title: Rituxan (anti-CD20 antibody)-induced translocation of CD20 into lipid rafts is crucial for calcium influx and apoptosis.
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.
authors.affiliation: Rheumatoid Arthritis Biology, RI-CEDD, Stevenage, UK. eva.x.janas@gsk.com
authors.forename: E
authors.initials: E
authors.lastname: Janas
authors.forename: R
authors.initials: R
authors.lastname: Priest
authors.forename: J I
authors.initials: JI
authors.lastname: Wilde
authors.forename: J H
authors.initials: JH
authors.lastname: White
authors.forename: R
authors.initials: R
authors.lastname: Malhotra
mesh_terms: D000911:Antibodies, Monoclonal / Q000494:pharmacology*; D058846:Antibodies, Monoclonal, Murine-Derived; D000937:Antigen-Antibody Reactions; D018951:Antigens, CD20 / Q000276:immunology*; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis; D001402:B-Lymphocytes / Q000276:immunology*; D001692:Biological Transport; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D002784:Cholesterol / Q000378:metabolism; D006801:Humans; D008055:Lipids / Q000276:immunology*; D017830:Octoxynol; D000069283:Rituximab; D015398:Signal Transduction
chemical_list: D000911:Antibodies, Monoclonal; D058846:Antibodies, Monoclonal, Murine-Derived; D018951:Antigens, CD20; D000970:Antineoplastic Agents; D008055:Lipids; D000069283:Rituximab; D017830:Octoxynol; D002784:Cholesterol; D002118:Calcium
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