Genetics and diet regulate vitamin A production via the homeobox transcription factor ISX

J Biol Chem. 2013 Mar 29;288(13):9017-27. doi: 10.1074/jbc.M112.444240. Epub 2013 Feb 7.

Abstract

Low dietary intake of β-carotene is associated with chronic disease and vitamin A deficiency. β-Carotene is converted to vitamin A in the intestine by the enzyme β-carotene-15,15'-monoxygenase (BCMO1) to support vision, reproduction, immune function, and cell differentiation. Considerable variability for this key step in vitamin A metabolism, as reported in the human population, could be related to genetics and individual vitamin A status, but it is unclear how these factors influence β-carotene metabolism and vitamin A homeostasis. Here we show that the intestine-specific transcription factor ISX binds to the Bcmo1 promoter. Moreover, upon induction by the β-carotene derivative retinoic acid, this ISX binding decreased expression of a luciferase reporter gene in human colonic CaCo-2 cells indicating that ISX acts as a transcriptional repressor of BCMO1 expression. Mice deficient for this transcription factor displayed increased intestinal BCMO1 expression and produced significantly higher amounts of vitamin A from supplemental β-carotene. The ISX binding site in the human BCMO1 promoter contains a common single nucleotide polymorphism that is associated with decreased conversion rates and increased fasting blood levels of β-carotene. Thus, our study establishes ISX as a critical regulator of vitamin A production and provides a mechanistic explanation for how both genetics and diet can affect this process.

Publication types

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

MeSH terms

  • Animal Feed
  • Animals
  • Caco-2 Cells
  • Chromatography, High Pressure Liquid / methods
  • Cloning, Molecular
  • DNA / metabolism
  • DNA, Complementary / metabolism
  • Diet*
  • Female
  • Gene Expression Regulation
  • Heterozygote
  • Homeodomain Proteins / metabolism*
  • Homeostasis
  • Humans
  • Lipids / chemistry
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Models, Genetic
  • Polymorphism, Single Nucleotide
  • Promoter Regions, Genetic
  • Protein Binding
  • Transcription Factors / metabolism*
  • Tretinoin / metabolism
  • Vitamin A / chemistry*
  • Vitamin A / metabolism
  • beta Carotene / metabolism

Substances

  • DNA, Complementary
  • Homeodomain Proteins
  • Isx protein, human
  • Isx protein, mouse
  • Lipids
  • Transcription Factors
  • beta Carotene
  • Vitamin A
  • Tretinoin
  • DNA