Methylome sequencing for fibrolamellar hepatocellular carcinoma depicts distinctive features

Abstract

<p>With the goal of studying epigenetic alterations in fibrolamellar hepatocellular carcinoma (FLC) and establish an associated DNA methylation signature, we analyzed <i>LINE-1</i> methylation in a cohort of FLC and performed next-generation sequencing of DNA methylation in a training set of pure-FLCs and non-cirrhotic hepatocellular carcinomas (nc-HCC). DNA methylation was correlated with gene expression. Furthermore, we established and validated an epigenetic signature differentiating pure-FLC from other HCCs. <i>LINE-1</i> methylation correlated with shorter recurrence-free survival and overall survival in resected pure-FLC patients. Unsupervised clustering using CG sites located in islands distinguished pure-FLC from nc-HCC. Major DNA methylation changes occurred outside promoters, mainly in gene bodies and intergenic regions located in the vicinity of liver developmental genes (i.e., <i>SMARCA4</i> and <i>RXRA</i>). Partially methylated domains were more prone to DNA methylation changes. Furthermore, we identified several putative tumor suppressor genes (e.g., <i>DLEU7</i>) and oncogenes (e.g., <i>DUSP4</i>). While ∼70% of identified gene promoters gaining methylation were marked by bivalent histone marks (H3K4me3/H3K27me3) in embryonic stem cells, ∼70% of those losing methylation were marked by H3K4me3. Finally, we established a pure FLC DNA methylation signature and validated it in an independent dataset. Our analysis reveals a distinct epigenetic signature of pure FLC as compared to nc-HCC, with DNA methylation changes occurring in the vicinity of liver developmental genes. These data suggest new options for targeting FLC based on cancer epigenome aberrations.</p