RT-qPCR Expression Profiles of Selected Oncogenic and Oncosuppressor miRNAs in Formalin-Fixed, Paraffin-Embedded Canine Mammary Tumors

SIMPLE SUMMARY: Early diagnosis of mammary gland cancer would allow intervention in the early stage of the disease, with a better prognosis for canine patients. MiRNAs are short non-transcribed RNA molecules that can be involved in cancer as molecular regulators of tumor development and progression and recognized as early, cancer-specific biomarkers with diagnostic and prognostic value and promising targeted for cancer therapy. Our results demonstrate that MiRNAs are differentially expressed in canine mammary tumors (CMTs) compared with normal mammary gland. In particular, oncogenic miR-18a, miR-18b and miR-21 were significantly overexpressed in malignant tumors and their involvement in receptor-mediated carcinogenesis and proteoglycan remodeling, making them candidate biomarkers with a prognostic value in CMTs. We also found downregulation of the oncosuppressor miR-146b in both benign and malignant CMTs compared with the normal mammary gland. MiR-146b may regulate the production of pro-inflammatory cytokines with a crucial role in cancer development and is predicted to target genes involved in Toll-like receptor and MAPK-signaling pathways. By virtue of their possible involvement in neoplastic transformation and progression, investigated miRNAs may represent candidate biomarkers with prognostic relevance in dogs with mammary tumors. ABSTRACT: MicroRNAs (miRNAs) can act as oncogenes or oncosuppressor genes, and their involvement in nearly all cancer-associated processes makes these small molecules promising diagnostic and prognostic biomarkers in cancer, as well as specific targets for cancer therapy. This study aimed to investigate the expression of 7 miRNAs (miR-18a, miR-18b, miR-22, miR-124, miR-145, miR-21, miR-146b) in formalin-fixed, paraffin-embedded canine mammary tumors (CMTs) by quantitative reverse transcription polymerase chain reaction (RT-qPCR). Twenty-six mammary samples were selected, including 22 CMTs (7 benign; 15 malignant) and 4 control samples (3 normal mammary gland and 1 case of lobular hyperplasia). Oncogenic miR-18a, miR-18b and miR-21 were significantly upregulated in malignant tumors compared with control tissues (p < 0.05). Conversely, oncosuppressor miR-146b was significantly downregulated in benign and malignant mammary tumors compared with control samples (p < 0.05) while, no group-related differences in the expression levels of miR-22, miR-124 and miR-145 were found (p > 0.05). Upregulated miRNAs found here, may regulate genes involved in receptor-mediated carcinogenesis and proteoglycan remodeling in cancer; while miRNA with reduced expression can regulate genes involved in Toll-like receptor and MAPK signaling pathways. According to the results obtained in the current study, the oncogenic and oncosuppressor miRNAs analyzed here are dysregulated in CMTs and the dysregulation of miRNA targets may lead to specific altered cellular processes and key pathways involved in carcinogenesis. Of note, since oncogenic miRNAs predicted to regulate neoplastic cell proliferation and hormonal activities, they may play an active role in neoplastic transformation and/or progression, having mechanistic and prognostic relevance in CMTs.