Vitamin D3 and Its Nuclear Receptor Increase the Expression and Activity of the Human Proton-Coupled Folate Transporter
Vitamin D3 and Its Nuclear Receptor Increase the Expression and Activity of the Human Proton-Coupled Folate Transporter
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DOI：
10.1124/mol.109.055392
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发表时间：
2009-11-01
影响因子：
3.6
通讯作者：
Kullak-Ublick, Gerd A.
中科院分区：
文献类型：
--
作者：
Eloranta, Jyrki J.;Hiller, Christian;Kullak-Ublick, Gerd A.
叶酸是核酸合成所必需的，特别是在肠上皮和造血细胞等快速增殖组织中。膳食中叶酸的可获得性是由它们在肠上皮的吸收决定的，吸收是由肠上皮顶端细胞膜上的质子偶联叶酸转运蛋白（PCFT）介导的。虽然PCFT的转运特性已经被很好地表征，但PCFT基因表达的调控仍然很少被阐明。我们研究了肠源性细胞中PCFT启动子活性和表达的调控机制。1,25-二羟基维生素D-3（维生素D-3）处理后Caco-2细胞PCFT mRNA水平呈剂量依赖性增加，维生素D-3诱导大鼠十二指肠PCFT mRNA的体外表达。在维生素D-3存在的情况下，PCFT启动子区域被维生素D受体（VDR）及其异二聚体伴侣类视黄醇X受体α (RXR α)反激活。计算机分析预测在PCFT启动子区-1694/-1680有一个VDR响应元件（VDRE）。DNA结合实验显示VDR: RXR α异源二聚体与PCFT（-1694/-1680）直接特异性结合，染色质免疫沉淀证实这种相互作用发生在活细胞内。突变启动子分析证实PCFT（-1694/-1680）基序介导对维生素D-3的转录反应。在这种调节机制的功能支持下，在pH为5.5时，维生素D-3显著增加了Caco-2细胞对[H-3]叶酸的摄取。综上所述，维生素D-3和VDR增加了肠道PCFT的表达，导致细胞叶酸摄取增加。对服用维生素D-3的患者进行药物治疗可能会增加叶酸的肠道吸收。
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-alpha (RXR alpha) in the presence of vitamin D-3. In silico analyses predicted a VDR response element (VDRE) in the PCFT promoter region -1694/-1680. DNA binding assays showed direct and specific binding of the VDR: RXR alpha heterodimer to the PCFT(-1694/-1680), and chromatin immunoprecipitations verified that this interaction occurs within living cells. Mutational promoter analyses confirmed that the PCFT(-1694/-1680) motif mediates a transcriptional response to vitamin D-3. In functional support of this regulatory mechanism, treatment with vitamin D-3 significantly increased the uptake of [H-3]folic acid into Caco-2 cells at pH 5.5. In conclusion, vitamin D-3 and VDR increase intestinal PCFT expression, resulting in enhanced cellular folate uptake. Pharmacological treatment of patients with vitamin D-3 may have the added therapeutic benefit of enhancing the intestinal absorption of folates.