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，以防止异常细胞增殖。所有三种活性都有助于体内肿瘤抑制。我们和其他人已经在缺乏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了p53的错义突变，而不是p53缺失。这种区别是至关重要的，因为p53错义突变在体内清楚地显示出功能获得性和/或显性负性活性。此外，编码p53抑制剂的MDM 2和MDM 4的过表达也是肿瘤发生中的常见事件，并有助于p53途径的失活。该提案的目的是在肿瘤细胞中遗传重建野生型p53，其具有在人类癌症中观察到的各种改变。来自我实验室的有趣的初步数据表明，由于p53突变而不是p53缺失而发展的肿瘤对野生型p53的重新激活的反应不同：在p53突变背景下的肿瘤反应是沉默的，并通过未知的机制导致肿瘤停滞，而不是肿瘤消退。目标1的重点是解开这些机制。尽管在高水平Mdm 2或Mdm 4的肿瘤中p53还没有被重新激活，但我们从它们对p53的精细调节中推测，高水平的Mdm 2和Mdm 4将淹没重新引入的p53的活性。我们计划在具有高水平Mdm 2和Mdm 4的肿瘤中增加野生型p53水平（目的2）。最后，数据表明肿瘤周围细胞的基因型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。我们计划建立和评估一个体细胞模型，在一个被正常细胞包围的单细胞中重现p53突变（目标3）。

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).