Molecular cloning of the human placental folate transporter.

We have isolated a cDNA clone from a human placental library which codes for a functional folate transporter (hFOLT). An RT-PCR product obtained from mouse intestinal mRNA using primers specific for the mouse folate transporter cDNA was used to screen the cDNA library. The hFOLT cDNA predicts a protein of 590 amino acids with twelve potential transmembrane domains. The amino acid sequence has 65% identity to the mouse and hamster folate transporters. When transfected into COS-1 and HeLa cells, the hFOLT cDNA causes a significant increase in the uptake of 5-methyltetrahydrofolate. The mRNA transcripts hybridizing to the hFOLT cDNA are detectable in the placenta and liver and also in several cell lines of human origin. The size of the principal transcript is 2.7 kb. This constitutes the first report on the cloning of a vitamin transporter from a human tissue.