Role of microtubules in estradiol-17β- d -glucuronide-induced alteration of canalicular Mrp2 localization and activity

Estradiol-17β-d-glucuronide (E 2 -17G) induces a marked but reversible inhibition of bile flow in the rat together with endocytic retrieval of multidrug resistance-associated protein 2 (Mrp2) from the canalicular membrane to intracellular structures. We analyzed the effect of pretreatment (100 min) with the microtubule inhibitor colchicine or lumicholchicine, its inactive isomer (1 μmol/kg iv), on changes in bile flow and localization and function of Mrp2 induced by E 2 -17G (15 μmol/kg iv). Bile flow and biliary excretion of bilirubin, an endogenous Mrp2 substrate, were measured throughout, whereas Mrp2 localization was examined at 20 and 120 min after E 2 -17G by confocal immunofluorescence microscopy and Western analysis. Colchicine pretreatment alone did not affect bile flow or Mrp2 localization and activity over the short time scale examined (3–4 h). Administration of E 2 -17G to colchicine-pretreated rats induced a marked decrease (85%) in bile flow and biliary excretion of bilirubin as well as internalization of Mrp2 at 20 min. These alterations were of a similar magnitude as in rats pretreated with lumicolchicine followed by E 2 -17G. Bile flow and Mrp2 localization and activity were restored to control levels within 120 min of E 2 -17G in animals pretreated with lumicolchicine. In contrast, in colchicine-pretreated rats followed by E 2 -17G, bile flow and Mrp2 activity remained significantly inhibited by 60%, and confocal and Western studies revealed sustained internalization of Mrp2 120 min after E 2 -17G. We conclude that recovery from E 2 -17G cholestasis, associated with exocytic insertion of Mrp2 in the canalicular membrane, but not its initial E 2 -17G-induced endocytosis, is a microtubule-dependent process.