title: A novel mutation within a transmembrane helix of the bile salt export pump (BSEP, ABCB11) with delayed development of cirrhosis.
abstract: OBJECTIVE
  The bile salt export pump (BSEP, ABCB11) is essential for bile salt secretion at the canalicular membrane of liver cells. Clinical phenotypes associated with BSEP mutations are commonly categorized as benign recurrent intrahepatic cholestasis (BRIC-2) or progressive familial intrahepatic cholestasis (PFIC-2).
  
  
  METHODS
  The molecular basis of BSEP-associated liver disease in a sibling pair was characterized by immunostaining, gene sequencing, bile salt analysis and recombinant expression in mammalian cells and yeast for localization and in vitro activity studies respectively.
  
  
  RESULTS
  Benign recurrent intrahepatic cholestasis was considered in a brother and sister who both suffered from intermittent cholestasis since childhood. Gene sequencing of ABCB11 identified the novel missense mutation p.G374S, which is localized in the putative sixth transmembrane helix of BSEP. Liver fibrosis was present in the brother at the age of 18 with progression to cirrhosis within 3 years. Immunofluorescence of liver tissue showed clear canalicular BSEP expression; however, biliary concentration of bile salts was drastically reduced. In line with these in vivo findings, HEK293 cells showed regular membrane targeting of human BSEP(G374S), whereas in vitro transport measurements revealed a strongly reduced transport activity.
  
  
  CONCLUSIONS
  The novel mutation p.G374S impairs transport function without disabling membrane localization of BSEP. While all other known BSEP mutations within transmembrane helices are associated with PFIC-2, the new p.G374S mutation causes a transitional phenotype between BRIC-2 and PFIC-2.
authors.affiliation: Department of Gastroenterology, Hepatology and Infectiology, University Hospital, Düsseldorf, Germany; Institute of Biochemistry, Heinrich-Heine-University Düsseldorf, Düsseldorf, Germany.
authors.forename: Jan
authors.initials: J
authors.lastname: Stindt
authors.forename: Philipp
authors.initials: P
authors.lastname: Ellinger
authors.forename: Katrin
authors.initials: K
authors.lastname: Weissenberger
authors.forename: Carola
authors.initials: C
authors.lastname: Dröge
authors.forename: Diran
authors.initials: D
authors.lastname: Herebian
authors.forename: Ertan
authors.initials: E
authors.lastname: Mayatepek
authors.forename: Bernhard
authors.initials: B
authors.lastname: Homey
authors.forename: Stephan
authors.initials: S
authors.lastname: Braun
authors.forename: Jan
authors.initials: J
authors.lastname: Schulte am Esch
authors.forename: Michael
authors.initials: M
authors.lastname: Horacek
authors.forename: Ali
authors.initials: A
authors.lastname: Canbay
authors.forename: Lutz
authors.initials: L
authors.lastname: Schmitt
authors.forename: Dieter
authors.initials: D
authors.lastname: Häussinger
authors.forename: Ralf
authors.initials: R
authors.lastname: Kubitz
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D001483:Base Sequence; D001647:Bile Acids and Salts / Q000032:analysis; D015153:Blotting, Western; D002851:Chromatography, High Pressure Liquid; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D005260:Female; D005455:Fluorescent Antibody Technique; D057809:HEK293 Cells; D006801:Humans; D008105:Liver Cirrhosis, Biliary / Q000235:genetics* / Q000473:pathology; D008297:Male; D008958:Models, Molecular; D008969:Molecular Sequence Data; D016296:Mutagenesis; D020125:Mutation, Missense / Q000235:genetics; D011487:Protein Conformation; D017422:Sequence Analysis, DNA; D035781:Siblings; D053719:Tandem Mass Spectrometry; D015003:Yeasts; D055815:Young Adult
chemical_list: 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
keywords: ABC transporter; ABCB11; BRIC; BSEP; PFIC; benign recurrent intrahepatic cholestasis; bile salt export pump; progressive familial intrahepatic cholestasis