Characterization of the Pathways Linking Ah Receptor

这一5年研究计划的总体目标有两个方面：（a）描述 TCDD和类二恶英对B细胞分化影响 化合物;和（B）开发描述调节B的生物化学途径的计算模型 细胞分化以及该途径与芳烃受体（AhR）的相互作用。先前 研究已经确定B细胞是TCDD的敏感细胞靶点， 免疫球蛋白（Ig）M通过对涉及AhR的B细胞的直接作用。此外，抑制IgM TCDD的反应是在转录水平介导的，部分是通过AhR与二恶英的结合而发生的 在IG重链（IgH）3 ′ a增强子内的调节结构域中的应答元件（ORE）。重要的是， 除了IgH抑制外，IG κ轻链（Igk）、IgM连接链（J链）和X盒蛋白-1 TCDD也明显抑制了IgM组装和分泌所必需的XBP-1的表达 这表明除了IgH 3 ′ a增强子之外还涉及其它靶点。此外，TCDD 改变了B淋巴细胞的水平诱导成熟蛋白-1（Blimp-1）是B细胞的主要调节因子 分化及其下游靶点Pax 5，一种B细胞分化的转录抑制因子， 抑制IgH、Igk、J链和XBP-1。我们还表明，TCDD处理B细胞：（a）改变了细胞的增殖能力， DNA甲基化的程度和DNA甲基化酶Dnmt 3b的mRNA水平， 影响对B细胞分化至关重要的基因的表达，包括Pax 5;（B）在功能上 （c）快速诱导细胞因子信号传导抑制因子-2（SOCS-2），一种蛋白质， 通过与JAK/STAT途径偶联的细胞因子受体负调节信号传导，例如 IFNg受体（IFNgR）。该项目的目标是检验假设：抑制原发性 AhR激动剂的体液免疫应答通过B细胞分化的变化介导 通过IFNg阻止的机制进行编程。生物化学途径的计算描述 的B细胞分化和AhR激动剂对这一途径的直接相互作用，将提供一个机制， 用于预测AhR激动剂单独和作为复杂混合物组合的作用的方法 途径和体液免疫反应。

The overall goal of this 5 year research plan is two-fold: (a) to characterize the molecular mechanism for impairment of B cell differentiation by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and dioxin-like compounds; and (b) to develop a computational model describing the biochemical pathways that regulate B cell differentiation and the interaction of this pathway with the aryl hydrocarbon reception (AhR). Previous studies have established the B cell as a sensitive cellular target for TCDD as evidenced by suppression of immunoglobulin (lg)M through a direct effect on B cells involving the AhR. Moreover, suppression of the IgM response by TCDD is mediated at the level of transcription and, in part, occurs through AhR binding to dioxin response elements (ORE) in regulatory domains within the Ig heavy chain (IgH) 3'a enhancer. Importantly, in addition to IgH suppression, the Ig kappa light chain (Igk), IgM joining chain (J chain) and X-box protein-1 (XBP-1), which are essential for IgM assembly and secretion, are also markedly suppressed by TCDD suggesting the involvement of additional targets other than just the IgH 3'a enhancer. Moreover, TCDD alters the levels of B lymphocyte.-induced maturation protein-1 (Blimp-1), a master regulatory of B cell differentiation and its downstream target, Pax5, a transcriptional represser of B cell differentiation, which represses IgH, Igk, J chain and XBP-1. We also show that TCDD treatment of B cells: (a) altered the magnitude of DNA methylation and MRNA levels of DNA methylating enzymes, Dnmt3b, which putatively influences the expression of genes crucial to B cell differentiation, including Pax5; (b) is functionally antagonized by IFNg; and (c) rapidly induces the suppressor of cytokine signaling-2 (SOCS-2), a protein that negatively regulates signaling through cytokine receptors coupled to the JAK/STAT pathway, such as the IFNg receptor (IFNgR). The project objective is to test the hypothesis: Suppression of the primary humoral immune response by AhR agonists is mediated through changes in the B cell differentiation program via a mechanism that is blocked by IFNg. A computational description of the biochemical pathway of B cell differentiation and the direct interactions of AhR agonists on this pathway, will provide a mechanistic approach for predicting the effects of AhR agonists, alone and in combination as complex mixtures, on the pathway and on humoral immune responses.