The Polycomb complex (PcG) consists of multiprotein factors that mediate the repression of various genes in the body. PcG proteins are divided into two distinct complexes, PRC1 and PRC2, with PRC1 having E3 ligase activity, catalyzing the mono-ubiquitination of histone H2A at lysine residues at position 119 (H2AK119ub), while PRC2 has methyltransferase activity, mediating mono, di, and trimethylation on histone H3 at lysine residues at position 27 (H3K27me2 / 3). It is known that PRC1 is subdivided into non-canonical and canonical complexes, the latter being composed of CBX proteins (CBX2, CBX4, CBX6, CBX7 or CBX8). Already PRC2, it comprises three central proteins: SUZ12, EED and EZH1 or EZH2, which is the methyltransferase protein responsible for conferring the main enzymatic activity to the PRC2 complex. It is known that deregulation of PcG proteins may alter developmental pathways, causing a disordered increase in cell proliferation, inhibition of apoptosis, and increase of tumor cells. Among the tumors with altered expression of PcG are mammary tumors. In canines, this type of tumor is the most frequent neoplasm in bitches. Thus, the objective of this study was to evaluate the methylation and expression pattern of the CBX2 and CBX7 (PRC1), and EED, EZH2 and SUZ12 (PRC2) genes in breast tumors in dogs from the state of Pará. Samples of neoplastic and non-neoplastic tissue from 40 animals collected at the Veterinary Hospital of the Federal Rural University of Amazônia. For the analysis of the methylation pattern, the samples were converted by sodium bisulfite and submitted to the Bissulfite sequence PCR technique to detect possible methylated areas. For analysis of RNA expression, cDNA conversion and subsequent quantification of transcripts were performed using Taqman probe detection. Fluorescence emission was captured with the aid of the ABI PRISM 7500 Sequence Detection System. Statistical analyzes were performed using the Kruskal-Wallis test and the Mann Whitnae test to evaluate the associations of methylation patterns with expression levels, and those with tumor progression and other clinicopathological characteristics. The results were considered significant when p <0, 05.
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