Abstract
GH stimulates the phosphorylation of tyrosine residues in the GH receptor (GHR), Janus kinase 2 (JAK2), and other signaling proteins in a transient manner that subsides within 1 h. To assess the possible roles of cytokine-induced Src homology domain 2 (SH2) (CIS/SOCS) proteins in these transient responses, we studied the expression and disposition of CIS/SOCS proteins in rat adipocytes, a physiological target of GH action. A tyrosine-phosphorylated protein that appears to be the GHR was coprecipitated from extracts of GH-treated adipocytes with alpha-CIS. In contrast, no tyrosine-phosphorylated adipocyte proteins were recovered after immunoprecipitation with alpha-SOCS3, although coprecipitation of GHR with SOCS3 was readily detected in extracts of 3T3-F442A fibroblasts. Interaction of GHR with CIS peaked between 2 and 10 min after adipocytes were treated with GH, when tyrosine phosphorylation of the GHR was maximal. By 60 min after GH, tyrosine phosphorylation of the GHR declined to very low levels, and its interaction with CIS was reduced correspondingly. Proteasome inhibitors prevented the decline in tyrosine-phosphorylated GHR and prolonged interaction of GHR and CIS for at least 1 h. These findings demonstrate the interaction of CIS with the GHR in vivo and suggest that CIS may enhance degradation of the receptor by a proteasomal pathway.
Publication types
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Research Support, U.S. Gov't, P.H.S.
MeSH terms
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Adipocytes / metabolism*
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Animals
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Carrier Proteins / analysis
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Carrier Proteins / genetics
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Cell Line
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Cells, Cultured
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Cysteine Endopeptidases / metabolism
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Cytokines / pharmacology*
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DNA-Binding Proteins*
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Gene Expression / drug effects
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Growth Hormone / pharmacology
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Humans
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Immunosorbent Techniques
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Intracellular Signaling Peptides and Proteins*
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Kidney
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Kinetics
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Male
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Multienzyme Complexes / antagonists & inhibitors
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Multienzyme Complexes / metabolism
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Phosphorylation
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Phosphotyrosine / metabolism
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Proteasome Endopeptidase Complex
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Proteins / analysis
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Proteins / genetics
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RNA, Messenger / analysis
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Rats
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Receptors, Somatotropin / analysis
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Receptors, Somatotropin / genetics
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Receptors, Somatotropin / metabolism*
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Repressor Proteins*
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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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Trans-Activators*
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Transcription Factors*
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Transfection
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src Homology Domains / physiology*
Substances
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Carrier Proteins
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Cytokines
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DNA-Binding Proteins
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Intracellular Signaling Peptides and Proteins
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Multienzyme Complexes
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Proteins
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RNA, Messenger
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Receptors, Somatotropin
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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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Socs1 protein, rat
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Socs2 protein, rat
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Socs3 protein, rat
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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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Trans-Activators
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Transcription Factors
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Phosphotyrosine
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Growth Hormone
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Cysteine Endopeptidases
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Proteasome Endopeptidase Complex