title: Effects of PS-341 on the activity and composition of proteasomes in multiple myeloma cells.
abstract: Multiple myeloma is a B-cell malignancy for which no curative therapies exist to date, despite enormous research efforts. The remarkable activity of the proteasome inhibitor bortezomib (PS-341, Velcade) observed in clinical trials of patients with relapsed refractory myeloma has led to investigations of the role of the ubiquitin-proteasome pathway in the pathogenesis of myeloma. Here we report a biochemical analysis of proteasome activity and composition in myeloma cells exposed to PS-341 in the presence or absence of cytokines present in the bone marrow milieu. We observed that the myeloma cell lines MM1.S, RPMI8226, and U266 contain active immunoproteasomes, the amount of which is enhanced by IFN-gamma and tumor necrosis factor-alpha. Using a radiolabeled active site-directed probe specific for proteasome catalytic subunits, we show that PS-341 targets the beta5 and beta1 subunits in a concentration-dependent manner. Furthermore, PS-341 also targeted the corresponding catalytic subunits of the immunoproteasome, beta5i and beta1i, respectively. These data suggest that PS-341 targets both normal and immunoproteasome species to a similar extent in myeloma cells.
authors.affiliation: Department of Pathology, Harvard Medical School, Boston, Massachusetts, USA.
authors.forename: Mikael
authors.initials: M
authors.lastname: Altun
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Galardy
authors.forename: Reshma
authors.initials: R
authors.lastname: Shringarpure
authors.forename: Teru
authors.initials: T
authors.lastname: Hideshima
authors.forename: Richard
authors.initials: R
authors.lastname: LeBlanc
authors.forename: Kenneth C
authors.initials: KC
authors.lastname: Anderson
authors.forename: Hidde L
authors.initials: HL
authors.lastname: Ploegh
authors.forename: Benedikt M
authors.initials: BM
authors.lastname: Kessler
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000276:immunology; D001897:Boronic Acids / Q000494:pharmacology*; D000069286:Bortezomib; D045744:Cell Line, Tumor; D016207:Cytokines / Q000494:pharmacology; D006367:HeLa Cells; D006801:Humans; D007371:Interferon-gamma / Q000494:pharmacology; D051379:Mice; D009101:Multiple Myeloma / Q000188:drug therapy* / Q000201:enzymology* / Q000276:immunology; D011480:Protease Inhibitors / Q000494:pharmacology*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000494:pharmacology*
chemical_list: D001897:Boronic Acids; D016207:Cytokines; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D000069286:Bortezomib; D007371:Interferon-gamma; D046988:Proteasome Endopeptidase Complex