title: Bortezomib inhibits PKR-like endoplasmic reticulum (ER) kinase and induces apoptosis via ER stress in human pancreatic cancer cells.
abstract: Bortezomib (Velcade, formerly known as PS-341) is a boronic acid dipeptide derivative that is a selective and potent inhibitor of the proteasome. We hypothesized that proteasome inhibition would lead to an accumulation of misfolded proteins in the cell resulting in endoplasmic reticulum (ER) stress. The ability of bortezomib to induce ER stress and the unfolded protein response was investigated in a human pancreatic cancer cell line, L3.6pl. Bortezomib increased expression of ER stress markers, CHOP and BiP, but inhibited PKR-like ER kinase and subsequent phosphorylation of eukaryotic initiation factor 2alpha (eif2alpha), both of which are key events in translational suppression. These effects resulted in an accumulation of ubiquitylated proteins leading to protein aggregation and proteotoxicity. Peptide inhibitor or small interfering RNA targeting ER-resident caspase-4 blocked DNA fragmentation, establishing a central role for caspase-4 in bortezomib-induced cell death. The translation inhibitor cycloheximide abrogated bortezomib-induced protein aggregation, caspase-4 processing, and all other characteristics of apoptosis. Because malignant cells have higher protein synthesis rates than normal cells, they may be more prone to protein aggregation and proteotoxicity and possess increased sensitivity to bortezomib-induced apoptosis. Taken together, the results show that bortezomib induces a unique type of ER stress compared with other ER stress agents characterized by an absence of eif2alpha phosphorylation, ubiquitylated protein accumulation, and proteotoxicity.
authors.affiliation: Department of Cancer Biology, University of Texas MD Anderson Cancer Center, Houston, 77030, USA.
authors.forename: Steffan T
authors.initials: ST
authors.lastname: Nawrocki
authors.forename: Jennifer S
authors.initials: JS
authors.lastname: Carew
authors.forename: Kenneth
authors.initials: K
authors.lastname: Dunner
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Boise
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Chiao
authors.forename: Peng
authors.initials: P
authors.lastname: Huang
authors.forename: James L
authors.initials: JL
authors.lastname: Abbruzzese
authors.forename: David J
authors.initials: DJ
authors.lastname: McConkey
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D002118:Calcium / Q000378:metabolism; D061945:Caspase Inhibitors; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D053471:Caspases, Initiator; D003513:Cycloheximide / Q000494:pharmacology; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins / Q000378:metabolism; D006801:Humans; D018832:Molecular Chaperones / Q000378:metabolism; D018384:Oxidative Stress; D010179:Pancreas / Q000187:drug effects / Q000378:metabolism / Q000473:pathology; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000187:drug effects; D011499:Protein Processing, Post-Translational; D011719:Pyrazines / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D019284:Thapsigargin / Q000494:pharmacology; D051742:Transcription Factor CHOP / Q000378:metabolism; D025801:Ubiquitin / Q000378:metabolism; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors* / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D000069286:Bortezomib; D002118:Calcium; D061945:Caspase Inhibitors; D020169:Caspases; D053471:Caspases, Initiator; D003513:Cycloheximide; D000091342:Endoplasmic Reticulum Chaperone BiP; D006360:Heat-Shock Proteins; D018832:Molecular Chaperones; D011719:Pyrazines; D034741:RNA, Small Interfering; D019284:Thapsigargin; D051742:Transcription Factor CHOP; D025801:Ubiquitin; D019892:eIF-2 Kinase; C093516:CASP4 protein, human