title: Human GH receptor-IGF-1 receptor interaction: implications for GH signaling.
abstract: GH signaling yields multiple anabolic and metabolic effects. GH binds the transmembrane GH receptor (GHR) to activate the intracellular GHR-associated tyrosine kinase, Janus kinase 2 (JAK2), and downstream signals, including signal transducer and activator of transcription 5 (STAT5) activation and IGF-1 gene expression. Some GH effects are partly mediated by GH-induced IGF-1 via IGF-1 receptor (IGF-1R), a tyrosine kinase receptor. We previously demonstrated in non-human cells that GH causes formation of a GHR-JAK2-IGF-1R complex and that presence of IGF-1R (even without IGF-1 binding) augments proximal GH signaling. In this study, we use human LNCaP prostate cancer cells as a model system to further study the IGF-1R's role in GH signaling. GH promoted JAK2 and GHR tyrosine phosphorylation and STAT5 activation in LNCaP cells. By coimmunoprecipitation and a new split luciferase complementation assay, we find that GH augments GHR/IGF-1R complex formation, which is inhibited by a Fab of an antagonistic anti-GHR monoclonal antibody. Short hairpin RNA-mediated IGF-1R silencing in LNCaP cells reduced GH-induced GHR, JAK2, and STAT5 phosphorylation. Similarly, a soluble IGF-1R extracellular domain fragment (sol IGF-1R) interacts with GHR in response to GH and blunts GH signaling. Sol IGF-1R also markedly inhibits GH-induced IGF-1 gene expression in both LNCaP cells and mouse primary osteoblast cells. On the basis of these and other findings, we propose a model in which IGF-1R augments GH signaling by allowing a putative IGF-1R-associated molecule that regulates GH signaling to access the activated GHR/JAK2 complex and envision sol IGF-1R as a dominant-negative inhibitor of this IGF-1R-mediated augmentation. Physiological implications of this new model are discussed.
authors.affiliation: Department of Medicine (Y.G., A.B., Y.L., Y.Z., A.J.P., J.J., S.J.F.), Division of Endocrinology, Diabetes, and Metabolism, and Departments of Radiology (K.R.Z.) and Cell, Developmental, and Integrative Biology (S.J.F.), University of Alabama at Birmingham, Birmingham, Alabama 35294; and Endocrinology Section (S.J.F.), Medical Service, Veterans Affairs Medical Center, Birmingham, Alabama 35233.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Gan
authors.forename: Ashiya
authors.initials: A
authors.lastname: Buckels
authors.forename: Ying
authors.initials: Y
authors.lastname: Liu
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhang
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Paterson
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.forename: Kurt R
authors.initials: KR
authors.lastname: Zinn
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Frank
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000378:metabolism*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D013006:Growth Hormone / Q000378:metabolism; D006801:Humans; D047468:Immunoprecipitation / Q000379:methods; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D053614:Janus Kinase 2 / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D060066:Protein Interaction Maps / Q000502:physiology*; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology*
chemical_list: D002352:Carrier Proteins; D050799:STAT5 Transcription Factor; D007334:Insulin-Like Growth Factor I; D013006:Growth Hormone; D017526:Receptor, IGF Type 1; C507924:JAK2 protein, human; D053614:Janus Kinase 2; C051815:somatotropin-binding protein