Impaired protein maturation of the conjugate export pump multidrug resistance protein 2 as a consequence of a deletion mutation in Dubin-Johnson syndrome.

Abstract	The Dubin-Johnson syndrome is an inherited disorder characterized by conjugated hyperbilirubinemia. The deficient hepatobiliary transport of anionic conjugates is caused by the absence of a functional multidrug-resistance protein 2 (MRP2, symbol ABCC2) from the apical (canalicular) membrane of hepatocytes. Mechanisms underlying this deficiency may include rapid degradation of mutated MRP2 messenger RNA (mRNA) or impaired MRP2 protein maturation and trafficking. We investigated the consequences of the mutation MRP2Delta(R,M), which leads to the loss of 2 amino acids from the second ATP-binding domain of MRP2. The MRP2Delta(R,M) mutation is associated with the absence of the MRP2 glycoprotein from the apical membrane of hepatocytes. Transfection of mutated MRP2 complementary DNA (cDNA) led to an MRP2Delta(R,M) protein that was only core glycosylated, sensitive to endoglycosidase H digestion, and located in the endoplasmic reticulum (ER) of transfected HEK293 and HepG2 cells. This indicated that deletion of Arg1392 and Met1393 leads to impaired maturation and trafficking of the protein from the ER to the Golgi complex. Inhibition of proteasome function resulted in a paranuclear accumulation of the MRP2Delta(R,M) protein, suggesting that proteasomes are involved in the degradation of the mutant protein. This is the first mutation in Dubin-Johnson syndrome shown to cause deficient MRP2 maturation and impaired sorting of this glycoprotein to the apical membrane.
Authors	V Keitel, J Kartenbeck, A T Nies, H Spring, M Brom, D Keppler
Journal	Hepatology (Baltimore, Md.) (Hepatology) Vol. 32 Issue 6 Pg. 1317-28 (Dec 2000) ISSN: 0270-9139 [Print] United States
PMID	11093739 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
Chemical References	ABCC2 protein, human ATP Binding Cassette Transporter, Subfamily B Indicators and Reagents Leupeptins Luminescent Proteins Membrane Transport Proteins Multidrug Resistance-Associated Protein 2 Multidrug Resistance-Associated Proteins Multienzyme Complexes Green Fluorescent Proteins Cysteine Endopeptidases Proteasome Endopeptidase Complex benzyloxycarbonylleucyl-leucyl-leucine aldehyde multidrug resistance-associated protein 1
Topics	ATP Binding Cassette Transporter, Subfamily B (genetics, metabolism) Amino Acid Sequence (genetics) Cell Line (metabolism) Cell Membrane (metabolism) Cell Nucleus (metabolism) Cysteine Endopeptidases (physiology) Fluorescent Antibody Technique Gene Deletion Green Fluorescent Proteins Hepatocytes (metabolism, ultrastructure) Humans Indicators and Reagents Jaundice, Chronic Idiopathic (genetics, metabolism) Leupeptins (pharmacology) Luminescent Proteins Membrane Transport Proteins Microscopy, Confocal Microscopy, Immunoelectron Molecular Sequence Data Multidrug Resistance-Associated Protein 2 Multidrug Resistance-Associated Proteins Multienzyme Complexes (antagonists & inhibitors, physiology) Mutation (genetics) Proteasome Endopeptidase Complex Protein Processing, Post-Translational Tissue Distribution

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