Functional characterization of human proton-coupled folate transporter/heme carrier protein 1 heterologously expressed in mammalian cells as a folate transporter.

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Nakai Y, Inoue K, Abe N, Hatakeyama M, Ohta KY, Otagiri M, Hayashi Y, Yuasa H

Functional characterization of human proton-coupled folate transporter/heme carrier protein 1 heterologously expressed in mammalian cells as a folate transporter.

J Pharmacol Exp Ther. 2007 Aug;322(2):469-76. Epub 2007 May 2.

PubMed ID

17475902 [ View in PubMed

]

Abstract

The functional characteristics of human proton coupled folate transporter (hPCFT)/heme carrier protein (HCP) 1 were investigated. hPCFT/HCP1 expressed transiently in human embryonic kidney 293 cells mediated the transport of folate at an acidic extracellular pH of 5.5 in a manner independent of Na(+) and insensitive to membrane potential, but its transport activity was absent at near-neutral pH. Folate transport mediated by hPCFT/hHCP1 at pH 5.5 was saturable with a K(m) of 1.67 microM and extensively inhibited by reduced folates, such as folinate, 5-methyltetrahydrofolate, and methotrexate (MTX). Sulfobro-mophthalein and 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid were also found to be potent inhibitors of hPCFT/hHCP1, but hemin was found to exhibit only minimal inhibitory effect. When expressed stably as a protein fused with green fluorescent protein (GFP-hPCFT/HCP1) in MDCKII cells, GFP-hPCFT/HCP1 was mainly localized at the apical membrane, and the cellular accumulation of MTX was higher from the apical side than from the basal side. These functional features of hPCFT/HCP1 are consistent with those of the well characterized carrier-mediated folate transport system in the small intestine, suggesting that hPCFT/HCP1 is responsible for the intestinal absorption of folate and also MTX. We also found that sulfasalazine is a potent inhibitor of hPCFT/HCP1, which would interfere with the intestinal absorption of MTX when coadministered in therapy for rheumatoid arthritis as well as folate.

DrugBank Data that Cites this Article

Drug Transporters

Drug	Transporter	Kind	Organism	Pharmacological Action	Actions
Folic acid	Proton-coupled folate transporter	Protein	Humans	Unknown	Substrate	Details
Methotrexate	Proton-coupled folate transporter	Protein	Humans	Unknown	Substrate Inhibitor	Details
Sulfasalazine	Proton-coupled folate transporter	Protein	Humans	No	Inhibitor	Details

Polypeptides

Name	UniProt ID
Proton-coupled folate transporter	Q96NT5	Details