title: ErbB2 degradation mediated by the co-chaperone protein CHIP.
abstract: ErbB2 overexpression contributes to the evolution of a substantial group of human cancers and signifies a poor clinical prognosis. Thus, down-regulation of ErbB2 signaling has emerged as a new anti-cancer strategy. Ubiquitinylation, mediated by the Cbl family of ubiquitin ligases, has emerged as a physiological mechanism of ErbB receptor down-regulation, and this mechanism appears to contribute to ErbB2 down-regulation induced by therapeutic anti-ErbB2 antibodies. Hsp90 inhibitory ansamycin antibiotics such as geldanamycin (GA) induce rapid ubiquitinylation and down-regulation of ErbB2. However, the ubiquitin ligase(s) involved has not been identified. Here, we show that ErbB2 serves as an in vitro substrate for the Hsp70/Hsp90-associated U-box ubiquitin ligase CHIP. Overexpression of wild type CHIP, but not its U-box mutant H260Q, induced ubiquitinylation and reduction in both cell surface and total levels of ectopically expressed or endogenous ErbB2 in vivo, and this effect was additive with that of 17-allylamino-geldanamycin (17-AAG). The CHIP U-box mutant H260Q reduced 17-AAG-induced ErbB2 ubiquitinylation. Wild type ErbB2 and a mutant incapable of association with Cbl (ErbB2 Y1112F) were equally sensitive to CHIP and 17-AAG, implying that Cbl does not play a major role in geldanamycin-induced ErbB2 down-regulation. Both endogenous and ectopically expressed CHIP and ErbB2 coimmunoprecipitated with each other, and this association was enhanced by 17-AAG. Notably, CHIP H260Q induced a dramatic elevation of ErbB2 association with Hsp70 and prevented the 17-AAG-induced dissociation of Hsp90. Our results demonstrate that ErbB2 is a target of CHIP ubiquitin ligase activity and suggest a role for CHIP E3 activity in controlling both the association of Hsp70/Hsp90 chaperones with ErbB2 and the down-regulation of ErbB2 induced by inhibitors of Hsp90.
authors.affiliation: Division of Rheumatology, Immunology, and Allergy, Department of Medicine, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts 02115, USA.
authors.forename: Pengcheng
authors.initials: P
authors.lastname: Zhou
authors.forename: Norvin
authors.initials: N
authors.lastname: Fernandes
authors.forename: Ingrid L
authors.initials: IL
authors.lastname: Dodge
authors.forename: Alagarsamy Lakku
authors.initials: AL
authors.lastname: Reddi
authors.forename: Navin
authors.initials: N
authors.lastname: Rao
authors.forename: Howard
authors.initials: H
authors.lastname: Safran
authors.forename: Thomas A
authors.initials: TA
authors.lastname: DiPetrillo
authors.forename: David E
authors.initials: DE
authors.lastname: Wazer
authors.forename: Vimla
authors.initials: V
authors.lastname: Band
authors.forename: Hamid
authors.initials: H
authors.lastname: Band
mesh_terms: D016227:Benzoquinones; D001710:Biotin / Q000494:pharmacology; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005822:Genetic Vectors; D018840:HSP70 Heat-Shock Proteins / Q000378:metabolism; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D006801:Humans; D015151:Immunoblotting; D047029:Lactams, Macrocyclic; D008025:Ligases / Q000378:metabolism*; D018832:Molecular Chaperones / Q000378:metabolism*; D009154:Mutation; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D011809:Quinones / Q000494:pharmacology; D018719:Erb-b2 Receptor Tyrosine Kinases / Q000737:chemistry / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D017828:Rifabutin / Q000031:analogs & derivatives* / Q000494:pharmacology; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection; D014407:Tumor Cells, Cultured; D025801:Ubiquitin / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases
chemical_list: D016227:Benzoquinones; D001710:Biotin; D018840:HSP70 Heat-Shock Proteins; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D008025:Ligases; D018832:Molecular Chaperones; D011809:Quinones; D018719:Erb-b2 Receptor Tyrosine Kinases; D011994:Recombinant Proteins; D017828:Rifabutin; D025801:Ubiquitin; D044767:Ubiquitin-Protein Ligases; C112765:tanespimycin; C467728:STUB1 protein, human; C001277:geldanamycin