Probing the Tumor Suppressor Function of BAP1 in CRISPR-Engineered Human Liver Organoids

Area of Science:

• Oncology
• Molecular Biology
• Genetics

Background:

• The deubiquitinating enzyme BAP1 functions as a tumor suppressor and is implicated in cholangiocarcinoma.
• BAP1 is known to deubiquitinate histone H2AK119, and has numerous proposed molecular targets.

Purpose of the Study:

• To investigate the role of BAP1 in maintaining cholangiocyte identity and its function as a tumor suppressor.
• To explore the molecular mechanisms by which BAP1 loss affects cellular characteristics and contributes to cancer development.

Main Methods:

• Utilized CRISPR/Cas9 gene editing to create BAP1 loss-of-function in normal human cholangiocyte organoids.
• Engineered human liver organoids with common cholangiocarcinoma mutations (TP53, PTEN, SMAD4, NF1) to study BAP1's role in a cancer-relevant genetic background.
• Employed xenotransplantation to assess malignant features in engineered organoids.

Main Results:

• BAP1 loss-of-function in cholangiocyte organoids led to altered expression of junctional and cytoskeleton components by regulating chromatin accessibility.
• Loss of epithelial characteristics and increased cell motility were observed following BAP1 disruption.
• Restoring BAP1's catalytic activity rescued the observed cellular and molecular changes.
• In a multi-mutated liver organoid model, BAP1 loss promoted the acquisition of malignant features upon xenotransplantation.

Conclusions:

• BAP1's tumor suppressor function is significantly linked to its control of epithelial identity via chromatin accessibility regulation.
• Organoid technology combined with CRISPR/Cas9 offers a powerful platform for studying cancer gene function in human models.
• Understanding BAP1's role provides insights into cholangiocarcinoma pathogenesis and potential therapeutic strategies.