Molecular cloning, chromosomal localization, and functional characterization of a human liver Na+/bile acid cotransporter.
We have used a cDNA probe from a cloned rat liver Na+/taurocholate cotransporting polypeptide (Ntcp) to screen a human liver cDNA library. A 1,599-bp cDNA clone that encodes a human Na+/taurocholate cotransporting polypeptide (NTCP) was isolated. The human NTCP consists of 349 amino acids (calculated molecular mass of 38 kD) and exhibits 77% amino acid homology with the rat Ntcp. In vitro translation experiments indicate that the protein is glycosylated and has a molecular weight similar to the rat Ntcp. Injection of in vitro transcribed cRNA into Xenopus laevis oocytes resulted in the expression of Na(+)-dependent taurocholate uptake. Saturation kinetics indicated that the human NTCP has a higher affinity for taurocholate (apparent Km = 6 microM) than the previously cloned rat protein (apparent Km = 25 microM). NTCP-mediated taurocholate uptake into oocytes was inhibited by all major bile acid derivatives (100 microM), bumetanide (500 microM), and bromosulphophthalein (100 microM). Southern blot analysis of genomic DNA from a panel of human/hamster somatic cell hybrids mapped the human NTCP gene to chromosome 14.
Hagenbuch
B
B
Department of Medicine, University Hospital, Zürich, Switzerland.
Meier
P J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D002874:Chromosome Mapping; D003001:Cloning, Molecular; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; D014982:Xenopus laevis
D002352:Carrier Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter