Bortezomib modulates surface CD20 in B-cell malignancies and affects rituximab-mediated complement-dependent cytotoxicity

Blood. 2010 May 6;115(18):3745-55. doi: 10.1182/blood-2009-09-244129. Epub 2010 Mar 3.


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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20 / genetics
  • Antigens, CD20 / metabolism*
  • Antineoplastic Agents / pharmacology*
  • B-Lymphocytes / drug effects
  • B-Lymphocytes / metabolism
  • Biotinylation
  • Blotting, Western
  • Boronic Acids / therapeutic use*
  • Bortezomib
  • Cells, Cultured
  • Cytotoxicity, Immunologic / immunology*
  • Flow Cytometry
  • Humans
  • Immunoprecipitation
  • Lymphoma, B-Cell / drug therapy*
  • Lymphoma, B-Cell / immunology
  • Protease Inhibitors / pharmacology*
  • Proteasome Inhibitors
  • Pyrazines / therapeutic use*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • Reverse Transcriptase Polymerase Chain Reaction
  • Rituximab


  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20
  • Antineoplastic Agents
  • Boronic Acids
  • Protease Inhibitors
  • Proteasome Inhibitors
  • Pyrazines
  • RNA, Messenger
  • Rituximab
  • Bortezomib