Abstract
The Csk tyrosine kinase negatively regulates the Src family kinases Lck and Fyn in T cells. Engagement of the T-cell antigen receptor results in a removal of Csk from the lipid raft-associated transmembrane protein PAG/Cbp. Instead, Csk becomes associated with an approximately 72-kDa tyrosine-phosphorylated protein, which we identify here as G3BP, a phosphoprotein reported to bind the SH3 domain of Ras GTPase-activating protein. G3BP reduced the ability of Csk to phosphorylate Lck at Y505 by decreasing the amount of Csk in lipid rafts. As a consequence, G3BP augmented T-cell activation as measured by interleukin-2 gene activation. Conversely, elimination of endogenous G3BP by RNA interference increased Lck Y505 phosphorylation and reduced TCR signaling. In antigen-specific T cells, endogenous G3BP moved into a intracellular location adjacent to the immune synapse, but deeper inside the cell, upon antigen recognition. Csk colocalization with G3BP occurred in this "parasynaptic" location. We conclude that G3BP is a new player in T-cell-antigen receptor signaling and acts to reduce the amount of Csk in the immune synapse.
Publication types
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Research Support, Non-U.S. Gov't
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adaptor Proteins, Signal Transducing
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CD3 Complex / immunology
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CD3 Complex / metabolism
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CSK Tyrosine-Protein Kinase
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Carrier Proteins / analysis
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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DNA Helicases
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Humans
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Jurkat Cells
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Ligands
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Lymphocyte Activation / immunology
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Lymphocyte Activation / physiology
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / metabolism*
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Membrane Microdomains / metabolism
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Membrane Microdomains / physiology
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Membrane Proteins / metabolism
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Phosphoproteins / metabolism
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Phosphorylation
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Phosphotransferases / analysis
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Phosphotransferases / metabolism
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Phosphotransferases / physiology*
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Poly-ADP-Ribose Binding Proteins
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Protein-Tyrosine Kinases
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Proto-Oncogene Proteins / analysis
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins / physiology*
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RNA Helicases
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RNA Recognition Motif Proteins
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RNA, Small Interfering / genetics
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Receptors, Antigen, T-Cell / immunology*
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Receptors, Antigen, T-Cell / physiology
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Signal Transduction / genetics
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Signal Transduction / immunology*
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Signal Transduction / physiology
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T-Lymphocytes / chemistry
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T-Lymphocytes / enzymology*
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T-Lymphocytes / immunology
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Tyrosine / metabolism
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src Homology Domains / physiology
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src-Family Kinases
Substances
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Adaptor Proteins, Signal Transducing
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CD3 Complex
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Carrier Proteins
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Ligands
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Membrane Proteins
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PAG1 protein, human
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Phosphoproteins
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Poly-ADP-Ribose Binding Proteins
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Proto-Oncogene Proteins
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RNA Recognition Motif Proteins
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RNA, Small Interfering
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Receptors, Antigen, T-Cell
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Tyrosine
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Phosphotransferases
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Protein-Tyrosine Kinases
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CSK Tyrosine-Protein Kinase
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
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src-Family Kinases
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CSK protein, human
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DNA Helicases
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G3BP1 protein, human
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RNA Helicases