Abstract
In resting T cells, Csk is constitutively localized in lipid rafts by virtue of interaction with a phosphorylated adaptor protein, Csk-binding protein (Cbp)/phosphoprotein associated with glycolipid-enriched microdomains, and sets an activation threshold in TCR signaling. In this study, we examined a kinase responsible for Cbp phosphorylation in T cell membrane rafts. By analyzing T cells from Fyn-/- mice, we clearly demonstrated that Fyn, but not Lck, has its kinase activity in membrane rafts, and plays a critical role in Cbp phosphorylation, Cbp-Csk interaction, and Csk kinase activity. Naive CD44(low)CD62 ligand(high) T cells were substantially reduced in Fyn-/- mice, presumably due to the inhibition of Cbp phosphorylation. Thus, Fyn mediates Cbp-Csk interaction and recruits Csk to rafts by phosphorylating Cbp. Csk recruited to rafts would then be activated and inhibit the kinase activity of Lck to keep resting T cells in a quiescent state. Our results elucidate a negative regulatory role for Fyn in proximal TCR signaling in lipid rafts.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing
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Animals
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Glycolipids / metabolism
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Humans
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Immunophenotyping
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Intercellular Signaling Peptides and Proteins
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Interphase / genetics
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Interphase / immunology*
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Jurkat Cells
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Lymphocyte Count
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / metabolism
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Membrane Microdomains / enzymology
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Membrane Microdomains / metabolism*
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Membrane Proteins / metabolism*
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Mice
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Mice, Inbred C57BL
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Mice, Knockout
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Phosphoproteins / metabolism*
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Phosphorylation
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Protein-Tyrosine Kinases / metabolism
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Protein-Tyrosine Kinases / physiology*
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Proto-Oncogene Proteins / deficiency
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins / physiology*
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Proto-Oncogene Proteins c-fyn
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Proto-Oncogene Proteins pp60(c-src)*
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T-Lymphocyte Subsets / cytology
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T-Lymphocyte Subsets / enzymology
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T-Lymphocyte Subsets / metabolism*
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Tyrosine / antagonists & inhibitors
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Tyrosine / metabolism*
Substances
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Adaptor Proteins, Signal Transducing
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Glycolipids
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Intercellular Signaling Peptides and Proteins
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Membrane Proteins
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PAG1 protein, human
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Pag protein, mouse
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Pag1 protein, mouse
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Phosphoproteins
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Proto-Oncogene Proteins
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Tyrosine
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Matk protein, mouse
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Protein-Tyrosine Kinases
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FYN protein, human
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Fyn protein, mouse
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
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Proto-Oncogene Proteins c-fyn
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Proto-Oncogene Proteins pp60(c-src)