Rosiglitazone induction of Insig-1 in white adipose tissue reveals a novel interplay of peroxisome proliferator-activated receptor gamma and sterol regulatory element-binding protein in the regulation of adipogenesis.
Insulin-induced gene 1 (INSIG-1) is a key regulator in the processing of the sterol regulatory element-binding proteins (SREBPs). We demonstrated that Insig-1 is regulated by peroxisome proliferator-activated receptor gamma (PPARgamma) providing a link between insulin sensitization/glucose homeostasis and lipid homeostasis. Insig-1 was identified as a PPARgamma target gene using microarray analysis of mRNA from the white adipose tissue of diabetic (db/db) animals treated with PPARgamma agonists. Insig-1 was induced in subcutaneous (9-fold) and epididymal (4-fold) fat pads from db/db mice treated for 8 days with the PPARgamma agonist rosiglitazone (30 mg/kg/day). This in vivo response was confirmed in differentiated C3H10T1/2 adipocytes treated with rosiglitazone. To elucidate the molecular mechanisms regulating INSIG-1 expression, we cloned and characterized the human INSIG-1 promoter. Co-expression of PPARgamma and RXRalpha transactivated the INSIG-1 promoter in the presence of PPARgamma agonists. This induction was attenuated when a dominant negative PPARgamma construct was transfected into cells. Furthermore, a PPARgamma antagonist repressed the transactivation of the INSIG-1 promoter-reporter construct. Truncations of the promoter resulted in the identification of a PPAR response element that mediated the regulation of the promoter. We demonstrated with recombinant proteins that the PPARgamma/RXRalpha heterodimer binds directly to this PPAR response element. In addition to regulation by PPARgamma/RXRalpha, we demonstrated that the INSIG-1 promoter is regulated by transcriptionally active SREBP. The sterol response element was identified 380 base pairs upstream of the transcriptional start site. These findings suggest that the regulation of Insig-1 by PPARgamma agonists could in turn regulate SREBP processing and thus couple insulin sensitizers with the regulation of lipid homeostasis.
Kast-Woelbern
Heidi R
HR
Department of Molecular and Cell Biology, Ligand Pharmaceuticals, Inc., San Diego, California 92121, USA. hwoelbern@ligand.com
Dana
Sharon L
SL
Cesario
Rosemary M
RM
Sun
Li
L
de Grandpre
Louise Y
LY
Brooks
Mason E
ME
Osburn
Deborah L
DL
Reifel-Miller
Anne
A
Klausing
Kay
K
Leibowitz
Mark D
MD
D017667:Adipocytes / Q000378:metabolism*; D000273:Adipose Tissue / Q000378:metabolism*; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins / Q000096:biosynthesis*; D002478:Cells, Cultured; D018076:DNA, Complementary / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000096:biosynthesis*; D004305:Dose-Response Relationship, Drug; D004822:Epididymis / Q000378:metabolism; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D007004:Hypoglycemic Agents / Q000494:pharmacology; D007328:Insulin / Q000378:metabolism; D047908:Intracellular Signaling Peptides and Proteins; D050356:Lipid Metabolism; D008099:Liver / Q000378:metabolism; D008297:Male; D008565:Membrane Proteins / Q000096:biosynthesis*; D051379:Mice; D008809:Mice, Inbred C3H; D008954:Models, Biological; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D000077154:Rosiglitazone; D051780:Sterol Regulatory Element Binding Protein 1; D045162:Thiazolidinediones / Q000494:pharmacology*; D013997:Time Factors; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D015533:Transcriptional Activation; D014162:Transfection
D022762:CCAAT-Enhancer-Binding Proteins; D018076:DNA, Complementary; D004268:DNA-Binding Proteins; D007004:Hypoglycemic Agents; C108626:INSIG1 protein, human; D007328:Insulin; D047908:Intracellular Signaling Peptides and Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; C497388:Srebf1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; D045162:Thiazolidinediones; D014157:Transcription Factors; D000077154:Rosiglitazone; D012313:RNA