Expression and promoter analysis of SLC19A2 in the human intestine

The molecular mechanism and regulation of the intestinal uptake process of dietary thiamine is not well understood. Previous studies have established the involvement of a carrier-mediated system for thiamine uptake in the human intestine. Recently a human thiamine transporter, SLC19A2, was cloned from a number of human tissues. Little, however, is known about expression of the SLC19A2 message along the native human gastrointestinal tract, and no analysis of its promoter in intestinal tissue is available. Therefore, the current studies were aimed at investigating the expression of SLC19A2 in the human gastrointestinal tract and at analyzing the promoter of this potential intestinal thiamine transporter. First we cloned SLC19A2 cDNA from a human intestinal cell line (Caco-2) by reverse transcriptase-polymerase chain reaction, then used this cDNA as a probe in Northern blot analysis. SLC19A2 message was found to be expressed in all gastrointestinal tissues in the following order: liver>stomach>duodenum>jejunum>colon>cecum>rectum>ileum. SLC19A2 was also expressed at the protein level in Caco-2 cells and in native human small intestine by Western blot analysis. We also cloned the 5'-regulatory region of the SLC19A2 gene and confirmed activity of its promoter following transfection into intestinal epithelial Caco-2 cells. Furthermore, we identified the minimal promoter region required for basal activity of SLC19A2 in these cells which was found to be mainly encoded in a sequence between -356 and -36, and included multiple cis-regulatory elements. Transcription initiation sites of the SLC19A2 gene in intestinal epithelial Caco-2 cells were also identified by 5'-rapid amplification of cDNA ends. These results demonstrate that SLC19A2 is expressed in various regions of the human gastrointestinal tract. In addition, the results provide the first characterization of the SLC19A2 promoter. These findings raise the possibility that SLC19A2 may play a role in the normal intestinal thiamine absorption process.