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Molecular mechanisms of hepatocarcinogenesis in c-Myc/Tgfa transgenic mice

ABSTRACT: A complete understanding of molecular mechanisms that underlie cancer onset and progression could provide a basis to improve early diagnosis and more effective treatment. However, this is still a challenge in human, partly due to the difficulty of analyzing the early stages of the disease. In this context, genetically engineered mice represent a valuable alternative to model human carcinogenesis. Here, we studied cancer development in c-Myc/Tgfa transgenic mice that developed liver tumors which closely reproduce a subset of human hepatocellular carcinoma (HCC) with a poor prognosis. By using a functional genomics approach from early to late stages of HCC development, we demonstrated that hepatocarcinogenesis in c-Myc/Tgfa mice resulted from a progressive accumulation of transcriptional alterations due to an active hepatocyte proliferation in a chronic oxidative stress environment generated by a general metabolic disorder. One striking observation was the deregulation of numerous immune-related genes starting from an early stage of the disease. Particularly, we showed that activating ligands for natural killer (NK) cells were specifically induced in dysplastic hepatocytes which simultaneously lost the expression of MHC-I molecules. Besides this early mechanism of NK-mediated immune surveillance, we further reported a drastic decrease in hepatic NK cell population which may indeed contribute to the emergence and clonal expansion of progenitors for liver tumors. In conclusion, our study provided a detailed and comprehensive characterization of hepatocarcinogenesis in c-Myc/Tgfa transgenic mice and emphasized the critical role of the innate immune surveillance disruption at the early stages of liver cancer.

ORGANISM(S): Mus musculus

PROVIDER: GSE25587 | GEO | 2011/09/28

SECONDARY ACCESSION(S): PRJNA134223

REPOSITORIES: GEO

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Project description:A complete understanding of molecular mechanisms that underlie cancer onset and progression could provide a basis to improve early diagnosis and more effective treatment. However, this is still a challenge in human, partly due to the difficulty of analyzing the early stages of the disease. In this context, genetically engineered mice represent a valuable alternative to model human carcinogenesis. Here, we studied cancer development in c-Myc/Tgfa transgenic mice that developed liver tumors which closely reproduce a subset of human hepatocellular carcinoma (HCC) with a poor prognosis. By using a functional genomics approach from early to late stages of HCC development, we demonstrated that hepatocarcinogenesis in c-Myc/Tgfa mice resulted from a progressive accumulation of transcriptional alterations due to an active hepatocyte proliferation in a chronic oxidative stress environment generated by a general metabolic disorder. One striking observation was the deregulation of numerous immune-related genes starting from an early stage of the disease. Particularly, we showed that activating ligands for natural killer (NK) cells were specifically induced in dysplastic hepatocytes which simultaneously lost the expression of MHC-I molecules. Besides this early mechanism of NK-mediated immune surveillance, we further reported a drastic decrease in hepatic NK cell population which may indeed contribute to the emergence and clonal expansion of progenitors for liver tumors. In conclusion, our study provided a detailed and comprehensive characterization of hepatocarcinogenesis in c-Myc/Tgfa transgenic mice and emphasized the critical role of the innate immune surveillance disruption at the early stages of liver cancer. In the present study, we reported a detailed and comprehensive dynamic characterization of the cellular and molecular alterations involved in tumor onset and progression in the liver of c-Myc/Tgfa double-transgenic mice (B6CBAxCD1 background). Liver samples from male animals were collected at various time-points ranging from 3 weeks to 9 months for c-Myc/Tgfa double-transgenic mice, or 18 months for c-Myc and Tgfa single-transgenic mice. Tissue samples were divided into two parts; one was fixed in 10% formalin for histological evaluation and the other was used for RNA analysis. Total RNAs were isolated from livers with moderate or severe hepatocyte dysplasia (at 3 weeks and 3 months, respectively), as well as from HCC and surrounding non-tumor livers (5-15 mice per group). Total RNAs were also isolated from the livers of B6CBAxCD1 wild-type mice at 3 weeks and 3 months. RNAs isolated from the normal livers of B6CBA WT mice (3 months old, n=10) were pooled and used as a common technical reference for all microarray experiments.

Project description:Hepatocarcinogenesis is a multi-stage process in which precursor lesions progress into early hepatocellular carcinomas (eHCC) by sequential accumulation of multiple genetic and epigenetic alterations. To decode the molecular events during early stages of liver carcinogenesis, we performed gene expression profiling on cirrhotic (regenerative) and dysplastic nodules (DN) as well as eHCC. Although considerable heterogeneity was observed at the regenerative and dysplastic stages, clear differences were detected between DN and eHCC which included 460 differentially expressed genes. Functional analysis of the significant gene set identified the MYC oncogene as a plausible driver gene for malignant conversion of the dysplastic nodules. In addition, gene set enrichment analysis (GSEA) revealed a remarkable enrichment of MYC up-regulated gene set in eHCC versus dysplasia. Presence of the MYC signature significantly correlated with increased expression of CSN5 as well as with the higher overall transcription rate of genes located in the 8q chromosome region. Furthermore, a classifier constructed from MYC target genes could robustly discriminate eHCC from high- and low-grade dysplastic nodules. In conclusion, our study identified unique expression patterns associated with the transition of high-grade dysplastic nodules to early HCC and demonstrated that activation of the MYC transcription signature is critical for the malignant conversion of pre-neoplastic liver lesions. Samples from forty-nine nodular liver lesions including 24 regenerative (cirrhotic) nodules (CN), 3 low-grade (LGDN), 12 high-grade dysplastic nodules (HGDN) and 10 early hepatocellular carcinomas (Early HCC) were used. The Human Operon V2 oligonucleotide library containing 22K features representing expressed sequences was printed to glass arrays in the Advanced Technology Center (National Cancer Institute, Gaithersburg, MD). The aRNA probes were fragmented and hybridized to the microarray slides following the standard procedures. All samples were hybridized against a common amplified reference RNA pooled from normal liver samples. Experimental duplicates were prepared following a reverse-flour design.

Project description:Mouse models of hepatocellular carcinoma (HCC) simulate specific subgroups of human HCC. We investigated hepatocarcinogenesis in Mdr2-KO mice, a model of inflammation-associated HCC, using gene expression profiling and immunohistochemical analyses. Gene expression profiling demonstrated 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 datasets. 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 RT-PCR analysis of 16 tumor samples confirmed down-regulation of several tumor suppressors in most tumors. We demonstrate 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 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 b-catenin activation. In conclusion, the Mdr2-KO mouse may serve as a model for b-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. Experiment Overall Design: The liver RNA samples from six Mdr2-KO tumors, six non-tumorous liver tissues (four matched and two unmatched), as well as from three control heterozygous mice at 16 months of age were subjected to gene expression profiling using the genome scale Affymetrix Mouse Genome 430 2.0 Array.

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Molecular mechanisms of hepatocarcinogenesis in c-Myc/Tgfa transgenic mice

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