G-protein coupled and tyrosine kinase receptors: evidence that activation of the insulin-like growth factor I receptor is required for thrombin-induced mitogenesis of rat aortic smooth muscle cells.
IGF I is an ubiquitous peptide that activates a membrane tyrosine kinase receptor and has autocrine/paracrine effects on vascular smooth muscle cells. Thrombin activates a G-protein coupled receptor and is also a mitogen for vascular smooth muscle cells. To assess the potential role of IGF I as a mediator of thrombin's effects, we characterized expression of IGF I and of its receptor on vascular smooth muscle cells exposed to thrombin. Thrombin dose-dependently decreased IGF I mRNA levels and caused a delayed decrease in IGF I secretion from vascular smooth muscle cells. This effect was mimicked by the hexapeptide SF-FLRN (that functions as a tethered ligand) and was inhibited by hirudin. In contrast, thrombin doubled IGF I receptor density on vascular smooth muscle cells, without altering binding affinity (Kd). An anti-IGF I antiserum markedly reduced thrombin-induced DNA synthesis, whereas nonimmune serum and an anti-fibroblast growth factor antibody were without effect. Cell counts confirmed these results. Downregulation of IGF I receptors by antisense phosphorothioate oligonucleotides likewise markedly inhibited thrombin-induced DNA synthesis. These data demonstrate that a functional IGF I-IGF I receptor pathway is essential for thrombin-induced mitogenic signaling and support the concept of cross talk between G-protein coupled and tyrosine kinase receptors.
Department of Medicine, Emory University, Atlanta, Georgia 30322, USA.
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Delafontaine
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Anwar
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D000595:Amino Acid Sequence; D000818:Animals; D000991:Antithrombins / Q000494:pharmacology; D001013:Aorta, Thoracic; D001483:Base Sequence; D002455:Cell Division; D002478:Cells, Cultured; D004247:DNA / Q000096:biosynthesis; D015536:Down-Regulation / Q000187:drug effects; D019204:GTP-Binding Proteins / Q000502:physiology*; D006629:Hirudins / Q000494:pharmacology; D007334:Insulin-Like Growth Factor I / Q000096:biosynthesis* / Q000378:metabolism; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D009842:Oligopeptides / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020794:Receptor Protein-Tyrosine Kinases / Q000502:physiology*; D017526:Receptor, IGF Type 1 / Q000096:biosynthesis / Q000502:physiology*; D015398:Signal Transduction; D013873:Thionucleotides / Q000494:pharmacology; D013917:Thrombin / Q000494:pharmacology*; D015854:Up-Regulation / Q000187:drug effects
D000991:Antithrombins; D006629:Hirudins; D016376:Oligonucleotides, Antisense; D009842:Oligopeptides; D012333:RNA, Messenger; D013873:Thionucleotides; D007334:Insulin-Like Growth Factor I; D004247:DNA; D020794:Receptor Protein-Tyrosine Kinases; D017526:Receptor, IGF Type 1; D013917:Thrombin; D019204:GTP-Binding Proteins