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

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

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  • 1Department of Pharmacology, Case Western Reserve University, School of Medicine, Cleveland, OH 44106, USA.


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.

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