In vitro and in vivo characterization of the minimal promoter region of the human thiamin transporter SLC19A2

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Abstract
The molecular mechanisms involved in the regulation of thiamin transport in mammalian cells are poorly understood. Previous studies established that a human thiamin transporter, SLC19A2, plays a role in thiamin uptake in human tissues. We cloned the 5′ regulatory region of the SLC19A2 gene, identified the minimal promoter required for basal activity, and located multiple putative cis elements. To further characterize the SLC19A2 promoter, we investigated, in the present study, the role of the putative cis elements in regulating the activity of the SLC19A2 promoter in vitro and confirmed the activity of the SLC19A2 promoter in vivo. In vitro studies demonstrated that mutation of specific cis elements in the SLC19A2 minimal promoter [Gut-enriched Krupple-like factor (GKLF), nuclear factor-1 (NF-1), and stimulating protein-1 (SP-1)] led to a decrease in activity. Using electrophoretic mobility shift assays, four specific DNA/protein complexes were identified. The interacting factors were determined by oligonucleotide competition and antibody supershift analysis and shown to be GKLF, NF-1, and SP-1. Cotransfection studies of the SLC19A2 promoter with an SP-1 containing vector in Drosophila SL2 cells further confirmed a role for SP-1 in regulating SLC19A2 promoter activity. In vivo studies using transgenic mice established the functionality of the full-length and minimal SLC19A2 promoters. Furthermore, our studies revealed that the pattern of expression of the SLC19A2 promoter-Luciferase constructs in transgenic mice was similar to the reported SLC19A2 RNA expression pattern in native human tissues. The results demonstrate the importance of GKLF, NF-1, and SP-1 in regulating the activity of the SLC19A2 promoter and provide direct in vivo confirmation of promoter activity.