Phenotypic differences in PFIC2 and BRIC2 correlate with protein stability of mutant Bsep and impaired taurocholate secretion in MDCK II cells.

[benign recurrent intrahepatic cholestasis]

Progressive familial cholestasis (PFIC ) 2 and benign recurrent intrahepatic cholestasis (BRIC ) 2 are caused by mutations in the bile salt export pump (BSEP , ABCB 11 ) gene ; however , their prognosis differs . PFIC 2 progresses to cirrhosis and requires liver transplantation , whereas BRIC 2 is clinically benign . To identify the molecular mechanism (s ) responsible for the phenotypic differences , eight PFIC 2 and two BRIC 2 mutations were introduced in rat Bsep , which was transfected in MDCK II cells . Taurocholate transport activity , protein expression , and subcellular distribution of these mutant proteins were studied in a polarized MDCK II monolayer . The taurocholate transport activity was approximately half of the wild-type (WT ) in BRIC 2 mutants (A 570 T and R 1050 C ), was substantially less in two PFIC 2 mutants (D 482 G and E 297 G ), and was almost abolished in six other PFIC 2 mutants (K 461 E , G 982 R , R 1153 C , R 1268 Q , 3767 -3768 insC , and R 1057 X ). Bsep protein expression levels correlated closely with transport activity , except for R 1057 X . The half -life of the D 482 G mutant was shorter than that of the WT (1 .35 h vs . 3 .49 h in the mature form ). BRIC 2 mutants and three PFIC mutants (D 482 G , E 297 G , and R 1057 X ) were predominantly distributed in the apical membrane . The other PFIC 2 mutants remained intracellular . The R 1057 X mutant protein was stably expressed and trafficked to the apical membrane , suggesting that the COOH-terminal tail is required for transport activity but not for correct targeting . In conclusion , taurocholate transport function was impaired in proportion to rapid degradation of Bsep protein in the mutants , which were aligned in the following order : A 570 T and R 1050 C > D 482 G > E 297 G > K 461 E , G 982 R , R 1153 C , R 1268 Q , 3767 -3768 insC , and R 1057 X . These results may explain the phenotypic difference between BRIC 2 and PFIC 2 .

Diseases
Validation

Diseases presenting "approximately half" symptom

benign recurrent intrahepatic cholestasis

classical phenylketonuria

epidermolysis bullosa simplex

erdheim-chester disease

hirschsprung disease

malignant atrophic papulosis

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