Molecular Mechanisms of Complex Mixture Toxicity

描述（由申请人提供）：本研究的长期目标是了解暴露于多环芳烃（PAH）和铬（一种致癌金属，通常作为多环芳烃的环境共污染物）的复杂混合物导致的不良健康影响和毒性的机制。本研究项目的目的是，（1）阐明铬影响诱导型基因表达的机制，（2）评价苯并[a]芘（B[a]P）（一种典型PAH）和铬的混合物对与基因表达的表观遗传调节相关的染色质重塑蛋白的翻译后修饰的影响。铬暴露已被证明可以改变诱导型基因表达，形成铬-DNA加合物和铬-DNA交联，并破坏转录激活因子/共激活因子复合物。在过去的4年中，我们已经证明，铬块基因表达的诱导基因的启动子处的生产性转录复合物的装配干扰。我们研究了铬对B[a]P诱导的基因表达的影响，结果表明，铬破坏了B[a] P依赖的Ah受体激活诱导的I相和II相解毒基因的转录调控，以及参与各种信号转导途径的50多个不同基因的诱导表达。铬的这些作用是抑制基因反式激活所必需的关键染色质重塑步骤的结果。考虑到组蛋白在维持染色质结构中的核心作用，在接下来的5年中，我们计划验证以下假设：暴露于铬和B[a]P的混合物会导致特定的组蛋白修饰，从而产生转录失活的染色质，并诱导非加性基因表达效应，这些效应无法从每个混合物组分的单独效应中预测。 这项工作的结果将有助于了解接触化学混合物所产生的风险，并制定有效的手段来预测其对健康的影响。

DESCRIPTION (provided by applicant): The long-range goal of this research is to develop an understanding of the mechanisms underlying the adverse health effects and toxicity resulting from exposure to complex mixtures of polycyclic aromatic hydrocarbons (PAH) and chromium, a carcinogenic metal often found as an environmental co-contaminant with PAHs. The objectives of this research project are, (1) to elucidate the mechanisms by which chromium affects inducible gene expression, and (2), to evaluate the effect of mixtures of benzo[a]pyrene (B[a]P), a prototypical PAH, and chromium on the post-translational modifications of chromatin remodeling proteins associated with epigenetic modulation of gene expression. Chromium exposure has been shown to alter inducible gene expression, to form chromium-DNA adducts and chromium-DNA cross-links, and to disrupt transcriptional activator/coactivator complexes. During the previous 4 years of this grant we have shown that chromium blocks gene expression by interfering with the assembly of productive transcriptional complexes at the promoters of inducible genes. We studied the effects of chromium on the expression of genes induced by B[a]P and showed that chromium disrupted the transcriptional regulation of phase I and phase II detoxification genes induced by B[a]P-dependent Ah receptor activation and the inducible expression of over 50 different genes involved in a variety of signal transduction pathways. These effects of chromium were the result of the inhibition of critical chromatin remodeling steps necessary for gene transactivation. Given the central role of histones in maintaining chromatin structure, for the next 5 years of this grant application we propose to test the hypothesis that exposure to mixtures of chromium and B[a]P causes specific histone modifications that generate transcriptionally inactive chromatin and induce non-additive gene expression effects that cannot be predicted from the individual effect of each mixture component. Results from this work will help to generate an understanding of the risks arising from exposure to chemical mixtures and to develop effective means to predict their health effects.