title: Functional collaboration of insulin-like growth factor-1 receptor (IGF-1R), but not insulin receptor (IR), with acute GH signaling in mouse calvarial cells.
abstract: GH signals through the GH receptor (GHR), a cytokine receptor linked to Janus kinase 2 (JAK2). GH activates signal transducer and activator of transcription 5 (STAT5), causing expression of genes including IGF-I. IGF-I binds IGF-I receptor (IGF-IR), a heterotetrameric (α2-β2) tyrosine kinase growth factor receptor similar to insulin receptor (IR). In addition to this GH -> GHR -> IGF-I -> IGF-IR pathway, GH induces a complex including GHR, JAK2, and IGF-IR and deletion of floxed IGF-1R in primary murine calvarial cells with Cre-recombinase-expressing adenovirus (Ad-Cre) desensitizes cells to GH for STAT5 activation and IGF-I mRNA accumulation. Diminished GH-induced STAT5 phosphorylation in Ad-Cre-treated cells is rescued by adenoviruses encoding either IGF-IR or IGF-IR lacking the β-chain intracellular domain. Reasoning that IGF-IR's extracellular portion (α or extracellular β) mediates functional interaction with GH signaling, we pursued reconstitution studies. Although structurally related to IGF-IR, IR expressed adenovirally did not rescue GH-induced STAT5 phosphorylation in Ad-Cre-treated cells. We thus created chimeras, swapping homologous IR extracellular regions into IGF-IR. IR and IGF-IR possess N-terminal L1, cysteine-rich (CR), and L2 α-chain domains. We created Ad-IGF-IR/IR-L1 and Ad-IGF-IR/IR-L1-CR-L2, in which L1 alone or L1, CR, and L2 of IR replace corresponding IGF-IR regions, respectively. Ad-IGF-IR/IR-L1, but not Ad-IGF-IR/IR-L1-CR-L2, rescued GH-induced STAT5 phosphorylation in Ad-Cre-treated cells. Additionally, medium containing a soluble IGF-IR (including only L1-CR-L2) dampened GH-induced STAT5 phosphorylation in calvarial cells and two other GH-responsive cell lines. Thus, an extracellular determinant(s), likely in CR-L2, specifically allows IGF-IR to collaborate with GHR and JAK2 for robust GH-induced acute STAT5 phosphorylation.
authors.affiliation: Department of Medicine (Y.G., A.J.P., Y.Z., J.J., S.J.F.), Division of Endocrinology, Diabetes, and Metabolism, and Department of 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: Andrew J
authors.initials: AJ
authors.lastname: Paterson
authors.forename: Yue
authors.initials: Y
authors.lastname: Zhang
authors.forename: Jing
authors.initials: J
authors.lastname: Jiang
authors.forename: Stuart J
authors.initials: SJ
authors.lastname: Frank
mesh_terms: D016475:3T3 Cells; D000818:Animals; D000831:Animals, Newborn; D001842:Bone and Bones / Q000378:metabolism*; D045744:Cell Line, Tumor; D005786:Gene Expression Regulation; D013006:Growth Hormone / Q000378:metabolism*; D057809:HEK293 Cells; D006801:Humans; D053614:Janus Kinase 2 / Q000378:metabolism; D051379:Mice; D010006:Osteoblasts / Q000166:cytology; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D017526:Receptor, IGF Type 1 / Q000235:genetics / Q000378:metabolism*; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry; D050799:STAT5 Transcription Factor / Q000378:metabolism; D015398:Signal Transduction
chemical_list: D011994:Recombinant Proteins; D050799:STAT5 Transcription Factor; D013006:Growth Hormone; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin; D053614:Janus Kinase 2