The phospholipid flippase ATP8B1 mediates apical localization of the cystic fibrosis transmembrane regulator.
Progressive familial intrahepatic cholestasis type 1 (PFIC1) is caused by mutations in the gene encoding the phospholipid flippase ATP8B1. Apart from severe cholestatic liver disease, many PFIC1 patients develop extrahepatic symptoms characteristic of cystic fibrosis (CF), such as pulmonary infection, sweat gland dysfunction and failure to thrive. CF is caused by mutations in the cystic fibrosis transmembrane conductance regulator (CFTR), a chloride channel essential for epithelial fluid transport. Previously it was shown that CFTR transcript levels were strongly reduced in livers of PFIC1 patients. Here we have investigated the hypothesis that ATP8B1 is important for proper CFTR expression and function. We analyzed CFTR expression in ATP8B1-depleted intestinal and pulmonary epithelial cell lines and assessed CFTR function by measuring short-circuit currents across transwell-grown ATP8B1-depleted intestinal T84 cells and by a genetically-encoded fluorescent chloride sensor. In addition, we studied CFTR surface expression upon induction of CFTR transcription. We show that CFTR protein levels are strongly reduced in the apical membrane of human ATP8B1-depleted intestinal and pulmonary epithelial cell lines, a phenotype that coincided with reduced CFTR activity. Apical membrane insertion upon induction of ectopically-expressed CFTR was strongly impaired in ATP8B1-depleted cells. We conclude that ATP8B1 is essential for correct apical localization of CFTR in human intestinal and pulmonary epithelial cells, and that impaired CFTR localization underlies some of the extrahepatic phenotypes observed in ATP8B1 deficiency.
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
Vincent A
VA
van der Mark
Department of Gastroenterology & Hepatology, Erasmus University Medical Centre, Rotterdam, The Netherlands.
Hugo R
HR
de Jonge
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
Jung-Chin
JC
Chang
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
Kam S
KS
Ho-Mok
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
Suzanne
S
Duijst
Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium.
Dragana
D
Vidović
Laboratory for Molecular Virology and Gene Therapy, Department of Pharmaceutical and Pharmacological Sciences, KU Leuven, Belgium.
Marianne S
MS
Carlon
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands.
Ronald P J
RP
Oude Elferink
Tytgat Institute for Liver and Intestinal Research, Academic Medical Center, Amsterdam, The Netherlands. Electronic address: c.c.paulusma@amc.uva.nl.
Coen C
CC
Paulusma
D000251:Adenosine Triphosphatases / Q000378:metabolism*; D000818:Animals; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D002712:Chlorides / Q000378:metabolism; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000235:genetics / Q000378:metabolism*; D004847:Epithelial Cells / Q000378:metabolism; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism; D015640:Ion Channel Gating; D008168:Lung / Q000166:cytology; D008297:Male; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D049294:Phospholipid Transfer Proteins / Q000378:metabolism*; D010743:Phospholipids / Q000378:metabolism*; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism
D002712:Chlorides; D049294:Phospholipid Transfer Proteins; D010743:Phospholipids; D012333:RNA, Messenger; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000251:Adenosine Triphosphatases; C111067:ATP8B1 protein, human; C491742:Atp8b1 protein, mouse
ATP8B1; CFTR; Chloride transport; Cystic fibrosis; PFIC1; Trafficking