B-catenin deficiency, but not c-Myc deletion, suppresses the immediate phenotypes of Apc loss in the liver

Dysregulated Wnt signalling is seen in approximately 30% of hepatocellular cancers, thus finding pathways downstream of activation of Wnt signalling is key. Using cre lox technology we have deleted the the adenomatous polyposis coli tumour suppressor protein (Apc) within the adult mouse liver and observed a rapid increase in nuclear beta-catenin and C-Myc. This is associated with an induction of proliferation leading to hepatomegally within 4 days of gene deletion. To investigate the downstream pathways responsible for these phenotypes we analysed the impact of inactivating Apc in the context of deficiency of the potentially key effectors beta-catenin and c-Myc. beta-catenin loss rescues both the proliferation and hepatomegally phenotypes following Apc loss. However c-Myc deletion, which rescues the phenotypes of Apc loss in the intestine, had no effect on the phenotypes of Apc loss. The consequences of deregulation the Wnt pathway within the liver are therefore strikingly different to those observed within the intestine, with the vast majority of Wnt targets beta-catenin dependent but c-Myc independent in the liver. Samples were collected from Genetcially modified mice of the genotypes indicated in the characteristics field. Gene recombination was induced using IP administration of beta-napthoflavone. Cohorts of samples were used to compare the affects of APC loss, cMYC loss and combined APC and cMYC loss in the liver (and compared to matched control samples in which the genes were not recombined).