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: Yujun Gan, Yue Zhang, Ashiya Buckels, Andrew J Paterson, Jing Jiang, Thomas L Clemens, Zhong-Yin Zhang, Keyong Du, Yingzi Chang, Stuart J Frank
• Journal: Molecular endocrinology (Baltimore, Md.) (Mol Endocrinol) Vol. 27 Issue 11 Pg. 1969-79 (Nov 2013) ISSN: 1944-9917 [Electronic] United States
• PMID: 24030252 (Publication Type: Journal Article, Research Support, N.I.H., Extramural)

Chemical References

• Benzofurans
• NSC-87877
• Nuclear Proteins
• Quinolines
• STAT5 Transcription Factor
• Growth Hormone
• COP1 protein, mouse
• Ubiquitin-Protein Ligases
• Receptor, IGF Type 1
• Jak2 protein, mouse
• Janus Kinase 2
• Protein Tyrosine Phosphatase, Non-Receptor Type 1
• Ptpn1 protein, mouse

Topics

• Animals
• Benzofurans (pharmacology)
• Cells, Cultured
• Growth Hormone (physiology)
• Humans
• Janus Kinase 2 (metabolism)
• Mice
• Mice, Transgenic
• Nuclear Proteins (genetics, metabolism)
• Osteoblasts (metabolism)
• Phosphorylation
• Protein Processing, Post-Translational
• Protein Tyrosine Phosphatase, Non-Receptor Type 1 (antagonists & inhibitors, metabolism)
• Quinolines (pharmacology)
• Receptor, IGF Type 1 (metabolism)
• STAT5 Transcription Factor (metabolism)
• Ubiquitin-Protein Ligases (genetics, metabolism)