MRPs are widely distributed throughout normal and malignant tissues. MRP1 and MRP5 are expressed in all tissues, whereas other members of the MRP family are confined to specific tissues. The MRP transporters are located at the plasma membranes and are also found on intracellular vesicles where they may traffic to the plasma membrane when required. MRP2 is located on apical membranes of polarized cells, whereas other MRPs are predominantly localized to basolateral membranes. MRP4 and MRP5 have been detected in both basolateral and apical membranes, depending on the cell type.
