Nuclear Dbf2-related Kinase 1 Functions as Tumor Suppressor in Glioblastoma by Phosphorylation of Yes-associated Protein
Glioblastoma (GBM) is the deadliest form of primary brain cancer, with a 5-year survival rate of less than 5%. Even with surgery, radiation, and chemotherapy, most patients live just 14–26 months after diagnosis. For decades, researchers have searched for molecular targets to halt GBM’s aggressive growth—and a new study from Peking University Third Hospital points to a previously underappreciated player: Nuclear Dbf2-related Kinase 1 (NDR1).
Led by Bin Chen, Bin Liu, Tao Yu, Yun-Feng Han, Chao Wu, and Zhen-Yu Wang from the Department of Neurosurgery, the research reveals that NDR1 acts as a tumor suppressor in GBM by targeting Yes-associated protein (YAP), a key driver of cancer cell growth. The findings, published in the Chinese Medical Journal in 2021, not only shed light on GBM’s biology but also expand our understanding of the Hippo signaling pathway—an essential “brake” on organ growth and tumor formation.
The Hippo-YAP Pathway: A Critical Player in Cancer
To understand NDR1’s role, let’s start with the basics: YAP is a protein that promotes cell growth. It’s controlled by the Hippo pathway, a molecular network that stops cells from dividing uncontrollably. When the Hippo pathway is active, another set of proteins (LATS1/2) adds a chemical tag—called phosphorylation—to YAP. This tag traps YAP in the cell’s cytoplasm, preventing it from entering the nucleus to turn on genes that drive growth.
In GBM, the Hippo pathway often fails. YAP escapes phosphorylation, moves to the nucleus, and fuels tumor growth. Until now, LATS1/2 were thought to be the only proteins that phosphorylate YAP. But the Peking University team found that NDR1—another kinase in the same family as LATS1/2—also plays this critical role.
NDR1 Is Low in GBM—and Correlates With Poor Survival
The first clue came from patient samples. The team analyzed 158 GBM tumors (collected between 2017–2018) and found that NDR1 protein levels were significantly lower in cancer tissue than in normal brain tissue. Patients with low NDR1 had shorter overall survival: their average survival time was worse than those with high NDR1.
Bioinformatics tools confirmed these findings. Data from ONCOMINE (a database of cancer gene expression) showed that NDR1 mRNA levels are reduced in GBM tumors compared to normal tissue. SurvExpress—a tool for linking gene expression to survival—revealed that low NDR1 correlated with a higher risk of poor outcomes.
Even tumor size played a role: patients with larger tumors (over 60 mm) had much lower NDR1 levels than those with smaller tumors. This suggested NDR1 acts as a brake on GBM growth.
NDR1 Stops GBM Growth—In Cells and Mice
To test NDR1’s function, the team turned to GBM cell lines (U87 and U251) and mouse models.
In Vitro: NDR1 Slows Proliferation and Blocks the Cell Cycle
When the researchers boosted NDR1 levels (via lentiviral overexpression) in U87 and U251 cells, three key things happened:
- Reduced viability: A CCK-8 assay showed NDR1-overexpressing cells grew 30–50% slower than controls.
- Fewer colonies: After 14 days, NDR1-overexpressing cells formed 40–60% fewer colonies (groups of dividing cells) than normal.
- Cell cycle arrest: Flow cytometry revealed NDR1 trapped cells in the G1 phase—the “resting” stage before DNA replication. This was confirmed by lower levels of cyclin E1, a protein needed for cells to enter the growth phase (S phase).
EdU staining—a technique to track DNA replication—further showed that NDR1-overexpressing cells had 50% fewer actively dividing cells than controls.
In Vivo: NDR1 Shrinks Tumors in Mice
To see if these results held in living organisms, the team injected NDR1-overexpressing U87 cells into the armpits of nude mice (a common model for human tumors). After 32 days:
- Tumors with high NDR1 were 50% smaller and 40% lighter than control tumors.
- IHC staining showed lower levels of Ki-67 (a marker of cell proliferation) and higher levels of TUNEL (a marker of apoptosis, or programmed cell death) in NDR1-overexpressing tumors.
In short: NDR1 didn’t just slow GBM growth—it actively killed cancer cells.
The Mechanism: NDR1 Phosphorylates YAP to Halt Growth
The team’s biggest breakthrough was uncovering how NDR1 works: it directly interacts with YAP and phosphorylates it at a specific site (Ser127).
Phosphorylation is a molecular “on/off switch”—adding a phosphate group to YAP changes its shape and function. For YAP, phosphorylation at Ser127 traps it in the cytoplasm, where it can’t enter the nucleus to drive growth.
Using co-immunoprecipitation (a technique to test protein interactions), the team showed that NDR1 and YAP bind to each other in GBM cells. Confocal microscopy confirmed they co-localize (exist in the same cell regions). Western blotting revealed that NDR1-overexpressing cells had 2–3 times more phosphorylated YAP (p-YAP) than controls—proof that NDR1 directly modifies YAP.
When the researchers added okadaic acid (a chemical that boosts NDR1 activity), even more YAP stayed in the cytoplasm. This confirmed that NDR1’s tumor-suppressive effect depends on its ability to “turn off” YAP.
Why This Matters for GBM Treatment
For years, LATS1/2 were considered the only kinases that regulate YAP. This study changes that: NDR1 is a new upstream regulator of YAP, expanding our understanding of the Hippo pathway.
For GBM, this has two critical implications:
- Biomarker potential: NDR1 levels could help predict prognosis—low NDR1 means higher risk of poor survival.
- Therapeutic target: Restoring NDR1 levels (via gene therapy) or mimicking its effect on YAP (via small molecules) could shut down GBM’s growth engine.
The team also found that NDR1 enhances apoptosis in GBM cells exposed to TNF-α (a protein that triggers cell death). This suggests NDR1 could work with immunotherapies to kill cancer cells more effectively.
Limitations and Future Directions
The study has gaps: it doesn’t explore how NDR1 interacts with standard GBM treatments like temozolomide (the only FDA-approved chemotherapy for GBM) or radiation. It also doesn’t test NDR1’s role in other GBM subtypes (e.g., mesenchymal or proneural).
But these questions open doors for future research. If NDR1 can sensitize GBM cells to temozolomide, it could become part of combination therapies. If it’s active in all GBM subtypes, it could be a universal target.
Conclusion
This study from Peking University Third Hospital offers a rare glimmer of hope for GBM patients. By identifying NDR1 as a YAP regulator, researchers have uncovered a new way to halt GBM’s aggressive growth. While more work is needed to translate these findings into treatments, the result is clear: NDR1 is a tumor suppressor in GBM—and a promising target for future therapies.
For a disease where every breakthrough counts, this is a step forward. And for patients fighting GBM, it’s a reminder that science is still searching for answers.
This research was published in the Chinese Medical Journal in 2021 by Bin Chen, Bin Liu, Tao Yu, Yun-Feng Han, Chao Wu, and Zhen-Yu Wang from the Department of Neurosurgery, Peking University Third Hospital. The full study is available at doi.org/10.1097/CM9.0000000000001653.
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