Abstract
The ability of thymocytes to assess T cell receptor (TCR) signaling strength and initiate the appropriate downstream response is crucial for determining their fate. We have previously shown that a c-Cbl RING finger mutant knock-in mouse, in which the E3 ubiquitin ligase activity of c-Cbl is inactivated, is highly sensitive to TCR-induced death signals that cause thymic deletion. This high intensity signal involves the enhanced tyrosine phosphorylation of the mutant c-Cbl protein promoting a marked increase in the activation of Akt. Here we show that this high intensity signal in c-Cbl RING finger mutant thymocytes also promotes the enhanced induction of two mediators of TCR-directed thymocyte apoptosis, Nur77 and the pro-apoptotic Bcl-2 family member, Bim. In contrast, a knock-in mouse harboring a mutation at Tyr-737, the site in c-Cbl that activates phosphatidylinositol 3-kinase, shows reduced TCR-mediated responses including suppression of Akt activation, a reduced induction of Nur77 and Bim, and greater resistance to thymocyte death. These findings identify tyrosine-phosphorylated c-Cbl as a critical sensor of TCR signal strength that regulates the engagement of death-promoting signals.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Animals
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Apoptosis Regulatory Proteins / genetics
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Apoptosis Regulatory Proteins / metabolism
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Apoptosis*
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Bcl-2-Like Protein 11
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Blotting, Western
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Cells, Cultured
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Flow Cytometry
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Immunoprecipitation
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Membrane Proteins / genetics
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Membrane Proteins / metabolism
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Mice
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Mice, Knockout
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Mutation / genetics
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Nuclear Receptor Subfamily 4, Group A, Member 1 / genetics
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Nuclear Receptor Subfamily 4, Group A, Member 1 / metabolism
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Phosphatidylinositol 3-Kinases / genetics
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Phosphatidylinositol 3-Kinases / metabolism*
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Phosphorylation
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism
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Proto-Oncogene Proteins c-akt / genetics
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Proto-Oncogene Proteins c-akt / metabolism*
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Proto-Oncogene Proteins c-cbl / physiology*
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RNA, Messenger / genetics
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RNA, Messenger / metabolism
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Receptors, Antigen, T-Cell / genetics
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Receptors, Antigen, T-Cell / metabolism*
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Reverse Transcriptase Polymerase Chain Reaction
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Signal Transduction
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Thymus Gland / cytology
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Thymus Gland / metabolism*
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Tyrosine / genetics
Substances
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Apoptosis Regulatory Proteins
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Bcl-2-Like Protein 11
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Bcl2l11 protein, mouse
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Membrane Proteins
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Nr4a1 protein, mouse
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Nuclear Receptor Subfamily 4, Group A, Member 1
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Proto-Oncogene Proteins
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RNA, Messenger
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Receptors, Antigen, T-Cell
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Tyrosine
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Proto-Oncogene Proteins c-cbl
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Phosphatidylinositol 3-Kinases
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Proto-Oncogene Proteins c-akt