This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Once a cell has locked into an abnormal state—the way cancer cells do—can it ever be restored to normal? A KAIST research team led by Professor Kwang-Hyun Cho of the Department of Bio and Brain Engineering has, for the first time, identified the causal circuits responsible for irreversibility in intracellular molecular networks and developed a fundamental control technology called ROOT that can regulate these circuits and restore biological states to their original conditions.
The paper is published in the journal Proceedings of the National Academy of Sciences. Cells in the human body change their state in response to external stimuli. In many cases, however, these state changes are irreversible, in the sense that cells do not return to their original state even after the stimulus disappears.
Irreversibility is essential for maintaining normal biological processes, such as a cell differentiating into one with a specific function. At the same time, it can also drive disease progression—for example, in epithelial–mesenchymal transition, which gives cancer cells the ability to migrate into and invade surrounding tissue. Complicating matters, the circuits that maintain these state changes inside a cell are highly intricate: More than a thousand positive feedback loops are woven throughout the network, in which one molecule activates a series of other molecules that in turn reactivate the original molecule.
This is similar to the feedback screech produced when a microphone is placed next to a speaker, where sound repeatedly amplifies itself. Even a change that starts with an external stimulus can persist after the stimulus is gone, simply because the cell's own molecules keep reinforcing one another. Until now, it has been extremely difficult to determine which of these countless circuits is actually responsible for locking a cell into an irreversible state.
To solve this problem, the team developed ROOT technology, short for Revelation Of the Original circuit of irreversible Transition, which works by representing intracellular regulatory processes as computational logic models and analyzing them through systems biology techniques. Using ROOT, the research team successfully simulated the process in which cells maintain a signal even after an external stimulus is removed, allowing them to identify a set of core circuits that cause irreversibility, which they defined as the "irreversibility kernel." Going beyond identifying the cause, the team also proposed two groundbreaking control strategies. The first, "resetting control," restores a cell to its state before the change while leaving the cell's underlying irreversible property intact—comparable to leaving the lock itself in place but opening the locked door and returning to the starting point.
The second, "reversing control," removes the source of irreversibility itself, allowing a cell to move freely between different states—comparable to disabling the mechanism that automatically locks a door each time it closes, so that afterward the door can be opened and closed again. The team applied the new technique to various biological models, including B-cell differentiation, epithelial–mesenchymal transition in lung cancer, and enterocyte and beta-cell differentiation models based on single-cell transcriptome data. In these models, the ROOT method accurately identified causal circuits that matched known cell-fate determinants.
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