Abstract 1423: A lncRNA MEG9 protects vasculature from DNA damage

Abstract

Abstract DNA damaging agents including ionizing radiation (IR) therapy are widely used in cancer patients. Previous studies have suggested that the tumor vasculature, specifically endothelial cell (ECs) dictate responses to IR. We recently showed how IR, among other DNA damaging agents, induced changes in microRNA programs and impacted tumor angiogenesis. Here, we describe how different DNA damaging agents affect long noncoding RNA (lncRNA) programs in vascular cells. Specifically, we identify lncRNA MEG9 (Maternally Expressed Gene 9 in humans, Mirg in mouse) as one of the most differentially expressed lncRNAs in angiogenic stimuli and stress responses. MEG9 is robustly induced by DNA damaging agents and suppressed by vascular growth factors. MEG9 is located in the DLK1-DIO3 imprinted cluster. Previous studies have shown how DLK1-DIO3 genes are associated with stem cell biology and with the pathogenesis of several diseases, such as cancer. Other studies have shown that microRNAs in this cluster are regulated by methylation. Consistent with this observation, we found that inhibition of DNA methylation either via 5-azacytidine or silencing of DNMT3b significantly upregulated de novo expression of MEG9. Gain and loss of function assays indicated an anti-apoptotic role of MEG9 via caspase 3/7 pathways in cultured ECs. Similarly, MEG9 inhibition decreased angiogenesis in a 3D sprouting angiogenesis assay. Interestingly, MEG9 inhibition in ECs accelerated fibrin formation suggesting a regulatory role for this lncRNA in thrombosis. Moreover, we observed that MEG9 inhibition affects vascular permeability in vitro and in vivo in bFGF-Matrigel plugs. Finally, systemic delivery of RNAi targeting Mirg (mouse MEG9) decreased tumor burden in a mouse model of triple negative mammary carcinoma. Our mechanistic studies indicated that MEG9 in ECs impacts pathways related to inflammation and thrombosis, both critical mediators of tumor responses to radiation. Taken together, our results show MEG9 as a novel DNA damage induced lncRNA with a protective role in the tumor vasculature functioning via multiple distinct mechanisms. Therefore, we propose that disruption of lncRNA MEG9 is a potent anti-angiogenic strategy that can synergize with DNA damaging agents. Citation Format: Cristina Espinosa-Diez, Eugenia Fraile-Bethencourt, Clayton Hudson, Rebecca Ruhl, Sudarshan Anand. A lncRNA MEG9 protects vasculature from DNA damage [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1423.