Trafficking and functional defects by mutations of the ATP‐binding domains in MRP2 in patients with Dubin‐Johnson syndrome

Dubin‐Johnson syndrome (DJS) is a hereditary disease characterized by hyperbilirubinemia. We investigated the consequences of 2 missense mutations, R768W and Q1382R, of nucleotide‐binding domains (NBDs) of the multidrug resistance protein 2 (MRP2; ABCC2) that were previously identified in patients with DJS. Pulse chase analysis revealed that the precursor form of the wild‐type and Q1382R MRP2 were converted to the mature form, which is resistant to endoglycosidase H (Endo H) in about 60 minutes. However, the precursor form of the R768W MRP2, which is sensitive to endoglycosidase H, was degraded within 120 minutes and did not mature to the fully glycosylated form. Proteasome inhibitors inhibited the degradation of the precursor form of the R768W MRP2. Unlike the R768W MRP2, the Q1382R MRP2 was mainly localized on the apical membrane in the wild‐type form. However, efflux of glutathione monochlorobimane (GS‐MCLB) and ATP‐dependent leukotriene C4 (LTC4) uptake into plasma membrane vesicles from cells expressing the Q1382R MRP2 were markedly reduced, suggesting that the Q1382R MRP2 on the apical membrane was nonfunctional. Vanadate‐induced nucleotide trapping with 8‐azido‐[α‐32P]ATP in the wild‐type MRP2 was stimulated by estradiol glucuronide (E217βG) in a concentration‐dependent manner but that in the Q1382R MRP2 was not. In conclusion, the R768W mutation causes deficient maturation and impaired sorting, and the Q1382R mutation does not affect maturation or sorting but impairs the substrate‐induced ATP hydrolysis.