title: Insulin signaling and its regulation of system A amino acid uptake in cultured rat vascular smooth muscle cells.
abstract: Hyperinsulinemia has been recognized as an independent risk factor for atherosclerosis. However, its exact mechanisms are still unclear. In our previous work, we showed that 10 nmol/L insulin stimulated neither mitogen-activated protein kinase (MAP kinase) activity nor [3H]thymidine incorporation but did stimulated S6 kinase through the specific insulin receptors in cultured rat vascular smooth muscle cells (VSMCs). In this study, we observed that > or = 1 nmol/L insulin stimulated tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and activated IRS-1-dependent phosphatidylinositol 3'-kinase (PI 3'-kinase) and p70 S6 kinase (p70S6K) but not MAP kinase (extracellular signal-regulated kinase 2) and p90 S6 kinase (p90RSK). However, 10 nmol/L insulin-like growth factor I stimulated all these pathways. Finally, 10 nmol/L insulin stimulated alpha-amino-isobutyric acid (AIB) uptake, and wortmannin (100 nmol/L) completely inhibited insulin-stimulated AIB uptake, whereas rapamycin (20 nmol/L) had no such effect. Furthermore, cycloheximide (10 micrograms/mL) completely inhibited insulin-stimulated AIB uptake, but actinomycin D (5 micrograms/mL) failed to inhibit this. Thus, we reached the following conclusions: (1) Insulin (1 nmol/L) induced phosphorylation of IRS-1 and activated the PI 3'-kinase and p70S6K pathways in VSMCs, even though 10 nmol/L insulin did not significantly stimulate MAP kinase or p90RSK. (2) Stimulation of AIB uptake by insulin was regulated at the translational level via wortmannin-sensitive pathways but not p70S6K pathways.
authors.affiliation: Third Department of Medicine, Shiga University of Medical Science, Otsu, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Obata
authors.forename: A
authors.initials: A
authors.lastname: Kashiwagi
authors.forename: H
authors.initials: H
authors.lastname: Maegawa
authors.forename: Y
authors.initials: Y
authors.lastname: Nishio
authors.forename: S
authors.initials: S
authors.lastname: Ugi
authors.forename: H
authors.initials: H
authors.lastname: Hidaka
authors.forename: R
authors.initials: R
authors.lastname: Kikkawa
mesh_terms: D000621:Aminoisobutyric Acids / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000378:metabolism*; D010750:Phosphoproteins / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases; D015398:Signal Transduction
chemical_list: D000621:Aminoisobutyric Acids; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526296:Irs1 protein, rat; D010750:Phosphoproteins; C100049:2-aminoisobutyric acid; D017346:Protein Serine-Threonine Kinases; D019893:Ribosomal Protein S6 Kinases