Introduction: MicroRNAs (miRNAs) are small non-coding RNAs (ncRNAs) 18-24 nucleotides in length that regulate gene expression primarily by targeting mRNAs according to the degree of complementarity with their 3’ untranslated region (UTR). MiRNAs are often dysregulated in cancer, suggesting they play a role in tumorigenesis. Canine mast cell tumors (MCT) are a common cutaneous tumor of dogs whose biological behavior varies from relatively benign disease that is cured with surgical excision to aggressive, locally invasive, highly metastatic disease that is poorly responsive even to multimodality therapy. We hypothesize that high grade MCTs possess a unique miRNA expression signature distinct from that found in benign MCTs and that this contributes to their aggressive behavior. In this study, we sought to determine which miRNAs are differentially expressed in benign and aggressive canine MCT.

Methods: Total RNA was isolated by the Trizol (Invitrogen) method from 12 biologically low grade (surgical cure) and 12 biologically high grade (patient died from MCT disease). Mature miRNA expression analysis of preamplified cDNA was done using TaqMan Low Density Arrays (TLDAs), interrogating the expression profile of 378 miRNAs, 151 of whose mature sequences are 100% conserved between human and dog (Sanger miRBase release 12). Normalization was performed with the small nuclear RNA U6 and microRNA expression was calculated utilizing the comparative Ct method. Statistical analysis was performed with RealTime Statminer software (Integromics). P-values of <0.05 were considered statistically significant.

Results: The expression of specific miRNAs was significantly different in biologically low grade and high grade MCTs. 51 miRNAs were differentially expressed in high grade versus low grade tumors (p<0.05). MiRNAs with known importance in human tumorigenesis, including several members of the miR 17-92 cluster (hsa-miR-17, −18a, −18b) and its paralog, the miR-106b-25 cluster (hsa-miR-106b, −93, −25) were significantly overexpressed in high grade tumors as compared to low grade tumors.

Conclusion: Our findings indicate that specific miRNAs contribute to the biologically aggressive canine MCT phenotype. Hierarchical clustering revealed distinct miRNA expression signatures in high grade tumors compared to low grade tumors. Characterization of miRNA expression in canine MCTs will facilitate our understanding the biology of this disease and has the potential to identify diagnostic/prognostic factors and targets for therapeutic intervention.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3011.