Abstract:
Primary liver cancer is a major health problem with markedly increasing incidence rates. It is mainly represented by hepatocellular carcinoma (HCC) and intrahepatic cholangiocarcinoma (ICC) which are quite different regarding their morphology and treatment options. Although both share many risk factors as chronic liver damage or inflammation and cirrhosis, the molecular determinants resulting in either HCC or ICC lineage are largely unknown.
Here, using two different transposon-based liver cancer mouse models we show that both HCC and ICC can be induced by overexpressing the same oncogenes.
Taking advantage of a lineage tracing mouse model we prove that both tumors are derived from adult hepatocytes. Lineage commitment is independent of somatic mutations but depends on the hepatic microenvironment in the pre-tumorigenic phase. While in an apoptotic milieu there is an outgrowth of HCC a necroptotic milieu determines ICC development. This is independent of the composition of infiltrating immune cells, however, it is associated with a specific cytokine signature. The specific cytokine signature can be reversed when inhibiting necroptosis chemically or genetically and is followed by a switch from ICC to HCC development.
Epigenetic and transcriptomic analyses of cell lines isolated from hepatocyte-derived HCC or ICC driven by the same oncogene showed specific signatures for each tumor type. Integrative analyses of epigenetic and transcriptomic data revealed Tbx3 and Prdm5 as differentially regulated transcription factors which could also be found in a large cohort of human patients. Functional validation further showed that the interplay of Tbx3 and Prdm5 is sufficient to switch tumor lineage commitment from HCC to ICC. Finally, we identified downstream targets for both transcription factors which revealed quite converse downstream pathways highlighting the importance for their simultaneous interaction in determining lineage commitment in primary liver cancer.
