The role of ribosomal proteins in the p53-MDM2 pathway

描述（由申请人提供）：我们研究的长期目标是了解控制细胞增殖、分化和凋亡的化学、分子和细胞机制，这些机制通常作为癌变的早期事件发生，涉及MDM2-p53反馈环。由我以前资助的R01和许多其他小组支持的研究现在已经牢固地建立了核糖体蛋白（RP）的作用，如RPL 11，RPL 5和RPL 23，在p53对各种细胞和环境致癌物或化学物质的反应中，包括内源性和外源性化合物，这些化合物可能会导致核糖体应激，通过直接结合MDM 2并抑制其对p53的E3泛素连接酶活性。此外，已经鉴定了更多的MDM2结合RP，包括RPL 26、RPS7、RPS3和RPS14，在该途径中发挥作用。现在人们认识到，这种核糖体应激-p53通路在细胞生长、凋亡和肿瘤发生中起着至关重要的作用，并且与癌症和癌症易感遗传疾病（如5q综合征和Diamond-Blackfan贫血（DBA））也高度相关。虽然在理解p53反应和肿瘤发生中该通路的生物学重要性方面已经取得了巨大进展，但仍有其他非常重要和具有挑战性的问题有待解决。例如，仍然令人困惑的是，这些RP如何机械地发挥作用以抑制MDM 2。另外，为什么需要如此多的RP来抑制MDM2和激活p53以响应引起核糖体应激的化学物质、致癌物和细胞内异常，这是特别有趣的。最后，这些MDM2结合核糖体蛋白是否在p53激活中发挥作用，作为5q综合征或DBA的发病机制？因此，我们将继续深入探讨这一信号通路在这个更新的申请。根据现有的信息，包括我们的初步研究，我提出，上述MDM2结合RP可能作为一个动态的亚核糖体复合物，而不是单独的，以抑制MDM2的活性，在一个良好的舞蹈方式组装在中央酸性和锌指结构域的E3泛素连接酶在响应RS引起的各种代理或遗传改变，包括代谢紊乱或遗传疾病，导致p53活化。计划有两个具体目标来检验这一假设：1）阐明RP抑制MDM2的结构和功能机制; 2）确定RP是否作为核糖体应激诱导的动态亚核糖体复合物抑制细胞和动物中的MDM2活性。实现这些短期目标将使我们能够更好地理解这些核糖体蛋白如何在细胞或动物中作为动态复合物发挥作用，以抑制MDM2介导的p53泛素化，以及暴露于引起核糖体应激的内源性和外源性化合物后的失活。这些实验的结果不仅为癌症或疾病相关表型提供了可能的机制解释，而且还为使用MDM2的锌指结构域作为未来开发抗癌药物的潜在靶点提供了框架。

DESCRIPTION (provided by applicant): The long-term goal of our research is to understand the chemical, molecular and cellular mechanisms that govern cell proliferation, differentiation, and apoptosis and often occur as the early events of carcinogenesis, involving the MDM2-p53 feedback loop. Research supported by my previously funded R01 and by many other groups has now firmly established the role of ribosomal proteins (RP), such as RPL11, RPL5, and RPL23, in p53 response to various cellular and environmental carcinogens or chemicals, including endogenous and exogenous compounds, which may cause ribosomal stress, by directly binding to MDM2 and inhibiting its E3 ubiquitin ligase activity toward p53. Also more MDM2-binding RPs including RPL26, RPS7, RPS3 and RPS14 have been identified to play a role in this pathway. It is now acknowledged that this ribosomal stress-p53 pathway plays a vital role in cell growth, apoptosis, and tumorigenesis, and is also highly pertinent to cancers and cancer-prone genetic diseases, such as 5q-syndrome and Diamond-Blackfan anemia (DBA). Although a tremendous progress has been made in understanding the biological importance of this pathway in p53 response and tumorigenesis, additional, remarkably important and challenging questions still remain to be addressed. For example, it still remains puzzling how mechanistically these RPs function to inactivate MDM2. Also it is particularly intriguing why so many RPs are needed to suppress MDM2 and to activate p53 in response to ribosomal stress-causing chemical, carcinogens and intracellular abnormalities. Finally, would these MDM2-binding ribosomal proteins play a role in p53 activation as pathogenesis of 5q-syndrome or DBA? Thus, we will continue our in-depth interrogation into this signaling pathway in this renewal application. In light of available information including our preliminary studies, I propose that the aforementioned MDM2- binding RPs may work as a dynamic sub-ribosomal complex, instead of individually, to suppress MDM2 activity in a well choreographic way assembled at the central acidic and Zinc Finger domains of this E3 ubiquitin ligase in response to RS caused by various agents or genetic alterations including metabolic disorder or genetic diseases, leading to p53 activation. Two specific aims are planned to test this hypothesis: 1) To illustrate structural and functional insight into the mechanisms governing the inhibition of MDM2 by RPs; 2) To determine if RPs act as a ribosomal stress-induced dynamic sub-ribosomal complex to suppress MDM2 activity in cells and animals. Achieving these short term goals would allow us to better understanding how these ribosomal proteins function as a dynamic complex in cells or animals to suppress MDM2- mediated p53 ubiquitination and consequent inactivation upon exposure to endogenous and exogenous compounds that cause ribosomal stress. The outcomes from the proposed experiments would not only provide a possible mechanistic explanation for cancer- or disease-related phenotype, but also offer a framework for using the Zinc Finger domain of MDM2 as a potential target for the development of anti-cancer drugs in the future.