Modulation of CCAAT/enhancer-binding Protein-Alpha Gene Expression by Metabolic Signals in Rodent Adipocytes

Endocrinology. 1999 Jul;140(7):2938-47. doi: 10.1210/endo.140.7.6793.

Abstract

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.

MeSH terms

  • 3T3 Cells
  • Adenosine Triphosphate / metabolism
  • Adipocytes / metabolism
  • Adipocytes / physiology*
  • Adipose Tissue / metabolism
  • Animals
  • CCAAT-Enhancer-Binding Proteins
  • DNA-Binding Proteins / genetics*
  • Gene Expression Regulation / physiology*
  • Glucosamine / pharmacology
  • Glucose / metabolism
  • Glucose / pharmacology
  • Glycosylation
  • Hexosamines / metabolism
  • Hormones / physiology
  • Mice
  • Nuclear Proteins / genetics*
  • Nucleotides / metabolism
  • Promoter Regions, Genetic / physiology
  • Proteins / metabolism
  • RNA, Messenger / metabolism
  • Rats
  • Rats, Wistar
  • Signal Transduction / physiology*
  • Xylitol / pharmacology

Substances

  • CCAAT-Enhancer-Binding Proteins
  • DNA-Binding Proteins
  • Hexosamines
  • Hormones
  • Nuclear Proteins
  • Nucleotides
  • Proteins
  • RNA, Messenger
  • Adenosine Triphosphate
  • Glucose
  • Glucosamine
  • Xylitol