Fatty acid induced insulin resistance in rat-1 fibroblasts overexpressing human insulin receptors: impaired insulin-stimulated mitogen-activated protein kinase activity.
Saturated fatty acids cause insulin resistance but the underlying molecular mechanism is still unknown. We examined the effect of saturated nonesterified fatty acids on insulin binding and action in transfected Rat-1 fibroblasts, which over-expressed human insulin receptors. Incubation with 1.0 mmol/l palmitate for 1-4 h did not affect insulin binding, insulin receptor autophosphorylation, insulin-stimulated tyrosine kinase activity toward poly(Glu4:Tyr1), pp185 and Shc phosphorylation and PI3-kinase activity in these cells. However, the dose response curve of insulin-stimulated glucose transport was right-shifted. Palmitate inhibited the maximally insulin-stimulated mitogen activated protein (MAP) kinase activity toward synthetic peptide to 7% that of control. The palmitate treatment influenced neither cytosolic protein kinase A activity nor cAMP levels. These results suggested that 1) palmitate did not inhibit the early steps of insulin action from insulin binding to pp185 or Shc phosphorylation but inhibited insulin-stimulated MAP kinase, and that 2) palmitate decreased insulin sensitivity as manifested by inhibited insulin-stimulated glucose uptake. In conclusion, the mechanism of saturated non-esterified fatty acid induced insulin resistance in glucose uptake may reside at post PI3-kinase or Shc steps, including the level of MAP kinase activation.
Usui
I
I
The First Department of Medicine, Toyama Medical and Pharmaceutical University, Japan.
Takata
Y
Y
Imamura
T
T
Morioka
H
H
Sasaoka
T
T
Sawa
T
T
Ishihara
H
H
Ishiki
M
M
Kobayashi
M
M
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000187:drug effects / Q000378:metabolism*; D002478:Cells, Cultured; D005347:Fibroblasts / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D051272:Glucose Transporter Type 1; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D015151:Immunoblotting; D007328:Insulin / Q000032:analysis / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D007457:Iodine Radioisotopes; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000032:analysis / Q000276:immunology; D010168:Palmitates / Q000494:pharmacology*; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D010750:Phosphoproteins / Q000032:analysis / Q000276:immunology / Q000378:metabolism; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000187:drug effects / Q000378:metabolism; D011233:Precipitin Tests; D011505:Protein-Tyrosine Kinases / Q000187:drug effects / Q000378:metabolism; D011506:Proteins / Q000032:analysis / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D011817:Rabbits; D011972:Receptor, Insulin / Q000032:analysis / Q000187:drug effects / Q000378:metabolism*; D055765:Shc Signaling Adaptor Proteins; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D013997:Time Factors
D048868:Adaptor Proteins, Signal Transducing; D033942:Adaptor Proteins, Vesicular Transport; D000911:Antibodies, Monoclonal; D051272:Glucose Transporter Type 1; C526292:IRS1 protein, human; D007106:Immune Sera; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007457:Iodine Radioisotopes; C526295:Irs1 protein, mouse; C526296:Irs1 protein, rat; D009004:Monosaccharide Transport Proteins; D010168:Palmitates; D010750:Phosphoproteins; D011506:Proteins; C528024:SHC1 protein, human; C495677:SLC2A1 protein, human; D055765:Shc Signaling Adaptor Proteins; C528034:Shc1 protein, mouse; C528035:Shc1 protein, rat; D000071425:Src Homology 2 Domain-Containing, Transforming Protein 1; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases