Abstract:
BACKGROUND & AIMS:Despite intensive investigations, very little is known about the molecular identity(ies) of the intestinal folate transport system(s), especially in humans. The aim of this study was to isolate a functional human intestinal folate carrier complementary DNA (cDNA) clone and determine the distribution of complementary RNA at the tissue and cellular levels. METHODS:Hybridization screening, modified Marathon cDNA amplification, expression in Xenopus oocytes, Northern analysis, and in situ hybridization were used. RESULTS:The hIFC-1 cDNA contains an open reading frame for 591 amino acids (relative molecular mass = 64,826, pI = 9.4, 12 transmembrane domains, three protein kinase C phosphorylation sites, and one N-glycosylation site) with 74% DNA and 66% amino acid sequence homologies with the mouse cDNA counterpart. Xenopus oocytes injected with hIFC-1 cRNA show induced folate uptake that was (1) saturable with substrate concentration (apparent Michaelis constant = 0.71 +/- 0.06 micromol/L; maximum velocity = 128 +/- 3 fmol x h(-1) x oocyte(-1)), (2) inhibited by methotrexate, folinic acid, and folic acid (Ki = 0.84 micromol/L, 0.71 micromol/L, and 10 micromol/L, respectively), and (3) sensitive to 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (Ki = 0.29 mmol/L). Northern analysis showed wide distribution of hIFC1-complementary messenger RNA species in various human tissues. In situ hybridization on sections of human jejunum showed preferential hIFC-1 expression in epithelial cells, especially in the upper half of the villi. CONCLUSIONS:These results represent the first molecular characterization of a human small intestinal folate carrier.
journal_name
Gastroenterologyjournal_title
Gastroenterologyauthors
Nguyen TT,Dyer DL,Dunning DD,Rubin SA,Grant KE,Said HMdoi
10.1053/gast.1997.v112.pm9041240subject
Has Abstractpub_date
1997-03-01 00:00:00pages
783-91issue
3eissn
0016-5085issn
1528-0012pii
S0016508597001170journal_volume
112pub_type
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