EPIG-15MicroRNA EXPRESSION HETEROGENEITY IN GLIOBLASTOMA

Abstract

Intratumor heterogeneity exists in many cancers, with clear evidence of differential gene expression temporo-spatially in glioblastoma multiforme (GBM). MicroRNA (miRNA) profiling studies have identified risk-stratifying signatures in GBM, but it has not been clarified whether microRNA profiles vary in a similar fashion to gene expression within individual GBM tumors. This study utilized primary GBM specimens resected from patients undergoing surgery in a regional UK Neurosurgery unit. Fresh frozen tissue underwent RNA extraction and miScript Human Brain Cancer miRNA PCR Array was used to assess 84 miRNA's expression levels between distinct spatial regions within primary GBMs. miRNA expression was analyzed with quantitative RT-PCR and gene targets for analysis were selected with miRtarget gene prediction software. Protein levels for the in silico predicted targets based on miRNA expression were validated through immunohistochemistry (IHC). A large degree of intratumor heterogeneity was apparent in the samples. Homology existed between individuals with 8 common miRNAs differentially expressed between central and edge regions of tumors. Protein levels of CDK6 and c-KIT nuclear accumulation were significantly elevated at tumor edges relative to core samples in concordance with the microRNA profiling. Intratumor heterogeneity in GBM produces significant miRNA profiling variation depending on spatial location of the sample within the tumor. Therefore, assessment of GBM miRNA signatures requires selective sampling from multiple distinct tumor regions and consideration of the overall patterns of miRNA expression across the entirety of the tumor.