Beta-catenin-specific regulation of the vitamin D pathway in colon cancer

描述(由申请人提供)： 流行病学研究表明，维生素D前体的饮食摄入量或紫外线激活与结肠癌的发病率之间存在关系。这种关系表明维生素D可能具有化学预防作用，动物研究证实了维生素D及其类似物对结肠癌的预防效果。然而，在许多情况下，人类癌细胞和肿瘤会对治疗产生抗药性。另一个主要的担忧是与维生素D的抗癌作用无关的副作用的发生率很高。尽管维生素D的癌症相关和非癌症相关的作用都是通过与其核受体(VDR)的相互作用来调节的，但它们是否可以分离尚不清楚。研究阐明维生素D发挥抗癌作用的确切机制(S)具有重要意义。对这些途径的详细了解可能会导致开发出对维生素治疗耐药的患者有效的药物或饮食方案，和/或开发副作用较少的治疗方法。初步数据表明，在结肠癌中几乎普遍激活的WNT/2-catenin/Tcf致癌途径是维生素D及其类似物预防结肠癌作用的关键中介。我们的数据显示，维生素D抑制2-连环蛋白信号，而2-连环蛋白激活VDR。重要的是，我们发现某些VDR突变体和维生素D类似物允许与2-连环蛋白相互作用，但不允许其他共激活剂相互作用。这项建议旨在探索和利用这样一个概念，即维生素D途径可以在表达高水平激活的2-连环蛋白的肠道癌细胞中选择性地激活。这样的策略将提供在VDR被激活的同时抑制2-连环蛋白信号的额外好处。在第一个目标中，我们提出了一系列的计算、结构和突变分析来确定VDR的结构特征，这些结构特征指定了它与2-连环蛋白的相互作用。在第二个目标中，我们将筛选虚拟和真实的文库，以确定允许2-连环蛋白而不是其他共激活子与VDR结合的配体。我们的目标是开发维生素D类似物，只有在结肠癌等2-连环蛋白升高的情况下才能激活VDR。在第三个目标中，我们将使用转基因动物来研究VDR、VDR突变体和2-连环蛋白特异性维生素D类似物在2-连环蛋白诱导的肿瘤保护中的作用。APC1638小鼠发生自发性肠癌，我们最近培育了APC1638/VDR-/-双基因动物。我们将使用APC1638、APC1638/VDR-/-、VDR-突变体和偶氮甲烷处理的动物来研究维生素D类似物支持VDR/2-连环蛋白相互作用的能力，以及VDR的切除是否在肠道肿瘤的发生中起作用。公共卫生相关性：在美国，结直肠癌是癌症相关死亡的第二大原因。几乎所有结直肠癌的发生都是由于结肠腺瘤性息肉病(APC)或2-连环蛋白基因突变所致。大量的流行病学和动物模型数据支持维生素D及其类似物(和阳光)是结直肠癌的有效抑制剂的假说，我们自己的工作表明，某些维生素D类似物可以2-连环素特异性的方式抑制结直肠癌的生长。我们现在提出了一系列计算、生化和动物模型研究，以探索和利用维生素D途径可以在结肠癌中优先激活的概念，因为结肠癌表达高水平的激活的2-连环蛋白。

DESCRIPTION (provided by applicant): Epidemiological studies show a relationship between the dietary intake or UV-activation of pre-vitamin D and the incidence of colon cancers. This relationship indicates that vitamin D may have a chemopreventive action and animal studies have confirmed the preventive efficacy of vitamin D and its analogues in colon cancer. However in many instances human cancer cells and tumors become resistant to treatment. Another major concern is the high incidence of side effects unrelated to the anti cancer actions of vitamin D. Even though both the cancer- and non-cancer-related actions of vitamin D are mediated via interaction with its nuclear receptor (VDR) it is not clear if they can be separated. Studies that elucidate the precise mechanism(s) whereby vitamin D exerts its anti-cancer effects are of great significance. A detailed understanding of these pathways may lead to the development of agents or dietary regimens that are effective in patients that are resistant to vitamin therapy and/or to the development of treatments with fewer side effects. Preliminary data demonstrates that the wnt/2- catenin/TCF oncogenic pathway, almost universally activated in colon cancer, is a key intermediary in the preventive action of vitamin D and its analogues in colon cancer. Our data shows that vitamin D represses 2-catenin signaling and that 2-catenin activates VDR. Importantly, we find that certain VDR mutants and vitamin D analogues allow interaction with 2-catenin but not other co-activators. This proposal seeks to explore and exploit the concept that the vitamin D pathway can be selectively activated in intestinal cancer cells expressing high levels of activated 2-catenin. Such a strategy would offer the additional benefit of repressing 2-catenin signaling at the same time as VDR is activated. In aim one we propose a series of computational, structural, and mutational analyses to identify structural features of the VDR, which specify its interaction with 2-catenin. In aim two we will screen virtual and real libraries to identify ligands which allow 2-catenin but not other co-activators to bind the VDR. Our goal is to develop vitamin D analogues that can activate VDR only in situations, such as colon cancer, in which 2-catenin is elevated. In aim three we will use transgenic animals to investigate the role of VDR, VDR mutants and 2- catenin specific vitamin D analogues in protection from 2-catenin induced neoplasia. The APC1638 mouse develops spontaneous intestinal cancers and we recently generated APC1638/VDR-/- bigenic animals. We will use APC1638 ,APC1638/VDR-/-, VDR-mutant and azoxymethane treated animals to investigate the ability of vitamin D analogues to support VDR/2-catenin interactions and whether ablation of VDR plays any role in intestinal tumor development. PUBLIC HEALTH RELEVANCE: Colorectal cancer is the second leading cause of cancer-related death in the United States. The development of virtually all colorectal cancer results from mutation in adenomatous polyposis coli (APC) or 2-catenin genes. A wealth of epidemiological and animal model data supports the hypothesis that vitamin D and its analogues (and sunlight) are potent inhibitors of CRC and our own work shows that certain analogues of vitamin D can inhibit the growth of CRC in a 2-catenin-specific manner. We now propose a series of computational, biochemical and animal model studies to explore and exploit the concept that the vitamin D pathway can be preferentially activated in colon cancers which express high levels of activated 2-catenin.