A family of AP-2 proteins down-regulate manganese superoxide dismutase expression.
Manganese superoxide dismutase (Mn-SOD) is a primary antioxidant enzyme whose expression is essential for life in oxygen. Mn-SOD has tumor suppressor activity in a wide variety of tumors and transformed cell systems. Our initial observations revealed that Mn-SOD expression was inversely correlated with expression of AP-2 transcription factors in normal human fibroblasts and their SV-40 transformed counterparts. Thus we hypothesized that AP-2 may down-regulate Mn-SOD expression. To examine the functional role of AP-2 on Mn-SOD promoter transactivation we cotransfected AP-2-deficient HepG2 cells with a human Mn-SOD promoter-reporter construct and expression vectors encoding each of the three known AP-2 family members. Our results indicated that AP-2 could significantly repress Mn-SOD promoter activity, and that this repression was both Mn-SOD promoter and AP-2-specific. The three AP-2 proteins appeared to play distinct roles in Mn-SOD gene regulation. Moreover, although all three AP-2 proteins could repress the Mn-SOD promoter, AP-2alpha and AP-2gamma were more active in this regard than AP-2beta. Transcriptional repression by AP-2 was not a general effect in this system, because another AP-2-responsive gene, c-erbB-3, was transactivated by AP-2. Repression of Mn-SOD by AP-2 was dependent on DNA binding, and expression of AP-2B, a dominant negative incapable of DNA binding, relieved the repression on Mn-SOD promoter and reactivated Mn-SOD expression in the AP-2 abundant SV40-transformed fibroblast cell line MRC-5VA. These results indicate that AP-2-mediated transcriptional repression contributes to the constitutively low expression of Mn-SOD in SV40-transformed fibroblasts and suggest a mechanism for Mn-SOD down-regulation in cancer.
Free Radical & Radiation Biology Program, Department of Radiology, University of Iowa, Iowa City 52242, USA.
C H
CH
Zhu
Y
Y
Huang
L W
LW
Oberley
F E
FE
Domann
D020816:Amino Acid Motifs; D000975:Antioxidants / Q000378:metabolism; D001665:Binding Sites; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D002478:Cells, Cultured; D004247:DNA / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D015971:Gene Expression Regulation, Enzymologic; D005799:Genes, Dominant; D017930:Genes, Reporter; D005822:Genetic Vectors / Q000378:metabolism; D006801:Humans; D008954:Models, Biological; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D020893:Receptor, ErbB-3 / Q000378:metabolism; D013482:Superoxide Dismutase / Q000096:biosynthesis* / Q000235:genetics; D050656:Transcription Factor AP-2; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D000975:Antioxidants; D004268:DNA-Binding Proteins; D012333:RNA, Messenger; C493673:TFAP2A protein, human; C493677:TFAP2B protein, human; C493679:TFAP2C protein, human; D050656:Transcription Factor AP-2; D014157:Transcription Factors; D004247:DNA; D013482:Superoxide Dismutase; D020893:Receptor, ErbB-3