Abstract
Restoration of normal DNA promoter methylation and expression states of cancer‑related genes may be an option for the prevention as well as the treatment of several types of cancer. Constitutional promoter methylation of BRCA1 DNA repair associated (BRCA1) gene is linked with a high risk of developing breast and ovarian cancer. Furthermore, hypomethylation of the proto‑oncogene γ synuclein (SNCG) is associated with the metastasis of breast and ovarian cancer and reduced disease‑free survival (DFS). In the present study, we evaluated the potential of curcumin to re‑express hypermethylated BRCA1 and to suppress hypomethylated SNCG in triple‑negative breast cancer (TNBC) cell line HCC‑38, the estrogen receptor‑negative/progesterone receptor‑negative (ER‑/PR‑) cell line UACC‑3199, and the ER+/PR+ cell line T47D. The cells were treated with 5 and 10 µM curcumin for 6 days and with 5‑aza‑2'‑deoxycytidine (5'‑aza‑CdR) for 48 h. Methylation‑specific PCR and bisulfite pyrosequencing assays were used to assess DNA promoter methylation while gene expression levels were analyzed using quantitative real‑time PCR and immunoblotting. We found that curcumin treatment restored BRCA1 gene expression by reducing the DNA promoter methylation level in HCC‑38 and UACC‑3199 cells and that it suppressed the expression of SNCG by inducing DNA promoter methylation in T47D cells. Notably, 5'‑aza‑CdR restored BRCA1 gene expression only in UACC‑3199, and not in HCC‑38 cells. Curcumin‑induced hypomethylation of the BRCA1 promoter appears to be realized through the upregulation of the ten‑eleven translocation 1 (TET1) gene, whereas curcumin‑induced hypermethylation of SNCG may be realized through the upregulation of the DNA methyltransferase 3 (DNMT3) and the downregulation of TET1. Notably, miR‑29b was found to be reversely expressed compared to TET1 in curcumin‑ and 5'‑aza‑CdR‑treated cells, suggesting its involvement in the regulation of TET1. Overall, our results indicate that curcumin has an intrinsic dual function on DNA promoter methylation. We believe that curcumin may be considered a promising therapeutic option for treating TNBC patients in addition to preventing breast and ovarian cancer, particularly in cancer‑free females harboring methylated BRCA1.