P53 AND MOUSE MAMMARY TUMORIGENESIS

p53肿瘤抑制基因是人类乳腺癌中最常见的突变基因之一，包括功能突变的获得和缺失突变。到目前为止，由于淋巴肉瘤导致p53基因缺失小鼠的早期死亡率，研究p53基因缺失在实验性乳腺肿瘤发生中的作用一直很困难。我们将原p53阴性小鼠与Balb/c小鼠回交，建立了p53阴性乳腺上皮细胞模型。将p53基因缺失的乳腺上皮细胞移植到同基因Balb/c小鼠的乳腺脂肪垫中，为研究p53基因缺失对乳腺上皮细胞形态发生和肿瘤发生的影响提供了一个独特的模型系统。初步数据表明，p53缺失的乳腺上皮细胞对肿瘤的发展非常敏感，肿瘤通常是非整倍体和转移性的。在这项拨款申请中，提出了三个具体目标来研究p53基因缺失在乳腺肿瘤发生中的作用。具体目标1将通过确定瘤前病理，肿瘤发生的激素相互作用和激素依赖性以及肿瘤发生非整倍体的时间来检查p53-null乳腺上皮细胞的生物学。特异性目标2将使用cDNA阵列检查p53基因缺失引起的基因表达修饰。基因表达将在p53野生型和零细胞群的未转化（正常）和肿瘤细胞中进行评估。特异性目标3将使用多种方法分析特异性目标2中鉴定的基因的功能特性，包括在空细胞中调节基因表达和恢复野生型p53基因活性。首先分析的基因将是谷胱甘肽过氧化物酶，该基因通过cDNA阵列分析在p53阴性乳腺细胞中被下调。综上所述，该模型允许利用移植方法分析原位乳腺中p53基因缺失的生物学、遗传学和分子后果。

The p53 tumor suppressor gene is one of the most frequently mutated genes in human breast cancer and includes gain of function mutations as well as deletion mutations. Until now, it has been difficult to examine the role of p53 gene deletion in experimental mammary tumorigenesis because of the early death rate of p53 null mice due to lymphosarcomas. We have developed a p53 null mammary epithelial model by backcrossing the original p53 null mouse into Balb/c mice. Transplantation of p53 null mammary epithelial cells into the mammary fat pads of syngeneic Balb/c mice provides a unique model system to examine the effects of p53 gene deletion on a single tissue: mammary epithelial cell morphogenesis and tumorigenesis. Preliminary data demonstrate that the p53 null mammary epithelial cells are highly susceptible to tumor development and the tumors are frequently aneuploid and metastatic. In this grant application, three specific aims are proposed to examine the role of p53 gene deletion on mammary tumorigenesis. Specific aim 1 will examine the biology of the p53-null mammary epithelial cell by determining the preneoplastic pathology, hormone interactions and hormone dependency for tumorigenesis, and the timing of aneuploidy in tumorigenesis. Specific aim 2 will examine modified gene expression due to p53 gene deletion using cDNA arrays. Gene expression will be evaluated in nontransformed (normal) and tumor cells from both p53 wild type and null cell populations. Specific aim 3 will analyze the functional properties of genes identified in specific aim 2 using a variety of approaches that include modulating gene expression and restoration of wild type p53 gene activity in null cells. The initial gene to be analyzed will be glutathione peroxidase which was identified as downregulated in p53 null mammary cells by cDNA array analysis. In summary, this model allows one to analyze the biological, genetic and molecular consequences of p53 gene deletion in the in situ mammary gland by taking advantage of transplantation methods.