AH RECEPTOR/TRANSCRIPTION FACTOR AS A REGULATOR OF HYDROCARBON BIOACTIVITY

多环芳烃(PAH)和相关的卤代烃是超级基金危险废物场地中高浓度存在的环境化学品。这些化合物会导致癌症，抑制免疫系统，并调节细胞生长。至少部分(如果不是全部)这些反应是由芳烃受体(AhR)介导的，AhR是一种胞质蛋白，在配体结合后被转化为DNA结合的转录因子。虽然主要以多环芳烃代谢酶的调节而闻名，但AhR调节几个基因的转录，并似乎影响细胞周期控制。在胚胎发育过程中，AHR被环境化学物质激活，导致多周期调控。AHR在胚胎发育过程中被环境化学物质激活，导致多种发育缺陷。对AhR/Null小鼠的研究表明，AhR的缺失也会扰乱器官的发育，这表明即使在缺乏外源配体的情况下，AhR也在发育中发挥着重要作用。这一结论得到了AhR转基因(AhR/TG)小鼠T淋巴细胞发育异常的支持。此外，AhR的上调伴随着抗原特异性的人类T细胞刺激，提示AhR在T细胞激活中发挥作用，并可能是AhR配体影响抗原特异性免疫应答的机制之一。鉴于这些观察，我们推测AhR在T细胞发育中发挥作用，环境化学物质不适当地激活AhR会损害T细胞的成熟和功能。为了验证这一假说并确定控制人类AhR表达的因素，人们提出了三个具体的目标：1.确定AhR转基因小鼠T细胞发育缺陷的机制。使用我们实验室培育的AhR/TG小鼠和AhR/Null小鼠，我们将确定AhR是否影响胸腺中自身反应克隆的删除和/或次级淋巴器官中T细胞的激活和控制。2.确定AhR在环境化学诱导的免疫抑制中的作用。AHR/TG小鼠将被用作一个高度敏感的系统，用于筛选潜在的免疫毒性环境化学品，并作为确定这些化学品介导免疫抑制的机制的最佳模型(S)。3.确定在原代人肽特异性CD8+T细胞活化过程中调节AhR基因表达的转录因子。在证明AhR在人类T和B淋巴细胞中上调后，我们将使用分子生物学技术来定位AhR启动子的调节区，并确定控制AhR转录的因素。总之，所获得的结果将有助于阐明AhR在T细胞成熟过程中的生理作用，以及AhR配体暴露在T细胞发育和激活过程中的后果。

Polycyclic aromatic hydrocarbons (PAH) and related halogenated hydrocarbons are environmental chemicals present at high concentrations in Superfund hazardous waste sites. These compounds induce cancer, suppress the immune system, and modulate cell growth. At least some, if not all of these responses are mediated by the aryl hydrocarbon receptor (AhR), a cytosolic protein that is converted into a DNA-binding transcription factor following ligand binding. Although primarily known for its regulation of PAH-metabolizing enzymes, the AhR regulates transcription of several genes and appears to affect cell cycle control. AhR activation by environmental chemicals during embryogenesis results in multiple cycle control. AhR activation by environmental chemicals during embryogenesis results in multiple developmental defects. Studies with AhR/null mice suggest that the absence of the AhR also disrupts organ development, indicating that the AhR plays an important role in development even in the absence of exogenous ligands. This conclusion is supported by our demonstration of abnormal T lymphocyte development in AhR transgenic (AhR/TG) mice. Furthermore, AhR up- regulation accompanies antigen-specific human T cell stimulation suggesting a role for the AhR in T cell activation and a mechanism through which AhR ligands may affect antigen-specific immune responsiveness. Given these observations, we have postulated that the AhR plays a role in T cell development and that inappropriate AhR activation by environmental chemicals compromises T cell maturation and function. Three specific aims have been proposed to test this hypothesis and to define factors which control human AhR expression: 1. Define the mechanism responsible for T cell developmental defects in AhR transgenic mice. Using AhR/TG mice produced in our laboratory and AhR/null mice we will determine if the AhR influences deletion of autoreactive clones in the thymus and/or T cell activation and control in secondary lymphoid organs. 2. Determine the role of the AhR in environmental chemical-induced immunosuppression. AhR/TG mice will be used as a highly sensitive system for screening potentially immunotoxic environmental chemicals and as an optimal model for defining the mechanism(s) through which these chemicals mediate immune suppression. 3. Define transcription factors regulating AhR gene expression during activation of primary human peptide specific CD8+ T cells. Having demonstrated AhR up-regulation in human T and B lymphocytes, we will use molecular biology techniques to map regulatory regions in the AhR promoter and to define factors which control AhR transcription. Collectively, results obtained will shed light on the physiological role of the AhR during T cell maturation and on the consequences of AhR ligand exposure during T cell development and activation.