Dexamethasone-induced insulin resistance in 3T3-L1 adipocytes is due to inhibition of glucose transport rather than insulin signal transduction.
Glucocorticoids reportedly induce insulin resistance. In this study, we investigated the mechanism of glucocorticoid-induced insulin resistance using 3T3-L1 adipocytes in which treatment with dexamethasone has been shown to impair the insulin-induced increase in glucose uptake. In 3T3-L1 adipocytes treated with dexamethasone, the GLUT1 protein expression level was decreased by 30%, which possibly caused decreased basal glucose uptake. On the other hand, dexamethasone treatment did not alter the amount of GLUT4 protein in total cell lysates but decreased the insulin-stimulated GLUT4 translocation to the plasma membrane, which possibly caused decreased insulin-stimulated glucose uptake. Dexamethasone did not alter tyrosine phosphorylation of insulin receptors, and it significantly decreased protein expression and tyrosine phosphorylation of insulin receptor substrate (IRS)-1. Interestingly, however, protein expression and tyrosine phosphorylation of IRS-2 were increased. To investigate whether the reduced IRS-1 content is involved in insulin resistance, IRS-1 was overexpressed in dexamethasone-treated 3T3-L1 adipocytes using an adenovirus transfection system. Despite protein expression and phosphorylation levels of IRS-1 being normalized, insulin-induced 2-deoxy-D-[3H]glucose uptake impaired by dexamethasone showed no significant improvement. Subsequently, we examined the effect of dexamethasone on the glucose uptake increase induced by overexpression of GLUT2-tagged p110alpha, constitutively active Akt (myristoylated Akt), oxidative stress (30 mU glucose oxidase for 2 h), 2 mmol/l 5-aminoimidazole-4-carboxamide ribonucleoside for 30 min, and osmotic shock (600 mmol/l sorbitol for 30 min). Dexamethasone treatment clearly inhibited the increases in glucose uptake produced by these agents. Thus, in conclusion, the GLUT1 decrease may be involved in the dexamethasone-induced decrease in basal glucose transport activity, and the mechanism of dexamethasone-induced insulin resistance in glucose transport activity (rather than the inhibition of phosphatidylinositol 3-kinase activation resulting from a decreased IRS-1 content) is likely to underlie impaired glucose transporter regulation.
Sakoda
H
H
Third Department of Internal Medicine, Faculty of Medicine, University of Tokyo, Japan.
Ogihara
T
T
Anai
M
M
Funaki
M
M
Inukai
K
K
Katagiri
H
H
Fukushima
Y
Y
Onishi
Y
Y
Ono
H
H
Fujishiro
M
M
Kikuchi
M
M
Oka
Y
Y
Asano
T
T
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D000620:Aminoimidazole Carboxamide / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D003907:Dexamethasone / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D015870:Gene Expression; D005938:Glucocorticoids / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D009124:Muscle Proteins; D009997:Osmotic Pressure; D018384:Oxidative Stress; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D011972:Receptor, Insulin; D012265:Ribonucleotides / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects*
D005938:Glucocorticoids; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D010750:Phosphoproteins; D012265:Ribonucleotides; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; D019000:Phosphotyrosine; D000620:Aminoimidazole Carboxamide; D003907:Dexamethasone; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; C031143:AICA ribonucleotide; D005947:Glucose