title: Haem and folate transport by proton-coupled folate transporter/haem carrier protein 1 (SLC46A1).
abstract: Haem carrier protein 1 (HCP1) was originally identified and characterised as a mammalian haem transporter. However, recent evidence has shown that it is also a proton-coupled folate transporter (PCFT) and mutations in the gene cause hereditary folate deficiency in humans. We therefore investigated haem and folate transport characteristics of PCFT/HCP1 both in vivo and in vitro in CD-1 mice and in the presence or absence of a blocking antibody for PCFT/HCP1, and also in cultured cells (which express PCFT/HCP1 endogenously) to elucidate the specificity and selectivity of PCFT/HCP1. The in vivo study showed that the addition of folic acid inhibited 59Fe-labelled haem transport in hypoxic mice but had no effect in normal mice. Using in vitro methods, the results showed increased [3H]folate uptake into everted duodenum from hypoxic mice but uptake was reduced by the addition of haem or PCFT/HCP1 antibodies to the medium. Caco-2 cells transiently transfected with small interfering RNA (siRNA) PCFT/HCP1 duplex oligos resulted in a 69 % reduction in PCFT/HCP1 mRNA when compared with the control siRNA. Both haem and folate uptake were significantly (P < 0.05) reduced in cells transfected with PCFT/HCP1 siRNA; however, the magnitude of reduction with folic acid uptake was greater (48 %) than that of haem (22.5 %). Overall the data support PCFT/HCP1 as a primary folate transporter with a lower affinity for haem. PCFT/HCP1 could therefore play a physiological role in Fe nutrition and the data highlight the potential for the interaction of folate and haem at the level of intestinal absorption.
authors.affiliation: Division of Nutritional Sciences, School of Biomedical and Health Sciences, King's College London, Franklin Wilkins Building, London SE1 9NH, UK. abas.h.laftah@kcl.ac.uk
authors.forename: Abas H
authors.initials: AH
authors.lastname: Laftah
authors.forename: Gladys O
authors.initials: GO
authors.lastname: Latunde-Dada
authors.forename: Sarah
authors.initials: S
authors.lastname: Fakih
authors.forename: Robert C
authors.initials: RC
authors.lastname: Hider
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Simpson
authors.forename: Andrew T
authors.initials: AT
authors.lastname: McKie
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D018938:Caco-2 Cells; D002478:Cells, Cultured; D005492:Folic Acid / Q000378:metabolism*; D006418:Heme / Q000378:metabolism*; D006801:Humans; D007408:Intestinal Absorption / Q000502:physiology*; D007413:Intestinal Mucosa / Q000378:metabolism; D007583:Jejunum / Q000378:metabolism; D008297:Male; D026901:Membrane Transport Proteins / Q000235:genetics / Q000502:physiology*; D051379:Mice; D008815:Mice, Inbred Strains; D058979:Proton-Coupled Folate Transporter; D034741:RNA, Small Interfering / Q000235:genetics; D013379:Substrate Specificity
chemical_list: D026901:Membrane Transport Proteins; D058979:Proton-Coupled Folate Transporter; D034741:RNA, Small Interfering; C516877:Slc46a1 protein, mouse; D006418:Heme; D005492:Folic Acid