London: For the first time, researchers have identified a specific molecular mechanism that underlies the early stages of programmed cell death or apoptosis, a process that plays a critical role in cancer prevention.
Dr Luke Clifton of the STFC ISIS Neutron and Muon Source (ISIS) in Oxfordshire led the project, which was co-ordinated by Professor Gerhard Gröbner of Umeå University and collaborators at the European Spallation Source in Sweden. This is the latest in a series of research collaborations by this team examining biological proteins that trigger apoptosis.
Apoptosis is essential for human life, and its disruption can cause cancer cells to proliferate and become unresponsive to cancer treatment. In healthy cells, it is regulated by two proteins known as Bax and Bcl-2.
The soluble Bax protein is responsible for the clearance of old or diseased cells, and when activated, it induces programmed cell death by forming pores in the mitochondrial membrane of cells. This can be offset by Bcl-2, which is embedded within the mitochondrial membrane, where it acts to prevent premature cell death by sequestering and sequestering Bax proteins.
In cancer cells, the survival protein Bcl-2 is overproduced, leading to uninhibited cell proliferation. Although this process has long been understood to be important for the development of cancer, the precise role of Bax and the mitochondrial membrane in apoptosis is still unclear.
Dr Luke Clifton, STFC ISIS Neutron and Muon Source Scientist and co-lead author, explains: “This work has increased our knowledge of basic mammalian cell processes and opened up exciting possibilities for future research. Understanding what things look like when cells are working properly is an important step towards understanding what goes wrong in cancer cells, so This could open doors to possible treatments.
The team used a technique known as neutron reflectometry (performed using state-of-the-art ISIS SURF, OffSpec equipment) that enabled them to study how Bax interacts with lipids in the mitochondrial membrane. This built on their previous studies of membrane-bound Bcl-2.
Using neutron reflectometry at SURF and OFFSPEC, they were able to study in real time the way the protein interacts with lipids in the mitochondrial membrane during the early stages of apoptosis. Using deuterium-isotope labeling, they determined for the first time that Bax sequesters lipids from the mitochondrial membrane to form lipid-Bax clusters on the mitochondrial surface while creating pores.
Using time-lapse neutron reflectometry combined with surface infrared spectroscopy at the ISIS BioLab, they were able to see that these pores occurred in two stages. The initial rapid uptake of Bax to the mitochondrial membrane surface was followed by the slow formation of membrane-disrupting pores and Bax-lipid clusters, which occurred simultaneously. This slow pore process occurred on time scales of several hours, comparable to cell death in vivo.
This is the first time scientists have found direct evidence of the involvement of mitochondrial lipids in membrane perturbation in cell death initiated by Bax proteins.
Dr. Luke Clifton continued, “As far as we can tell, this mechanism by which Bax initiates cell death has not been seen before. As we learn more about the interaction between Bax and Bcl-2 and how it relates to this mechanism, we will gain a more complete picture of a process that is fundamental to human life. In structural studies of membrane biochemistry This work demonstrates the capabilities of neutron reflectometry.”
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