Identification of a novel 2026G→C mutation of the MRP2 gene in a Japanese patient with Dubin-Johnson syndrome

Abstract

Dubin-Johnson syndrome is a recessive inherited disorder with conjugated hyperbilirubinemia caused by a dysfunction of multidrug resistance protein 2 (MRP2) on the canalicular membrane of hepatocytes. A mutational analysis of the MRP2 gene was carried out in three Japanese patients and their family members. In two patients, the homozygous mutations c.1901del67 and c,2272del168 were found. In the third patient, a )24C fi T polymorphism and the two mutations c.1901del67 and 2026G fi C were detected. The 2026G fi C mutation was a novel mutation in exon 16 affecting the conversion of Gly 676 to Arg 676 (G676R) in the MRP2 protein, and was not detected in fifty healthy volunteers. The G676R mutation was located in the Walker A motif of the first nucleotide binding domain in the MRP2 protein, and it was suggested that the mutation induced the dysfunction of the MRP2 protein. It was concluded that the compound heterozygosity of the two mutations of the MRP2 gene in the third patient contributed to the induction of hyperbilirubinemia in this case.Keywords Dubin-Johnson syndrome AE Multidrug resistance 2 (MRP2) AE ATP-binding cassette AE Walker A motif AE Mutation Introduction Dubin-Johnson syndrome (DJS) is an inherited metabolic disorder characterized by conjugated hyperbilirubinemia and a re-increase of serum bromosulfophtalein (BSP) in the BSP tolerance test, characteristics that are caused by a dysfunction of the canalicular multispecific anion transporter (cMOAT, multidrug resistance protein 2; MRP2).The human MRP2 gene was identified in cisplatinresistant tumor cells by Taniguchi et al. (1996) following the identification of the rat cmoat (mrp2) gene in hyperbilirubinemia rats (TR ) rats) by Paulusma et al. (1996). The human MRP2 gene was mapped to chromosome 10 at q24 (Taniguchi et al. 1996) and was found to consist of 32 exons (Toh et al. 1999).MRP2 protein is a membrane protein with 1545 amino acids; it contains two ATP-binding cassettes (ABCs) and 17 transmembrane sequences (Taniguchi et al. 1996). It is expressed at the canalicular membrane of hepatocytes and apical membrane of the renal uriniferous tuble (Paulusma et al.1996) and is involved in the excretion of glucronide-conjugated bilirubin and glutathione-conjugates from the liver (Taniguchi et al. 1996;Wada et al. 1998).The first mutation of the MRP2 gene causing hyperbilirubinemia was found by Paulusma et al. (1997) in DJS, and a total of 10 mutations have been found as listed in Table 1.In the present study, we conducted a mutational analysis in three Japanese DJS patients and found two known deletion mutations (c.1901del67, c.2272del168) and a novel missense mutation of G676R in the first nucleotide-binding domain (NBD1) in the MRP2 protein. Subjects and methods Study participantsThree DJS patients and their family members were included in the present study.

Neonatal Dubin-Johnson Syndrome: Long-Term Follow-up and MRP2 Mutations Study

“…The reported missense mutations involving the two ABC in the MRP2 include G676R and R768W in the first ABC and Q1382R in the second ABC (11,13,17,18). The functional study showed that R768W causes deficient maturation and impaired sorting of protein, Q1382R impairs the substrateinduced ATP hydrolysis, and Del R1392, M1393 leads to impaired maturation and trafficking of protein from endoplasmic reticulum (ER) to the Golgi complex (19,20).…”

Variable Expression of Mrp2 (Abcc2) in Human Placenta: Influence of Gestational Age and Cellular Differentiation

“…Various polymorphisms in the MRP2 gene contribute to the etiology of the Dubin-Johnson syndrome (Paulusma et al, 1996;Wada et al, 1998;Tsujii et al, 1999;Mor-Cohen et al, 2001;Tate et al, 2002;Materna and Lage, 2003;Wakusawa et al, 2003). It was shown that single nucleotide changes like the 3517 A/T transition in exon 25 are associated with lower efflux of MRP2 substrates and altered distribution of the protein in transfected cells (Mor-Cohen et al, 2001;Keitel et al, 2003).…”

Role of Multidrug Resistance Associated Proteins in Drug Development

“…The absence of functional MRP2 is the molecular basis of transport defect of DJS (283). Many single nucleotide polymorphisms in DJS patients have been reported (Table 2) (118,(284)(285)(286)(287)(288). These include C-24T (promoter), G1249A (exon 10), G2026C (exon 16), T2125C (exon 17), C2302T (exon 18), C2366 (exon 18), A3517T (exon 25), G3449 (exon 25), C3972T (exon 28) and G4348A (Exon 31) ( Table 2).…”