Polymorphic variants in the human bile salt export pump (BSEP; ABCB11): functional characterization and interindividual variability.
OBJECTIVE
Our aims were to identify and functionally characterize coding region nonsynonymous single nucleotide polymorphisms in the hepatic efflux transporter, bile salt export pump (BSEP; ABCB11), and to assess interindividual variability in BSEP expression.


METHODS
We identified 24 single nucleotide polymorphisms, including nine nonsynonymous variants, in ABCB11 from genomic DNA of approximately 250 ethnically diverse healthy individuals using denaturing high-performance liquid chromatography analysis and DNA sequencing. Wild type and variant BSEP were generated and functionally characterized for taurocholate transport activity in vitro in HeLa cells using a recombinant vaccinia-based method. BSEP expression was assessed by real-time mRNA analysis, western blot analysis, and immunofluorescence confocal microscopy.


RESULTS
For the most part, polymorphisms were rare and ethnic-dependent. In vitro functional studies revealed several rare variants, including 616A>G, 1674G>C, 1772A>G, and 3556G>A, to be associated with significantly impaired taurocholate transport activity while the 890A>G variant trended towards impaired function but was not statistically significant. The 3556G>A variant was associated with reduced cell surface to total protein expression compared with wild-type BSEP. Expression of BSEP by mRNA and protein analysis was determined from a bank of human liver samples. Wide interindividual variability was noted in both mRNA (19-fold) and protein (31-fold) expression levels. The common variant 1331T>C was associated with significantly reduced hepatic BSEP mRNA levels.


CONCLUSIONS
Accordingly, our study indicates there are functionally relevant polymorphisms in ABCB11 which may be of potential relevance in the predisposition to acquired liver disorders such as drug-induced cholestasis.
Ho
Richard H
RH
Department of Pediatrics and Pharmacology, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Leake
Brenda F
BF
Kilkenny
Dawn M
DM
Meyer Zu Schwabedissen
Henriette E
HE
Glaeser
Hartmut
H
Kroetz
Deanna L
DL
Kim
Richard B
RB
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D001647:Bile Acids and Salts / Q000378:metabolism; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D015870:Gene Expression / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D008099:Liver / Q000378:metabolism; D018613:Microscopy, Confocal; D016297:Mutagenesis, Site-Directed; D016133:Polymerase Chain Reaction; D020641:Polymorphism, Single Nucleotide / Q000235:genetics*; D012333:RNA, Messenger / Q000032:analysis; D011993:Recombinant Fusion Proteins / Q000235:genetics; D014616:Vaccinia virus / Q000235:genetics
C093491:ABCB11 protein, human; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D012333:RNA, Messenger; D011993:Recombinant Fusion Proteins