Gain of function mutant p53 in telomere uncapping-driven breast tumorigenesis

描述(申请人提供)：人类散发性乳腺癌的特点是存在复杂的细胞遗传学异常。这种复杂性是乳腺癌研究人员开发实验模型系统以确定乳腺癌发生的分子遗传学病因所面临的最大挑战之一。我们的长期目标是建立“染色体不稳定”的小鼠乳腺癌模型，该模型概括了高度重排和突变的人类乳腺癌基因组的显著特征，并发现体内参与乳腺癌发生的“因果”基因组事件。导致乳腺癌基因组不稳定的一个重要机制是端粒功能障碍，端粒是染色体的物理末端，保护自然染色体末端不被识别为DNA损伤，并抑制不适当的DNA修复。另一方面，最近对人类乳腺癌的系统基因组分析表明，抑癌基因P53是最常见的警示基因，主要是通过错义突变导致突变的P53蛋白积累获得致癌功能增强。为了与人类乳腺癌中观察到的染色体不稳定性和功能获得突变型P53的表达这两个重要特征非常相似，我们一直在设计一种新的小鼠乳腺癌模型，该模型具有端粒功能异常引起的染色体不稳定性和乳腺上皮细胞表达“热点”的功能获得突变型P53。我们的初步结果表明，端粒去封顶导致功能失调的端粒，激活DNA损伤反应(DDR)介导的凋亡途径，在没有p53的情况下抑制染色体不稳定驱动的肿瘤发生，而“热点”突变体P53抑制端粒去封顶诱导的细胞死亡，促进细胞转化。此外，我们观察到突变的p53与乳腺上皮中功能失调的端粒协同作用，促进了体内肿瘤向浸润性乳腺癌的进展。在这个应用中，我们将检验我们的假设，即功能获得突变体P53抑制端粒去封顶诱导的DDR介导的凋亡，以增强体内染色体不稳定驱动的乳腺癌发生。这两个具体目标旨在检验这一假设。在目标1中，我们将建立小鼠模型来测试功能获得突变体P53与端粒去封顶启动的染色体不稳定协同促进体内乳腺癌发生的可能性。在目标2中，我们将研究功能获得突变体P53促进染色体不稳定驱动的乳腺肿瘤发展的分子机制。我们预计，我们设计的染色体不稳定小鼠模型将忠实地概括人类乳腺癌复杂的细胞遗传学异常，并帮助我们确定新的分子靶点，以改进乳腺癌的预防和治疗策略。

DESCRIPTION (provided by applicant): Human sporadic breast carcinomas are characterized by the presence of complex cytogenetic aberrations. This complexity represents one of the foremost challenges for breast cancer researchers developing the experimental model systems to identify the molecular genetic etiology of breast tumor development. Our long term goal is to establish "chromosomal instability" mouse breast cancer models that recapitulate the salient features of highly rearranged and mutated human breast cancer genomes and discover the "causal" genomic events involved in mammary carcinogenesis in vivo. One important mechanism that can give rise to the unstable genome in breast cancer is the dysfunction of telomeres, the physical termini of chromosomes that protect natural chromosomal ends from being recognized as damaged DNA and inhibit inappropriate DNA repair. On the other hand, recent systematic genomic analyses in human breast carcinomas have revealed that tumor suppressor p53 is the most commonly alerted gene, predominantly through missense mutations that result in accumulation of mutant p53 protein to acquire oncogenic gain-of-function. To faithfully resemble these two important features observed in human breast carcinomas, chromosomal instability and expression of gain- of-function mutant p53, we have been engineering a novel mouse breast cancer model bearing dysfunctional telomere-induced chromosomal instability and expression of "hot spot" gain-of-function mutant p53 in breast epithelium. Our preliminary results suggest that telomere uncapping causes dysfunctional telomeres that activate DNA Damage Response (DDR)-mediated apoptotic pathway to suppress chromosomal instability- driven tumorigenesis in the absence of p53, while "hot spot" mutant p53 inhibits telomere uncapping-induced cell death and promotes cell transformation. Furthermore, we observe that mutant p53 cooperates with dysfunctional telomeres in breast epithelium to promote tumor progression to invasive breast carcinomas in vivo. In this application, we will test our hypothesis that gain-of-function mutant p53 inhibits telomere uncapping-induced DDR-mediated apoptosis to enhance chromosomal instability-driven mammary carcinogenesis in vivo. The two specific aims are designed to test the hypothesis. In Aim 1, we will generate mouse models to test the possibility that gain-of-function mutant p53 cooperates with telomere uncapping- initiated chromosomal instability to promote mammary carcinogenesis in vivo. In Aim 2, we will investigate the molecular mechanism underlying gain-of-function mutant p53 promotes chromosomal instability-driven breast tumor development. We anticipate that our engineered chromosomal instability mouse models will faithfully recapitulate the complex cytogenetic aberrations of human breast cancer and help us identify novel molecular targets to improve strategies for the prevention and treatment of breast cancer.