What the mechanical forces behind protein folding can tell us about metastatic cancer

Talin is a protein that controls cellular attachment and movement, but its malfunctioning also allows cancer cells to spread. DCL1 is a tumor suppressor protein. But scientists don’t quite understand how either protein works — or what happens when they don’t work the way they should.

One thing scientists do know: When present in a cell, DCL1 can interact with talin and perhaps interfere with talin’s ability to group cells together. If scientists knew the exact steps in the process, they could potentially identify a treatment option to prevent cancer from spreading.

To find answers, a team of researchers at the University of Wisconsin-Milwaukee used a unique tool they built to apply the exact mechanical forces acting on talin in the body, triggering a process called protein unfolding that needed for the protein to perform. its function.

With the tool, called “single molecule magnetic tweezers,” the scientists measured intracellular mechanical forces and experimented with it in the lab so they can find out what happens to talin when DCL1 is both present and absent in the cell.

They have discovered a unique behavior of talin, induced by mechanical forces, that shows a strong interaction that may explain the antitumor effect of DLC1 when the two proteins bind.

“We still don’t know exactly what goes wrong with talin functioning when cancer cells metastasize,” said Ionel Popa, a UWM physics professor who led the team. “But it seems that talin plays a role in activating the spread of cells when the tumor-suppressing DCL1 is missing. And when DCL1 binds to talin, it seems to prevent talin from activating cell proliferation.”

The work was published today in the magazine scientific progress.

Like all proteins, talin forms a specific three-dimensional shape that defines its function. Known as protein folding, it is one of the most complex processes in nature, and when the folding goes wrong, it often leads to disease. Popa’s lab is investigating forces that affect protein folding, which could lead to new treatments for diseases that start when proteins misfold.

Some proteins, including talin, require mechanical forces inside and outside the cell to shape the protein that unlocks its function. Within the cells, mechanical forces cause talin to unfold, revealing receptors where other proteins can bind to form the necessary message connections.

“The process is like a mechanical computer because it calculates how much force it takes to make all the connections,” Popa said. “These forces tell the cell what is happening around it.”

The cell produces several ligands, which convert mechanical forces into chemical signals when they bind to a protein. And the mechanical fine-tuning by these ligands, including DCL1, made the researchers so interested in talin in the beginning.

The site, or domain, where DCL1 binds to talin has the highest number of ligands available of all binding stations on the protein. In fact, messages pass both inside and outside the cell, as ligands help orchestrate the task. By correlating and measuring the force mechanism of the folding, the researchers were able to study this process more closely.

How the tweezers can ‘see’

Scientists already knew that DCL1 binds to only one particular domain on the talin protein. The UWM researchers revealed how: in response to an applied force, talin unfolds and refolds, forming a structure in which DCL1 binds almost irreversibly.

“We collected the data from the talin molecule as it unfolded and refolded, and then added DCL1 to see how it changed,” Popa said. “Previous research pointed to a weak interaction, suggesting that it probably isn’t the cause of DCL1’s suppressor abilities. But when we tested it, we found the opposite: the resulting molecule becomes super stable.”

With the magnetic tweezers, the researchers were able to take measurements on a protein molecule only a few nanometers in size. After attaching it between a glass surface and a paramagnetic bead, the researchers measured the position of the paramagnetic bead on a free-moving end of the molecule, and that of a non-magnetic bead glued to the same surface as the other end of the molecule. the protein. They then apply a magnetic force, mimicking the exact mechanical perturbations exerted on a protein in the body, and measure its unfolding and refolding to understand how its structure changes.

The magnetic tweezers allow the researchers to examine the effect of those forces over days rather than minutes, similar to their timelines in the body.

The role of hormones

The activation of talin during cell proliferation and tissue construction is controlled by hormones. In this phase, the protein undergoes cycles of stretching and binding with other proteins. Mechanical forces come into play as more proteins join the process.

To activate talin, it must be brought to the cell membrane by messengers that signal from the cell cytoskeleton to the extracellular matrix, the environment in which the cells are embedded.

Popa’s team monitored the effect of DCL1 in this process.

“During this hormone-driven ‘inside-out’ activation, if DLC1 also binds to talin, that recruitment to the membrane will not be possible,” he said. “Any of the steps that control cell proliferation can be hijacked by cancer cells to become metastatic. In some cases, DLC1 is completely suppressed.”

Missing or defective DCL1 may not be the only factor in cancer spread, Popa said. But the work illustrates the alternative behavior of proteins under duress and points to a direction for further research for this protein interaction as a potential target for cancer drugs.