Exome sequencing of hepatoblastoma reveals novel mutations and cancer genes in the Wnt pathway and ubiquitin ligase complex

Abstract

Hepatoblastoma (HB) is the most common primary liver tumor in children. Mutations in the b-catenin gene that lead to constitutive activation of the Wnt pathway have been detected in a large proportion of HB tumors. To identify novel mutations in HB, we performed whole-exome sequencing of six paired HB tumors and their corresponding lymphocytes. This identified 24 somatic nonsynonymous mutations in 21 genes, many of which were novel, including three novel mutations targeting the CTNNB1 (G512V) and CAPRIN2 (R968H/S969C) genes in the Wnt pathway, and genes previously shown to be involved in the ubiquitin ligase complex (SPOP, KLHL22, TRPC4AP, and RNF169). Functionally, both the CTNNB1 (G512V) and CAPRIN2 (R968H/S969C) were observed to be gain-of-functional mutations, and the CAPRIN2 (R968H/S969C) was also shown to activate the Wnt pathway in HB cells. These findings suggested the activation of the Wnt pathway in HB, which was confirmed by immunohistochemical staining of the b-catenin in 42 HB tumors. We further used short hairpin RNA (shRNA)-mediated interference to assess the effect of 21 mutated genes on HB cell survival. The results suggested that one novel oncogene (CAPRIN2) and three tumor suppressors (SPOP, OR5I1, and CDC20B) influence HB cell growth. Moreover, we found that SPOP S119N is a loss-of-function mutation in HB cells. We finally demonstrated that one of the mechanisms by which SPOP inhibits HB cell proliferation is through regulating CDKN2B expression. Conclusion: These results extend the landscape of genetic alterations in HB and highlight the dysregulation of Wnt and ubiquitin pathways in HB tumorigenesis.

Aberrant KLK4 gene promoter hypomethylation in pediatric hepatoblastomas

“…Although its pathogenesis and progression have been extensively studied for the last two decades, its etiology remains to be fully elucidated. Through a previous study that involved sequencing of the HB exome, we recently detected a novel oncogene (caprin family member 2) and three tumor suppressors (speckle-type POZ protein, olfactory receptor family 5 subfamily I member 1 and cell division cycle 20B) that influence HB cell growth (18). The present group has also detected an association between long non-coding RNA (lncRNA) and HB in a previous study (19).…”

Genome-wide analysis of DNA methylation in hepatoblastoma tissues

“…The present authors recently sequenced the HB exome and identified a novel oncogene (caprin family member 2) and three tumor suppressors (speckle-type POZ protein, olfactory receptor family 5 subfamily I member 1 and cell division cycle 20B) that influence HB cell growth (22). A link between long non-coding RNA and HB was also detected (23).…”

miR-27b synergizes with anticancer drugs via p53 activation and CYP1B1 suppression

“…The hepatoblastoma cell line HepG2 was employed in the screen, because it retains better hepatic characteristics, has been widely used for cytotoxicity studies [21], and shares some important genetic alterations with hepatocellular carcinoma (HCC) [22]. In addition, doxorubicin, a widely used front-line chemotherapeutic drug, was used in the screen.…”