Mutant p53 Gain of Function in Tumorigenesis

p53突变发生在超过50%的所有肿瘤中，包括结肠癌、乳腺癌和肺癌。肿瘤 突变型p53表达水平升高可能与比p53缺失型癌症更差的预后有关。 这项研究计划的长期目标是继续关注突变体的机制， p53参与肿瘤发生。突变型p53增强p53阴性细胞系的致瘤性 这种活性长期以来被认为与其选择性反式激活人类 多药耐药（MDR 1）启动子。我们先前已经确定突变型p53调节内源性 MDR 1和c-myc基因表达，并且这种活性需要完整的C-末端。在此前的融资中， 我们鉴定了这个结构域中的关键赖氨酸，这些赖氨酸在野生型p53中通常会被乙酰化， 细胞应激，这是突变型p53反式激活所必需的。最重要但矛盾的是，我们 证明了该区域是突变型p53促进致瘤性的区域。这些结果解耦合 并代表了考虑突变型p53获得模型的范式转变 的功能。相反，我们的数据支持突变型p53结合并稳定Mdm 2原蛋白的机制。 癌基因蛋白，其可导致非整倍体、增生和最终肿瘤细胞生长。一致 基于这种推理，我们产生了缺乏p19 ARF、Mdm 2和p53的三重敲除小鼠模型。鼠标 来自这些小鼠的胚胎成纤维细胞（MEFs）不是致瘤性的，但值得注意的是，双敲除 缺乏p53和ARF的MEFs容易在裸鼠中形成肿瘤。这些结果表明Mdm 2可能是 是肿瘤细胞生长所必需的。本研究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）Mdm 2 与突变型p53协同致瘤性; 2)Mdm 2对突变型p53的体内作用是什么 功能增益？翻译后修饰是否影响突变型p53功能的获得？我们 研究结果表明野生型和突变型p53的结构要求存在显著差异 功能，这可能为开发治疗癌症的治疗方法提供可利用的基础。

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.