T

here’s a special protein in plants that helps them crawl toward the sun. Now, scientists have harnessed that protein to glean new insights into cancer metastasis.

Researchers at the University of California, San Francisco, placed that light-sensitive protein into a cancer cell line to illuminate how cells move around in vivid detail.

STAT chatted with biomedical researcher Torsten Wittmann about the work, published in Nature Cell Biology.

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How does the technique work?

We have devised a new light switch to turn off and back on specific proteins within seconds inside living cells using light. We insert a light-sensitive module in between different parts of a protein that need to work together to function in a cell. This protein then falls apart, or is inactive, when the blue light is on and comes back together when the light is turned off.  Light can be turned on and off very quickly, and we can also very precisely control the location of light exposure, and only illuminate a small part of a cell. … We think this is a broadly useful tool to figure out how proteins make cells work.

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Your study focused on a cell’s microtubules. What are they, and why did they interest you?

Microtubules form a network of hundreds of thin fibers throughout the cell that, for example, work as a highway system for transport of vesicles and other cargo inside cells. Microtubules are also very dynamic and continuously switch between getting longer and shorter. Think of it as roads that are being built and then taken apart again. Because we are interested in how the microtubule cytoskeleton helps cells accomplish complex tasks, such as change their shape, move or divide, we chose a protein as proof-of-principle that controls how microtubules interact with other structures inside cells.

What happened when you put the light-sensitive protein into microtubules?

We replaced this protein in a cancer cell line with our light-sensitive version and demonstrated that we can stop microtubules from elongating within seconds by turning on blue light. This allowed us for the first time to directly show that microtubule elongation in the front of cancer cells is required for them to move directionally, and we could prevent a cancer cell from leaving a virtual blue light box for many hours. Even though microtubules are a target of several chemotherapy drugs, it is still quite mysterious how these drugs kill cancer cells. Our results support the idea that they not only target cell division, but also movement of cancer cells that underlies metastasis, which is in fact the most deadly aspect of many cancers.

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