title: Upregulation of DR5 by proteasome inhibitors potently sensitizes glioma cells to TRAIL-induced apoptosis.
abstract: This study was undertaken to explore the potential of new therapeutic approaches designed to reactivate cell death pathways in apoptosis-refractory gliomas and to characterize the underlying molecular mechanisms of this reactivation. Here we investigated the sensitivity of a panel of glioma cell lines (U87, U251, U343, U373, MZ-54, and MZ-18) to apoptosis induced by the death receptor ligand tumor necrosis factor-related apoptosis-inducing ligand (TRAIL), TRAIL in combination with gamma irradiation, and TRAIL in combination with proteasome inhibitors (MG132 and epoxomicin). Analysis of these six glioma cell lines revealed drastic differences in their sensitivity to these treatments, with two of the six cell lines revealing no significant induction of cell death in response to TRAIL alone. Interestingly, the proteasome inhibitors MG132 and epoxomicin were capable of potentiating TRAIL-induced apoptosis in TRAIL-sensitive U87 and U251 cells and of reactivating apoptosis in TRAIL-resistant U343 and U373 cells. In contrast, gamma irradiation had no synergistic effects with TRAIL in the two TRAIL-resistant cell lines. RNA interference against death receptor 5 (DR5) revealed that reactivation of TRAIL-induced apoptosis by proteasome inhibitors depended on enhanced transcription and surface expression of DR5. Transient knockdown of the transcription factor GADD153/C/EBP homologous protein and application of the synthetic c-Jun N-terminal kinase inhibitor SP600125 indicated that enhanced DR5 expression occurred independently of GADD153/C/EBP homologous protein, but required activation of the c-Jun N-terminal kinase/c-Jun signaling pathway. Novel therapeutic approaches using TRAIL or agonistic TRAIL receptor antibodies in combination with proteasome inhibitors may represent a promising approach to reactivate apoptosis in therapy-resistant high-grade gliomas.
authors.affiliation: Department of Neurosurgery, Centre for Neurology and Neurosurgery, Johann Wolfgang Goethe University Clinics, Theodor-Stern-Kai 7, Frankfurt/Main, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Hetschko
authors.forename: Valerie
authors.initials: V
authors.lastname: Voss
authors.forename: Volker
authors.initials: V
authors.lastname: Seifert
authors.forename: Jochen H M
authors.initials: JH
authors.lastname: Prehn
authors.forename: Donat
authors.initials: D
authors.lastname: Kögel
mesh_terms: D017209:Apoptosis / Q000187:drug effects* / Q000528:radiation effects; D045744:Cell Line, Tumor; D005910:Glioma / Q000378:metabolism* / Q000473:pathology*; D006801:Humans; D048031:JNK Mitogen-Activated Protein Kinases / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D034622:RNA Interference; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000235:genetics / Q000378:metabolism*; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*; D051742:Transcription Factor CHOP / Q000235:genetics / Q000378:metabolism; D015854:Up-Regulation / Q000187:drug effects*
chemical_list: C497249:DDIT3 protein, human; D061988:Proteasome Inhibitors; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D051742:Transcription Factor CHOP; D048031:JNK Mitogen-Activated Protein Kinases; D046988:Proteasome Endopeptidase Complex