Role of p53 Missense Mutations on Tumorigenesis in Vivo

描述(由申请人提供)：P53肿瘤抑制因子启动细胞周期停滞、衰老和凋亡程序，以防止细胞异常增殖。所有这三种活性都有助于体内肿瘤的抑制。我们和其他人在缺乏p53的肿瘤中进行了野生型p53重建实验，并观察到肿瘤消退。然而，p53的缺失在人类癌症中并不常见。事实上，超过80%的p53基因改变的肿瘤获得的是p53的错义突变，而不是p53的缺失。这一区别是至关重要的，因为p53错义突变在体内明显表现出功能获得和/或显性负活动。此外，编码P53抑制物的MDM2和MDM4的过度表达也是肿瘤发生中的常见事件，并导致P53途径的失活。这项提议的目的是在具有人类癌症中观察到的变化的肿瘤细胞的背景下，从基因上重建野生型p53。来自我的实验室的耐人寻味的初步数据表明，由于p53突变而不是p53缺失而发展起来的肿瘤对野生型p53的重新激活做出了不同的反应：p53突变背景中的肿瘤反应是沉默的，并通过未知的机制导致肿瘤停滞，而不是肿瘤退化。目标1专注于解开这些机制。虽然高水平MDM2或MDM4的肿瘤尚未重新激活P53，但我们从它们对P53的精细调控推测，高水平的MDM2和MDM4将淹没重新引入的P53的活性。我们计划在MDM2和MDM4水平高的肿瘤中增加野生型P53的水平(目标2)。最后，数据表明，肿瘤周围细胞的基因型别影响肿瘤生长和治疗反应。目前的小鼠模型没有解决周围正常组织的作用，因为转基因小鼠的所有细胞都有p53缺陷。我们计划创建和评估一个体细胞模型，它概括了正常细胞包围的单个细胞中的p53突变(目标3)。 公共卫生相关性：P53的细胞周期停滞、衰老和凋亡活性有助于肿瘤抑制，正常细胞必须克服这些活性才能增殖并形成肿瘤细胞。在人类癌症中，多种机制使P53途径失活。这项提议的目的是在具有人类癌症中观察到的变化的肿瘤细胞的背景下，从基因上重建野生型p53。

DESCRIPTION (provided by applicant): The p53 tumor suppressor initiates cell cycle arrest, senescence, and apoptosis programs to prevent abnormal cell proliferation. All three activities contribute to tumor suppression in vivo. We and others have performed wild-type p53 reconstitution experiments in tumors that lacked p53 and observed tumor regression. Deletions of p53 are, however, uncommon in human cancers. In fact, more than 80% of tumors with alterations of the p53 gene acquire missense mutations in p53 rather than p53 deletions. This distinction is critical because p53 missense mutations clearly display gain-of-function and/or dominant-negative activities in vivo. Additionally, over-expression of MDM2 and MDM4 which encode p53 inhibitors are also common events in tumorigenesis and contribute to inactivation of the p53 pathway. The objective of this proposal is to genetically reconstitute wild-type p53 in the context of a tumor cell with the kinds of alterations that are observed in human cancers. Intriguing preliminary data from my laboratory indicates that tumors that develop as a result of a p53 mutation rather than loss of p53 respond differently to reactivation of wild-type p53: tumor responses in the p53 mutant background are muted and lead to tumor stasis, not tumor regression, by unknown mechanisms. Aim 1 is focused on unraveling these mechanisms. Although p53 has not yet been reactivated in tumors with high levels of Mdm2 or Mdm4, we surmise from their exquisite regulation of p53 that high levels of Mdm2 and Mdm4 would swamp out the activities of a reintroduced p53. We plan to increase wild-type p53 levels in tumors with high levels of Mdm2 and Mdm4 (aim 2). Lastly, data suggest that the genotype of the cells surrounding the tumor affects tumor growth and therapeutic response. Current mouse models do not address the role of the surrounding normal tissue as all cells of the genetically modified mouse have p53 defects. We plan to create and evaluate a somatic model that recapitulates a p53 mutation in a single cell surrounded by normal cells (aim 3). PUBLIC HEALTH RELEVANCE: The cell cycle arrest, senescence, and apoptosis activities of p53 contribute to tumor suppression and a normal cell must overcome these activities to proliferate and form a tumor cell. Multiple mechanisms inactivate the p53 pathway in human cancers. The objective of this proposal is to genetically reconstitute wild-type p53 in the context of a tumor cell with the kinds of alterations that are observed in human cancers.