PPARgamma induces the insulin-dependent glucose transporter GLUT4 in the absence of C/EBPalpha during the conversion of 3T3 fibroblasts into adipocytes.
To define the molecular mechanisms that control GLUT4 expression during adipogenesis, NIH-3T3 fibroblasts ectopically expressing different adipogenic transcription factors (C/EBPbeta, C/EBPdelta, C/EBPalpha, and PPARgamma) under the control of a tetracycline-responsive inducible (C/EBPs) or a constitutive retroviral (PPARgamma) expression system were used. Enhanced production of C/EBPbeta (beta2 cell line), C/EBPbeta together with C/EBPdelta (beta/delta39 cell line), C/EBPalpha (alpha1 cell line), or PPARgamma (Pgamma2 cell line) in cells exposed to dexamethasone and the PPARgamma ligand ciglitazone (a thiazolidinedione) resulted in expression of GLUT4 mRNA as well as other members of the adipogenic gene program, including aP2 and adipsin. Focusing our studies on the beta/delta39 cells, we have demonstrated that C/EBPbeta along with C/EBPdelta in the presence of dexamethasone induces PPARgamma, adipsin, and aP2 mRNA production; however, GLUT4 mRNA is only expressed in cells exposed to ciglitazone. In addition, enhanced expression of a ligand-activated form of PPARgamma in the beta/delta39 fibroblasts stimulates synthesis of GLUT4 protein and gives rise to a population of adipocytic cells that take up glucose in direct response to insulin. C/EBPalpha is not expressed in the beta/delta39 cells under conditions that stimulate the adipogenic program. This observation suggests that PPARgamma alone or in combination with C/EBPbeta and C/EBPdelta is capable of activating GLUT4 gene expression.
Wu
Z
Z
Department of Biochemistry, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
Xie
Y
Y
Morrison
R F
RF
Bucher
N L
NL
Farmer
S R
SR
D016475:3T3 Cells; D033962:Adaptor Protein Complex 2; D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D017667:Adipocytes / Q000166:cytology / Q000378:metabolism*; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D002454:Cell Differentiation; D011416:Complement Factor D; D004268:DNA-Binding Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology; D008024:Ligands; D008565:Membrane Proteins / Q000096:biosynthesis / Q000235:genetics; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000096:biosynthesis* / Q000235:genetics; D009124:Muscle Proteins; D009687:Nuclear Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism; D012697:Serine Endopeptidases / Q000235:genetics / Q000378:metabolism; D013844:Thiazoles / Q000494:pharmacology; D045162:Thiazolidinediones; D014157:Transcription Factors / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*
C439123:AP2A1 protein, Bos taurus; D033962:Adaptor Protein Complex 2; D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D008024:Ligands; D008565:Membrane Proteins; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D009687:Nuclear Proteins; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; C495693:Slc2a4 protein, mouse; D013844:Thiazoles; D045162:Thiazolidinediones; D014157:Transcription Factors; D003907:Dexamethasone; D012697:Serine Endopeptidases; D011416:Complement Factor D; C493491:complement factor D, mouse; C039671:ciglitazone