MLL3/4-complexes in nuclear receptor-mediated metabolism

MLL3/4 复合物在核受体介导的代谢中的作用

• 批准号: 8723155
• 负责人: JAE W LEE
• 金额: $ 33.36万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-08-20 至 2017-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8723155
• 关键词: Bile Acid Biosynthesis Pathway; Bile Acids; Biochemical; Biological Models; Cell membrane; Chromatin; Complex; Cyclic AMP; Defect; Dimensions; Dipeptidyl Peptidases; Down-Regulation; Energy Metabolism; Enzymes; Funding; Gene Expression; Gene Targeting; Genes; Genetic; Genetic Transcription; Glucose; Hepatic; Homeostasis; Iodothyronine Deiodinase; Knockout Mice; Ligands; Link; Liver; Lysine; Mediating; Metabolic; Metabolic Diseases; Metabolic syndrome; Metabolism; Methylation; Methyltransferase; Modeling; Molecular; Mus; Mutant Strains Mice; Names; Nuclear Receptors; Outcome Study; Pathway interactions; Peroxisome Proliferator-Activated Receptors; Phenotype; Physiological; Play; Recruitment Activity; Regulation; Role; Signal Pathway; Signal Transduction; Societies; Testing; Thyroid Hormones; Transactivation; Transcriptional Activation; Transgenic Mice; Up-Regulation; base; blood glucose regulation; chromatin immunoprecipitation; chromatin remodeling; drug development; genome-wide; glucagon-like peptide; improved; in vivo; insulin secretagogues; mutant; novel; pandemic disease; public health relevance; receptor; research study; response; tool; transcriptome sequencing

DESCRIPTION (provided by applicant): The homeostatic regulation of bile acid (BA) signaling requires a complex network of nuclear receptors (NRs), but their coactivators that remodel chromatin and regulate gene transcription in response to BA signaling are poorly understood. Our discovery of the NR coactivator ASC-2 led to our subsequent purification of 'ASC-2- complex' (ASCOM), the first mammalian complex that contains the H3 lysine 4 methyltransferase (H3K4MT) MLL3 or its paralogue MLL4. Later, ASCOM has also been found to contain the H3-lysine 27-demethylase (H3K27DM) UTX. Trimethylated H3K4 and trimethylated H3K27 mark transcriptionally active and inactive chromatin, respectively. Thus, ASCOM contains two types of enzymes that are linked to transcriptional activation. Excitingly, we found that the major physiological function of ASCOM is to regulate metabolism under a variety of different conditions primarily attributed by the ability of ASC-2 to recruit ASCOM to multiple metabolic NRs, including PPAR?, LXRs, and FXR, the NR for BAs. In particular, we discovered that ASCOM functions as a critical coactivator for FXR in regulating BA synthesis. Consistently, one of the most salient phenotypes of our MLL3 mutant mice was a significant increase in BA levels, suggesting that MLL3-mediated H3K4MT activity of ASCOM is essential for maintaining BA homeostasis. Intriguingly, our MLL3 mutant mice also displayed favorable metabolic profiles, which we propose is via defects in the ability of ASCOM to antagonize signaling by Tgr5, the plasma membrane receptor for BAs. Tgr5 triggers a signaling pathway that leads to upregulation of 'the cyclic-AMP-dependent thyroid hormone activating enzyme type 2 iodothyronine deiodinase' (D2) and to enhance secretion of glucagon-like peptide-1 (GLP-1), an insulin secretagogue, thereby resulting in enhanced energy expenditure and improved glucose homeostasis. Our preliminary results suggest that ASCOM inhibits Tgr5 signaling not only through decreasing BA levels but also directly through the regulation of a gene encoding a key modifier of Tgr5 signaling, 'dipeptidyl peptidase-4' (Dpp4), which inactivates GLP-1. Together, these results support the central hypothesis of this study: ASCOM functions as a master coactivator of 'the homeostatic regulation of BA signaling' by controlling the expression of genes in multiple pathways that regulate BA metabolism and signaling. This renewal has two objectives: 1) We will test the mechanisms of action for ASCOM in NR transactivation (primarily for FXR and RAR) by using the discoveries made during the previous funding period. 2) By focusing specifically on the role of ASCOM in BA homeostasis, we will establish a new paradigm for understanding the diverse metabolic roles of ASCOM. This is a well-integrated study, as the first part of the study is critical to understand the molecular basis for the functio of ASCOM in BA homeostasis and signaling (the second part of the study). We will tackle these two issues in three specific aims, utilizing a combination of biochemical, cellular and genetic approaches. This study will help us to understand the molecular basis for how NRs regulate transcription and metabolism.

描述（由申请人提供）：胆汁酸（BA）信号传导的稳态调节需要复杂的核受体（NR）网络，但对其响应BA信号传导重塑染色质和调节基因转录的共激活因子了解甚少。我们对NR共激活因子ASC-2的发现导致我们随后纯化了“ASC-2-复合物”（ASCOM），这是第一个含有H3赖氨酸4甲基转移酶（H3 K4 MT）MLL 3或其副产物MLL 4的哺乳动物复合物。后来，ASCOM也被发现含有H3-赖氨酸27-脱甲基酶（H3 K27 DM）UTX。三甲基化H3 K4和三甲基化H3 K27分别标记转录活性和非活性染色质。因此，ASCOM包含两种与转录激活相关的酶。令人兴奋的是，我们发现ASCOM的主要生理功能是在各种不同条件下调节代谢，这主要归因于ASC-2将ASCOM募集到多种代谢NR（包括PPAR？）的能力，LXR和FXR，BA的NR。特别地，我们发现ASCOM作为FXR调节BA合成的关键共活化剂发挥作用。一致地，我们的MLL 3突变小鼠的最显著的表型之一是BA水平的显著增加，表明MLL 3介导的H3 K4 MT活性的ASCOM是维持BA稳态所必需的。有趣的是，我们的MLL 3突变小鼠也显示出良好的代谢特征，我们认为这是通过ASCOM拮抗Tgr 5（BA的质膜受体）信号传导的能力缺陷。Tgr 5触发信号通路，导致“环AMP依赖性甲状腺激素激活酶2型碘甲腺原氨酸脱碘酶”（D2）上调，并增强胰高血糖素样肽-1（GLP-1）（一种胰岛素促分泌素）的分泌，从而导致能量消耗增加和葡萄糖稳态改善。我们的初步研究结果表明，ASCOM抑制Tgr 5信号不仅通过降低BA水平，但也直接通过调节一个基因编码的Tgr 5信号的关键修饰剂，'二肽基肽酶-4'（Dpp 4），它失活GLP-1。总之，这些结果支持本研究的中心假设：ASCOM功能作为一个主辅激活因子的“BA信号的稳态调节”通过控制基因的表达在多个途径，调节BA代谢和信号。本次更新有两个目标：1）我们将通过使用上一个资助期的发现来测试ASCOM在NR反式激活（主要是FXR和RAR）中的作用机制。2)通过特别关注ASCOM在BA稳态中的作用，我们将建立一个新的范式来理解ASCOM的多种代谢作用。这是一项整合良好的研究，因为研究的第一部分对于理解ASCOM在BA稳态和信号传导中的功能的分子基础至关重要（研究的第二部分）。我们将解决这两个问题在三个具体目标，利用生物化学，细胞和遗传方法的组合。这项研究将有助于我们了解核受体如何调节转录和代谢的分子基础。