The Gly-->Arg972 amino acid polymorphism in insulin receptor substrate-1 affects glucose metabolism in skeletal muscle cells.
Molecular scanning of insulin receptor substrate-1 (IRS-1) revealed several amino acid substitutions. The most common IRS-1 variant, a Gly to Arg972 change, is more prevalent among type 2 diabetic patients. In this study we overexpressed wild-type and Arg972IRS-1 variant in L6 skeletal muscle cells and examined the functional consequences of this polymorphism on insulin metabolic signaling. L6 cells expressing Arg972-IRS-1 (L6-Arg972) showed a decrease in insulin-stimulated IRS-1-associated phosphatidylinositol 3-kinase (PI 3-kinase) activity compared with L6 cells expressing wild-type IRS-1 (L6-WT) as a consequence of decreased binding of p85 subunit of PI 3-kinase to IRS-1. L6-Arg972 exhibited a decrease in both basal and insulin-stimulated glucose transport due to a reduction in the amount of both GLUT1 and GLUT4 translocated to the plasma membrane. Both basal and insulin-stimulated Akt phosphorylations were decreased in L6-Arg972 compared with L6-WT. Basal glycogen synthase kinase-3 (GSK-3) activity was increased in L6-Arg972 compared with L6-WT, and insulin-induced inactivation of GSK-3 was also reduced in L6-Arg972. This change was associated with a significant decrease in insulin-stimulated glucose incorporation into glycogen and glycogen synthase activity in L6-Arg972 compared with L6-WT. These results indicate that the Arg972-IRS-1 polymorphism impairs the ability of insulin to stimulate glucose transport, glucose transporter translocation, and glycogen synthesis by affecting the PI 3-kinase/Akt/GSK-3 signaling pathway. The present data indicate that the polymorphism at codon 972 of IRS-1 may contribute to the in vivo insulin resistance observed in carriers of this variant.
Hribal
M L
ML
Department of Internal Medicine, University of Rome-Tor Vergata, Rome, Italy.
Federici
M
M
Porzio
O
O
Lauro
D
D
Borboni
P
P
Accili
D
D
Lauro
R
R
Sesti
G
G
D019943:Amino Acid Substitution; D000818:Animals; D001120:Arginine; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D014644:Genetic Variation; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D005998:Glycine; D006003:Glycogen / Q000096:biosynthesis; D006801:Humans; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics*; D010766:Phosphorylation; D011110:Polymorphism, Genetic; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D001120:Arginine; D005947:Glucose; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D005998:Glycine; D006003:Glycogen; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D011994:Recombinant Proteins; C526292:IRS1 protein, human; C495677:SLC2A1 protein, human; C495692:SLC2A4 protein, human; C494918:AKT1 protein, human