Molecular consequences of SOD2 expression in epigenetically silenced pancreatic carcinoma cell lines

Abstract

Manganese superoxide dismutase (SOD2) is an enzyme that catalyses the dismutation of superoxide in the mitochondria, leading to reduced levels of reactive oxygen species. Reduced expression levels of SOD2 have been shown to result in increased DNA damage and sod2 heterozygous mice have increased incidences of cancer. It has also been shown that SOD2 expression is lost in pancreatic cell lines, with reintroduction of SOD2 resulting in decreased rate of proliferation. The mechanism of decreased SOD2 expression in pancreatic carcinoma has not been previously determined. We demonstrate, through sodium bisulphite sequencing, that the sod2 locus is methylated in some pancreatic cell lines leading to a corresponding decrease in SOD2 expression. Methylation can be reversed by treatment with zebularine, a methyltransferase inhibitor, resulting in restored SOD2 expression. Furthermore, we demonstrate that sensitivity of pancreatic carcinoma cell lines to 2-methoxyestradiol correlates with SOD2 expression and SOD2 modulation can alter the sensitivity of these cells. Using both genomics and proteomics, we also identify molecular consequences of SOD2 expression in MIA-PaCa2 cells, including dephosphorylation of VEGFR2 and the identification of both SOD2-regulated genes and transcription factors with altered binding activity in response to SOD2 expression.

Differentially expressed genes from the glioblastoma cell line SHG-44 treated with all-trans retinoic acid in vitro

“…The lower levels of the SOD2 enzyme in tumor cells, resulting from the epigenetic silencing of SOD2 expression, may increase accumulation of ROS leading to enhanced cell proliferation and AP-1 activation. [16][17][18] A reduction in the levels of SOD2 is frequently observed in tumor cells, and the restoration of this important antioxidant enzyme results in reduced levels of cell proliferation. Hodge et al 18 reported that restoring the expression of SOD2 in IM-9 cells results in a decrease of cell proliferation, and a reduction in AP-1 transcription factor binding activity is due to the reduction of oxidative free radicals mediated by the increased expression of SOD2.…”

MnSOD in Oxidative Stress Response-Potential RegulationviaMitochondrial Protein Influx

“…In mammalian cells, protein glutathionylation is involved in redox signaling and the defense against oxidative stress. In mitochondria, the high concentration of glutathione has been related to the presence of several glutathionylated proteins (83). The known sensitivity of human mitochondrial MnSOD to reducing agents (108) has been associated with a highly reactive cysteine residue (Cys 196) exposed on the surface of the tetrameric enzyme.…”

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.…”