Altered DNA methylation is associated with docetaxel resistance in human breast cancer cells

Abstract

Abstract. Docetaxel is an effective chemotherapy drug to treat breast cancer but the underlying molecular mechanisms of drug resistance are not fully understood. DNA methylation is an epigenetic event, involved in the control of gene expression, which is known to play an important role in cancer and chemotherapy drug resistance. To investigate the role of DNA methylation in docetaxel resistance in breast cancer we used two human breast cancer cell lines (MCF-7 and MDA-MB-231) that were made resistant to docetaxel. Docetaxel-resistant sub-lines were treated with different concentrations of decitabine. Global methylation and DNA methyltransferase (DNMT) activity was measured using an ELISA-based assay. Quantitative real-time PCR was used to study DNMT gene expression. Cell viability was studied by MTT assay. Global methylation was increased in MCF-7 but not significantly changed in MDA-MB-231 docetaxel-resistant cells. Decreased DNMT activity and decreased DNMT1 and DNMT3b mRNA expression was associated with docetaxel resistance in both cell lines. To investigate how the components of the DNA methylation machinery may contribute towards docetaxel resistance, decitabine (5-aza-2'-deoxycytidine), an inhibitor of DNA methylation, was used. Decitabine treatment decreased global methylation, DNMT activity and DNMT1, DNMT3a and DNMT3b mRNA expression in MDA-MB-231 docetaxel-resistant cells. In contrast, decitabine-treated MCF-7 docetaxel-resistant cells showed increased DNMT1, DNMT3a and DNMT3b mRNA expression indicating a cell line specific effect of decitabine. Decitabine treatment increased resistance in MCF-7 docetaxel-resistant cells and in the parental MCF-7 and MDA-MB231 docetaxel-sensitive cell lines, however, it did not alter response to docetaxel in MDA-MB-231 docetaxelresistant cells. This study demonstrates that changes in the DNA methylation machinery are associated with resistance to docetaxel in breast cancer cells. The use of epigenetic therapies, as a strategy to overcome drug resistance, needs to be investigated more fully to determine their effectiveness in different cancers and for different chemotherapy drugs.

DNMT1 facilitates proliferation and metastasis of breast cancer cells by promoting MEG3 promoter methylation in MEG3/miR-494-3p/OTUD4 regulatory axis

“…DNA hypermethylation is a major epigenetic feature that distinguishes cancer cells from normal cells, which causes insensitivity of cancer cells to growth inhibitory signals and evades programmed cell death by inhibiting tumor-suppressor genes 3 . DNA hypermethylation is involved in the occurrence and cell survival of breast cancer, and its initiation mechanism is the abnormal expression of DNA methyltransferases (DNMTs), including DNMT1, DNMT3a and DNMT3b [4][5][6] . DNMT1 is an important methyltransferase being high in dividing cells compared with nondividing cells and has become the main therapeutic target for methylation inhibition in tumor cells 7 .…”