Regulation of cyp1a1 by Ah Receptor and NFkB Interaction

描述(申请人提供)：二恶英和相关的卤代芳香烃是普遍存在的持久性环境污染物，对人类和野生动物造成不良反应。二恶英引起的大多数毒性反应是由芳烃受体(AhR)介导的。因此，我们理解二恶英毒性的核心是阐明AhR调控基因表达的机制。在早期的研究中，我们已经发现AhR和NF-kB通路之间存在物理联系和功能上的相互抑制(J.Biol。化学。274,510)。由于核因子-kB是一种多效性转录因子，参与了许多已知受到二恶英不利影响的生理功能，因此AhR介导的抑制核因子-kB为迄今知之甚少的二恶英毒性反应的某些方面提供了一种机制，如免疫抑制和异常皮肤增殖。反过来，通过激活核因子-kB抑制AhR也为长期观察到炎性细胞因子和脂多糖抑制AhR调节的细胞色素P4501A1/1A2和降低异物(包括临床药物)代谢能力提供了潜在的机制(J.Biol)。化学。276,39638)。在最近的研究中，我们利用染色质免疫沉淀(ChIP)实验获得了新的结果，表明AhR/NF-kB相互作用在转录水平上收敛，涉及(1)转录延伸的控制和(2)染色质的修饰。在本提案的目的I中，我们将研究AhR/NF-kB相互作用通过直接与在延伸控制中起关键作用的p-TEFb(正转录延伸因子b)相互作用来调节cyp1a1转录延伸的机制。在AIM II中，我们将研究组蛋白修饰(组蛋白乙酰化和甲基化)对AhR和NF-kB截然相反的作用的响应，并建立与cyp1a1的“开”和“关”状态相关的组蛋白修饰(组蛋白编码)的残基特异性和组合模式。我们还将研究一种新的AhR相互作用蛋白(通过CytoTrap酵母双杂交筛选鉴定)SUV39H2甲基转移酶在AhR介导的基因沉默中的作用，这可能在男性印记中起重要作用。这些研究将有助于我们从机制上了解AhR和NF-kB在正常生理中的作用，以及二恶英及其相关化合物诱导的发病机制。

DESCRIPTION (provided by applicant): Dioxin and related halogenated aromatic hydrocarbons are ubiquitous, persistent environmental contaminants causing adverse responses to human and wildlife. Most of the toxic responses induced by dioxin are mediated by the aryl hydrocarbon receptor (AhR). Therefore, central to our understanding of dioxin-induced toxicity is to elucidate the mechanism of the AhR-regulated gene expressions. In earlier studies, we have found a physical association and functional reciprocal repression between the AhR and NF-kB pathways (J. Biol. Chem. 274,510). Because NF-kB is a pleiotropic transcription factor involved in many physiological functions that are known to be adversely affected by dioxin, the AhR-mediated suppression of NF-kB offers a mechanism for some aspects of hitherto poorly understood dioxin-induced toxic responses, such as the immune suppression and abnormal skin proliferation. Reciprocally, suppression of AhR by NF-kB activation has also offered an underlying mechanism for the long-standing observation that inflammatory cytokines and lipopolysaccharide suppress AhR-regulated cytochrome P450 1A1/1A2 and decrease capacity of xenobiotic (including clinical drugs) metabolism (J. Biol. Chem. 276,39638). In recent studies, by using chromatin immunoprecipitation (CHIP) assay, we have obtained new results revealing that the AhR/NF-kB interaction converges at level of transcription involving (1) control of transcription elongation and (2) chromatin modifications. In AIM I of this proposal we will investigate a mechanism in which AhR/NF-kB interaction regulates cyp1a1 transcription elongation by directly interacting with p-TEFb (positive transcription elongation factor b), which plays a critical role in elongation control. In AIM II, we will investigate histone modifications (histone acetylation and methylation) in response to the diametrically opposing actions of AhR and NF-kB and to establish the residue-specific and combinatorial patterns of histone modifications (histone code) associated with "on and off" states of cyp1a1. We will also investigate a novel AhR interactive protein (identified by CytoTrap yeast two hybrid screening) SUV39H2 methyltransferase for its role in AhR-mediated gene silencing, which may be important for male imprinting. The proposed studies will help us gain mechanistic understandings of the functions of AhR and NF-kB in normal physiology as well as pathogenesis induced by dioxin and related compounds.