ABSTRACT
BACKGROUND: Defects of manganese superoxide dismutase (MnSOD) have long been implicated in generation of oxidative stress and risk susceptibility to various cancers. Two functional polymorphisms within the MnSOD gene, including the Val-9Ala of the mitochondrial targeting sequence (MTS) and the Ile58Thr of the exon-3, have been proposed to reduce its enzyme activity and antioxidant potential. MATERIALS AND METHODS: A high- throughput multiplex SNaPshot® system was developed herein for simultaneous analyses of Val-9Ala and Ile58Thr in a single reaction. Genomic DNA extracted from each whole blood sample of 248 patients including 107 with cervical cancer and 141 with breast cancer and from 136 healthy women as controls was analyzed by the multiplex SNaPshot® system. RESULTS: The Val/Val, Val/Ala genotypes and the Val allele of the MTS were predominant in patients with cervical or breast cancer as well as healthy women in Thailand. The Ile/Ile genotype and the Ile allele of the exon-3 were found in all of them whereas none of the Ile/Thr, the Thr/Thr genotypes and the Thr allele was detected. Genotypic association of both Val-9Ala and Ile58Thr polymorphisms with cervical cancer and breast cancer of these patients comparing to healthy women was not statistically significant (p<0.05). CONCLUSIONS: The Val/Val, Val/Ala genotypes and the Val allele of the MTS were found predominantly but the Ile/Ile genotype and the Ile allele of the exon-3 were detected in patients with cervical cancer, breast cancer and healthy women in Thailand. These two functional polymorphisms (Val-9Ala and Ile58Thr) in MnSOD gene did not associate with susceptibility risk of these cancer patients in Thailand.
Subject(s)
Breast Neoplasms/genetics , Polymorphism, Single Nucleotide/genetics , Superoxide Dismutase/genetics , Uterine Cervical Neoplasms/genetics , Adult , Aged , Alleles , Case-Control Studies , Female , Follow-Up Studies , Free Radical Scavengers , Genetic Predisposition to Disease , Genotype , Humans , Middle Aged , Neoplasm Staging , Prognosis , Risk Factors , Thailand , Young AdultABSTRACT
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.
