Mutações do gene TP53 em tumores caninos e sua relação com a expressão de genes associados à apoptose, controle de ciclo celular e angiogênese

Abstract

The p53 protein is frequently associated with human and animal cancer. This protein is involved in the regulation of cell cycle, angiogenesis and apoptosis. The aim of this work was to analyze modification on TP53 gene sequence, as well as the relative expression of several cancer related genes in dog´s tumors. A total of 50 neoplasias were evaluated by classical histopathological analysis, SSCP profiles of exons 5, 6 and 7, and sequencing of intron5-exon7 region of TP53. Most of these tumors (n=45) were evaluated for the expression of TP53, p21, MDM2, Bax, Bcl2, IGF-BP3, VEGF and bFGF genes by qRTPCR. The results showed that breast cancer, particularly the complex tubular-papilary, are the most common in dogs. The prevalence of cancer in dogs is related with the age and breed. High frequency of SSCP altered patterns were detected in canine tumors. However, this technique, pointed out as efficient by several authors, has complex and subjective interpretation, and it did not show relation with our sequence data. Heterozygotic alterations in exons 6 and/or 7 of TP53, which may compromise p53 protein function, were detected in 40% of the tumors. A homozygotic transition GA at the codon 270 (arghis), known as a hotspot on the DNA-binding domain of p53, was detected in an osteossarcoma. Alteration detected in the intronic regions 5 and 6 of TP53 are probably not involved in RNA processing. High variation of the relative expression of TP53, p21, MDM2, Bax, Bcl2, IGF-BP3, VEGF and bFGF genes were detected in both mammary and skin tumors. However, it was not possible to establish clear relation among genes expression, or between expression and TP53 alterations. IGF-BP3gene was over or under express in 60% of skin tumors, but no alterations were found in mammary tumors. Conversely, 82.9% of mammary tumors exhibited Bax over-expression, while skin tumors showed a control-like behavior. Although considered as prognostic markers, it was not detected relation between TP53, p21, MDM2, Bax, Bcl2, IGF-BP3, VEGF and bFGF genes and histopathological grade.