title: Overexpression of antioxidant enzymes upregulates aryl hydrocarbon receptor expression via increased Sp1 DNA-binding activity.
abstract: We previously reported upregulation of aryl hydrocarbon receptor (AhR) expression as a mechanism by which overexpression of Cu/Zn-superoxide dismutase (SOD) and/or catalase accelerates benzo(a)pyrene (BaP) detoxification in mouse aorta endothelial cells (MAECs). The objective of this study was to investigate the regulatory role of specificity protein-1 (Sp1) in AhR expression in MAECs that overexpress Cu/Zn-SOD and/or catalase. Our data demonstrated comparable levels of nuclear Sp1 protein in the transgenic and wild-type MAECs; however, binding of Sp1 protein to the AhR promoter region was more than 2-fold higher in MAECs overexpressing Cu/Zn-SOD and/or catalase than in wild-type cells. Inhibition of Sp1 binding to the AhR promoter by mithramycin A reduced AhR expression and eliminated the differences between wild-type MAECs and three lines of transgenic cells. Functional promoter analysis indicated that AhR promoter activity was significantly higher in MAECs overexpressing catalase than in wild-type cells. Mutation of an AhR promoter Sp1-binding site or addition of hydrogen peroxide to the culture medium reduced AhR promoter activity, and decreased the differences between wild-type MAECs and transgenic cells overexpressing catalase. These results suggest that increased Sp1 binding to the AhR promoter region is an underlying mechanism for upregulation of AhR expression in MAECs that overexpress Cu/Zn-SOD and/or catalase.
authors.affiliation: Department of Physiology, Meharry Medical College, Nashville, TN 37208, USA.
authors.forename: Tian
authors.initials: T
authors.lastname: Tang
authors.forename: Xinghua
authors.initials: X
authors.lastname: Lin
authors.forename: Hong
authors.initials: H
authors.lastname: Yang
authors.forename: Lichun
authors.initials: L
authors.lastname: Zhou
authors.forename: Zefen
authors.initials: Z
authors.lastname: Wang
authors.forename: Guang
authors.initials: G
authors.lastname: Shan
authors.forename: Zhongmao
authors.initials: Z
authors.lastname: Guo
mesh_terms: D000818:Animals; D001564:Benzo(a)pyrene / Q000378:metabolism; D002374:Catalase / Q000235:genetics* / Q000378:metabolism; D004730:Endothelium, Vascular / Q000187:drug effects / Q000378:metabolism; D006861:Hydrogen Peroxide / Q000494:pharmacology; D008658:Inactivation, Metabolic; D051379:Mice; D008822:Mice, Transgenic; D008926:Plicamycin / Q000031:analogs & derivatives / Q000494:pharmacology; D011401:Promoter Regions, Genetic / Q000187:drug effects; D018336:Receptors, Aryl Hydrocarbon / Q000096:biosynthesis / Q000235:genetics*; D016329:Sp1 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D013482:Superoxide Dismutase / Q000235:genetics* / Q000378:metabolism; D015854:Up-Regulation
chemical_list: D018336:Receptors, Aryl Hydrocarbon; D016329:Sp1 Transcription Factor; D001564:Benzo(a)pyrene; C066851:mithramycin A; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase; D008926:Plicamycin