Mun Seog Chang

The activation of the rat copper/zinc superoxide dismutase gene by hydrogen peroxide through the hydrogen peroxide-responsive element and by paraquat and heat shock through the same heat shock element.

Copper/zinc superoxide dismutase (SOD1) protects cells against oxidative hazards by the dismutation of superoxide radicals. The promoter activity of theSOD1 gene was increased 3–5-fold by hydrogen peroxide, paraquat (PQ) and heat shock. Functional analyses of the regulatory region of the SOD1 gene by deletions, mutations, and heterologous promoter systems confirmed the induction of theSOD1 gene by H2O2 through the hydrogen peroxide-responsive element (HRE) (between nucleotides −533 and −520). Gel mobility shift assays showed that the existence of an H2O2-inducible protein bound to the oligonucleotide of the HRE. Similar analyses showed that the heat shock activated the SOD1 promoter through the heat shock element (HSE) (between nucleotides −185 and −171). A strong specific far-shifted complex with the oligonucleotide of the HSE was observed by the treatment of heat shock. When cells were treated with PQ, a strong far-shifted complex with the HSE was observed and was competed out by the cold HSE probe, indicating that PQ also activated theSOD1 promoter through the same HSE site. It is very interesting to note that chemical and physical stresses, such as PQ and heat shock, respectively, activated the SOD1 promoter through the same cis-element HSE. These results indicate that the SOD1 was inducible by H2O2through the HRE and by PQ and heat shock through the same HSE to protect cells from oxidative hazards.

Transcriptional activation of Cu/Zn superoxide dismutase and catalase genes by panaxadiol ginsenosides extracted from Panax ginseng.

Superoxide dismutase (SOD) converts superoxide radical to H2O2, which is in turn broken down to water and oxygen by catalase. Thus, SOD and catalase constitute the first coordinated unit of defence against reactive oxygen species. A wide variety of chemical and environmental factors are known to induce these antioxidant enzymes. Here, we examined the effect of ginseng saponins on the induction of SOD and catalase gene expression. To explore this possibility, the upstream regulatory promoter region of Cu/Zn superoxide dismutase (SOD1) and catalase genes were linked to the chloramphenicol acetyltransferase (CAT) structural gene and introduced into human hepatoma HepG2 cells. Total saponin and panaxatriol did not activate the transcription of SOD1 and catalase genes but panaxadiol increased the transcription of these genes about 2–3 fold. Among the panaxadiol ginsenosides, the Rb2 subfraction appeared to be a major inducer of SOD1 and catalase genes. The specificity of the Rb2 effect was further confirmed by time course‐ and dose‐dependent induction experiments. These results suggest that the panaxadiol fraction and its ginsenosides could induce the antioxidant enzymes which are important for maintaining cell viability by lowering the level of oxygen radical generated from intracellular metabolism. Copyright

Heavy metal-mediated activation of the rat Cu/Zn superoxide dismutase gene via a metal-responsive element.

Abstract The Cu/Zn superoxide dismutase (SOD1) catalyzes the dismutation of superoxide radicals produced in the course of biological oxidations. When placed under the control of the rat SOD1 gene promoter and transfected into human HepG2 hepatoma cells, the activity of a chloramphenicol acetyltransferase reporter gene was found to increase three- to four-fold in the presence of heavy metals (cadmium, zinc and copper). Functional analysis of mutant derivatives of the SOD1 gene promoter and the use of a heterologous promoter system confirmed that the induction of the SOD1 gene by metal ions requires a metal-responsive element (MRE) located between positions −273 and −267 (GCGCGCA). It was also shown by gel mobility shift assays that an MRE binding protein is induced by the exposure of the human liver cell line HepG2 to heavy metals. These results suggest that the MRE participates in the induction of the SOD1 gene by heavy metals.

C/EBPα is a major activator for the transcription of rat Cu/Zn superoxide dismutase gene in liver cell

The rat Cu/Zn superoxide dismutase (SOD1) is expressed in all tissues. Sequence analysis of the SOD1 promoter region showed that none of the cis‐elements of hepatocyte‐specific nuclear factors (HNF) were observed. The cis‐element of C/EBPα in the proximal region of the SOD1 promoter and the high level of C/EBPα in the liver tissue led us to focus on the transcriptional regulation of the SOD1 gene by C/EBPα. Cotransfection assays with the plasmid expressing transcription factor C/EBPα showed that C/EBPα transactivated SOD1 gene by 27 fold. The marked transactivation and direct binding of C/EBPα to the SOD1 promoter were confirmed by deletion analyses and mobility shift assays. These results suggested that C/EBPα plays a major role in the tissue distribution of SOD1.

Transcriptional activation of the human Cu/Zn superoxide dismutase gene by 2,3,7,8-tetrachlorodibenzo-p-dioxin through the xenobiotic-responsive element.

Abstract. Cu/Zn superoxide dismutase (SOD1) catalyzes the dismutation of superoxide radicals produced during biological oxidations and environmental stress. Here we have investigated the effect of the most toxic dioxin, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), on the promoter of the Cu/Zn superoxide dismutase (SOD1) gene in HepG2 and HeLa cells using the chloramphenicol acetyltransferase gene as a reporter. The SOD1 promoter was activated 4- to 5-fold by TCDD treatment, in a concentration-dependent manner. In addition, the level of SOD1 mRNA and the enzymatic activity of the SOD1 protein were also enhanced on exposure of the cells to TCDD. Functional analysis of the regulatory region of the SOD1 gene by deletion and point mutation, and the use of a heterologous promoter system, showed that the SOD1 gene was transactivated by TCDD via the xenobiotic-responsive element (XRE). Gel mobility shift assays also confirmed the induction and the inducible binding of a receptor-ligand complex to XRE. Yeast cells that overexpress hSOD1 appeared to be more resistant to TCDD than the wild type. These results demonstrate that SOD1 is induced by TCDD via the XRE. The induced SOD1 may accelerate the neutralization of the superoxide anion and thus reduce the oxidative damage associated with dioxin toxicity.