cDNA Cloning of the Hepatocyte Canalicular Isoform of the Multidrug Resistance Protein, cMrp, Reveals a Novel Conjugate Export Pump Deficient in Hyperbilirubinemic Mutant Rats

Abstract

ATP-dependent transport of glutathione and glucuronate conjugates from hepatocytes into bile is mediated by a distinct member of the ATP-binding cassette superfamily. We have cloned and sequenced the canalicular isoform of the multidrug resistance protein from rat liver, and termed it cMrp. This membrane glycoprotein is composed of 1541 amino acids with an identity of 47.8% with the human multidrug resistance protein (MRP) and of 41.9% with the yeast cadmium factor (YCF1). The carboxyl-terminal 130 amino acids of the human hepatocyte canalicular isoform of MRP (cMRP) were 80.2% identical with rat cMrp. cMrp was not expressed in the liver of two mutant rat strains, the Eisai hyperbilirubinemic rat and the GY/TR- mutant, which are deficient in the ATP-dependent transport of conjugates across the canalicular membrane. Immunoblotting using an antibody raised against the carboxyl terminus of cMrp detected the glycoprotein of about 190 kDa only in the canalicular membrane from normal liver. Double immunofluorescence and confocal laser scanning microscopy localized cMrp exclusively to the canalicular membrane domain of hepatocytes and demonstrated its loss in the hyperbilirubinemic mutant rat. The results identify cMrp as a canalicular transport protein with a novel sequence and with a function similar to the one of the MRP.

Expression of the multidrug resistance proteins MRP2 and MRP3 in human hepatocellular carcinoma

“…14 The FDS antibody was raised in rabbits against the 24 C-terminal amino acids (FDSPANLIAARGIFYG-MARDAGLA) and the ALL antibody against the 20 -amino acid peptide (ALLIEDTLSNHTDLTDNDPV) corresponding to amino acids 876 -895 of the human MRP3 sequence. 19 The monoclonal antibody (MAb) QCRL1 against MRP1 22 and the MAb M 2 III-6 against MRP2 23 were from Alexis (San Diego, CA).…”

“…13 MRP2 was cloned from rat and human liver 14 -16 and localized to the hepatocyte canalicular membrane. 14,17 Recombinant MRP2, expressed in polarized cells, confers resistance to cisplatin, anthracyclines and etoposide. 18 Another hepatic MRP isoform, MRP3, was cloned from human liver and localized to the basolateral membrane of hepatocytes.…”

Vinblastine and sulfinpyrazone export by the multidrug resistance protein MRP2 is associated with glutathione export

“…Another ABC-transporter that shows homology to MRP1 is the canalicular multispecific organic anion transporter (cMOAT or MRP2) (Büchler et al, 1996;Paulusma et al, 1996;Ito et al, 1997). It is plausible that MRP2 could play a role in drug resistance, just as MRP1 does.…”

Dexamethasone- and osmolarity-dependent expression of the multidrug-resistance protein 2 in cultured rat hepatocytes1

“…MRP2 sequence [16]. This was a generous gift from Professor D. Keppler (Deutsches Krebsforschungszentrum, Heidelberg, Germany), who also provided a sample of a preparation of rat canalicular membrane.…”