Exon-intron organization of the human multidrug-resistance protein 2 ( MRP2) gene mutated in Dubin–Johnson syndrome

Abstract

Background & Aims: The Dubin–Johnson syndrome is characterized by conjugated hyperbilirubinemia and by impaired secretion of anionic conjugates from hepatocytes into bile. Absence of the multidrug-resistance protein 2 (MRP2; symbol ABCC2), an adenosine triphosphate–dependent conjugate export pump, from the hepatocyte canalicular membrane is the molecular basis of this syndrome. The aim of this study was the elucidation of all exon-intron boundaries of the MRP2 gene as a prerequisite for the analysis of mutations in patients with Dubin–Johnson syndrome. Methods: Exon-intron boundaries of MRP2 were determined, and the amplified exons were screened for mutations. Immunofluorescence microscopy served to localize the MRP2 protein in human liver. Results: The human MRP2 gene is ~45 kilobases long; it contains 32 exons and a high proportion of class 0 introns. In 2 patients with Dubin–Johnson syndrome, we detected a nonsense mutation at codon 1066 and a 6-nucleotide deletion mutation affecting codons 1392–1394. The MRP2 protein was absent from the canalicular membrane of both patients. Conclusions: The mutations detected so far show that various mutations in the MRP2 gene can lead to the Dubin–Johnson syndrome. The exon-intron boundaries established in this article will facilitate the analysis of additional mutations in the MRP2 gene. GASTROENTEROLOGY 1999;117:653-660