Perturbed regulation of ZAP-70 and sustained tyrosine phosphorylation of LAT and SLP-76 in c-Cbl-deficient thymocytes.
Recent studies indicate that c-Cbl and its oncogenic variants can modulate the activity of protein tyrosine kinases. This finding is supported by studies showing that c-Cbl interacts directly with a negative regulatory tyrosine in ZAP-70, and that the levels of tyrosine-phosphorylated ZAP-70 and numerous other proteins are increased in TCR-stimulated ... thymocytes from c-Cbl-deficient mice. Here, we demonstrate that this enhanced phosphorylation of ZAP-70 and that of two substrates, LAT and SLP-76, is not due to altered protein levels but is the consequence of two separate events. First, we find increased expression of tyrosine-phosphorylated TCRzeta chain in c-Cbl-deficient thymocytes, which results in a higher level of zeta-chain-associated ZAP-70 that is initially accessible for activation. Thus, more ZAP-70 is activated and more of its substrates (LAT and SLP-76) become tyrosine-phosphorylated after TCR stimulation. However, an additional mechanism of ZAP-70 regulation is evident at a later time poststimulation. At this time, ZAP-70 from both normal and c-Cbl-/- thymocytes becomes hyperphosphorylated; however, only in normal thymocytes does this correlate with ZAP-70 down-regulation and a diminished ability to phosphorylate LAT and SLP-76. In contrast, c-Cbl-deficient thymocytes display altered phosphorylation kinetics, for which LAT phosphorylation is increased and SLP-76 phosphorylation is sustained. Thus, the ability to down-regulate the phosphorylation of two ZAP-70 substrates is impaired in c-Cbl-/- thymocytes. These findings provide evidence that c-Cbl is involved in the negative regulation of the phosphorylation of LAT and SLP-76 by ZAP-70.
Mesh Terms:
Adaptor Proteins, Signal Transducing, Animals, Antigens, CD4, Carrier Proteins, Kinetics, Lymphocyte Specific Protein Tyrosine Kinase p56(lck), Membrane Proteins, Mice, Mice, Inbred C57BL, Mice, Knockout, Phosphoproteins, Phosphorylation, Protein-Tyrosine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-cbl, Receptors, Antigen, T-Cell, Substrate Specificity, T-Lymphocytes, Time Factors, Tyrosine, Ubiquitin-Protein Ligases, ZAP-70 Protein-Tyrosine Kinase, src Homology Domains
Adaptor Proteins, Signal Transducing, Animals, Antigens, CD4, Carrier Proteins, Kinetics, Lymphocyte Specific Protein Tyrosine Kinase p56(lck), Membrane Proteins, Mice, Mice, Inbred C57BL, Mice, Knockout, Phosphoproteins, Phosphorylation, Protein-Tyrosine Kinases, Proto-Oncogene Proteins, Proto-Oncogene Proteins c-cbl, Receptors, Antigen, T-Cell, Substrate Specificity, T-Lymphocytes, Time Factors, Tyrosine, Ubiquitin-Protein Ligases, ZAP-70 Protein-Tyrosine Kinase, src Homology Domains
J. Immunol.
Date: Jun. 15, 1999
PubMed ID: 10358158
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