A Bright New Tool to Record Cellular Interactions

ABOVE: Cancer cells (green) in this microscopy image send GFP granules to neurons (purple), illuminating how cells interact with their neighbors.
© NICHOLAS J. KRAMER, ELIFE, 9:E61080, 2020

When cancers metastasize, diseased cells travel to distant parts of the body, where they can invade many different tissues and cause tumors to grow in these new locations. Monte Winslow, an immunologist at Stanford University, investigates the mechanics of cancer metastasis with a blend of in vivo models and genomics. But he’s long faced a challenge in understanding just what causes cells to move—mainly, he says, because it’s difficult to study how tumor cells are physically interacting with one another or with surrounding cells.

Existing methods using green fluorescent protein (GFP) or spatial transcriptomics only allow researchers to study interactions indirectly, says Winslow. They give researchers an idea of “who’s close to who, but not who’s touching who, and not who touched who yesterday,” he says. 

Struggling with this problem a few years ago, Rui Tang, a postdoc in Winslow’s lab, decided to work on an alternative, and spent the better part of a year devising a new technique. Specifically, he created a system that allowed GFP on one cell’s surface to be transferred to a recipient cell upon interaction. The team named the result GFP-based Touching Nexus (G-baToN). One cell bears the label tethered to its surface, and when it interacts with another cell, that marker is passed on to engineered receptors for that marker on the recipient, not only indicating that the cells interacted, but also where contact was made.

One cell bears the label tethered to its surface, and when it interacts with another cell, that marker is passed on.

Although the system wasn’t infallible, Winslow says, he was amazed during the development process at how well it seemed to work. It would highlight interactions between two cells of the same type, and also between completely different cell types, such as lung cancer cells interacting with cortical neurons in vitro. “Rui does this, and it works, and then he does it across other cells, and it works,” Winslow says. “Then the lady from the lab next door says, ‘Yeah, but it’s never gonna work in primary cells, it’s just gonna be cell lines’”—the thinking being that primary cells have a greater variety of protein receptors than cell lines do, and thus would work less consistently with the receptor-tagging system. “And then Rui has it work across all of these primary cells.” 

This broad applicability is key, Winslow says, if the technique is to be used for understanding the dynamic nature of how cancers metastasize. Tang also developed red and blue fluorescent tags to use in addition to the green one, so that researchers could tag different sender cells in different colors and thus observe interactions between multiple cells at once.

Now, in what they refer to as their beta-testing phase, Winslow and Tang are providing vectors and instructions to other scientists to try in their own labs. Vanderbilt University cell biologist Ian Macara, who was not involved in its development, has tried G-baToN to explore epithelial cell extrusion mechanisms to understand how human skin is able to reject a dying or irregular cell, such as a metastasizing tumor cell, without compromising the integrity of the barrier. In short, he says, the technology is “a powerful and adaptable system.”

Tang’s vision for the approach also goes beyond merely recording the interactions. “It’s also [a] sort of cell-cell contact–based delivery system,” Tang says, referring to early signs that the system could also be used to transport DNA, proteins, and other macromolecules from one cell to another. Going forward, this system could be used to alter the function of the receiver cell, he adds.

To Geoff Wahl, who runs the Gene Expression Laboratory at the Salk Institute and did not participate in the research, G-baToN holds promise to “identify and isolate normal cells that had come into contact with, and perhaps had been changed by, their interactions with cancer cells.” In his lab, Wahl studies breast and pancreatic cancers, the latter of which is notorious for going undetected until the disease advances and spreads. Wahl’s lab is currently collaborating with Winslow’s group to create the next iteration of G-baToN, which Wahl says they hope will enable them to track receiver cells over time. 

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Winslow says he’s excited about how the technique could allow researchers to ask new questions that couldn’t be addressed before. For now, to get a better sense of G-baToN’s full capabilities as well as its shortcomings, they invite other labs with different research interests to try it out. “If you’re doing the brain, if you’re doing immune cells, whatever it is,” Winslow says, “[we want to know if] it can work or not.”