Induction of manganese superoxide dismutase mRNA by okadaic acid and protein synthesis inhibitors

We have reported that the phorbol ester phorbol 12-myristate 13-acetate (PMA) enhances the expression of manganese superoxide dismutase (Mn-SOD) mRNA [Fujii and Taniguchi (1991) J. Biol. Chem. 266, 23,142-23,146]. Okadaic acid, an inhibitor of type I and type IIa phosphatases, was also found to induce Mn-SOD mRNA at submicromolar concentrations in HeLa cells. Addition of cycloheximide resulted in superinduction of PMA- or tumour necrosis factor-stimulated expression of the mRNA, but not of okadaic acid-stimulated expression. When the effect of cycloheximide on the decay of Mn-SOD mRNA was examined by inhibiting mRNA synthesis with actinomycin D, cycloheximide had virtually no effect on mRNA stability, suggesting that accumulation of the mRNA was caused by activation by this reagent of transcription of the gene. PMA pretreatment of HeLa cells markedly enhanced cycloheximide-dependent superinduction of Mn-SOD mRNA. These data suggest that phosphorylation of several proteins is implicated in the regulation of Mn-SOD gene expression.