Function of a molecular target of cancer chemoprevention

描述（由申请人提供）：癌症当局认识到，可能仅次于戒烟，选择含有新鲜水果和蔬菜的饮食是避免癌症的最佳策略。虽然这已经成为一个老生常谈，一些营养化学品已被证明具有抗癌特性，但人们对膳食营养素可以预防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，其中包括异硫氰酸酯（ITC）等化合物，可以预防致癌物质诱导的动物癌症。流行的模型是ITCs转录增加致癌物解毒酶的表达，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初期肿瘤细胞中引发凋亡细胞死亡反应。饮食ITCs诱导细胞凋亡和改变信号转导级联的能力强烈支持这一模型。缺乏解释ITCs抗癌活性的分子机制。虽然亲电体如ITC可以共价修饰蛋白质，但ITC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蛋白质共价修饰的化学预防异硫氰酸酯，无论是在体外，在细胞中，甚至在完整的动物。我们已经表明，也许令人惊讶的是，ITC共价修饰细胞内的蛋白质很少，我们已经确定了一个单一的蛋白质，代表超过90%的共价ITC修饰的蛋白质在人类肿瘤细胞。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。还已知该靶分子控制依赖于API转录应答元件的转录应答，表明其可通过其控制2期基因表达的机制，并证实其作为癌症化学预防靶标的可能作用。我们建议使用敲除动物在这个目标的缺陷，以进一步表征这种蛋白质在癌症化学预防中的作用，并开发它作为生物标志物用于量化ITC化学预防的效果。除了体内致癌实验之外，我们还将证实之前的结果，即缺乏该ITC靶点的基因敲除动物的细胞更难转化为肿瘤细胞，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.