title: Effects of cell-permeable ceramides and tumor necrosis factor-alpha on insulin signaling and glucose uptake in 3T3-L1 adipocytes.
abstract: Incubation of 3T3-L1 adipocytes with C2- and C6-ceramides (N-acetyl- and N-hexanoylsphingosines) but not dihydro-C2-ceramide increased 2-deoxyglucose uptake in the absence of insulin. This effect was inhibited by PD 98059, LY 294002, and rapamycin, which block the activation of mitogen-activated protein kinase, phosphatidylinositol (PI) 3-kinase, and ribosomal S6 kinase, respectively. Long-term increases in PI 3-kinase activity associated with insulin receptor substrate 1 (IRS-1) increased GLUT1 and GLUT4 concentrations in plasma membranes. This together with increased GLUT1 (but not GLUT4) synthesis explains the increase in non-insulin-dependent glucose uptake. C2-ceramide inhibited insulin-stimulated glucose uptake after 2 h by decreasing insulin-induced translocation of GLUT1 and GLUT4 to plasma membranes. This occurred when there was no increase in basal glucose uptake or decrease in activation of IRS-1 or PI 3-kinase. Incubation for 24 h with tumor necrosis factor-alpha (TNF-alpha) but not C2-ceramide decreased the concentration and insulin-induced tyrosine phosphorylation of IRS-1 in this experimental system. Cell-permeable ceramides mimic some effects of TNF-alpha, especially in stimulating basal glucose uptake. We identified a site for inhibiting insulin-stimulated glucose uptake that is downstream of PI 3-kinase. Our work provides further mechanisms for the effects of TNF-alpha and ceramides in increasing non-insulin-dependent glucose uptake and decreasing insulin-stimulated uptake in vivo.
authors.affiliation: Department of Biochemistry, University of Alberta, Edmonton, Canada.
authors.forename: C N
authors.initials: CN
authors.lastname: Wang
authors.forename: L
authors.initials: L
authors.lastname: O'Brien
authors.forename: D N
authors.initials: DN
authors.lastname: Brindley
mesh_terms: D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D002462:Cell Membrane / Q000737:chemistry / Q000502:physiology; D002463:Cell Membrane Permeability / Q000187:drug effects / Q000502:physiology; D002518:Ceramides / Q000493:pharmacokinetics / Q000494:pharmacology*; D002867:Chromones / Q000494:pharmacology; D003847:Deoxyglucose / Q000378:metabolism / Q000493:pharmacokinetics; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D005419:Flavonoids / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology / Q000502:physiology*; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D008954:Models, Biological; D009004:Monosaccharide Transport Proteins / Q000032:analysis / Q000378:metabolism; D009025:Morpholines / Q000494:pharmacology; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000032:analysis / Q000378:metabolism / Q000502:physiology; D010750:Phosphoproteins / Q000032:analysis / Q000378:metabolism; D010766:Phosphorylation; D011090:Polyenes / Q000494:pharmacology; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D020123:Sirolimus; D014409:Tumor Necrosis Factor-alpha / Q000493:pharmacokinetics / Q000494:pharmacology*
chemical_list: D002518:Ceramides; D002867:Chromones; D004791:Enzyme Inhibitors; D005419:Flavonoids; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D009004:Monosaccharide Transport Proteins; D009025:Morpholines; D009124:Muscle Proteins; D010750:Phosphoproteins; D011090:Polyenes; C495678:Slc2a1 protein, mouse; C495693:Slc2a4 protein, mouse; D014409:Tumor Necrosis Factor-alpha; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D003847:Deoxyglucose; D019869:Phosphatidylinositol 3-Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D005947:Glucose; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D020123:Sirolimus