GSE174571
The landscape of circular RNAs in neuroblastoma I
Circular RNAs (circRNAs), a noncoding RNA class originating from alternative splicing, are highly abundant in neural tissues and were shown to regulate gene expression e.g. by interacting with microRNAs and RNA-binding proteins. Neuroblastoma is an embryonal neoplasia, which arises from undifferentiated neural crest cells. Here, we aimed to explore, whether circRNAs influence the pathogenesis of high-risk neuroblastoma. We performed whole-transcriptome sequencing of 104 primary neuroblastoma samples of all risk-groups and identified 5,203 unique circRNAs involving 2,302 genes. Candidate circRNA expression did not correlate with host gene expression, indicating independent regulatory mechanisms. circRNAs were significantly downregulated in the MYCN-amplified high-risk tumors. These findings were independently reproduced in a tetracycline-inducible MYCN-overexpression system based on a non MYCN-amplified neuroblastoma cell line, suggesting that MYCN drives this global circRNA repression. We identified the RNA helicase DHX9 as a mediator of this global suppressive effect of MYCN on circRNAs. Comparing our RNA sequencing data with other cancers and controls revealed a circRNA subset specifically upregulated in neuroblastoma that included a circRNA derived from the ARID1A tumor suppressor gene. Specific circARID1A knockdown resulted in reduced proliferation, cell numbers and viability, prompted apoptosis and induced a differentiated phenotype. Neither knockdown, nor overexpression of circARID1A influenced ARID1A mRNA and protein levels significantly. To dissect the potential mode of function, we performed a pulldown assay with subsequent mass spectrometry. We identified the RNA-binding protein KHSRP as an interaction partner that participates in the mechanism of action of circARID1A. In summary, this study highlights an important role of circRNAs in neuroblastoma biology and may establish this RNA class as a future therapeutic target and biomarker. Overall design: Knockdown of DHX9 with 2 different siRNAs in the neuroblastoma cell line IMR-5