Genomic and transcriptomic analyses of chemical hepatocarcinogenesis aggravated by oncoprotein loss

Abstract

Background and Aims: The chemical carcinogen diethylnitrosamine (DEN) is often used to induce hepatocellular carcinoma (HCC) in mice. Curiously, several labs have reported that removal of oncoproteins from hepatocytes exacerbated DEN-induced HCC, with mechanisms unknown. This study aimed at deciphering molecular mechanisms underlying the tumor suppressive effect of oncoproteins. Methods and Results: We generated mutant mouse lines with hepatocyte-specific deletions of Met, Ptpn11/Shp2, Ikk, or ctnnb1/-catenin, and assessed DEN-induced tumorigenesis in the wild type (WT) and mutant mice. To systematically examine genetic and molecular signaling alternations, we performed whole exome and RNA sequencing on liver samples collected at the pre-cancer and established cancer stages. Although the mutational profiles of DEN-induced tumors were barely different in WT and mutant mice, oncoprotein ablation increased DEN-induced mutational burdens, especially in Shp2-deficient tumors. RNA-sequencing revealed multiple changes in signaling pathways, in particular upregulated epithelial-mesenchymal transition (EMT), cell migration and tumor metastasis as well as downregulated small molecule metabolism that were affected by oncoprotein ablation. We identified key molecules and pathways that are associated with hepatic innate immunity and implicated in liver tumorigenesis. In addition, we unveiled markedly changed expression of a few miRNAs in human HCC database. Conclusion: The aggravation of DEN-induced HCC progression seen on oncoprotein ablation could be caused by common and distinct genomic and signaling alterations. This study reveals a new level of complexity in hepato-carcinogenesis and elucidates molecular mechanisms underlying tumor evolution and recurrence.