Epigenetic Regulation of Manganese Superoxide Dismutase Expression in Human Breast Cancer Cells

Abstract

Malignant breast cancer cells often exhibit lower expression and activity of manganese superoxide dismutase (MnSOD) than their normal cell counterparts; however, the mechanism(s) responsible for this change remains unclear. We examined whether SOD2, the gene encoding MnSOD, was epigenetically repressed in breast cancer cell lines by DNA methylation and histone acetylation. RT-PCR analysis of SOD2 mRNA showed the nontumorigenic breast epithelial cell line MCF-10A to have two to three fold higher expression levels than either UACC-893 or MDA-MB-435 breast carcinoma cells. Analysis of a region in the SOD2 promoter by sodium bisulfite genomic sequencing demonstrated significantly higher levels of CpG methylation in both human breast carcinoma cell lines assessed than in MCF-10A cells. CREB binding in vitro to a cognate site derived from this region was repressed by DNA methylation, and CREB binding to the 5' regulatory region of the SOD2 gene in vivo as determined by ChIP was significantly lower in breast carcinoma cells than in MCF-10A. Increased cytosine methylation was also accompanied by a significant decrease in the level of acetylated histones in the same region of the SOD2 promoter. Finally, a causal link between cytosine methylation and transcriptional repression was established by increasing MnSOD mRNA, protein and activity in breast carcinoma cells using the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine. These findings indicate that epigenetic silencing of SOD2 constitutes one mechanism leading to the decreased expression of MnSOD observed in many breast cancers.

Up-regulation of mitochondrial antioxidation signals in ovarian cancer cells with aggressive biologic behavior

“…The epigenetic silencing, including DNA methylation and histone acetylation, constitutes one mechanism leading to the decreased expression of SOD2 in breast cancer (Hitchler et al, 2006) and some pancreatic cell lines (Hurt et al, 2007). Mutations in the promoter region of the SOD2 gene might activate AP-2-dependent dysregulation of SOD2 expression in cancer cells.…”

A role for epigenetics in hearing: Establishment and maintenance of auditory specific gene expression patterns

“…There are now emerging connections between epigenetics and ROS. The connection between epigenetic mechanisms of transcriptional silencing of genes important to ROS such as MnSOD has been firmly established (Hitchler et al, 2006). Increases in ROS can also effect glutathione levels which in turn can change SAM synthesis and hence DNA methylation patterns.…”

Antioxidant Enzymes as New Biomarkers for Prediction of Tumor Progression in Breast Cancer

“…Two molecular mechanisms are identified to be involved in the low basal MnSOD expression in nonmetastatic breast cancer cells. Epigenetic processes, such as methylation of CpG islands localized in the proximal gene promoter and a decrease in the histone modifications (methylations and acetylations) are involved in the transcriptional repression of MnSOD gene in some breast cancer cell lines (Hitchler et al, 2006). The other mechanism involves the occupancy of the proximal promoter of MnSOD gene by the both transcription factor Activator protein-2 alpha (AP-2) and the Damaged DNA binding 2 (DDB2) protein.…”