title: Taurocholate transport by hepatic and intestinal bile acid transporters is independent of FIC1 overexpression in Madin-Darby canine kidney cells.
abstract: BACKGROUND
  Mutations in the human familial intrahepatic cholestasis gene, FIC1, result in progressive familial intrahepatic cholestasis type 1 in children and benign recurrent intrahepatic cholestasis. The present study was performed to determine whether FIC1 transports bile acids and/or influences the activity of apical bile acid transporters.
  
  
  METHODS
  The apical secretion assay utilized transfected Madin-Darby canine kidney (MDCK) cells, which stably express the bile acid uptake protein, Na+/taurocholate co-transporting polypeptide (NTCP). These cells were then transiently transfected with FIC1 and/or the bile salt export pump (BSEP) and were grown on Transwell filters to form a polarized monolayer. [(3)H]Taurocholate was added to the basal medium and the taurocholate secretion was measured in the apical medium. A second assay, apical uptake assays, utilized polarized MDCK-II cells, which were transiently transfected with FIC1, FIC1 mutants and/or the apical sodium-dependent bile acid transporter (ASBT). [(3)H]Taurocholate was added to the apical media and intracellular uptake of taurocholate was measured.
  
  
  RESULTS
  Apical secretion assays: FIC1 expression in MDCK/NTCP cells had no effect on taurocholate secretion compared to controls. In contrast, apical secretion of taurocholate in BSEP-transfected cells was approximately twofold higher than in non-transfected MDCK/NTCP cells (P < 0.01). The BSEP-mediated secretion was unaffected by co-transfection with FIC1. Apical uptake assays: taurocholate uptake in ASBT expressing cells was 6.5-fold higher than in controls and was unaffected by co-transfection of cells with FIC1 or FIC1 mutants.
  
  
  CONCLUSIONS
  These results indicate that FIC1 does not transport taurocholate and, when overexpressed in MDCK cells, had no effect on the function of BSEP or ABST.
authors.affiliation: Tufts University School of Medicine, Department of Physiology, Boston, Massachusetts, USA.
authors.forename: Matthew J
authors.initials: MJ
authors.lastname: Harris
authors.forename: Tatehiro
authors.initials: T
authors.lastname: Kagawa
authors.forename: Paul A
authors.initials: PA
authors.lastname: Dawson
authors.forename: Irwin M
authors.initials: IM
authors.lastname: Arias
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000378:metabolism*; D000818:Animals; D001693:Biological Transport, Active; D015153:Blotting, Western; D018929:Cell Culture Techniques; D002780:Cholestasis, Intrahepatic / Q000235:genetics* / Q000378:metabolism; D004285:Dogs; D005786:Gene Expression Regulation; D007668:Kidney / Q000166:cytology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D027981:Symporters / Q000378:metabolism*; D013656:Taurocholic Acid / Q000378:metabolism*
chemical_list: C093491:ABCB11 protein, human; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid