Cells are ever-changing, intricate, minute, and often difficult to observe in environments that react unpredictably to external influences. Recently, scientists have discovered new methods for remotely regulating cell functions.
Picture a huge celebration event, such as the Super Bowl, filled with the cheers of fans, the aroma of food, and a kaleidoscope of team colors creating a mesmerizing chaos. While the electrifying atmosphere undoubtedly enhances the experience, it can make it challenging to reconnect with your group if you become separated. Whether trying to call them or waving from your seat, it can feel like an exhausting game of tag amidst all the noise.
Now, envision having a way to guide them back to you with exceptional accuracy—an application that pins down their precise location and gently directs them to you. This is essentially what bioengineer Lukasz Bugaj and his team at the University of Pennsylvania have accomplished; however, instead of an arena, they’re navigating the complexities of the human body, directing engineered cells to perform specific tasks like combating cancer or mending injuries.
“Living systems are incredibly complex, so when we introduce modified cells into the body to carry out a particular function, such as targeting pathogens or cancer cells, wouldn’t it be wonderful if we could communicate with them, guide them, and ensure they go exactly where they are needed at the right time?” Bugaj muses.
In a recent paper, the Bugaj Lab presents tools that enable researchers to “remotely and non-invasively communicate with and control the activity of cells” once they are inside the body. Published in Nature Methods, the research centers on a temperature-sensitive protein they developed, named Melt.
From light to heat: developing Melt
The manipulation of cell behavior using light—known as optogenetics—revolutionized biology nearly twenty years ago. This technique involves employing light-sensitive proteins to activate or deactivate specific cellular pathways. However, there is a limitation: light doesn’t penetrate deeply into tissues, making it unsuitable for many therapeutic usages.
“We required something that could penetrate more effectively,” Bugaj explains. “That’s why temperature was a key focus. Heat can travel through tissues more effectively than visible light can.”
The breakthrough was inspired by a surprising organism, a fungus called Botrytis cinerea, notorious for causing rotting in strawberries and grapes. This fungus produces a protein named BcLOV4, initially researched for its light sensitivity, but when Bugaj’s lab introduced this protein into human cell lines, they encountered unexpected results.
“We realized that the protein did more than just respond to light; it also reacted to temperature,” shares Will Benman, the first author and former Ph.D. student in the Bugaj Lab. “That’s when we thought, ‘this is genuinely exciting,’ because while many known proteins respond to light, very few respond to temperature.”
The researchers pondered whether they could engineer the protein to react solely to temperature. After extensive experimentation over several months, they transformed BcLOV4 into a novel temperature-sensitive protein: Melt, which stands for Membrane Localization using Temperature.
“We eliminated its light sensitivity and adjusted its temperature sensitivity to function at human body temperatures,” states Pavan Iyengar, a former undergraduate researcher in the Bugaj Lab. “Now we have a mechanism that works like a dimmer switch—raise the temperature, and it activates; lower it, and it deactivates.”
By linking Melt to various cellular pathways, the team showcased precise control over processes like cell signaling, peptide degradation, and even cell apoptosis. In one striking experiment, they demonstrated that applying a cooling device—a “glorified icepack”—to an animal model could induce cancer cell death without the systemic toxicity linked to conventional chemotherapy.
Melt in action
The team also examined Melt’s potential in basic research, where controlling cellular pathways in real-time can yield fresh insights into cellular functions.
“It’s quite unusual for a protein to possess so many diverse functions,” remarks Zikang (Dennis) Huang, co-first author of the Melt paper and a Ph.D. student in the Bugaj Lab. “It can detect light, it can sense temperature, it can localize to membranes, and also perform various molecular functions, unlike many known natural proteins that typically have a single function. Once we understand how this operates, we may be able to design new proteins that integrate these functions into one entity.”
In the near future, the team believes Melt may assist in essential discoveries related to cancer treatments, paving the way for therapies that are more precise and less harmful.
“This project was made possible through funding from the federal government and pilot grants from the Center for Precision Engineering for Health at Penn. Building on this initial support and our foundational results, our lab recently secured a significant NIH grant to advance and assess the effectiveness of temperature-controlled tumor cell ablation in cancer physiological models,” Bugaj adds. “Ultimately, these tools could lead to novel types of cell therapies that react to physiological changes like fever or inflammation.”
