Study of somatic mutations identified in exome sequencing of hepatoblastoma

Abstract

Hepatoblastomas (HB) are embryonal tumors of the liver presenting with histological features that resemble the differentiation stages of hepatic cells. Molecular data on HB carcinogenesis is still scarce because of its rarity. The identification of the molecular pathways involved in the origin of HBs can expand the understanding of the connections between disruption of differentiation and cancer. We have the hypothesis that recurrent mutations in hepatoblastomas can occur, thus driving the carcinogenesis in addition to other mechanisms. To disclose rare somatic mutations, we performed a whole-exome sequencing of 6 HBs and their paired non-tumoral adjacent liver samples (capture method 244K Agilent SureSelect Target Enrichment; sequencing in Illumina HiSeq2000). Rare somatic variants (non-synonimous) were validated using target sequencing (capture method SureSelectXT Target Enrichment System for Illumina Paired-End Sequencing Library, and Illumina MiSeq Multiplexed Sequencing Platform). An additional step of biological validation was performed using an independent cohort of 13 hepatoblastomas samples. Bioinformatic analysis of the exome data resulted in the identification of a total of 76 rare somatic variants mapped in coding sequences, and 46 of them have been validated in the target sequencing. The analysis detected four different pathogenic mutations in the CTNNB1 gene, in 4 tumors. The protein expression of beta-catenin was evaluated in 8 of the studied HBs, as well as in tissue-microarray consisting of 30 hepatoblastomas; the findings corroborated the activation of the Wnt, showing in most HBs the translocation of the protein beta-catenin to the nucleus in tumors in which CTNNB1 mutations were detected. Additionally, it was validated a recurrent somatic mutation affecting the exon 3 of the CX3CL1 in two HBs. Therefore, this gene has become an important candidate for this type of tumor and is currently under investigation. (AU)