Keng, Vincent W.

Abstract Hepatic steatosis is a strong risk factor for the development of hepatocellular carcinoma (HCC), yet little is known about the molecular pathology associated with this factor. In this study, we performed a forward genetic screen using Sleeping Beauty (SB) transposon insertional mutagenesis in mice treated to induce hepatic steatosis and compared the results to human HCC data. In humans, we determined that steatosis increased the proportion of female HCC patients, a pattern also reflected in mice. Our genetic screen identified 203 candidate steatosis-associated HCC genes, many of which are altered in human HCC and are members of established HCC-driving signaling pathways. The protein kinase A/cyclic AMP signaling pathway was altered frequently in mouse and human steatosis-associated HCC. We found that activated PKA expression drove steatosis-specific liver tumorigenesis in a mouse model. Another candidate HCC driver, the N-acetyltransferase NAT10, which we found to be overexpressed in human steatosis–associated HCC and associated with decreased survival in human HCC, also drove liver tumorigenesis in a steatotic mouse model. This study identifies genes and pathways promoting HCC that may represent novel targets for prevention and treatment in the context of hepatic steatosis, an area of rapidly growing clinical significance. Cancer Res; 77(23); 6576–88. ©2017 AACR.

Abstract Hepatocellular carcinoma (HCC), or liver cancer, is the second leading cause of death from cancer worldwide (Ferlay et al, Lyon, France: International Agency for Research on Cancer, 2013). HCC is linked with hepatic steatosis, or fatty liver disease, the most common chronic liver disease in the US. Both hepatic steatosis and HCC are increasing in prevalence in the US. However, the molecular mechanisms that cause HCC in a steatotic liver are not entirely understood. To uncover mutations promoting cancer in fatty livers and elucidate the role of steatosis in HCC, we performed a forward genetic screen using the conditional Sleeping Beauty (SB) transposon insertional mutagenesis system in mice treated with ethanol and a choline deficient diet to induce steatosis. Mice developed hepatic steatosis and liver cancer without sex bias, modeling the pattern seen in humans in whom HCC's with steatosis as a preceding condition are represented by a nearly equal number of males and females. We found that hepatic steatosis caused a downregulation of liver Foxa1 expression and increased Foxa2 inactivating phosphorylation, thus providing a molecular explanation for the loss of gender bias in our mouse model. Transposon insertion sites were mapped from the mouse HCC tumors, and genes near or in which more insertions were observed than expected by chance were identified as common insertion sites (CIS), which we consider putative steatosis-associated liver cancer genes. Wnt/b-catenin signaling, which defines a subclass of HCC and can induce tumors in mice without sex bias, was one of the top CIS associated pathways identified. Interestingly, alpha-adrenergic and dopamine signaling were also among the top steatosis-specific CIS associated pathways, suggesting a role for the sympathetic nervous system and cAMP signaling in fatty liver-associated cancer. Further studies are underway to test the roles of the pathways and individual genes identified in this study in driving HCC. Our studies implicate Wnt/beta-catenin and sympathetic nervous system signaling in steatosis-associated HCC and suggest methods for treatment or prevention in such cases. Citation Format: Barbara R. Tschida, N. Alpay Temiz, Ju D. Yang, Vincent W. Keng, David A. Largaespada. A transposon-based forward genetic screen for steatosis-associated liver cancer drivers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 63.

Abstract Insertional mutagenesis screens play an integral part in the annotating of functional data for all sequenced genes in the postgenomic era. Chemical mutagenesis screens are highly efficient but identifying the causative gene can be a laborious task. Other mutagenesis platforms, such as transposable elements, have been successfully applied for insertional mutagenesis screens in both the mouse and rat. However, relatively low transposition efficiency has hampered their use as a high-throughput forward genetic mutagenesis screen. Here we report the first evidence of germline activity in the mouse using a naturally active DNA transposon derived from the medaka fish called Tol2, as an alternative system for high-throughput forward genetic mutagenesis screening tool.