Prestera T, Holtzclaw W D, Zhang Y, Talalay P
Department of Pharmacology and Molecular Sciences, Johns Hopkins University School of Medicine, Baltimore, MD 21205-2185.
Proc Natl Acad Sci U S A. 1993 Apr 1;90(7):2965-9. doi: 10.1073/pnas.90.7.2965.
Inductions of detoxication (phase 2) enzymes, such as glutathione transferases and NAD(P)H:(quinone-acceptor) oxidoreductase, are a major mechanism for protecting animals and their cells against the toxic and neoplastic effects of carcinogens. These inductions result from enhanced transcription, and they are evoked by diverse chemical agents: oxidizable diphenols and phenylenediamines; Michael reaction acceptors; organic isothiocyanates; other electrophiles--e.g., alkyl and aryl halides; metal ions--e.g., HgCl2 and CdCl2; trivalent arsenic derivatives; vicinal dimercaptans; organic hydroperoxides and hydrogen peroxide; and 1,2-dithiole-3-thiones. The molecular mechanisms of these inductions were analyzed with the help of a construct containing a 41-bp enhancer element derived from the 5' upstream region of the mouse liver glutathione transferase Ya subunit gene ligated to the 5' end of the isolated promoter region of this gene, and inserted into a plasmid containing a human growth hormone reporter gene. When this construct was transfected into Hep G2 human hepatoma cells, the concentrations of 28 compounds (from the above classes) required to double growth hormone production, and the concentrations required to double quinone reductase specific activities in Hepa 1c1c7 cells, spanned a range of four orders of magnitude but were closely linearly correlated. Six compounds tested were inactive in both systems. A 26-bp subregion of the above enhancer oligonucleotide (containing the two tandem "AP-1-like" sites but lacking the preceding ETS protein binding sequence) was considerably less responsive to the same inducers. We conclude that the 41-bp enhancer element mediates most, if not all, of the phase 2 enzyme inducer activity of all of these widely different classes of compounds.
解毒（第二阶段）酶的诱导，如谷胱甘肽转移酶和NAD(P)H:（醌-受体）氧化还原酶，是保护动物及其细胞免受致癌物毒性和肿瘤形成作用的主要机制。这些诱导是由转录增强引起的，并且由多种化学试剂诱发：可氧化的二酚和苯二胺；迈克尔反应受体；有机异硫氰酸酯；其他亲电试剂，如烷基和芳基卤化物；金属离子，如HgCl2和CdCl2；三价砷衍生物；邻二硫醇；有机氢过氧化物和过氧化氢；以及1,2-二硫杂环戊烯-3-硫酮。借助一个构建体分析了这些诱导的分子机制，该构建体包含一个41bp的增强子元件，其来源于小鼠肝脏谷胱甘肽转移酶Ya亚基基因5'上游区域，连接到该基因分离的启动子区域的5'末端，并插入到一个含有人生长激素报告基因的质粒中。当将该构建体转染到Hep G2人肝癌细胞中时，使生长激素产量加倍所需的28种化合物（来自上述类别）的浓度，以及使Hepa 1c1c7细胞中醌还原酶比活性加倍所需的浓度，跨度达四个数量级，但呈密切的线性相关。测试的六种化合物在两个系统中均无活性。上述增强子寡核苷酸的一个26bp亚区域（包含两个串联的“AP-1样”位点，但缺少前面的ETS蛋白结合序列）对相同诱导剂的反应性明显较低。我们得出结论，41bp的增强子元件介导了所有这些广泛不同类别的化合物的大部分（如果不是全部）第二阶段酶诱导活性。
