The sister of P-glycoprotein represents the canalicular bile salt export pump of mammalian liver.
Canalicular secretion of bile salts is a vital function of the vertebrate liver, yet the molecular identity of the involved ATP-dependent carrier protein has not been elucidated. We cloned the full-length cDNA of the sister of P-glycoprotein (spgp; Mr approximately 160,000) of rat liver and demonstrated that it functions as an ATP-dependent bile salt transporter in cRNA injected Xenopus laevis oocytes and in vesicles isolated from transfected Sf9 cells. The latter demonstrated a 5-fold stimulation of ATP-dependent taurocholate transport as compared with controls. This spgp-mediated taurocholate transport was stimulated solely by ATP, was inhibited by vanadate, and exhibited saturability with increasing concentrations of taurocholate (Km approximately 5 microM). Furthermore, spgp-mediated transport rates of various bile salts followed the same order of magnitude as ATP-dependent transport in canalicular rat liver plasma membrane vesicles, i.e. taurochenodeoxycholate > tauroursodeoxycholate = taurocholate > glycocholate = cholate. Tissue distribution assessed by Northern blotting revealed predominant, if not exclusive, expression of spgp in the liver, where it was further localized to the canalicular microvilli and to subcanalicular vesicles of the hepatocytes by in situ immunofluorescence and immunogold labeling studies. These results indicate that the sister of P-glycoprotein is the major canalicular bile salt export pump of mammalian liver.
Gerloff
T
T
Division of Clinical Pharmacology and Toxicology, Department of Medicine, University Hospital, CH-8091 Zurich, Switzerland.
Stieger
B
B
Hagenbuch
B
B
Madon
J
J
Landmann
L
L
Roth
J
J
Hofmann
A F
AF
Meier
P J
PJ
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001647:Bile Acids and Salts / Q000378:metabolism*; D001648:Bile Canaliculi / Q000378:metabolism*; D002460:Cell Line; D003001:Cloning, Molecular; D017931:DNA Primers; D005260:Female; D007700:Kinetics; D008099:Liver / Q000378:metabolism*; D008969:Molecular Sequence Data; D009865:Oocytes / Q000502:physiology; D016133:Polymerase Chain Reaction; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D018411:Spodoptera; D013656:Taurocholic Acid / Q000378:metabolism; D014162:Transfection; D014982:Xenopus laevis
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D001647:Bile Acids and Salts; D017931:DNA Primers; D011994:Recombinant Proteins; D013656:Taurocholic Acid; D000255:Adenosine Triphosphate