The tumour suppressor p53 transcriptionally regulates a range of target genes that control cell growth and survival. Mutations of p53 have been implicated in the development of ∼50% of human cancers, including those instigated by exposure to mutagens. Although numerically rare, cancers can arise as a consequence of inherited mutations, such as in the Li–Fraumeni syndrome, which is caused by mutation of one p53 allele. Gene-targeted mice deficient for p53 have been generated to study this familial cancer syndrome. On a C57BL/6 background, p53 -deficient mice develop primarily thymic lymphoma and more rarely sarcoma. Evasion of apoptosis is considered to be essential for neoplastic transformation. As proteins of the Bcl-2 family are the critical regulators of apoptosis, we investigated the role of the pro-survival members Bcl-2, Bcl-x L and Bcl-w in cancer development in p53 +/− and p53 −/− mice by testing whether ABT-737, a pharmacological inhibitor of these proteins, could prevent or delay tumourigenesis. Our studies showed that ABT-737 prophylaxis only caused a minor delay and reduction in γ -radiation-induced thymic lymphoma development in p53 −/− mice, but this was accompanied by a concomitant increase in sarcoma. These data show that, collectively, Bcl-2, Bcl-x L and Bcl-w have only minor roles in thymic lymphoma development elicited by defects in p53, and this may indicate that Mcl-1 and/or A1 may feature more prominently in this process.

ABSTRACT Our previous mouse genetic studies showed that loss of the transcription repressor MNT enhanced apoptosis of premalignant lymphoid cells over-expressing MYC and inhibited lymphoma development. Here, we have explored the consequences of inducing Mnt deletion in fully malignant lymphoma cells. MNT loss provoked apoptosis of p53 wt and, albeit more slowly, p53 mutant Eμ-Myc lymphoma cells, preceded by elevated levels of major BH3-only proteins BIM and PUMA. By inhibiting apoptosis, we showed that MNT loss also impaired cell cycling and increased senescence. Eμ-Myc lymphoma cells depend on the BCL-2 ortholog MCL-1 for survival and expansion and, importantly, MNT loss enhanced their sensitivity to the MCL-1 inhibitor S63845 and to several chemotherapeutic agents. In BCL-2-overexpressing Eμ-Myc lymphoma cells, which model aggressive human ‘Double Hit Lymphomas’, MNT loss enhanced sensitivity to the BCL-2 inhibitor ABT-199, even after BAX loss. Furthermore, MNT deletion improved drug responses of two long-established Burkitt Lymphoma cell lines. SIGNIFICANCE This study establishing the MNT dependency of Eμ-Myc lymphoma cells and demonstrating that MNT loss enhances their sensitivity to apoptosis induced by conventional chemotherapeutics and BH3 mimetic drugs provides strong proof-of-concept for developing MNT inhibitors to improve treatment of MYC-driven blood cancers.

Abstract Medulloblastoma (MB) is the most common malignant paediatric brain tumour and comprises four molecular subgroups with distinct biological and clinical characteristics. Although survival outcomes have improved for some patients, current multimodal therapies, including surgery, craniospinal irradiation, and intensive chemotherapy remain highly toxic and frequently cause severe long-term neurocognitive side effects. There is therefore a critical need for more effective and less harmful treatment strategies, particularly for high-risk MYC-driven disease. Anti-apoptotic members of the BCL-2 family, including BCL-XL and MCL-1, are commonly dysregulated in MB and contribute to tumour cell survival and therapeutic resistance. BH3 mimetics are small-molecule inhibitors that selectively antagonise these pro-survival proteins, enabling BAK/BAX activation and induction of intrinsic mitochondrial apoptotic cell death. In parallel, altered tumour metabolism represents an emerging vulnerability in cancer. Dihydroorotate dehydrogenase (DHODH), catalyses a key step in de novo pyrimidine synthesis and is upregulated in rapidly proliferating tumour cells. DHODH inhibitors such as BAY-2402234 exploit this metabolic dependency. Here, we investigated the therapeutic potential of combining BH3 mimetics with the standard-of-care chemotherapeutic cyclophosphamide or the DHODH inhibitor BAY-2402234 in MYC-driven MB cell lines in vitro. In D425 and D283 MB cells, the BCL-XL inhibitor A1331852 or the MCL-1 inhibitor S63845 significantly enhanced tumour cell death when combined with cyclophosphamide or BAY-2402234. Increased apoptotic signalling was confirmed by elevated cleavage of caspase-3 and PARP-1. Combined treatments with BAY-2402234 and BH3-mimetics was highly synergistic, as confirmed by BLISS synergy assays. Genetic deletion of the pro-apoptotic effectors BAK and BAX conferred resistance to BH3 mimetic induced apoptosis, confirming on-target engagement of mitochondrial cell death pathways. In contrast, loss of BAK/BAX did not protect cells from BAY-2402234–mediated cytotoxicity, suggesting additional apoptosis-independent mechanisms. Mechanistically, BAY-2402234 induced S-phase cell cycle arrest, whereas cyclophosphamide triggered G2/M-phase arrest. Finally, we explored ferroptosis as an additional programmed cell death vulnerability. The ferroptosis inducers erastin and RSL3 demonstrated cooperative killing when combined with either BCL-XL or MCL-1 inhibition. Together, these findings support a novel combination treatment paradigm integrating BH3-mimetics with chemotherapy, metabolic inhibition, or ferroptosis induction, and highlight programmed cell death-based strategies as promising therapeutic avenues for medulloblastoma.

Abstract BH3 mimetic drugs are showing great success in the clinic, particularly in hematological cancers. However, p53-mutant hematological cancers remain a major clinical challenge and BH3 mimetic drugs have not shown marked single-agent effects in solid cancers. BH3-mimetic drugs inhibit BCL-2 pro-survival proteins to promote cancer cell apoptosis. Despite acting downstream of the tumor suppressor p53 (TP53, TRP53), functional p53 is required for maximal cancer cell killing by BH3-mimetic drugs. Here, we report that p53 can be activated following BH3-mimetic induced mitochondrial outer membrane permeabilization, which leads to further induction of BH3-only proteins, thereby potentiating the pro-apoptotic signal. p53-deficient blood cancers lack this feed-forward loop, providing opportunities for survival and disease relapse after BH3-mimetic treatment. Of note, the therapeutic barrier imposed by defects in p53 could be overcome by direct activation of the cGAS/STING pathway in malignant cells. This causes killing of blood cancer cells through p53-independent up-regulation of pro-apoptotic BH3-only proteins. Combining clinically relevant STING agonists with BH3-mimetic drugs efficiently killed p53-mutant mouse B lymphoma, human extranodal NK/T lymphoma and human acute myeloid leukemia cells. This represents a promising therapy regime that can be fast-tracked to tackle p53-mutant blood cancers, and possibly also other cancers, in the clinic. Citation Format: Sarah T Diepstraten, John E La Marca, Yin Yuan, Fiona C Brown, Andrew W Roberts, Andrew H Wei, Gemma L Kelly, Andreas Strasser. Enhancing BH3 mimetic drug induced killing of malignant cells for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2026; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts); 2026 Apr 17-22; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2026;86(8_Suppl):Abstract nr SY35-01.

Survival rates for many blood cancers have improved significantly over the last decade; however, those with mutations in the tumor suppressor gene p53 are aggressive, associated with poor outcomes, and remain a major clinical challenge.BH3-mimetic drugs, a new class of anticancer therapy, trigger apoptosis in cancer cells by inhibiting prosurvival BCL-2 family proteins downstream of p53. The leading BH3-mimetic venetoclax has been approved for therapy of certain blood cancers; however, we found that p53 mutations blunt the effectiveness of BH3-mimetic drugs. Recently, we discovered the underlying mechanism – a novel role for p53 in enforcing apoptosis downstream of mitochondrial outer membrane permeabilization.Additionally, we discovered a new way to kill aggressive blood cancer cells with p53 mutations by directly activating the DNA-sensing protein STING. Although STING agonists have previously been investigated as immune modulators, we showed that this drug class can directly induce apoptosis in blood cancer cells. Combining BH3-mimetics and STING agonists was incredibly effective at killing human blood cancer cells in vitro and in vivo, even those with currently dismal prognoses like natural killer/T-cell lymphoma and p53-mutant acute myeloid leukemia.As STING agonists have already been shown to be safe in humans, this combination therapy represents a novel therapeutic direction that can be fast-tracked to the clinic for treatment of aggressive blood cancers.

In the ongoing project ESPRIT, a goal is to investigate the contribution of the chemical composition and associated chemical reactions to the Earth’s upper atmosphere. This is realized through a combined analysis of thermospheric neutral density estimates and the exploration of external parameters of the interplanetary space, including variations in the magnetic field and the merged electric field. Regarding changes in the chemical composition of the Earth’s atmosphere, which might cause heating and cooling effects, we investigated TIMED/SABER measurements in conjunction with findings from the 1D first-principles hydrodynamic upper atmosphere model Kompot code, which shows some significant expansion in the density profile mainly based on the increased XUV flux from the Sun. The neutral mass densities were processed based on accelerometer measurements as well as on kinematic orbit information (Süsser-Rechberger et al. 2022). This allowed us to successfully process kinematic orbits for 19 different satellites at an altitude range of approximately 400 to 1300 km. Both approaches are realized using the in-house software package GROOPS. During the evaluation, significant improvements in the processing and parametrization could be achieved compared to previous solutions, especially through refined models for solar radiation pressure, the Earth’s re-radiation, the thermal radiation of the satellite itself and the consideration of the chemical composition of the atmosphere. Based on these new neutral density estimates, investigations regarding the effects of solar eruptions on the various satellites are performed and used for attempting to forecast the orbital decay of LEO satellites.

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.

Hair follicles cycle through expansion, regression and quiescence. To investigate the role of MCL‑1, a BCL‑2 family protein with anti‑apoptotic and apoptosis‑unrelated functions, we delete Mcl‑1 within the skin epithelium using constitutive and inducible systems. Constitutive Mcl‑1 deletion does not impair hair follicle organogenesis but leads to gradual hair loss and elimination of hair follicle stem cells. Acute Mcl‑1 deletion rapidly depletes activated hair follicle stem cells and completely blocks depilation‑induced hair regeneration in adult mice, while quiescent hair follicle stem cells remain unaffected. Single‑cell RNA‑seq profiling reveals the engagement of P53 and DNA mismatch repair signaling in hair follicle stem cells upon depilation‑induced activation. Trp53 deletion rescues hair regeneration defects caused by acute Mcl‑1 deletion, highlighting a critical interplay between P53 and MCL‑1 in balancing proliferation and death. The ERBB pathway plays a central role in sustaining the survival of adult activated hair follicle stem cells by promoting MCL‑1 protein expression. Remarkably, the loss of a single Bak allele, a pro‑apoptotic Bcl‑2 effector gene, rescues Mcl‑1 deletion‑induced defects in both hair follicles and mammary glands. These findings demonstrate the pivotal role of MCL‑1 in inhibiting proliferation stress‑induced apoptosis when quiescent stem cells activate to fuel tissue regeneration.

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.

The landmark discovery of the BCL-2 gene and then its function marked the identification of inhibition of apoptotic cell death as a crucial novel mechanism driving cancer development and launched the quest to discover the molecular control of apoptosis. This work culminated in the generation of specific inhibitors that are now in clinical use, saving and improving tens of thousands of lives annually. Here, some of the original players of this story, describe the sequence of critical discoveries. The t(14;18) chromosomal translocation, frequently observed in follicular lymphoma, allowed the identification and the cloning of a novel oncogene (BCL-2) juxtaposed to the immunoglobulin heavy chain gene locus (IgH). Of note, BCL-2 acted in a distinct manner as compared to then already known oncogenic proteins like ABL and c-MYC. BCL-2 did not promote cell proliferation but inhibited cell death, as originally shown in growth factor dependent haematopoietic progenitor cell lines (e.g., FDC-P1) and in Eμ-Myc/Eμ-Bcl-2 double transgenic mice. Following a rapid expansion of the BCL-2 protein family, the Abbott Laboratories solved the first structure of BCL-XL and subsequently the BCL-XL/BAK peptide complex, opening the way to understanding the structures of other BCL-2 family members and, finally, to the generation of inhibitors of the different pro-survival BCL-2 proteins, thanks to the efforts of Servier/Norvartis, Genentech/WEHI, AbbVie, Amgen, Prelude and Gilead. Although the BCL-2 inhibitor Venetoclax is in clinical use and inhibitors of BCL-XL and MCL-1 are undergoing clinical trials, several questions remain on whether therapeutic windows can be achieved and what other agents should be used in combination with BH3 mimetics to achieve optimal therapeutic impact for cancer therapy. Finally, the control of the expression of BH3-only proteins and pro-survival BCL-2 family members needs to be better understood as this may identify novel targets for cancer therapy. This story is still not concluded!

Global Navigation Satellite System (GNSS) products are an integral part of a wide range of scientific and commercial applications such as precise orbit determination for low Earth orbit satellites, earthquake monitoring, GNSS reflectometry, tropospheric and ionospheric research, surveying and many more. These products, consisting of GNSS orbits, clocks, phase biases and more, are generated by the International GNSS Service (IGS) analysis centres by processing observations from a global network of ground stations to one or more GNSS constellations. The processing consists of a combined station position and GNSS satellite orbit determination using a least squares approach donated as global multi-GNSS processing. Within the IGS 3rd reprocessing (repro3) campaign for the new release of the International Terrestrial Reference Frame (ITRF), Graz University of Technology (TUG), Working Group Satellite Geodesy has contributed as an Analysis Centre (AC) for global multi-GNSS processing. TUG has demonstrated high quality results on par with other ACs using its self-developed geodetic processing software Gravity Recovery Object Oriented Programming System (GROOPS). Within GROOPS the global multi-GNSS processing uses the raw observation approach. The raw observation approach uses all measurements as observed by the receivers without explicitly creating any linear combinations or differences. This allows the information contained in each individual observation to be fully exploited. GROOPS has been shown to be capable of global multi-GNSS processing using GPS, Galileo and GLONASS. With more publicly available metadata for the BeiDou system, GROOPS has been further developed to use BeiDou within global multi-GNSS processing using the raw observation approach. Therefore, in this contribution we present the improvements in GROOPS global multi-GNSS processing using BeiDou and discuss the quality of the resulting orbit, station position time series, clock and phase bias products.

Hair follicles (HFs) cycle between expansion, regression and quiescence. To investigate the role of MCL-1, a BCL-2 family protein with anti-apoptotic and apoptosis-unrelated functions in this dynamic process, we deleted Mcl-1 within the skin epithelium using both constitutive and inducible systems. Constitutive deletion of Mcl-1 did not impair HF organogenesis but resulted in gradual hair loss and elimination of HF stem cells (HFSC) while acute Mcl-1 deletion rapidly depleted activated HFSCs in adult mice. Single-cell RNA-seq profiling revealed that HFSCs are under proliferation-associated stress during depilation-induced anagen. The ERBB pathway was shown to play a central function in conferring the survival of adult activated HFSCs through promoting MCL-1 protein expression. Remarkably, the loss of a single Bak allele rescued Mcl-1 deletion-induced defects in HFs. These findings demonstrate the pivotal role of MCL-1 in inhibiting stress-induced apoptosis when quiescent stem cells undergo activation to fuel tissue regeneration. Hui San Chin, Jinming Cheng, Shih Han Hsu, Guo Guang Lum, Maria TK Zaldiva, Fusheng Guo, Keerthana Mallavarapu, Felicity C. Jackling, Gordon K. Smyth, Geoffrey J. Lindeman, Andreas Strasser, Jane E. Visvader, Yunshun Chen, Ting Chen, Nai Yang Fu. MCL-1 safeguards activated hair follicle stem cells to enable adult hair regeneration [abstract]. In: Proceedings of Frontiers in Cancer Science 2024; 2024 Nov 13-15; Singapore. Philadelphia (PA): AACR; Cancer Res 2025;85(15_Suppl):Abstract nr P51.

Excessive inflammation and cytokine release are hallmarks of severe COVID-19. Certain programmed cell death processes can drive inflammation, however, their role in the pathogenesis of severe COVID-19 is unclear. Pyroptosis is a pro-inflammatory form of regulated cell death initiated by inflammasomes and executed by the pore-forming protein gasdermin D (GSDMD). Using an established mouse adapted SARS-CoV-2 virus and a panel of gene-targeted mice we found that deletion of the inflammasome (NLRP1/3 and the adaptor ASC) and pore forming proteins involved in pyroptosis (GSDMA/C/D/E) only marginally reduced IL-1β levels and did not impact disease outcome or viral loads. Furthermore, we found that SARS-CoV-2 infection did not trigger GSDMD activation in mouse lungs. Finally, we did not observe any difference between WT animals and mice with compound deficiencies in the pro-inflammatory initiator caspases (C1/11/12−/−). This indicates that the classical canonical and non-canonical pro-inflammatory caspases known to process and activate pro-IL-1β, pro-IL-18 and GSDMD do not substantially contribute to SARS-CoV-2 pathogenesis. However, the loss of IL-1β, but not the absence of IL-18, ameliorated disease and enhanced survival in SARS-CoV-2 infected animals compared to wildtype mice. Collectively, these findings demonstrate that IL-1β is an important factor contributing to severe SARS-CoV-2 disease, but its release was largely independent of inflammasome and pyroptotic pathways.

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.

BH3 mimetic drugs that selectively target the pro-survival BCL2 proteins are highly promising for cancer treatment, most notably for treating blood cancers. Venetoclax, which inhibits BCL2, is now approved for treating chronic lymphocytic leukemia (CLL) and acute myeloid leukemia (AML). Preferably, robust and validated assays would identify patients most likely to benefit from therapy with venetoclax itself or with inhibitors of other pro-survival proteins. A sophisticated method that has been developed is the BH3 profiling assay. In this assay, permeabilized, instead of intact, cells are treated for a few hours with inhibitors of the pro-survival BCL2 proteins, and the resultant mitochondrial depolarization measured. Sensitivity to a specific inhibitor (e.g., venetoclax or other BH3 mimetics) is then used to infer the reliance of a tumor (e.g., CLL) on one or more pro-survival BCL2 proteins. However, we found that this methodology cannot reliably identify such dependencies. In part, this is because almost all cells express multiple pro-survival BCL2 proteins that restrain BAX and BAK which must be inhibited before mitochondrial depolarization and apoptosis can proceed. Using genetic and pharmacological tools across multiple cell line models of blood cancer, we demonstrated that selective BCL2 inhibitors have important flow-on effects that includes the redistribution of BH3-only proteins to ancillary pro-survival proteins not directly engaged by the inhibitor. These secondary effects, critical to the biological action of selective inhibitors, were not accurately recapitulated in permeabilized cells, probably due to the limited time frame possible in such assays or the altered biophysical conditions when cells are permeabilized. While we could consistently define the sensitivity of a tumor cell to a particular BH3 mimetic drugs using intact cells, this was not reliable with permeabilized cells. These studies emphasize the need to carefully evaluate assays on permeabilized cells undertaken with inhibitors of the pro-survival BCL2 proteins.

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.

Inflammation and excess cytokine release are hallmarks of severe COVID-19. While programmed cell death is known to drive inflammation, its role in SARS-CoV-2 pathogenesis remains unclear. Using gene-targeted murine COVID-19 models, we here find that caspase-8 is critical for cytokine release and inflammation. Loss of caspase-8 reduces disease severity and viral load in mice, and this occurs independently of its apoptotic function. Instead, reduction in SARS-CoV-2 pathology is linked to decreased IL-1β levels and inflammation. Loss of pyroptosis and necroptosis mediators in gene-targeted animals provides no additional benefits in mitigating disease outcomes beyond that conferred by loss of caspase-8. Spatial transcriptomic and proteomic analyses of caspase-8-deficient mice confirm that improved outcomes are due to reduced pro-inflammatory responses, rather than changes in cell death signalling. Elevated expression of caspase-8 and cFLIP in infected lungs, alongside caspase-8-mediated cleavage of N4BP1, a suppressor of NF-kB signalling, indicates a role of this signalling axis in pathological inflammation. Collectively, these findings highlight non-apoptotic functions of caspase-8 as a driver of severe COVID-19 through modulation of inflammation, not through the induction of apoptosis.