The function of HNRNPH1 in processing the EWS-FLI1 pre-mRNA in a subset of Ewing sarcoma cells

Authors

• CN Neckles
• B Boer
• S Kim
• J Schneekloth
• NJ Caplen

Abstract

The primary oncogenic event in ~85% of Ewing sarcomas involves a chromosomal translocation that generates a fusion gene containing the 5’ end of EWSR1 and 3’ end of FLI1 (EWS-FLI1). Although the exact genomic breakpoints within the EWSR1 and FLI1 genes vary, translocations that retain exon 8 of EWSR1 generate an out-of-frame transcript unless this exon is removed. We have previously demonstrated that heterogeneous nuclear ribonucleoprotein H1 (HNRNPH1) binds to G-rich sequences within EWSR1 exon 8 in a subgroup of Ewing sarcoma (EWS) cells and this binding event is required to express an in-frame EWS-FLI1 mature mRNA. Here, we demonstrate that RNA oligomers, corresponding to sequences in these G-rich regions, fold into guanine quadruplex (G4) structures using CD spectroscopy and antibody binding assays. Furthermore, we show that HNRNPH1 binds preferentially to these G4 structures. Treatment with a G4-binding molecule, pyridostatin, selectivity inhibits the growth of EWS cell lines harboring EWSR1 exon 8 fusions, decreases EWS-FLI1 activity in a cell-based reporter assay, and restores mRNA expression of EWS-FLI1 deregulated transcriptional targets. Our studies suggest that targeting the HNRNPH1-mediated processing of the EWS-FLI1 pre-mRNA is a potential strategy for targeting the fusion oncogene expressed in a third of Ewing sarcoma.

Scientific Focus Area: Molecular Biology and Biochemistry

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