Interindividual Variability in Human Microsomal Epoxide Hydrolase

描述（由申请方提供）：异生物质代谢主要导致解毒。然而，在某些情况下，会产生生物活化和高毒性的中间体。细胞水平的环氧化物部分产生的化学代谢似乎是关键的启动剂的毒性损害，包括基因突变。作为一个恰当的例子，多环芳烃（PAHs）是有机物质不完全燃烧的产物，是广泛的环境污染物，并被认为是前致癌物，因为它们需要代谢活化亲电活性代谢物发挥其致突变和致肿瘤活性。微粒体环氧化物水解酶，EPHX 1，生物活化多环芳烃，有助于形成高活性和致癌的海湾地区和峡湾地区的二醇-环氧化物中间体。以前，我们的特点是人类EPXH 1的基因结构，并确定了两个结构多态性，外显子3多态性编码Y/H取代在氨基酸位置113，和外显子4 H/R取代在位置139。许多分子流行病学研究的结果已经将EPHX 1等位基因变异作为各种疾病的风险因素，最显著的是肺癌。最近，我们实验室的一份范式转换报告表明，人EPHX 1基因的表达是由使用替代启动子驱动的，其中一个远上游启动子称为E1-B，优先驱动EPHX 1在大多数人体组织中的表达。新的研究结果表明，E1-B启动子本身是遗传多态性的，并通过饮食化学预防剂，如萝卜硫素的转录调节。在这项研究计划中，我们设计了实验来测试几个关键和综合的假设，包括：1）EPHX 1最常见的结构遗传变异（Y113 H; H139 R）通过它们在PAH环氧化物中的底物特异性催化活性的性质赋予它们与PAH诱导的癌症风险的关联，特别是对于表现出非常高的致瘤潜力的峡湾区域环氧化物; 2）E1-B启动子区域的相关转录活性受遗传多态性和组织中的转座遗传元件的存在的个体间调节，所述遗传多态性和转座遗传元件是异生物素诱导的毒性的主要靶点;以及3）EPHX 1在人体组织中的表达受暴露于异硫氰酸酯衍生物的差异调节，所述异硫氰酸酯衍生物是目前研究作为化学预防剂的膳食物质。这些调查的结果将描绘的重要功能，包括酶学，转录调控和人类EPXH 1的遗传学和阐明这些过程作为人类疾病的潜在风险调节剂的功能作用。公共卫生相关性：微粒体环氧化物水解酶是一种存在于大多数组织中的酶，在代谢许多环境化学物质中起关键作用。这种酶的遗传学和调节可能部分决定了化学品暴露（包括癌症）导致的毒性个体间差异的性质和程度。这项研究计划将描述这些差异的关键特征，并研究它们作为人类疾病风险调节剂的作用。

DESCRIPTION (provided by applicant): Xenobiotic metabolism results principally in detoxication. However, in certain instances, bioactivated and highly toxic intermediates are generated. Cellular levels of epoxide moieties resulting from chemical metabolism appear to be critical initiators of toxic damage, including genetic mutation. As a case in point, polyaromatic hydrocarbons (PAHs) are products of incomplete combustion of organic matter, are widespread environmental contaminants and are considered procarcinogens because they require metabolic activation to electrophilic reactive metabolites to exert their mutagenic and tumorigenic activities. Microsomal epoxide hydrolase, EPHX1, bioactivates PAHs, contributing to the formation of highly reactive and carcinogenic bay region and fjord region diol-epoxide intermediates. Previously, we characterized the gene structure for human EPXH1 and identified two structural polymorphisms, an exon 3 polymorphism encoding Y/H substitutions at amino acid position 113, and an exon 4 H/R substitution at position 139. Results of many molecular epidemiological studies have since associated EPHX1 allelic variation as a risk factor for various diseases, most notably lung cancer. Recently, a paradigm-shifting report from our laboratory demonstrated that the expression of the human EPHX1 gene is driven by the use of alternative promoters, with a far upstream promoter, termed E1-b, preferentially driving expression EPHX1 in most human tissues. New findings demonstrate that the E1-b promoter is itself genetically polymorphic and is transcriptionally modulated by dietary chemopreventive agents, such as sulforaphane. In this research program, we have designed experiments to test several key and integrated hypotheses, including: 1) that the most common structural genetic variants of EPHX1 (Y113H; H139R) confer their association with PAH-induced cancer risk by nature of their substrate-specific catalytic activity among PAH epoxides, specifically towards fjord-region epoxides that exhibit extraordinarily high tumorigenic potential; 2) that the associated transcriptional activity of the E1-b promoter region is interindividually regulated by the presence of genetic polymorphism and transposable genetic elements in tissues that are principle targets of xenobiotic-induced toxicity; and, 3) that EPHX1 expression in human tissues is differentially regulated by exposures to isothiocyanate derivatives, dietary substances under current study as chemoprevention agents. The results of these investigations will delineate critical features comprising the enzymology, transcriptional regulation and genetics of human EPXH1 and elucidate the functional roles of these processes as potential risk modifiers of human disease. PUBLIC HEALTH RELEVANCE: Microsomal epoxide hydrolase is an enzyme that is present in most tissues and plays a key role in metabolizing numerous environmental chemicals. The genetics and regulation of this enzyme likely determines, in part, the nature and extent of interindividual differences in toxicity that result from chemical exposures, including cancers. This research program will characterize the critical features that account for these differences and investigate their roles as risk modifiers of human diseases.