MUTANT P53 GAIN OF FUNCTION IN TURMORIGENISIS

肿瘤的发生通常以多种遗传改变为特征 同时存在于显性癌基因和肿瘤抑制基因中。的p53 肿瘤抑制基因是人类中最常见的突变基因， 癌野生型p53肿瘤抑制基因产物被认为是 而突变型p53功能作为一种 癌基因并促进肿瘤发生。突变型p53可能在 肿瘤发生通过三种不同的机制：1）通过野生型的损失 肿瘤抑制功能; 2）野生型p53蛋白的失活， 反式显性否定方式; 3）通过功能的增益， 促进细胞的致瘤潜力。长期目标是 研究建议是为了进一步了解 突变型p53促进恶性转化。 关于突变型p53表达的“功能获得”， 促进致瘤性。突变型p53功能表型的获得是 支持这一发现的是，外源突变型p53在一个细胞中的表达， 非致瘤性且缺乏内源性p53蛋白的细胞系可 将这些细胞转化为致瘤细胞系。此外，突变 p53蛋白必须定位于细胞核才能增强其致瘤性 这表明突变型p53可能是细胞凋亡的调节因子， 基因表达。与这一假设相一致，突变的人p53 与野生型p53蛋白不同， 人多药耐药启动子在瞬时转染试验中的表达 使用缺乏内源性p53蛋白的细胞。 为了进一步了解突变型p53功能获得性 表型，我们特别建议详细的分子机制， 突变型p53作为基因表达的反式激活因子， 讨论下列问题： 1)突变型p53转基因需要MDR启动子的哪些DNA序列 激励？ 2)突变型p53是否能稳定激活内源性MDR基因 转染细胞 3)反式激活需要突变型p53的哪些结构域？ 4)p53相关蛋白mdm-2介导或调节突变型p53吗 反式激活功能？ 拟议的研究将有助于我们对如何 突变型p53可能与其他因子，如MDM-2， 以促进致瘤性。

Tumorigenesis is generally charactenzed by multiple genetic alterations occurring in both dominant oncogenes and tumor suppressor genes. The p53 tumor suppressor gene is the most commonly mutated gene detected in human cancer. The wild-type p53 tumor suppressor gene product is believed to act as a safeguard against cancer whereas, mutant p53 fiinctions as an oncogene and promotes tumorigenesis. Mutant p53 may function in tumorigenesis by three different mechanisms: 1) By a loss of wild-type tumor suppressor function; 2) Inactivation of the wild-type p53 protein in a trans-dominant negative manner; and 3) by a gain of fiinction that promotes the tumorigenic potential of the cell. The long term goal of this research proposal is to further our understanding of the function of mutant p53 in promoting malignant transformation. Little is known about the "gain of fiinction" expressed by mutant p53 in promoting tumorigenicity. The gain of fiinction phenotype of mutant p53 is supported by the finding that the expression of exogenous mutant p53 in a cell line that is non-tumorigenic and devoid of endogenous p53 protein can transform these cells into a tumorigenic cell line. In addition, mutant p53 protein must be nuclear localized to enhance the tumorigenlc potential of the ceU, suggesting that mutant p53 may fiinction as a regulator of gene expression. Consistent with this hypothesis, mutant human p53 alleles, unlike the wild-type p53 protein, can selectively transactivate the human multi-drug resistance promoter in transient transfection assays using cells that are devoid of endogenous p53 protein. To advance our understanding of the mutant p53-gain-of-fiinction phenotype, we specifically propose to detail the molecular mechanisms by which mutant p53 fiinctions as a transactivator of gene expression by addressing the following questions: 1) What DNA sequences of the MDR promoter are required for mutant p53 trans tivation? 2) Is the endogenous MDR gene transactivated by mutant p53 in stably transfected cells? 3) What domains of mutant p53 are required for transactivation? 4) Does mdm-2, a p53 associated protein, mediate or regulate mutant p53 transactivation function? The proposed research will contribute to our general understanding of how mutant p53 may fiinction in cooperation with other factors, such as mdm-2, to promote tumorigenicity.