title: Celastrol targets proteostasis and acts synergistically with a heat-shock protein 90 inhibitor to kill human glioblastoma cells.
abstract: Glioblastoma multiforme is a devastating disease of the central nervous system and, at present, no effective therapeutic interventions have been identified. Celastrol, a natural occurring triterpene, exhibits potent anti-tumor activity against gliomas in xenograft mouse models. In this study, we describe the cell death mechanism employed by celastrol and identify secondary targets for effective combination therapy against glioblastoma cell survival. In contrast to the previously proposed reactive oxygen species (ROS)-dependent mechanism, cell death in human glioblastoma cells is shown here to be mediated by alternate signal transduction pathways involving, but not fully dependent on, poly(ADP-ribose) polymerase-1 and caspase-3. Our studies indicate that celastrol promotes proteotoxic stress, supported by two feedback mechanisms: (i) impairment of protein quality control as revealed by accumulation of polyubiquitinated aggregates and the canonical autophagy substrate, p62, and (ii) the induction of heat-shock proteins, HSP72 and HSP90. The Michael adduct of celastrol and N-acetylcysteine, 6-N-acetylcysteinyldihydrocelastrol, had no effect on p62, nor on HSP72 expression, confirming a thiol-dependent mechanism. Restriction of protein folding stress with cycloheximide was protective, while combination with autophagy inhibitors did not sensitize cells to celastrol-mediated cytotoxicity. Collectively, these findings imply that celastrol targets proteostasis by disrupting sulfyhydryl homeostasis, independently of ROS, in human glioblastoma cells. This study further emphasizes that targeting proteotoxic stress responses by inhibiting HSP90 with 17-N-Allylamino-17-demethoxygeldanamycin sensitizes human glioblastoma to celastrol treatment, thereby serving as a novel synergism to overcome drug resistance.
authors.affiliation: Department of Pharmacology and Therapeutics, Faculty of Medicine, McGill University, McIntyre Medical Building, Montreal, Quebec, Canada.
authors.forename: S
authors.identifier: 0000000310876770
authors.initials: S
authors.lastname: Boridy
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada.
authors.forename: P U
authors.initials: PU
authors.lastname: Le
authors.affiliation: Department of Neurology and Neurosurgery, Montreal Neurological Institute and Hospital, McGill University, Montreal, Quebec, Canada.
authors.forename: K
authors.initials: K
authors.lastname: Petrecca
authors.affiliation: Department of Pharmacology and Therapeutics, Faculty of Medicine, McGill University, McIntyre Medical Building, Montreal, Quebec, Canada.
authors.forename: D
authors.initials: D
authors.lastname: Maysinger
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D016227:Benzoquinones / Q000494:pharmacology*; D001932:Brain Neoplasms / Q000378:metabolism* / Q000473:pathology; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D005909:Glioblastoma / Q000378:metabolism* / Q000473:pathology; D018841:HSP90 Heat-Shock Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism; D006706:Homeostasis; D006801:Humans; D047029:Lactams, Macrocyclic / Q000494:pharmacology*; D008247:Lysosomes / Q000187:drug effects / Q000378:metabolism; D053978:Pentacyclic Triterpenes; D046988:Proteasome Endopeptidase Complex / Q000187:drug effects / Q000378:metabolism; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D015398:Signal Transduction / Q000187:drug effects; D013438:Sulfhydryl Compounds / Q000378:metabolism; D014315:Triterpenes / Q000494:pharmacology*; D014407:Tumor Cells, Cultured; D054875:Ubiquitination
chemical_list: D016227:Benzoquinones; D018841:HSP90 Heat-Shock Proteins; D047029:Lactams, Macrocyclic; D053978:Pentacyclic Triterpenes; D013438:Sulfhydryl Compounds; D014315:Triterpenes; C112765:tanespimycin; D046988:Proteasome Endopeptidase Complex; C050414:celastrol