Gassmann M, Kvietikova I, Rolfs A, Wenger R H
Institute of Physiology, University of Zürich-Irchel, Switzerland.
Kidney Int. 1997 Feb;51(2):567-74. doi: 10.1038/ki.1997.81.
The discovery that the oxygen-regulated transcription factor HIF-1 alpha and the dioxin receptor AhR share the common heterodimerization partner ARNT (HIF-1 beta) raised the question whether a cross-talk between oxygen and dioxin signal transduction pathways exists. To answer this question we investigated an ARNT-deficient mutant cell line (Hepa1C4), which has lost its capability of responding to dioxin. The results demonstrate that the presence of ARNT is indispensable for hypoxia-inducible HIF-1 DNA binding as well as for oxygen-regulated reporter gene activity mediated by the EPO 3' hypoxia response element (HRE). Hypoxic induction of the vascular endothelial growth factor (VEGF) gene, however, was only partially abrogated in Hepa1C4 cells, suggesting that HIF-1-independent oxygen signaling pathways might exist. We further studied HIF-1 and AhR/ARNT DNA binding activity as well as the regulation of oxygen- and xenobiotic-responsive genes by treating mouse Hepa1 hepatoma cells with hypoxia and/or the dioxin analogue ICZ. Hypoxia-inducible VEGF expression was found to be independent of ICZ-treatment, whereas ICZ-inducible cytochrome P-450IA1 expression was slightly reduced by hypoxic treatment of the cells. Interestingly, the enhancer function of a xenobiotic response element (XRE) linked to a reporter gene was induced by hypoxia, but expression of a HRE-containing reporter gene was not affected by ICZ treatment.
氧调节转录因子HIF-1α与二噁英受体AhR共享共同的异源二聚化伴侣ARNT（HIF-1β）这一发现，引发了氧信号转导途径与二噁英信号转导途径之间是否存在相互作用的问题。为了回答这个问题，我们研究了一种ARNT缺陷型突变细胞系（Hepa1C4），该细胞系已丧失对二噁英的反应能力。结果表明，ARNT的存在对于缺氧诱导的HIF-1与DNA结合以及由促红细胞生成素3'缺氧反应元件（HRE）介导的氧调节报告基因活性是必不可少的。然而，血管内皮生长因子（VEGF）基因的缺氧诱导在Hepa1C4细胞中仅部分被消除，这表明可能存在不依赖HIF-1的氧信号通路。我们通过用缺氧和/或二噁英类似物ICZ处理小鼠Hepa1肝癌细胞，进一步研究了HIF-1和AhR/ARNT与DNA的结合活性以及氧和外源性物质反应基因的调控。发现缺氧诱导的VEGF表达与ICZ处理无关，而细胞的缺氧处理会使ICZ诱导的细胞色素P-450IA1表达略有降低。有趣的是，与报告基因相连的心源性反应元件（XRE）的增强子功能可被缺氧诱导，但含HRE的报告基因的表达不受ICZ处理的影响。
