School of Molecular and Biomedical Science (Biochemistry) and Australian Research Council Special Research Centre for the Molecular Genetics of Development, the University of Adelaide, Adelaide, South Australia, Australia.
Mol Pharmacol. 2012 Dec;82(6):1082-93. doi: 10.1124/mol.112.078873. Epub 2012 Aug 30.
The aryl hydrocarbon receptor (AhR) is a signal-regulated transcription factor, which is canonically activated by the direct binding of xenobiotics. In addition, switching cells from adherent to suspension culture also activates the AhR, representing a nonxenobiotic, physiological activation of AhR signaling. Here, we show that the AhR is recruited to target gene enhancers in both ligand [isopropyl-2-(1,3-dithietane-2-ylidene)-2-[N-(4-methylthiazol-2-yl)carbamoyl]acetate (YH439)]-treated and suspension cells, suggesting a common mechanism of target gene induction between these two routes of AhR activation. However, gene expression profiles critically differ between xenobiotic- and suspension-activated AhR signaling. Por and Cldnd1 were regulated predominantly by ligand treatments, whereas, in contrast, ApoER2 and Ganc were regulated predominantly by the suspension condition. Classic xenobiotic-metabolizing AhR targets such as Cyp1a1, Cyp1b1, and Nqo1 were regulated by both ligand and suspension conditions. Temporal expression patterns of AhR target genes were also found to vary, with examples of transient activation, transient repression, or sustained alterations in expression. Furthermore, sequence analysis coupled with chromatin immunoprecipitation assays and reporter gene analysis identified a functional xenobiotic response element (XRE) in the intron 1 of the mouse Tiparp gene, which was also bound by hypoxia-inducible factor-1α during hypoxia and features a concatemer of four XRE cores (GCGTG). Our data suggest that this XRE concatemer site concurrently regulates the expression of both the Tiparp gene and its cis antisense noncoding RNA after ligand- or suspension-induced AhR activation. This work provides novel insights into how AhR signaling drives different transcriptional programs via the ligand versus suspension modes of activation.
芳香烃受体 (AhR) 是一种信号调节转录因子，通常通过外源性物质的直接结合而被激活。此外，将细胞从贴壁培养转换为悬浮培养也会激活 AhR，这代表了 AhR 信号的非外源性生理激活。在这里，我们表明，配体[异丙基-2-(1,3-二硫戊环-2-亚基)-2-[N-(4-甲基噻唑-2-基)氨基甲酰基]乙酸酯 (YH439)]处理和悬浮细胞中，AhR 均被募集到靶基因增强子上，这表明两种激活 AhR 的途径之间存在共同的靶基因诱导机制。然而，外源性物质和悬浮激活的 AhR 信号之间的基因表达谱存在显著差异。Por 和 Cldnd1 主要受配体处理调节，而相反，ApoER2 和 Ganc 则主要受悬浮条件调节。经典的外源性物质代谢 AhR 靶基因，如 Cyp1a1、Cyp1b1 和 Nqo1，均受配体和悬浮条件的调节。AhR 靶基因的时间表达模式也存在差异，包括瞬时激活、瞬时抑制或持续改变表达。此外，序列分析结合染色质免疫沉淀分析和报告基因分析，在小鼠 Tiparp 基因的内含子 1 中鉴定出一个功能性外源性物质反应元件 (XRE)，该元件在缺氧时也被缺氧诱导因子-1α 结合，并具有四个 XRE 核心 (GCGTG) 的串联体。我们的数据表明，这个 XRE 串联位点在配体或悬浮诱导的 AhR 激活后，同时调节 Tiparp 基因及其顺式反义非编码 RNA 的表达。这项工作为 AhR 信号通过配体与悬浮激活模式驱动不同转录程序提供了新的见解。
