Ezrin and radixin both regulate the apical membrane localization of ABCC2 (MRP2) in human intestinal epithelial Caco-2 cells

Multidrug resistance-associated protein ABCC2 (MRP2) is widely expressed in mammalian tissues including intestine, liver and kidney, and it has been shown to be located exclusively on the apical membrane of polarized cells. Recently, several reports suggest that apical membrane localization of ABCC2 (Mrp2) was regulated by radixin in rodent liver. To investigate the mechanism underlying this apical membrane targeting of MRP2 in human intestine, we chose Caco-2 cells as a model to examine the unique roles of ezrin and radixin. Following immunostaining, radixin and ezrin were found to be concentrated at the apical membrane of Caco-2 cells. Using the RNAi method, radixin and ezrin stable knockdown Caco-2 cells were constructed. A cell surface biotinylation experiment with radixin or ezrin stable knockdown Caco-2 cells showed that radixin or ezrin deficiency caused the loss of ABCC2 (MRP2) from the cell surface. An immunoprecipitation assay showed that radixin and ezrin were associated with ABCC2 (MRP2). These findings indicate that both ezrin and radixin are independently required for the apical membrane localization of ABCC2 (MRP2) in Caco-2 cells. Radixin and ezrin play similar roles in the apical membrane localization of ABCC2 (MRP2) and their expression level and subcellular distribution are important factors in the regulation of ABCC2 (MRP2) at the post-transcriptional level.