Defeating EpCAM+ liver cancer stem cells by targeting chromatin remodeling enzyme CHD4 in human hepatocellular carcinoma

Abstract

Hepatocellular carcinoma is composed of a subset of cells with enhanced tumorigenicity and chemoresistance that are called cancer stem (or stem-like) cells. We explored the role of chromodomain-helicase-DNA-binding protein 4, which is encoded by the CHD4 gene and is known to epigenetically control gene regulation and DNA damage responses in EpCAM(+) liver cancer stem cells. Gene and protein expression profiles were determined by microarray and immunohistochemistry in 245 and 144 hepatocellular carcinoma patients, respectively. The relationship between gene/protein expression and prognosis was examined. The functional role of CHD4 was evaluated in primary hepatocellular carcinoma cells and in cell lines in vitro and in vivo. CHD4 was abundantly expressed in EpCAM(+) hepatocellular carcinoma with expression of hepatic stem cell markers and poor prognosis in two independent cohorts. In cell lines, CHD4 knockdown increased chemosensitivity and CHD4 overexpression induced epirubicin chemoresistance. To inhibit the functions of CHD4 that are mediated through histone deacetylase and poly (ADP-ribose) polymerase, we evaluated the effect of the histone deacetylase inhibitor suberohydroxamic acid and the poly (ADP-ribose) polymerase inhibitor AG-014699. Treatment with either suberohydroxamic acid or AG-014699 reduced the number of EpCAM(+) liver cancer stem cells in vitro, and suberohydroxamic acid and AG-014699 in combination successfully inhibited tumor growth in a mouse xenograft model. CHD4 plays a pivotal role in chemoresistance and the maintenance of stemness in liver cancer stem cells and is therefore a good target for the eradication of hepatocellular carcinoma.