Identification and Characterization of a Novel Nontranslated Sequence Variant of the Human Intestinal Di-/Tripeptide Transporter, hPEPT1.

The human H(+)-coupled di-/tripeptide transporter (hPEPT1) mediates intestinal absorption of dietary di- and tripeptides, as well as several peptidomimetic drug compounds. The aim of the present study was to investigate the possible role of the hPEPT1 variant hPEPT1-RF in hPEPT1 regulation. However, the proposed hPEPT1-RF mRNA sequence could not be detected in Caco-2 cells or in human intestinal samples. Instead, a new sequence variant, hPEPT1-RFI, was found, which is almost identical to the proposed hPEPT1-RF, except for two nucleotide insertions and one deletion that resulted in a changed open reading frame as compared to hPEPT1-RF. In vitro translation analysis showed that hPEPT1-RFI was not translated. In conclusion, the existence of hPEPT1-RF could not be confirmed; furthermore, the identified sequence variant, hPEPT1-RFI, does not appear to be translated and is therefore unlikely to have a regulatory effect on hPEPT1 transport activity.