MiRNA-34a is considered as a potential prognostic marker for glioma, as studies suggest that its expression negatively correlates with patient survival in grade III and IV glial tumors. Here, we show that expression of miR-34a was decreased in a graded manner in glioma and glioma stem cell-lines as compared to normal brain tissues. Ectopic expression of miR-34a in glioma stem cell-lines HNGC-2 and NSG-K16 decreased the proliferative and migratory potential of these cells, induced cell cycle arrest and caused apoptosis. Notably, the miR-34a glioma cells formed significantly smaller xenografts in immuno-deficient mice as compared with control glioma stem cell-lines. Here, using a bioinformatics approach and various biological assays, we identify Rictor, as a novel target for miR-34a in glioma stem cells. Rictor, a defining component of mTORC2 complex, is involved in cell survival signaling. mTORC2 lays downstream of Akt, and thus is a direct activator of Akt. Our earlier studies have elaborated on role of Rictor in glioma invasion (Das et al., 2011). Here, we demonstrate that miR34a over-expression in glioma stem cells profoundly decreased levels of p-AKT (Ser473), increased GSK-3β levels and targeted for degradation β-catenin, an important mediator of Wnt signaling pathway. This led to diminished levels of the Wnt effectors cyclin D1 and c-myc. Collectively, we show that the tumor suppressive function of miR-34a in glioblastoma is mediated via Rictor, which through its effects on AKT/mTOR pathway and Wnt signaling causes pronounced effects on glioma malignancy.
Keywords: Beta-catenin; CNS, central nervous system; EGF, epidermal growth factor; EMT, epithelial–mesenchymal transition; EV, empty vector; GBM, glioblastoma multiforme; GIC, glioma initiating cell; GSC, glioma stem cell; GSK-3β, glycogen synthase kinase 3β; Glioblastoma; Heterogeneity; Mesenchymal; NOD/SCID, nonobese diabetic/severe combined immunodeficiency; PARP, poly ADP-ribose polymerases; PDGFRA, platelet-derived growth factor receptor-α; Rictor; TCGA, the cancer genome atlas database; bFGF, basic fibroblast growth factor; qRT-PCR, quantitative real time PCR.