Suppression of Hepatocellular Carcinoma by Deletion of SIRT2 in Hepatocytes via Elevated C/EBPβ/GADD45γ.

BACKGROUND & AIMS: There is a gap in our understanding of mechanisms promoting hepatocellular carcinoma (HCC), and this limits our ability to provide targeted therapy interventions for HCC. In HCC samples, NAD-dependent deacetylase sirtuin 2 (SIRT2) levels are increased and associated with a significantly worse prognosis, but the role of SIRT2 in hepatocarcinogenesis remains controversial. METHODS: To assess the role of SIRT2 in hepatocarcinogenesis, we used a hepatocyte-specific knockout of SIRT2 and two plasmid overexpression HCC models: c-MET (MET)/β-catenin (CAT) and protein kinase B (AKT)/Nras. RNA sequencing of mouse liver tissue was performed, and mechanistic findings were confirmed using immunohistochemistry (IHC), quantitative polymerase chain reaction, Western blot, and Cell Counting Kit-8. RESULTS: Using the MET/CAT and AKT/Nras models, we found that SIRT2 is a significant mediator of liver tumorigenesis, with the knockout of SIRT2 delaying tumor growth. RNA sequencing of MET/CAT-driven tumor tissue showed an increase in growth arrest and DNA-damage-inducible protein gamma (GADD45γ) in SIRT2 knockout mice compared with wild-type. GADD45γ is a known tumor suppressor, but the regulation of GADD45γ by SIRT2 has not been shown. CCAAT/enhancer-binding protein beta (C/EBPβ) proteins are known to regulate GADD45γ expression, and we found that C/EBPβ expression was increased in SIRT2 knockout livers and HCC cells. Also, C/EBPβ knockdown reversed GADD45γ expression and growth suppression following SIRT2 inhibition. Finally, C/EBPβ or GADD45γ overexpression significantly suppressed MET/CAT-induced HCC development. CONCLUSIONS: SIRT2 is a potent tumor promotor in HCC that negatively regulates GADD45γ expression through C/EBPβ. The SIRT2-C/EBPβ-GADD45γ pathway elucidates a novel mechanism in HCC and establishes SIRT2 as a therapeutic target for patients with HCC.