Carbohydrate response element binding protein directly promotes lipogenic enzyme gene transcription.
Carbohydrate response element (ChRE)-binding protein (ChREBP) is a recently discovered transcription factor that is activated in response to high glucose concentrations in liver independently of insulin. ChREBP was first identified by its ability to bind the ChRE of the liver pyruvate kinase (LPK) gene. We recently reported that the increase in expression of multiple liver lipogenic enzyme mRNAs elicited by feeding a high-carbohydrate diet as well as that of LPK mRNA is markedly reduced in mice lacking ChREBP gene expression (ChREBP(-/-)) in comparison to WT mice. The present study provides evidence for a direct and dominant role of ChREBP in the glucose regulation of two key liver lipogenic enzymes, acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS). ACC, FAS, and LPK mRNA levels were higher in WT hepatocytes cultured with high (25 mM) rather than low (5.5 mM) glucose medium, but there was no effect of glucose concentration on these mRNA levels in ChREBP(-/-) hepatocytes. Similarly, reporter constructs containing ACC, FAS, or LPK gene ChREs were responsive to glucose when transfected into WT but not ChREBP(-/-) hepatocytes, and glucose transactivation of the constructs in ChREBP(-/-) hepatocytes was restored by cotransfection with a ChREBP expression plasmid. ChREBP binding to ACC, FAS, and LPK ChRE sequences in vitro was demonstrated by electrophoretic mobility super shift assays. In vivo binding of ChREBP to ACC, FAS, and LPK gene promoters in intact liver nuclei from rats fed a high-carbohydrate diet was demonstrated by using a formaldehyde crosslinking and chromatin immunoprecipitation procedure.
Ishii
Seiji
S
Departments of Biochemistry and Internal Medicine, University of Texas Southwestern Medical School, 4500 South Lancaster Road, Dallas, TX 75216, USA.
Iizuka
Katsumi
K
Miller
Bonnie C
BC
Uyeda
Kosaku
K
D000103:Acetyl-CoA Carboxylase / Q000235:genetics; D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001665:Binding Sites / Q000235:genetics; D047369:Chromatin Immunoprecipitation; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D064429:Fatty Acid Synthases / Q000235:genetics; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D066298:In Vitro Techniques; D008055:Lipids / Q000096:biosynthesis*; D051379:Mice; D018345:Mice, Knockout; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D011770:Pyruvate Kinase / Q000235:genetics; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D008055:Lipids; C506001:Mlxipl protein, mouse; D009687:Nuclear Proteins; D011994:Recombinant Proteins; D014157:Transcription Factors; D004247:DNA; D064429:Fatty Acid Synthases; D011770:Pyruvate Kinase; D000103:Acetyl-CoA Carboxylase; D005947:Glucose