MicroRNAs contribute to biological robustness by buffering cellular processes from external perturbations. Here we report an unexpected link between DNA damage response and angiogenic signaling that is buffered by two distinct microRNAs. We demonstrate that genotoxic stress-induced miR-494 and miR-99b inhibit the DNA repair machinery by targeting the MRE11a-RAD50-NBN (MRN) complex. Functionally, gain and loss of function experiments show that miR-494 and miR-99b affect telomerase activity, activate p21 and Rb pathways and diminish angiogenic sprouting in vitro and in vivo.Genetic and pharmacological disruption of VEGFR-2 signaling and the MRN complex reveal a surprising co-dependency of these pathways in regulating endothelial senescence and proliferation. Vascular-targeted delivery of miR-494 decreases both growth factorinduced and tumor angiogenesis in mouse models. Mechanistically, disruption of the MRN complex induced CD44, a known driver of senescence and regulator of VEGF signaling in addition to suppressing IL-13 a stimulator of VEGF signaling. Our work identifies a putative miR-facilitated mechanism by which endothelial cells can be insulated against VEGF signaling to facilitate the onset of senescence and highlight the potential of targeting DNA repair to disrupt pathological angiogenesis.
Increased cellular production of vascular endothelial growth factor (VEGF) is responsible for the development and progression of multiple cancers and other neovascular conditions, and therapies targeting post-translational VEGF products are used in the treatment of these diseases. Development of methods to control and modify the transcription of the VEGF gene is an alternative approach that may have therapeutic potential. We have previously shown that isoforms of the transcriptional enhancer factor 1-related (TEAD4) protein can enhance the production of VEGF. In this study we describe a new TEAD4 isoform, TEAD4216, which represses VEGF promoter activity. The TEAD4216 isoform inhibits human VEGF promoter activity and does not require the presence of the hypoxia responsive element (HRE), which is the sequence critical to hypoxia inducible factor (HIF)-mediated effects. The TEAD4216 protein is localized to the cytoplasm, whereas the enhancer isoforms are found within the nucleus. The TEAD4216 isoform can competitively repress the stimulatory activity of the TEAD4434 and TEAD4148 enhancers. Synthesis of the native VEGF165 protein and cellular proliferation is suppressed by the TEAD4216 isoform. Mutational analysis indicates that nuclear or cytoplasmic localization of any isoform determines whether it acts as an enhancer or repressor, respectively. The TEAD4216 isoform appears to inhibit VEGF production independently of the HRE required activity by HIF, suggesting that this alternatively spliced isoform of TEAD4 may provide a novel approach to treat VEGF-dependent diseases.
Endothelial cells are highly responsive to environmental changes that allow them to adapt to intrinsic and extrinsic stimuli and switch their transcriptome accordingly to go back to vascular homeostasis. Our previous data demonstrated that small non-coding-RNAs respond quickly to genotoxic stressors and determined endothelial cell fate and DNA damage response. To further understand the contribution of non-coding-RNAs, we profiled differentially expressed long non-coding RNAs in response to genotoxic stress and compared them to pro-angiogenic growth factor signaling. We identified the Maternally expressed gene 9 (MEG9) as a cytoprotective lncRNA in the endothelium. Gain and Loss-of-function studies indicate that MEG9 prevents endothelial cells from cell death, suggesting that MEG9 responses to genotoxic stress can be an adaptive and protective mechanism. Consistent with this phenotype, the knockdown of MEG9 decreases growth factor-dependent angiogenesis in a 3D fibrin gel angiogenesis assay. Deletion of the MEG9 ortholog, Mirg, in mice results in increased vascular leak in Matrigel plugs and a sex and age-dependent decrease in platelets. Mechanistically, we observed that both MEG9 knockdown in vitro and Mirg-deleted mice in vivo activated common pathways, including apoptosis, clotting, and inflammation. Indeed, the proinflammatory adhesion molecule ICAM1 was significantly increased in human and mouse endothelial cells in a MEG9-dependent manner, supporting the increased vascular permeability observed on MEG9 deficient cells. Taken together, our findings illustrate how genotoxic stress responses through dynamic modulation of lncRNAs, such as MEG9, trigger adaptive mechanisms to maintain endothelial function, while loss of these molecules contributes to maladaptive responses and endothelial cell dysfunction.
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