Abstract B54: Molecular basis of oncogene cooperation in liver cancer

Abstract

Abstract Combinations of genetic alterations in cancer genes lead to aberrant signaling properties and drive cellular transformation. Whether each oncogene gives rise to unique signals or combinations of oncogenes lead to new properties of cancer cells remains unclear. Using cell-based and animal model systems it has been shown that certain oncogenes can cooperate with each other to induce a fully malignant tumor phenotype. In addition, the combination of oncogenes and the extent of cooperation between them to give rise to a tumor may vary in different cancers. Cooperativity between MYC and RAS oncogenes has been observed in different cancer types. MYC is often overexpressed and sometimes amplified in cancer, while, activating RAS mutations occur in about 30% human cancers. Hepatocellular carcinoma (HCC) is among the four leading causes of cancer-related death. Currently, except for early surgical intervention or liver transplantation, no effective cures exist. Overexpression of both MYC and activated HRAS together in primary human liver tumors has been associated with aggressive forms of liver cancer with an especially poor prognosis. However, a systematic approach to understanding MYC and RAS cooperation in liver cancer has not yet been undertaken. We have discovered that transgenic mice overexpressing MYC, RAS or both MYC and RAS in their liver, give rise to distinct liver tumors. MYC and RAS coexpression led to faster tumor development and decreased survival. To gain a comprehensive view of the molecular changes that contribute to MYC and RAS oncogene cooperation in de novo liver tumors, we combined the conditional transgenic models of liver cancer with global gene expression, signaling pathway analyses and functional studies. Comparisons were made to clinically annotated human tumors and key pathways validated in cell lines and animal models. We show that tumors driven by either oncogene or a combination of both are phenotypically and molecularly distinct from each other with differential regulation of multiple genes and pathways. Our work suggests that MYC and RAS cooperate through specific genes, such as CCNE1 and multiple signaling pathways including proliferation, apoptosis, angiogenesis and multiple metabolic pathways, to contribute to liver cancer development. We also show molecular alterations across signaling pathways are comparable between mouse and human liver cancers. Primary human liver tumors can be segregated into distinct subsets based on differentially regulated gene sets from cooperating MYC and RAS tumors. These results indicate that molecular changes underlying MYC and RAS cooperation may serve as ideal molecular markers and therapeutic targets for liver cancer. Citation Information: Clin Cancer Res 2010;16(14 Suppl):B54.