Avaliação do papel funcional do gene NDRG4 na tumorigênese de mama / Evaluation of the functional role of gene NDRG4 in breast tumorigenesis

Em trabalho anterior realizado pelo nosso grupo, descrevemos que o gene NDRG4 se encontra silenciado em linhagens tumorais de mama devido a presença de metilação na sua região promotora. Neste trabalho, exploramos o papel do silenciamento do gene NDRG4 na tumorigênese da mama. Em um primeiro momento, investigamos a associação entre a presença de metilação na região promotora do gene NDRG4 em 61 amostras de tumores de mama e os dados clínico-patológicos das pacientes. Observamos uma associação estatisticamente significativa entre a presença de metilação do DNA na região promotora do gene NDRG4 e fatores de pior prognóstico, tais como: número de linfonodos positivos (p=0,025), níveis elevados da proteína p53 (p=0,014) e o tamanho do tumor (p=0,036); bem como com uma menor taxa de sobrevida livre de metástase em 10 anos (p=0,001). Em análise multivariada, a presença de metilação do DNA na região promotora do gene NDRG4 se mostrou um fator independente de prognóstico para sobrevida livre de mestástase (HR=5.5 e p=0.006). Paralelamente, realizamos o silenciamento do gene NDRG4 na linhagem de tumor de mama MCF7 utilizando a metodologia de shRNA. Variantes celulares, silenciadas para o gene NDRG4, apresentaram uma redução significativa na taxa de proliferação e na capacidade de formação de colônias isoladas e um aumento significativo na capacidade de migração. No entanto, não foram observadas diferenças significativas na capacidade de adesão e na susceptibilidade a taxanos dos clones silenciados

Correlation of MGMT promoter methylation status with gene and protein expression levels in glioblastoma

OBJECTIVES: 1) To correlate the methylation status of the O6-methylguanine-DNA-methyltransferase (MGMT) promoter to its gene and protein expression levels in glioblastoma and 2) to determine the most reliable method for using MGMT to predict the response to adjuvant therapy in patients with glioblastoma. BACKGROUND: The MGMT gene is epigenetically silenced by promoter hypermethylation in gliomas, and this modification has emerged as a relevant predictor of therapeutic response. METHODS: Fifty-one cases of glioblastoma were analyzed for MGMT promoter methylation by methylation-specific PCR and pyrosequencing, gene expression by real time polymerase chain reaction, and protein expression by immunohistochemistry. RESULTS: MGMT promoter methylation was found in 43.1 percent of glioblastoma by methylation-specific PCR and 38.8 percent by pyrosequencing. A low level of MGMT gene expression was correlated with positive MGMT promoter methylation (p = 0.001). However, no correlation was found between promoter methylation and MGMT protein expression (p = 0.297). The mean survival time of glioblastoma patients submitted to adjuvant therapy was significantly higher among patients with MGMT promoter methylation (log rank = 0.025 by methylation-specific PCR and 0.004 by pyrosequencing), and methylation was an independent predictive factor that was associated with improved prognosis by multivariate analysis. DISCUSSION AND CONCLUSION: MGMT promoter methylation status was a more reliable predictor of susceptibility to adjuvant therapy and prognosis of glioblastoma than were MGMT protein or gene expression levels. Methylation-specific polymerase chain reaction and pyrosequencing methods were both sensitive methods for determining MGMT promoter methylation status using DNA extracted from frozen tissue.