@article {Hayashi143, author = {Hisamitsu Hayashi and Yuichi Sugiyama}, title = {Short-Chain Ubiquitination Is Associated with the Degradation Rate of a Cell-Surface-Resident Bile Salt Export Pump (BSEP/ABCB11)}, volume = {75}, number = {1}, pages = {143--150}, year = {2009}, doi = {10.1124/mol.108.049288}, publisher = {American Society for Pharmacology and Experimental Therapeutics}, 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. The American Society for Pharmacology and Experimental Therapeutics}, issn = {0026-895X}, URL = {https://molpharm.aspetjournals.org/content/75/1/143}, eprint = {https://molpharm.aspetjournals.org/content/75/1/143.full.pdf}, journal = {Molecular Pharmacology} }