Functional Mimicry of the p53 C-terminal Tail by the Ubiquitin-like Molecule SUMO

描述（由申请人提供）：p53肿瘤抑制因子在预防肿瘤发生中起关键作用。p53通常响应于各种应激信号，并且在细胞中激活p53的主要公认触发因素是由于癌基因产物的存在而导致的DNA损伤或DNA复制应激的存在。一旦激活，p53可以执行不同的程序，包括衰老，凋亡和细胞周期停滞。众所周知，翻译后修饰影响p53将细胞导向这些不同细胞程序的能力，这取决于信号的性质。在本申请中，我们研究了p53的α-翻译后修饰，sumo化的后果。SUMO是一种与多种靶底物共价结合的泛素样分子。通过进行这些研究，我们已经发现，sumoylated p53调节的表达水平的酶，酸还原酮双加氧酶，ARD/ADI 1的蛋氨酸补救途径的功能。这是调节甲硫氨酸再循环的关键途径。这一途径的一个重要副产物是S-腺苷甲硫氨酸（SAM），它是所有涉及DNA和蛋白质甲基转移酶的甲基转移反应的主要甲基供体。对这一代谢途径的兴趣源于几个观察结果。首先，大多数癌细胞系是甲硫氨酸依赖性的，有证据表明MTA途径的改变导致了这种依赖性。其次，甲基硫代腺苷（MTA），SAM代谢的产物，对DNA复制和细胞周期进程有重要影响，这是在肿瘤细胞中改变。第三，酒精中毒的肿瘤易感性影响，以及众所周知的几种饮食因素，如叶酸，维生素B12和co-balamine的肿瘤保护作用，已与蛋氨酸的代谢有关。本申请中提供的证据首次表明，p53和SUMO通过ARD/ADI 1作为蛋氨酸代谢的潜在调节剂。这一途径的调节可以反过来改变对饮食因素的易感性，影响SAM水平，从而导致表观遗传变化，提供癌症易感环境。这种探索性应用的范围是测试这些假设，并了解p53和SUMO调节蛋氨酸代谢的分子机制。这些研究收集的数据有可能确定一个新的循环，通过这个循环，p53肿瘤抑制因子直接影响细胞对营养物质的反应，从而影响癌症易感性。 癌症是一系列异常事件的表现，涉及遗传和表观遗传变化。表观遗传变化是通过修饰与DNA密切接触的蛋白质（如染色质）的活性以及通过DNA本身的甲基化来实现的。产生这种变化的各种调节蛋白，包括DNA甲基转移酶、甲基-CpG结合蛋白和染色质重塑因子，利用氨基酸甲硫氨酸代谢的生物产物SAM进行反应。现在人们已经认识到，表观遗传事件的变化可以解释许多环境和饮食因素对癌症易感性的影响。涉及DNA和蛋白质的甲基化反应异常是大多数癌症的标志。我们已经确定了一个潜在的反馈回路，通过这个回路，一个典型的肿瘤抑制因子p53可能直接影响细胞对营养物质的反应，从而影响癌症易感性。本申请的一般范围是更好地理解肿瘤抑制途径、饮食和翻译后修饰之间的联系，这些修饰有可能影响表观遗传变化。

DESCRIPTION (provided by applicant): The p53 tumor suppressor plays a key role in preventing tumorigenesis. p53 usually responds to various stress signals, and a major recognized trigger for activating p53 in cells is the presence of DNA damage or of DNA-replication stress due to the presence of oncogene products. Once activated, p53 can execute different programs, including senescence, apoptosis and cell cycle arrest. It is well recognized that post-translational modifications affect the ability of p53 to direct cells towards these different cellular programs, depending upon the nature of the signal. In this application we have studied the consequences of a-post-translational modifications of p53, sumoylation. SUMO is a ubiquitin-like molecule which is covalently attached to a variety of target substrates. By conducting these studies we have discovered that sumoylated p53 regulates the expression levels of an enzyme, acireductone dioxygenase, ARD/ADI1 that functions in the methionine salvage pathway. This is a key pathway that regulates the recycling of methionine. One important by-product of this pathway is S-adenosyl methionine (SAM), the major methyl donor for all trans-methylation reactions that involve DNA- and protein-methyltransferases. Interest in this metabolic pathway stems from several observations. First, the majority of cancer cell lines are methionine dependent, and there is evidence that alterations in the MTA pathway account for such dependency. Second, methylthioadenosine (MTA), a product of SAM metabolism, has important effects on DNA replication and cell cycle progression, which are altered in tumor cells. Third, the tumor-predisposing effects of alcoholism, as well as the well-known tumor-protective effects of several dietary factors, such as folates, vitamine B12 and co-balamine, have been linked to the metabolism of methionine. Evidence presented in this application implicate, for the first time, p53 and SUMO as potential modulators of the metabolism of methionine, via ARD/ADI1. Regulation of this pathway could in turn alter susceptibility to dietetic factors, affect SAM levels, and consequently, lead to epigenetic changes that provide a cancer-predisposing milieu. The scope of this exploratory application is the testing of these hypotheses and to understand the molecular mechanisms by which p53 and SUMO regulate the metabolism of methionine. Data gathered with these studies have the potential to identify a novel loop by which the p53 tumor suppressor directly influences cellular responses to nutrients and, thus, cancer predisposition. PUBLIC HEALTH RELEVANCE: Cancer is the manifestation of a series of abnormal events that involve both genetic and epigenetic changes. Epigenetic changes are achieved via modifications of the activity of proteins that are in intimate contact with the DNA, such as chromatin, and via methylation of the DNA itself. A variety of regulatory proteins that produce such changes, including DNA methyltransferases, methyl-CpG binding proteins, and chromatin remodeling factors, utilize a bio-product of the metabolism of the amino acid methionine, called SAM, for their reactions. It is now well recognized that changes in epigenetic events account for the effects of many environmental and dietetic factors on cancer predisposition. An abnormality of methylation reactions that involve both DNA and proteins is a hallmark of most cancers. We have identified a potential feedback-loop by which a prototypical tumor suppressor, p53, might directly influence cellular responses to nutrients and, thus, cancer predisposition. The general scope of this application is to develop a better understanding of the link between tumor-suppressor pathways, diet, and post-translational modifications that have the potential to influence epigenetic changes.