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

描述（由申请人提供）：维甲酸（RA）是维生素A的生物活性形式，主要通过与核RA受体（RAR）和类维生素A受体X（RXR）结合来调节基因表达。但是RAR和RXR的活动最终取决于辅调节因子的募集。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辅阻遏物，后来发现它是许多其他转录因子的广谱辅调节因子。先前的进展包括NRIP1的系统表征，涉及其在RA靶向基因、功能结构域和改变其性质和亚细胞定位的翻译后修饰（PTM）中的广谱共抑制活性（即，输出到细胞质中）以引发RA基因调控之外的额外生物活性。这些新的非基因组活性的NRIP1被证明在调节胰岛素敏感性，葡萄糖摄取，脂肪分解和脂联素分泌的脂肪细胞。NRIP1的基因组和非基因组活性共同确立了其在与维生素A信号传导相关的代谢疾病的发展和进展中的关键作用。最近的结果揭示了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。这是调节RA，也影响RA的合成能力在巨噬细胞。我们假设i）NRIP1以细胞环境和染色质基因座依赖性方式作为特异性共调节因子，即，它可以是辅激活子或辅阻遏子，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的多功能性由PTM调节，并且与RA稳态相关，和iii）NRIP1的多功能性增强巨噬细胞基因组可塑性（或表观遗传学）以响应营养（维生素A）或病理挑战。我们提出两个目标来解决这些假设。目的1阐明NRIP1在巨噬细胞中差异协同调节功能的分子机制。目的2将通过利用具有或不具有维生素A缺乏的巨噬细胞特异性NRIP1敲除小鼠模型来确定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）和RA合成酶RALDH 2 mRNA水平升高。我们还将通过使用在特定PTM中突变的各种NRIP1蛋白来采用拯救策略。这些结果将是靶向NRIP1的未来翻译应用的关键，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.