title: Proteasome inhibitors induce a terminal unfolded protein response in multiple myeloma cells.
abstract: Multiple myeloma (MM) is an incurable plasma cell malignancy. The 26S proteasome inhibitor, bortezomib, selectively induces apoptosis in MM cells; however, the nature of its selectivity remains unknown. Here we demonstrate that 5 different MM cell lines display similar patterns of sensitivity to 3 proteasome inhibitors (PIs) but respond differently to specific NF-kappaB inhibition. We further show that PIs initiate the unfolded protein response (UPR), a signaling pathway activated by the accumulation of misfolded proteins within the endoplasmic reticulum (ER). Consistent with reports that prosurvival/physiologic UPR components are required for B-cell differentiation into antibody-secreting cells, we found that MM cells inherently expressed the ER chaperones GRP78/Bip and GRP94/gp96. However, bortezomib rapidly induced components of the proapoptotic/terminal UPR, including PERK, the ER stress-specific eIF-2alpha kinase; ATF4, an ER stress-induced transcription factor; and its proapoptotic target, CHOP/GADD153. Consistent with our hypothesis that PIs induce the accumulation of misfolded ER-processed proteins, we found that the amount of immunoglobulin subunits retained within MM cells correlated with their sensitivity to PIs. These findings suggest that MM cells have a lower threshold for PI-induced UPR induction and ER stress-induced apoptosis because they constitutively express ER stress survival factors to function as secretory cells.
authors.affiliation: Department of Microbiology and Immunology, University of Miami Miller School of Medicine, Miami, FL 33101, USA.
authors.forename: Esther A
authors.initials: EA
authors.lastname: Obeng
authors.forename: Louise M
authors.initials: LM
authors.lastname: Carlson
authors.forename: Delia M
authors.initials: DM
authors.lastname: Gutman
authors.forename: William J
authors.initials: WJ
authors.lastname: Harrington
authors.forename: Kelvin P
authors.initials: KP
authors.lastname: Lee
authors.forename: Lawrence H
authors.initials: LH
authors.lastname: Boise
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D001897:Boronic Acids / Q000494:pharmacology* / Q000627:therapeutic use; D000069286:Bortezomib; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000201:enzymology; D000091342:Endoplasmic Reticulum Chaperone BiP; D006801:Humans; D009101:Multiple Myeloma / Q000188:drug therapy / Q000201:enzymology*; D009363:Neoplasm Proteins / Q000096:biosynthesis; D010950:Plasma Cells / Q000201:enzymology / Q000473:pathology; D011480:Protease Inhibitors / Q000494:pharmacology* / Q000627:therapeutic use; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D017510:Protein Folding; D011719:Pyrazines / Q000494:pharmacology* / Q000627:therapeutic use; D015398:Signal Transduction / Q000187:drug effects*
chemical_list: D001897:Boronic Acids; D000091342:Endoplasmic Reticulum Chaperone BiP; C000717247:HSPA5 protein, human; D009363:Neoplasm Proteins; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D000069286:Bortezomib; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease