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Neurofibromatosis type 2/Merlin: sharpening the myth of prometheus
Oliver Drvarov1, Francisco Javier Cubero
1University Hospital, University Aachen, Germany.
Abstract:
The molecular signals that control the maintenance and activation of liver stem/progenitor cells are poorly understood, and the role of liver progenitor cells in hepatic tumorigenesis is unclear. We report here that liver-specific deletion of the neurofibromatosis type 2 (NF2) tumor suppressor gene in the developing or adult mouse specifically yields a dramatic, progressive expansion of progenitor cells throughout the liver without affecting differentiated hepatocytes. All surviving mice eventually developed both cholangiocellular and hepatocellular carcinoma,suggesting that Nf2-/-progenitors can be a cell of origin for these tumors. Despite the suggested link between NF2 and the Hpo/Wts/Yki signaling pathway in Drosophila, and recent studies linking the corresponding Mst/Lats/Yap pathway to mammalian liver tumorigenesis, our molecular studies suggest that Merlin is not a major regulator of YAP in liver progenitors,and that the overproliferation of Nf2-/-liver progenitors is instead driven by aberrant epidermal growth factor receptor (EGFR) activity. Indeed, pharmacologic inhibition of EGFR blocks the proliferation of Nf2-/-liver progenitors in vitro and in vivo, consistent with recent studies indicating that the NF2-encoded protein Merlin can control the abundance and signaling of membrane receptors such as EGFR. Together,our findings uncover a critical role for NF2/Merlin in controlling homeostasis of the liver stem cell niche.
Insights
The neurofibromatosis type 2 (NF2) gene deletion in mice causes liver progenitor cell expansion and liver cancer. Aberrant epidermal growth factor receptor (EGFR) activity drives this overproliferation, not YAP signaling.
Area of Science:
- Hepatology and Cancer Biology
- Molecular and Cellular Biology
- Tumorigenesis Research
Background:
- The molecular mechanisms governing liver stem/progenitor cell maintenance and activation remain largely unknown.
- The precise role of liver progenitor cells in the development of liver cancer (hepatic tumorigenesis) is not fully elucidated.
- Understanding these processes is crucial for developing targeted therapies for liver diseases and cancers.
Discussion:
- Loss of the neurofibromatosis type 2 (NF2) tumor suppressor gene in mice leads to significant expansion of liver progenitor cells.
- These Nf2-deficient liver progenitors are implicated as the cell of origin for both cholangiocarcinoma and hepatocellular carcinoma.
- Contrary to expectations, the Hippo-YAP pathway is not the primary driver; instead, dysregulated epidermal growth factor receptor (EGFR) signaling is identified as the key factor in Nf2-/- progenitor overproliferation.
Key Insights:
- NF2/Merlin plays a critical role in maintaining the homeostasis of the liver stem cell niche.
- Aberrant EGFR activity, rather than YAP pathway dysregulation, drives the expansion of Nf2-/- liver progenitors.
- Pharmacologic inhibition of EGFR effectively suppresses the proliferation of these abnormal liver progenitors both in vitro and in vivo.
Outlook:
- These findings highlight EGFR as a potential therapeutic target for liver progenitor cell-driven cancers.
- Further research into the NF2-EGFR axis could reveal novel strategies for preventing or treating liver tumors.
- This study provides a new model for investigating liver stem cell biology and hepatic tumorigenesis.
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