Abstract 169: An investigation into the role of miRNAs in the pathogenesis of pediatric gastrointestinal stromal tumor
Authors: Kelly Lorna , Bryan Kenneth , Kim Su Young , Debiec-Rychter Maria , O'Sullivan Maureen J. 
Published: June 2012

Abstract
The pathogenesis of pediatric gastrointestinal stromal tumors [GISTs] is poorly understood. In adults, GISTs are characterized by activating mutations of tyrosine kinase III receptors KIT or PDGFRα while pediatric GISTs are KIT and PDGFRα wild-type (WT), yet downstream KIT signaling is similar in pediatric and adult tumors. Adult GISTs show genomic losses at 14q, 22q, 1p and 9p with disease progression, findings again absent in the pediatric setting and prompting our miRNA study. 29 adult mutant, 29 pediatric and 16 adult WT gastric GISTs formed the cohort. DNA extracted from tumor micro-dissected from paraffin sections was used for PCR amplification of KIT exons 9,11,13,17 and PDGFRα exons 12, 14 and 18 and the products examined by high resolution melt analysis. Products with aberrant melt curves were subjected to sequencing for definitive mutation status categorization. RNA was similarly extracted from micro-dissected tumor [RecoverAll™ Total Nucleic Acid Isolation Kit for FFPE, Ambion®]. MicroRNA profiling was conducted using Applied Biosystems TaqMan® Low-Density Arrays (TLDAs), investigating 667 targets for each sample and validation was with individual TaqMan® assays. From the heatmap generated from this data a cluster dendrogram is derived, whereby pediatric WT and adult mutant cases are clearly separated. The adult mutant group is further split by differential expression of miRNAs located on chromosome 14q32. This is not explained by simple genomic loss of 14q as analyzed by array comparative genomic hybridization (aCGH). The data were interrogated for miRNAs showing differential expression &gt;5-fold and of statistical significance between the paired groups: 1) adult mutant versus pediatric WT, 2) adult WT versus pediatric WT 3) adult mutant versus adult WT, 4) KIT versus PDGFRα mutant and 5) high- versus low-risk adult mutant GISTs. Included in miRNAs fulfilling these criteria are many which target members of key biological pathways important in GIST. Indeed in comparisons 1) and 2) above, the number of predicted interactions between miRNAs and targets are significantly greater than expected (p-values&lt;0.05), indicating a possible functional role for these miRNAs in the pathogenesis of pediatric GIST. The likely importance of miRNAs in regulating genes important in GIST biology is further substantiated by our finding of expression of miRNA/predicted target pairs in opposite directions, for example between adult mutant and pediatric WT cases, where IGF1R, BAALC and PLAG1 are over-expressed in the pediatric WT cases relative to adult mutant cases and in tandem, miRNA 139-5p and 455-5p, both predicted to target IGF1R, are relatively over-expressed in the adult cases, as are 365 and 455-5p, predicted to target BAALC and 193b predicted to target PLAG1. These findings suggest an important, as yet unrecognised, biological role for miRNAs in the development of pediatric GIST.
Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 169. doi:10.1158/1538-7445.AM2011-169