Neutron reflectometry reveals how cancer cells can avoid programmed cell death
Mar 26, 2026
Researchers have revealed a mechanism by which cancer cells can avoid programmed cell death. The team, from ISIS, the European Spallation Source (ESS), Lund University, the University of Umeå, the Institut Laue-Langevin (ILL) and Diamond Light Source, used an integrated combination of techniques to investigate how the Bax and Bcl-2 proteins involved in regulating programmed cell death, or apoptosis, interact at the surface of the mitochondrial outer membrane.
Apoptosis is one of the processes our body uses to control cell growth and proliferation. It plays a vital role in embryo development, in removing old or damaged cells, and in our immune systems. However, when it goes wrong, as in many cancers, those cells can escape their apoptotic removal and rapidly multiply to form tumours. Many cancer therapies, such as chemotherapy or radiotherapy, treat cancers by causing DNA damage or stressing cells, which leads to apoptosis. However, many tumours can also become treatment resistant by escaping even treatment-induced apoptotic death.
Controlling apoptosis
One of the key proteins that controls apoptosis is called Bax. Bax works by creating pores in mitochondrial membranes to start a biochemical cascade that results in cell death. Bax is usually tightly controlled by Bcl-2 proteins, which bind Bax and prevents it forming pores. The gene for Bcl-2 is involved in almost 50% of human cancers; these cancerous cells often produce more Bcl-2, leading to tumour development and protecting the cancerous cells from therapies.
To understand precisely how Bcl-2 and Bax interact, the researchers used a combination of neutron reflectometry on the Surf and Offspec instruments at ISIS and on Figaro at the Institut Laue Langevin, electron microscopy at eBIC, and attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). They created a supported lipid bilayer resembling the mitochondrial outer membrane and which contained Bcl-2 proteins.
A two-step process in avoiding apoptosis
- Kinetics of Bax sequestration by Bcl-2 at membrane level: from initial contact to oligomerization
The team found that, without Bcl-2, introducing Bax disrupted the membrane. When the membrane contained Bcl-2 the researchers initially saw a direct correlation between the amount of Bcl-2 in the membrane and the amount of Bax on the membrane surface, suggesting the Bcl-2 was binding directly to the Bax and preventing it from forming pores. Over time, however, they saw a second, slower process. The Bax proteins formed clusters, or oligomers, standing vertically upwards from the membrane surface, which sequestered Bax, prevented pore formation.
This mechanism indicated that Bcl-2 containing membranes can sequester more Bax, than the previously suggested 1:1 protein complex. The results suggest that cancer cells that produce slightly more Bcl-2 could still be protected from apoptosis, without needing to produce large quantities of Bcl-2.
The team also examined the effects of a lipid, cardiolipin, on the interplay between Bax and Bcl-2. Cardiolipin promotes apoptosis in cells and encourages Bax pore formation in the membrane. At low Bcl-2 content and high cardiolipin content, membrane disruption and pore formation was observed showing the interplay of different components of membranes on cell survival. Cardiolipin containing membranes with a high enough BcL-2 content were still protected from Bax pore formation.
“This work was a really nice opportunity to take advantage of our sensitivity to isotopic labelling (selective deuteration of molecules) with neutron reflectometry,” says Sophie Ayscough, the paper’s first author. “Through deuteration of either the lipid or a protein, we could track the relative position of different proteins within the membrane elucidating the cell death blocking mechanism. This data was collected during my postdoctoral research project, during which I spent a year at ISIS with the reflectometry group where I benefited greatly from their expertise as well as the support of the sample environment and laboratory support teams.” Dr Sophie Ayscough, first author on the paper.
“This is fundamental work which used an advanced neutron experimental approach to unravel the molecular mechanism of the Bcl-2 protein in protecting many cancers against therapy-induced death. Here, we could show how this key protein is preventing cancer cell killing proteins (e.g. Bax) from exerting their lethal action inside cells at membranous interface. This work paves the pathway for novel avenues towards Bcl-2 targeting therapies.” Professor Gerhard Gröbner, Umeå University.
Hanna Wacklin-Knect, Head of the Scientific Support Division at the ESS, adds: "This collaboration with Gerhard Gröbner’s group at Umeå University and ISIS, funded by the Swedish Research Council’s neutron scattering and ISIS collaboration grant schemes, has been an important driver for developing key deuteration capabilities at ESS for elucidating membrane protein mechanisms related to disease development and prevention”.
Read the full paper here: Avoiding Mitochondrial Apoptosis by the Bcl-2-Driven Bax Oligomerization on Membrane Surfaces | ACS Chemical Biology
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