title: Colocalization of the B cell receptor and CD20 followed by activation-dependent dissociation in distinct lipid rafts.
abstract: The B cell Ag receptor (BCR) and CD20, a putative calcium channel, inducibly associate with cholesterol-dependent membrane microdomains known as lipid rafts. A functional association between the BCR and CD20 is suggested by the effects of CD20-specific mAbs, which can modulate cell cycle transitions elicited by BCR signaling. Using immunofluorescence microscopy we show here that the BCR and CD20 colocalize after receptor ligation and then rapidly dissociate at the cell surface before endocytosis of the BCR. After separation, surface BCR and CD20 were detected in distinct lipid rafts isolated as low density, detergent-resistant membrane fragments. Pretreatment with methyl-beta-cyclodextrin, which we have previously shown to enhance receptor-mediated calcium mobilization, did not prevent colocalization of the BCR and CD20, but slowed their dissociation. The data demonstrate rapid dynamics of the BCR in relation to CD20 at the cell surface. Activation-dependent dissociation of the BCR from CD20 occurs before receptor endocytosis and appears to require in part the integrity of lipid rafts.
authors.affiliation: Department of Biochemistry and Molecular Biology, Immunology Research Group, Faculty of Medicine, University of Calgary, Calgary, Alberta, Canada.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Petrie
authors.forename: Julie P
authors.initials: JP
authors.lastname: Deans
mesh_terms: D018951:Antigens, CD20 / Q000276:immunology / Q000378:metabolism*; D001402:B-Lymphocytes / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D002462:Cell Membrane / Q000276:immunology / Q000378:metabolism; D003505:Cyclodextrins / Q000494:pharmacology; D003902:Detergents / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000276:immunology; D006801:Humans; D007700:Kinetics; D008213:Lymphocyte Activation; D021962:Membrane Microdomains / Q000187:drug effects / Q000276:immunology* / Q000378:metabolism*; D008856:Microscopy, Fluorescence; D011947:Receptors, Antigen, B-Cell / Q000037:antagonists & inhibitors / Q000276:immunology / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D047392:beta-Cyclodextrins
chemical_list: D018951:Antigens, CD20; D003505:Cyclodextrins; D003902:Detergents; D011947:Receptors, Antigen, B-Cell; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin