title: 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.
authors: Free Radical and Radiation Biology Program, Department of Radiation Oncology, University of Iowa, Iowa City, IA, USA.
authors: M L
authors: ML
authors: Teoh-Fitzgerald
authors: Free Radical and Radiation Biology Program, Department of Radiation Oncology, University of Iowa, Iowa City, IA, USA.
authors: M P
authors: MP
authors: Fitzgerald
authors: Department of Pathology and Laboratory Medicine, University of Wisconsin-Madison, Madison, WI, USA.
authors: W
authors: W
authors: Zhong
authors: Department of Pathology, University of Iowa, Iowa City, IA, USA.
authors: R W
authors: RW
authors: Askeland
authors: Free Radical and Radiation Biology Program, Department of Radiation Oncology, University of Iowa, Iowa City, IA, USA.
authors: F E
authors: FE
authors: Domann
mesh_terms: D000818:Animals; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D018929:Cell Culture Techniques; D002454:Cell Differentiation / Q000235:genetics*; D002460:Cell Line; D045744:Cell Line, Tumor; D002471:Cell Transformation, Neoplastic / Q000235:genetics* / Q000378:metabolism; D002478:Cells, Cultured; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007150:Immunohistochemistry; D008175:Lung Neoplasms / Q000235:genetics / Q000378:metabolism / Q000556:secondary; D042361:Mammary Glands, Human / Q000166:cytology / Q000378:metabolism; D008325:Mammary Neoplasms, Experimental / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D009367:Neoplasm Staging; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D014183:Transplantation, Heterologous
chemical_list: C441642:SOD3 protein, human; C499090:Sod3 protein, mouse; D013482:Superoxide Dismutase