Study Probes Link Between Mechanical Forces in Protein Folding and Metastatic Cancer

Researchers from the University of Wisconsin-Milwaukee (UWM) have uncovered new details about the mechanical forces involved in cellular attachment and movement and say the findings could inform therapeutic avenues to prevent tumor metastasis. The work focused on two enigmatic proteins: talin, which controls cellular attachment and movement but when malfunctioning allows cancer cells to spread, and DCL1, a tumor-suppressing protein that can interfere with talin’s ability to group cells together.

Using “single molecule magnetic tweezers” the team built for this purpose, they measured intracellular mechanical forces and experimented with them in the lab so that they can find what happens to talin when DCL1 is both present and not present in the cell. They discovered a unique behavior of talin, induced by mechanical forces, that demonstrates a strong interaction that can 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,” says Ionel Popa, a UWM physics professor who led the team. “But it looks like talin plays a role in activating the spread of cells when the tumor-suppressing DCL1 is missing. And when DCL1 binds to talin, it appears to block talin from activating cell-spreading.”

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 folding goes awry, it often leads to disease. Popa’s lab investigates forces affecting protein folding, which can lead to new treatments for diseases that start when proteins misfold.

For some proteins, including talin, mechanical forces inside and outside the cell are necessary for the protein to obtain the shape that unlocks its function. Inside the cells, mechanical forces prompt talin to unfold, revealing receptors where other proteins can bind to form needed messaging connections. “The process is like a mechanical computer because it calculates how much force is needed for all the connections to happen,” Popa says. “These forces tell the cell what’s going on around it.”

The cell produces various ligands, which convert mechanical forces to chemical signals when they bind to a protein. And the mechanical fine-tuning by these ligands, including DCL1, are what made the researchers so interested in talin to begin with. The location, or domain, where DCL1 binds with talin has the highest number of ligands available among all binding stations on the protein. In fact, messaging goes on both inside and outside the cell as ligands help orchestrate the task. Correlating and measuring the force mechanism of the folding has allowed the researchers to study this process in further detail.

Scientists already knew that DCL1 binds at 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 where DCL1 binds almost irreversibly. “We gathered the data from the talin molecule as it unfolded and refolded, and then added DCL1 to see how it changed,” Popa says. “Previous research indicated a weak interaction, suggesting it’s probably not the driver of DCL1’s suppressor abilities. But when we tested it, we found the opposite—the resulting molecule becomes super-stable.”

The activation of talin during cell-spreading and tissue-building is controlled by hormones. In this stage, the protein undergoes cycles of stretching and binding with other proteins. Mechanical forces come into play as more proteins join the process. For talin to be activated, it must be brought to the cell membrane by messengers that signal from the cell cytoskeleton to the extracellular matrix, the surrounding environment that cells are embedded in.

Popa’s team tracked the effect of DCL1 in this process. “During this hormone-driven ‘inside-out’ activation, if DLC1 also binds to talin, it will not allow for that recruitment to the membrane,” he says. “Any of the steps controlling cell spreading might be highjacked by cancer cells to become metastatic. In some cases, DLC1 is completely suppressed.”

Missing or malfunctioning DCL1 may not be the only factor in cancer spread, Popa said. But the work illustrates the alternate behaviors of proteins under force and points to a direction for further study for this protein interaction as a potential target for cancer drugs.