Received for publication January 29, 2008.
Revised March 14, 2008.
Accepted for publication March 31, 2008.

Identification of Regions Required for Apical Membrane Localization of Human Multidrug Resistance Protein (MRP) 2

Abstract

Multidrug Resistance Proteins, MRP1 and MRP2, transport a wide range of endo- and xenobiotics. However, with the exception of certain parts of the brain, MRP1 traffics to basolateral membranes of polarized cells, while MRP2 is apical in location and thus is particularly important for systemic elimination of such compounds. Different regions of MRP1 and MRP2 appear to target them to their respective membrane locations. In addition to two 'core' membrane spanning domains (MSDs) characteristic of ABC transporters, MRP1 and MRP2 have a third NH₂-terminal MSD (MSD0), which, is not required for basolateral targeting of MRP1, or for transport of at least some substrates. Here, we demonstrate that all elements necessary for apical targeting of MRP2 reside in MSD0 and the adjacent cytoplasmic loop (CL) 3. Furthermore, we show that this region of MRP2 can target the 'core' of MRP1 to an exclusively apical location. Within MRP2 CL3, we identified a lysine rich element that is essential for apical targeting. When introduced into MRP1, this element alone is sufficient to result in partial apical localization. However, exclusive targeting to the apical membrane appears to require the integrity of the entire region encompassing MSD0 and CL3 of MRP2. Since CL3 of MRP1 is critical for binding and/or transport of a number compounds, we also examined the function of hybrids containing all, or portions of MRP2 MSD0 and CL3. Our results indicate that CL3 is important for interaction with both the GSH and glucuronide conjugates tested, but that different regions may be involved.

Key words: Lipid rafts/microdomains, MDR/p-Glycoprotein, Organic anion, Fluorescence techniques, Immunocytochemistry, Liver transporters, Leukotrienes, Membrane targets