Generation of combined hepatocellular-cholangiocarcinoma through transdifferentiation and dedifferentiation in p53-knockout mice

Abstract

The two principal histological types of primary liver cancers, hepatocellular carcinoma (HCC) and cholangiocarcinoma, can coexist within a tumor, comprising combined hepatocellular-cholangiocarcinoma (cHCC-CCA). Although the possible involvement of liver stem/progenitor cells has been proposed for the pathogenesis of cHCC-CCA, the cells might originate from transformed hepatocytes that undergo ductular transdifferentiation or dedifferentiation. We previously demonstrated that concomitant introduction of mutant HRAS^V12 (HRAS) and Myc into mouse hepatocytes induced dedifferentiated tumors that expressed fetal/neonatal liver genes and proteins. Here, we examine whether the phenotype of HRAS- or HRAS/Myc-induced tumors might be affected by the disruption of the Trp53 gene, which has been shown to induce biliary differentiation in mouse liver tumors. Hepatocyte-derived liver tumors were induced in heterozygous and homozygous p53-knockout (KO) mice by hydrodynamic tail vein injection of HRAS- or Myc-containing transposon cassette plasmids, which were modified by deleting loxP sites, with a transposase-expressing plasmid. The HRAS-induced and HRAS/Myc-induced tumors in the wild-type mice demonstrated histological features of HCC, whereas the phenotype of the tumors generated in the p53-KO mice was consistent with cHCC-CCA. The expression of fetal/neonatal liver proteins, including delta-like 1, was detected in the HRAS/Myc-induced but not in the HRAS-induced cHCC-CCA tissues. The dedifferentiation in the HRAS/Myc-induced tumors was more marked in the homozygous p53-KO mice than in the heterozygous p53-KO mice and was associated with activation of Myc and YAP and suppression of ERK phosphorylation. Our results suggest that the loss of p53 promotes ductular differentiation of hepatocyte-derived tumor cells through either transdifferentiation or Myc-mediated dedifferentiation.

Keywords: animal model for carcinogenesis; cell differentiation; characteristics of cancer cells; experimental animal models and genetically engineered animals; gene-manipulated animal models; oncogenes and tumor-suppressor genes; p53-related genes.