title: Proteasome inhibitors disrupt the unfolded protein response in myeloma cells.
abstract: Novel agents that target the proteasome, a proteolytic complex responsible for the degradation of ubiquitinated proteins, have demonstrated remarkable therapeutic efficacy in multiple myeloma, a plasma cell malignancy. However, the mechanism by which these compounds act remains unknown. A signaling pathway called the unfolded protein response (UPR) allows cells to handle the proper folding of proteins. The transcription factor XBP-1, a regulator of the UPR, is also required for plasma cell differentiation, suggesting a link between the UPR and plasma cell differentiation. Here we show that proteasome inhibitors target XBP-1 and the UPR in myeloma cells. Proteasome inhibitors suppress the activity of the translumenal endoplasmic reticulum endoribonuclease/kinase, IRE1 alpha, to impair the generation of the active, spliced XBP-1 species and simultaneously stabilize the unspliced species that acts as a dominant negative. Myeloma cells rendered functionally deficient in XBP-1 undergo increased apoptosis in response to endoplasmic reticulum stress. Identification of compounds that target the activity of IRE1 alpha/XBP-1 may yield novel therapies for the treatment of multiple myeloma and other malignancies that rely on an intact UPR.
authors.affiliation: Department of Immunology and Infectious Diseases, Harvard School of Public Health, Boston, MA 02115-6017, USA.
authors.forename: Ann-Hwee
authors.initials: AH
authors.lastname: Lee
authors.forename: Neal N
authors.initials: NN
authors.lastname: Iwakoshi
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Anderson
authors.forename: Laurie H
authors.initials: LH
authors.lastname: Glimcher
mesh_terms: D016475:3T3 Cells; D000818:Animals; D017209:Apoptosis / Q000187:drug effects; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000187:drug effects; D004722:Endoribonucleases; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D008565:Membrane Proteins; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000235:genetics / Q000378:metabolism*; D009363:Neoplasm Proteins / Q000235:genetics / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D012326:RNA Splicing / Q000187:drug effects; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014407:Tumor Cells, Cultured; D014415:Tunicamycin / Q000494:pharmacology; D000071717:X-Box Binding Protein 1
chemical_list: D015853:Cysteine Proteinase Inhibitors; D004268:DNA-Binding Proteins; D007976:Leupeptins; D008565:Membrane Proteins; D009097:Multienzyme Complexes; D009363:Neoplasm Proteins; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C000605544:Xbp1 protein, mouse; D014415:Tunicamycin; C403982:ERN2 protein, human; C486556:Ern2 protein, mouse; D017346:Protein Serine-Threonine Kinases; D004722:Endoribonucleases; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde