Rituxan (anti-CD20 Antibody)-Induced Translocation of CD20 Into Lipid Rafts Is Crucial for Calcium Influx and Apoptosis

Clin Exp Immunol. 2005 Mar;139(3):439-46. doi: 10.1111/j.1365-2249.2005.02720.x.

Abstract

Rituxan, a chimeric anti-CD20 antibody, is the first antibody approved for immunotherapy in non-Hodgkin's B-cell lymphoma and other B-cell lymphoproliferative disorders. Additionally, efficacy of Rituxan treatment has been reported in nonmalignant autoimmune diseases such as rheumatoid arthritis. Crosslinking of CD20 molecules by Rituxan induces therapeutic B-cell depletion. CD20 is a B-lymphocyte specific integral membrane protein, proposed to function as a store-operated calcium channel, which is activated upon receptor-stimulated calcium depletion of intracellular stores. Crosslinking of CD20 by antibodies has been reported to induce a redistribution of CD20 molecules to specialized microdomains at the plasma membrane known as lipid rafts. Here, we report that in the absence of Rituxan, CD20 exhibits a low affinity to lipid rafts. However, binding of Rituxan significantly increases the affinity of CD20 for lipid rafts resulting in its redistribution to a fraction resistant to Triton X-100 solubilization. Furthermore, we demonstrate that disturbing the raft integrity by cholesterol extraction results in dissociation of CD20 from a Triton X-100 resistant fraction followed by complete inhibition of Rituxan-induced calcium entry and apoptosis. The integrity of lipid rafts seems to play a crucial role for CD20-induced caspase activation. These data show, for the first time, that Rituxan-induced translocation of CD20 to lipid rafts is important for increased intracellular Ca(2+) levels and downstream apoptotic signalling.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antibodies, Monoclonal / pharmacology*
  • Antibodies, Monoclonal, Murine-Derived
  • Antigen-Antibody Reactions
  • Antigens, CD20 / immunology*
  • Antineoplastic Agents / pharmacology*
  • Apoptosis
  • B-Lymphocytes / immunology*
  • Biological Transport
  • Calcium / metabolism*
  • Cell Line
  • Cell Membrane / metabolism
  • Cholesterol / metabolism
  • Humans
  • Lipids / immunology*
  • Octoxynol
  • Rituximab
  • Signal Transduction

Substances

  • Antibodies, Monoclonal
  • Antibodies, Monoclonal, Murine-Derived
  • Antigens, CD20
  • Antineoplastic Agents
  • Lipids
  • Rituximab
  • Octoxynol
  • Cholesterol
  • Calcium