INTERACTION OF APC AND P53 IN COLORECTAL CARCINOGENESIS

结肠癌是美国第二常见的癌症。 各州，这一年估计有95,600例新病例和47,700例死亡 1998(美国癌症协会-癌症事实和数字；2月6日， 1998年)。腺瘤性息肉病的表达改变与其相关性 Coli(APC)抑癌基因在结肠癌中预后不良 患者是公认的；然而，人们对APC知之甚少 生物学功能，而且几乎不知道关于 APC基因表达的调控。这个项目的长期目标是 是为了了解APC基因的调控机制，以及 其产物在正常细胞和癌细胞中的功能。发展中的 结肠癌是一个多步骤的过程，经常涉及突变。 在APC和P53基因中都存在。我们的初步结果表明 APC mRNA在P53依赖的细胞中转录激活 DNA烷基化试剂N-甲基-N‘-硝基-N-亚硝基 (MNNG)。本研究的目的是阐明心绞痛的发病机制。 损伤药物对APC的P53依赖的转录调控 DNA基于我们之前的研究和其他人的工作，我们建议 在对基因毒剂产生的信号作出反应时， 磷酸化的P53蛋白增加并形成转录活性 P53/TFIIH复合体，提高APC转录速度，导致 APC介导的结肠癌细胞周期停滞或凋亡。 这一假设将通过以下几个方面得到验证：1)表征 DNA损伤诱导的P53介导的APC转录复合体 利用氯霉素乙酰化评价启动子的功能 转移酶(CAT)报告基因的表达；2)机制分析 体外径流转录中P53对APC基因调控的研究 系统。我们的研究结果有望建立起功能上的联系 APC和P53--两个最常发生突变的抑癌基因 参与结肠癌细胞周期停滞和细胞凋亡。因此， 新的治疗策略可能出现在潜在的新 结肠癌化疗干预的靶点。

Colon cancer is the second most frequent cancer diagnosed in the United States, with an estimated 95,600 new cases and 47,700 deaths in the year 1998 (American Cancer Society - Cancer Facts and Figures; February 6, 1998). The association of altered expression of adenomatous polyposis coli (APC) tumor suppressor gene with poor prognosis in colon cancer patients is well established; however, little is known about APC's biological functions, and virtually nothing is known concerning the regulation of APC gene expression. The long-term goal of this project is to understand the mechanisms by which the APC gene is regulated, and the function of its product in normal and cancer cells. Development of colon cancer is a multistep process that frequently involves mutations in both the APC and p53 genes. Our preliminary results indicate that expression of APC mRNA is transcriptionally activated in a p53-dependent manner by the DNA-alkylating agent N-methyl-N'-nitro-N-nitrosoguanidine (MNNG). The objective of this study is to elucidate the mechanisms of p53-dependent transcriptional regulation of APC by agents that damage DNA. Based on our prior studies and the work of others, we propose that, in response to signals generated by genotoxic agents, levels of phosphorylated p53 protein increase and form transcriptionally active p53/TFIIH complex that enhance the rate of APC transcription, resulting in APC-mediated cell cycle arrest or apoptosis of colon cancer cells. This hypothesis will be tested by: 1) characterizing the assembly of the DNA damage-induced, p53-mediated transcriptional complex on the APC promoter and evaluating its functions by using a chloramphenicol acetyl transferase (CAT)-reporter expression; and 2) analyzing the mechanisms of APC gene regulation by p53 in an in vitro run-off transcription system. Our results are expected to establish a functional link between APC and p53, the two most frequently mutated tumor suppressor genes involved in cell cycle arrest and apoptosis in colon cancer. Therefore, novel therapeutic strategies may emerge with respect to potential new targets for chemotherapeutic intervention in colon cancer.