Evaluation of expression of the Wnt signaling components in canine mammary tumors via RT2 Profiler PCR Array and immunochemistry assays

The Wnt signaling pathway and its key component β-catenin have critical roles in the development of diseases such as tumors in mammals. However, little has been reported about involvement of the Wnt/β-catenin signaling pathway in canine mammary tumors (CMTs). The present study detected expression of 30 Wnt signaling pathway-related genes in CMTs; the results are potentially useful for molecular-based diagnosis of CMTs and the development of new targeted therapies. Significant upregulations of dickkopf-1 protein, secreted frizzled-related sequence protein 1 (SFRP1), frizzled 3, β-catenin, and lymphoid enhancer-binding factor 1 (LEF1) were detected in highly malignant CMTs compared to levels in normal mammary gland tissues; moreover, highly significant upregulation of WNT5A was observed in low malignancy CMTs. Downregulation was only detected for SFRP4 in malignant CMT samples. The subcellular location of β-catenin and cyclin D1 in 100 CMT samples was investigated via immunohistochemical analysis, and significantly increased expressions of β-catenin in cytoplasm and cyclin D1 in nuclei were revealed. Western blotting analysis revealed that the expression of β-catenin and LEF1 increased in in the majority of CMT samples. Taken together, the results provide important evidence of the activation status of the Wnt pathway in CMTs and valuable clues to identifying biomarkers for molecular-based diagnosis of CMT.