title: Short-chain ubiquitination is associated with the degradation rate of a cell-surface-resident bile salt export pump (BSEP/ABCB11).
abstract: The reduced expression of the bile salt export pump (BSEP/ABCB11) at the canalicular membrane is associated with cholestasis-induced hepatotoxicity due to the accumulation of bile acids in hepatocytes. We demonstrated previously that 4-phenylbutyrate (4PBA) treatment, a U.S. Food and Drug Administration-approved drug for the treatment of urea cycle disorders, induces the cell-surface expression of BSEP by prolonging the degradation rate of cell-surface-resident BSEP. On the other hand, BSEP mutations, E297G and D482G, found in progressive familial intrahepatic cholestasis type 2 (PFIC2), reduced it by shortening the degradation rate of cell-surface-resident BSEP. Therefore, to help the development of the medical treatment of cholestasis, we investigated the underlying mechanism by which 4PBA and PFIC2-type mutations affect the BSEP degradation from cell surface, focusing on short-chain ubiquitination. In Madin-Darby canine kidney II (MDCK II) cells expressing BSEP and rat canalicular membrane vesicles, the molecular mass of the mature form of BSEP/Bsep shifted from 170 to 190 kDa after ubiquitin modification (molecular mass, 8 kDa). Ubiquitination susceptibility of BSEP/Bsep was reduced in vitro and in vivo by 4PBA treatment and, conversely, was enhanced by BSEP mutations E297G and D482G. Moreover, biotin-labeling studies using MDCK II cells demonstrated that the degradation of cell-surface-resident chimeric protein fusing ubiquitin to BSEP was faster than that of BSEP itself. In conclusion, BSEP/Bsep is modified with two to three ubiquitins, and its ubiquitination is modulated by 4PBA treatment and PFIC2-type mutations. Modulation of short-chain ubiquitination can regulate the change in the degradation rate of cell-surface-resident BSEP by 4PBA treatment and PFIC2-type mutations.
authors.affiliation: Department of Molecular Pharmacokinetics, Graduate School of Pharmaceutical Sciences, The University of Tokyo, Tokyo, Japan.
authors.forename: Hisamitsu
authors.initials: H
authors.lastname: Hayashi
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Sugiyama
mesh_terms: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism*; D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D001648:Bile Canaliculi / Q000187:drug effects / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002460:Cell Line; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism; D002780:Cholestasis, Intrahepatic / Q000235:genetics* / Q000378:metabolism*; D004285:Dogs; D007668:Kidney / Q000166:cytology; D007700:Kinetics; D008297:Male; D009154:Mutation; D010654:Phenylbutyrates / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: D000074020:ATP Binding Cassette Transporter, Subfamily B, Member 11; D018528:ATP-Binding Cassette Transporters; C490548:Abcb11 protein, rat; D000970:Antineoplastic Agents; D010654:Phenylbutyrates; D025801:Ubiquitin; C075773:4-phenylbutyric acid