Annexin A6 emerges as a hidden switch controlling leukaemia cell survival and drug response

Scientists at the University of Barcelona and collaborating institutions across Europe and Australia have identified a surprising new player in the survival machinery of acute lymphoblastic leukaemia (ALL), the most common childhood cancer. The protein Annexin A6 (ANXA6), long known as a calcium-dependent membrane-binding molecule involved in cellular signalling and membrane dynamics, now appears to act as a molecular rheostat that sets how close leukaemia cells sit to the brink of self-destruction. The discovery, published in Cell Death Discovery, suggests that ANXA6 levels could help predict which patients will respond to a class of targeted anticancer drugs known as BH3 mimetics, and it opens a potential new avenue for manipulating the apoptotic threshold of cancer cells.

The research team, led by Joan Montero and Carles Rentero, set out to understand how membrane-associated proteins influence the intrinsic pathway of apoptosis, the controlled self-destruction programme that healthy cells and many cancer therapies rely on. At the centre of this pathway lies the mitochondrial outer membrane, where members of the BCL-2 protein family engage in a delicate tug-of-war. Pro-apoptotic effectors such as BAK and BAX, when unleashed, punch holes in the mitochondrial membrane and trigger cell death, while pro-survival guardians such as BCL-2 and BCL-xL keep them in check. The balance between these opposing forces determines what researchers call apoptotic priming, a measure of how readily a cell will commit to mitochondrial apoptosis when stressed.

To quantify this balance, the investigators employed BH3 profiling, a functional precision medicine technique that uses synthetic peptides derived from BH3 domains, the interaction motifs of BCL-2 family proteins, to probe the mitochondrial priming state of living cells. When the researchers depleted ANXA6 in HeLa cells, a widely used laboratory model, they observed a striking reduction in apoptotic priming. In other words, cells lacking ANXA6 became more resistant to mitochondrial apoptosis, effectively raising their threshold for self-destruction. This finding positioned ANXA6, for the first time, as a regulator of the apoptotic machinery rather than merely a structural component of cellular membranes.

Digging deeper into the molecular consequences of ANXA6 loss, the team found that the reduced priming was accompanied by two key changes in the BCL-2 family landscape: an increase in BCL-2 expression, the canonical anti-apoptotic guardian, and a decrease in BAK, one of the essential executioner proteins that directly mediates mitochondrial membrane permeabilisation. Importantly, these changes occurred independently of any alterations in mitochondrial mass or morphology, indicating that ANXA6 does not simply reshape the organelle but instead rewires the signalling networks that govern the BCL-2 family. The phenotype therefore reflects a genuine shift in the regulatory circuitry of apoptosis rather than a passive consequence of altered mitochondrial biology.

The mechanistic clue emerged when the researchers examined pro-survival signalling pathways upstream of the BCL-2 family. ANXA6-deficient cells displayed enhanced activation of AKT, a well-characterised kinase that promotes cell survival and is known to modulate the activity and abundance of BCL-2 family members through phosphorylation-dependent mechanisms. This observation supports a model in which ANXA6 functions as a negative regulator of pro-survival signalling: when ANXA6 is present, AKT activity is held in check, the BCL-2 family balance tilts toward apoptosis, and cells remain primed for death. When ANXA6 is lost, the brakes come off pro-survival pathways, BCL-2 accumulates, BAK dwindles, and the cell becomes fortressed against mitochondrial apoptosis.

Having established this mechanism in a cellular model, the team turned to acute lymphoblastic leukaemia, a disease where the BCL-2 family has direct clinical relevance. Across a panel of ALL cell lines and patient samples, the researchers uncovered a consistent correlation pattern: ANXA6 expression inversely correlated with BCL-2 levels and positively correlated with the pro-apoptotic proteins BAK and BAD. This inverse relationship mirrors the mechanism defined in HeLa cells and suggests that ANXA6 abundance may serve as a biomarker of the apoptotic wiring state in leukaemia cells, potentially distinguishing primed, drug-sensitive tumours from resistant ones.

The functional consequences of this correlation were tested directly in selected ALL cell models. When ANXA6 was depleted, apoptotic priming dropped, confirming that the mechanism operates in leukaemia cells and is not an artefact of the HeLa system. More strikingly, ANXA6 depletion increased sensitivity to pharmacological inhibition of both BCL-2 and BCL-xL, the two major pro-survival proteins targeted by BH3 mimetics, a class of drugs that includes venetoclax, an agent already approved for certain blood cancers. This result carries a paradoxical but clinically meaningful implication: although ANXA6 loss lowers apoptotic priming and makes cells more resistant to intrinsic death signals, it simultaneously renders them more dependent on BCL-2 family pro-survival proteins for their survival, creating a therapeutic vulnerability that BH3 mimetics can exploit.

This apparent paradox resolves once the BCL-2 family balance is viewed as a system. By reducing BAK and increasing BCL-2, ANXA6 depletion shifts the survival of leukaemia cells from a state where death effectors are readily activated to one where survival hinges almost entirely on the anti-apoptotic shield. In such a state, blocking the shield with a BH3 mimetic leaves the cell with few remaining defences, and apoptosis proceeds efficiently. The finding suggests that ANXA6 expression levels could help stratify ALL patients by their likely dependency on BCL-2 family proteins, guiding the selection of those most likely to benefit from venetoclax or related agents, an approach consistent with the broader movement toward functional precision medicine in haematological malignancies.

The study also fills a conceptual gap in cancer biology by connecting membrane dynamics to apoptotic regulation. ANXA6 is a calcium-dependent phospholipid-binding protein involved in endocytosis, membrane repair, and signalling platform organisation, processes that have been implicated in cancer progression but rarely linked directly to the mitochondrial apoptosis machinery. The new data indicate that these membrane-oriented functions may feed into survival signalling cascades such as the AKT pathway, which in turn sculpt the BCL-2 family. If confirmed in further models, this positions annexins and other membrane-associated proteins as upstream nodes in the network that determines whether a cancer cell lives or dies in response to therapy.

For patients with acute lymphoblastic leukaemia, particularly those with relapsed or refractory disease where treatment options remain limited, the findings offer a potential path toward more rational drug selection. Rather than relying solely on genetic mutations to guide therapy, clinicians may one day incorporate measurements of apoptotic priming and ANXA6 expression to identify tumours primed for BCL-2 dependency. The Barcelona team, working alongside collaborators at Charité-Universitätsmedizin Berlin, the German Cancer Consortium, Prinses Máxima Centrum in Utrecht, the University of Heidelberg, and the University of Sydney, emphasises that their results position ANXA6 as a modulator of the apoptotic threshold and a potential determinant of BCL-2 dependency and response to BH3 mimetics in ALL. Further studies will be needed to validate ANXA6 as a predictive biomarker in prospective clinical cohorts and to explore whether pharmacologically targeting ANXA6 or its downstream signalling partners can sensitise resistant leukaemias to existing apoptotic therapies.

Subject of Research: The role of Annexin A6 in regulating apoptotic priming and BCL-2 family protein balance in acute lymphoblastic leukaemia

Article Title: Annexin A6 modulates apoptotic priming and BCL-2 dependency in acute lymphoblastic leukaemia

Article References: Bernaus-Esqué, M., Alcon, C., Manzano-Muñoz, A., Liu, Y., Lazaro-Navarro, J., Alasfar, L., Eckert, C., Lissat, A., Garrabou, G., Lu, A., Tebar, F., Grewal, T., Enrich, C., Montero, J., & Rentero, C. (2026). Annexin A6 modulates apoptotic priming and BCL-2 dependency in acute lymphoblastic leukaemia. Cell Death Discovery. https://doi.org/10.1038/s41420-026-03336-z

Image Credits: AI Generated

DOI: 10.1038/s41420-026-03336-z

Keywords: Annexin A6, apoptotic priming, BCL-2, acute lymphoblastic leukaemia, BH3 mimetics, AKT signalling, BAK, BAD, mitochondrial apoptosis, functional precision medicine, venetoclax, haematological malignancies