The human genome encodes thousands of unique long non-coding RNAs (lncRNAs), many of which are emerging as critical regulators of cell fate. However, their functions as well as their transcriptional regulation are only partially understood. The E2F1 transcription factor induces both proliferation and apoptosis, and is a critical downstream target of the tumor suppressor, RB. Here, we provide evidence that a novel lncRNA named GASL1 is transcriptionally regulated by E2F1; GASL1 levels are elevated upon activation of exogenous E2F1 or endogenous E2Fs. Inhibition of GASL1 expression induced cell cycle progression, and in particular, G1 exit. Moreover, GASL1 silencing enhanced cell proliferation, while, conversely, its ectopic expression inhibited proliferation. Knockdown of GASL1 also enhanced E2F1-induced apoptosis, suggesting the existence of an E2F/GASL1 negative feedback loop. In agreement with this notion, silencing of GASL1 led to increased levels of phosphorylated pRB and loss of Rb impaired the effect of GASL1 silencing on G1 exit. Importantly, xenograft experiments demonstrated that GASL1 deletion enhances tumor growth. Moreover, low levels of GASL1 are associated with decreased survival of liver cancer patients. Taken together, our data identify GASL1 as a novel lncRNA regulator of cell cycle progression and cell proliferation with a potential role in cancer.

The transcription factor E2F1 induces both proliferation and apoptosis and is a critical downstream target of the tumor suppressor RB.Long non-coding RNAs (lncRNAs) are major regulators of many cellular processes, including cell cycle progression and cell proliferation. However, the mode of action as well as the transcriptional regulation of most lncRNAs are only beginning to be understood.Here, we report that a novel human lncRNA, LAPAS1, is an E2F1-regulated lncRNA that affects S phase progression. Inhibition of LAPAS1 expression increases percentage of S phase cells, and its silencing in synchronized cells delays their progression through S phase. In agreement with its suggested role in cell cycle progression, prolonged inhibition of LAPAS1 attenuates proliferation of human cancer cells.Our data demonstrate that LAPAS1 predominantly functions in trans to repress expression of Sphingolipid Transporter 2 (SPNS2). Importantly, knockdown of SPNS2 rescues the effect of LAPAS1 silencing on cell cycle and cell proliferation.Notably, low levels of LAPAS1 are associated with increased survival of kidney cancer patients.Summarily, we identify LAPAS1 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 SPNS2.

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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.

Long noncoding RNAs (lncRNAs) are major regulators of many cellular processes including cell cycle progression, cell proliferation and tumorigenesis. In this study, we identify a novel lncRNA, GTF2A1-AS1, and reveal its effects on cell cycle progression and cancer growth. Inhibition of GTF2A1-AS1 expression alters cell cycle distribution, leading to a decrease in the number of G1 cells and a concomitant increase in all other stages of the cell cycle, and in particular S phase, suggesting its involvement in the regulation of G1/S transition. Accordingly, knock down of GTF2A1-AS1 enhances G1 phase exit upon release from a late G1 block. In agreement with its suggested role in G1/S transition, prolonged silencing of GTF2A1-AS1 enhances proliferation of human cancer cells. GTF2A1-AS1 RNA is mostly nuclear and its gene is localized upstream to the protein-coding gene GTF2A1. GTF2A1-AS1 functions in trans to repress the expression of EIF5A2 and HOXA13. Knockdown of either EIF5A2 or HOXA13 rescues the effects of GTF2A1-AS1 silencing on cell proliferation, indicating that it functions mainly by modulating the levels of these two proteins. In agreement with the effect of GTF2A1-AS1 silencing on cell cycle progression and cell proliferation, low levels of GTF2A1-AS1 are associated with reduced survival in brain cancer patients. In conclusions, our data identify GTF2A1-AS1 as a novel lncRNA that regulates cell-cycle progression and cell proliferation and has a potential role in human cancer. Citation Format: Yael Goldstein, Tali Nizri-Megnaji, Doron Ginsberg. A novel lncRNA, GTF2A1-AS1, is required for cell cycle progression and cell proliferation. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3762.