title: Role of the cytokine-inducible SH2 protein CIS in desensitization of STAT5b signaling by continuous growth hormone.
abstract: Growth hormone (GH)-inducible suppressors of cytokine signaling (SOCS/CIS proteins) inhibit GH receptor (GHR) signaling to STAT5b via phosphotyrosine-dependent binding interactions with the tyrosine kinase JAK2 (SOCS-1) and/or the cytoplasmic tail of GHR (CIS and SOCS-3). Presently, we investigate the mechanism of CIS inhibition and CIS's role in down-regulating GHR-JAK2 signaling to STAT5b in cells exposed to GH continuously. CIS is shown to inhibit GHR-JAK2 signaling by two distinct mechanisms: by a partial inhibition that is decreased at elevated STAT5b levels and may involve competition between CIS and STAT5b for common GHR cytoplasmic tail phosphotyrosine-binding sites; and by a time-dependent inhibition, not seen with SOCS-1 or SOCS-3, that involves proteasome action. Investigation of the latter mechanism revealed that GH stimulates degradation of CIS, but not SOCS-3. The proteasome inhibitor MG132 blocked this protein degradation and also blocked the inhibitory action of CIS, but not that of SOCS-1 or SOCS-3, on STAT5b signaling. Proteasome-dependent degradation of CIS, most likely in the form of a (GHR-JAK2)-CIS complex, is therefore proposed to be an important step in the time-dependent CIS inhibition mechanism. Finally, the down-regulation of GHR-JAK2 signaling to STAT5b seen in continuous GH-treated cells could be prevented by treatment of cells with the proteasome inhibitor MG132 or by expression of CIS-R107K, a selective, dominant-negative inhibitor of CIS activity. These findings lead us to propose that the cytokine signaling inhibitor CIS is a key mediator of the STAT5b desensitization response seen in cells and tissues exposed to GH chronically, such as adult female rat liver.
authors.affiliation: Division of Cell and Molecular Biology, Department of Biology, Boston University, Boston, Massachusetts 02215, USA.
authors.forename: P A
authors.initials: PA
authors.lastname: Ram
authors.forename: D J
authors.initials: DJ
authors.lastname: Waxman
mesh_terms: D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D015153:Blotting, Western; D019556:COS Cells; D002352:Carrier Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism; D003546:Cysteine Endopeptidases / Q000378:metabolism; D016207:Cytokines / Q000378:metabolism*; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D004789:Enzyme Activation; D005260:Female; D005799:Genes, Dominant; D051599:Glucose-1-Phosphate Adenylyltransferase; D013006:Growth Hormone / Q000494:pharmacology*; D017874:Immediate-Early Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D053614:Janus Kinase 2; D007976:Leupeptins / Q000494:pharmacology; D008099:Liver / Q000378:metabolism; D018613:Microscopy, Confocal; D008856:Microscopy, Fluorescence; D008894:Milk Proteins; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000378:metabolism; D009713:Nucleotidyltransferases; D019000:Phosphotyrosine / Q000378:metabolism; D010940:Plant Proteins / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011518:Proto-Oncogene Proteins; D051381:Rats; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; D015398:Signal Transduction; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors; D014162:Transfection
chemical_list: D002352:Carrier Proteins; D003546:Cysteine Endopeptidases; D016207:Cytokines; D004268:DNA-Binding Proteins; D051599:Glucose-1-Phosphate Adenylyltransferase; D013006:Growth Hormone; D017874:Immediate-Early Proteins; D053614:Janus Kinase 2; D007976:Leupeptins; D008894:Milk Proteins; D009097:Multienzyme Complexes; D009713:Nucleotidyltransferases; D019000:Phosphotyrosine; D010940:Plant Proteins; D046988:Proteasome Endopeptidase Complex; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D050799:STAT5 Transcription Factor; D000071222:Suppressor of Cytokine Signaling 1 Protein; D000071223:Suppressor of Cytokine Signaling 3 Protein; D050826:Suppressor of Cytokine Signaling Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C111076:Sh2 protein, plant; C491589:Socs1 protein, rat; C491410:Socs3 protein, rat; C494097:Stat5b protein, rat; C507927:Jak2 protein, rat; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde