HDAC1-Dependent Repression of Markers of Hepatocytes and P21 Is Involved in Development of Pediatric Liver Cancer

Background & Aims: Epigenetic regulation of gene expression plays a critical role in the development of liver cancer; however, the molecular mechanisms of epigenetic-driven liver cancers are not well understood. The aims of this study were to examine molecular mechanisms that cause the dedifferentiation of hepatocytes into cancer cells in aggressive hepatoblastoma and test if the inhibition of these mechanisms inhibits tumor growth. Methods: We have analyzed CCAAT/Enhancer Binding Protein alpha (C/EBPα), Transcription factor Sp5, and histone deacetylase (HDAC)1 pathways from a large biobank of fresh hepatoblastoma (HBL) samples using high-pressure liquid chromatography-based examination of protein-protein complexes and have examined chromatin remodeling on the promoters of markers of hepatocytes and p21. The HDAC1 activity was inhibited in patient-derived xenograft models of HBL and in cultured hepatoblastoma cells and expression of HDAC1-dependent markers of hepatocytes was examined. Results: Analyses of a biobank showed that a significant portion of HBL patients have increased levels of an oncogenic de-phosphorylated-S190-C/EBPα, Sp5, and HDAC1 compared with amounts of these proteins in adjacent regions. We found that the oncogenic de-phosphorylated-S190-C/EBPα is created in aggressive HBL by protein phosphatase 2A, which is increased within the nucleus and dephosphorylates C/EBPα at Ser190. C/EBPα-HDAC1 and Sp5-HDAC1 complexes are abundant in hepatocytes, which dedifferent