LPS-induced dissociation of multidrug resistance-associated protein 2 (Mrp2) and radixin is associated with Mrp2 selective internalization in rats.

Multidrug resistance-associated protein 2 (Mrp2) is an ATP-dependent export pump that mediates the formation of bile-salt-independent bile flow. Disruption of the canalicular localization of Mrp2, without changes in its expression, is observed in chronic liver failure and is accompanied by oxidative stress. We reported previously that Mrp2 is rapidly internalized from the canalicular membrane during acute oxidative stress induced by lipopolysaccharide (LPS) in the rat liver. A disturbance in the colocalization of Mrp2 and radixin (which crosslinks actin with interacting membrane proteins) and endocytic retrieval of Mrp2 are present in chronic liver failure. However, the C-terminal phosphorylation status of radixin (p-radixin; functional form) and its protein-protein interaction with Mrp2 were not examined in the pathological cholestatic situation. In this study, we examined whether the C-terminal phosphorylation status of radixin and its interaction with Mrp2 were affected by LPS-induced experimental liver failure with cholestasis, and whether this condition was accompanied by Mrp2 internalization in the rat liver. At 3h after LPS treatment, the canalicular expression of Mrp2 was decreased, without variation of the other canalicular transporters. Similarly, the canalicular localization of radixin was decreased after LPS treatment. These results show that LPS treatment decreased the total amount of the active form of p-radixin and the amount of radixin that coimmunoprecipitated with Mrp2, and that LPS treatment impaired the protein-protein interaction between Mrp2 and radixin. In conclusion, LPS-induced cholestasis seems to be caused by posttranscriptional regulation of Mrp2, which is due to the disruption of its interaction with radixin and by its dephosphorylation.