Abstract
Mouse models of hepatocellular carcinoma (HCC) simulate specific subgroups of human HCC. We investigated hepatocarcinogenesis in Mdr2-knockout (Mdr2-KO) mice, a model of inflammation-associated HCC, using gene expression profiling and immunohistochemical analyses. Gene expression profiling showed that although Mdr2-KO mice differ from other published murine HCC models, they share several important deregulated pathways and many coordinately differentially expressed genes with human HCC data sets. Analysis of genome positions of differentially expressed genes in liver tumors revealed a prolonged region of down-regulated genes on murine chromosome 8 in three of the six analyzed tumor samples. This region is syntenic to human chromosomal regions that are frequently deleted in human HCC and harbor multiple tumor suppressor genes. Real-time reverse transcription-PCR analysis of 16 tumor samples confirmed down-regulation of several tumor suppressors in most tumors. We show that in the aged Mdr2-KO mice, cyclin D1 nuclear level is increased in dysplastic hepatocytes that do not form nodules; however, it is decreased in most dysplastic nodules and in liver tumors. We found that this decrease is mostly at the protein, rather than the mRNA, level. These findings raise the question on the role of cyclin D1 at early stages of hepatocarcinogenesis in the Mdr2-KO HCC model. Furthermore, we show that most liver tumors in Mdr2-KO mice were characterized by the absence of beta-catenin activation. In conclusion, the Mdr2-KO mouse may serve as a model for beta-catenin-negative subgroup of human HCCs characterized by low nuclear cyclin D1 levels in tumor cells and by down-regulation of multiple tumor suppressor genes.
Highlights
Human hepatocellular carcinoma (HCC) is one of the major health care burdens, the molecular pathogenesis of which is still not well understood
We show an intriguing pattern of nuclear staining of cyclin D1 in hepatocytes, which raises a question about the role of this well-known oncogene in hepatocarcinogenesis in the Mdr2-KO HCC model
Some tumors were classified as moderately differentiated HCC, based on predominantly trabecular and solid growth patterns, prominent nucleoli observed in >50% of hepatocytes, and marked hepatocyte pleomorphism compared with surrounding nontumorous liver tissue
Summary
Human hepatocellular carcinoma (HCC) is one of the major health care burdens, the molecular pathogenesis of which is still not well understood. Mouse models of HCC have been widely used to study the molecular mechanisms of the disease and to test new therapeutic approaches. Mdr2-knockout (Mdr2KO) mice represent a model of inflammation-associated HCC [3]. They lack the liver-specific P-glycoprotein responsible for phosphatidylcholine transport across the bile canalicular membrane. It was previously found that both tumor necrosis factor a and nuclear factor nB are elevated in inflamed portal tracts of Mdr2-KO mice, and that reduction of tumor necrosis factor-a levels or nuclear factor nB inactivation prevented tumor development, providing a rational link between inflammation and tumorigenesis in this HCC model [6]
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