Deleting the β-catenin degradation domain in mouse hepatocytes drives hepatocellular carcinoma or hepatoblastoma-like tumor growth

Background & Aims: One-third of hepatocellular carcinomas (HCCs) harbor mutations activating the beta-catenin pathway, predominantly via mutations in the CTNNBI gene itself. Mouse models of Apc loss-of-function are widely used to mimic beta-catenin-dependent tumorigenesis. Given the low prevalence of APC mutations in human HCCs, we aimed to generate liver tumors through CTNNBI exon 3 deletion (beta cat(Delta ex3)). We then compared beta cat(Delta ex3) liver tumors with liver tumors generated via frameshift in exon 15 of Apc (Apc(f)(s-ex15)). Methods: We used hepatocyte-specific and inducible mouse models generated through either a Cre-Lox or a CRISPR/Cas9 approach using adeno-associated virus vectors. Tumors generated by the Cre-Lox models were phenotypically analyzed using immunohistochemistry and were selected for transcriptomic analysis by RNA-sequencing (RNAseq). Mouse RNAseq data were compared to human RNAseq data (8 normal tissues, 48 HCCs, 9 hepatoblastomas) in an integrative analysis. Tumors generated via CRISPR were analyzed using DNA sequencing and immunohistochemistry. Results: Mice with CTNNB1 exon 3 deletion in hepatocytes developed liver tumors indistinguishable from Apc(fs-ex15) liver tumors. Both Apc(fs-ex15 )and beta cat(Delta ex3) mouse models induced growth of phenotypically distinct tumors (differentiated or undifferentiated). Integrative analysis of human and mouse tumors showed that differentiated mouse tumors cluster with well-differentiated human CTNNB1-mutated tumors. Conversely, undifferentiated mouse tumors cluster with human mesenchymal hepatoblastomas and harbor activated YAP signaling. Conclusion: Apc(fs-ex15) and Bcat(Delta ex3) mouse models both induce growth of tumors that are transcriptionally similar to either well-differentiated and beta-catenin-activated human HCCs or mesenchymal hepatoblastomas. Lay summary: New and easy-to-use transgenic mouse models of primary liver cancers have been generated, with mutations in the gene encoding beta-catenin, which are frequent in both adult and pediatric primary liver cancers. The mice develop both types of cancer, constituting a strong preclinical model. (C) 2022 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.

Automated summary

The study explored the relationship between the deletion of exon 3 in the CTNNBI gene and liver tumor development, and compared it with the mutation in exon 15 of the APC gene. The results showed that both mutation models could generate tumors similar to human liver cancer, providing a powerful preclinical model.