Genetic Variants of the Human Dipeptide Transporter PEPT1

Abstract

We tested whether genetic polymorphisms affect activity of the dipeptide transporter PEPT1, which mediates bioavailability of peptidomimetic drugs. All 23 exons and adjoining intronic sections of PEPT1 (SLC15A1) were sequenced in 247 individuals of various ethnic origins (Coriell collection). Of 38 single nucleotide polymorphisms (SNPs), 21 occurred in intronic and noncoding regions and 17 in exonic coding region, of which nine were nonsynonymous. Eight nonsynonymous variants were cloned into expression vectors and functionally characterized after transient transfection into Cos7 and Chinese hamster ovary cells. None of the variants had altered transport activity for various ligands, supporting previous results, except for the new, low-frequency PEPT1-F28Y. This variant displayed significantly reduced cephalexin uptake attributable to increased K m . Altered pH dependence of substrate transport suggested a role for F28Y in H ϩ -driven translocation. Haplotype analysis revealed significant differences among ethnic populations. To search for cis-acting polymorphisms affecting transcription and mRNA processing, we measured allelic PEPT1 mRNA expression in human intestinal biopsy samples using a frequentmarker SNP in exon 17. Of 24 heterozygous samples, significant differences in allelic mRNA levels of 20 to 30% were observed in seven tissues. However, the small difference suggests that cis-acting regulatory factors have only limited effects on transporter activity. We also measured the relative formation of a splice variant (PEPT1-RF). PEPT1-RF mRNA levels ranged from 2 to 44% of total PEPT1-related mRNA, with potential consequences for drug absorption. Together with previous results, this study reveals a relatively low level of genetic variability in polymorphisms affecting both protein function and gene regulation.Endogenous peptides with regulatory functions serve as hormones, neuropeptides or neurotransmitters, and cytokines, stimulating interest in their therapeutic use. Moreover, small peptides represent an important nutritional source of amino acids. Membrane transporters such as the proton-coupled oligopeptide transporters PEPT1 and PEPT2 (SLC15A1 and SLC15A2) facilitate absorption and distribution of small peptides (two to three residues) and polar peptoid drugs that would otherwise not cross lipid membranes.The intestinal PEPT1 transporter is involved in carrier-mediated uptake of peptide-like drugs such as cephalexin, angiotensin-converting enzyme inhibitors, and 5Ј-amino acid esters of the antiviral nucleosides, acyclovir, azidothymidine, and ganciclovir (Ganapathy et al., 1995;Han et al., 1998). Bioavailability of the prodrug L-valacyclovir (VAC) is substantially increased by PEPT1 transport activity.Response to drug therapy varies in patients, in part because of genetic differences among individuals. Polymorphisms of drug receptors, metabolizing enzymes, and transporters each can affect therapeutic efficacy (Licinio and Wong, 2002). Whereas the effect of genetic variants has been well document...

Molecular interactions between dipeptides, drugs and the human intestinal H+–oligopeptide cotransporter hPEPT1

“…These findings are supported by more limited studies of the variants expressed in HeLa, Cos7 and CHO cells (Zhang et al 2004;Anderle et al 2006).…”

Xenobiotic, Bile Acid, and Cholesterol Transporters: Function and Regulation

“…Nucleotide position was confirmed by PharmGKB (Hewett et al, 2002). PEPT1 data from Zhang et al (2004b) and Anderle et al (2006). PEPT2 data from Pinsonneault et al (2004) and Terada et al (2004).…”

Human Intestinal PEPT1 Transporter Expression and Localization in Preterm and Term Infants

“…Third, variability might be due to genetic polymorphisms in the SLC15A1 gene, causing a change in PEPT1 expression. However, thus far no polymorphism has been proven to be clinically relevant, and therefore we did not genotype our samples (Anderle et al, 2006).…”