Abstract
LAT is a linker protein essential for activation of T lymphocytes. Its rapid tyrosine-phosphorylation upon T cell receptor (TCR) stimulation recruits downstream signaling molecules for membrane targeting and activation. LAT is physically concentrated in cholesterol-enriched membrane microdomains and is known a substrate for Syk/Zap70 kinase. In this study, we demonstrate that LAT serves as a dual substrate for both Lck and Syk kinases. LAT phosphorylation is absent in Lck-deficient J.CaM1.6 cells and Lck is co-precipitated with LAT in pervanadate-activated Jurkat cells. Further, the in vitro kinase assay using purified Lck and LAT shows that Lck directly phosphorylates LAT. Both Lck and Syk, phosphorylate the ITAM-like motifs on LAT at Y171Y191, which is essential for induction of the interaction of LAT with downstream signaling molecules such as Grb2, PLC-gamma1 and c-Cbl, and for activation of MAPK-ERK. Collectively, our data indicate that LAT is an immediate substrate for Lck in one of the earliest events of T cell activation.
Publication types
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Research Support, N.I.H., Extramural
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Research Support, Non-U.S. Gov't
MeSH terms
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Adaptor Proteins, Signal Transducing / metabolism*
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Cells, Cultured
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GRB2 Adaptor Protein / metabolism
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Humans
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Intracellular Signaling Peptides and Proteins / metabolism*
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Jurkat Cells / metabolism
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Kidney / cytology
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Kidney / metabolism
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Lymphocyte Activation
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / metabolism*
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Membrane Proteins / metabolism*
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Mitogen-Activated Protein Kinase 1 / metabolism
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Mitogen-Activated Protein Kinase 3 / metabolism
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Mitogen-Activated Protein Kinases / metabolism
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Phospholipase C gamma / metabolism
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Phosphorylation
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Protein-Tyrosine Kinases / metabolism*
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Proto-Oncogene Proteins c-cbl / metabolism
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Signal Transduction
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Syk Kinase
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T-Lymphocytes / metabolism*
Substances
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Adaptor Proteins, Signal Transducing
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GRB2 Adaptor Protein
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Intracellular Signaling Peptides and Proteins
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LAT protein, human
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Membrane Proteins
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Proto-Oncogene Proteins c-cbl
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Protein-Tyrosine Kinases
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Lymphocyte Specific Protein Tyrosine Kinase p56(lck)
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SYK protein, human
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Syk Kinase
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Mitogen-Activated Protein Kinase 1
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Mitogen-Activated Protein Kinase 3
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Mitogen-Activated Protein Kinases
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Phospholipase C gamma
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CBL protein, human