The Promoter-Associated Noncoding RNA Assembles a Protein-RNA Complex to Regulate Cyclin D1 Transcription in Ewing Sarcoma.

Most Ewing sarcomas are characterized by the in-frame chromosomal translocation t(11;22) generating the EWS-FLI1 oncogene. EWS-FLI1 protein interacts with the RNA helicase DHX9 and affects transcription and processing of genes involved in neoplastic transformation, including (the cyclin D1 gene), which contributes to cell-cycle dysregulation in cancer. In this study, we found that expression is significantly higher in patients with Ewing sarcoma compared with other sarcomas and that the RNA, a previously uncharacterized promoter-associated noncoding (pnc) transcript, is expressed in Ewing sarcoma cells. interacted with the RNA-binding protein Sam68 and repressed expression. Notably, knockdown of Sam68 affected subcellular localization and cyclin D1 expression. Pharmacologic impairment of DHX9/EWS-FLI1 interaction promoted RNA-dependent association of Sam68 with DHX9 and recruitment of Sam68 to the promoter, thus repressing it. Conversely, mitogenic stimulation of Ewing sarcoma cells with IGF1 impaired Sam68/DHX9 interaction and positively regulated expression. These studies uncover a fine-tuned modulation of the proto-oncogene in Ewing sarcoma cells via alternative complexes formed by DHX9 with either EWS-FLI1 or -Sam68. SIGNIFICANCE: A pncRNA-based mechanism represses expression of through the formation of a protein-RNA complex and provides new therapeutic opportunities for patients with Ewing sarcoma. http://cancerres.aacrjournals.org/content/canres/79/14/3570/F1.large.jpg.