MicroRNA expression in putative cancer stem cells isolated from canine mammary gland tumour cells with differing sensitivity to doxorubicin

Cancer stem cells (CSCs) are capable of initiating tumour development and causing recurrence after treatment. The objective of this study was to determine the miRNAs, downstream target mRNAs, and signalling pathways in CSCs isolated from doxorubicin-sensitive and doxorubicin-resistant canine mammary adenocarcinoma cell lines. MicroRNA expression was profiled using Agilent SurePrint® microarrays. MicroRNA data were analyzed using Agilent GeneSpring® software, and TargetScan and WikiPathways were used to identify genes and pathways targeted by the differentially expressed miRNAs. Six miRNAs were differentially expressed in CSCs isolated from doxorubicinsensitive cells, while fourteen miRNAs were differentially expressed in CSCs isolated from doxorubicin-resistant cells. The differentially expressed miRNAs in CSCs are associated with reduced proliferation and maintenance of the CSC phenotype, including drug resistance. Wnt signalling, EGFR1 signalling, Transforming Growth Factor (TGF)-beta receptor signalling, Toll-like receptor signalling and Type II interferon signalling (IFNG) were among the major pathways regulated by the dysregulated miRNAs in CSCs. These genes and pathways are involved in stem-cell maintenance, drug resistance and enhanced survival, making them potential therapeutic targets that warrant further study. This work identified miRNAs in drug-resistant CSCs that have not been previously linked to doxorubicin (or other drug) resistance in canine mammary tumour. Moreover, it identified miRNAs not previously characterized in cancer.