title: NF-κB is required for Smac mimetic-mediated sensitization of glioblastoma cells for γ-irradiation-induced apoptosis.
abstract: Evasion of apoptosis contributes to radioresistance of glioblastoma, calling for novel strategies to overcome apoptosis resistance. In this study, we investigated the potential of the small molecule Smac mimetic BV6 to modulate radiosensitivity of glioblastoma cells. Here, we identify a novel proapoptotic function of NF-κB in γ-irradiation-induced apoptosis of glioblastoma cells by showing, for the first time, that NF-κB is critically required for Smac mimetic-mediated radiosensitization. BV6 significantly increases γ-irradiation-triggered apoptosis in several glioblastoma cell lines in a dose- and time-dependent manner. Calculation of combination index (CI) reveals that the interaction of BV6 and γ-irradiation is highly synergistic (CI < 0.3). Molecular studies show that BV6 stimulates NF-κB activation, which is critical for radiosensitization, because genetic inhibition of NF-κB by overexpression of the dominant-negative superrepressor IκBα-SR significantly decreases BV6- and γ-irradiation-induced apoptosis. Also, the BV6-mediated enhancement of γ-irradiation-triggered caspase activation, drop of mitochondrial membrane potential, and cytochrome c release is abolished in cells overexpressing IκBα-SR. Similarly, NF-κB inhibition by ectopic expression of a kinase dead mutant of IKKβ prevents the BV6-mediated sensitization for γ-irradiation. The clinical relevance is underscored by experiments with primary tumor samples showing that BV6 sensitizes primary cultured glioma cells as well as glioblastoma-initiating cancer stem cells derived from surgical specimens for γ-irradiation. In conclusion, we identify NF-κB as a critical mediator of Smac mimetic-conferred radiosensitization of glioblastoma cells. These results have important implications for the development of Smac mimetic-based combination protocols for radiosensitization of glioblastoma.
authors.affiliation: Department of Neurology, University of Ulm, Ulm, Germany.
authors.forename: Rebecca
authors.initials: R
authors.lastname: Berger
authors.forename: Claudia
authors.initials: C
authors.lastname: Jennewein
authors.forename: Viola
authors.initials: V
authors.lastname: Marschall
authors.forename: Sabine
authors.initials: S
authors.lastname: Karl
authors.forename: Silvia
authors.initials: S
authors.lastname: Cristofanon
authors.forename: Liane
authors.initials: L
authors.lastname: Wagner
authors.forename: Sri HariKrishna
authors.initials: SH
authors.lastname: Vellanki
authors.forename: Stephanie
authors.initials: S
authors.lastname: Hehlgans
authors.forename: Franz
authors.initials: F
authors.lastname: Rödel
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Debatin
authors.forename: Albert C
authors.initials: AC
authors.lastname: Ludolph
authors.forename: Simone
authors.initials: S
authors.lastname: Fulda
mesh_terms: D017209:Apoptosis / Q000187:drug effects / Q000528:radiation effects; D051017:Apoptosis Regulatory Proteins; D040761:Biomimetic Materials / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D005720:Gamma Rays; D005909:Glioblastoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology / Q000532:radiotherapy*; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins / Q000737:chemistry / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000737:chemistry / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism*; D011838:Radiation-Sensitizing Agents / Q000494:pharmacology*
chemical_list: D051017:Apoptosis Regulatory Proteins; C412403:DIABLO protein, human; D051034:Inhibitor of Apoptosis Proteins; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D016328:NF-kappa B; D011838:Radiation-Sensitizing Agents