Function of a molecular target of cancer chemoprevention

描述（由申请人提供）：癌症当局认识到，选择含有新鲜水果和蔬菜的饮食是避免癌症的最佳策略，这可能仅次于戒烟。虽然这已成为一个真理，而且一些营养化学物质已被证明具有抗癌特性，但人们对膳食营养素预防癌症发生的机制知之甚少。然而，从近50年前开始，人们发现某些化学物质，其中包括异硫氰酸酯（ITCs）等化合物，可以预防致癌物引起的动物癌症。流行的模型是ITCs通过转录增加致癌解毒酶的表达，称为2期基因。我们和其他人提出了一个不同的模型，其中化学预防的一个主要特征是在早期肿瘤细胞中引发凋亡细胞死亡反应。饮食中的ITCs诱导凋亡细胞死亡和改变信号转导级联的能力有力地支持了这一模型。目前还缺乏解释ITCs抗癌活性的分子机制。虽然像ITCs这样的亲电试剂可以共价修饰蛋白质，但ITCs共价标记靶效应蛋白的能力尚未被探索。我们开发了一种新的方法来检测和纯化由化学预防异硫氰酸酯共价修饰的蛋白质，无论是在体外，在细胞中，甚至在完整的动物中。我们已经证明，也许令人惊讶的是，ITCs共价修饰细胞内很少的蛋白质，我们已经确定了一个单一的蛋白质，代表了人类肿瘤细胞内超过90%的共价ITCs修饰蛋白质。这种蛋白质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表达。已知该靶分子还控制依赖于API转录反应元件的转录反应，这表明它可能通过一种机制控制2期基因的表达，并证实其可能作为癌症化学预防的靶标。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，并将其开发为可用于量化ITC化学预防效果的生物标志物。除了体内癌变实验外，我们将证实先前的结果，即缺乏ITC靶点的敲除动物的细胞更难以转化为肿瘤细胞，并确定可以解释ITC化学预防的具体机制。

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.