ARNT PROTEIN, DEVELOPMENT AND CARCINOGENESIS

Ah受体介导所有或几乎所有的毒理学效应 卤化芳族烃（HAH），例如2，3，7，8- 四氯二苯并对二恶英（TCDD）。 这些化合物作为肿瘤 啮齿动物中的启动子。 Ah受体也直接参与 许多引发剂的致癌作用。 受体也可能发挥作用， 在胚胎发育中的作用。 DNA结合，转录活性 培养的肝细胞中Ah受体的形式是Ah受体的异二聚体。 受体核转运蛋白（Arnt）和配体结合 Ah受体的亚基。 然而，目前尚不清楚是否有一些 配体结合亚基和Arnt的活性可以表现为 独立于其他蛋白质。 该项目建议使用 转基因小鼠技术，以解决Arnt的潜在作用 蛋白质在非遗传毒性和遗传毒性致癌物致癌作用中的作用，以及 在发展过程中。 胚胎干（ES）中的一个Arnt等位基因 细胞系将通过同源重组失活。 目标 ES细胞将用于产生对于破坏的Arnt纯合的小鼠 等位基因 如果他们不能存活， 在纯合子胎儿或新生儿的生殖系统中， 决定，以提供洞察阿恩特在 发展 如果Arnt缺陷小鼠发育到足够晚的阶段， 将确定它们是否能抵抗TCDD的毒性作用， 发展 如果Arnt基因敲除小鼠完全存活， 成年小鼠是否对TCDD的急性毒性反应有抵抗力， 从而验证了其他人提出的假设， 的TCDD是通过Arnt非依赖性途径产生的。 如果阿恩特- 敲除小鼠是完全可行的，我们还将产生衍生物， 小鼠染色体上lacI/q基因串联体纯合子 4. lacI/q基因可用于定量所有细胞中的突变， 身体 我们将使用lacI/q导数来检验假设， TCDD（在细菌中无遗传毒性，但完全致癌， 小鼠肝脏），增强自发诱变或致突变性 发起人在鼠标饲料，如果是这样，是否增强依赖于 阿恩特 我们还将确定肝脏和结肠致癌物质，2- 氨基-3-甲基咪唑并[4，5-f]喹喔啉（IQ）增加 喂食该化合物的小鼠的肝脏和结肠突变， TCDD（因此刺激Ah受体活性）影响 致突变性，如果观察到TCDD的任何影响，这些影响是否 依赖于Arnt。

The Ah receptor mediates all, or nearly all, of the toxicological effects of halogenated aromatic hydrocarbons (HAHs), such as 2,3,7,8- tetrachlorodibenzo-p-dioxin (TCDD). These compounds act as tumor promoters in rodents. The Ah receptor is also directly involved in carcinogenesis by many initiating agents. The receptor may also play a role in embryonic development. The DNA-binding, transcriptionally active form of the Ah receptor in cultured liver cells is a heterodimer of the Ah receptor nuclear translocator (Arnt) protein and the ligand-binding subunit of the Ah receptor. However, it is not clear whether some activities of the ligand-binding subunit and of Arnt can be manifested independently of the other protein. This project proposes to use transgenic mouse technology to address the potential role of the Arnt protein in carcinogenesis by non-genotoxic and genotoxic carcinogens, and in developmental processes. One Arnt allele in an embryonal stem (ES) cell line will be inactivated by homologous recombination. The targeted ES cells will be used to generate mice homozygous for the disrupted Arnt allele. If they are inviable, the developmental abnormalities and defects in the reproductive system of homozygous fetuses or newborns will be determined, in order to provide insight into the role of Arnt in development. If Arnt deficient mice develop to a late enough stage, we will determine whether they are resistant to the toxic effects of TCDD on development. If Arnt-knockout mice are fully viable we will investigate whether the adult mice are resistant to acute toxic responses to TCDD, thus testing the hypothesis, proposed by others, that some toxic effects of TCDD are produced via an Arnt-independent pathway. If the Arnt- knockout mice are fully viable we will also generate derivatives which are homozygous for a concatemer of the lacI/q gene located on mouse chromosome 4. The lacI/q gene can be used to quantitate mutations in all cells of the body. We will use the lacI/q derivatives to test the hypothesis that TCDD (which is non-genotoxic in bacteria but a complete carcinogen to mouse liver), enhances spontaneous mutagenesis or mutagenicity of initiators in mouse fee, and if so, whether enhancement is dependent on Arnt. We will also ascertain whether the liver and colon carcinogen, 2- amino-3-methylimidazo[4,5-f]quinoxaline (IQ) increases the frequency of liver and colon mutations in mice fed with the compound, whether cofeeding with TCDD (and therefore stimulation of Ah receptor activity) affects mutagenicity, and if any effects of TCDD are observed, whether these are dependent on Arnt.