Key Points Endothelial cells secrete exosomes containing miR-214, which suppress senescence and stimulates an angiogenic program in target cells. Exosomal miR-214 regulates ataxia telangiectasia mutated expression in recipient endothelial cells.

Background Glioblastoma (GBM) is a malignant brain tumor with dismal prognosis. GBM patients have a median survival of less than 2 years. GBM is characterized by fast cell proliferation, infiltrative migration, and by the induction of angiogenesis. MicroRNAs and polycomb group (PcG) proteins have emerged as important regulators of gene expression. Methods Here we determined that miR-101 is down-regulated in GBM, resulting in overexpression of the miR-101 target PcG protein EZH2, a histone methyltransferase affecting gene expression profiles in an epigenetic manner. Results Inhibition of EZH2 in vitro by pre-miR-101, EZH2 siRNA, or small molecule DZNep, attenuated GBM cell growth, migration/invasion, and GBM-induced endothelial tubule formation. In addition, for each biological process we identified ontology-associated transcripts that significantly correlate with EZH2 expression. Inhibition of EZH2 in vivo by systemic DZNep administration in a U87-Fluc-mCherry GBM xenograft mouse imaging model resulted in reduced tumor growth. Conclusion Our results indicate that EZH2 has a versatile function in GBM progression and that its overexpression is at least partly due to decreased miR-101 expression. Inhibition of EZH2 may be a potential therapeutic strategy to target GBM proliferation, migration, and angiogenesis.

In patients with glioblastomas, vascular endothelial growth factor (VEGF) is a key mediator of tumor-associated angiogenesis. Glioblastomas are notorious for their capacity to induce neovascularization, driving continued tumor growth. Here we report that miR-125b is down-regulated in glioblastoma-associated endothelial cells, resulting in increased expression of its target, myc-associated zinc finger protein (MAZ), a transcription factor that regulates VEGF. The down-regulation of miR-125b was also observed on exposure of endothelial cells to glioblastoma-conditioned medium or VEGF, resulting in increased MAZ expression. Further analysis revealed that inhibition of MAZ accumulation by miR-125b, or by MAZ-specific shRNAs, attenuated primary human brain endothelial cell migration and tubule formation in vitro, phenomena considered to mimick angiogenic processes in vitro. Moreover, MAZ expression was elevated in brain blood vessels of glioblastoma patients. Altogether these results demonstrate a functional feed-forward loop in glioblastoma-related angiogenesis, in which VEGF inhibits the expression of miR-125b, resulting in increased expression of MAZ, which in its turn causes transcriptional activation of VEGF. This loop is functionally impeded by the VEGF receptor inhibitor vandetanib, and our results may contribute to the further development of inhibitors of tumor-angiogenesis.

Purpose: Medulloblastoma is the most common malignant brain tumor in children. Despite recent improvements, the molecular mechanisms driving medulloblastoma are not fully understood and further elucidation could provide cues to improve outcome prediction and therapeutic approaches.Experimental Design: Here, we conducted a meta-analysis of mouse and human medulloblastoma gene expression data sets, to identify potential medulloblastoma tumor suppressor genes.Results: We identified DAB2IP, a member of the RAS-GTPase-activating protein family (RAS GAP), and showed that DAB2IP expression is repressed in medulloblastoma by EZH2-induced trimethylation. Moreover, we observed that reduced DAB2IP expression correlates significantly with a poor overall survival of patients with medulloblastoma, independent of metastatic stage. Finally, we showed that ectopic DAB2IP expression enhances stress-induced apoptosis in medulloblastoma cells and that reduced expression of DAB2IP in medulloblastoma cells conveys resistance to irradiation-induced cell death.Conclusion: These results suggest that repression of DAB2IP may at least partly protect medulloblastoma cells from apoptotic cell death. Moreover, DAB2IP may represent a molecular marker to distinguish patients with medulloblastoma at high risk from those with a longer survival prognosis.