Insulin and dexamethasone induce GLUT4 gene expression in foetal brown adipocytes: synergistic effect through CCAAT/enhancer-binding protein alpha.
Treatment of foetal brown adipocytes in primary culture with either dexamethasone or insulin, at physiological concentrations, for 24 h up-regulates the expression of the GLUT4 gene, producing a synergistic effect on mRNA accumulation (20-fold increase), in the amount of protein in the total membrane fraction (8-fold increase) and in the transactivation of a full-promoter GLUT4 -chloramphenicol acetyltransferase gene ( CAT ) construct (7-fold increase). However, GLUT1 expression remains essentially unmodified regardless of the presence of the hormones. As a consequence, exposure of brown adipocytes to dexamethasone and insulin results in a dramatic increase of glucose uptake (12-fold). Dexamethasone induces the expression of CCAAT/enhancer-binding protein (C/EBP) alpha, insulin promotes myocyte enhancer factor-2 DNA-binding activity and both combined produces a significant increase in C/EBPalpha DNA-binding activity. Moreover, co-transfection with a wild-type C/EBPalpha construct transactivates a full-promoter GLUT4 - CAT fusion gene, whereas a dominant-negative C/EBPalpha expression vector impairs the hormonal effects. Our results show that the synergism between insulin and glucocorticoids on glucose uptake is a consequence of the activation of the GLUT4 promoter by the transcription factor C/EBPalpha.
Hernandez
Rosario
R
Departamento de Bioquimica y Biologia Molecular, Facultad de Farmacia, Universidad Complutense, 28040-Madrid, Spain.
Teruel
Teresa
T
Lorenzo
Margarita
M
D017667:Adipocytes / Q000187:drug effects* / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000166:cytology; D000818:Animals; D022763:CCAAT-Enhancer-Binding Protein-alpha / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D015500:Chloramphenicol O-Acetyltransferase / Q000235:genetics; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D004357:Drug Synergism; D005786:Gene Expression Regulation; D005799:Genes, Dominant; D005938:Glucocorticoids / Q000494:pharmacology*; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D064326:MEF2 Transcription Factors; D009004:Monosaccharide Transport Proteins / Q000235:genetics* / Q000378:metabolism; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection; D015854:Up-Regulation
D022763:CCAAT-Enhancer-Binding Protein-alpha; D004268:DNA-Binding Proteins; D005938:Glucocorticoids; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D064326:MEF2 Transcription Factors; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D018006:Myogenic Regulatory Factors; D012333:RNA, Messenger; C495694:Slc2a4 protein, rat; D014157:Transcription Factors; D003907:Dexamethasone; D015500:Chloramphenicol O-Acetyltransferase; D005947:Glucose