title: Indirect participation of Hsp90 in the regulation of the cyclin E turnover.
abstract: Cyclin E is the Cdk2-regulatory subunit required for the initiation of DNA replication at the G1/S transition. It accumulates in late G1 phase and gets rapidly degraded by the ubiquitin/proteasome pathway during S phase. The degradation of cyclin E is a consequence of its phosphorylation and subsequent isomerization by the peptidyl-prolyl isomerase Pin1. We show that in the colon cancer cells HT-29 the inhibition of the chaperone function of Hsp90 by geldanamycin (GA) enhances the ubiquitinylation of cyclin E and triggers active degradation via the proteasome pathway. As Hsp90 forms multiprotein complexes with and regulates the function and cell contents of numerous signaling proteins, this observation suggests a direct interaction between Hsp90 and cyclin E. However, experiments using cell lysate fractionation did not reveal the presence of complexes containing both Hsp90 and cyclin E. Coupled transcription/translation experiments also failed to detect the formation of complexes between newly synthesized cyclin E and Hsp90. We conclude that Hsp90 can regulate the degradation of cellular proteins without binding to them, by an indirect mechanism. This conclusion postulates a new category of proteins that are affected by the inactivation of Hsp90. Our observations do not support the possible involvement of a PPIase in this indirect mechanism. Besides, we did not observe active geldanamycin-dependent degradation of cyclin E in the prostate cancer-derived cell line DU-145, indicating that the Hsp90-dependent stabilization of cyclin E requires specific regulatory mechanism which may be lost in certain types of cancer cells.
authors.affiliation: INSERM U893, UPMC-Paris 6, Paris, France. Monique.Bedin@inserm.fr
authors.forename: Monique
authors.initials: M
authors.lastname: Bedin
authors.forename: Maria-Grazia
authors.initials: MG
authors.lastname: Catelli
authors.forename: Lucien
authors.initials: L
authors.lastname: Cabanié
authors.forename: Anne-Marie
authors.initials: AM
authors.lastname: Gaben
authors.forename: Jan
authors.initials: J
authors.lastname: Mester
mesh_terms: D000903:Antibiotics, Antineoplastic / Q000494:pharmacology*; D016590:Aphidicolin / Q000494:pharmacology; D016227:Benzoquinones / Q000494:pharmacology*; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D003110:Colonic Neoplasms; D019927:Cyclin E / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D004261:DNA Replication / Q000502:physiology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors / Q000502:physiology*; D006706:Homeostasis; D006801:Humans; D047029:Lactams, Macrocyclic / Q000494:pharmacology*; D008297:Male; D009363:Neoplasm Proteins / Q000096:biosynthesis / Q000187:drug effects; D011471:Prostatic Neoplasms; D014176:Protein Biosynthesis; D014158:Transcription, Genetic; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D016227:Benzoquinones; D019927:Cyclin E; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D009363:Neoplasm Proteins; D025801:Ubiquitin; D016590:Aphidicolin; C001277:geldanamycin