Identification of the apical membrane-targeting signal of the multidrug resistance-associated protein 2 (MRP2/cMOAT)

The human canalicular multispecific organic anion transporter (cMOAT), know n as the multidrug resistance-associated protein 2 (MRP2), is normally expr essed in the liver and to a lesser extent in the kidney proximal tubules. I n these tissues MRP2 specifically localizes to the apical membrane. The con struction of MRP2 fused to the green fluorescent protein, and subsequent si te-directed mutagenesis enabled the identification of a targeting signal in MRP2 that is responsible for its apical localization in polarized cells. T he specific apical localization of MRP2 is due to a C-terminal tail that is not present in the basolaterally targeted MRP1. Deletion of three amino ac ids from the C-terminal of MRP2 (Delta MRP2) causes the protein to be local ized predominantly in the basolateral membrane in polarized Madin-Darby can ine kidney cells. Interestingly, MRP2 expressed in a mouse leukemia cell li ne (L1210 cells) predominantly accumulates intracellularly with minimal cel l membrane localization. In contrast, Delta MRP2 was shown to predominantly localize in the cell membrane in L1210 cells. Increased transport of 2,4-d initrophenyl glutathione from L1210 cells expressing Delta MRP2 showed that the re-targeted protein retains its normal function.