PT  - JOURNAL ARTICLE
AU  - Nakai, Yasuhiro
AU  - Inoue, Katsuhisa
AU  - Abe, Naoki
AU  - Hatakeyama, Mai
AU  - Ohta, Kin-ya
AU  - Otagiri, Masaki
AU  - Hayashi, Yayoi
AU  - Yuasa, Hiroaki
TI  - Functional Characterization of Human Proton-Coupled Folate Transporter/Heme Carrier Protein 1 Heterologously Expressed in Mammalian Cells as a Folate Transporter
AID  - 10.1124/jpet.107.122606
DP  - 2007 Aug 01
TA  - Journal of Pharmacology and Experimental Therapeutics
PG  - 469--476
VI  - 322
IP  - 2
4099  - http://jpet.aspetjournals.org/content/322/2/469.short
4100  - http://jpet.aspetjournals.org/content/322/2/469.full
SO  - J Pharmacol Exp Ther2007 Aug 01; 322
AB  - 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 Km of 1.67 μM 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. The American Society for Pharmacology and Experimental Therapeutics