Abstract
Glioblastomas show heterogeneous histological features, and tumor cells show distinct phenotypic states that confer different functional attributes and an aggressive character. However, the molecular mechanisms underlying the heterogeneity in this disease are poorly understood. Glioma stem-like cells (GSCs) are considered able to aberrantly differentiate into diverse cell types and may contribute to the establishment of tumor heterogeneity. Using a GSC model, we investigated differentially expressed microRNAs (miRNAs) and associated epigenetic mechanisms that regulate the differentiation of GSCs. miRNA profiling using microarray technology showed that 13 and 34 miRNAs were commonly up-regulated and down-regulated in two independent GSC lines during differentiation, respectively. Among this set of miRNAs, quantitative PCR analysis showed that miRNA-1275 (miR-1275) was consistently down-regulated during GSC differentiation, along with the up-regulation of its target, CLDN11, an important protein during oligodendroglial lineage differentiation. Inhibition of miR-1275 with a specific antisense oligonucleotide (anti-miR-1275) in GSCs increased the expression of CLDN11, together with significant growth suppression. Epigenetic analysis revealed that gain of histone H3 lysine 27 trimethylation (H3K27me3) in the primary microRNA-1275 promoter was closely associated with miR-1275 expression. Treatment with 3-deazaneplanocin A, an inhibitor of H3K27 methyltransferase, attenuated CLDN11 induction by serum stimulation in parallel with sustained miR-1275 expression. Our results have illuminated the epigenetic regulatory pathways of miR-1275 that are closely associated with oligodendroglial differentiation, which may contribute to the tissue heterogeneity seen in the formation of glioblastomas. Given that inhibition of miR-1275 induces expression of oligodendroglial lineage proteins and suppresses tumor cell proliferation, this may be a potential therapeutic target for glioblastomas.