Lipid mediators of insulin resistance: ceramide signalling down-regulates GLUT4 gene transcription in 3T3-L1 adipocytes.
We have previously demonstrated that chronic exposure of 3T3-L1 adipocytes to tumour necrosis factor-alpha (TNF) resulted in a marked decrease (approximately 90%) in cellular GLUT4 (insulin-responsive glucose transporter) mRNA content as a result of a decreased transcription rate of the GLUT4 gene (approximately 75%) and a reduced half-life of its mRNA (9 to 4.5 h). Investigation of the signalling mechanism responsible for this regulation demonstrated that in the 3T3-L1 adipocytes, sphingomyelin levels decreased to 50% of control levels within 40 min of exposure to TNF, consistent with activation of a sphingomyelinase. In the same manner as with TNF, treatment of the adipocytes with 1-3 microM C6-ceramide, a membrane-permeable analogue of ceramide, decreased GLUT4 mRNA content by approximately 60%. Subsequent investigations revealed that transcription of the GLUT4 gene was reduced by approximately 65% in response to C6-ceramide, demonstrating that the decrease in mRNA content is mediated by a reduction in the transcription of the genc. No effect on GLUT4 mRNA stability was observed after exposure of the adipocytes to C6-ceramide. These observations are interesting in light of our previous data demonstrating that TNF affects both GLUT4 transcription and mRNA stability in the 3T3-L1 adipocytes. In conclusion, the effect of ceramide on GLUT4 gene expression is at the level of transcription, suggesting that another pathway controls mRNA stability. These data establish that ceramide-initiated signal transduction pathways exist within the adipocyte, and provide a potential mechanism for control of GLUT4 gene expression.
Long
S D
SD
Department of Biochemistry, School of Medicine, East Carolina University, Greenville, NC 27858, USA.
Pekala
P H
PH
D016475:3T3 Cells; D015117:5,8,11,14-Eicosatetraynoic Acid / Q000378:metabolism; D000273:Adipose Tissue / Q000187:drug effects* / Q000378:metabolism; D000818:Animals; D016718:Arachidonic Acid / Q000378:metabolism; D002518:Ceramides / Q000494:pharmacology*; D002794:Choline / Q000378:metabolism; D015536:Down-Regulation; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D005786:Gene Expression Regulation; D051275:Glucose Transporter Type 4; D007333:Insulin Resistance; D007527:Isoenzymes / Q000378:metabolism; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D009124:Muscle Proteins; D016328:NF-kappa B / Q000378:metabolism; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism; D051745:Protein Kinase C-delta; D012333:RNA, Messenger / Q000378:metabolism; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism; D013109:Sphingomyelins / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D002518:Ceramides; D051275:Glucose Transporter Type 4; D007527:Isoenzymes; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D016328:NF-kappa B; D012333:RNA, Messenger; C495693:Slc2a4 protein, mouse; D013109:Sphingomyelins; D014409:Tumor Necrosis Factor-alpha; C101954:N-caproylsphingosine; D015117:5,8,11,14-Eicosatetraynoic Acid; D016718:Arachidonic Acid; C497259:Prkcd protein, mouse; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D013108:Sphingomyelin Phosphodiesterase; D002794:Choline