title: Quercetin-induced ubiquitination and down-regulation of Her-2/neu.
abstract: Her-2/neu (ErbB2) is a transmembrane tyrosine kinase and acts as a co-receptor for the other EGFR family members. It is well known that high expression of Her-2/neu is associated with a poor prognosis in breast cancer. Quercetin, a flavonoid present in many vegetables and fruits, has been studied extensively as a chemoprevention agent in several cancer models. In this study, we observed that quercetin decreased the level of Her-2/neu protein in time- and dose-dependent manners and also inhibited the downstream survival PI3K-Akt signaling pathway in Her-2/neu-overexpressing breast cancer SK-Br3 cells. We also observed that quercetin induced polyubiquitination of Her-2/neu. When the proteasome pathway was blocked by MG-132 during quercetin treatment, accumulation of the NP-40 insoluble form of Her-2/neu occurred. Interestingly, data from immunocomplex studies revealed that quercetin promoted interaction between Her-2/neu and Hsp90 which is a molecular chaperone involved in stabilization of Her-2/neu. In this condition, inhibition of Hsp90 activity by a specific inhibitor, geldanamycin (GA), or intracellular ATP depletion caused dissociation of Hsp90 from Her-2/neu and promoted ubiquitination and down-regulation of Her-2/neu protein. In addition, the carboxyl terminus of Hsc70-interacting protein (CHIP), a chaperone-dependent E3 ubiquitin ligase, played a crucial role in the quercetin-induced ubiquitination of Her-2/neu. Inhibition of tyrosine kinase activity of Her-2/neu by quercetin could indicate an lateration in the Her-2/neu structure which promotes CHIP recruitments and down-regulation of Her-2/neu. We believe that by using quercetin, new therapeutic strategies can be developed to treat Her-2/neu overexpressing cancers.
authors.affiliation: Department of Surgery, School of Medicine, University of Pittsburgh, Pittsburgh, Pennsylvania 15213, USA.
authors.forename: Jae-Hoon
authors.initials: JH
authors.lastname: Jeong
authors.forename: Jee Young
authors.initials: JY
authors.lastname: An
authors.forename: Yong Tae
authors.initials: YT
authors.lastname: Kwon
authors.forename: Lu-Yuan
authors.initials: LY
authors.lastname: Li
authors.forename: Yong J
authors.initials: YJ
authors.lastname: Lee
mesh_terms: D045744:Cell Line, Tumor; D018890:Chemoprevention; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation / Q000187:drug effects*; D005260:Female; D018841:HSP90 Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D011794:Quercetin / Q000494:pharmacology*; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism*; D054875:Ubiquitination / Q000187:drug effects*
chemical_list: D018841:HSP90 Heat-Shock Proteins; D011794:Quercetin; D018719:Erb-b2 Receptor Tyrosine Kinases; D044767:Ubiquitin-Protein Ligases; C467728:STUB1 protein, human; C508053:ERBB2 protein, human