Abstract
Organic anion-transporting polypeptide 1A2 (OATP1A2) (gene symbol, SLCO1A2) mediates cellular uptake of a wide range of endogenous substrates, as well as drugs and xenobiotics. OATP1A2 is expressed in several tissues, including apical membranes of small intestinal epithelial cells. Given its role in intestinal drug absorption, a detailed analysis of the mechanisms that regulate SLCO1A2 gene expression is potentially of great pharmacological relevance. We show here that treatment of human intestine-derived Caco-2 cells with vitamin D3 markedly increased endogenous OATP1A2 mRNA and protein levels. Suppression of endogenous vitamin D receptor (VDR) expression with siRNAs significantly reduced this induction. Two alternative promoter regions exist in genomic databases for the SLCO1A2 gene. One putative VDR response element (VDRE) that was predicted to interact efficiently with VDR-retinoid X receptor α (RXRα) was identified in silico within SLCO1A2 promoter variant 1. This VDRE served as a strong binding site for the recombinant VDR-RXRα heterodimers in vitro and was potently activated by VDR in the presence of vitamin D3 in heterologous promoter assays. In reporter assays using native promoter constructs, SLCO1A2 promoter variant 1 was strongly induced by VDR, and site-directed mutagenesis of a single VDRE within this region abolished this activation. Native VDR-RXRα also interacted with this element both in vitro and in living cells. We showed that expression of the SLCO1A2 gene is induced by vitamin D3 at the transcriptional level through the VDR. Our results suggest that pharmacological administration of vitamin D3 may allow modulation of intestinal absorption of OATP1A2 transport substrates.
Footnotes
This study was supported by the Swiss National Science Foundation [Grant 320030-120463], the Zurich Center of Integrative Human Physiology, the Center of Clinical Research at the University Hospital Zurich, and the Novartis Foundation for Biomedical Research.
Article, publication date, and citation information can be found at http://molpharm.aspetjournals.org.
ABBREVIATIONS:
- OATP
- organic anion-transporting polypeptide
- VDR
- vitamin D receptor
- VDRE
- vitamin D response element
- RXR
- retinoid X receptor
- LCA
- lithocholic acid
- DR-3
- direct repeat-3
- PCFT
- proton-coupled folate transporter
- siRNA
- short interfering RNA
- EMSA
- electrophoretic mobility shift assay
- ChIP
- chromatin immunoprecipitation
- MRP
- multidrug resistance-associated protein
- PXR
- pregnane X receptor
- PBS
- phosphate-buffered saline
- PBS-T
- PBS/Tween 20
- PCR
- polymerase chain reaction
- BQ-123
- cyclo(d-Trp,d-Asp,l-Pro,d-Val,l-Leu)
- CRC-220
- 4-methoxy-2,3,6-trimethylphenylsulfonyl-l-aspartyl-d-4-amidinophenylalanyl-piperidide.
- Received January 27, 2012.
- Accepted April 3, 2012.
- Copyright © 2012 The American Society for Pharmacology and Experimental Therapeutics
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