The role of bile salt export pump mutations in progressive familial intrahepatic cholestasis type II.
PFIC II is a subtype of progressive familial intrahepatic cholestasis (PFIC) that is associated with mutations in the ABCB11 gene encoding the bile salt export pump (BSEP). However it is not known how these mutations cause this disease. To evaluate these mechanisms, we introduced seven PFIC II-associated missense mutations into rat Bsep and assessed their effects on Bsep membrane localization and transport function in MDCK and Sf9 cells, respectively. Five mutations, G238V, E297G, G982R, R1153C, and R1268Q, prevented the protein from trafficking to the apical membrane, and E297G, G982R, R1153C, and R1268Q also abolished taurocholate transport activity, possibly by causing Bsep to misfold. Mutation C336S affected neither Bsep transport activity nor the apical trafficking of Bsep, suggesting that this mutation alone may not cause this disease. D482G did not affect the apical expression but partially decreased the transport activity of Bsep. Mutant G238V was rapidly degraded in both MDCK and Sf9 cells, and proteasome inhibitor resulted in intracellular accumulation of this and other mutants, suggesting proteasome-mediated degradation plays an important role in expression of these PFIC II mutants. Our studies highlight the heterogeneous nature of PFIC II mutations and illustrate the significance of these mutations in the function and expression of Bsep.
Wang
Lin
L
The Yale Liver Center, Yale University School of Medicine, New Haven, Connecticut 06510, USA. wang1@yale.edu
Soroka
Carol J
CJ
Boyer
James L
JL
D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000737:chemistry / Q000235:genetics* / Q000502:physiology; D000818:Animals; D001692:Biological Transport; D002478:Cells, Cultured; D002780:Cholestasis, Intrahepatic / Q000209:etiology / Q000235:genetics*; D003546:Cysteine Endopeptidases / Q000502:physiology; D004285:Dogs; D006801:Humans; D009097:Multienzyme Complexes / Q000502:physiology; D009154:Mutation; D046988:Proteasome Endopeptidase Complex; D017510:Protein Folding; D018411:Spodoptera; D025801:Ubiquitin / Q000378:metabolism
C093491:ABCB11 protein, human; D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D009097:Multienzyme Complexes; D025801:Ubiquitin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex