TPA-activated transcription of the human MnSOD gene: Role of transcriptionfactors SP-1 and Egr-1

Induction of manganese superoxide dismutase (MnSOD) in response to oxidativ e stress has been well established in animals, tissues, and cell culture. H owever, the role of the human MnSOD (hMnSOD) promoter in stimulus-dependent activation of transcription is unknown. The hMnSOD promoter lacks both a T ATA and a CAAT box but possesses several GC motifs. In a previous study, we showed that the basal promoter contains multiple Sp1 and AP-2 binding site s and that Sp1 is essential for the constitutive expression of the hMnSOD g ene. In this study, we identified an Egr-1 binding site in the basal promot er of hMnSOD. We also found that the basal promoter is responsive to 12-O-t etradecanoylphorbol-13-acetate (TPA)-activated hMnSOD transcription in the human hepatocarcinoma cell line HepG2. The contributions of these binding s ites and the roles of the transcription factors Egr-1, AP-2, and Sp1 in the activation of hMnSOD transcription by TPA were investigated by site-direct ed mutation analysis, Western blotting, and overexpression of transcription factors. The results showed that Sp1 plays a positive role for both basal and TPA-activated hMnSOD transcription, whereas overexpression of Egr-1 has a negative role in the basal promoter activity without any effect on TPA-m ediated activation of hMnSOD transcription.