FIC1-mediated stimulation of FXR activity is decreased with PFIC1 mutations in HepG2 cells.
OBJECTIVE
Progressive familial intrahepatic cholestasis type 1 (PFIC1) is a specific form of genetic cholestasis caused by functional defects in FIC1/ATP8B1. Although the way FIC1 deficiency leads to PFIC1 remains unclear, some reports suggest that the loss of FIC1 function results in decreased activity of the farnesoid X receptor (FXR) in PFIC1 patients. In this study, in order to elucidate the molecular mechanism of the pathogenesis of PFIC1, we constructed an experimental system for the evaluation of FIC1-mediated stimulatory effects on FXR activity.


RESULTS
Luciferase assays revealed that FIC1 expression increased FXR-dependent transcription and that the effects of three PFIC1 mutants (G308V, T456M and D554N) were smaller than that of wild-type FIC1. In addition, the PFIC1 mutants could not locate to the plasma membrane even in the presence of CDC50A, which brings wild-type FIC1 to the plasma membrane. The results of coprecipitation assays suggested a defect in the ability of the PFIC1 mutants to interact with CDC50A. Furthermore, it was revealed that the expression of CDC50A elevated the FIC1-mediated transcriptional stimulation when coexpressed with wild-type FIC1, but not with mutated FIC1.


CONCLUSIONS
These results suggest that the PFIC1 mutants have a lower stimulatory effect on FXR activity and cannot interact with CDC50A, which may lead to the development of the features of PFIC1.
Koh
Saori
S
Department of Pharmacy, The University of Tokyo Hospital, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.
Takada
Tappei
T
Kukuu
Ikuya
I
Suzuki
Hiroshi
H
D000251:Adenosine Triphosphatases / Q000235:genetics*; D015153:Blotting, Western; D002478:Cells, Cultured; D004721:Endoplasmic Reticulum / Q000502:physiology; D005822:Genetic Vectors; D051272:Glucose Transporter Type 1 / Q000235:genetics*; D006801:Humans; D007150:Immunohistochemistry; D008565:Membrane Proteins / Q000235:genetics; D009154:Mutation; D021381:Protein Transport / Q000502:physiology; D018160:Receptors, Cytoplasmic and Nuclear / Q000502:physiology*; D014162:Transfection; D000099150:Receptor, Farnesoid X-Activated
D000251:Adenosine Triphosphatases; D051272:Glucose Transporter Type 1; D008565:Membrane Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D000099150:Receptor, Farnesoid X-Activated; C495677:SLC2A1 protein, human; C526978:TMEM30a protein, human; C111067:ATP8B1 protein, human