Abstract 4080: An inducible zebrafish model to dissect the role of beta catenin signaling in hepatocellular carcinoma
Authors: Kotiyal Srishti , Kalasekar Sharanya Maanasi , Davis Kathryn , Barba Cindy , Young Annika , Evason Kimberley J. 
Published: August 2018

Abstract
Hepatocellular carcinoma (HCC) is the third highest contributor to cancer-related mortality in the world. This disease is molecularly heterogeneous in nature, which obfuscates our understanding of the molecular etiology of the disease, giving rise to the essential and urgent need of delineating HCC mechanisms based on molecular subtypes.
Various signaling pathways have been implicated in HCC development. The Wnt/β-catenin pathway remains of particular significance with more than a third of all HCC cases characterized by aberrant activation of the Wnt/β-catenin signaling axis. About 20% of HCC cases are characterized by activating mutations in the β-catenin gene (ctnnb1). These activating mutations prevent β-catenin degradation and allow it to enter the nucleus and activate transcription of various genes involved in cell proliferation and apoptosis. The need to elucidate the role of aberrant β-catenin gene activation in the development of liver malignancy is thwarted by the lack of relevant animal models. In mice, β-catenin mutation alone is not sufficient to induce HCC. To address this bottleneck, we have designed a vertebrate HCC model system of activated β-catenin-driven HCC in an inducible background using zebrafish (Danio rerio).
In our previous work, we demonstrated that zebrafish expressing a mutated, phosphorylation-resistant, and constitutively-activated version of β-catenin develop HCC morphologically and transcriptionally similar to human HCC. Here, we describe a system in which spatially and temporally controlled expression of activated β-catenin is achieved using hepatocyte-specific, tamoxifen-induced expression of Cre recombinase.
Using hepatocyte-specific constitutive/induced Cre-recombinase zebrafish lines together with floxed β-catenin and/or floxed fluorescent reporter lines, we show here that Cre recombinase is successfully able to switch on the expression of floxed transgenes in fishes at larval, juvenile and adult stages. Through histology and longitudinal studies, we are determining the ability of our inducible system to increase cellular β-catenin levels and Wnt signaling in the liver and to stimulate HCC when activated β-catenin is turned on at different developmental stages including adulthood.
This inducible system will be useful for studying the impact of β-catenin activation on liver size and malignancy at different stages of liver development. The ability to induce the oncogene in adulthood will allow us to study HCC in a physiologically relevant setting. We will use this temporal and spatial control for further studies aimed at understanding the role of activated β-catenin in HCC initiation and developing treatment strategies.
Citation Format: Srishti Kotiyal, Sharanya Maanasi Kalasekar, Kathryn Davis, Cindy Barba, Annika Young, Kimberley J. Evason. An inducible zebrafish model to dissect the role of beta catenin signaling in hepatocellular carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4080.