The effect of alcohol on Sirt1 expression and function in animal and human models of hepatocellular carcinoma (HCC).

Abstract

Chronic heavy alcohol use is an independent risk factor for developing hepatocellular carcinoma (HCC). Sirtuin-1 (Sirt1) is a NAD+-dependent deacetylase implicated in alcohol-induced liver injury and overexpressed in human HCC. The aims of this study were to investigate Sirt1 expression in mouse models of HCC and chronic EtOH-feeding, and in human HCC cells expressing alcohol metabolizing enzymes. C57BL/6 and B6C3 mice were injected with DEN and randomized to receive drinking water (DW) or EtOH-DW for 8 weeks at 36 weeks. Livers were analyzed for HCC incidence, size, and Sirt1 expression. In parallel, human HepG2 cells or HepG2 cells transfected to express ADH and CYP2E1 (VL-17a cells) were treated with alcohol (0-50 mM) and/or CAY10591 (Sirt1 activator) or EX-527 (Sirt1 inhibitor). B6C3 mice exhibited significantly elevated Sirt-1 expression vs. C57BL/6 mice and Sirt-1 expression was elevated in HCC vs. non-tumor liver. However, EtOH-feeding did not further affect Sirt1 expression in mice of either background despite EtOH increasing HCC size and incidence in B6C3 mice. In vitro, EtOH treatment significantly decreased Sirt1 expression in VL-17a-cells and stimulated cell growth, an effect not observed in HepG2 cells. The effects of ethanol on VL-17a cells were abrogated by pretreatment with CAY10591. Sirt1 expression correlates with susceptibility to form HCC, but is not further affected by alcohol feeding. Conversely Sirt1 expression and function is impacted by alcohol metabolism capacity in human HCC cells in vitro. These discrepancies in Sirt1-expression-function may reflect differences in enzyme expression compared to activity, or more complex changes in genes targeted for deacetylation during tumor progression in the setting of chronic alcohol ingestion.