title: Bortezomib primes glioblastoma, including glioblastoma stem cells, for TRAIL by increasing tBid stability and mitochondrial apoptosis.
abstract: OBJECTIVE
  Searching for novel approaches to sensitize glioblastoma for cell death, we investigated the proteasome inhibitor bortezomib.
  
  
  METHODS
  The effect of bortezomib on tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced apoptosis signaling pathways was analyzed in glioblastoma cell lines, primary glioblastoma cultures, and in an in vivo model.
  
  
  RESULTS
  Bortezomib and TRAIL synergistically trigger cell death and reduce colony formation of glioblastoma cells (combination index < 0.1). Investigations into the underlying molecular mechanisms reveal that bortezomib and TRAIL act in concert to cause accumulation of tBid, the active cleavage product of Bid. Also, the stability of TRAIL-derived tBid markedly increases on proteasome inhibition. Notably, knockdown of Bid significantly decreases bortezomib- and TRAIL-mediated cell death. By comparison, silencing of Noxa, which is also upregulated by bortezomib, does not confer protection. Coinciding with tBid accumulation, the activation of Bax/Bak and loss of mitochondrial membrane potential are strongly increased in cotreated cells. Overexpression of Bcl-2 significantly reduces mitochondrial perturbations and cell death, underscoring the functional relevance of the mitochondrial pathway. In addition, bortezomib cooperates with TRAIL to reduce colony formation of glioblastoma cells, showing an effect on long-term survival. Of note, bortezomib profoundly enhances TRAIL-triggered cell death in primary cultured glioblastoma cells and in patient-derived glioblastoma stem cells, underlining the clinical relevance. Importantly, bortezomib cooperates with TRAIL to suppress tumor growth in an in vivo glioblastoma model.
  
  
  CONCLUSIONS
  These findings provide compelling evidence that the combination of bortezomib and TRAIL presents a promising novel strategy to trigger cell death in glioblastoma, including glioblastoma stem cells, which warrants further investigation.
authors.affiliation: University Children's Hospital, Ulm, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Unterkircher
authors.forename: Silvia
authors.initials: S
authors.lastname: Cristofanon
authors.forename: Sri Hari Krishna
authors.initials: SH
authors.lastname: Vellanki
authors.forename: Lisa
authors.initials: L
authors.lastname: Nonnenmacher
authors.forename: Georg
authors.initials: G
authors.lastname: Karpel-Massler
authors.forename: Christian Rainer
authors.initials: CR
authors.lastname: Wirtz
authors.forename: Klaus-Michael
authors.initials: KM
authors.lastname: Debatin
authors.forename: Simone
authors.initials: S
authors.lastname: Fulda
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D051023:BH3 Interacting Domain Death Agonist Protein / Q000378:metabolism*; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D016923:Cell Death / Q000187:drug effects; D045744:Cell Line, Tumor; D053418:Death Domain Receptor Signaling Adaptor Proteins / Q000378:metabolism; D005909:Glioblastoma / Q000473:pathology*; D006801:Humans; D008928:Mitochondria / Q000187:drug effects*; D014411:Neoplastic Stem Cells / Q000187:drug effects*; D055550:Protein Stability / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D011719:Pyrazines / Q000494:pharmacology*; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D053221:TNF-Related Apoptosis-Inducing Ligand / Q000378:metabolism*
chemical_list: D000970:Antineoplastic Agents; D051023:BH3 Interacting Domain Death Agonist Protein; D001897:Boronic Acids; D053418:Death Domain Receptor Signaling Adaptor Proteins; C498702:PMAIP1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D011719:Pyrazines; D053220:Receptors, TNF-Related Apoptosis-Inducing Ligand; D053221:TNF-Related Apoptosis-Inducing Ligand; D000069286:Bortezomib