Lipid rafts associate with intracellular B cell receptors and exhibit a B cell stage-specific protein composition.
Lipid rafts serve as platforms for BCR signal transduction. To better define the molecular basis of these membrane microdomains, we used two-dimensional gel electrophoresis and mass spectrometry to characterize lipid raft proteins from mature as well as immature B cell lines. Of 51 specific raft proteins, we identified a total of 18 proteins by peptide mass fingerprinting. Among them, we found vacuolar ATPase subunits alpha-1 and beta-2, vimentin, gamma-actin, mitofilin, and prohibitin. None of these has previously been reported in lipid rafts of B cells. The differential raft association of three proteins, including a novel potential signaling molecule designated swiprosin-1, correlated with the stage-specific sensitivity of B cells to BCR-induced apoptosis. In addition, MHC class II molecules were detected in lipid rafts of mature, but not immature B cells. This intriguing finding points to a role for lipid rafts in regulating Ag presentation during B cell maturation. Finally, a fraction of the BCR in the B cell line CH27 was constitutively present in lipid rafts. Surprisingly, this fraction was neither expressed at the cell surface nor fully O-glycosylated. Thus, we conclude that partitioning the BCR into lipid rafts occurs in the endoplasmic reticulum/cis-Golgi compartment and may represent a control mechanism for surface transport.
Mielenz
Dirk
D
Division of Molecular Immunology, Department of Internal Medicine III, University of Erlangen, Erlangen, Germany. dmielenz@molmed.uni-erlangen.de
Vettermann
Christian
C
Hampel
Martin
M
Lang
Christiane
C
Avramidou
Athanasia
A
Karas
Michael
M
Jäck
Hans-Martin
HM
D000818:Animals; D017209:Apoptosis; D001402:B-Lymphocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism*; D002454:Cell Differentiation; D002460:Cell Line; D003902:Detergents; D015180:Electrophoresis, Gel, Two-Dimensional; D006031:Glycosylation; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry* / Q000276:immunology* / Q000378:metabolism; D051379:Mice; D010449:Peptide Mapping; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D015398:Signal Transduction; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D003902:Detergents; D000949:Histocompatibility Antigens Class II; D008565:Membrane Proteins; D011947:Receptors, Antigen, B-Cell