ESCRT-dependent YAP degradation by AKT blockade overcomes adaptive resistance to RAS(ON) inhibition in pancreatobiliary cancer

Cancer cells are masters of survival, constantly rewiring their internal machinery to escape the drugs designed to kill them. In aggressive cancers of the pancreas and bile ducts, a common strategy for resistance involves a protein called YAP. This protein acts as a master switch, turning on genes that help the tumor grow and ignore treatment. For years, scientists have known that another protein, AKT, helps keep YAP active, but they did not understand the full picture of how they interact. The prevailing belief was that cells get rid of unwanted proteins by shredding them in a cellular recycling center called the proteasome. However, this view left a gap in understanding how to permanently stop YAP when cancer cells decide to fight back.

A team of researchers at Mayo Clinic has now uncovered a different, hidden pathway that cells use to destroy YAP, and they found a way to force cancer cells to use it. By blocking the AKT protein with a drug already approved for breast cancer, they discovered that the cancer cells do not just stop making YAP; they actively route the existing protein to a different disposal system, the lysosome, where it is dissolved. This discovery is significant because it reveals a new vulnerability in how these deadly tumors survive. The researchers showed that combining this AKT blocker with a drug that targets the RAS protein, a common driver of these cancers, could overcome the resistance that usually stops treatment from working. In laboratory models, this combination did not just slow the tumors down; it led to near-complete tumor resolution in four out of six mice in a specific orthotopic model.

The study began by looking at the complex signaling networks inside human bile duct tumors. The researchers analyzed the activity of hundreds of different enzymes, known as kinases, which act as the cell's internal messengers. They found that AKT was one of the most active and important drivers in these tumors. When they treated cancer cells in a dish with capivasertib, a drug that blocks AKT, they expected the cells to simply stop growing. Instead, they observed something surprising: the levels of the YAP protein dropped dramatically within hours. This was not because the cells stopped making the protein; the instructions for making it were still there. The protein itself was being destroyed.

To understand how this destruction happened, the team looked at the cellular machinery responsible for breaking down proteins. They first checked the proteasome, the cell's standard shredder for unwanted proteins. They found that blocking the proteasome did not stop the loss of YAP, proving that this was not the usual disposal route. Instead, the evidence pointed toward the lysosome, a different part of the cell that digests materials using powerful enzymes. When the researchers used drugs to block the lysosome, the YAP protein remained safe, confirming that the cell was routing YAP to this specific digestive system for destruction.

The researchers then identified the specific guide that directs YAP to this lysosomal trash can. They found that a protein called AMOTL2 acts as the essential bridge. Under normal conditions, the active AKT protein keeps AMOTL2 in check, preventing it from grabbing YAP. When the researchers blocked AKT, AMOTL2 was released and immediately bound to YAP, escorting it to the lysosome. To prove this was the critical step, they removed the gene for AMOTL2 from the cancer cells. Without this guide, the cells could no longer destroy YAP, even when AKT was blocked. This confirmed that AMOTL2 is the necessary key that unlocks the door to YAP's destruction.

This mechanism offered a powerful new strategy for treating cancers that have become resistant to standard therapies. The researchers knew that many of these tumors eventually stop responding to drugs that target the RAS protein, a common mutation in these cancers. They suspected that this resistance was driven by YAP stepping in to keep the cells alive. They tested this by creating cancer cells that had learned to ignore a potent RAS-blocking drug. These resistant cells showed high levels of active AKT and low levels of YAP phosphorylation, a chemical tag that usually marks proteins for destruction. When they treated these resistant cells with the AKT blocker, the cells became highly sensitive to the drug, and the YAP protein was rapidly degraded.

The most compelling results came from testing this approach in living animals. The researchers used a mouse model that closely mimics human bile duct cancer, growing tumors directly inside the liver. They treated the mice with the RAS-blocking drug alone, the AKT-blocking drug alone, or a combination of both. The mice receiving the RAS drug alone saw their tumors grow, and most did not survive long. The mice receiving the AKT drug alone had some benefit, but the tumors persisted. However, the mice receiving both drugs together showed a dramatic response. In the group treated with the combination, four out of six mice were still alive at the end of the study, while only one out of six survived in the group treated with the RAS drug alone. In these surviving animals, the tumors had nearly vanished, leaving behind healthy liver tissue.

To see if this discovery mattered for human patients, the team looked at data from large groups of people with bile duct cancer. They found that patients whose tumors had high levels of the machinery needed for this lysosomal disposal system, specifically a component called PDCD6IP, had a worse outlook. This suggests that while these tumors are aggressive, they are also primed to be vulnerable to the AKT-blocking strategy. The researchers proposed that the very machinery that makes these tumors dangerous could be turned against them. If a tumor has a high level of this disposal system, blocking AKT could trigger a massive, self-destructive cleanup of the YAP protein, effectively disarming the cancer's resistance.

The study also clarified what does not happen. The researchers explicitly showed that the destruction of YAP does not depend on the cell's autophagy process, a different method of self-cleaning that some other studies had suggested. They also ruled out the idea that the drug simply stops the cell from making new YAP; the protein was already there and was being actively removed. The findings provide a clear, step-by-step map of a new biological process: blocking AKT releases a brake on AMOTL2, which then guides YAP to the lysosome for destruction.

This work moves beyond simply observing that a drug works; it explains the physical mechanism of how the cancer cell is dismantled. By identifying the specific guide protein and the disposal route, the researchers have opened a new path for combination therapy. The results suggest that for patients with these difficult-to-treat cancers, adding an AKT blocker to existing treatments could prevent the tumor from adapting and surviving. The study concludes that this endogenous pathway of protein destruction is a real, actionable target that could help overcome the adaptive resistance that has long limited the success of cancer therapy in the pancreas and bile ducts.