EGCG Inhibits AhR and Carcinogenesis by Modulating Hsp90

描述（由申请人提供）：绿色茶（GT）及其成分预防某些类型癌症的可能性已成为越来越多的健康关注点。研究表明，GT在化学致癌和自发性肿瘤的动物模型中发挥预防作用。GT及其组分的确切作用机制尚不清楚。初步研究表明，GT提取物和几种组分可有效拮抗由2，3，7，8-四氯二苯并-p-二恶英（TCDD）（一种强效毒物和致癌物）与芳烃受体（AhR）结合介导的转录事件。已确定表没食子儿茶素-3-没食子酸酯（EGCG）（GT的一种组分）不是通过与AhR结合而是通过其与90 kDa热休克伴侣蛋白（hsp 90）的相互作用来阻断AhR介导的转录。据推测，EGCG是一种热休克蛋白90抑制剂，这有助于其报告的抗癌活性。使用分离的啮齿动物和人类细胞系和无细胞模型系统，我们将确定热休克蛋白90上的EGCG的确切结合位点，并研究这种结合如何改变热休克蛋白90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hsp 90相关的AhR蛋白复合物，以确定AhR的DNA结合如何被抑制。Hsp 90调节大量客户蛋白的功能，其中许多在癌细胞的生长和存活中是重要的。进一步的研究将确定EGCG是否改变了几种可能在肿瘤细胞恶性转化或生长中发挥作用的HSP 90客户蛋白的水平和/或活性。

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.