Function of a molecular target of cancer chemoprevention

描述(由申请人提供)：癌症专家认识到，选择含有新鲜水果和蔬菜的饮食可能是避免癌症的最佳策略，这可能仅次于戒烟。虽然这已经成为老生常谈，而且一些营养化学物质已被证明具有抗癌特性，但人们对饮食营养物质防止癌症出现的机制知之甚少。然而，从近50年前开始，研究表明，某些化学物质，其中包括化合物，如异硫氰酸酯(ITCs)，可以预防动物致癌物质诱发的癌症。流行的模型是ITCs在转录水平上增加致癌物解毒酶的表达，被称为第二阶段基因。我们和其他人提出了一个不同的模型，在该模型中，化学预防的一个主要特征是在初期的肿瘤细胞中引发凋亡细胞死亡反应。饮食中的ITCs诱导细胞凋亡和改变信号转导通路的能力强烈支持这一模型。目前还缺乏解释ITCs抗癌活性的分子机制。虽然像ITCs这样的亲电体可以共价修饰蛋白质，但ITCs共价标记靶标效应蛋白的能力还没有被探索过。我们开发了一种新的方法来检测和纯化化学预防性异硫氰酸酯共价修饰的蛋白质，无论是在体外，在细胞内，甚至在完整的动物中。我们已经证明，也许令人惊讶的是，ITCs在细胞内共价修饰极少数的蛋白质，我们已经鉴定出一种蛋白质，它代表了人类肿瘤细胞中超过90%的共价ITC修饰的蛋白质。这种蛋白与几种类型的人类癌症有关；例如，它在结肠癌和非小细胞肺癌中高度过度表达。该靶分子还被认为依赖于API转录反应元件来控制转录反应，这表明它可能通过一种机制来控制第二阶段基因的表达，并证实了它可能作为癌症化学预防的靶点的作用。我们建议使用缺乏该靶点的敲除动物来进一步表征该蛋白在癌症化学预防中的作用，并将其开发为有助于量化ITC化学预防效果的生物标记物。除了体内致癌实验外，我们还将证实先前的结果，即缺乏ITC靶点的敲除动物的细胞更难转化为肿瘤细胞，并确定可以解释ITCs化学预防的特定机制。

DESCRIPTION (provided by applicant): Cancer authorities recognize that perhaps second only to smoking cessation, the choice of a diet containing fresh fruits and vegetables is the best strategy to avoid cancer. While this has become a truism, and some nutritional chemicals have been shown to have anti-cancer properties, little is known about the mechanisms by which dietary nutrients may prevent the appearance of cancer. However, beginning nearly 50 years ago, it was shown that certain chemicals, among them compounds such as isothiocyanates (ITCs), prevent carcinogen-induced cancers in animals. The prevailing model is that ITCs transcriptionally increase expression of carcinogen-detoxifying enzymes, termed Phase 2 genes. We and others propose a different model in which a major feature of chemoprevention is the instigation of an apoptotic cell death response in incipient tumor cells. The ability of dietary ITCs to induce apoptotic cell death and to alter signal transduction cascades acutely supports this model. Molecular mechanisms that explain the anti-cancer activities of ITCs are lacking. While electrophiles like ITCs could covalently modify proteins, the ability of ITCs to covalently label target effector proteins has not been explored. We developed a novel method to detect and purify proteins covalently modified by chemopreventive isothiocyanates, either in vitro, in cells, or even in intact animals. We have shown that perhaps surprisingly, ITCs covalently modify very few proteins within the cell, and we have identified a single protein that represents over 90% of the covalent ITC-modified protein within human tumor cells. This protein has been implicated in several types of human cancers; for example it is highly overexpressed in cancers of colonic and non-small cell lung origin. This target molecule is also known to control transcriptional responses dependent on the API transcription response element, suggesting a mechanism through which it may control expression of Phase 2 genes, and corroborating its likely role as a target of cancer chemoprevention. We propose to use knockout animals deficient in this target to further characterize the role of this protein in cancer chemoprevention, and to develop it as a biomarker useful for quantifying the effect of ITC chemopreventives. In addition to in vivo carcinogenesis experiments, we will confirm previous results that cells from knockout animals lacking this ITC target are more difficult to transform into tumor cells, and identify specific mechanisms that could explain chemoprevention by ITCs.