Tag: cell death

Neutron reflectometry reveals how cancer cells can avoid programmed cell death

Neutron reflectometry reveals how cancer cells can avoid programmed cell death

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.

Read more on the Diamond website

Repairing genetic damage with sunlight

Repairing genetic damage with sunlight

DNA damage to the genetic material DNA drives cancer, ageing, and cell death. Therefore, DNA repair is crucial for all organisms, and a deeper understanding of this basic function helps us better comprehend how life around us survives and thrives. An international team of researchers has now revealed how the enzyme photolyase efficiently channels the energy of sunlight into DNA repair chemistry.

All life under the sun must cope with harmful UV rays. UV damage can take many forms, but DNA, the molecule that carries the genetic information of all living organisms, is especially vulnerable. For instance, UV can drive chemical cross-linking reactions of DNA, potentially introducing errors into the genetic code. This cross-linking can lead to cell death or – in the worst cases – mutagenesis and cancer. Such damage is not uncommon; under bright sunlight, a human skin cell can undergo 50-100 cross linking reactions per second.

“To survive, life has evolved powerful DNA repair mechanisms. One especially elegant solution is provided by the enzyme photolyase,” explains DESY scientist Thomas J. Lane, who is also a researcher in the Cluster of Excellence “CUI: Advanced Imaging of Matter” at Universität Hamburg. The enzyme uses sunlight to repair damage caused by sunlight. Photolyase is able to recognize the location where UV irradiation has cross-linked DNA and grabs onto those bits of damaged DNA. Then, it can capture a blue photon from the sun, and use it to perform repair chemistry, turning the DNA back into its original, healthy form.

To better understand how photolyase works, the scientists were particularly interested first in the form of the enzyme immediately after absorbing a photon, but before repairing the DNA. Second, they wanted to find out the exact sequence of bond-breaking chemical reactions necessary to turn damaged DNA into healthy DNA. As a third step, the team sought to better understand how photolyase can specifically recognize which DNA is damaged.

Conducting time-resolved crystallography at the SwissFEL X-ray free-electron laser of PSI the scientists were able to capture the excited state of the photolyase chromophore, letting them understand how the enzyme efficiently channels the energy of sunlight into DNA repair chemistry. “This research was only made possible by the recent development of X-ray free-electron laser sources. Their intense femtosecond-duration pulses let us record flash X-ray photographs that freeze all atomic motion so that we can follow the reaction step by step at the speed of molecules,” says first author Nina-Eleni Christou from DESY.

Read more on PSI website

Image: PSI researcher Camila Bacellar is pleased about the success in precisely analysing the DNA repair enzyme photolyase at the Alvra beamline of the Swiss X-ray free-electron laser SwissFEL.

Credit: Paul Scherrer Institute/Markus Fischer