Identification of a Growth-Promoting Gene Cluster in the Region 2q24 as a Driver of Tumorigenesis in Childhood Hepatoblastoma

Abstract

Hepatoblastoma (HB) represents the most common primary malignancy of the liver in childhood. Cytogenetic studies uncovered characteristic copy number alterations in HB. The frequent gain of chromosome 2q and particularly the recurrent 2q24 amplification suggest the presence of a so far unidentified oncogenic driver within this amplicon. Herein, high-resolution copy number profiles from 76 patients with HB were generated by using molecular inversion probe array technology. 2q gain was present in 63.2%, and 2q24 high-gain/amplification was present in 14.5% of patients analyzed. In the smallest overlapping region at 2q24.2q24.3, spanning >5.2 Mbp, 22 protein-coding genes, 2 long noncoding RNA genes, and one miRNA gene were mapped. RNA expression analysis of these smallest overlapping region genes identified RBMS1, BAZ2B, MARCH7, DPP4, FIGN, and TANK as overexpressed in 2q24 high-gain/amplified HB cases. Accordingly, these six genes were selected for further investigation. In situ, immunohistochemical staining showed higher protein expression of these genes in 2q24 high-gain HB tissue sections. In vitro, functional analyses were performed in established human HB cell lines carrying a 2q (high-)gain. Knockdown of these genes by specific siRNAs resulted in reduced proliferation and marked reduction of Wnt pathway activity. These genes located within the 2q24 amplicon might collaborate in driving cellular growth by interaction with the Wnt pathway that is known to be activated pathologically in HB.