Functional expression of the rat liver canalicular isoform of the multidrug resistance-associated protein

Area of Science:

• Biochemistry
• Molecular Biology
• Hepatology

Background:

• The canalicular multispecific organic anion transporter (cMOAT) is crucial for the biliary excretion of various organic anions in the liver.
• Understanding the molecular identity and function of cMOAT is essential for comprehending drug and metabolite transport.
• Previous studies suggested a role for multidrug resistance-associated protein 2 (mrp2) in this process, but direct functional evidence was lacking.

Purpose of the Study:

• To clone and functionally characterize the rat hepatocanalicular isoform of multidrug resistance-associated protein (mrp2).
• To confirm whether mrp2 mediates the transport of glutathione conjugates and other organic anions.
• To establish the identity of mrp2 as the canalicular multispecific organic anion transporter (cMOAT).

Main Methods:

• Cloning and transient expression of rat mrp2 in COS-7 cells and Xenopus laevis oocytes.
• Measurement of [14C]2,4-dinitrophenyl-S-glutathione and [3H(N)]leukotriene C4 efflux.
• Analysis of mrp2 mRNA levels in the liver of transport mutant TR rats.

Main Results:

• Transient expression of rat mrp2 significantly increased the efflux of [14C]2,4-dinitrophenyl-S-glutathione in both COS-7 cells and oocytes.
• Injection of mrp2 cRNA into oocytes stimulated the efflux of [3H(N)]leukotriene C4.
• A marked decrease in mrp2 mRNA was observed in the liver of TR rats, which exhibit defective biliary excretion of organic anions.

Conclusions:

• The study provides direct evidence for the transport function of rat mrp2.
• These findings strongly support the identification of mrp2 as the canalicular multispecific organic anion transporter (cMOAT) in mammalian liver.
• This research advances the understanding of hepatic transport mechanisms for organic anions and their conjugates.