Axin1 deletion induced hepatocarcinogenesis requires intact β-Catenin but not Notch cascade in mice.

Inactivating mutations of AXIN1, a negative regulator of the Wnt/β-Catenin cascade, are among the common genetic events in human hepatocellular carcinoma (HCC), affecting around 10% of cases. In the present manuscript, we sought to define the genetic crosstalk between Axin1 mutants and Wnt/β-catenin as well as Notch signaling cascades along hepatocarcinogenesis. We discovered that c-MET activation and AXIN1 mutations occur concomitantly in ~3 to 5% of human HCC samples. Subsequently, we generated a murine HCC model via CRISPR/Cas9 based gene deletion of Axin1 (sgAxin1) in combination with transposon-based expression of c-Met in the mouse liver (c-Met/sgAxin1). Global gene expression analysis of mouse normal liver, HCCs induced by c-Met/sgAxin1 as well as HCCs induced by c-Met/∆N90-β-Catenin revealed activation of the Wnt/β-Catenin and Notch signaling in c-Met/sgAxin1 HCCs. However, only a few of the canonical Wnt/β-Catenin target genes were induced in c-Met/sgAxin1 HCC when compared to corresponding lesions from c-Met/∆N90-β-Catenin mice. To study whether endogenous β-Catenin is required for c-Met/sgAxin1 driven HCC development, we expressed c-Met/sgAxin1 in liver-specific Ctnnb1 null mice, which completely prevented HCC development. Consistently, in AXIN1 mutant or null human HCC cell lines, silencing of β-Catenin strongly inhibited cell proliferation. In striking contrast, blocking the Notch cascade via expression of either the dominant negative form of RBP-J or the ablation of Notch2, did not significantly affect c-Met/sgAxin1-driven hepatocarcinogenesis. Conclusion: We demonstrated here that loss of Axin1 cooperates with c-Met to induce HCC in mice, in a β-Catenin signaling dependent but Notch cascade independent way. This article is protected by copyright. All rights reserved.