Wilson disease protein ATP7B is localized in the late endosomes in a polarized human hepatocyte cell line.
Wilson disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. The gene responsible for Wilson disease has been cloned, however, the precise localization of this gene product ATP7B, a copper-transporting ATPase, is still controversial. We examined the localization of ATP7B by expressing a chimeric protein, ATP7B-tagged with green fluorescent protein (GFP) (GFP-ATP7B), in HEK293, Hep3B and a highly polarized human hepatocyte line (OUMS29). Intracellular organelles were visualized by immunofluorescence microscopy. The effects of bathocuproine disulfonate, a copper chelator, and copper sulfate were examined. GFP-ATP7B colocalized with a late endosome marker, but not with endoplasmic reticulum, Golgi, or lysosome markers in a copper-depleting condition. Treatment with copper sulfate did not affect the localization of ATP7B. ATP7B is localized in the late endosomes in both copper-depleting and copper-loaded conditions. ATP7B seems to translocate copper from the cytosol into the late endosomes, and copper may be excreted to bile via lysosomes. We believe that the disturbed incorporation of copper into the late endosomes caused by mutated ATP7B is the main defect in Wilson disease.
Harada
Masaru
M
Second Department of Medicine, Kurume University School of Medicine, Kurume 830-0011, Japan. harada@med.kurume-u.ac.jp
Kumemura
Hiroto
H
Sakisaka
Shotaro
S
Shishido
Shoichiro
S
Taniguchi
Eitaro
E
Kawaguchi
Takumi
T
Hanada
Shinichiro
S
Koga
Hironori
H
Kumashiro
Ryukichi
R
Ueno
Takato
T
Suganuma
Tatsuo
T
Furuta
Koh
K
Namba
Masayoshi
M
Sugiyama
Toshihiro
T
Sata
Michio
M
D000251:Adenosine Triphosphatases / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D027682:Cation Transport Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002460:Cell Line; D016764:Cell Polarity; D002614:Chelating Agents / Q000378:metabolism / Q000494:pharmacology; D003300:Copper / Q000378:metabolism; D019327:Copper Sulfate / Q000494:pharmacology; D000073840:Copper-Transporting ATPases; D011992:Endosomes / Q000187:drug effects / Q000378:metabolism*; D049452:Green Fluorescent Proteins; D022781:Hepatocytes / Q000378:metabolism*; D006801:Humans; D008164:Luminescent Proteins / Q000378:metabolism; D009154:Mutation; D010618:Phenanthrolines / Q000494:pharmacology; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D027682:Cation Transport Proteins; D002614:Chelating Agents; D008164:Luminescent Proteins; D010618:Phenanthrolines; D011994:Recombinant Proteins; D049452:Green Fluorescent Proteins; D003300:Copper; C002478:bathocuproine; D000251:Adenosine Triphosphatases; C000612464:ATP7B protein, human; D000073840:Copper-Transporting ATPases; D019327:Copper Sulfate