Stephen W. G. Tait

Through mitochondrial outer membrane permeabilization (MOMP), mitochondria are central to apoptosis. MOMP is pro-inflammatory, impacting diverse processes including anti-tumor immunity and cellular senescence. Despite this, how damaged mitochondria activate inflammation remains unclear. Recent studies have shown that following MOMP, mitochondria are extensively ubiquitinated activating pro-inflammatory NF-κB signaling. We identify the E3 ligase, RNF213, as essential for pro-inflammatory mitochondrial ubiquitination following MOMP. RNF213 has an established role in pro-inflammatory, cell-autonomous immunity to bacteria and other pathogens. We discover that RNF213 is required for mitochondrial M1-linked (linear) ubiquitination. Interestingly, this was found to be independent of the canonical M1-ubiquitin ligase complex LUBAC. RNF213 can directly catalyze M1-linked ubiquitination. By promoting mitochondrial M1-linked ubiquitination, RNF213 initiates the recruitment of the essential NF-κB adaptor molecule, NEMO, and subsequently activates pro-inflammatory NF-κB signaling. Collectively, our findings highlight striking similarities between how cells detect damaged mitochondria and intracellular pathogens, leading to inflammation.

Ferroptosis is an iron-dependent form of non-apoptotic cell death driven by catastrophic lipid peroxidation1,2. Sensitivity to ferroptosis in cancer is a hallmark of chemotherapy-resistant cells3,4,5 and low-density in vitro cultures6,7. Hypotheses for heightened ferroptosis sensitivity include the Hippo effectors YAP and TAZ7 and the adoption of a mesenchymal state5. However, whether analogous ferroptosis-sensitive states exist in haematological malignancies, and how they are regulated in these contexts, remains an open and important question. Here, using acute lymphoblastic leukaemia (ALL) as a disease model we demonstrate that at high cell density and in bulk disease before chemotherapy, the Warburg effect drives accumulation of NADPH, triggering activation of the NADPH sensors MARCHF6 and FTO. We find that MARCHF6 mediated squalene accumulation and enhanced selenium handling, paired with FTO mediated SREBP1 activation, is sufficient to circumvent reliance on GPX4 in ALL cells. Consistently, single-cell transcriptomic analysis of minimal residual disease (MRD) samples from B- and T-cell ALL patients revealed genes involved in glycolysis to be transiently downregulated at MRD, enabling effective in vivo GPX4 targeting after chemotherapy in a patient derived xenograft (PDX) model. Furthermore, we observed that glycolysis-driven Diffuse large B-cell lymphoma (DLBCL) models were more resistant to GPX4 inhibition or genetic deletion than models displaying oxidative phosphorylation (OXPHOS) dependency. Collectively, these findings establish a role for the Warburg effect in protecting against ferroptosis and uncover a dual NADPH-dependent resistance mechanism, positioning metabolic state as a therapeutically exploitable context-dependent vulnerability in lymphoid malignancy.

It took decades from the discovery of BCL-2, initially identified in chromosomal translocations associated with lymphoid malignancies, to understand how BCL-2 and its family members regulate apoptosis, launching a transformative journey in cancer biology often called “the road to ruin”. Developing powerful BCL-2 inhibitors for clinical use required decades. Yet, this remains as one of the most successful achievements in a field that started ~40 years ago, as recounted by its pioneers. BCL-2 was later found to inhibit apoptosis by preventing mitochondrial outer membrane permeabilization (MOMP), a breakthrough that clarified its role in cancer pathogenesis. Such effects of BCL-2 on MOMP prevent cytochrome c release and caspase activation, while its family members—anti-apoptotic proteins (e.g. BCL-2, BCL-XL) and pro-apoptotic proteins (e.g. BAX, BAK, BH3-only proteins)—orchestrate a delicate balance in cell death regulation. MicroRNAs like miR-15/16, often deleted in chronic lymphocytic leukaemia (CLL), modulate BCL-2 expression, driving oncogenesis. Mechanistically, BAX/BAK oligomerization forms mitochondrial pores, with sublethal MOMP triggering inflammation via cGAS-STING and NF-κB pathways. Alternative MOMP inducers (e.g. BOK) and mitochondrial dynamics further refine apoptotic control. Clinically, the BCL-2 inhibitor venetoclax has revolutionized CLL and acute myeloid leukemia (AML) treatment, showing efficacy in TP53-mutant CLL and elderly AML patients when combined with CD20 antibodies or hypomethylating agents. However, resistance, driven by BCL-2 mutations (e.g. Gly101Val) or MCL-1 upregulation, poses challenges. Limited success in solid tumors underscores the complexity of BCL-2 family dependencies. Future directions include novel inhibitors targeting MCL-1 or BCL-XL, BH3 profiling for precision therapy, and combinations with immune or DNA repair modulators. Non-apoptotic roles of BCL-2 in metabolism also warrant exploration. This review highlights the clinical success of BCL-2 inhibitors, addresses resistance mechanisms, and explores future directions, including sublethal MOMP, inflammatory outcomes, and novel inhibitors. Celebrating the collaborative, interdisciplinary efforts that transformed fundamental discoveries into life-saving therapies, this account underscores both the triumphs and the “potholes” encountered on the path to understanding apoptosis, while identifying open questions for ongoing research.

The leptomeninges present a challenging tumour microenvironment with cells receiving low levels of nutrients and oxygen from cerebrospinal fluid (CSF), however these metabolic constraints are yet to be exploited therapeutically. Central nervous system (CNS) relapse in acute lymphoblastic leukaemia (ALL) remains a formidable clinical challenge because the leptomeningeal niche restricts drug penetration and immune surveillance. Current CNS-directed treatments rely on neurotoxic intrathecal chemotherapy, underscoring the urgent need for novel targeted strategies. Here, we uncover a profound niche-specific metabolic vulnerability in CNS-resident ALL cells, characterised by an obligate reliance on LRP8-mediated selenium uptake to sustain selenocysteine biosynthesis and GPX4 activity under profound glutathione limitation. We show that scarcity of thiols and cystine in CSF creates an inherently pro-ferroptotic microenvironment. Interference with selenocysteine biosynthesis under these conditions induces synthetic lethality in both in vitro and in vivo CNS-ALL models. This vulnerability is exploitable both by genetic targeting of the selenocysteine biosynthesis pathway and, notably, through repurposing the FDA-approved agent Auranofin, which disrupts selenium utilisation, induces lipid peroxidation, and demonstrates CNS-specific anti-leukaemic efficacy with excellent tolerability in vivo. These findings identify a novel mechanistically grounded approach, leveraging features of the unique leptomeningeal microenvironment to selectively kill invading cells, with potential implications for all leptomeningeal-tropic malignancies.

Regulated necrosis is a known direct consequence of activation of the necroptosis‐ and pyroptosis‐ pathways, but may also result from apoptosis in a process referred to as secondary necrosis. Apoptosis is well understood to be mediated by caspase activation, but the mechanisms that lead to plasma membrane rupture in secondary necrosis remain considerably obscure. Recent data suggested a caspase‐mediated cleavage of gasdermin E (GSDME), a member of the gasdermin family. Here, apoptosis induced by diphtheria toxin (DT) is employed as a novel tool to study secondary necrosis. In addition, cisplatin and anti‐Fas monoclonal antibody Jo2 are employed to study secondary necrosis in cell culture and in vivo, respectively. Despite prominent, yet epiphenomenal cleavage of GSDME, it is demonstrated that silencing or CRISPR/Cas9‐mediated knockout of GSDME does not compromise the kinetics of secondary necrosis induced by DT or cisplatin. During Jo2‐induced acute liver toxicity in mice, GSDME expressed in the necrotic liver is detected predominantly in its uncleaved form. In conclusion, the hypothesis of GSDME to be a central mediator of secondary necrosis in these model systems is disproved.

Upon cell death signals, the apoptotic protease-activating factor Apaf1 and cytochrome c interact to form the apoptosome complex. The apoptosome is crucial for mitochondrial apoptosis, as it activates caspases that dismantle the cell. However, the in vivo assembly mechanism and appearance of the apoptosome remain unclear. We show that upon onset of apoptosis, Apaf1 molecules accumulate into multiple foci per cell. Disassembly of the foci correlates with cell survival. Structurally, Apaf1 foci resemble organelle-sized, cloud-like assemblies. They form through specific interactions with cytochrome c, contain caspase-9, and depend on procaspase-9 expression for their formation. We propose that Apaf1 foci correspond to the apoptosome in cells. Transientness and ultrastructure of Apaf1 foci suggest that the dynamic spatiotemporal organisation of apoptosome components regulates progression of apoptosis.

Apoptotic cell death is fundamental to the life of multicellular organisms, making central contributions to processes ranging from embryonic development to tissue homeostasis. Two distinct apoptosis pathways have been defined: extrinsic apoptosis and mitochondrial apoptosis. As we discuss, apoptosis is an evolutionary conserved process that is, unsurprisingly, tightly regulated. Inhibition of apoptosis can promote cancer, whereas inappropriate apoptosis has been associated with various neurodegenerative diseases. At its core, apoptosis is initiated and executed by proteases called caspases that, once activated, rapidly dismantle dying cells, ensuring that apoptosis is immunologically silent. In this chapter, we discuss the molecular mechanisms of apoptosis and its evolutionary conservation. Secondly, we highlight the emerging concept that apoptosis signalling can be engaged at non-lethal levels with diverse biological effects. Finally, we provide an overview of how apoptosis can impact health and disease, discussing ways in which apoptosis can be therapeutically targeted.