Insulin and IGF-I action on insulin receptors, IGF-I receptors, and hybrid insulin/IGF-I receptors in vascular smooth muscle cells
2006 (English)In: American Journal of Physiology. Endocrinology and Metabolism, ISSN 0193-1849, Vol. 291, no 5, 1124-1130 p.Article in journal (Refereed) Published
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-14C]Glucose accumulation and [6-3H]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) β-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 β-subunit and immunoblot with anti-phosphotyrosine antibody, we found two distinct bands indicating phosphorylation of both the IGF-IR and the IR β-subunit. Stimulation with 10–10–10–9 M insulin and IP against the IGF-IR did not show phosphorylation of either β-subunit, whereas after IP of the IR we found phosphorylation of the IR β-subunit. [14C]Glucose accumulation and [3H]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 β-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.
Place, publisher, year, edition, pages
Rockville Pike: American Physiological Society , 2006. Vol. 291, no 5, 1124-1130 p.
insulin-like growth factor I, ligand binding, receptor phosphorylation, immunoprecipitation, deoxyribonucleic acid synthesis, glucose metabolism
Cell and Molecular Biology
IdentifiersURN: urn:nbn:se:liu:diva-18629DOI: 10.1152/ajpendo.00565.2005OAI: oai:DiVA.org:liu-18629DiVA: diva2:220823