Malignant glioma (Glioblastoma multiforme, GBM, glioma) is the most common and aggressive primary adult brain tumor. The prognosis of GBM patients remains poor, despite surgery, radiation and chemotherapy. Significantly, genes that play a role in neural stem cell maintenance, including BMI1 and SUZ12, are highly expressed in GBM. BMI1 acts as part of the polycomb repressor complex 1 (PRC1) and SUZ12 as a part of PRC2. These complexes play critical role in epigenetic silencing by modifying chromatin structure. PRC1/2 have been shown to contribute to glioma cells tumorigenicity and glioma "stem-like" cells (GSCs) self-renewal. Through their regulation of multiple genes, microRNAs (miRNA) orchestrate complex programs of gene expression and act as master regulators of cellular processes. MiRNA-based therapeutics could thus impact broad cellular programs, leading to cancer cell differentiation, cell cycle arrest, apoptosis, inhibition of invasion and sensitization to radio/chemotherapy. Our data show that miR-128 targets BMI1 and SUZ12 in glioma cells and GSCs. This particular miR is weakly expressed in GBM, and, miR-128 directly targets BMI1 and PRC2 component SUZ12. This simultaneous targeting of both PRCs prevents their partially redundant functions. We demonstrated that miR-128 increases radio-sensitivity of GSCs and, using mouse genetic model of glioma, that loss of miR-128 in early event in gliomagenesis. Therefore, our overall hypothesis is that restoration of the expression of this particular miR in GSCs will result in reduced self-renewal and increased radio- sensitivity through a mechanism that involves members of PRC1/2 complexes. To pursue the validity of this overall hypothesis, we thus propose to: Aim 1: Characterize in vitro the influence of miR-128 on therapy sensitization and subsequent cell death in extended panel of GSCs; Aim 2: Validate the role of miR-128 in regulation of PRC in mouse genetic models of glioblastoma; Aim 3: Determine if miR-128 can be exploited to sensitize glioblastoma to conventional therapies in vivo. Successful completion of the proposed experiments will provide additional mechanistic insights into miR based regulation of PRC's role in gliomagenesis and maintenance and a rationale for the clinical translation of a novel therapeutic strategy using miRs that target members of PRC in GSCs for the treatment of gliomas.