Vitamin D₃ and Its Nuclear Receptor Increase the Expression and Activity of the Human Proton-Coupled Folate Transporter

Abstract

Folates are essential for nucleic acid synthesis and are particularly required in rapidly proliferating tissues, such as intestinal epithelium and hemopoietic cells. Availability of dietary folates is determined by their absorption across the intestinal epithelium, mediated by the proton-coupled folate transporter (PCFT) at the apical enterocyte membranes. Whereas transport properties of PCFT are well characterized, regulation of PCFT gene expression remains less elucidated. We have studied the mechanisms that regulate PCFT promoter activity and expression in intestine-derived cells. PCFT mRNA levels are increased in Caco-2 cells treated with 1,25-dihydroxyvitamin D 3 (vitamin D 3 ) in a dose-dependent fashion, and the duodenal rat Pcft mRNA expression is induced by vitamin D 3 ex vivo. The PCFT promoter region is transactivated by the vitamin D receptor (VDR) and its heterodimeric partner retinoid X receptor-␣

The Major Facilitative Folate Transporters Solute Carrier 19A1 and Solute Carrier 46A1: Biology and Role in Antifolate Chemotherapy of Cancer

“…Studies have begun to identify transcriptional regulatory factors and cis elements which regulate the hPCFT gene (Gonen et al, 2008;Eloranta et al, 2009;Stark et al, 2009;Gonen and Assaraf, 2010;Furumiya et al, 2013). Three nuclear respiratory factor-1 sites (positions 2108 to 297, 293 to 282, and 210 to +1) were identified in the hPCFT minimal promoter, and nuclear respiratory factor-1 binds and transactivates the hPCFT gene, leading to increased hPCFT transcripts (Gonen and Assaraf, 2010).…”

“…Three nuclear respiratory factor-1 sites (positions 2108 to 297, 293 to 282, and 210 to +1) were identified in the hPCFT minimal promoter, and nuclear respiratory factor-1 binds and transactivates the hPCFT gene, leading to increased hPCFT transcripts (Gonen and Assaraf, 2010). 1,25-Dihydroxyvitamin D3 (vitamin D3) induced hPCFT levels in Caco-2 cells in vitro and in rat duodenal biopsies ex vivo (Eloranta et al, 2009). Induction of hPCFT by vitamin D3 resulted in enhanced transport at pH 5.5.…”

Intestinal Absorption Of Folates

“…There was also an increase in rat duodenal PCFT mRNA levels in vivo in response to vitamin D 3 (118). Vitamin D 3 activated the PCFT promoter in Caco-2 cells, with an additional increase in the presence of the vitamin D receptor (VDR) partner RXRα (retinoic X receptor α) and its ligand, retinoic acid.…”

“…Mutation or deletion of that putative binding site (1694 to −1680) resulted in decreased binding of a VDR:RXRα heterodimer and a 50% decrease in PCFT promoter activity. This finding suggested the presence of additional binding elements between −843 and +96 or vitamin D interactions with other, unrelated DNA-binding factors (118). Vitamin D 3 and the VDR have been associated with modulation of the expression of various transporters, such as the sodium-dependent bile acid transporter (119), oligopeptide transporter 1, and the multidrug-resistance-associated proteins (120,121), are found in the intestine.…”

Regulation of the gene encoding the intestinal bile acid transporter ASBT by the caudal-type homeobox proteins CDX1 and CDX2

“…Chromatin immunoprecipitation (ChIP) assays were carried out essentially as described previously (18). Briefly, T84 cells were grown on 10-cm plates to 80% confluence, and the cells were harvested by cross-linking with 1% methanol-free formaldehyde and processed through chromatin immunoprecipitations using the ChIP-IT Express kit (Active Motif, Rixensart, Belgium).…”