Oncofusion driven de novo enhancer assembly promotes malignancy in Ewing sarcoma via aberrant expression of the stereociliary protein LOXHD1 [hypoxia]

Ewing Sarcoma (EwS) is a highly aggressive tumor of bone and soft tissues that mostly affects children and adolescents. The pathognomonic oncofusion EWSR1-ETS (EWS-FLI1/EWSR1-ERG) transcription factors drive EwS by orchestrating an oncogenic transcription program through de novo enhancers. Pharmacological targeting of these oncofusions has been challenged by unstructured prion-like domains and common DNA binding motifs in the EWSR1 and ETS protein, respectively. Alternatively, identification and characterization of mediators and downstream targets of EWS-FLI1 dependent or independent function could offer novel therapeutic options. By integrative analysis of thousands of transcriptome datasets representing pan-cancer cell lines, primary cancer, metastasis, and normal tissues, we have identified a 32 gene signature (ESS32) that could stratify EwS from pan-cancer. Of the ESS32 (Ewing Sarcoma Specific 32), LOXHD1 - coding for a stereociliary protein was the most exquisite gene expressed in EwS. CRISPR-Cas9 mediated deletion or silencing of EWS-FLI1 bound upstream de novo enhancer elements in EwS cells led to the loss of LOXHD1 expression and altered the EWS-FLI1, MYC, and HIF1? pathway genes, resulting in decreased proliferation and invasion in vitro and in vivo. These observations open up new avenues for developing LOXHD1-targeted drugs or cellular therapies for this deadly disease. Overall design: Gene expression analysis in normoxia and hypoxia in control and LOXHD1 enhancer knockdown (eKD1 and eKD2) SKNMC cell lines.