Functional studies of genes associated with DNA methylation changes in hepatoblastomas

Abstract

Hepatoblastoma is the most common liver cancer in childhood. These hepatic embryonal tumors exhibit the lowest mutational burden among pediatric tumors, raising the question if epigenetic changes could be relevant players in their tumorigenesis. We previously disclosed a pattern of low-level hypomethylation in non-repetitive sequences of hepatoblastomas in comparison to control liver tissues, evidencing a crucial role for epigenetic dysregulation in this type of cancer. Aiming to explore the underlying mechanisms related to hepatoblastoma hypomethylation, we have analyzed the expression profile of a set of genes engaged in the epigenetic machinery related to DNA methylation, as well as the 5-hydroxymethylcytosine (5hmC) global level. Our preliminary findings support a model of active demethylation by TETs in hepatoblastomas, probably during early stages of liver development, which in combination with the detected UHRF1 overexpression would lead to DNA hypomethylation as well as increased overall 5hmC content (manuscript under review). Additionally, our previous methylome data from hepatoblastomas also revealed hypermethylation at the promoter region of the NNMT gene, which was found to occur in association with downregulation of NNMT expression and consequent protein reduction. The present project intends to expand the analysis of these candidate genes, which have been identified in previous studies from our group in Brazilian hepatoblastoma patients, in other hepatoblastoma cohorts, as well as to perform functional studies of the most promising gene, focusing on epigenetic changes in this tumor type. We present previous work from the group that led to this project, as well as preliminary results that provide a basis for modulation of candidate genes in hepatoblastoma tumor cell lines. The knowledge gathered in this project could validate our previous results and broaden the understanding of the involvement of the proposed genes in cell biology of hepatoblastomas. (AU)