Methylation analysis of LINE-1 elements in canine cutaneous mast cell tumors

LINE-1 (long interspersed nuclear element-1) is a family of related class I transposable elements in the DNA that is dispersed throughout the entire genome and the study of its methylation pattern is used in the understanding of several neoplasms. Canine mast cell tumors represent a frequent cutaneous neoplasm in veterinary practice presenting different degrees of malignancy and being classified according to their histological differentiation. In view of the current scientific scarcity of information in relation to the epigenetic pattern of neoplasms in domestic animals, this study aimed to verify whether there is correlation between the methylation pattern of LINE-1 with the different grading of canine mast cell tumors according to Kiupel classification. DNA and RNA were extracted from paraffinized healthy and neoplastic (classified as low-grade and high-grade) tissue samples using the phenol/chloroform/isoamyl alcohol and TRIzol® methods, respectively. LINE-1 methylation pattern and expression were quantified by qPCR. A higher LINE-1 expression was observed in neoplasms characterized with a higher degree of malignancy in relation to healthy samples and tumors with a lower degree of malignancy. It was also noted hypomethylation of the LINE-1 promoter region in both neoplastic mast cell tumor grades in relation to the healthy tissue, but no significant difference was found between low-grade and high-grade groups. Thus, high-grade tumors presented higher expression of LINE-1, suggesting the potential use of LINE-1 as a biomarker of genomic instability.