Canine Model for the Study of the Epigenetic Factors Involved in Mammary Tumor Development

Cancer is a multifactorial disease involving reprogramming of the gene function in normal cells through both genetic and epigenetic factors. The latter ones are essentially represented by chromatin remodeling factors as transcriptional control of gene expression at the nucleus level. Certain sets of tumor suppression genes controlling vital cell functions such as cell cycle, DNA repair, cell adhesion, and apoptosis are considered candidate genes for defining specific types of cancer. Their silencing may be achieved through somatic mutations or by epigenetic factors as DNA methylation and histone covalent modification. Two major DNA methylation patterns have been described in mammary gland tumors: genome hypomethylation and concomitant "in situ" hypermethylation in critical genes. Human mammary gland cancer has been studied through animal models, canine one offering opportunity to investigate the molecular aspects that better define the borderline between the primary inflammatory and tumor progression processes. In contrast, both humans and dogs share the same challenging environment. This work presents the preliminary results in a study of the transcriptional epigenetic markers identified in canine mammary glands during tumor development. Bisulfite mutagenesis based methylation-specific (MS)- PCR has been performed for the estimation of BRCA1, and BRCA2 gene promoter hyper-methylation profiles, concomitant to methylation sensible restriction of genomic DNA in order to estimate the global hypo-methylation status have been performed on 9 DNA samples obtained from clinically selected canine tumor tissues. Histone H3K9 trimethylated was stained by immunohistochemical methods (IHC) in normal and tumor tissues. The results are discussed through their crosstalk with DNA methylation dynamics in order to highlight the cancer initiation and progression processes in the context of heritability and the causes of sporadic cases.