Differential regulation of sterol regulatory element-binding protein 1c transcriptional activity by insulin and liver X receptor during liver development

J Biol Chem. 2005 Jan 7;280(1):199-206. doi: 10.1074/jbc.M406522200. Epub 2004 Oct 27.

Abstract

Sterol regulatory element-binding proteins (SREBPs) are transcription factors involved in the synthesis of cholesterol and fatty acids. In adults, the isoform SREBP-1c is the predominant transcript in the liver of fed animals, and it activates triglyceride production from glucose when diet is enriched in carbohydrates. Studies have shown that SREBP-1c expression is dependent on insulin but also on the availability of oxysterols, ligands of the nuclear liver X receptor (LXR). The aim of this study was to investigate the regulation of the hepatic SREBP-1c expression in vivo in situations where drastic nutritional and hormonal changes occur, from the gestation to the weaning period. In this paper, we report the discovery of LXR-independent SREBP-1c transcriptional activity during late gestation. In utero insulin injection prior to the natural rise in insulin in late gestation triggers SREBP-1c mRNA elevation, nuclear SREBP-1c binding activity, and expression of its target genes independently of LXR transactivation. On the other hand, during suckling, we observed strong SREBP-1c mRNA expression despite very low plasma insulin, an expression that may be due to LXR transactivation. In contrast to insulin, LXR is not sufficient to trigger nuclear SREBP-1c binding activity and target gene induction. This could be due to the concomitant induction of INSIG-2a by LXR and subsequent retention of SREBP-1c in the endoplasmic reticulum.

MeSH terms

  • Animals
  • CCAAT-Enhancer-Binding Proteins / genetics*
  • CCAAT-Enhancer-Binding Proteins / metabolism
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism
  • Endoplasmic Reticulum / metabolism
  • Female
  • Gene Expression Regulation, Developmental*
  • Insulin / metabolism*
  • Intracellular Signaling Peptides and Proteins / genetics
  • Intracellular Signaling Peptides and Proteins / metabolism
  • Liver / embryology
  • Liver / metabolism*
  • Liver X Receptors
  • Male
  • Mice
  • Orphan Nuclear Receptors
  • Pregnancy
  • Protein Binding
  • Protein Transport
  • Receptors, Cytoplasmic and Nuclear
  • Signal Transduction
  • Sterol Regulatory Element Binding Protein 1
  • Transcription Factors / genetics*
  • Transcription Factors / metabolism
  • Transcriptional Activation

Substances

  • CCAAT-Enhancer-Binding Proteins
  • DNA-Binding Proteins
  • Insulin
  • Intracellular Signaling Peptides and Proteins
  • Liver X Receptors
  • Orphan Nuclear Receptors
  • Receptors, Cytoplasmic and Nuclear
  • Srebf1 protein, mouse
  • Sterol Regulatory Element Binding Protein 1
  • Transcription Factors