The functional evaluation of human peptide/histidine transporter 1 (hPHT1) in transiently transfected COS-7 cells

Eur J Pharm Sci. 2006 Apr;27(5):533-42. doi: 10.1016/j.ejps.2005.09.014. Epub 2005 Nov 10.


Recently, the expression of the human peptide/histidine transporter (hPHT1, SLC15A4) mRNA was observed in the GI tract and in Caco-2 cells, suggesting that it may participate in the intestinal absorption of peptide-based agents. This study aims to elucidate the: (i) protein expression pattern of hPHT1 (SLC15A4) in human small intestine; (ii) cloning of the hPHT1 full-length sequence; (iii) functional characterization of hPHT1 in transiently transfected COS-7 cells. The expression of hPHT1 was measured using Western blot and immunohistochemical analysis. The hPHT1 full-sequence was amplified from BeWo cells, inserted into the pcDNA3.1-V5/His TOPO plasmid and transiently transfected into COS-7 cells to investigate the uptake kinetics of [3H]histidine and [3H]carnosine. Time, pH and sodium-dependent uptake studies were performed in mock (empty vector) and hPHT1-COS-7 cells. Results demonstrated hPHT1 protein expression in different intestinal regions. Histidine and carnosine uptake was linear in hPHT1-COS-7 cells over 15 min and was found to be pH-dependent. These substrates and valacyclovir showed significantly higher uptake at pH 5.0 in the hPHT1 transients when contrasted to the mock COS-7 cells, whereas glycylsarcosine uptake was significantly lower and unaffected by pH. Other di- and tripeptides also showed affinity for hPHT1. This study presents the initial functional characterization, the protein expression of the hPHT1 transporter and provides insight into a potentially different route for increasing peptide and peptide-based drug transport.

Publication types

  • Comparative Study

MeSH terms

  • Acyclovir / analogs & derivatives
  • Acyclovir / metabolism
  • Animals
  • Base Sequence
  • COS Cells
  • Carnosine / metabolism
  • Carrier Proteins / biosynthesis
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism
  • Chlorocebus aethiops
  • Cloning, Molecular
  • Histidine / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Immunohistochemistry
  • Intestine, Small / chemistry
  • Intestine, Small / metabolism*
  • Male
  • Membrane Transport Proteins
  • Molecular Sequence Data
  • Nerve Tissue Proteins / biosynthesis
  • Nerve Tissue Proteins / genetics*
  • Nerve Tissue Proteins / metabolism
  • Sequence Analysis, DNA
  • Transfection
  • Valacyclovir
  • Valine / analogs & derivatives
  • Valine / metabolism


  • Carrier Proteins
  • Membrane Transport Proteins
  • Nerve Tissue Proteins
  • SLC15A4 protein, human
  • Histidine
  • Carnosine
  • Valine
  • Valacyclovir
  • Acyclovir