Cellular Mechanisms Controlling Myc Protein Stability

控制 Myc 蛋白稳定性的细胞机制

• 批准号: 7119211
• 负责人: ROSALIE C SEARS
• 金额: $ 37.52万
• 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 2008-06-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/7119211
• 关键词: enzyme activity; oncoproteins; peptidylprolyl isomerase; phosphoprotein phosphatase; phosphorylation; protein degradation; protein localization; serine; threonine; tissue /cell culture; ubiquitin; western blottings

DESCRIPTION (provided by applicant): The Myc oncoprotein is overexpressed in a wide variety of human tumors. In order to maintain normal levels of Myc protein in quiescent cells, newly synthesized Myc is rapidly degraded via the ubiquitin/proteasome pathway. Ubiquitin-mediated degradation of Myc is cell growth regulated, dependent upon the action of two Ras effector pathways. Specifically, Ras activated Raf-MEK-ERK-mediated phosphorylation of Myc at Serine 62 stabilizes Myc, whereas phosphorylation of Myc at Threonine 58 by GSK-3Beta, which is dependent on prior phosphorylation of Serine 62 and is regulated by Ras activated PI3K-Akt, stimulates Myc degradation. In addition, loss of Serine 62 phosphorylation precedes ubiquitination of Myc and the Protein Phosphatase 2A (PP2A) is responsible for this dephosphorylation. PP2A is a conformation-specific phosphatase whose activity is enhanced by the phospho-specific prolyl isomerase Pin1. Pin1 facilitates the removal of the Serine 62 phosphate in Myc by PP2A, thus promoting Myc degradation. These observations have defined a cascade of programmed events that insure the transient accumulation of Myc during the initial phase of a cellular growth response. This grant proposal is intended to further elucidate cellular mechanisms that regulate Myc protein stability, with the goal of better understanding Pin1 and PP2A actions on Myc and discovering other cellular proteins that specifically promote Myc degradation. These Myc-degrading proteins will then be used to inhibit Myc-induced cellular transformation. The following specific aims will be pursued: 1. Investigate cellular mechanisms regulating Myc protein stability, 2. Analyze Pin1 and PP2A regulation of Myc degradation and their contribution to Myc overexpression in human tumors, 3. Identify the E3 ubiquitin ligase involved in Myc degradation and study the effects of forced Myc degradation on Myc-mediated oncogenesis. Research has previously shown that inhibition of one of the cellular events in the genesis of cancer can revert tumor formation. Thus, analysis of molecular mechanisms that control Myc accumulation and identification of proteins that specifically target Myc for degradation could be instrumental in developing specific inhibitors of Myc, with the ultimate goal of designing a therapeutic approach for human cancers that are dependent upon high levels of Myc protein.

描述（由申请人提供）：Myc 癌蛋白在多种人类肿瘤中过度表达。为了维持静止细胞中 Myc 蛋白的正常水平，新合成的 Myc 通过泛素/蛋白酶体途径快速降解。泛素介导的 Myc 降解受细胞生长调节，依赖于两条 Ras 效应通路的作用。具体而言，Ras 激活 Raf-MEK-ERK 介导的 Myc 在丝氨酸 62 处的磷酸化可稳定 Myc，而 GSK-3Beta 对 Myc 在苏氨酸 58 处的磷酸化（依赖于丝氨酸 62 的先前磷酸化并受 Ras 激活的 PI3K-Akt 调节）刺激 Myc 降解。此外，丝氨酸 62 磷酸化的丧失先于 Myc 泛素化，而蛋白磷酸酶 2A (PP2A) 负责这种去磷酸化。 PP2A 是一种构象特异性磷酸酶，其活性可通过磷酸特异性脯氨酰异构酶 Pin1 增强。 Pin1 有助于 PP2A 去除 Myc 中的丝氨酸 62 磷酸盐，从而促进 Myc 降解。这些观察结果定义了一系列程序化事件，确保 Myc 在细胞生长反应的初始阶段短暂积累。该资助提案旨在进一步阐明调节 Myc 蛋白稳定性的细胞机制，目的是更好地了解 Pin1 和 PP2A 对 Myc 的作用，并发现特异性促进 Myc 降解的其他细胞蛋白。这些 Myc 降解蛋白随后将用于抑制 Myc 诱导的细胞转化。我们将追求以下具体目标：1.研究调节Myc蛋白稳定性的细胞机制，2.分析Pin1和PP2A对Myc降解的调节及其对人类肿瘤中Myc过度表达的贡献，3.鉴定参与Myc降解的E3泛素连接酶并研究强制Myc降解对Myc介导的肿瘤发生的影响。此前的研究表明，抑制癌症发生过程中的一种细胞事件可以逆转肿瘤的形成。因此，分析控制 Myc 积累的分子机制并鉴定特异性靶向 Myc 降解的蛋白质可能有助于开发 Myc 的特异性抑制剂，最终目标是设计一种针对依赖高水平 Myc 蛋白的人类癌症的治疗方法。