Regulation of insulin-stimulated glucose transporter GLUT4 translocation and Akt kinase activity by ceramide.
The sphingomyelin derivative ceramide is a signaling molecule implicated in numerous physiological events. Recently published reports indicate that ceramide levels are elevated in insulin-responsive tissues of diabetic animals and that agents which trigger ceramide production inhibit insulin signaling. In the present series of studies, the short-chain ceramide analog C2-ceramide inhibited insulin-stimulated glucose transport by approximately 50% in 3T3-L1 adipocytes, with similar reductions in hormone-stimulated translocation of the insulin-responsive glucose transporter (GLUT4) and insulin-responsive aminopeptidase. C2-ceramide also inhibited phosphorylation and activation of Akt, a molecule proposed to mediate multiple insulin-stimulated metabolic events. C2-ceramide, at concentrations which antagonized activation of both glucose uptake and Akt, had no effect on the tyrosine phosphorylation of insulin receptor substrate 1 (IRS-1) or the amounts of p85 protein and phosphatidylinositol kinase activity that immunoprecipitated with anti-IRS-1 or antiphosphotyrosine antibodies. Moreover, C2-ceramide also inhibited stimulation of Akt by platelet-derived growth factor, an event that is IRS-1 independent. C2-ceramide did not inhibit insulin-stimulated phosphorylation of mitogen-activated protein kinase or pp70 S6-kinase, and it actually stimulated phosphorylation of the latter in the absence of insulin. Various pharmacological agents, including the immunosuppressant rapamycin, the protein synthesis inhibitor cycloheximide, and several protein kinase C inhibitors, were without effect on ceramide's inhibition of Akt. These studies demonstrate ceramide's capacity to inhibit activation of Akt and imply that this is a mechanism of antagonism of insulin-dependent physiological events, such as the peripheral activation of glucose transport and the suppression of apoptosis.
Howard Hughes Medical Institute and Departments of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.
S A
SA
Summers
L A
LA
Garza
H
H
Zhou
M J
MJ
Birnbaum
D016475:3T3 Cells; D017667:Adipocytes / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002454:Cell Differentiation; D002518:Ceramides / Q000494:pharmacology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology*; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000096:biosynthesis / Q000378:metabolism*; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000096:biosynthesis / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins / Q000096:biosynthesis / Q000378:metabolism; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D014162:Transfection
D002518:Ceramides; D004791:Enzyme Inhibitors; D005947:Glucose; D051275:Glucose Transporter Type 4; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D019869:Phosphatidylinositol 3-Kinases; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011994:Recombinant Proteins; D013110:Sphingosine; C064769:N-acetylsphingosine; C495693:Slc2a4 protein, mouse; C109343:dihydroceramide