Cellular Mechanisms Controlling Myc Protein Stability

控制 Myc 蛋白稳定性的细胞机制

• 批准号: 8458583
• 负责人: ROSALIE C SEARS
• 金额: $ 32.29万
• 依托单位: OREGON HEALTH & SCIENCE UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2003
• 资助国家: 美国
• 起止时间: 2003-09-30 至 2015-04-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/8458583
• 关键词: AXIN1 gene; Address; Affect; Animal Model; Binding; Biological; Cancer Model; Cancer Patient; Cancer cell line; Cell Culture Techniques; Cell physiology; Cells; Complex; Coupled; Data; Degradation Pathway; Development; Future; Gene Targeting; Genetic Transcription; Goals; Human; In Vitro; Knowledge; Lesion; Link; Malignant Neoplasms; Mediating; Mitogens; Molecular; Mutation; Oncogene Proteins; Oncogenic; Pathway interactions; Peptidylprolyl Isomerase; Phosphorylation; Phosphorylation Site; Phosphotransferases; Play; Positioning Attribute; Post-Translational Regulation; Primary Neoplasm; Process; Proline; Protein Phosphatase 2A Regulatory Subunit PR53; Protein phosphatase; Proteins; Proteolysis; Proto-Oncogene Proteins c-myc; Regulation; Research; Role; Sampling; Scaffolding Protein; Serine; Signal Pathway; Site; Testing; Threonine; Time; Tissues; Translations; Tumor Suppressor Proteins; Ubiquitin; Ubiquitination; Withdrawal; c-myc Genes; cancer cell; cell growth; in vivo; inorganic phosphate; mRNA Stability; mouse model; novel; overexpression; promoter; protein expression; public health relevance; response; therapeutic target; transcription factor; tumor; tumorigenesis; tumorigenic; ubiquitin ligase; ubiquitin-protein ligase

DESCRIPTION (provided by applicant): The c-Myc oncoprotein is a critical regulator of cellular function and its overexpression has been tightly linked to human cancer. Expression of c-Myc is regulated at many levels including protein stability. A complex signaling pathway affects c-Myc protein stability through the sequential phosphorylation of two highly conserved sites, Serine 62 (S62) and Threonine 58 (T58). These phosphorylation sites have opposing effects on c-Myc stability, where phosphorylation at S62 can stabilize c-Myc; subsequent phosphorylation at T58 promotes c-Myc ubiquitin-dependent proteolysis. Mitogen stimulation induces S62 phosphorylation through a number of kinases including MAPKs and CDKs to allow transient stabilization of c-Myc following a cell growth response. Protein levels are then downregulated through T58 phosphorylation, mediated by GSK3 . The dually phosphorylated form of c-Myc is then recognized by a phosphorylation-directed prolyl isomerase, Pin1, which catalyzes a cis to trans isomerization at Proline 63. This allows the trans-specific protein phosphatase PP2A-B56 to remove the stabilizing S62 phosphate. T58 phosphorylated c-Myc is then a substrate for poly- ubiquitination and degradation by the E3 ubiquitin ligase SCFFBW7. Recent research demonstrates that the Axin1 scaffold protein coordinates this c-Myc degradation pathway. Importantly, this process can be impaired in human cancer as multiple tested samples show enhanced S62 phosphorylation, reduced T58 phosphorylation, and increased c-Myc stability; and lesions in Axin1 have been identified in human cancers with stabilized c-Myc. Moreover, Axin1 is present at Myc target gene promoters suggesting that c-Myc activity and degradation may be coupled. New data demonstrates that Pin1 plays a dual role in regulating c-Myc, both enhancing its transcriptional activity and stimulating its turnover. The central hypothesis of this proposal is that Pin1 increases the transcriptional activity of S62 phosphorylated c-Myc by enhancing its recruitment to promoters, where it is subsequently shut off at the promoter by an Axin1-nucleated destruction complex containing GSK3 , PP2A-B56 and Pin1, and this process can be deregulated in cancer cells potentiating Myc's oncogenic activity. This hypothesis will be tested with the following three specific aims: 1) examine a role for Pin1 in coordinating c-Myc transcriptional activity with Axin1-mediated destruction; 2) analyze regulation of the Axin1-Myc destruction complex in non-transformed and cancer cells; and 3) investigate the biological relevance of Pin1-mediated activation and Axin1-mediated degradation of c- Myc in human cancer and model this in vitro and in vivo. Completion of these aims will reveal novel molecular mechanisms that control c-Myc activity and expression involving the tumor suppressor protein, Axin1, and the multifunctional Pin1 prolyl-isomerase. Together, these aims will provide critical new information about cellular mechanisms that regulate the tumorigenic potential of the c-Myc oncoprotein, which could greatly aid in the search for c-Myc targeted therapy to treat cancer patients.

描述（由申请人提供）：c-Myc癌蛋白是细胞功能的关键调节因子，其过表达与人类癌症密切相关。c-Myc的表达在许多水平上受到调节，包括蛋白质稳定性。一个复杂的信号通路通过两个高度保守位点丝氨酸62（S62）和苏氨酸58（T58）的连续磷酸化影响c-Myc蛋白的稳定性。这些磷酸化位点对c-Myc稳定性有相反的影响，其中S62处的磷酸化可以稳定c-Myc;随后T58处的磷酸化促进c-Myc泛素依赖性蛋白水解。促分裂原刺激通过许多激酶（包括MAPK和CDK）诱导S62磷酸化，以允许c-Myc在细胞生长应答后的瞬时稳定。然后通过T58磷酸化下调蛋白水平，由GSK 3介导。然后，c-Myc的双重磷酸化形式被磷酸化指导的脯氨酰异构酶Pin 1识别，Pin 1催化脯氨酸63处的顺式至反式异构化。这允许反式特异性蛋白磷酸酶PP 2A-B56去除稳定的S62磷酸。然后，T58磷酸化的c-Myc是E3泛素连接酶SCFFBW 7的聚泛素化和降解的底物。最近的研究表明，Axin 1支架蛋白协调这一c-Myc降解途径。重要的是，这一过程可能在人类癌症中受损，因为多个测试样品显示S62磷酸化增强，T58磷酸化减少，c-Myc稳定性增加;并且在具有稳定c-Myc的人类癌症中已经鉴定出Axin 1中的病变。此外，Axin 1存在于Myc靶基因启动子处，表明c-Myc活性和降解可能是偶联的。新的数据表明，Pin 1在调节c-Myc中起着双重作用，既增强其转录活性，又刺激其周转。该提议的中心假设是Pin 1通过增强其向启动子的募集来增加S62磷酸化的c-Myc的转录活性，随后在启动子处通过含有GSK 3、PP 2A-B56和Pin 1的Axin 1有核破坏复合物关闭，并且该过程可以在增强Myc的致癌活性的癌细胞中去调节。该假设将通过以下三个具体目标进行检验：1）检查Pin 1在协调c-Myc转录活性与Axin 1介导的破坏中的作用; 2）分析非转化细胞和癌细胞中Axin 1-Myc破坏复合物的调节;以及3）研究Pin 1介导的c-10活化和Axin 1介导的c-10降解的生物学相关性。Myc在人类癌症中的作用以及体外和体内模型。这些目标的完成将揭示新的分子机制，控制c-Myc的活性和表达，涉及肿瘤抑制蛋白，Axin 1，和多功能Pin 1脯氨酰异构酶。总之，这些目标将提供有关调节c-Myc癌蛋白致瘤潜力的细胞机制的重要新信息，这将极大地有助于寻找c-Myc靶向治疗癌症患者的方法。