Identification of the functional vitamin D response elements in the human MDR1 gene.
P-glycoprotein, encoded by the multidrug resistance 1 (MDR1) gene, is an efflux transporter and plays an important role in pharmacokinetics. The expression of MDR1 is induced by a variety of compounds, of which 1alpha,25-dihydroxyvitamin D(3) is known to be an effective inducer. However, it remains unclear how 1alpha,25-dihydroxyvitamin D(3) regulates the expression of MDR1. In this study, we demonstrated that the vitamin D receptor (VDR) induces MDR1 expression in a 1alpha,25-dihydroxyvitamin D(3)-dependent manner. Luciferase assays revealed that the region between -7.9 and -7.8k bp upstream from the transcription start site of the MDR1 is responsible for the induction by 1alpha,25-dihydroxyvitamin D(3). Electrophoretic mobility shift assays revealed that several binding sites for the VDR/retinoid X receptor alpha (RXRalpha) heterodimer are located between the -7880 and -7810 bp region, to which the three molecules of VDR/RXRalpha are able to simultaneously bind with different affinities. Luciferase assays using mutated constructs revealed that the VDR-binding sites of DR3, DR4(I), MdC3, and DR4(III) contribute to the induction, indicating that these binding sites act as vitamin D response elements (VDREs). The contribution of each VDRE to the inducibility was different for each response element. An additive effect of the individual VDREs on induced luciferase activity by 1alpha,25-dihydroxyvitamin D(3) was also observed. These results indicate that the induction of MDR1 by 1alpha,25-dihydroxyvitamin D(3) is mediated by VDR/RXRalpha binding to several VDREs located between -7880 and -7810bp, in which every VDRE additively contributes to the 1alpha,25-dihydroxyvitamin D(3) response.
Saeki
Mayumi
M
Division of Medicinal Safety Science, National Institute of Health Sciences, 1-18-1 Kamiyoga, Setagaya-ku, Tokyo 158-8501, Japan.
Kurose
Kouichi
K
Tohkin
Masahiro
M
Hasegawa
Ryuichi
R
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000235:genetics*; D001665:Binding Sites; D005786:Gene Expression Regulation / Q000187:drug effects; D019450:Genes, MDR / Q000235:genetics*; D006801:Humans; D018167:Receptors, Calcitriol / Q000378:metabolism; D047488:Retinoid X Receptors / Q000378:metabolism; D014807:Vitamin D / Q000031:analogs & derivatives / Q000494:pharmacology; D030181:Vitamin D Response Element
D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D018167:Receptors, Calcitriol; D047488:Retinoid X Receptors; C118756:dihydroxy-vitamin D3; D014807:Vitamin D