title: Bortezomib modulates surface CD20 in B-cell malignancies and affects rituximab-mediated complement-dependent cytotoxicity.
abstract: Unresponsiveness to rituximab treatment develops in many patients prompting elucidation of underlying molecular pathways. It was recently observed that rituximab-resistant lymphoma cells exhibit up-regulation of components of the ubiquitin-proteasome system (UPS). Therefore, we investigated in more detail the role of this system in the regulation of CD20 levels and the influence of proteasome inhibitors on rituximab-mediated complement-dependent cytotoxicity (R-CDC). We observed that incubation of Raji cells with rituximab leads to increased levels of ubiquitinated CD20. However, inhibition of the UPS was not associated with up-regulation of surface CD20 levels, although it significantly increased its ubiquitination. Short-term (24 hours) incubation of Raji cells with 10 or 20 nM bortezomib did not change surface CD20 levels, but sensitized CD20(+) lymphoma cells to R-CDC. Prolonged (48 hours) incubation with 20 nM bortezomib, or incubation with 50 nM bortezomib for 24 hours led to a significant decrease in surface CD20 levels as well as R-CDC. These effects were partly reversed by bafilomycin A1, an inhibitor of lysosomal/autophagosomal pathway of protein degradation. These studies indicate that CD20 levels are regulated by 2 proteolytic systems and that the use of proteasome inhibitors may be associated with unexpected negative influence on R-CDC.
authors.affiliation: Department of Immunology, Center of Biostructure Research, Medical University of Warsaw, 02-097 Warsaw, Poland.
authors.forename: Jacek
authors.initials: J
authors.lastname: Bil
authors.forename: Magdalena
authors.initials: M
authors.lastname: Winiarska
authors.forename: Dominika
authors.initials: D
authors.lastname: Nowis
authors.forename: Kamil
authors.initials: K
authors.lastname: Bojarczuk
authors.forename: Anna
authors.initials: A
authors.lastname: Dabrowska-Iwanicka
authors.forename: Grzegorz W
authors.initials: GW
authors.lastname: Basak
authors.forename: Kazimierz
authors.initials: K
authors.lastname: Sułek
authors.forename: Marek
authors.initials: M
authors.lastname: Jakobisiak
authors.forename: Jakub
authors.initials: J
authors.lastname: Golab
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20 / Q000235:genetics / Q000378:metabolism*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001402:B-Lymphocytes / Q000187:drug effects / Q000378:metabolism; D019921:Biotinylation; D015153:Blotting, Western; D001897:Boronic Acids / Q000627:therapeutic use*; D000069286:Bortezomib; D002478:Cells, Cultured; D003602:Cytotoxicity, Immunologic / Q000276:immunology*; D005434:Flow Cytometry; D006801:Humans; D047468:Immunoprecipitation; D016393:Lymphoma, B-Cell / Q000188:drug therapy* / Q000276:immunology; D011480:Protease Inhibitors / Q000494:pharmacology*; D061988:Proteasome Inhibitors; D011719:Pyrazines / Q000627:therapeutic use*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000069283:Rituximab
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D001897:Boronic Acids; D011480:Protease Inhibitors; D061988:Proteasome Inhibitors; D011719:Pyrazines; D012333:RNA, Messenger; D000069283:Rituximab; D000069286:Bortezomib