TRANSGENIC MICE, GENE KNOCKOUT MICE, AND CYTOCHROME P450 FUNCTION

细胞色素P450领域的两个主要问题仍然没有答案。 首先，在化学致癌过程中是否需要P450？ 一只完整的动物？只有在体外和细胞培养中进行的研究才能推断 这些酶的重要性。第二，做异体代谢 P450在新陈代谢中也起着重要的生理作用 动物体内的内源性激素或其他化学物质？这些是酶吗？ 发展和生存所必需的？这些问题是可以回答的 通过“基因敲除”构建缺乏功能性P450的小鼠 策略。我们重点研究了两个P450，即CYP1A2和CYP2E1，它们属于 在动物中保存最好的，并通过新陈代谢激活的已知 化学致癌物。CYP1A2是主要的P450，负责 芳胺类和杂环芳胺类致癌物质的代谢活化 和最强的人类肝癌致癌物黄曲霉毒素B1。细胞色素P450-2 激活低分子亚硝胺和一些低分子 体重癌症怀疑包括苯和卤化乙烯在内的化学物质。我们 也在研究外国化学物质的受体。这些都是未知的 在动物中发挥作用，没有明确定义的内源性配体。 因此，编码过氧化酶体的外源受体基因 增殖物激活受体、PPAR和ah受体正在 受制于基因敲除策略。过氧化物酶体增殖物是 啮齿类动物中的肿瘤促进剂，还激活编码P450和 过氧化物酶。许多需要AH受体的诱导剂是 已知的致癌物质和肿瘤促进剂。因此，基因敲除研究 可以深入了解内源性功能和在疾病中的作用 结合外来化学物质的受体。这些受体也高度 在哺乳动物中保守，表明可能具有关键功能。他们的 致癌物和肿瘤促进剂的结合可能需要 化学致癌过程。受损的生殖系传播 已获得了CYP1A2、PPAR和ah受体的等位基因。这个 每种基因只有一个拷贝的子代小鼠看起来是正常的。 杂合子目前正在进行交配，以产生纯合子小鼠 缺乏基因。

Two major questions in the cytochrome P450 field remain unanswered. First, are P450s required for the process of chemical carcinogenesis in an intact animal? Only studies done in vitro and in cell culture infer the importance of these enzymes. Second, do xenobiotic-metabolizing P450s also have an important, physiologically-relevant role in metabolism of endogenous hormones or other chemicals in animals? Are these enzymes required for development and survival? These questions can be answered by constructing mice that lack a functional P450 by the "gene knockout" strategy. We have focused on two P450s, CYP1A2 and CYP2E1 that are among the most well conserved in animals and that metabolically activate known chemical carcinogens. CYP1A2 is the principal P450 responsible for metabolic activation of arylamine and heterocyclic arylamine carcinogens and the most potent human hepatocarcinogen aflatoxin B1. CYP2E1 activates low molecular weight nitrosamines and a number of low molecular weight cancer suspect chemicals including benzene and vinyl halides. We are also studying receptors for foreign chemicals. These have no known function in animals and no clearly defined endogenous ligands. Therefore, the xenobiotic-receptor genes encoding the peroxisome proliferator-activated receptor, PPAR, and the Ah receptor are being subjected to the gene knockout strategy. Peroxisome proliferators are tumor promoters in rodents and also activate genes encoding P450s and peroxisomal enzymes. Many inducers that require the Ah receptor are known carcinogens and tumor promoters. Thus, the gene knockout studies can yield insight into the endogenous function and role in disease of receptors that bind foreign chemicals. These receptors are also highly conserved in mammals indicating a possible critical function. Their binding of carcinogens and tumor promoters might be required for the process of chemical carcinogenesis. Germ line transmissions of damaged alleles for CYP1A2, PPAR and the Ah receptor have been obtained. The progeny mice containing only one copy of each gene appear to be normal. The heterozygotes are currently being mated to produce homozygous mice lacking the genes.