Yap-Sox9 signaling determines hepatocyte plasticity and lineage-specific hepatocarcinogenesis

Published:November 15, 2021DOI:


      • Sox9 is required for Yap-induced hepatocyte plasticity during hepatocarcinogenesis in mice.
      • Sox9 removal in hepatocytes with Yap activation resulted in more aggressive HCC.
      • Sox9 expression is sufficient to promote cell fate plasticity in less differentiated hepatocytes in vivo.
      • YAP activity and SOX9 expression are strongly correlated with liver tumor plasticity in human patients.


      Background & Aims

      Primary liver tumors contain distinct subtypes. A subset of iCCAs can arise from cell fate reprogramming of mature hepatocytes in mouse models. However, the underpinning of cell fate plasticity during hepatocarcinogenesis is still poorly understood, hampering therapeutic development to treat HCC and iCCA. As YAP activation induces liver tumor formation and cell fate plasticity, we investigated the role of Sox9, a transcription factor downstream of Yap activation and expressed in biliary epithelial cells (BECs), in Yap-induced cell fate plasticity during hepatocarcinogenesis.


      To evaluate the function of Sox9 in YAP-induced hepatocarcinogenesis in vivo, we performed inducible hepatocyte-specific YAP activation with simultaneous Sox9 removal in several mouse genetic models. Cell fate reprogramming was determined by lineage tracing and immunohistochemistry. The molecular mechanism underlying Yap and Sox9 function in hepatocyte plasticity was investigated by transcription and transcriptomic analyses of mouse and human liver tumors.


      Sox9, a marker of liver progenitor cells (LPCs) and BECs, is differentially required in YAP-induced stepwise hepatocyte programming. While Sox9 has limited function in hepatocyte dedifferentiation to LPCs, it is required for BEC differentiation from LPCs. YAP activation in Sox9-deficient hepatocytes resulted in more aggressive HCC with enhanced Yap activity at the expense of iCCA-like tumors. Furthermore, we showed that 20% of primary human liver tumors were associated with a YAP activation signature, and tumor plasticity is highly correlated with YAP activation and SOX9 expression.


      Our data demonstrated that Yap-Sox9 signaling determines hepatocyte plasticity and tumor heterogeneity in hepatocarcinogenesis in both mouse and human liver tumors. We identified Sox9 as a critical transcription factor required for Yap-induced hepatocyte cell fate reprogramming during hepatocarcinogenesis.

      Lay summary

      Sox9, a marker of liver progenitor cells and bile duct lining cells, is a downstream target of YAP protein activation. Here we found that YAP activation in hepatocytes leads to a transition from mature hepatocytes to first liver progenitor cells and then the formation of the bile duct lining cells and Sox9 is required in the second step during mouse hepatocarcinogenesis. We also found that human YAP and SOX9 may play similar roles in liver cancers.

      Graphical abstract



      HCC (hepatocellular carcinoma), iCCA (intrahepatic cholangiocarcinoma), BEC (biliary epithelial cell), LPC (liver progenitor cell), TBG (thyroxine-binding globulin), AAV8 (adeno-associated virus 8), qRT-PCR (quantitative RT-PCR), RNA-seq (RNA Sequencing), ATAC-seq (Assay for Transposase-Accessible Chromatin using sequencing), FACS (fluorescence-activated cell sorting), GSEA (gene set enrichment analysis), TUNEL (terminal deoxynucleotidyl transferase dUTP nick end labeling), EdU (5-Ethynyl-2´-deoxyuridine)
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