Sustained intrahepatic glutathione depletion causes proteasomal degradation of multidrug resistance-associated protein 2 in rat liver

Multidrug resistance-associated protein 2 (MRP2) is a member of a family of efflux transporters that are involved in biliary excretion of organic anions from hepatocytes. Disrupted canalicular localization and decreased protein expression of MRP2 have been observed in patients with chronic cholestatic disorder and hepatic failure without a change in its mRNA expression. We have previously demonstrated that post-transcriptional regulation of the rapid retrieval of rat MRP2 from the canalicular membrane to the intracelluar compartment occurs under conditions of acute (~ 30 min) oxidative stress. However, it is unclear whether MRP2 expression is decreased during its sustained internalization during chronic oxidative stress. The present study employed buthionine sulfoximine (BSO) to induce chronic oxidative stress in the livers of Sprague–Dawley rats and then examined the protein expression and localization of MRP2. Canalicular MRP2 localization was altered by BSO treatment for 2 h without changing the hepatic protein expression of MRP2. While the 8 h after exposure to BSO, hepatic MRP2 protein expression was decreased, and the canalicular localization of MRP2 was disrupted without changing the mRNA expression of MRP2. The BSO-induced reduction in MRP2 protein expression was suppressed by pretreatment with N-benzyloxycarbonyl (Cbz)-Leu-Leu-leucinal ( MG-132), a proteasomal inhibitor. Furthermore, the modification of MRP2 by small ubiquitin-relatedmodifier 1 (SUMO-1) was impaired in BSO-treated rat liver,while that by ubiquitin (Ub) and MRP2 was enhanced. Taken together, the results of this study suggest the sustained periods of low GSH content coupled with altered modification of MRP2 by Ub/SUMO-1 were accompanied by proteasomal degradation of MRP2.

► At 2 h after BSO treatment, intrahepatic GSH decrease causes Mrp2 internalization. ► At 8 h after BSO treatment, Mrp2 protein expression is decreased in proteasomal-degradation dependent manner. ► Ubiquitination and de-SUMOylation of Mrp2 can be observed in the liver treated with BSO for 8 h.