PROSTAGLANDINS AND GASTROINTESTINAL DNA DAMAGE

前列腺素和胃肠道 DNA 损伤

• 批准号: 6707968
• 负责人: Courtney Wayne Houchen
• 金额: $ 15.3万
• 依托单位: WASHINGTON UNIVERSITY
• 依托单位国家: 美国
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-02-01 至 2006-11-30
• 项目状态: 已结题
• 来源: https://reporter.nih.gov/project-details/6707968
• 关键词: DNA damage; SDS polyacrylamide gel electrophoresis; apoptosis; azo compounds; biological signal transduction; carcinogenesis inhibitor; carcinogens; cell surface receptors; colorectal neoplasms; gastrointestinal epithelium; immunocytochemistry; laboratory mouse; ligands; nonsteroidal antiinflammatory agent; polymerase chain reaction; prostaglandin E; prostaglandin endoperoxide synthase; radiobiology; radioprotective agents; western blottings

DESCRIPTION (provided by applicant): Colorectal cancer, the second leading cause of cancer death in the western world, arises through the acquisition of multiple, independent genetic mutations and subsequent clonal expansion of mutated crypt epithelial stem cells. Programmed cell death, or apoptosis, is an effective method of removal of these genetically damaged epithelial cells. Azoxymethane (AOM) is a potent DNA damaging agent and carcinogen that induces intestinal and colonic tumors in rodents. NSAIDs inhibit AOM-mediated carcinogenesis. This occurs by inhibition of prostaglandin (PG) production through cyclooygenases (COX) COX-1 or COX-2. COX-2 and not COX-1 however is frequently reported to have a key role in tumor progression. PGE2 is critically important in the maintenance of gastrointestinal integrity and is thought to be a major protective component against environmentally-induced damage. PGs, specifically PGE2 has been shown to regulate intestinal stem cell survival and crypt epithelial apoptosis in response to radiation injury. Furthermore PGE2 mediated radioprotection is COX-1 dependent. In order to determine the effects of AOM on intestinal and colonic injury, we administered AOM (10mg/kg) IP to adult C57/BL6 mice. AOM treatment resulted in marked apoptosis in crypt epithelial cells of the jejunum and distal colon within 8 h. Furthermore, we observed a 3-fold induction in COX-1 mRNA, and a 4-fold increase in intestinal PGE2 levels in WT mice. AOM did not increase PGE2 levels in Cox-1 -/- mice. These data taken together suggest that Cox-1 mediated PGE2 synthesis plays a role in the intestinal response to azoxymethane induced DNA damage. The biologic effects of PGE2 are mediated by binding to membrane bound G-protein coupled receptors, termed EP receptors. The EP receptors are encoded by four separate genes (EP1, EP2, EP3 and EP4). These receptors differ in their ligand binding specificity and in down stream signaling pathways. We have recently demonstrated that the EP2 receptor is expressed in the mouse gastrointestinal tract and is upregulated in the mouse intestine following radiation injury. Moreover, we have demonstrated that the EP2 receptor mediates PGE2's radioprotective effects on apoptosis and crypt stem cell survival. These data taken together support our central hypothesis that the EP2 receptor an important component of an adaptive response in crypt epithelial cells in response to genotoxic injury, in which PGE2 signaling through the EP2 receptor regulates stem cell survival and crypt epithelial cell apoptosis. In this proposal we have chosen to examine the role of PGE2 and EP2 receptors in the regulation of gastrointestinal epithelial apoptosis in response to DNA damage induced by AOM through the following specific aims. 1.To correlate the regional differences in AOM -induced crypt epithelial cell apoptosis along the duodenal to colonic axis with regional differences in EP2 receptor distribution 2.To define the mechanisms of AOM-induced radioprotection in the mouse gastrointestinal tract. 3. To determine the role of COX-1 and PGE2 in AOM-mediated tumorigenesis. We believe that a more complete understanding of the role of PGE2 and EP receptor signaling in the regulation of stem cell fate, will be of great importance in improving our knowledge of the pathogenesis of gastrointestinal malignancy.

描述（由申请人提供）： 结直肠癌是西方世界癌症死亡的第二大原因，是通过获取多个独立的遗传突变以及随后突变的隐窝上皮干细胞的克隆扩张而产生的。程序性细胞死亡或凋亡是去除这些遗传受损的上皮细胞的有效方法。甲氧基烷（AOM）是一种有效的DNA损伤剂和致癌物，可诱导啮齿动物中的肠道和结肠肿瘤。 NSAIDS抑制AOM介导的致癌作用。这是通过抑制前列腺素（PG）通过环氧酶（COX）COX-1或COX-2产生的。然而，COX-2而不是Cox-1在肿瘤进展中具有关键作用。 PGE2在维持胃肠道完整性方面至关重要，被认为是针对环境诱发的损害的主要保护组件。 PGS，特别是PGE2已显示可调节肠道干细胞的存活和隐窝上皮细胞凋亡，以响应辐射损伤。此外，PGE2介导的放射保护是COX-1依赖性的。为了确定AOM对肠道和结肠损伤的影响，我们对成年C57/BL6小鼠施用了AOM（10mg/kg）IP。 AOM治疗在8小时内导致空肠和远端结肠的隐窝上皮细胞的明显凋亡。此外，我们观察到COX-1 mRNA的3倍诱导，WT小鼠的肠PGE2水平增加了4倍。 AOM在COX-1 - / - 小鼠中没有增加PGE2水平。这些数据一起表明，COX-1介导的PGE2合成在对二氧甲烷诱导的DNA损伤的肠反应中起作用。 PGE2的生物学效应是通过与膜结合的G蛋白偶联受体结合（称为EP受体）介导的。 EP受体由四个独立的基因（EP1，EP2，EP3和EP4）编码。这些受体在配体结合特异性和下流信号通路上有所不同。我们最近证明，EP2受体在辐射损伤后在小鼠胃肠道中表达，并在小鼠肠道中上调。此外，我们已经证明EP2受体介导了PGE2对凋亡和隐窝干细胞存活的辐射保护作用。这些数据共同支持了我们的中心假设，即EP2受体是对遗传毒性损伤的隐窝上皮细胞中适应性反应的重要组成部分，其中PGE2通过EP2受体信号传导调节干细胞的存活和隐窝上皮细胞细胞凋亡。在此提案中，我们选择检查PGE2和EP2受体在胃肠道上皮凋亡调节中的作用，以响应AOM通过以下特定目的引起的DNA损伤。 1.将AOM诱导的沿十二指肠到结肠轴的隐窝上皮细胞凋亡的区域差异与EP2受体分布的区域差异相关联。 3。确定COX-1和PGE2在AOM介导的肿瘤发生中的作用。我们认为，对PGE2和EP受体信号在干细胞命运调节中的作用有了更全面的了解，对于提高我们对胃肠道恶性肿瘤发病机理的了解将非常重要。