Abstract
We have previously shown that ASK1 undergoes ubiquitination and degradation in resting endothelial cells (EC) and that proinflammatory cytokine tumor necrosis factor (TNF) induces deubiquitination and stabilization, leading to ASK1 activation. However, the mechanism for the regulation of ASK1 stability is not known. In the present study, we have shown that SOCS1, a member of suppressor of cytokine signaling, induces ASK1 degradation. SOCS1 was constitutively expressed in EC and formed a labile complex with ASK1 that can be stabilized by proteasomal inhibitors. The phosphotyrosine-binding SH2 domain of SOCS1 was critical for its association with ASK1. Thus a SOCS1 mutant defective in phosphotyrosine binding failed to bind to and induce ASK1 degradation. Phosphotyrosine of ASK1 was induced in response to growth factors, and TNF induced dephosphorylation and dissociation of ASK1 from SOCS1. ASK1 with a mutation at Tyr-718 diminished the binding to SOCS1, suggesting that the phosphotyrosine-718 of ASK1 is critical for SOCS1 binding. Moreover, ASK1 expression and activity were up-regulated in SOCS1-deficient mice and derived EC, resulting in enhanced TNF-induced activation of JNK, expression of proinflammatory molecules, and apoptotic responses. We concluded that SOCS1 functions as a negative regulator in TNF-induced inflammation in EC, in part, by inducing ASK1 degradation.
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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Animals
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Cattle
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Cells, Cultured
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Endothelial Cells / cytology
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Endothelial Cells / metabolism
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Enzyme Activation
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Inflammation / metabolism*
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Intracellular Signaling Peptides and Proteins / genetics
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Intracellular Signaling Peptides and Proteins / metabolism*
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JNK Mitogen-Activated Protein Kinases / genetics
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JNK Mitogen-Activated Protein Kinases / metabolism*
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MAP Kinase Kinase Kinase 5 / genetics
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MAP Kinase Kinase Kinase 5 / metabolism*
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Mice
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Mice, Knockout
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Recombinant Fusion Proteins / genetics
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Recombinant Fusion Proteins / metabolism
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Repressor Proteins / genetics
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Repressor Proteins / metabolism*
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Signal Transduction / physiology*
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Suppressor of Cytokine Signaling 1 Protein
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Suppressor of Cytokine Signaling 3 Protein
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Suppressor of Cytokine Signaling Proteins / genetics
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Suppressor of Cytokine Signaling Proteins / metabolism*
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Tumor Necrosis Factor-alpha / metabolism*
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src Homology Domains
Substances
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Intracellular Signaling Peptides and Proteins
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Recombinant Fusion Proteins
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Repressor Proteins
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SOCS1 protein, human
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SOCS2 protein, human
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SOCS3 protein, human
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SOCS6 protein, human
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Suppressor of Cytokine Signaling 1 Protein
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Suppressor of Cytokine Signaling 3 Protein
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Suppressor of Cytokine Signaling Proteins
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Tumor Necrosis Factor-alpha
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JNK Mitogen-Activated Protein Kinases
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MAP Kinase Kinase Kinase 5
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MAP3K5 protein, human