Análise de mutações no gene TP53 em casos de câncer de mama e estudo da proteína p53 mutante: aspectos fisiopatológicos do tumor

Abstract

Breast cancer is the most frequent cancer in women, with 1 million of new cases in the world each year. The TP53 gene is responsible for the regulation of the cell s fate in response to genotoxic and non-genotoxic stress. Somatic TP53 mutations are found in, approximately, 50% of human cancers. In breast cancer, TP53 mutation is the most frequent genetic alteration, being present in 20 to 50% of cases. These mutations may change the protein conformation, impairing the transcription of target genes, and may lead the mutant p53 to aggregate. In this study, we analyzed the presence of mutations in exons 5-10 of TP53 in breast cancer biopsies of women resident in the metropolitan area of Rio de Janeiro. After the determination of samples with mutation, some of them were selected to investigate the behavior of different mutants in the formation of p53 aggregates in tumors using A11 and DO-1 antibodies, which recognizes pre-fibrillar oligomers and mutant or wild-type p53, respectively. So, we utilized a immunofluorescence co-localization assay using confocal microscope. TP53 mutations were detected in 19% of the breast cancer cases, with 88.2% of missense type. These mutations, in tumors classified as infiltrating ductal carcinoma (CDI), were associated with a later and aggressive stage of cancer, represented by Elston s Grade III (p< 0.0001). A relation was also observed between these mutations and p53 accumulation (p= 0.0184). Furthermore, a different pattern of p53 mutants for the tendency to aggregate was observed and we detected that the mutants R273H and P278A showed a greater aggregation. Thus, the mutant p53 aggregation observed in vivo and described in this study, seems to depend on the type of mutation found in breast cancer cases.