Characterization of the human peptide transporter PEPT1 promoter: Sp1 functions as a basal transcriptional regulator of human PEPT1.

H+-coupled peptide transporter 1 (PEPT1, SLC15A1) localized at the brush-border membranes of intestinal epithelial cells plays an important role in the intestinal absorption of small peptides and a variety of peptidemimetic drugs. PEPT1 is regulated by various factors, including hormones, dietary conditions, some pharmaceutics, and diurnal rhythm. But there is little information about the transcriptional regulation of PEPT1. In the present study, therefore, we cloned the human (h)PEPT1 promoter region and examined its promoter activity using a human intestinal cell line, Caco-2. Deletion analysis of the hPEPT1 promoter suggested that the region spanning -172 to -35 bp was essential for basal transcriptional activity. This region lacked a TATA-box but contained some GC-rich sites that supposedly bind with the transcription factor Sp1. Mutational analysis revealed that three of these putative Sp1 sites contributed to the transcriptional activity. EMSA showed that Sp1 bound to two GC-rich sites. Furthermore, inhibition of Sp1 binding by mithramycin A treatment significantly reduced the transcriptional activity. Finally, overexpression of Sp1 increased the transcriptional activity in a dose-dependent manner. This study reports the first characterization of the hPEPT1 promoter and shows the significant role of Sp1 in the basal transcriptional regulation of hPEPT1.