Mutational analysis of the MRP2 gene and long-term follow-up of Dubin-Johnson syndrome in Japan.

BACKGROUND: Recent studies have indicated that dysfunction or loss of the multidrug resistance protein 2 (MRP2) is the molecular basis of Dubin-Johnson syndrome (DJS). To clarify the genetic basis of the disease and the long-term stability of serum bilirubin levels, we conducted a mutational analysis of the MRP2 gene and followed up serum bilirubin levels in Japanese DJS patients 30 years after they were originally diagnosed, based on traditional criteria. METHODS: Patients were interviewed by telephone, and blood tests, including a genetic analysis of MRP2, were performed on the patients and family members who gave informed consent. RESULTS: Over the 30 years, hyperbilirubinemia remained unchanged in four of the five patients studied, while it worsened in 1 patient whose DJS was complicated by chronic hepatitis C. From an MRP2 gene mutational analysis, six mutations, including the novel mutation 1177C>T, were found. Three patients of a consanguineous family were homozygotes for three mutations (298C>T, 1967+2T>C, and 2439+2T>C). Two patients were compound heterozygotes (1177C>T/2302C>T and 1967+2T>C/2026G>C). A familial study showed no difference in serum bilirubin levels between mutant/wild heterozygotes and wild/wild homozygotes. CONCLUSIONS: The hyperbilirubinemia of four Japanese patients with DJS, one of whom had a novel mutation, 1177C>T, of the MRP2 gene, had not worsened with aging.

Mutation analysis of the multidrug resistance protein 2 (MRP2) gene in a Japanese patient with Dubin-Johnson syndrome.

Dubin-Johnson syndrome (DJS) 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 a Japanese female with DJS. In this patient, we found a homozygous 2125T > C mutation in exon 17. This mutation affects the conversion of tryptophan(709) to arginine(709) (W709R) in the first ATP-binding cassette in the MRP2 protein. It was concluded that this homozygous mutation of the MRP2 gene contributed to the induction of hyperbilirubinemia in this case.

Improvement of serum bilirubin levels after venesection in a patient with Dubin-Johnson syndrome and HCV-positive chronic liver disease.

Direct-type hyperbilirubinemia in Dubin-Johnson syndrome is due to the genetic dysfunction of multidrug resistance protein 2. However, serum bilirubin levels may fluctuate as a result of acquired conditions. Iron-reduction therapy by venesection, an alternative to interferon, was performed in a 55-year-old male patient with Dubin-Johnson syndrome complicated by hepatitis C virus-positive chronic liver disease and hepatic iron overload. His pretreatment serum total bilirubin was 10.2 mg/dl, with a dominant direct fraction. The treatment induced a significant reduction in serum total bilirubin, although it remained as high as 7.9 mg/dl. A negative correlation between serum total bilirubin and cumulative bled volume suggested that venesection could suppress bilirubin production from aged erythrocytes. The hepatic iron overload was distributed in hepatocyte lysosomes with Dubin-Johnson granules; thus, it seems that iron removal from the lysosomal granules may also help to reduce serum bilirubin. In conclusion, deep jaundice in a patient with Dubin-Johnson syndrome complicated by hepatitis C virus-positive chronic liver disease and iron overload was partially improved by iron-reduction therapy.

Reduction of MDR3 mRNA levels by forskolin in Chang liver cells.

BACKGROUND: MDR3 is a phospholipid translocator and a putative transporter of several drugs in the canalicular membrane of hepatocytes. To clarify the regulatory system for the expression of MDR3 mRNA in comparison with MDR1 mRNA, we examined the effect of cyclic AMP using forskolin. MATERIALS AND METHODS: Chang liver cells were treated with forskolin, and then MDR3 and MDR1 mRNA levels were examined by RT-PCR and the MDR3 protein level was examined by Western blotting. RESULTS: The MDR3 mRNA level decreased while the MDR1 mRNA level increased, and the effects of forskolin were inhibited by a protein kinase A inhibitor, H-89. The MDR3 protein level was not changed by forskolin. However, forskolin decreased the induction of MDR3 mRNA expression by doxorubicin. CONCLUSION: The level of MDR3 mRNA was negatively-regulated by a cyclic AMP- and protein kinase A-dependent system.

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

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-->T polymorphism and the two mutations c.1901del67 and 2026G-->C were detected. The 2026G-->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.