title: Peroxisome proliferator-activated receptor-gamma represses GLUT4 promoter activity in primary adipocytes, and rosiglitazone alleviates this effect.
abstract: The synthetic thiazolidinedione ligands of peroxisome proliferator-activated receptor-gamma (PPARgamma) improve insulin sensitivity in type II diabetes and induce GLUT4 mRNA expression in fat and muscle. However, the molecular mechanisms involved are still unclear. We studied the regulatory effects of PPARgamma and its ligands on GLUT4 gene expression in primary rat adipocytes and CHO-K1 cells cotransfected with PPARgamma and the GLUT4 promoter reporter. PPARgamma1 and PPARgamma2 repressed the activity of the GLUT4 promoter in a dose-dependent manner. Whereas this repression was augmented by the natural ligand 15Delta-prostaglandin J2, it was completely alleviated by rosiglitazone (Rg). Ligand binding-defective mutants PPARgamma1-L468A/E471A and PPARgamma2-L496A/E499A retained the repression effect, which was unaffected by Rg, whereas the PPARgamma2-S112A mutant exhibited a 50% reduced capacity to repress GLUT4 promoter activity. The -66/+163 bp GLUT4 promoter region was sufficient to mediate PPARgamma inhibitory effects. The PPARgamma/retinoid X receptor-alpha heterodimer directly bound to this region, whereas binding was abolished in the presence of Rg. Thus, we show that PPARgamma represses transcriptional activity of the GLUT4 promoter via direct and specific binding of PPARgamma/retinoid X receptor-alpha to the GLUT4 promoter. This effect requires an intact Ser112 phosphorylation site on PPARgamma and is completely alleviated by Rg, acting via its ligand-binding domain. These data suggest a novel mechanism by which Rg exerts its antidiabetic effects via detaching PPARgamma from the GLUT4 gene promoter, thus leading to increased GLUT4 expression and enhanced insulin sensitivity.
authors.affiliation: Institute of Endocrinology, Diabetes, and Metabolism, Rambam Medical Center and Rappaport Faculty of Medicine, Technion-Israel Institute of Technology, Haifa 31096, Israel. amichal@tx.technion.ac.il
authors.forename: Michal
authors.initials: M
authors.lastname: Armoni
authors.forename: Natalia
authors.initials: N
authors.lastname: Kritz
authors.forename: Chava
authors.initials: C
authors.lastname: Harel
authors.forename: Fabiana
authors.initials: F
authors.lastname: Bar-Yoseph
authors.forename: Hui
authors.initials: H
authors.lastname: Chen
authors.forename: Michael J
authors.initials: MJ
authors.lastname: Quon
authors.forename: Eddy
authors.initials: E
authors.lastname: Karnieli
mesh_terms: D017667:Adipocytes / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D016466:CHO Cells; D006224:Cricetinae; D019281:Dimerization; D005347:Fibroblasts / Q000166:cytology; D005786:Gene Expression Regulation / Q000187:drug effects / Q000502:physiology; D005816:Genetic Complementation Test; D051275:Glucose Transporter Type 4; D006801:Humans; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007155:Immunologic Factors / Q000494:pharmacology; D051379:Mice; D009004:Monosaccharide Transport Proteins / Q000235:genetics*; D009124:Muscle Proteins; D011401:Promoter Regions, Genetic / Q000502:physiology; D015230:Prostaglandin D2 / Q000031:analogs & derivatives / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000737:chemistry / Q000235:genetics; D047488:Retinoid X Receptors; D000077154:Rosiglitazone; D013489:Suppression, Genetic; D013844:Thiazoles / Q000494:pharmacology*; D045162:Thiazolidinediones; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic / Q000187:drug effects / Q000502:physiology
chemical_list: C097240:15-deoxy-delta(12,14)-prostaglandin J2; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007155:Immunologic Factors; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; C495692:SLC2A4 protein, human; C495693:Slc2a4 protein, mouse; C495694:Slc2a4 protein, rat; D013844:Thiazoles; D045162:Thiazolidinediones; D014157:Transcription Factors; D000077154:Rosiglitazone; C089946:2,4-thiazolidinedione; D015230:Prostaglandin D2