The Multidrug Resistance Protein - Essay Example

Swarna1 Word count: 1359 P.Sarnalatha ID 5448 Order # 155330 5th March 2007 MRP-2 (Multi drug resistance protein-2) Introduction Multidrug resistancecan be defined as the ability of pathologic cells to withstand or resist chemicals that are designed to aid in the eradication of such cells. These pathologic cells include bacterial and neoplastic cells. Several bacteria exhibit multidrug resistance which include staphylococci, enterococci, gonococci, streptococci, salmonella, and others. Moreover, some resistant bacteria transfer copies of DNA that codes for a mechanism of resistance to other bacteria, thereby conferring resistance to their neighbors, who then are also able to pass on the resistant gene. The multidrug resistance protein 2 (MRP2 plays an important role in the transport of glutathione conjugates in the liver (König et al., 1999). It also has importance in renal excretion. This transporter belongs to the superfamily of ATP-Binding Cassette (ABC) proteins, and couples ATP hydrolysis to the transport of bulky organic anions. MRP2 is located predominantly in liver canalicular membranes (Büchler et al., 1996; Paulusma et al., 1996). It is also present in luminal membranes of intestine (van aubel et al., 2000) and kidney proximal tubular cells (Schaub et al., 1997). MRPs are organic anion transporters; i.e., they transport anionic drugs, exemplified by methotrexate, and neutral drugs conjugated to acidic ligands, such as glutathione (GSH), glucuronate, or sulfate. Multi drug resistance associated family This family consists of multi drug resistance-associated protein (MRP) in eukaryotes. The multidrug resistance-associated protein is defined as an integral membrane protein that causes multidrug resistance when over expressed in mammalian cells. It belongs to the ABC transporter superfamily. The human multidrug resistance-associated protein (MRP) family currently has seven members. The ability of several of these membrane proteins to transport a wide range of anticancer drugs out of cells and their presence in many tumors make them prime suspects in unexplained cases of drug resistance. However, MRP1, MRP2, and MRP3 can also cause resistance to neutral organic drugs that are not known to be conjugated to acidic ligands by transporting these drugs together with free GSH. MRPs also have a role in resistance against nucleoside analogues used in cancer chemotherapy. MRP2 is the major transporter responsible for the secretion of bilirubin glucuronides into bile, and humans without MRP2 develop a mild liver disease known as the Dubin-Johnson Syndrome (DJS). Structure of MRP-2 The human MRP2/cMOAT (canalicular multispecific organic anion transporter) gene contains 32 exons, and its structure is highly conserved with that of another ATP-binding-cassette gene. Three mutations were identified in MRP-2 protein. All mutations identified to date are in the cytoplasmic domain, which includes the two ATP-binding cassettes and the linker region. The research results confirm that MRP2/cMOAT is the gene responsible for DJS. When was MRP-2 was first identified? MRP2 was first identified as a hepatocellular canalicular organic anion transporter (Jansen et al., 1993). The range of molecules transported by this protein is broad which includes amphipathic anions and glucuronide-, glutathione-, and sulfate-conjugates. The gene was first cloned in the rat (Buchler et al., 1996) and mutations in the human isoform were found to cause Dubin-Johnson syndrome . Where MRP-2 is expressed? The multidrug resistance protein 2 (MRP2) is an ATP-binding cassette transporter which accepts a diverse range of substrates like glutathione, glucuronide, and sulfate conjugates of many endo- and xenobiotics. MRP2 is generally expressed on the apical domain of hepatocytes, enterocytes of the proximal small intestine, and proximal renal tubular cells, as well as in the brain and the placenta. MRP2 is important clinically as it regulates the pharmacokinetics of many drugs, and its expression and activity are also changed by certain drugs. In normal tissues MRP2 was expressed in liver, gastrointestinal tract, and kidney tubular epithelial cells with both antibodies. MRP2 expression was found to be highest in moderate to poorly differentiated tumours from colon, lung, gastric, and ovarian carcinomas and in grade 2 and 3 breast and renal carcinomas. The expression of MRP2 in many solid human tumors suggests that inherent multi drug resistance may play an important role as a biomarker for predictive chemotherapy treatment (Sandusky et al., 2002). Function of MRP-2 The multi-drug resistance protein 2 (MRP2 plays an important role in detoxification and chemoprotection by transporting a wide range of compounds, especially conjugates of lipophilic substances with glutathione, glucuronate and sulfate, which are collectively known as phase II products of biotransformation. Moreover, it can also transport uncharged compounds in cotransport with glutathione, and hence it can modulate the pharmacokinetics of many drugs. The Eisai hyperbilirubinemic rat (EHBR) and the transport deficient (TR-) Wistar mutant rat strain have an hereditary defect in Mrp2, which leads to the absence of the transport protein (Büchler et al., 1996; Paulusma et al., 1996; Ito et al., 1997) which suggests that MRP-2 is crucial in transportation.. Dubin Johnson Syndrome and MRP-2 Dubin-Johnson syndrome (DJS) is a type of hereditary hyperbilirubinemia that was first described independently in 1954 by Dubin and Johnson and by Sprinz and Nelson. Dubin-Johnson syndrome is an autosomal recessive disease which presents shortly after birth with an increase of conjugated bilirubin without elevation of liver enzymes (ALT, AST). The transport of bilirubin from the liver is dysfunctional in people with this condition. Liver will present with dark brown appearance due to pigment accumulation. Bilirubrin is a product of the livers metabolism of worn-out red blood cells and is normally sent into the digestive system. When bilirubin is not properly processed, it builds up in the bloodstream and causes the skin and the whites of the eyes take on a yellow tinge. Severely high levels can damage the brain and other organs. Theres a lack of canalicular multi-drug resistant protein which causes dysfunction on bilirubin transfer to bile canaliculi. Hence MRP-2 has direct relation with this disease. DJS is an autosomal recessive disorder that is caused by a mutation in the gene responsible for the human canalicular multispecific organic anion transporter (cMOAT) protein. This protein mediates ATP-dependent transport of certain organic anions across the canalicular membrane of the hepatocyte. The human MRP2 gene has been localized to band 10q23-10q24. A defect in the cMOAT (MRP2) protein may lead to the impaired hepatobiliary transport of non–bile salt organic anions and hence is directly responsible for the conjugated hyperbilirubinemia. Hereditary hyperbilirubinemias may be classified into conjugated forms and unconjugated forms. While Gilbert syndrome and Crigler-Najjar syndrome are examples of the unconjugated hyperbilirubinemias, DJS and Rotor syndrome represent the 2 types of familial conjugated hyperbilirubinemias. References: Buchler, M., Konig, G, J., Brom, M., Kartenbeck, J., Spring, H., Horie, T. & Keppler, D. 1996. cDNA cloning of the hepatocyte canalicular isoform of the multidrug resistance protein, cMrp, reveals a novel conjugate export pump deficient in hyperbilirubinemic mutant rats. J. Biol. Chem. 271: 15091−15098. Ito, K., Suzuki, H., Hirohashi, T., Kume, K., Shimizu, T. & Suziyama, Y. 1997. Molecular cloning of canalicular multispecific organic anion transporter defective in EHBR. Am. J. Physiol 272: Jansen P.L., van Klinken J.W., van Gelder M, Ottenhoff, R. and Elferink R.P. 1993. Preserved organic anion transport in mutant TR- rats with a hepatobiliary secretion defect. Am J Physiol  265: G445-G452. König, J., Nies, A.T., Cui, Y., Leier, I. & Keppler, D. 1999. Conjugate export pumps of the multidrug resistance protein (MRP) family: localization, substrate specificity, and MRP2-mediated drug resistance. Biochim. Biophys. Acta 1461: 377−394.  Paulusma, C.C., Bosma, P.J., Zaman, G.J.R., Bakker, C.T.M., Otter, M., Scheffer, G.L., Schepper, R.J., Borst, P. & Oude Elferink, R.P.J. 1996. Congenital jaundice in rats with a mutation in a multidrug resistance-associated protein gene. Science 271: Sandusky, G. E.; Mintze, K. S.; Pratt, S. E.& Danzig, A. H. 2002. Expression of multidrug resistance-associated protein 2 (MRP2) in normal human tissues and carcinomas using tissue microarrays. Histopathology. Vol. 41, no1, pp. 65-74. Schaub, T.P., Kartenbeck, J., Konig, J., Vogel, O., Witzgall, R., Kriz, W. & Keppler, D. 1997. Expression of the conjugate export pump encoded by the mrp2 gene in the apical membrane of kidney proximal tubules. J. Am. Soc. Nephrol. 8: 1213−1221.  Van Aubel, R.A.M.H., Hartog, A, Bindels, R.J.M., Van Os, C.H. & Russel, F.G.M. 2000. Expression and immunolocalization of multidrug resistance protein 2 in rabbit small intestine. Eur. J. Pharmacol. 400: 195−198.  Read More