EGCG Inhibits AhR and Carcinogenesis by Modulating Hsp90

描述(由申请人提供)：绿茶(GT)及其成分预防某些类型的癌症的可能性已成为越来越多的健康兴趣。研究表明，GT在化学致癌和自发性肿瘤动物模型中具有预防作用。GT及其组件的确切作用机制尚不清楚。初步研究表明，GT提取物和几个组分可以有效地拮抗2，3，7，8-四氯二苯并对二恶英(TCDD)与芳烃受体(AhR)结合的转录事件。表没食子儿茶素没食子酸酯(EGCG)是GT的一种成分，它不是通过与AhR结合而是通过与90 kDa热休克伴侣蛋白(HSP90)相互作用来阻断AhR介导的转录。据推测，EGCG是一种HSP90抑制剂，这有助于其抗癌活性的报道。利用分离的啮齿动物和人类细胞系和无细胞模型系统，我们将确定EGCG在HSP90上的确切结合位置，并研究这种结合如何改变HSP90的构象和功能。使用类似的程序和免疫沉淀，将进行实验，以进一步表征与EGCG结合的HSP90相关的AhR蛋白复合体，以确定AhR的DNA结合是如何被抑制的。HSP90调节大量客户蛋白的功能，其中许多对癌细胞的生长和生存至关重要。其他研究将确定EGCG是否会改变几种HSP90客户蛋白的水平和/或活性，这些蛋白可能在肿瘤细胞的恶性转化或生长中发挥作用。

DESCRIPTION (provided by applicant): The possibility that green tea (GT) and its components protect against certain types of cancer has become an increasing health interest. Studies indicate that GT exerts preventive effects in animal models of chemical carcinogenesis and spontaneously developing tumors. The exact mechanism by which GT and its components act is unknown. Preliminary studies demonstrated that GT extracts and several components are effective at antagonizing transcriptional events mediated by binding of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD), a potent toxicant and carcinogen, to the aryl hydrocarbon receptor (AhR). It was determined that epigallocatechin-3-gallate (EGCG), a component of GT, blocks AhR-mediated transcription not by binding to the AhR, but through its interaction with the 90 kDa heat shock chaperone protein (hsp90). It is hypothesized that EGCG is a hsp90 inhibitor and this contributes to its reported anti-cancer activity. Using isolated rodent and human cell lines and cell-free model systems, we will determine the exact binding site for EGCG on hsp90 and examine how this binding alters hsp90 conformation and function. Using similar procedures and immunoprecipitation, experiments will be performed to further characterize the AhR protein complex associated with EGCG-bound hsp90 to determine how DNA binding of the AhR is inhibited. Hsp90 regulates the function of a large number of client proteins, many of which are important in the growth and survival of cancer cells. Additional studies will determine if EGCG alters the levels and/or activity of several hsp90 client proteins that may play a role in the malignant transformation or growth of tumor cells.