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J Gastroenterol. 2009;44(6):592-600. doi: 10.1007/s00535-009-0041-y. Epub 2009 Apr 21.

FIC1-mediated stimulation of FXR activity is decreased with PFIC1 mutations in HepG2 cells.

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  • 1Department of Pharmacy, The University of Tokyo Hospital, Faculty of Medicine, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8655, Japan.

Abstract

PURPOSE:

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.

METHODS AND 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.

PMID:
19381753
[PubMed - indexed for MEDLINE]
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