title: Repression of human GSTA1 by interleukin-1beta is mediated by variant hepatic nuclear factor-1C.
abstract: Down-regulation of glutathione transferase A1 (GSTA1) expression has profound implications in cytoprotection against toxic by-products of lipid peroxidation produced during inflammation. We investigated the role of hepatic nuclear factor 1 (HNF-1) in repression of human GSTA1 expression by interleukin (IL)-1beta in Caco-2 cells. In luciferase reporter assays, overexpression of HNF-1alpha increased GSTA1 transcriptional activity via an HNF-1 response element (HRE) in the proximal promoter. In addition, constitutive mRNA levels of GSTA1 and HNF-1alpha rose concurrently in Caco-2 cells with increasing stage of confluence. IL-1beta reduced GSTA1 mRNA levels at all stages of confluence; however, HNF-1alpha mRNA levels were not altered. IL-1beta repressed GSTA1 transcriptional activity, an effect that was abolished by mutating the HRE. Similar results were observed in HT-29 and HepG2 cells. Overexpression of HNF-1alpha did not counteract IL-1beta-mediated repression of GSTA1 transcription either in reporter assays or at the mRNA level. Involvement of the transdominant repressor C isoform of variant HNF-1 (vHNF-1C) in GSTA1 repression was demonstrated, because vHNF-1C overexpression significantly reduced GSTA1 transcriptional activity. Finally, IL-1beta caused concentration-related up-regulation of vHNF-1C mRNA levels and increased binding of vHNF-1C protein to the HRE, whereas HNF-1alpha-HRE complex formation was reduced. These findings indicate that IL-1beta represses GSTA1 transcription via a mechanism involving overexpression of vHNF-1C.
authors.affiliation: Department of Biomedical Sciences, University of Guelph, Guelph, ON, Canada N1G 2W1.
authors.forename: Lorraine
authors.initials: L
authors.lastname: Ng
authors.forename: Kathleen
authors.initials: K
authors.lastname: Nichols
authors.forename: Kelly
authors.initials: K
authors.lastname: O'Rourke
authors.forename: Ann
authors.initials: A
authors.lastname: Maslen
authors.forename: Gordon M
authors.initials: GM
authors.lastname: Kirby
mesh_terms: D001483:Base Sequence; D045744:Cell Line, Tumor; D017931:DNA Primers; D004794:Enzyme Repression; D005982:Glutathione Transferase / Q000096:biosynthesis* / Q000235:genetics; D051537:Hepatocyte Nuclear Factor 1 / Q000235:genetics*; D006801:Humans; D053583:Interleukin-1beta / Q000494:pharmacology*; D007700:Kinetics; D016297:Mutagenesis, Site-Directed; D012333:RNA, Messenger / Q000235:genetics; D011994:Recombinant Proteins / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D015533:Transcriptional Activation
chemical_list: D017931:DNA Primers; D053583:Interleukin-1beta; D012333:RNA, Messenger; D011994:Recombinant Proteins; D051537:Hepatocyte Nuclear Factor 1; C484555:GSTA1 protein, human; D005982:Glutathione Transferase