Ng Lorraine, Nichols Kathleen, O'Rourke Kelly, Maslen Ann, Kirby Gordon M
Department of Biomedical Sciences, University of Guelph, Guelph, ON, Canada N1G 2W1.
Mol Pharmacol. 2007 Jan;71(1):201-8. doi: 10.1124/mol.106.028563. Epub 2006 Oct 4.
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.
谷胱甘肽转移酶A1（GSTA1）表达的下调对抵抗炎症期间产生的脂质过氧化有毒副产物的细胞保护具有深远影响。我们研究了肝细胞核因子1（HNF-1）在白细胞介素（IL）-1β抑制Caco-2细胞中人GSTA1表达中的作用。在荧光素酶报告基因检测中，HNF-1α的过表达通过近端启动子中的HNF-1反应元件（HRE）增加了GSTA1的转录活性。此外，随着Caco-2细胞汇合阶段的增加，GSTA1和HNF-1α的组成型mRNA水平同时上升。IL-1β在汇合的所有阶段均降低了GSTA1 mRNA水平；然而，HNF-1α mRNA水平未改变。IL-1β抑制了GSTA1的转录活性，这种作用通过突变HRE而被消除。在HT-29和HepG2细胞中观察到了类似的结果。在报告基因检测或mRNA水平上，HNF-1α的过表达均未抵消IL-1β介导的GSTA1转录抑制。已证明变体HNF-1（vHNF-1）的反式显性阻遏物C异构体参与了GSTA1的抑制，因为vHNF-1C的过表达显著降低了GSTA1的转录活性。最后，IL-1β导致vHNF-1C mRNA水平的浓度相关上调，并增加了vHNF-1C蛋白与HRE的结合，而HNF-1α-HRE复合物的形成减少。这些发现表明，IL-1β通过涉及vHNF-1C过表达的机制抑制GSTA1转录。
