Abstract 4982: Oncogenic role of THOR, a conserved cancer/testis long noncoding RNA

Large scale transcriptome sequencing efforts have vastly expanded the catalog of long non-coding RNAs (lncRNAs) with varying evolutionary conservation, lineage expression, and cancer specificity. Through a recent large-scale transcriptomic analysis over 6,500 tumor RNA-seq samples, we discovered over 50,000 lncRNAs in the human genome, many of which exhibited highly evolutionarily conserved sequence patterns. Building upon the discovery of these highly conserved lncRNAs, we functionally characterized a novel ultraconserved lncRNA, THOR, which exhibits expression exclusively in testis and a broad range of human cancers. We establish THOR as the first discovered cancer/testis lncRNA, and further investigated its functional significance. THOR knockdown and overexpression in multiple cell lines and animal models alters cell or tumor growth supporting an oncogenic role. Namely, we generated CRISPR knockout cell line models, showing a definitive role for THOR in cancer progression. Additionally, given the sequence conservation of THOR through the mouse and zebrafish, we generated a zebrafish knockout model, and also a zebrafish overexpression model for THOR. Through RNA-pulldown followed by mass spectrometry, we discovered a conserved interaction of THOR with the RNA binding protein, IGF2BP1, in both human and zebrafish cells. We further show that THOR contributes to the mRNA stabilization activities of IGF2BP1. These findings are corroborated by iCLIP data for IGF2BP1. Notably, transgenic THOR knockout produced fertilization defects in zebrafish and also conferred a resistance to melanoma onset in an NRAS K61-induced zebrafish melanoma model. Likewise, ectopic expression of human THOR in zebrafish accelerated the onset of melanoma. THOR represents a novel class of functionally important cancer/testis lncRNAs whose structure and function have undergone positive evolutionary selection. Citation Format: Yashar Niknafs, Yasuyuki Hosono, Matthew K, John Prensner, Rohit Mehra, Sethuramasundaram Pitchiaya, Jean Tien, Rohit Malik, Weibin Zhao, Arul Chinnaiyan. Oncogenic role of THOR, a conserved cancer/testis long noncoding RNA [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 4982.