Abstract
The isoforms of SH2-B, APS, and Lnk form a family of signaling proteins that have been described as activators, mediators, or inhibitors of cytokine and growth factor signaling. We now show that the three alternatively spliced isoforms of human SH2-B readily homodimerize in yeast two-hybrid and cellular transfections assays, and this is mediated specifically by a unique domain in its amino terminus. Consistent with previous reports, we further show that the SH2 domains of SH2-B and APS bind JAK2 at Tyr813. These findings suggested a model in which two molecules of SH2-B or APS homodimerize with their SH2 domains bound to two JAK2 molecules, creating heterotetrameric JAK2-(SH2-B)2-JAK2 or JAK2-(APS)2-JAK2 complexes. We further show that APS and SH2-B isoforms heterodimerize. At lower levels of SH2-B or APS expression, dimerization approximates two JAK2 molecules to induce transactivation. At higher relative concentrations of SH2-B or APS, kinase activation is blocked. SH2-B or APS homodimerization and SH2-B/APS heterodimerization thus provide direct mechanisms for activating and inhibiting JAK2 and other kinases from the inside of the cell and for potentiating or attenuating cytokine and growth factor receptor signaling when ligands are present.
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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Amino Acid Sequence
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Animals
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Carrier Proteins / chemistry*
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Carrier Proteins / genetics
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Carrier Proteins / metabolism*
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Cell Line
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Cloning, Molecular
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DNA-Binding Proteins / metabolism
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Dimerization
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Enzyme Activation
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Humans
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Janus Kinase 2
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Mice
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Milk Proteins / metabolism
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Models, Molecular
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Molecular Sequence Data
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Phosphorylation / drug effects
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Phosphotransferases (Alcohol Group Acceptor) / chemistry
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Phosphotransferases (Alcohol Group Acceptor) / genetics
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Phosphotransferases (Alcohol Group Acceptor) / metabolism
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Phosphotyrosine / metabolism
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Protein Binding
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Protein Isoforms / chemistry
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Protein Isoforms / genetics
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Protein Isoforms / metabolism
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Protein Kinases / chemistry
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Protein Kinases / metabolism*
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Protein Structure, Quaternary
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Protein-Tyrosine Kinases / antagonists & inhibitors
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Protein-Tyrosine Kinases / genetics
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Protein-Tyrosine Kinases / metabolism
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Proto-Oncogene Proteins / antagonists & inhibitors
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Proto-Oncogene Proteins / genetics
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Proto-Oncogene Proteins / metabolism
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STAT5 Transcription Factor
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Trans-Activators / metabolism
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Two-Hybrid System Techniques
Substances
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Adaptor Proteins, Signal Transducing
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Carrier Proteins
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DNA-Binding Proteins
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Milk Proteins
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Protein Isoforms
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Proto-Oncogene Proteins
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SH2B1 protein, human
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STAT5 Transcription Factor
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Trans-Activators
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Phosphotyrosine
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Protein Kinases
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Phosphotransferases (Alcohol Group Acceptor)
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adenylylsulfate kinase
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Protein-Tyrosine Kinases
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JAK2 protein, human
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Jak2 protein, mouse
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Janus Kinase 2