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

描述（由申请人提供）：视黄酸（RA），维生素A的生物活性形式，主要通过与核RA受体（RAR）和类视黄酸受体X （RXR）结合来调节基因表达。但RAR和RXR的活动最终取决于共同监管者的招募。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依赖性RAR共抑制因子，后来发现它是许多其他转录因子的广谱共调节因子。之前的研究进展包括系统表征NRIP1在RA靶向基因、功能域和翻译后修饰（PTMs）中的广谱共抑制活性，这些修饰会改变其性质和亚细胞定位（即输出到细胞质），从而引发RA基因调控之外的其他生物活性。NRIP1的这些新的非基因组活性在调节胰岛素敏感性、葡萄糖摄取、脂肪分解和脂肪细胞的脂联素分泌中得到证实。NRIP1的基因组和非基因组活性共同确定了其在与维生素A信号相关的代谢性疾病的发生和进展中的关键作用。最近的研究结果揭示了NRIP1通过增强M1和抑制M2巨噬细胞来控制先天免疫的新作用。这是由RA调节的，也影响巨噬细胞的RA合成能力。我们假设i) NRIP1在细胞环境和染色质位点依赖的方式下作为一个特定的共调节因子，即，它可以是一个共激活因子或一个共抑制因子，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位点；ii) NRIP1的多功能性由PTM调节，与RA稳态有关。iii) NRIP1的多功能性增强了巨噬细胞基因组的可塑性（或表观遗传学），以应对营养（维生素A）或病理挑战。我们提出两个目标来解决这些假设。目的1将探讨巨噬细胞中NRIP1差异协同调节功能的分子机制。目的2将通过利用巨噬细胞特异性NRIP1敲低的小鼠模型，确定NRIP1在先天免疫控制中的生理和营养相关性，该模型有或没有维生素a缺乏症。该小鼠模型显示炎症（M1）减少，伤口愈合（M2）改善，RA合成酶RALDH2 mRNA水平升高。我们还将通过使用在特定PTMs中突变的各种NRIP1蛋白来采用拯救策略。这些结果将是未来靶向NRIP1的翻译应用的关键，例如维持营养（维生素A）和代谢状态的稳态，以及管理代谢疾病。

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.