Insulin and IGF-I action on insulin receptors, IGF-I receptors, and hybrid insulin/IGF-I receptors in vascular smooth muscle cells

• Published in: American journal of physiology: endocrinology and metabolism Vol. 291; no. 5; pp. E1124 - E1130
• Main Authors: Johansson, Git S, Arnqvist, Hans J
• Format: Journal Article
• Language: English
• Published: United States American Physiological Society 01.11.2006
• Subjects: Animals; Aorta, Thoracic - cytology; Binding sites; Carbon Radioisotopes; Cell biology; Cellbiologi; Cells, Cultured; Cellular biology; deoxyribonucleic acid synthesis; Dimerization; Glucose; Glucose - pharmacokinetics; glucose metabolism; Hypoglycemic Agents - metabolism; Hypoglycemic Agents - pharmacology; immunoprecipitation; Insulin; Insulin - metabolism; Insulin - pharmacology; insulin-like growth factor I; Insulin-Like Growth Factor I - metabolism; Insulin-Like Growth Factor I - pharmacology; Iodine Radioisotopes; ligand binding; Ligands; Male; Medical cell biology; MEDICIN; MEDICINE; Medicinsk cellbiologi; Metabolism; Morfologi, cellbiologi, patologi; Morphology, cell biology, pathology; Muscle, Smooth, Vascular - cytology; Muscle, Smooth, Vascular - metabolism; Phosphorylation; Rats; Rats, Sprague-Dawley; receptor phosphorylation; Receptor, IGF Type 1 - chemistry; Receptor, IGF Type 1 - metabolism; Receptor, Insulin - chemistry; Receptor, Insulin - metabolism; Studies; Thymidine - pharmacokinetics; Tritium
• ISSN: 0193-1849; 1522-1555; 1522-1555
• DOI: 10.1152/ajpendo.00565.2005

1 Department of Biomedicine and Surgery, Division of Cell Biology; and 2 Diabetes Research Centre, Faculty of Health Sciences, Linköping University, Linköping, Sweden Submitted 18 November 2005 ; accepted in final form 20 June 2006 Insulin and insulin-like growth factor I (IGF-I) are known to affect cardiovascular disease. We have investigated ligand binding and the dose-response relationship for insulin and IGF-I on vascular smooth muscle cells (VSMCs) at the receptor level. VSMCs from rat thoracic aorta were serum starved, stimulated with IGF-I or insulin, lysed, immunoprecipitated, and analyzed by Western blot. D -[U- 14 C]Glucose accumulation and [6- 3 H]thymidine incorporation into DNA were also measured. Specific binding of both insulin and IGF-I was demonstrated, being higher for IGF-I. Both IGF-I receptor (IGF-IR) and insulin receptor (IR) -subunits were detected and coprecipitated after immunoprecipitation (IP) against either of the two. No coprecipitation was found after reduction of disulphide bonds with dithiotreitol before IP. After stimulation with 10 –10 –10 –9 M IGF-I, IP of the IGF-IR, or IR -subunit and immunoblot with anti-phosphotyrosine antibody, we found two distinct bands indicating phosphorylation of both the IGF-IR and the IR -subunit. Stimulation with 10 –10 –10 –9 M insulin and IP against the IGF-IR did not show phosphorylation of either -subunit, whereas after IP of the IR we found phosphorylation of the IR -subunit. [ 14 C]Glucose accumulation and [ 3 H]thymidine incorporation were elevated in cells stimulated with IGF-I at 10 –10 –10 –7 M, reaching maximum by 10 –9 M. Insulin stimulation showed measurable effects only at supraphysiological concentrations, 10 –8 –10 –7 M. In conclusion, coprecipitation of both the IGF-IR and the IR -subunit indicates the presence of hybrid insulin/IGF-I receptors in VSMC. At a physiological concentration, insulin activates the IR but does not affect either glucose metabolism or DNA synthesis, whereas IGF-I both activates the receptor and elicits biological effect. insulin-like growth factor I; ligand binding; receptor phosphorylation; immunopreciptation; dexoyribonucleic acid synthesis; glucose metabolism Address for reprint requests and other correspondence: G. Johansson, Dept. of Biomedicine and Surgery, Division of Cell Biology, Linköping University, S-581 85 Linköping, Sweden (e-mail: git.johansson{at}ibk.liu.se )