Differences in DNA Methylation Status Between Epithelial and Mesenchymal Phenotypes in Canine Malignant Mucosal Melanoma

Canine malignant mucosal melanoma is one of the common cancers with a high mortality rate. Pathologically, malignant melanomas show multiple morphological patterns including epithelioid, spindle and round, indicating that neoplastic cells change their morphology. Regarding morphological change, epithelial‐mesenchymal transition (EMT) has been considered to be an important mechanism. EMT is a reversible biologic process being suggested the correlation with DNA methylation in human cancer. The aim of this study was to assess the difference in DNA methylation status between epithelial and mesenchymal phenotypes and correlation with EMT in canine oral malignant melanoma. Sixteen samples were classified into epithelial phenotype and eight samples were classified into mesenchymal phenotype based on E‐cadherin expression using immunohistochemistry or western blotting. We analysed DNA methylation level of 46 673 cytosine‐guanine dinucleotides (CpG sites) in all samples and compared average DNA methylation level between epithelial and mesenchymal phenotypes. In a comparison of average DNA methylation level at each site in CpG island promoters (3089 sites), 17 and 6 hypermethylated sites were identified in epithelial phenotype and mesenchymal phenotype, respectively. Finally, 10 out of 23 sites showed de novo hypermethylation, and two genes, NEUROG1 and ITGAV , which are associated with cell adhesion, were found to be hypermethylated in epithelial phenotype. This study revealed the difference of DNA methylation status between epithelial and mesenchymal phenotypes suggesting the influence of DNA methylation on EMT in canine malignant mucosal melanoma.