title: Bortezomib-resistant myeloma cell lines: a role for mutated PSMB5 in preventing the accumulation of unfolded proteins and fatal ER stress.
abstract: Bortezomib is an effective agent for treating multiple myeloma (MM). To investigate the underlying mechanisms associated with acquired resistance to this agent, we established two bortezomib-resistant MM cell lines, KMS-11/BTZ and OPM-2/BTZ, the 50% inhibitory concentration values of which were respectively 24.7- and 16.6-fold higher than their parental cell lines. No activation of caspase and BH3-only proteins such as Noxa was noted in bortezomib-resistant cells after exposure to the drug. The accumulation of polyubiquitinated proteins was reduced in bortezomib-resistant cells compared with the parental cells, associated with avoidance of catastrophic ER stress as assessed by downregulation of CHOP expression. These resistant MM cells have a unique point mutation, G322A, in the gene encoding the proteasome beta5 subunit (PSMB5), likely resulting in conformational changes to the bortezomib-binding pocket of this subunit. KMS-11 parental cells transfected to express mutated PSMB5 also showed reduced bortezomib-induced apoptosis compared with those expressing wild-type PSMB5 or the parental cells. Expression of mutated PSMB5 was associated with the prevention of the accumulation of unfolded proteins. Thus, a fraction of MM cells may acquire bortezomib resistance by suppressing apoptotic signals through the inhibition of unfolded protein accumulation and subsequent excessive ER stress by a mutation of the PSMB5 gene.
authors.affiliation: Department of Medical Oncology and Immunology, Nagoya City University Graduate School of Medical Sciences, Nagoya, Aichi, Japan.
authors.forename: M
authors.initials: M
authors.lastname: Ri
authors.forename: S
authors.initials: S
authors.lastname: Iida
authors.forename: T
authors.initials: T
authors.lastname: Nakashima
authors.forename: H
authors.initials: H
authors.lastname: Miyazaki
authors.forename: F
authors.initials: F
authors.lastname: Mori
authors.forename: A
authors.initials: A
authors.lastname: Ito
authors.forename: A
authors.initials: A
authors.lastname: Inagaki
authors.forename: S
authors.initials: S
authors.lastname: Kusumoto
authors.forename: T
authors.initials: T
authors.lastname: Ishida
authors.forename: H
authors.initials: H
authors.lastname: Komatsu
authors.forename: Y
authors.initials: Y
authors.lastname: Shiotsu
authors.forename: R
authors.initials: R
authors.lastname: Ueda
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D001483:Base Sequence; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D017931:DNA Primers; D019008:Drug Resistance, Neoplasm / Q000235:genetics; D004721:Endoplasmic Reticulum / Q000378:metabolism*; D006801:Humans; D009101:Multiple Myeloma / Q000473:pathology*; D009154:Mutation; D009363:Neoplasm Proteins / Q000378:metabolism*; D017354:Point Mutation; D046988:Proteasome Endopeptidase Complex / Q000235:genetics* / Q000378:metabolism; D011489:Protein Denaturation; D011719:Pyrazines / Q000494:pharmacology*; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D000970:Antineoplastic Agents; D001897:Boronic Acids; D017931:DNA Primers; D009363:Neoplasm Proteins; D011719:Pyrazines; D025801:Ubiquitin; D000069286:Bortezomib; C088874:PSMB5 protein, human; D046988:Proteasome Endopeptidase Complex