Epigenetic reprogramming governs EcSOD expression during human mammary epithelial cell differentiation, tumorigenesis and metastasis

Abstract

Expression of the antioxidant enzyme EcSOD in normal human mammary epithelial cells was not recognized until recently. Although expression of EcSOD was not detectable in non-malignant human mammary epithelial cells (HMEC) cultured in conventional two-dimensional (2D) culture conditions, EcSOD protein expression was observed in normal human breast tissues, suggesting that the 2D-cultured condition induces a repressive status of EcSOD gene expression in HMEC. With the use of laminin-enriched extracellular matrix (lrECM), we were able to detect expression of EcSOD when HMEC formed polarized acinar structures in a 3D-culture condition. Repression of the EcSOD-gene expression was again seen when the HMEC acini were sub-cultured as a monolayer, implying that lrECM-induced acinar morphogenesis is essential in EcSOD-gene activation. We have further shown the involvement of DNA methylation in regulating EcSOD expression in HMEC under these cell culture conditions. EcSOD mRNA expression was strongly induced in the 2D-cultured HMEC after treatment with a DNA methyltransferase inhibitor. In addition, epigenetic analyses showed a decrease in the degree of CpG methylation in the EcSOD promoter in the 3D versus 2D-cultured HMEC. More importantly, >80% of clinical mammary adenocarcinoma samples showed significantly decreased EcSOD mRNA and protein expression levels compared with normal mammary tissues and there is an inverse correlation between the expression levels of EcSOD and the clinical stages of breast cancer. Combined bisulfite restriction analysis analysis of some of the tumors also revealed an association of DNA methylation with the loss of EcSOD expression in vivo. Furthermore, overexpression of EcSOD inhibited breast cancer metastasis in both the experimental lung metastasis model and the syngeneic mouse model. This study suggests that epigenetic silencing of EcSOD may contribute to mammary tumorigenesis and that restoring the extracellular superoxide scavenging activity could be an effective strategy for breast cancer treatment.

Role of NOX2-Derived Reactive Oxygen Species in NK Cell–Mediated Control of Murine Melanoma Metastasis

“…The increased ROS may promote mutagenesis and may also render tumor cells more prone to expand and produce distant metastases (34)(35)(36)(37). In agreement, overexpression of the antioxidant SOD3 inhibits murine breast cancer cell metastasis (38), and the ROS scavenger N-acetyl-cysteine reduces the tumorigenicity of murine melanoma cells (15). High endogenous ROS concentrations in malignant cells may also render these cells more vulnerable to further stresses (34,39,40).…”

Targeting ROS for Cancer Therapy

“…Antioxidants like NAC and vitamin C could prevent HIF stabilization and diminish MYC-mediated tumorigenesis38. Other studies also reported antitumorigenic results of antioxidant treatments, including overexpression of SOD3, which inhibited breast cancer metastasis indicating the potential anti-tumorigenic effect of restoring extracellular superoxide scavenging capacity [73][74][75]. However, most clinical trials were failed to show beneficial effects of antioxidants on a variety of cancer [76,77].…”

Induction of a novel isoform of the lncRNA HOTAIR in Claudin‐low breast cancer cells attached to extracellular matrix

“…Emerging evidence from lrECM 3D culture suggests epigenetic regulation of gene expression by the ECM signaling in cancer cells (Lelievre, 2010; Li et al ., 2016; Teoh‐Fitzgerald et al ., 2014). However, ECM‐regulated expression and functions of lncRNA have not been examined in Claudin‐low breast cancer cells.…”