Abstract 2492: Identification of RBMS1 in the amplified region 2q24 as a major driver of cellular growth in childhood hepatoblastoma
Authors: Rodemann Martin , Dreschmann Verena , Dörner Evelyn , von Schweinitz Dietrich , Vokuhl Christian , Pietsch Torsten 
Published: June 2022

Abstract
Hepatoblastoma represents the most common primary malignancy of the liver in childhood. Pathological activation of the WNT signaling pathway is characteristic for hepatoblastoma caused by mutations of CTNNB1 or other genes encoding components of the pathway. Genome-wide chromosomal analyses uncovered recurrent chromosomal alterations, in particular gain of chromosome 2q, and in some cases amplification of the region 2q24 that suggests the presence of a so far unidentified oncogene in this chromosomal region. The aim of this study was to identify and further characterize this oncogene.
In the framework of the clinical hepatoblastoma study of the German Society for Pediatric Oncology and Hematology, we had the opportunity to study samples of 76 hepatoblastoma patients. Using molecular inversion probe (MIP) array technology, genome-wide, high-resolution, quantitative chromosomal copy number profiles were generated and the smallest overlapping amplified region was identified. RNA and protein expression in normal and diseased tissues as well as ascribed functions of the genes located in this area were evaluated in silico in available databases. RNA expression levels of these genes were analyzed by Nanostring method and Affymetrix arrays and compared between 2q24-amplified tumors versus non-amplified tumors and normal liver tissue. The most promising candidate gene regarding its expression pattern and described function was selected for further analysis. Its protein expression was studied in situ by immunohistochemistry in hepatoblastoma tissue microarrays. The biological function was analyzed in vitro by targeted siRNA-mediated knockdown experiments in 3 hepatoblastoma cell lines (HepT1, HepG2, HuH6) und subsequent cell growth assays (MTT) and WNT signaling pathway specific luciferase reporter assays.
Gain of chromosome 2q was present in 44.7% of the cases. Amplification of the 2q24.2-24.3 region was detected in 11.8%. In the smallest overlapping amplified region of 5.6 Mbp, we could accurately map 20 protein coding genes, three genes encoding long noncoding RNAs and one gene encoding a micro-RNA. The RBMS1 gene encoding a single-stranded DNA/RNA binding protein showed significant RNA overexpression in 2q24 amplified tumors. This overexpression was validated by immunohistochemical studies at the protein level. RBMS1 knockdown by specific siRNA transfection resulted in a significantly reduced proliferation of hepatoblastoma cells. RBMS1 knockdown also resulted in a marked reduction of the WNT pathway activity in these cells.
We identified RBMS1 located within the amplicon on chromosome 2q24 as a potential oncogenic driver in hepatoblastoma. Initial data suggest that RBMS1 may exert this function by interaction with the WNT signaling pathway that is pathologically activated in hepatoblastoma.
Citation Format: Martin Rodemann, Verena Dreschmann, Evelyn Dörner, Dietrich von Schweinitz, Christian Vokuhl, Torsten Pietsch. Identification of RBMS1 in the amplified region 2q24 as a major driver of cellular growth in childhood hepatoblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2492.