Modulation of CCAAT/enhancer-binding protein-alpha gene expression by metabolic signals in rodent adipocytes.
The transcription factor CCAAT/enhancer-binding protein-alpha (C/EBPalpha) is a positive modulator of transcription for several adipocyte-specific genes that play a role in energy metabolism. However, there is little information available regarding the regulation of its expression by metabolic signals. Exposure to insulin for 5-24 h attenuated C/EBPalpha expression when 3T3-L1 adipocytes were incubated in 24 mM glucose, but not in 5.7 mM glucose. Nuclear run-on transcription assays indicated a transcriptional repression of C/EBPalpha gene, but not that of C/EBPbeta. Glucosamine, a product of the hexosamine pathway, in the presence of low glucose mimicked high glucose's ability to reduce C/EBPalpha messenger RNA expression in insulin-treated cells. Similar results were obtained with xylitol, an activator of the pentose phosphate pathway. There was no correlation between the accumulation of hexosamine pathway metabolites (e.g. UDP-N-acetylhexosamines) and/or changes in intracellular protein glycosylation with the ability of high glucose, glucosamine, or xylitol to down-regulate C/EBPalpha gene expression. None of these treatments caused a reduction in intracellular ATP levels. Stable transfection of 3T3-L1 cells with the 5'-flanking 468-bp sequence of the mouse C/EBPalpha gene fused to luciferase demonstrated that promoter activity was also reduced by these nutrients. Of interest, treatment of rats with glucose or glucosamine led to a reduction in C/EBPalpha messenger RNA levels in epididymal, but not omental, fat. Taken together, these results suggest that metabolic signals serve to down-regulate C/EBPalpha expression both in vitro and in vivo.
Wang
Y
Y
Laboratory of Clinical Investigation, National Institute on Aging, National Institutes of Health, Baltimore, Maryland 21224-6825, USA.
Lee-Kwon
W
W
Martindale
J L
JL
Adams
L
L
Heller
P
P
Egan
J M
JM
Bernier
M
M
D016475:3T3 Cells; D000255:Adenosine Triphosphate / Q000378:metabolism; D017667:Adipocytes / Q000378:metabolism / Q000502:physiology*; D000273:Adipose Tissue / Q000378:metabolism; D000818:Animals; D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins / Q000235:genetics*; D005786:Gene Expression Regulation / Q000502:physiology*; D005944:Glucosamine / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism / Q000494:pharmacology; D006031:Glycosylation; D006595:Hexosamines / Q000378:metabolism; D006728:Hormones / Q000502:physiology; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics*; D009711:Nucleotides / Q000378:metabolism; D011401:Promoter Regions, Genetic / Q000502:physiology; D011506:Proteins / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D015398:Signal Transduction / Q000502:physiology*; D014993:Xylitol / Q000494:pharmacology
D022762:CCAAT-Enhancer-Binding Proteins; D004268:DNA-Binding Proteins; D006595:Hexosamines; D006728:Hormones; D009687:Nuclear Proteins; D009711:Nucleotides; D011506:Proteins; D012333:RNA, Messenger; D000255:Adenosine Triphosphate; D005947:Glucose; D005944:Glucosamine; D014993:Xylitol