TPA-Activated Transcription of the HumanMnSODGene: Role of Transcription Factors SP-1 and Egr-1

Abstract

Induction of manganese superoxide dismutase (MnSOD) in response to oxidative stress has been well established in animals, tissues, and cell culture. However, the role of the human MnSOD (hMnSOD) promoter in stimulus-dependent activation of transcription is unknown. The hMnSOD promoter lacks both a TATA 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 sites and that Sp1 is essential for the constitutive expression of the hMnSOD gene. In this study, we identified an Egr-1 binding site in the basal promoter of hMnSOD. We also found that the basal promoter is responsive to 12-O-tetradecanoylphorbol-13-acetate (TPA)-activated hMnSOD transcription in the human hepatocarcinoma cell line HepG2. The contributions of these binding sites 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-directed 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-mediated activation of hMnSOD transcription.

Delayed radioprotection by nuclear transcription factor κB -mediated induction of manganese superoxide dismutase in human microvascular endothelial cells after exposure to the free radical scavenger WR1065

“…When elevated in cells, it is known to confer among other things an enhanced resistance against the cytotoxic effects of ionizing radiation [4,[8][9][10]23,24]. The MnSOD gene contains multiple transcription factor-binding motifs that include sites for AP1, AP2, Sp1, CREB, and NFκB [19][20][21][22]. As shown in Fig.…”

“…2 and 3). While this gene contains several NFκB-binding motifs [19][20][21], it is an intronic NFκB site that has been identified as being most associated with a stress and/or redox-mediated inducible effect on MnSOD transcription [22].…”

“…In particular, amifostine, NAC, and oltipraz have each been observed to be effective in activating the redox sensitive nuclear transcription factor κB (NFκB) and enhancing the expression of the antioxidant gene MnSOD [14,16,18]. While the MnSOD gene contains binding motifs for a number of transcription factors including NFκB, activator proteins 1 (AP1) and 2 (AP2), specificity protein 1 (Sp1), and adenosine 3′,5′-cyclic monophosphate-regulator elementbinding factor (CREB), it is the NFκB transcription factor that has been linked most closely with the process of inducible as compared to constitutive expression of MnSOD [19][20][21][22]. Sp1 is essential for transcription of MnSOD, while AP2 down-regulates transcription via its interaction with Sp1 [19].…”

“…Sp1 is essential for transcription of MnSOD, while AP2 down-regulates transcription via its interaction with Sp1 [19]. These transcription factors are involved with the constitutive expression of MnSOD [19,21]. Inhibition of NFκB activation either through the use of inhibitors such as BAY 11-7082 ([E]3-[(4-methylphenyl)-sulfonyl]-2-propenenitrile), a propenenitrile compound that inhibits IκB phosphorylation and subsequent NFκB activation, or through the stable transfection of a mutant IκBα gene in cells prevents both an enhancement of MnSOD expression and the elevation of MnSOD protein levels following exposure to NPT [23].…”

Epigenetic Regulation of Manganese Superoxide Dismutase Expression in Human Breast Cancer Cells

“…1 Issue 4 EGR-1, and SP-1, 14 all of which play important roles in regulating SOD2 transcription. Upstream sequences also control SOD2 expression through NFkB, 15 CREB 16 and FOXO3a 17 transcription factors.…”