title: Disulfide linkage of growth hormone (GH) receptors (GHR) reflects GH-induced GHR dimerization. Association of JAK2 with the GHR is enhanced by receptor dimerization.
abstract: The growth hormone (GH) receptor (GHR) binds GH in its extracellular domain and transduces activating signals via its cytoplasmic domain. Both GH-induced GHR dimerization and JAK2 tyrosine kinase activation are critical in initiation of GH signaling. We previously described a rapid GH-induced disulfide linkage of GHRs in human IM-9 cells. In this study, three GH-induced phenomena (GHR dimerization, GHR disulfide linkage, and enhanced GHR-JAK2 association) were examined biochemically and immunologically. By using the GH antagonist, G120K, and an antibody recognizing a dimerization-sensitive GHR epitope, we demonstrated that GH-induced GHR disulfide linkage reflects GH-induced GHR dimerization. GH, not G120K, promoted both GHR disulfide linkage and enhanced association with JAK2. Measures that diminished GH-dependent JAK2 and GHR tyrosine phosphorylation diminished neither GH-induced GHR disulfide linkage nor GH-enhanced GHR-JAK2 association. By using both transient and stable expression systems, we determined that cysteine 241 (an unpaired extracellular cysteine) was critical for GH-induced GHR disulfide linkage; however, GH-induced GHR dimerization, GHR-JAK2 interaction, and GHR, JAK2, and STAT5 tyrosine phosphorylation still proceeded when this cysteine residue was mutated. We conclude GH-induced GHR disulfide linkage is not required for GHR dimerization, and activation and GH-enhanced GHR-JAK2 association depends more on GHR dimerization than on GHR and/or JAK2 tyrosine phosphorylation.
authors.affiliation: Department of Medicine, Division of Endocrinology and Metabolism, Birmingham, Alabama 35294, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Zhang
authors.forename: J
authors.initials: J
authors.lastname: Jiang
authors.forename: J J
authors.initials: JJ
authors.lastname: Kopchick
authors.forename: S J
authors.initials: SJ
authors.lastname: Frank
mesh_terms: D000818:Animals; D000906:Antibodies / Q000276:immunology / Q000494:pharmacology; D002460:Cell Line; D003545:Cysteine / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D019281:Dimerization; D004220:Disulfides / Q000737:chemistry*; D019382:Human Growth Hormone / Q000494:pharmacology; D006801:Humans; D053614:Janus Kinase 2; D008894:Milk Proteins; D009154:Mutation; D010446:Peptide Fragments / Q000494:pharmacology; D010766:Phosphorylation; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000378:metabolism*; D011518:Proto-Oncogene Proteins; D011986:Receptors, Somatotropin / Q000037:antagonists & inhibitors / Q000737:chemistry*; D050799:STAT5 Transcription Factor; D015534:Trans-Activators / Q000378:metabolism; D014162:Transfection
chemical_list: D000906:Antibodies; D004268:DNA-Binding Proteins; D004220:Disulfides; D008894:Milk Proteins; D010446:Peptide Fragments; D011518:Proto-Oncogene Proteins; D011986:Receptors, Somatotropin; D050799:STAT5 Transcription Factor; D015534:Trans-Activators; D019382:Human Growth Hormone; D011505:Protein-Tyrosine Kinases; C507924:JAK2 protein, human; D053614:Janus Kinase 2; D003545:Cysteine