Hepatocyte identity and zonal position determine tumourigenic potential of mutant β-catenin

Oncogenic mutations in otherwise normal tissue are common in many adult tissues. This suggests multiple events need to converge to drive tumourigenesis and that many processes such as tissue differentiation may be protective against carcinogenesis. Within the liver Wnt/β-catenin signalling maintains zonal differentiation during liver homeostasis. However, the CTNNB1 oncogene—encoding β-catenin—is also frequently mutated in hepatocellular carcinoma, resulting in aberrant Wnt signalling that promotes cell growth. Here we investigated the antagonistic interplay between Wnt-driven growth and differentiation in zonal hepatocyte populations during liver tumorigenesis. In a model that acutely recombined mutant Wnt (Ctnnb1-ex3) and MYC alleles, we found that β-catenin mutants transiently stimulated growth in zone-1 and -2 hepatocytes within the Wnt-low region of the liver lobule – before inducing a differentiated zone-3 fate. To investigate the role of translation in this model of wnt and myc driven growth we performed Ribosome sequencing of whole liver at the early proliferative stage and the later differentiated stage. We found that Mutamt B-Catenin and MYC livers had a unique tanslational efficiency , which promted translation of RNA transcripts associated with growth. RPFs represent ribosome protected fragments and Totals represents the paired cytoplasmic RNA control, which was extracted with TRIzol from the lysate, prior to RNase digestion. For example, WT_day4_1_RPFs and WT_day4_1_Totals represents the RPFs and total cytoplasmic RNA sample from the first replicate of the day4 WT samples. Each sample represents an individual mouse and therefore a unique biological replicate. Day4 and Day10 mice were induced at different times so that all mice could be sacrificed and harvested at the same time.