Functional expression cloning and characterization of the hepatocyte Na+/bile acid cotransport system.
Liver parenchymal cells continuously extract high amounts of bile acids from portal blood plasma. This uptake process is mediated by a Na+/bile acid cotransport system. A cDNA encoding the rat liver bile acid uptake system has been isolated by expression cloning in Xenopus laevis oocytes. The cloned transporter is strictly sodium-dependent and can be inhibited by various non-bile-acid organic compounds. Sequence analysis of the cDNA revealed an open reading frame of 1086 nucleotides coding for a protein of 362 amino acids (calculated molecular mass 39 kDa) with five possible N-linked glycosylation sites and seven putative transmembrane domains. Translation experiments in vitro and in oocytes indicate that the transporter is indeed glycosylated and that its polypeptide backbone has an apparent molecular mass of 33-35 kDa. Northern blot analysis with the cloned probe revealed crossreactivity with mRNA species from rat kidney and intestine as well as from liver tissues of mouse, guinea pig, rabbit, and man.
Hagenbuch
B
B
Department of Medicine, University Hospital, Zürich, Switzerland.
Stieger
B
B
Foguet
M
M
Lübbert
H
H
Meier
P J
PJ
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000235:genetics* / Q000302:isolation & purification / Q000378:metabolism; D003001:Cloning, Molecular; D004247:DNA / Q000235:genetics / Q000302:isolation & purification; D005260:Female; D015723:Gene Library; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D008970:Molecular Weight; D009865:Oocytes / Q000378:metabolism; D029363:Organic Anion Transporters, Sodium-Dependent; D011487:Protein Conformation; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D015183:Restriction Mapping; D012964:Sodium / Q000378:metabolism*; D027981:Symporters; D013656:Taurocholic Acid / Q000378:metabolism*; D014982:Xenopus laevis
D002352:Carrier Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; D027981:Symporters; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid; D004247:DNA; D012964:Sodium