Context-specific Functions of CDK8

CDK8 的上下文特定功能

• 批准号: 9002041
• 负责人: Jun-yuan Ji
• 金额: $ 30.64万
• 依托单位: TEXAS A&M UNIVERSITY HEALTH SCIENCE CTR
• 依托单位国家: 美国
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-02-25 至 2018-01-31
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/9002041
• 关键词: Address; Animal Model; Binding Proteins; Biological; Cardiovascular Diseases; Colorectal Cancer; Complex; Cues; Cyclin-Dependent Kinases; DNA Binding; Data; Defect; Development; Diabetes Mellitus; Disease; Drosophila genus; Drosophila melanogaster; Ecdysone; Eukaryota; Fatty acid glycerol esters; Feedback; Gene Expression; Gene Targeting; Genes; Genetic Transcription; Goals; Growth; Health; Homeostasis; Homologous Gene; Human; Insulin; Insulin Signaling Pathway; Larva; Link; Lipids; Malignant Neoplasms; Malignant neoplasm of liver; Mediating; Mediator of activation protein; Metabolism; Modeling; Molecular; Mutate; Nuclear Receptors; Nutrient; Obesity; Organism; Pathway interactions; Phenotype; Phosphorylation; Phosphotransferases; Physiological; Play; Proteins; RNA Polymerase II; RXR; Receptor Signaling; Recruitment Activity; Regulation; Regulatory Element; Research; Risk; Role; Signal Pathway; Signal Transduction; Staging; Sterols; Threonine; Time; Trans-Activators; Transcription Coactivator; Transcriptional Regulation; Up-Regulation; Work; cancer therapy; cancer type; cyclin C; ecdysteroid receptor; in vivo; insulin signaling; leukemia; lipid biosynthesis; lipid metabolism; loss of function mutation; melanoma; mutant; novel; programs; protein function; response; steroid hormone receptor; transcription factor; tumorigenesis

DESCRIPTION (provided by applicant): The highly conserved co-factor Mediator Complex, comprising up to 30 subunits, serves as a molecular bridge between transcriptional activators and the core transcription machinery, and is thought to be required for most RNA polymerase II-dependent transcription. As the only known enzymatic subunit of Mediator complex, CDK8 (Cyclin-Dependent Kinase 8) can either positively or negatively regulate transcription. However, whether CDK8 acts as an activator or repressor at every gene, or whether it acts differently at different classes of genes, is a key unexplored field that would dramatically refine our view of how Mediator facilitates transcription. Furthermore, understanding the function and regulation of CDK8 is critical to elucidate how dysregulation of both CDK8 and its regulatory partner CycC (Cyclin C) contributes to a variety of human cancers. Depletion of CDK8 effectively blocks the growth of melanoma and colorectal cancer, which underscores the centrality of CDK8 in gene expression and demonstrates why CDK8 is considered an attractive and promising target for cancer treatment. Currently, how dysregulation of CDK8-CycC contributes to tumorigenesis is poorly understood. To determine the normal and dysregulated functions of these proteins, it is essential to identify the downstream effectors and upstream regulators of CDK8-CycC. Analyses of function and regulation of CDK8 have been hampered by the lack of phenotypes for CDK8 activity in multicellular organisms. We have solved this challenge by using Drosophila, which provides unparalleled sophistication in manipulating CDK8 activity in vivo. We have recently identified two important downstream transactivators of CDK8, SREBP (Sterol Regulatory Element-Binding Protein) and the EcR (Ecdysteroid Receptor), which play essential roles in regulating lipogenesis and developmental maturation, respectively. Our analyses suggest that CDK8 inhibits SREBP-dependent transcription but activates EcR-activated gene expression. Thus, the objective of this proposal is to determine how CDK8 plays fundamentally different roles in modulating the activities of SREBP and EcR. Specifically, we will elucidate how CDK8 regulates SREBP- and EcR-mediated transcription by determining the molecular mechanism underlying the interactions between CDK8 and both SREBP and EcR, and the effects of SREBP and EcR phosphorylation by CDK8 in vivo. We will also examine the physiological regulation of CDK8-CycC by the insulin-signaling pathway and analyze the role of CDK8 in coordinating lipid homeostasis and developmental timing. This study will significantly advance our understanding of how CDK8 plays distinct roles in lipogenesis and development. Because CDK8 and CycC are well conserved in eukaryotes, the molecular mechanisms that we identify in Drosophila are highly likely to provide working models in human studies. The importance of this project is highlighted by the fact that dysregulation of lipid homeostasis durin development is closely linked to diseases such as diabetes, obesity, cardiovascular diseases, and certain types of cancers.

描述（由申请人提供）：高度保守的辅因子介体复合物包含多达 30 个亚基，充当转录激活子和核心转录机制之间的分子桥梁，并且被认为是大多数 RNA 聚合酶 II 依赖性转录所必需的。作为介体复合物中唯一已知的酶亚基，CDK8（细胞周期蛋白依赖性激酶 8）可以正向或负向调节转录。然而，CDK8 是否在每个基因上充当激活子或阻遏子，或者它是否在不同类别的基因上发挥不同的作用，是一个尚未探索的关键领域，它将极大地完善我们对介体如何促进转录的看法。此外，了解 CDK8 的功能和调节对于阐明 CDK8 及其调节伙伴 CycC (Cyclin C) 的失调如何导致多种人类癌症至关重要。 CDK8 的耗竭可有效阻止黑色素瘤和结直肠癌的生长，这强调了 CDK8 在基因表达中的中心地位，并证明了为什么 CDK8 被认为是有吸引力且有前途的癌症治疗靶点。目前，人们对 CDK8-CycC 失调如何导致肿瘤发生知之甚少。为了确定这些蛋白质的正常和失调功能，必须确定 CDK8-CycC 的下游效应子和上游调节子。由于缺乏多细胞生物中 CDK8 活性的表型，对 CDK8 功能和调节的分析受到阻碍。我们通过使用果蝇解决了这一挑战，果蝇在体内操纵 CDK8 活性方面​​提供了无与伦比的复杂性。我们最近发现了 CDK8 的两个重要的下游反式激活因子，SREBP（甾醇调节元件结合蛋白）和 EcR（蜕皮类固醇受体），它们分别在调节脂肪生成和发育成熟中发挥重要作用。我们的分析表明，CDK8 抑制 SREBP 依赖性转录，但激活 EcR 激活的基因表达。因此，本提案的目的是确定 CDK8 如何在调节 SREBP 和 EcR 的活性中发挥根本不同的作用。具体来说，我们将通过确定CDK8与SREBP和EcR之间相互作用的分子机制，以及体内CDK8对SREBP和EcR磷酸化的影响，阐明CDK8如何调节SREBP和EcR介导的转录。我们还将研究胰岛素信号通路对 CDK8-CycC 的生理调节，并分析 CDK8 在协调脂质稳态和发育时序中的作用。这项研究将显着增进我们对 CDK8 如何在脂肪生成和发育中发挥独特作用的理解。由于 CDK8 和 CycC 在真核生物中非常保守，因此我们在果蝇中鉴定的分子机制很可能为人类研究提供工作模型。发育过程中脂质稳态失调与糖尿病、肥胖、心血管疾病和某些类型的癌症等疾病密切相关，这一事实凸显了该项目的重要性。