Impaired expression and function of the bile salt export pump due to three novel ABCB11 mutations in intrahepatic cholestasis.
OBJECTIVE
Inherited dysfunction of the bile salt export pump BSEP (ABCB11) causes a progressive and a benign form of familial intrahepatic cholestasis, denominated as PFIC2 and BRIC2, respectively. We functionally characterized novel ABCB11 mutations encountered in two patients with a PFIC2 and a BRIC2 phenotype, respectively.


METHODS
BSEP expression was determined in liver biopsies by immunohistochemistry. ABCB11 mutations were functionally characterized by taurocholate transport in SF9 cells transfected with human ABCB11.


RESULTS
The PFIC2 patient was compound heterozygous for a splicing mutation in intron 4 ((+3)A > C) combined with an early stop codon at position 930 (R930X), while the BRIC2 patient was compound heterozygous for two nonsynonymous mutations in exon 9 (E297G) and exon 12 (R432T), respectively. Hepatic BSEP expression was absent in PFIC2 and preserved in BRIC2. In BRIC2, taurocholate transport was decreased to 13% and 20% of reference levels for R432T and E297G, respectively.


CONCLUSIONS
The intron 4 (+3)A > C, R930X and R432T represent previously undescribed mutations of the ABCB11 gene that confer a PFIC2 and a BRIC2 phenotype, respectively. By combining functional in-vitro characterization with immunohistochemical detection of variant BSEP we provide direct evidence for the role of ABCB11 mutations in the pathogenesis of different forms of intrahepatic cholestasis.
Noe
Johannes
J
Division of Clinical Pharmacology and Toxicology, Department of Internal Medicine, University Hospital Zurich, Rämistrasse 100, E RAE 09, 8091 Zürich, Switzerland.
Kullak-Ublick
Gerd A
GA
Jochum
Wolfram
W
Stieger
Bruno
B
Kerb
Reinhold
R
Haberl
Michael
M
Müllhaupt
Beat
B
Meier
Peter J
PJ
Pauli-Magnus
Christiane
C
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D000595:Amino Acid Sequence; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism; D001692:Biological Transport; D002780:Cholestasis, Intrahepatic / Q000235:genetics*; D017931:DNA Primers; D005260:Female; D005786:Gene Expression Regulation; D006801:Humans; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009154:Mutation; D010375:Pedigree; D011487:Protein Conformation; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism
C093491:ABCB11 protein, human; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D001647:Bile Acids and Salts; D017931:DNA Primers; D011994:Recombinant Proteins