Role of Foxa2 in ligand-dependent activation of nuclear receptors

项目摘要/摘要 核受体的激活是一种配体依赖的转录因子家族 广泛从事药理学研究，以开发针对不同医疗条件的药物靶点，包括 代谢性疾病和癌症。而核受体的合成激动剂和拮抗剂 改善许多疾病的症状，临床使用这些化合物会导致频繁的副作用 严重程度不一的影响。II型受体，如FXR、LXR和PPAR，它们 在脂肪酸、胆汁酸、胆固醇和葡萄糖代谢中的作用是永久性的 在原子核中，而不考虑配基状态。关于配基活化的公认范式 对II型受体的研究是一个分两步进行的过程：1)受体与DNA结合在带有辅酶A的复合体中。 2)配体的结合引起构象变化，共- 抑制子/共激活子交换，并启动转录。然而，我们观察到， 开放染色质位置的分布随着核受体的配体激活而改变。在这 项目中，我假设先驱因子Foxa2通过驱逐 核小体在配体激活时使LxRα结合，这挑战了公认的 范例。 考虑到当前的局限性，开发高选择性的核合成配体 没有明显副作用的受体，我们建议一种分离LXR的基因组方法 靶标进入不同的调控模式，其特征是染色质状态和有/没有 FOXA2和LXRα结合位点将允许具有不同生理功能的基因 单独锁定目标。我们将测试Foxa2和LxRα结合在配基过程中是否相互依赖 目标1.我们将确定Foxa2/LxRα相互作用的机制，区分 在AIM 2中的三种可能性之间。LXR可以在没有结合的情况下扮演辅助激活剂的角色 FoxA2和LxRα需要在近端相互作用或远端结合 互动。我们项目的成功完成将改变目前关于激活的想法 配体依赖基因的表达，改变靶向核的药理学方法 新陈代谢所必需的受体。

Project Summary/Abstract Activation of nuclear receptors, a family of ligand-dependent transcription factors, is used extensively in pharmacology to develop drug targets for diverse medical conditions, including metabolic disease and cancer. While synthetic agonists and antagonists of nuclear receptors ameliorate symptoms of many diseases, clinical use of these compounds leads to frequent side effects that range in their severity. Type II receptors, such as FXR, LXR, and PPAR, which function in fatty acid, bile acid, cholesterol, and glucose metabolism, are permanently positioned in the nucleus regardless of the ligand status. The accepted paradigm regarding ligand activation of type II receptors is a two-step process: 1) the receptor is bound to DNA in complex with a co- repressor in absence of the ligand; 2) binding of the ligand induces a conformational change, co- repressor/co-activator exchange, and initiation of transcription. However, we observe that distribution of open chromatin sites changes upon ligand activation of nuclear receptors. In this project, I hypothesize that pioneer factor Foxa2 modulates chromatin accessibility by evicting nucleosomes to enable LXRα binding upon ligand activation, which challenges the accepted paradigm. Considering current limitations to develop highly selective synthetic ligands for nuclear receptors without significant side effects we propose that a genomic approach that separates LXR targets into distinct regulatory modes characterized by chromatin state and presence/absence of Foxa2 and LXRα binding sites will allow for genes with different physiological function to be targeted separately. We will test whether Foxa2 and LXRα binding is interdependent during ligand activation in Aim 1. We will ascertain the mechanism of Foxa2/LXRα interaction, discriminating between three possibilities in Aim 2. LXR could play the role of a co-activator without binding DNA, or both Foxa2 and LXRα need to be bound either in a proximal interaction or distal interaction. Successful completion of our project will change current thinking regarding activation of ligand-dependent gene expression and change the pharmacological approach to target nuclear receptors essential to metabolism.