title: The lipid flippase heterodimer ATP8B1-CDC50A is essential for surface expression of the apical sodium-dependent bile acid transporter (SLC10A2/ASBT) in intestinal Caco-2 cells.
abstract: Deficiency of the phospholipid flippase ATPase, aminophospholipid transporter, class I, type 8B, member 1 (ATP8B1) causes progressive familial intrahepatic cholestasis type 1 (PFIC1) and benign recurrent intrahepatic cholestasis type 1 (BRIC1). Apart from cholestasis, many patients also suffer from diarrhea of yet unknown etiology. Here we have studied the hypothesis that intestinal ATP8B1 deficiency results in bile salt malabsorption as a possible cause of PFIC1/BRIC1 diarrhea. Bile salt transport was studied in ATP8B1-depleted intestinal Caco-2 cells. Apical membrane localization was studied by a biotinylation approach. Fecal bile salt and electrolyte contents were analyzed in stool samples of PFIC1 patients, of whom some had undergone biliary diversion or liver transplantation. Bile salt uptake by the apical sodium-dependent bile salt transporter solute carrier family 10 (sodium/bile acid cotransporter), member 2 (SLC10A2) was strongly impaired in ATP8B1-depleted Caco-2 cells. The reduced SLC10A2 activity coincided with strongly reduced apical membrane localization, which was caused by impaired apical membrane insertion of SLC10A2. Moreover, we show that endogenous ATP8B1 exists in a functional heterodimer with transmembrane protein 30A (CDC50A) in Caco-2 cells. Analyses of stool samples of post-transplant PFIC1 patients demonstrated that bile salt content was not changed, whereas sodium and chloride concentrations were elevated and potassium levels were decreased. The ATP8B1-CDC50A heterodimer is essential for the apical localization of SLC10A2 in Caco-2 cells. Diarrhea in PFIC1/BRIC1 patients has a secretory origin to which SLC10A2 deficiency may contribute. This results in elevated luminal bile salt concentrations and consequent enhanced electrolyte secretion and/or reduced electrolyte resorption.
authors.affiliation: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands. Electronic address: v.a.vandermark@amc.nl.
authors.forename: Vincent A
authors.initials: VA
authors.lastname: van der Mark
authors.affiliation: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: D Rudi
authors.initials: DR
authors.lastname: de Waart
authors.affiliation: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Kam S
authors.initials: KS
authors.lastname: Ho-Mok
authors.affiliation: Department of Paediatric Gastroenterology and Nutrition, Emma Children's Hospital, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Merit M
authors.initials: MM
authors.lastname: Tabbers
authors.affiliation: Department of Paediatric Gastroenterology and Nutrition, Emma Children's Hospital, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Heleen W
authors.initials: HW
authors.lastname: Voogt
authors.affiliation: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Ronald P J
authors.initials: RP
authors.lastname: Oude Elferink
authors.affiliation: Institute of Liver Studies, King's College Hospital, London, UK.
authors.forename: A S
authors.initials: AS
authors.lastname: Knisely
authors.affiliation: Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
authors.forename: Coen C
authors.initials: CC
authors.lastname: Paulusma
mesh_terms: D000251:Adenosine Triphosphatases / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D001647:Bile Acids and Salts / Q000378:metabolism; D001692:Biological Transport / Q000235:genetics; D015153:Blotting, Western; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism; D002780:Cholestasis, Intrahepatic / Q000235:genetics / Q000378:metabolism; D005243:Feces / Q000737:chemistry; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D008565:Membrane Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D009154:Mutation; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D055503:Protein Multimerization; D034622:RNA Interference; D020133:Reverse Transcriptase Polymerase Chain Reaction; D027981:Symporters / Q000378:metabolism*; D013656:Taurocholic Acid / Q000378:metabolism / Q000493:pharmacokinetics
chemical_list: D001647:Bile Acids and Salts; D008565:Membrane Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D027981:Symporters; C526978:TMEM30a protein, human; C071908:sodium-bile acid cotransporter; D013656:Taurocholic Acid; D000251:Adenosine Triphosphatases; C111067:ATP8B1 protein, human
keywords: ATP8B1; Diarrhea; Enterohepatic circulation; PFIC1; SLC10A2