Investigation of tumor suppressive miR-148a in IDH mutant gliomas

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Project Summary/Abstract Gliomas presently remain incurable with currently available radiation and chemotherapeutic modalities. Intensive molecular characterization of gliomas have revealed a rich molecular diversity of aberrations that give rise to the hope that we can significantly impact this disease through translation of the most promising targets into personalized therapies. This proposal directly addresses this need by investigating the tumor suppressive mechanism of a novel target, miR-148a, identified using an innovative and powerful DNA methylation profiling strategy established in the PI's laboratory. Although not yet studied in glioma, miRNA-148a is emerging as a tumor suppressive miRNA in other cancers. As small non-coding RNAs that suppress gene expression, miRNAs occupy key roles in cancer mechanisms and provide emerging therapeutic targets as either themselves or genes they regulate. Extensive genomic characterization of cancer tissue has revealed the widespread presence of aberrant DNA CpG island methylation, which can be associated with the epigenetic silencing of some miRNAs. The recently discovered isocitrate dehydrogenase (IDH) mutation is thought not only to provide a biomarker of secondary gliomas but also represent an initiating event in gliomagenesis. Our research in IDHMUT gliomas has contributed to the recognition of an IDHMUT-associated genome-wide hypermethylation profile, glioma-CpG island methylator phenotype (G-CIMP), that is not found in normal tissue or IDH wild-type gliomas. This has led to a widely accepted but as yet unsupported hypothesis that G-CIMP occupies a pivotal role in gliomagenesis through silencing of tumor suppressive genes and/or genes involved in differentiation. Thus, we hypothesized that IDHMUT-associated DNA hypermethylation may silence the expression of important tumor-suppressive miRNAs in glioma. As shown in our preliminary data, we used unbiased methylation profiling to identify hypermethylated miRNA genes in the context of G-CIMP, and among these candidates, miRNA-148a appears not only to have tumor suppressive properties but also to directly regulate DNMT1, a key gene involved in DNA methylation maintenance. In this proposal, we test the central hypotheses that IDHMUT causes epigenetic silencing of the tumor suppressive miR-148a and that re-expression of miR-148a provides a novel strategy for glioma treatment, particularly for the IDHMUT subset. To do so, the aims are: 1) to investigate the molecular basis linking IDH mutation and miR148a downregulation, 2) to establish miR-148a downstream target genes contributing to tumor suppression, and 3) to explore the therapeutic potential of miR-148a in IDHMUT glioma. These aims will be accomplished combining an unbiased high-resolution methylation profiling technique, extensive patient tissue resources, and a variety of cell models including patient-derived glioma neurospheres cells. Accomplishment of the stated aims will have a significant contribution towards the development of novel tailored treatments for gliomas based on restoration of deficient miRNAs.