MicroRNA expression in canine mammary cancer
MicroRNAs (miRNAs) play a vital role in differentiation, proliferation and tumorigenesis by binding to messenger RNAs (mRNA) and inhibiting translation. To initiate an investigation into the identification of miRNAs in the domestic dog, an emerging model for human disease, a comparison of the human and canine genetic databases was conducted. The bioinformatics work revealed significant conservation of miRNA genes between the two species. Proof of principle experiments, including serial dilutions and sequencing, were performed to verify that primers made to amplify human mature miRNAs can be used to amplify canine miRNAs, providing that the mature sequences are conserved. TaqMan? Real-time RT-PCR, a sensitive and specific method, was used to isolate the first miRNA mature products from canine tissues. The expression levels of miR-17-3p, miR-17-5p, miR-18, miR-19a, miR-19b, miR-20, and miR-92 were evaluated in five canine tissues (heart, lung, brain, kidney, and liver). Because miRNAs have been found to act as both tumor suppressors and oncogenes in several different cancers, expression patterns of ten miRNAs (miR-15a, miR-16, miR-17-5p, miR-21, miR-29b, miR-125b, miR-145, miR-155, miR-181b, let-7f) known to be associated with human breast cancer were compared between malignant canine mammary tumors (n=6) and normal canine mammary tissue (n=10). Resulting data revealed miR-29b and miR-21 to have a statistically significant (p<0.05) up-regulation in cancerous samples. Overall expression patterns showed nine of the ten miRNAs follow the same pattern of expression in the domestic dog as the human, while the miR-145 expression does not show a difference between the normal and cancerous samples.