title: Dephosphorylation of Sp1 at Ser-59 by protein phosphatase 2A (PP2A) is required for induction of CYP1A1 transcription after treatment with 2,3,7,8-tetrachlorodibenzo-p-dioxin or omeprazole.
abstract: The aryl hydrocarbon receptor (AhR) is a transcription factor that is activated by either 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) or omeprazole (OP). Activated AhR can induce CYP1A1 transcription by binding to the xenobiotic responsive element (XRE). However, the mechanism of activation of the CYP1A1 promoter region is poorly understood. Previous reports showed that Sp1 could bind to a GC-rich region near the CYP1A1 promoter. This study sought to clarify the function of Sp1 in CYP1A1 transcription. Phosphorylation of Sp1 at Ser-59 (pSer-59) was previously reported to be closely related to transcriptional regulation. We used a site-specific phospho-antibody to show that treatment with TCDD or OP drastically reduced the level of pSer-59 in Sp1 from HepG2 cells. This reduction was too much, we hypothesized that the reduced phosphorylation level resulted from activation of phosphatase activity. Given that pSer-59 is dephosphorylated by PP2A, we examined the effect of a PP2A inhibitor, okadaic acid (OA), on pSer-59 and transcription of CYP1A1. The results showed that OA blocked dephosphorylation of Ser-59 and drastically inhibited transcription of CYP1A1. Similar results were obtained after knockdown of PP2A. Treatment with OA had no effect on the expression of AhR, its nuclear translocation, or its ability to bind to the XRE. Furthermore, dephosphorylation of Sp1 at Ser-59 was not affected by knockdown of AhR. These results indicate that the signals from TCDD or OP caused PP2A-mediated dephosphorylation of Sp1 at Ser-59 and induced CYP1A1 transcription. This signaling pathway was independent of the AhR-mediated pathway.
authors.affiliation: Science of Bioresources, The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Japan; Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan.
authors.forename: Shuji
authors.initials: S
authors.lastname: Shimoyama
authors.affiliation: Science of Bioresources, The United Graduate School of Agricultural Sciences, Iwate University, Morioka, Japan; Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan; Department of Tumor Biology, Institute of Biomedical Science, Iwate Medical University, Morioka, Japan.
authors.forename: Shuya
authors.initials: S
authors.lastname: Kasai
authors.affiliation: INSERM, UMR1090 TAGC, Marseille, F-13288, France; Aix-Marseille Université, UMR1090 TAGC, Marseille, F-13288, France.
authors.forename: Brigitte
authors.initials: B
authors.lastname: Kahn-Perlès
authors.affiliation: Department of Biochemistry and Molecular Biology, Faculty of Agriculture and Life Science, Hirosaki University, Hirosaki, Japan. Electronic address: hkikuchi@cc.hirosaki-u.ac.jp.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Kikuchi
mesh_terms: D015153:Blotting, Western; D018938:Caco-2 Cells; D002614:Chelating Agents / Q000494:pharmacology; D019363:Cytochrome P-450 CYP1A1 / Q000235:genetics / Q000378:metabolism*; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D056945:Hep G2 Cells; D006801:Humans; D061986:MCF-7 Cells; D008957:Models, Genetic; D019319:Okadaic Acid / Q000494:pharmacology; D009853:Omeprazole / Q000494:pharmacology*; D010766:Phosphorylation / Q000187:drug effects; D000072317:Polychlorinated Dibenzodioxins / Q000494:pharmacology*; D011401:Promoter Regions, Genetic / Q000235:genetics; D011485:Protein Binding; D054648:Protein Phosphatase 2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D054328:Proton Pump Inhibitors / Q000494:pharmacology; D034622:RNA Interference; D018336:Receptors, Aryl Hydrocarbon / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012694:Serine / Q000378:metabolism; D016329:Sp1 Transcription Factor / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects
chemical_list: D002614:Chelating Agents; D004791:Enzyme Inhibitors; D000072317:Polychlorinated Dibenzodioxins; D054328:Proton Pump Inhibitors; D018336:Receptors, Aryl Hydrocarbon; D016329:Sp1 Transcription Factor; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D019319:Okadaic Acid; D012694:Serine; D004533:Egtazic Acid; D019363:Cytochrome P-450 CYP1A1; D054648:Protein Phosphatase 2; D009853:Omeprazole
keywords: Aryl hydrocarbon receptor; CYP1A1; Protein phophatase 2A; Sp1