title: Insulin-like growth factor-I (IGF-I) regulates IGF-binding protein-5 synthesis through transcriptional activation of the gene in aortic smooth muscle cells.
abstract: Previous studies have shown that porcine aortic smooth muscle cells (SMCs) secrete two insulin-like growth factor-binding proteins (IGFBP), IGFBP-2 and -4, and that these IGFBPs modulate IGF-I-stimulated SMC proliferation and migration. In this study we demonstrate that porcine SMCs express IGFBP-5 mRNA and synthesize and secrete the protein. In this cell type, the biosynthesis of IGFBP-5 is up-regulated by IGF-I. This increase in IGFBP-5 synthesis is accompanied by an increase in the steady-state mRNA levels. The induction of IGFBP-5 mRNA by IGF-I is time- and dose-dependent and requires de novo protein synthesis. IGF-II and insulin also increase IGFBP-5 mRNA levels at high doses. An IGF-I analog with normal affinity for the IGF-I receptor but reduced affinity for IGFBPs evokes a similar increase. Another analog that binds to IGFBPs but not to the receptor has no effect, indicating that this effect of IGF-I is mediated through the IGF-I receptor. The IGF-I-induced IGFBP-5 gene expression is cell type-specific because IGF-I had no such effect in other cell types examined. Nuclear run-on assays revealed that IGF-I increased transcription rate of the IGFBP-5 gene, while IGF-I did not change the IGFBP-5 mRNA stability. Furthermore, the IGFBP-5 promoter was 3.5-fold more active in directing expression of the luciferase reporter gene in IGF-I-treated aortic SMCs as compared to control cells, whereas the luciferase activity remained the same in control- and IGF-I-treated fibroblasts. These results suggest that IGF-I up-regulates IGFBP-5 synthesis by transcriptionally activating the IGFBP-5 gene in aortic SMCs.
authors.affiliation: Department of Medicine, University of North Carolina, Chapel Hill, 27599, USA.
authors.forename: C
authors.initials: C
authors.lastname: Duan
authors.forename: S B
authors.initials: SB
authors.lastname: Hawes
authors.forename: T
authors.initials: T
authors.lastname: Prevette
authors.forename: D R
authors.initials: DR
authors.lastname: Clemmons
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000378:metabolism*; D001483:Base Sequence; D015152:Blotting, Northern; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D017931:DNA Primers; D005786:Gene Expression Regulation / Q000187:drug effects*; D018975:Insulin-Like Growth Factor Binding Protein 5 / Q000096:biosynthesis*; D007334:Insulin-Like Growth Factor I / Q000378:metabolism / Q000494:pharmacology*; D007700:Kinetics; D008715:Methionine / Q000378:metabolism; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000378:metabolism*; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000096:biosynthesis* / Q000302:isolation & purification; D017526:Receptor, IGF Type 1 / Q000378:metabolism; D011994:Recombinant Proteins / Q000096:biosynthesis; D013462:Sulfur Radioisotopes; D013552:Swine; D014158:Transcription, Genetic; D015533:Transcriptional Activation / Q000187:drug effects*; D014162:Transfection
chemical_list: D017931:DNA Primers; D018975:Insulin-Like Growth Factor Binding Protein 5; D012333:RNA, Messenger; D011994:Recombinant Proteins; D013462:Sulfur Radioisotopes; D007334:Insulin-Like Growth Factor I; D008715:Methionine; D017526:Receptor, IGF Type 1