Long non-coding RNAs (lncRNAs) are major regulators of many cellular processes including cell cycle progression and cell proliferation. The pivotal transcription factor E2F1 induces both proliferation and cell death and is a critical downstream target of the tumor suppressor RB. The RB/E2F pathway is often inactivated in human tumors resulting in deregulated E2F activity. Here, we report that the human lncRNA XLOC_000190 is an E2F1- regulated lncRNA that plays a role in S phase progression. XLOC_000190 levels are elevated upon activation of E2F1. Furthermore, knockdown of E2F1 and E2F3 reduce XLOC_000190 levels and endogenous E2F1 binds the XLOC_000190 promoter. Moreover, expression of XLOC_000190 is cell cycle regulated and peaks near G1/S transition and in early S. Inhibition of XLOC_000190 expression increases percentage of S phase cells, suggesting that XLOC_000190 plays a role in S phase progression. Also, silencing of XLOC_000190 in cells that are synchronized at the G1/S delays progression of cells through S phase. In agreement with its suggested role in S phase, prolonged silencing of XLOC_000190 inhibits proliferation of human cancer cells in culture. XLOC_000190 is a nuclear lncRNA and its gene is localized downstream to the protein-coding gene CDKN2C that encodes the p18ink4c CDK inhibitor. In search for XLOC_000190 mode of action we do not detect any changes in the expression of this neighbor upon XLOC_000190 silencing. However, XLOC_000190 silencing leads to a significant decrease in the level of Ribonucleotide Reductase Regulatory Subunit M2 (RRM2), which is a critical player in S phase progression. Additional data indicate that RRM2 mediates, at least in part, the effect of XLOC_000190 on S phase progression. Importantly, low levels of XLOC_000190 are associated with increased survival of kidney cancer patients.

In conclusions, our data identify XLOC_000190 as a novel E2F-regulated lncRNA that has a potential role in human cancer and regulates cell-cycle progression and cell proliferation, at least in part, via regulation of RRM2.

Citation Format: Doron Ginsberg, Tali Nizri-Megnaji, Esther Baruch. A novel E2F1-regulated lncRNA, XLOC_000190, is required for S phase progression and cell proliferation [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 3567.