Alteration in E-Cadherin/β-Catenin Expression in Canine Melanotic Tumors

β-Catenin, encoded by the ctnnb1 gene, plays a critical role in intercellular adhesion, and its altered expression has been implicated in tumor progression in humans and animals. The aims of this study were to examine the alterations in β-catenin expression in canine melanoma as well as the causes of these changes (eg, E-cadherin or exon 3 mutations) and to compare identified changes between skin and oral melanomas. Forty-two primary canine skin and oral melanoma tissue samples were used in the study. The expression levels of ctnnb1 and the levels of E-cadherin/β-catenin complex in the tissues were determined by semiquantitative RT-PCR and immunohistochemistry, respectively. The mutational status of β-catenin exon 3 was examined by DNA sequencing. RT-PCR revealed higher levels of ctnnb1 expression in oral melanoma tissues compared with normal melanocytes, irrespective of sex or histopathological appearance of the tissue (ie, amelanotic vs melanotic). Immunohistochemistry revealed simultaneous loss of membrane E-cadherin/β-catenin complex and cytoplasmic accumulation of both proteins in 37 cases (84%). Intranuclear β-catenin was also detected in all tissues with reduced membrane β-catenin expression. In mutational analyses, one amelanotic oral melanoma showed 13 single nucleotide polymorphisms (SNPs); however, after protein translation, all the SNPs were silent mutations. The present study demonstrates that dysregulation of E-cadherin/β-catenin complexes is involved in both types of canine melanotic tumors and that the disruption of E-cadherin/β-catenin complexes and increased β-catenin may induce tumor progression and malignancy.