Altered DNA methyltransferases promoter methylation and mRNA expression are associated with tamoxifen response in breast tumors.

Tamoxifen is a standard anti-hormone treatment in estrogen receptor positive breast carcinoma patients. Unfortunately, about 50% of patients relapse during treatment. Promoter hypermethylation contributes to the epigenetic modulation of tamoxifen resistance-related genes. To evaluate the contribution of DNMTs expression and their promoter methylation as diagnostic biomarkers in development of breast malignancy and tamoxifen resistance, the present study was designed and 107 breast tumors and normal breast tissues were recruited. Methylation-specific high-resolution melt curve analysis and quantitative RT-PCR were performed to evaluate DNMTs promoter methylation and mRNA expression, respectively. Our results indicated that DNMT3A and DNMT3B promoters were demethylated in breast tumors as compared to control tissues. The mRNA expression levels of all three DNMTs were significantly increased in tumor specimens in comparison to control tissues (p < 0.05). Among tumor tissues, DNMT3A promoter methylation was significantly higher in tamoxifen sensitive patients (p = 0.001). Overexpression of DNMT3A (p = 0.037) and DNMT3B (p < 0.001) mRNA were observed in tamoxifen resistance group. Multivariate logistic regression analysis indicated that low methylation status of DNMT3A and overexpression of DNMT3B could be as independent predictors of disease recurrence. Multivariate Cox regression analysis, revealed that high methylation status of DNMT3A could be an independent and favorable predictor for disease free survival (p = 0.002) and overall survival (p = 0.026); high expression of DNMT1 (p = 0.03) remained significant and unfavorable predictive factor for overall survival. In conclusion, our data for the first time indicated that low methylation status of DNMT3A promoter and overexpression of DNMT3B could contribute to disease recurrence in tamoxifen-treated breast cancer patients.