A mutation of the Wilson disease protein, ATP7B, is degraded in the proteasomes and forms protein aggregates.
OBJECTIVE
Wilson disease is a genetic disorder characterized by the accumulation of copper in the body as a result of a defect of copper excretion from hepatocytes. The intracellular localization of the Wilson disease gene product, ATP7B, was recently identified as the late endosomes. Various mutations have been documented in patients with Wilson disease. The clinical manifestations vary greatly among the patients; however, there is little information on the genotype-phenotype correlation.


METHODS
We investigated the distribution of a common ATP7B mutant His1069Gln and a mutant Asp1270Ser by expressing the mutants tagged with green fluorescent protein in Huh7 and HEK293 cells. Intracellular organelles were visualized by fluorescence microscopy.


RESULTS
Although the wild-type ATP7B and Asp1270Ser mutant localized in the late endosomes, His1069Gln mutant did not locate in the late endosomes and was degraded by the proteasomes in the cytoplasm. Furthermore, His1069Gln formed aggresomes composed of the degradates and intermediate filaments at the microtubule-organizing center. These aggresomes were similar to Mallory bodies on electron microscopy.


CONCLUSIONS
The different protein properties of ATP7B mutants may explain the variety of clinical spectrums in patients with Wilson disease.
Second Department of Medicine, Kurume University School of Medicine, Kurume, Japan.
M
M
Harada
S
S
Sakisaka
K
K
Terada
R
R
Kimura
T
T
Kawaguchi
H
H
Koga
M
M
Kim
E
E
Taniguchi
S
S
Hanada
T
T
Suganuma
K
K
Furuta
T
T
Sugiyama
M
M
Sata
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D000251:Adenosine Triphosphatases / Q000235:genetics* / Q000378:metabolism; D002352:Carrier Proteins / Q000235:genetics* / Q000378:metabolism; D027682:Cation Transport Proteins; D002460:Cell Line; D000073840:Copper-Transporting ATPases; D003546:Cysteine Endopeptidases / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D003599:Cytoskeleton / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009097:Multienzyme Complexes / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D009154:Mutation / Q000502:physiology*; D046988:Proteasome Endopeptidase Complex; D014018:Tissue Distribution
D002352:Carrier Proteins; D027682:Cation Transport Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; C063261:acetylleucyl-leucyl-norleucinal; C067713:lactacystin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex; D000251:Adenosine Triphosphatases; C000612464:ATP7B protein, human; D000073840:Copper-Transporting ATPases; D000111:Acetylcysteine