Mutant p53 Gain of Function in Tumorigenesis

超过50%的肿瘤中存在P53基因突变，包括结肠癌、乳腺癌和肺癌。肿瘤 突变型P53的高水平表达可能与P53缺失的癌症相比预后更差。 这项研究计划的长期目标继续集中在突变株 P53与肿瘤的发生有关。突变型P53增强P53阴性细胞系的致瘤能力 长期以来，这种活动一直被认为与其选择性激活人类的能力有关 多药耐药(MDR1)启动子。我们先前证实突变型P53调节内源性 Mdr1和c-myc基因的表达，这种活性需要一个完整的C末端。在之前的资助中 期间，我们确定了该结构域中的关键赖氨酸，这些赖氨酸在野生型p53中通常在 细胞压力，这是突变型P53反式激活所必需的。最重要但又矛盾的是，我们 证明该区域对于突变型P53促进肿瘤的致瘤性是必不可少的。这些结果是不一致的 肿瘤致瘤性的反式激活，代表着考虑突变型p53获得模型的范式转变 功能的一部分。相反，我们的数据支持一种机制，通过这种机制，突变的p53结合并稳定MDM2原- 癌基因蛋白，这可能导致非整倍体，增殖，并最终肿瘤细胞生长。一致 根据这一推理，我们建立了一个缺失p19ARF、MDM2和P53的三重基因敲除小鼠模型。小白鼠 来自这些小鼠的胚胎成纤维细胞(MEF)不会致瘤，但值得注意的是，双基因敲除 同时缺乏P53和ARF的MEF很容易在裸鼠体内形成肿瘤。这些结果表明，MDM2可能是 是肿瘤细胞生长所必需的。这项研究中提出的实验就是为了验证这一假设 通过解决以下具体问题使用基于细胞和动物的方法：1)MDM2 与突变型p53在致瘤性上的协同作用？2)MDM2对突变型p53的体内贡献是什么？ 功能的获得；以及3)翻译后修饰是否影响突变型P53的功能获得？我们的 研究结果显示野生型和突变型P53的结构要求有显著差异 功能，这可能为开发治疗癌症的方法提供可开发的基础。

Mutation of p53 occurs in more than 50% of all tumors, including those of colon, breast and lung. Tumors expressing elevated levels of mutant p53 may be associated with a worse prognosis than p53-null cancers. The long.term goal of this research program continues to focus on the mechanisms by which mutant p53 contributes to tumorigenesis. Mutant p53 enhances the tumorigenic potential of p53-negative cell lines and this activity has long been considered to be linked to its ability to selectively transactivate the human multi-drug resistance (MDR1) promoter. We previously established that mutant p53 regulates endogenous MDR1 and c-myc gene expression and that this activity requires an intact C-terminus. In the previous funding period we identified key lysines in this domain, which normally become acetylated in wild-type p53 during cell stress, that are required for mutant p53-transactivation. Most importantly but paradoxically, we demonstrated that this region is dispensable for mutant p53 to promote tumorigenicity. These results uncouple transactivation from tumorigenicity and represent a paradigm shift in considering models for mutant p53 gain of function. Rather, our data support a mechanism by which mutant p53 binds and stabilizes the Mdm2 proto- oncogene protein, which could lead to aneuploidy, hyperplasia and ultimately tumor cell growth. Consistent with this reasoning, we generated a triple knockout mouse model that lacks p19 ARF,Mdm2 and p53. Mouse embryo fibroblasts (MEFs) derived from these mice are not tumorigenic, but remarkably, double knockout MEFs lacking both p53 and ARF readily form tumors in nude mice. These results suggest that Mdm2 may be required for tumor cell growth. The experiments proposed in this study are designed to test this hypothesis using cell and animal based approaches by addressing the following specific questions: 1) Does Mdm2 cooperate with mutant p53 in tumorigenicity?; 2) What is the in vivo contribution of Mdm2 to mutant p53 gain of function?; and 3) Do post-translational modifications influence mutant p53 gain of function? Our findings demonstrate significant differences in the structural requirements for wild-type and mutant p53 function, which may provide an exploitable basis for developing therapeutic approaches to treating cancer.