Role of MicroRNA Regulatory Networks in Pediatric Pilocytic Astrocytoma

Fausto J. Rodriguez, M.D., Johns Hopkins University School of Medicine

Progress Update:
One-year funding

The main goal of this proposal is to compare changes in the abundance of a group of molecules that have been recently discovered and named “microRNAs” in pilocytic astrocytoma (PA), the most frequent low grade glioma in children. MicroRNAs are of very small size and do not produce proteins themselves, but are responsible for controlling the amount of numerous key proteins with cells. Altered micro RNA levels have been found to play a role in numerous diseases, including cancer, but their role in pediatric low grade gliomas remains understudied. In this project we have been studying concurrently microRNA, protein-coding mRNA, and protein targets in excess brain tumor tissue in pathology archives of pediatric PA. We have identified a subset of microRNAs that were differentially expressed in pediatric PAs versus normal brain tissue: 13 microRNAs were under-expressed, and 20 microRNAs were over-expressed in tumors. Differences were validated by qRT-PCR in a subset, with mean fold change in tumor versus brain of –17 (miR-124), -15 (miR-129, and 19.8 (miR-21). Searching for predicted protein targets, we identified a number of known and putative oncogenes that were predicted targets of microRNA sets relatively under-expressed in PA. Predicted targets with increased expression at the mRNA sets and/or protein level in PA included PBX3, METAP2, and NFIB (Ho CY et al. MicroRNA profiling in pediatric pilocytic astrocytoma reveals biologically relevant targets, including PBX3, NFIB, and METAP2. NeuroOncol. 2013; 15:59-82).

To identify altered microRNAs specific to PA, we subsequently compared microRNA expression levels of PA with other low grade glia/glioneuronal tumor types using NanoString technology that analyzes the expression levels of approximately 800 microRNAs. This platform performs well on formalin-fixed paraffin-embedded tissue, which is a routinely available clinical archival tissue form ideal for biomarker discovery, and that may be applied for diagnosis, disease monitoring and therapeutic target identification. Functional characterization of the key microRNAs of interest is currently being performed using available pediatric low grade glioma cell lines.

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