GLUCOCORTICOIDS REPRESS BASAL AND STIMULATED MANGANESE SUPEROXIDE-DISMUTASE LEVELS IN RAT INTESTINAL EPITHELIAL-CELLS

Background/Aims: Elevated expression of manganese superoxide dismutase (SOD) has been shown to mitigate the toxic effects of cytokine and free radical production. Because of the multiple anti-inflammatory effects of glucocorticoids, we hypothesized that the MnSOD gene may be under glucocorticoid regulation. Methods: IEC-6 cells were treated with 0.5 mu mol/L dexamethasone (DEX), 50 mu mol/L cycloheximide, 4 mu mol/L actinomycin D, 0.5 mu g/mL lipopolysaccharide, or 10 ng/mL tumor necrosis factor alpha. MnSOD messenger RNA was evaluated by Northern analysis. MnSOD protein levels were evaluated by Western analysis. Results: IEC-6 treatment with DEX reduced MnSOD messenger RNA by 77% at 8 hours. Treatment with DEX plus cycloheximide or actinomycin showed a requirement for protein synthesis and implicated transcriptional regulation of MnSOD messenger RNA by DEX. DEX cotreatment inhibited the induction of MnSOD messenger RNA by lipopolysaccharide or tumor necrosis factor alpha. Twenty-four hours of DEX exposure reduced basal MnSOD protein levels by 43%, whereas 24-hour treatment with lipopolysaccharide or tumor necrosis factor a resulted in a 3.5-fold and 2.4-fold increase in MnSOD protein levels, respectively, that was blocked by DEX. Conclusions: DEX represses both basal and stimulated MnSOD messenger RNA and protein levels. Repression of MnSOD seems detrimental; however, this may not be the case because DEX also inhibits oxygen free radical production as well as cytokine release and action.