Glucose activates ChREBP by increasing its rate of nuclear entry and relieving repression of its transcriptional activity

J Biol Chem. 2008 Aug 29;283(35):24029-38. doi: 10.1074/jbc.M801539200. Epub 2008 Jun 30.

Abstract

Carbohydrate response element-binding protein (ChREBP) is a glucose-responsive transcription factor that activates genes involved in de novo lipogenesis in mammals. The current model for glucose activation of ChREBP proposes that increased glucose metabolism triggers a cytoplasmic to nuclear translocation of ChREBP that is critical for activation. However, we find that ChREBP actively shuttles between the cytoplasm and nucleus in both low and high glucose in the glucose-sensitive beta cell-derived line, 832/13. Glucose stimulates a 3-fold increase in the rate of ChREBP nuclear entry, but trapping ChREBP in the nucleus by mutagenesis or with a nuclear export inhibitor does not lead to constitutive activation. In fact, mutational studies targeting the nuclear export signal of ChREBP also identified a distinct function essential for glucose-dependent transcriptional activation. From this, we conclude that an additional event independent of nuclear translocation is required for activation. The N-terminal segment of ChREBP (amino acids 1-298) has previously been shown to repress activity under basal conditions. This segment has five highly conserved regions, Mondo conserved regions 1-5 (MCR1 to -5). Based on activating mutations in MCR2 and MCR5, we propose that these two regions act coordinately to repress ChREBP in low glucose. In addition, other mutations in MCR2 and mutations in MCR3 were found to prevent glucose activation. Hence, we conclude that both relief of repression and adoption of an activating form are required for ChREBP activation.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Active Transport, Cell Nucleus / drug effects
  • Active Transport, Cell Nucleus / physiology
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / genetics
  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors / metabolism*
  • Cell Line
  • Cell Nucleus / genetics
  • Cell Nucleus / metabolism*
  • Cytoplasm / genetics
  • Cytoplasm / metabolism
  • Glucose / metabolism*
  • Glucose / pharmacology
  • Humans
  • Lipids / biosynthesis
  • Models, Biological*
  • Mutation
  • Protein Structure, Tertiary / physiology
  • Repressor Proteins / genetics
  • Repressor Proteins / metabolism*
  • Sweetening Agents / metabolism
  • Sweetening Agents / pharmacology
  • Transcription, Genetic / drug effects
  • Transcription, Genetic / physiology*

Substances

  • Basic Helix-Loop-Helix Leucine Zipper Transcription Factors
  • Lipids
  • MLXIPL protein, human
  • Repressor Proteins
  • Sweetening Agents
  • Glucose