title: (-)-Epigallocatechin-3-gallate is a novel Hsp90 inhibitor.
abstract: (-)-Epigallocatechin-3-gallate (EGCG), a major component of green tea, protects against certain types of cancers, although the mechanism has not yet been determined. It was previously demonstrated that EGCG blocks aryl hydrocarbon receptor (AhR)-mediated transcription induced by the potent carcinogen 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Unlike other AhR antagonists that directly bind to the AhR, EGCG inhibits AhR-mediated transcription by binding to hsp90. We hypothesize that EGCG exerts anti-AhR and anticancer effects by acting as an hsp90 inhibitor. Using proteolytic footprinting, immunoprecipitation, and an ATP-agarose pull-down assay, EGCG was found to directly modulate the conformation of hsp90 and bind at or near to a C-terminal ATP binding site. Hsp90 chaperone function, as assessed by its ability to mediate refolding of denatured luciferase, was inhibited by EGCG treatment. Hsp90 dimerization, which occurs at the C-terminal end, was also inhibited by EGCG treatment. Coimmunoprecipitation studies showed that EGCG stabilizes an AhR complex that includes hsp90 and XAP2 (hepatitis B virus X-associated protein 2), and decreases the association of aryl hydrocarbon nuclear translocator (Arnt) with ligand-activated AhR. Thus, EGCG, through its ability to bind to hsp90, blocks AhR response element (AhRE) recognition. These studies indicate a novel mechanism whereby EGCG inhibits ligand-induced AhRE binding and AhR-mediated transcriptional activity. In EGCG-treated human ovarian carcinoma SKOV3 cells, decreased levels of several cancer-related hsp90 client proteins, such as ErbB2, Raf-1 and phospho-AKT, were observed. EGCG also modified the association of hsp90 with several cochaperones. Overall, these data indicate that EGCG is a novel hsp90 inhibitor. Further studies are needed to determine if this has a role in the antitumor actions of EGCG.
authors.affiliation: Department of Environmental Medicine, University of Rochester Medical Center, Rochester, New York 14642, USA.
authors.forename: Zhengyu
authors.initials: Z
authors.lastname: Yin
authors.forename: Ellen C
authors.initials: EC
authors.lastname: Henry
authors.forename: Thomas A
authors.initials: TA
authors.lastname: Gasiewicz
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000235:genetics; D002392:Catechin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D002645:Chickens; D019281:Dimerization; D004305:Dose-Response Relationship, Drug; D005982:Glutathione Transferase / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000302:isolation & purification; D006801:Humans; D008024:Ligands; D051379:Mice; D008954:Models, Biological; D018832:Molecular Chaperones / Q000037:antagonists & inhibitors / Q000235:genetics; D010449:Peptide Mapping; D010957:Plasmids; D011485:Protein Binding / Q000235:genetics; D011487:Protein Conformation / Q000187:drug effects; D018336:Receptors, Aryl Hydrocarbon / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D020218:Response Elements / Q000187:drug effects; D013662:Tea / Q000235:genetics; D013997:Time Factors; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: D018841:HSP90 Heat-Shock Proteins; D008024:Ligands; D018832:Molecular Chaperones; D018336:Receptors, Aryl Hydrocarbon; D011993:Recombinant Fusion Proteins; D013662:Tea; D002392:Catechin; C045651:epigallocatechin gallate; D005982:Glutathione Transferase