MSH2 prevents liver tumorigenesis by regulating cell cycle checkpoints under chronic inflammation.

The DNA mismatch repair (MMR) system plays a critical role in maintaining genomic integrity and preventing tumorigenesis. Although MutS homolog 2 (MSH2) is a key component of the MMR system and is dysregulated in human hepatocellular carcinoma (HCC), the molecular mechanism of MSH2 in the process of HCC development under chronic inflammatory conditions remains unclear. To investigate the function of MSH2 in inflammation-associated hepatocarcinogenesis, we treated hepatocyte-specific Msh2-knockout (Msh2 KO) mice with 0.02% thioacetamide for 30 weeks to induce chronic liver inflammation and examined their phenotype. Msh2 KO mice exhibited higher liver tumor incidence than wild-type mice, with no major differences in inflammation or fibrosis. Whole-exome sequencing analysis revealed that genetic alterations with defective MMR-associated signatures were increased in Msh2 KO tumors, though no common cancer driver genes were identified. Transcriptome analysis revealed enrichment of cell cycle-related gene sets, including the G2M checkpoint and E2F targets. Functional assays further demonstrated that MSH2 downregulation impaired ATM-CHK2-mediated DNA damage response and promoted cell cycle acceleration. MSH2 exerts its tumor-suppressive effects in hepatocytes not only through canonical MMR but also by regulating the cell cycle via the ATM-CHK2 axis.