Deletion of IGF-I Receptor (IGF-IR) in Primary Osteoblasts Reduces GH-Induced STAT5 Signaling
| Autor: | David P. Carbone, Xuemei Cao, Douglas J. DiGirolamo, Yue Zhang, Yujun Gan, Kurt R. Zinn, Thomas L. Clemens, Xiangdong Wang, Stuart J. Frank, Jing Jiang |
|---|---|
| Rok vydání: | 2010 |
| Předmět: |
MAPK/ERK pathway
Immunoblotting Growth hormone receptor Polymerase Chain Reaction Article Adenoviridae Cell Line Receptor IGF Type 1 Mice Transactivation Endocrinology Cell surface receptor STAT5 Transcription Factor Animals Humans Immunoprecipitation Molecular Biology Cells Cultured STAT5 Osteoblasts Janus kinase 2 biology Human Growth Hormone General Medicine Molecular biology biology.protein Electrophoresis Polyacrylamide Gel Signal transduction Tyrosine kinase Signal Transduction |
| Zdroj: | Molecular Endocrinology. 24:644-656 |
| ISSN: | 1944-9917 0888-8809 |
| Popis: | GH promotes longitudinal growth and regulates multiple cellular functions in humans and animals. GH signals by binding to GH receptor (GHR) to activate the tyrosine kinase, Janus kinase 2 (JAK2), and downstream pathways including signal transducer and activator of transcription 5 (STAT5), thereby regulating expression of genes including IGF-I. GH exerts effects both directly and via IGF-I, which signals by activating the IGF-I receptor (IGF-IR). IGF-IR is a cell surface receptor that contains intrinsic tyrosine kinase activity within its intracellular domain. In this study, we examined the potential role of IGF-IR in facilitating GH-induced signal transduction, using mouse primary calvarial osteoblasts with Lox-P sites flanking both IGF-IR alleles. These cells respond to both GH and IGF-I and in vitro infection with an adenovirus that drives expression of Cre recombinase (Ad-Cre) dramatically reduces IGF-IR abundance without affecting the abundance of GHR, JAK2, STAT5, or ERK. Notably, infection with Ad-Cre, but not a control adenovirus, markedly inhibited acute GH-induced STAT5 activity (more than doubling the ED(50) and reducing the maximum activity by nearly 50%), while sparing GH-induced ERK activity, and markedly inhibited GH-induced transactivation of a STAT5-dependent luciferase reporter. The effect of Ad-Cre on GH signaling was specific, as platelet-derived growth factor-induced signaling was unaffected by Ad-Cre-mediated reduction of IGF-IR. Ad-Cre-mediated inhibition of GH signaling was reversed by adenoviral reexpression of IGF-IR, but not by infection with an adenovirus that drives expression of a hemagglutination-tagged somatostatin receptor, which drives expression of the unrelated somatostatin receptor, and Ad-Cre infection of nonfloxed osteoblasts did not affect GH signaling. Notably, infection with an adenovirus encoding a C-terminally truncated IGF-IR that lacks the tyrosine kinase domain partially rescued both acute GH-induced STAT5 activity and GH-induced IGF-I gene expression in cells in which endogenous IGF-IR was reduced. These data, in concert with our earlier findings that GH induces a GHR-JAK2-IGF-IR complex, suggest a novel function for IGF-IR. In addition to its role as a key IGF-I signal transducer, this receptor may directly facilitate acute GH signaling. The implications of these findings are discussed. |
| Databáze: | OpenAIRE |
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