Abnet C C, Tanguay R L, Heideman W, Peterson R E
School of Pharmacy and Environmental Toxicology Center, University of Wisconsin, Madison, Wisconsin, 53706, USA.
Toxicol Appl Pharmacol. 1999 Aug 15;159(1):41-51. doi: 10.1006/taap.1999.8719.
Transactivation assays were used to compare the potency and efficacy of polychlorinated dibenzo-p-dioxin (PCDD), dibenzofuran (PCDF), and biphenyl (PCB) congeners in activating aryl hydrocarbon receptors (AhRs) from rainbow trout (rtAhR2alpha and rtAhR2beta), zebrafish (zfAhR2), and human (huAhR), respectively. All AhRs were expressed with their species-specific AhR nuclear translocator (ARNT) in COS-7 cells. Transactivation activity was determined for two PCDD, two PCDF, and seven PCB congeners with each of the four AhR/ARNT pairs using prt1Aluc, a luciferase reporter driven by two dioxin-responsive enhancer elements (DREs) from the rainbow trout cyp1A gene. Maximal-fold induction, EC50, and relative potency values were calculated for congeners that exhibited dose-related activity in the assay. Of the four AhR/ARNT pairs tested with PCDD, PCDF, and non-ortho PCB congeners, three exhibited high activity (rainbow trout AhR2alpha, zebrafish AhR2, and human AhR), while rainbow trout AhR2beta had very weak or no activity. Comparisons between these AhRs showed that while mono-ortho PCBs were able to activate the human AhR, they were generally ineffective in activating rainbow trout and zebrafish AhR2s. This supports the hypothesis that structural differences between mammalian and fish AhRs may account for differences in relative potencies of the mono-ortho PCBs between mammals and fish. Another important finding was a significant difference in transactivation activity between the two rainbow trout AhR2 isoforms despite the fact that they are 95% identical at the amino acid level. For all PCDD, PCDF, and PCB agonists tested, rainbow trout AhR2alpha was significantly more active than AhR2beta. However, rainbow trout AhR2beta is active as a 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)-activated transcription factor, with enhancer elements from the mouse cyp1A gene. This suggests that AhR2beta may have evolved to serve a different physiological function than AhR2alpha in salmonid fish species.
采用反式激活分析方法，比较多氯代二苯并 - 对 - 二噁英（PCDD）、二苯并呋喃（PCDF）和联苯（PCB）同系物分别激活虹鳟（rtAhR2alpha和rtAhR2beta）、斑马鱼（zfAhR2）和人类（huAhR）芳烃受体（AhRs）的效力和效能。所有AhRs均与它们物种特异性的AhR核转运蛋白（ARNT）在COS - 7细胞中表达。使用prt1Aluc（一种由虹鳟cyp1A基因的两个二噁英反应增强子元件（DREs）驱动的荧光素酶报告基因），测定了四种AhR/ARNT对中两种PCDD、两种PCDF和七种PCB同系物的反式激活活性。对于在分析中表现出剂量相关活性的同系物，计算了最大诱导倍数、半数有效浓度（EC50）和相对效力值。在用PCDD、PCDF和非邻位PCB同系物测试的四种AhR/ARNT对中，三种表现出高活性（虹鳟AhR2alpha、斑马鱼AhR2和人类AhR），而虹鳟AhR2beta活性非常弱或无活性。这些AhRs之间的比较表明，虽然单邻位PCBs能够激活人类AhR，但它们通常无法有效激活虹鳟和斑马鱼的AhR2s。这支持了以下假设：哺乳动物和鱼类AhRs之间的结构差异可能解释了哺乳动物和鱼类中单邻位PCBs相对效力的差异。另一个重要发现是，尽管两种虹鳟AhR2亚型在氨基酸水平上有95%的同一性，但它们在反式激活活性上存在显著差异。对于所有测试的PCDD、PCDF和PCB激动剂，虹鳟AhR2alpha的活性明显高于AhR2beta。然而，虹鳟AhR2beta作为一种由2,3,7,8 - 四氯二苯并 - 对 - 二噁英（TCDD）激活的转录因子是有活性的，其带有来自小鼠cyp1A基因的增强子元件。这表明在鲑科鱼类中，AhR2beta可能已经进化为具有与AhR2alpha不同的生理功能。
