PT  - JOURNAL ARTICLE
AU  - Xianghai Chen
AU  - Frank Chen
AU  - Shanjun Liu
AU  - Hartmut Glaeser
AU  - Paul A. Dawson
AU  - Alan F. Hofmann
AU  - Richard B. Kim
AU  - Benjamin L. Shneider
AU  - K. Sandy Pang
TI  - Transactivation of Rat Apical Sodium-Dependent Bile Acid Transporter and Increased Bile Acid Transport by 1α,25-Dihydroxyvitamin D<sub>3</sub> via the Vitamin D Receptor
AID  - 10.1124/mol.105.020792
DP  - 2006 Jun 01
TA  - Molecular Pharmacology
PG  - 1913--1923
VI  - 69
IP  - 6
4099  - http://molpharm.aspetjournals.org/content/69/6/1913.short
4100  - http://molpharm.aspetjournals.org/content/69/6/1913.full
SO  - Mol Pharmacol2006 Jun 01; 69
AB  - Transactivation of the rat apical sodium-dependent bile acid transporter (ASBT; Slc10a2) by 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3] via the vitamin D receptor (VDR), was studied. Levels of ASBT protein and mRNA were low in the duodenum and high in the ileum, and both were induced by 1,25(OH)2D3. The nuclear receptor protein, VDR, was present uniformly in the duodenum, jejunum, and ileum of the rat small intestine. The physiological relevance of ASBT induction by 1,25(OH)2D3 was assessed by measuring absorption of cholylsarcosine, a non-metabolized synthetic bile acid analog, from duodenal or ileal closed loops of the perfused rat small intestine preparation. Absorption of cholylsarcosine was much greater from the ileal segment (28-fold that of the duodenum under control conditions) and was enhanced with 1,25(OH)2D3 treatment. Transient transfection analysis of the rat ASBT promoter in Caco-2 cells revealed concentration-dependent enhancement of luciferase reporter activity after treatment with 1,25(OH)2D3. The activation by 1,25(OH)2D3 was abrogated after site-directed mutagenesis or deletion of the vitamin D response element (VDRE) in the ASBT promoter. Gel-shift mobility assays of nuclear extracts from rat ileum showed that both rat retinoid X receptor and VDR were bound to the VDRE. The results indicate that rat ASBT gene expression is activated by 1,25(OH)2D3 by specific binding to the VDRE and that such activation enhances ileal bile acid transport. Human ABST mRNA and promoter activity were also increased in Caco-2 cells treated with 1,25(OH)2D3, suggesting a physiological role of VDR in human ileal bile acid homeostasis.