SALL4 Is Required for YAP1-Dependent Malignant and Regenerative Hepatocyte-to-Cholangiocyte Reprogramming.

Hepatocytes (HC), which share a developmental origin with cholangiocytes (CC), have the capacity to undergo reparative reprogramming into CCs in response to liver injury and, under specific conditions, can also transform malignantly into cholangiocarcinoma (CCA). However, the molecular mechanisms governing HC plasticity in liver diseases remain poorly understood. In this study, we investigated the role of spalt-like transcription factor 4 (SALL4), an oncofetal transcription factor, in both malignant and regenerative HC fate transitions toward the biliary lineage. Using Sleeping Beauty hydrodynamic tail vein injection-mediated murine liver cancer models, we explored HC-to-CCA transformation, whereas the 3,5-diethoxycarbonyl-1,4-dihydrocollidine (DDC) diet-induced cholestasis model was used to investigate regenerative HC-to-CC reprogramming. Our findings reveal that SALL4 is specifically required for myristoylated Akt-YAP1S127A-driven HC-to-CCA transformation, as its loss significantly suppressed malignant reprogramming and clonal expansion. Surprisingly, Sall4 overexpression also prevented YAP1S127A-driven CCA development while promoting the expansion of liver progenitor cell (LPC)-like fatty HCs. Mechanistically, we propose Bmi1 as a key downstream effector of SALL4 in YAP1-dependent HC-to-CCA transformation. Additionally, in the DDC-fed cholestasis model, Sall4 deletion enhanced HC-to-LPC activation while impairing LPC differentiation into mature CCs. These findings establish SALL4 as a critical regulator of HC plasticity in both malignant and regednerative contexts and highlight its potential as a therapeutic target for specific liver cancer subtypes. SIGNIFICANCE: HC plasticity supports repair but can drive malignancy, acting as a double-edged sword. We identify SALL4 as regulator of YAP1-driven HC-to-CC reprogramming, revealing the YAP1-SALL4-BMI1 axis as a therapeutic target for CCA.