The proteasome inhibitor bortezomib sensitizes cells to killing by death receptor ligand TRAIL via BH3-only proteins Bik and Bim

• Published in: Molecular cancer therapeutics Vol. 4; no. 3; pp. 443 - 449
• Main Authors: Nikrad, Malti, Johnson, Thomas, Puthalalath, Hamsa, Coultas, Leigh, Adams, Jerry, Kraft, Andrew S
• Format: Journal Article
• Language: English
• Published: United States American Association for Cancer Research 01.03.2005
• Subjects: Animals; Antineoplastic Agents - pharmacology; Apoptosis; Apoptosis Regulatory Proteins; Bcl-2-Like Protein 11; Bik; Bim; Blotting, Western; Boronic Acids - pharmacology; Bortezomib; Carrier Proteins - metabolism; Cell Line; Cell Line, Tumor; Cell Survival; Cells, Cultured; Colonic Neoplasms - drug therapy; Dose-Response Relationship, Drug; Down-Regulation; Fibroblasts - metabolism; Green Fluorescent Proteins - metabolism; Humans; Immunoprecipitation; Male; Membrane Glycoproteins - chemistry; Membrane Glycoproteins - metabolism; Membrane Proteins - metabolism; Mice; Peptide Fragments - chemistry; Plasmids - metabolism; Prostatic Neoplasms - drug therapy; Proteasome Endopeptidase Complex - metabolism; Proto-Oncogene Proteins - chemistry; Proto-Oncogene Proteins - metabolism; Proto-Oncogene Proteins c-bcl-2 - chemistry; Pyrazines - pharmacology; Reverse Transcriptase Polymerase Chain Reaction; RNA - chemistry; RNA Interference; RNAi; TNF-Related Apoptosis-Inducing Ligand; TRAIL; Transfection; Tumor Necrosis Factor-alpha - chemistry; Tumor Necrosis Factor-alpha - metabolism
• ISSN: 1535-7163; 1538-8514
• DOI: 10.1158/1535-7163.MCT-04-0260

Previously, we showed that the proteasome inhibitor bortezomib/Velcade (formerly PS-341) synergizes with the protein tumor necrosis factor α–related apoptosis-inducing ligand (TRAIL), a ligand for certain death receptors, to induce apoptosis in cell lines derived from prostate and colon cancers. Because apoptosis is often triggered by BH3-only proteins of the Bcl-2 family, we have explored the hypothesis that bortezomib contributes to the apoptosis by up-regulating their levels. Indeed, bortezomib induced increases of Bik and/or Bim in multiple cell lines but not notably of two other BH3-only proteins (Puma and Bid) nor other family members (Bax, Bak, Bcl-2, and Bcl-x L ). The increase in Bik levels seems to reflect inhibition by bortezomib of its proteasome-mediated degradation. Importantly, both Bik and Bim seem central to the proapoptotic function of bortezomib, because mouse embryo fibroblasts in which the genes for both Bik and Bim had been disrupted were refractory to its cytotoxic action. Similarly, the synergy between bortezomib and TRAIL in killing human prostate cancer cells was impaired in cells in which both Bik and Bim were down-regulated by RNA interference. Further evidence that bortezomib acts through the mitochondrial pathway regulated by the Bcl-2 family is that deficiency for APAF-1, which acts downstream of Bcl-2, also blocked its apoptotic effect. These results implicate BH3-only proteins, in particular both Bik and Bim, as important mediators of the antitumor action of bortezomib and establish their role in its enhancement of TRAIL-induced apoptosis.