The B cell-specific major raft protein, Raftlin, is necessary for the integrity of lipid raft and BCR signal transduction.
Recent evidence indicates that membrane microdomains, termed lipid rafts, have a role in B-cell activation as platforms for B-cell antigen receptor (BCR) signal initiation. To gain an insight into the possible functioning of lipid rafts in B cells, we applied liquid chromatography electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS) methodologies to the identification of proteins that co-purified with lipid rafts of Raji cells. Among these raft proteins, we characterized a novel protein termed Raftlin (raft-linking protein). Like the Src family kinase, Raftlin is localized exclusively in lipid rafts by fatty acylation of N-terminal Gly2 and Cys3, and is co-localized with BCR before and after BCR stimulation. Disruption of the Raftlin gene in the DT40 B-cell line resulted in a marked reduction in the quantity of lipid raft components, including Lyn and ganglioside GM1, while overexpression of Raftlin increased the content of raft protein. Moreover, BCR-mediated tyrosine phosphorylation and calcium mobilization were impaired by the lack of Raftlin and actually potentiated by overexpression of Raftlin. These data suggest that Raftlin plays a pivotal role in the formation and/or maintenance of lipid rafts, therefore regulating BCR-mediated signaling.
Saeki
Kazuko
K
Division of Molecular and Cellular Immunology, Medical Institute of Bioregulation, Kyushu University, 3-1-1 Maidashi, Higashi-ku, Fukuoka 812-8582, Japan.
Miura
Yoshiki
Y
Aki
Daisuke
D
Kurosaki
Tomohiro
T
Yoshimura
Akihiko
A
D000215:Acylation; D000595:Amino Acid Sequence; D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D002458:Cell Fractionation; D002460:Cell Line; D002645:Chickens; D006801:Humans; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000235:genetics / Q000378:metabolism; D021962:Membrane Microdomains / Q000737:chemistry* / Q000378:metabolism*; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D011947:Receptors, Antigen, B-Cell / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D016415:Sequence Alignment; D015398:Signal Transduction / Q000502:physiology*; D021241:Spectrometry, Mass, Electrospray Ionization; D014018:Tissue Distribution
D008565:Membrane Proteins; C476398:RFTN1 protein, human; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck)