, with implications for liver health and disease.

5-Methylcytosine (5mC) is a common source of somatic mutations. Deamination of 5mC to thymine generates a G/T mismatch, which occurs spontaneously and must be repaired prior to DNA replication to avoid mutation. We generated genetically engineered mice and cell lines to define DNA repair pathways that protect against 5mC deamination. We observed a low background mutation rate in mouse bone marrow or colon, typically 0.2-0.5 CG > TG mutations/genome/day. This increased 3-7 fold in cells lacking the glycosylase methyl-binding domain 4 (Mbd4), one of the few glycosylases capable of excising thymine from G/T mismatches. We found no role for thymine DNA glycosylase (Tdg) in the repair of 5mC deamination in these tissues. Instead, our results flag potential cooperation between Mbd4 and the mismatch repair (MMR) complex MutSα (Msh6:Msh2), evident through elevated rates of CG > TG mutations in Msh6-deficient cells: 2.6-4.8 CG > TG mutations/genome/day in primary cells and 13.9 CG > TG mutations/genome/day in cell lines. Loss of Mbd4 results in a specific increase in DNA damage from 5mC deamination, whereas the broader functionality of MutSα explains why mutational signatures linked to Msh6 deficiency are more variable and reflect the replicative history of the cell. Our findings support the emerging view that MutSα has broader DNA repair activity outside of replication.

Transitioning a candidate therapeutic target from bench to bedside requires significant time and financial investment, yet clinical success remains low often due to poor on-target toxicity assessment during preclinical validation. Tag-degraders provide a tool to improve target validation by enabling degradation of any protein of interest via a degron-tag. This drug-based, reversible, and dose-dependent method of protein removal can mimic degrader-based drug treatments and assess the implications of target protein depletion in vivo. However, each degrader has a distinct pharmacokinetic profile that will influence its effectiveness across tissues. To create a resource to enable the most appropriate choice of tag-degrader, we benchmark the dTAG, HaloPROTAC, and NanoTAC systems in vivo by employing a transgenic mouse expressing a reporter protein targetable by these tag-degraders. Through various treatment regimes, we characterise each degrader profile across a panel of 20 tissues and organs, highlighting the superior degradation by dTAG molecules, and identify differences between degradation in whole tissues versus single cell populations. Using an FKBPF36V knock-in mouse expressing 65K-FKBPF36V, we reveal target specific degradation kinetics, and a critical requirement for 65K in mice. Together, this resource will assist researchers in choosing the right degrader and tag for their own applications.

The pro-inflammatory programmed cell death pathway, necroptosis, relies on phosphorylation of the terminal effector, MLKL, by RIPK3. RIPK3-deficient mice or those harboring the kinase-inactivating mutation, RIPK3K51A, are ostensibly normal in the absence of challenge, indicating that RIPK3 and its kinase activity are dispensable for development. However, another kinase-inactivating mutation, RIPK3D161N, results in embryonic lethality in mice due to widespread apoptosis. As a result, the RIPK3D161N mutation is thought to confer a toxic gain-of-function. Here, to further explore the impacts of RIPK3 inactivation, we compared the stability and cellular interactions of RIPK3D161N and RIPK3K51A to a third previously-uncharacterized kinase-dead variant, RIPK3D143N. We show that RIPK3K51A was unstable and did not associate with RIPK1, RIPK3D161N was unstable but interacted with RIPK1, whereas RIPK3D143N was stable and bound RIPK1 in a manner comparable to wild-type RIPK3. Thus, all three variants scaffold differently, suggesting that the assembly of cell death machinery by RIPK3 is finely tuned, not just by its kinase activity, but also by the conformation of its kinase domain. Physiologically, Ripk3D143N/D143N mice exhibited a partially penetrant lethality in utero. However, once born, Ripk3D143N/D143N mice were fertile and phenotypically indistinguishable from wild-type mice in the absence of challenge. Full blockade of necroptotic signaling was shown in cells from Ripk3D143N/D143N mice, with the RIPK3D143N mutation also protecting Casp8-/- mice from lethal necroptosis during embryogenesis and preventing necroptotic ileitis in mice that lacked intestinal epithelial caspase-8 expression. Our studies support the idea that RIPK3 is a nexus between apoptotic and necroptotic signaling, and highlight the importance of considering kinase domain conformation in RIPK3 inhibitor development.

KAT6A (MOZ) and KAT6B (QKF/MORF) are related histone lysine acetyltransferases (KATs) that have a high degree of functional redundancy during development. In the absence of KAT6A, embryos undergo an anterior homeotic transformation of the axial skeleton, develop an interrupted aortic arch, have ventricular septal defects and fail to form definitive hematopoietic stem cells. KAT6B has roles in brain, skeletal and hematopoietic system development. Because loss of KAT6A leads to highly penetrant phenotypes, this allows us to determine whether the acetylation function is essential for all activities. We show that loss of acetyltransferase activity did not phenocopy the loss of the KAT6A protein in mice. Although mutation of the KAT domains of both KAT6A and KAT6B together increased the severity of phenotypes observed, these were milder than complete KAT6A loss of function. KAT domain mutants displayed ventricular septal defects and reduced (but not eliminated) hematopoietic stem cell activity. However, they did not display homeotic transformations or aortic arch defects, suggesting that, while acetylation is important for some functions, others can proceed without this activity. Accordingly, KAT6 proteins appear to have functions beyond acetylation.

Phagocytosis of apoptotic cells maintains tissue homeostasis and regulates inflammation. A proposed facilitator of apoptotic cell clearance is the fragmentation of these cells into apoptotic bodies (ApoBDs) through cell-autonomous processes involving caspases and cytoskeletal rearrangement. Although this fragmentation process is considered a hallmark of apoptosis, its progression in tissue environments remains underexplored. Here, we examine the in vivo apoptotic dynamics of mouse thymocytes and pluripotent cells from zebrafish embryos. We show that the in vivo biogenesis of ApoBDs is independent of known cell-intrinsic regulators. Instead, fragmentation depends on actin-rich protrusions from neighboring resident phagocytes, which mechanically compress apoptotic cells to break them into smaller particles. Four-dimensional in vivo tracking of apoptotic cells reveals that both phagocyte-mediated fragmentation and phagocytosis are size sensitive, indicating that apoptotic size reduction mediated by phagocytes enhances their own clearance abilities. This non-cell-autonomous fragmentation ensures rapid apoptotic cell clearance, crucial for maintaining tissue homeostasis in physiological settings.

Suppressor of cytokine signaling (SOCS) 1 is a key negative regulator of interferon (IFN), interleukin (IL)12, and IL-2 family cytokine signaling through inhibition of the Janus kinase-signal transducer and activator of transcription (JAK-STAT) pathway. To investigate the temporal induction of SOCS1 in response to cytokine in live cells and its selective regulation of signaling pathways, we generated a mouse expressing a Halo-tag-SOCS1 fusion protein (Halo-SOCS1) under control of the endogenous Socs1 promoter. Homozygous Halo-SOCS1 mice (Halo-Socs1KI/KI) were viable with minor T cell abnormalities, most likely due to enhanced Halo-SOCS1 expression in thymocytes compared with the untagged protein. IFNγ and IL-4 induced Halo-SOCS1 expression in macrophages derived from Halo-Socs1KI/KI mice, and a critical level of SOCS1 expression was required for inhibition of both IFNγ and granulocyte macrophage-colony stimulating factor (GM-CSF)-driven JAK-STAT signaling. In contrast, IFNγ priming to induce SOCS1 did not cross-regulate IL-4 signaling. This study indicates that while SOCS1 expression needs to exceed a critical threshold to inhibit IFNγ signaling, its selective regulation of cytokine signaling results from an as yet undetermined, level of regulatory control.

The anti-apoptotic protein MCL-1 (myeloid cell leukemia-1) is essential for embryogenesis and the survival of many cell types that tolerate loss of its relatives, BCL-XL and BCL-2. Apoptosis-unrelated roles of MCL-1 in metabolism may contribute to this requirement, although their relevance for embryogenesis and postnatal life remains unclear. We hypothesized that BCL-XL and BCL-2 may substitute MCL-1's anti-apoptotic but not its apoptosis-unrelated functions. Replacing MCL-1 with BCL-XL or BCL-2 supported embryo development by rescuing the Mcl-1-/- preimplantation lethality. Mcl-1Bcl-xL/Bcl-xL but not Mcl-1Bcl-2/Bcl-2 mice were born on a mixed background, although they showed metabolic defects. Thus MCL-1's apoptosis-unrelated functions appear critical in later development, with BCL-XL, but not BCL-2, partially compensating. These findings clarify MCL-1's distinct physiological roles, critically informing MCL-1 inhibitor development as cancer therapeutics.

CRISPR activation (CRISPRa) enables precise, locus-specific upregulation of gene expression, offering potential for both ex vivo and in vivo applications. However, the lack of scalable, high-coverage tools has limited its use in comprehensive genetic screens, particularly in murine models. Here, we introduce Partita, a next-generation, whole-genome CRISPRa sgRNA platform designed for unparalleled efficiency and depth in gene activation studies. Partita employs a high-density targeting strategy, deploying 10 sgRNAs per transcription start site, structured into five gene family-specific sub-libraries to maximize transcriptional induction. To demonstrate its capabilities, we performed a series of large-scale screens: an in vitro enrichment/depletion screen in iBMDMs, whole-genome CRISPRa screens in a double-hit lymphoma model to uncover genes driving resistance to pro-apoptotic drugs (venetoclax, nutlin-3a, etoposide), and an in vivo whole-genome screen identifying accelerators of Myc-driven lymphomagenesis. Each experiment revealed both expected and novel regulators of cellular phenotypes, with a high validation rate in secondary assays. By enabling robust, high-throughput gain-of-function screening, Partita unlocks new avenues for functional genomics and expands the toolkit for discovering key drivers of biological processes across diverse research fields. ### Competing Interest Statement KMD and AH are current employees of Genentech, and BH and JPF have previously been employees of Genentech, where the CRISPRa mouse libraries presented in this work were developed. A provisional patent application that relates to the work has been filed.

DNMT3A mutations are prevalent in haematologic malignancies. In our mouse model the murine homologue (R878H) of the human 'hotspot' R882H mutation is introduced into the mouse Dnmt3a locus. This results in globally reduced DNA methylation in all tissues. Mice with heterozygous R878H DNMT3A mutations develop γ-radiation induced thymic lymphoma more rapidly than control mice, suggesting a vulnerability to stress stimuli in Dnmt3aR878H/+ cells. In competitive transplantations, Dnmt3aR878H/+ Lin-Sca-1+Kit+ (LSK) haematopoietic stem/progenitor cells (HSPCs) have a competitive advantage over WT HSPCs, indicating a self-renewal phenotype at the expense of differentiation. RNA sequencing of Dnmt3aR878H/+ LSKs exposed to low dose γ-radiation shows downregulation of the p53 pathway compared to γ-irradiated WT LSKs. Accordingly, reduced PUMA expression is observed by flow cytometry in the bone marrow of γ-irradiated Dnmt3aR878H/+ mice due to impaired p53 signalling. These findings provide new insights into how DNMT3A mutations cause subtle changes in the transcriptome of LSK cells which contribute to their increased self-renewal and propensity for malignant transformation.

Cullin-5 (Cul5) coordinates assembly of cullin-RING-E3 ubiquitin (Ub) ligase (CRL) complexes that include Suppressor of Cytokine Signaling (SOCS)-box-containing proteins. The SOCS-box proteins function to recruit specific substrates to the complex for ubiquitination and degradation. In hematopoiesis, SOCS-box proteins are best known for regulating the actions of cytokines that utilize the JAK-STAT signaling pathway. However, the roles of most SOCS-box proteins have not been studied in physiological contexts and any actions for Cul5/SOCS complexes in signaling by several hematopoietic cytokines, including thrombopoietin (TPO) and interleukin-3 (IL-3), remain unknown. To define additional potential roles for Cul5/SOCS complexes, we generated mice lacking Cul5 in hematopoiesis; the absence of Cul5 is predicted to impair the SOCS-box-dependent actions of all proteins that contain this motif. Here, we show that Cul5-deficient mice develop excess megakaryopoiesis and thrombocytosis revealing a novel mechanism of negative regulation of megakaryocyte-committed stem cells, a distinct population within the hematopoietic stem cell pool that have been shown to rapidly, perhaps directly, generate megakaryocytes, and which are produced in excess in the absence of Cul5. Cul5-deficient megakaryopoiesis is distinctive in being largely independent of TPO/Mpl and involves signaling via the beta-common and/or beta-IL-3 receptors, with evidence of deregulated responses to IL-3. This process is independent of the interferon-alpha/beta receptor (IFNARI), previously implicated in inflammation-induced activation of stem-like megakaryocyte progenitor cells.

Aims: Cancer cachexia affects up to 80 % of patients with advanced cancer and accounts for >20 % of all cancer- related deaths. Sarcolemmal localization of dystrophin, a key protein within the dystrophin-glycoprotein complex (DGC), is perturbed in multiple muscle wasting conditions, including cancer cachexia, indicating a potential role for dystrophin in the maintenance of muscle mass. Strategies to preserve dystrophin expression at the sarcolemma might therefore combat muscle wasting. Phosphorylation of dystrophin serine 3059 (S3059) enhances the interaction between dystrophin and beta-dystroglycan and attenuates atrophy of mouse muscle myotubes in vitro when cultured in the presence of colon-26 (C-26) cancer cells. Whether dystrophin S3059 phosphorylation can attenuate cachexia in tumor-bearing mice has not been determined. Materials and methods: Mice with systemic mutations of serine 3059 to alanine (DmdS3059A; phospho-null) or glutamate (DmdS3059E; phosphomimetic) were generated to investigate the impact of S3059 phosphorylation on survival and skeletal muscle health in the C-26 tumor-bearing mouse model of cancer cachexia using measures of skeletal muscle function in situ combined with biochemical and histological assessments. Key findings: In a model of mild cachexia, loss of skeletal muscle mass and function was greater in DmdS3059A mice. Conversely, in a model of severe cachexia, overall survival was prolonged, and markers of protein degradation were decreased in skeletal muscles of DmdS3059E mice. Thus, manipulating dystrophin S3059 phosphorylation can alter the progression of cachexia in tumor-bearing mice. Significance: Strategies to increase phosphorylation of this site, and/or increase dystrophin protein expression, have therapeutic potential for cancer cachexia.

Pro-survival BCL-2 proteins (e.g., MCL-1, BCL-XL, BCL-2, A1) are over-expressed in human cancers, making them critical targets for anti-cancer therapies 1. While the BCL-2 inhibitor Venetoclax is highly successful in treating certain blood cancers, inhibitors of BCL-XL and MCL-1 cause toxicity to non-malignant tissues, including hematopoietic cells 2. These findings from gene targeted mice showed that different pro-survival BCL-2 proteins are critical for the survival of distinct hematopoietic cell subsets. Notably, MCL-1 is essential for implantation, with Mcl-1-/- embryos dying at E3.5, the survival of hematopoietic stem and progenitor cells as well as many immature and mature lymphoid and myeloid cell populations3. In contrast, the essential roles for BCL-2 and BCL-XL are restricted to the survival of select hematopoietic cell populations. Of note MCL-1 (and to a minor extent BCL-XL) but not BCL-2 have been ascribed some apoptosis unrelated functions in cellular metabolism, such as mitochondrial import of long chain fatty acids. We aim to determine the unique anti-apoptotic and apoptosis unrelated roles of MCL-1 in comparison to the other pro-survival BCL-2 family members in embryogenesis and hematopoiesis.We used CRISPR to produce “gene-swap” mice in which the MCL-1 coding region was replaced with the coding region for BCL-2 (Mcl-1Bcl-2), BCL-XL (Mcl-1Bcl-xL) or A1. Remarkably, homozygous Mcl-1Bcl-xL/Bcl-xL and Mcl-1Bcl-2/Bcl-2 embryos could develop until at least E11.5 on a C57BL/6 background. This demonstrates that only the anti-apoptotic function of MCL-1 - but not its apoptosis-unrelated roles - are essential for early embryogenesis.To examine the impact of replacement of MCL-1 by BCL-XL on hematopoiesis, lethally irradiated mice were reconstituted with Mcl-1Bcl-xL/Bcl-xL hematopoietic stem progenitor cells from E12.5 embryos. Interestingly, the expression of BCL-XL in place of MCL-1 in the hematopoietic system allowed the generation of all blood cell types with a marked increase in platelets and B lymphocytes. Notably, adult heterozygous Mcl-1Mcl-1/Bcl-2 mice showed even more substantial accumulations of B cells and antibody secreting plasma cells in their spleen and bone marrow, and with progressing age they develop SLE-like autoimmune disease similar to what is seen in vav-bcl-2 transgenic mice that overexpress BCL-2 4. These findings show that distinct pro-survival BCL-2 proteins with their differences in protein stability and interactions with the pro-apoptotic members of the BCL-2 family are best suited to safeguard normal hematopoietic cell survival, with too much pro-survival activity causing disease. References1.Adams, J. M. & Cory, S. Cell Death Differ 25, 27-36 (2018).2.Kelly, G. L. & Strasser, A. Annu Rev Cancer Biol 4, 299-313 (2020).3.Opferman, J. T. et al. Nature 426, 671-676 (2003).4.Ogilvy, S. et al. Proceedings of the National Academy of Sciences 96, 14943-14948 (1999). Annli Tee, Andrew J. Kueh, Leonie Gibson, Shezlie Malelang, Marco J. Herold, Gemma Kelly, Andreas Strasser, Kerstin Brinkmann. Discovering the essential functions of MCL-1 in hematopoiesis using gene-swap mice [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 1379.

Identifying tumor suppressor genes is predicted to inform on the development of novel strategies for cancer therapy. To identify new lymphoma driving processes that cooperate with oncogenic MYC, which is abnormally highly expressed in ~70% of human cancers, we use a genome-wide CRISPR gene knockout screen in Eµ-Myc;Cas9 transgenic hematopoietic stem and progenitor cells in vivo. We discover that loss of any of the GATOR1 complex components - NPRL3, DEPDC5, NPRL2 - significantly accelerates c-MYC-driven lymphoma development in mice. MYC-driven lymphomas lacking GATOR1 display constitutive mTOR pathway activation and are highly sensitive to mTOR inhibitors, both in vitro and in vivo. These findings identify GATOR1 suppression of mTORC1 as a tumor suppressive mechanism in MYC-driven lymphomagenesis and suggest an avenue for therapeutic intervention in GATOR1-deficient lymphomas through mTOR inhibition.

Conventional methods for generating knock-out or knock-in mammalian cell models using CRISPR-Cas9 genome editing often require tedious single-cell clone selection and expansion. In this study, we develop and optimise rapid and robust strategies to engineer homozygous fluorescent reporter knock-in cell pools with precise genome editing, circumventing clonal variability inherent to traditional approaches. To reduce false-positive cells associated with random integration, we optimise the design of donor DNA by removing the start codon of the fluorescent reporter and incorporating a self-cleaving T2A peptide system. Using fluorescence-assisted cell sorting (FACS), we efficiently identify and isolate the desired homozygous fluorescent knock-in clones, establishing stable cell pools that preserve parental cell line heterogeneity and faithfully reflect endogenous transcriptional regulation of the target gene. We evaluate the knock-in efficiency and rate of undesired random integration in the electroporation method with either a dual-plasmid system (sgRNA and donor DNA in two separate vectors) or a single-plasmid system (sgRNA and donor DNA combined in one vector). We further demonstrate that coupling our single-plasmid construct with an integrase-deficient lentivirus vector (IDLV) packaging system efficiently generates fluorescent knock-in reporter cell pools, offering flexibility between electroporation and lentivirus transduction methods. Notably, compared to the electroporation methods, the IDLV system significantly minimises random integration. Moreover, the resulting reporter cell lines are compatible with most of the available genome-wide sgRNA libraries, enabling unbiased CRISPR screens to identify key transcriptional regulators of a gene of interest. Overall, our methodologies provide a powerful genetic tool for rapid and robust generation of fluorescent reporter knock-in cell pools with precise genome editing by CRISPR-Cas9 for various research purposes.

Cas12a is a next-generation gene editing tool that enables multiplexed gene targeting. Here, we present a mouse model that constitutively expresses enhanced Acidaminococcus sp. Cas12a (enAsCas12a) linked to an mCherry fluorescent reporter. We demonstrate efficient single and multiplexed gene editing in vitro, using primary and transformed cells from enAsCas12a mice. We further demonstrate successful in vivo gene editing, using normal and cancer-prone enAsCas12a stem cells to reconstitute the haematopoietic system of wild-type mice. We also present compact, genome-wide Cas12a knockout libraries, with four crRNAs per gene encoded across one (Scherzo) or two (Menuetto) vectors, and demonstrate the utility of these libraries across methodologies: in vitro enrichment and drop-out screening in lymphoma cells and immortalised fibroblasts, respectively, and in vivo screens to identify lymphoma-driving events. Finally, we demonstrate CRISPR multiplexing via simultaneous gene knockout (via Cas12a) and activation (via dCas9-SAM) using primary T cells and fibroblasts. Our enAsCas12a mouse and accompanying crRNA libraries enhance genome engineering capabilities and complement current CRISPR technologies. Cas12a represents the next generation of gene editing. Here, the authors present the generation and validation of a Cas12a transgenic mouse model. Additionally, the authors create whole-genome Cas12a knockout libraries, and demonstrate their utility across multiple in vitro and in vivo screens.

MYCN and c-MYC are critical driver oncogenes in several childhood cancers, including neuroblastoma. Currently, the clinical development of MYC inhibitors has been hindered by the intrinsically disordered structure of MYC proteins, which lack well-defined ligand-binding pockets. Proliferation-associated protein 2G4 (PA2G4) directly binds to and stabilizes MYCN protein, leading to markedly increased MYCN levels in neuroblastoma cells. Here, we demonstrate that PA2G4 is essential for MYCN-driven tumor growth in neuroblastoma in vivo. Moreover, PA2G4 elevates c-MYC protein levels in neuroblastoma cells by inhibiting its ubiquitin-mediated degradation. In turn, c-MYC upregulates the transcription and protein expression of PA2G4, creating an oncogenic feed-forward expression loop. A small molecule PA2G4 inhibitor, WS6, directly disrupts the PA2G4-c-MYC protein-protein interaction, resulting in decreased levels of both PA2G4 and c-MYC. WS6 exhibited selective cytotoxicity in c-MYC-overexpressing cell lines. Together, these findings identify PA2G4 as a shared cofactor for both the c-MYC and MYCN oncoproteins and highlight its interaction with MYC family oncoproteins as a promising therapeutic vulnerability in MYC-driven cancers.

Hemophagocytic lymphohistiocytosis (HLH) is a potentially fatal cytokine storm syndrome. Its high mortality rate reflects limited therapeutic options and a poor understanding of disease-causing signaling. We show that the NLRP3 inflammasome is responsible for increased mortality in a model of secondary HLH (sHLH). Unexpectedly, neither deletion of the NLRP3-activated pyroptotic effector GSDMD nor combined deletion of the inflammasome-activated cytokines interleukin-1β (IL-1β) and IL-18 conferred strong protection from sHLH. Instead, co-deletion of GSDMD and caspase-8-activated GSDME limited sHLH-driven lethality, demonstrating redundancy in the pyroptotic machinery required to induce sHLH. We also found that bromodomain and extraterminal domain (BET) inhibitors prevent NLRP3-driven pyroptosis, which acted by blocking inflammasome priming. BET inhibitors prevented increased NLRP3 levels in diseased tissue, limited the production of sHLH-associated IL-1β, interferon-γ, and tumor necrosis factor, and protected from sHLH pathogenesis. These findings suggest that targeting NLRP3 could limit sHLH and identify clinically relevant bromodomain-selective BET inhibitors capable of eliminating NLRP3-driven pyroptosis and the sHLH cytokine storm.

MYCN amplification predicts poor prognosis in childhood neuroblastoma. To identify MYCN oncogenic signal dependencies we performed N-ethyl-N-nitrosourea (ENU) mutagenesis on the germline of neuroblastoma-prone TH-MYCN transgenic mice to generate founders which had lost tumorigenesis. Sequencing of the mutant mouse genomes identified the Ring Finger Protein 121 (RNF121WT) gene mutated to RNFM158R associated with heritable loss of tumorigenicity. While the RNF121WT protein localised predominantly to the cis-Golgi Complex, the RNF121M158R mutation in Helix 4 of its transmembrane domain caused reduced RNF121 protein stability and absent Golgi localisation. RNF121WT expression markedly increased during TH-MYCN tumorigenesis, whereas hemizygous RNF121WT gene deletion reduced TH-MYCN tumorigenicity. The RNF121WT-enhanced growth of MYCN-amplified neuroblastoma cells depended on RNF121WT transmembrane Helix 5. RNF121WT directly bound MYCN protein and enhanced its stability. High RNF121 mRNA expression associated with poor prognosis in human neuroblastoma tissues and another MYC-driven malignancy, laryngeal cancer. RNF121 is thus an essential oncogenic cofactor for MYCN and a target for drug development. A chemical mutagenesis screen identifies RNF121 as an oncogenic cofactor for MYCN in neuroblastoma.