Studies of nuclear receptor corepressor, NRIP1, in vitamin A signaling pathways

描述(申请人提供)：维甲酸(RA)是维生素A的生物活性形式，主要通过与核维甲酸受体(RAR)和维甲酸X受体(RXR)结合来调节基因表达。但RAR和RXR的活动最终取决于联合监管机构的招募。该项目最初专注于一种名为核受体相互作用蛋白1(NRIP1，也称为RIP140)的RA依赖的RAR辅抑制子，后来发现它是许多其他转录因子的广谱辅助调节因子。以往的研究进展包括对NRIP1在RA靶向基因、功能结构域和翻译后修饰(PTM)中的广谱协同抑制活性进行了系统的表征，这些修饰改变了NRIP1的性质和亚细胞定位(即输出到细胞质中)，从而引发了超出RA基因调控的额外生物学活性。NRIP1的这些新的非基因组活性在调节脂肪细胞的胰岛素敏感性、葡萄糖摄取、脂肪分解和脂联素分泌方面得到了证实。NRIP1的基因组和非基因组活性共同确立了它在与维生素A信号有关的代谢性疾病的发生和发展中的关键作用。最近的结果显示，NRIP1通过增强M1和抑制M2巨噬细胞在控制先天免疫方面发挥了新的作用。这是由RA调节的，也影响巨噬细胞合成RA的能力。我们假设：i)NRIP1以细胞上下文和染色质基因座依赖的方式作为特定的辅助调节因子发挥作用，即，它可以是辅助激活因子或辅助抑制因子，这取决于它相互作用的转录因子的类型、细胞状态和特定的染色质基因座；ii)NRIP1的S多功能性受PTM调节并与RA的动态平衡有关；以及iii)NRIP1的S多功能性增强了巨噬细胞基因组的可塑性(或表观遗传学)，以响应营养(维生素A)或病理挑战。我们提出了两个目标来解决这些假设。目的1将探讨NRIP1的S在巨噬细胞中的差异协同调节功能的分子机制。目的2通过建立有或无维生素A缺乏的巨噬细胞特异性NRIP1基因敲除小鼠模型，确定NRIP1在先天免疫控制中的生理和营养相关性。该小鼠模型显示炎症减轻(M1)，伤口愈合改善(M2)，RA合成酶RALDH2 mRNA水平升高。我们还将通过使用在特定PTM中突变的各种NRIP1蛋白来采取救援策略。这些结果将是靶向NRIP1的未来翻译应用的关键，例如在维持营养(维生素A)和代谢状态的动态平衡方面，以及在管理代谢性疾病方面。

DESCRIPTION (provided by applicant): Retinoic acid (RA), the biologically active form of vitamin A, acts, primarily, by binding to nuclear RA receptor (RAR) and retinoid receptor X (RXR) to regulate gene expression. But the activities of RAR and RXR ultimately depend on the recruitment of coregulators. The project has initially focused on an RA-dependent RAR corepressor named Nuclear Receptor Interacting Protein 1 (NRIP1, also known as RIP140), which was later found as a wide spectrum coregulator for many other transcription factors. Previous progress includes systemic characterization of NRIP1 with regards to its wide spectrum corepressive activity in RA-targeted genes, functional domains, and post-translational modifications (PTMs) that alter its property and subcellular localization (i.e., export into cytoplasm) to elicit additional biological activities beyond RA gene regulation. These novel non-genomic activities of NRIP1 were demonstrated in regulating insulin sensitivity, glucose uptake, lipolysis and adiponectin secretion in adipocytes. The genomic and non-genomic activities of NRIP1 together establish its critical role in the development and progression of metabolic diseases in relation to vitamin A signaling. More recent results revealed a new role for NRIP1 in controlling innate immunity by enhancing M1 and repressing M2 macrophages. This is modulated by RA and also affects RA synthesis capacity in macrophages. We hypothesize that i) NRIP1 acts as a specific coregulator in a cell-context and chromatin-locus dependent manner, i.e., it can be a coactivator or a corepressor depending upon the type of transcription factor it interacts, the cellular state and specific chromatin loci, ii) NRIP1's versatility is reglated by PTM and is relevant to RA homeostasis, and iii) NRIP1's versatility enhances macrophage genome plasticity (or epigenetics) in response to nutritional (vitamin A) or pathological challenges. We propose two aims to address these hypotheses. Aim 1 will address the molecular mechanisms of NRIP1's differential coregulatory functions in macrophages. Aim 2 will determine the physiological and nutritional relevance of NRIP1 in innate immunity control by exploiting a macrophage-specific NRIP1-knockdown mouse model with or without vitamin A deficiency. This mouse model shows reduced inflammation (M1), improved wound healing (M2) and elevated RA synthesizing enzyme RALDH2 mRNA level. We will also employ rescue strategies by using various NRIP1 proteins mutated in specific PTMs. The results will be key to future translational application of targeting NRIP1, such as in maintaining the homeostasis of nutritional (vitamin A) and metabolic status, and in managing metabolic diseases.