Negative Regulation of Mir-1275 by H3K27me3 is Critical for Glial Induction of Glioblastoma Cells.

Activation of the cyclic adenosine monophosphate/protein kinase A (cAMP/PKA) pathway induces glial differentiation of glioblastoma (GBM) cells, but the mechanism by which microRNA (miRNA) regulate this process remains poorly understood. In this study, by performing miRNA genomics and loss- and gain-of-function assays in dibutyryl-cAMP-treated GBM cells, we identified a critical negative regulator, hsa-miR-1275, that modulates a set of genes involved in cancer progression, stem cell maintenance, and cell maturation and differentiation. Additionally, we confirmed that miR-1275 directly and negatively regulates the protein expression of glial fibrillary acidic protein (GFAP), a marker of mature astrocytes. Of note, tri-methyl-histone H3 (Lys27) (H3K27me3), downstream of the PKA/polycomb repressive complex 2 (PRC2) pathway, accounts for the downregulation of miR-1275. Furthermore, decreased miR-1275 expression and induction of GFAP expression were also observed in dibutyryl-cAMP-treated primary cultured GBM cells. In a patient-derived glioma stem cell tumor model, a cAMP elevator and an inhibitor of H3K27me3 methyltransferase inhibited tumor growth, induced differentiation, and reduced expression of miR-1275. In summary, our study shows that epigenetic inhibition of miR-1275 by the cAMP/PKA/PRC2/H3K27me3 pathway mediates glial induction of GBM cells, providing a new mechanism and novel targets for differentiation-inducing therapy.