Evaluating the landscape of gene cooperativity with receptor tyrosine kinases in liver tumorigenesis using transposon-mediated mutagenesis

International audienceBackground & Aims: The variety of alterations found in hepatocellular carcinoma (HCC) makes the identification of functionally relevant genes and their combinatorial actions in tumorigenesis challenging. Deregulation of receptor tyrosine kinases (RTKs) is frequent in HCC, yet little is known about the molecular events that cooperate with RTKs and whether these cooperative events play an active role at the root of liver tumorigenesis.Methods: A forward genetic screen was performed using Sleeping Beauty transposon insertional mutagenesis to accelerate liver tumour formation in a genetic context in which subtly increased MET RTK levels predispose mice to tumorigenesis. Systematic sequencing of tumours identified common transposon insertion sites, thus uncovering putative RTK cooperators for liver cancer. Bioinformatic analyses were applied to transposon outcomes and human HCC datasets. In vitro and in vivo (through xenografts) functional screens were performed to assess the relevance of distinct cooperative modes to the tumorigenic properties conferred by RTKs.Results: We identified 275 genes, most of which are altered in patients with HCC. Unexpectedly, these genes are not restricted to a small set of pathway/cellular processes, but cover a large spectrum of cellular functions, including signalling, metabolism, chromatin remodelling, mRNA degradation, proteasome, ubiquitination, cell cycle regulation, and chromatid segregation. We validated 15 tumour suppressor candidates, as shRNA-mediated targeting confers tumorigenicity to RTK-sensitized cells, but not to cells with basal RTK levels. This demonstrates that the context of enhanced RTK levels is essential for their action in tumour initiation.Conclusion: Our study identifies unanticipated genetic interactions underlying gene cooperativity with RTKs in HCC. Moreover, these results show how subtly increased levels of wild-type RTKs provide a tumour permissive cellular environment allowing a large spectrum of deregulated mechanisms to initiate liver cancer