title: IGF-1R modulation of acute GH-induced STAT5 signaling: role of protein tyrosine phosphatase activity.
abstract: GH is a potent anabolic and metabolic factor that binds its cell surface receptor (GHR), activating the GHR-associated tyrosine kinase, Janus kinase 2, which phosphorylates and activates the latent transcription factor, signal transducer and activator of transcription 5 (STAT5). Some GH actions are mediated by the elaboration of IGF-1, which exerts effects by binding and activating the heterotetrameric tyrosine kinase growth factor receptor, IGF-1R. In addition to this GH-GHR-IGF-1-IGF-1R scheme, we have demonstrated in primary osteoblasts and in islet β-cells that then deletion or silencing of IGF-1R results in diminished GH-induced STAT5 phosphorylation, suggesting that the presence of IGF-1R may facilitate GH signaling. In this study, we explore potential roles for protein tyrosine phosphatase activity in modulating GH-induced signaling, comparing conditions in which IGF-1R is present or diminished. We confirm that in mouse primary osteoblasts harboring loxP sites flanking the IGF-1R gene, infection with an adenovirus that expresses the Cre recombinase results in IGF-1R deletion and diminished acute GH-induced STAT5 phosphorylation. Furthermore, we present a new model of IGF-1R silencing, in which expression of short hairpin RNA directed at IGF-1R greatly reduces IGF-1R abundance in LNCaP human prostate cancer cells. In both models, treatment with a chemical inhibitor of protein tyrosine phosphatase-1B (PTP-1B), but not one of src homology region 2 domain-containing phosphotase-1 (SHP-1) and SHP-2, reverses the loss of GH-induced STAT5 phosphorylation in cells lacking IGF-1R but has no effect in cells with intact IGF-1R. Furthermore, expression of either a dominant-negative PTP-1B or the PTP-1B-interacting inhibitory protein, constitutive photomorphogenesis 1, also rescues acute GH-induced STAT5 signaling in IGF-1R-deficient cells but has no effect in IGF-1R replete cells. By expressing a substrate-trapping mutant PTP-1B, we demonstrate that tyrosine phosphorylated Janus kinase-2 is a PTP-1B substrate only in cells lacking IGF-1R. Collectively, our data suggest that IGF-1R positively regulates acute GH signaling by preventing access of PTP-1B activity to Janus kinase 2 and thereby preventing PTP-1B-mediated suppression of GH-induced STAT5 activation.
authors.affiliation: MD, University of Alabama at Birmingham, 1530 Third Avenue South, BDB 720, Birmingham, Alabama 35294-0012. sjfrank@uab.edu.
authors.forename: Yujun
authors.initials: Y
authors.lastname: Gan
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhang
authors.forename: Ashiya
authors.initials: A
authors.lastname: Buckels
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Paterson
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.forename: Thomas L
authors.initials: TL
authors.lastname: Clemens
authors.forename: Zhong-Yin
authors.initials: ZY
authors.lastname: Zhang
authors.forename: Keyong
authors.initials: K
authors.lastname: Du
authors.forename: Yingzi
authors.initials: Y
authors.lastname: Chang
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Frank
mesh_terms: D000818:Animals; D001572:Benzofurans / Q000494:pharmacology; D002478:Cells, Cultured; D013006:Growth Hormone / Q000502:physiology*; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D051379:Mice; D008822:Mice, Transgenic; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism; D010006:Osteoblasts / Q000378:metabolism; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D011804:Quinolines / Q000494:pharmacology; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D050799:STAT5 Transcription Factor / Q000378:metabolism*; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism
chemical_list: D001572:Benzofurans; C512715:NSC-87877; D009687:Nuclear Proteins; D011804:Quinolines; D050799:STAT5 Transcription Factor; D013006:Growth Hormone; C471982:COP1 protein, mouse; D044767:Ubiquitin-Protein Ligases; D017526:Receptor, IGF Type 1; C507926:Jak2 protein, mouse; D053614:Janus Kinase 2; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; C516609:Ptpn1 protein, mouse
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