Copper does not alter the intracellular distribution of ATP7B, a copper-transporting ATPase.

Wilson's disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. However, the mechanism of biliary copper excretion has not been fully clarified. We examined the effect of copper on the intracellular localization of the Wilson disease gene product (ATP7B) and green fluorescent protein (GFP)-tagged ATP7B in a human hepatoma cell line (Huh7). The intracellular organelles were visualized by fluorescence microscopy. GFP-ATP7B colocalized with late endosome markers, but not with endoplasmic reticulum, Golgi, or lysosome markers in both the steady and copper-loaded states. ATP7B mainly localized at the perinuclear regions in both states. These results suggest that the main localization of ATP7B is in the late endosomes in both the steady and copper-loaded states. ATP7B seems to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes.

Harada M ，Sakisaka S ，Kawaguchi T ，Kimura R ，Taniguchi E ，Koga H ，Hanada S ，Baba S ，Furuta K ，Kumashiro R ，Sugiyama T ，Sata M ... -  《BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS》

Role of ATP7B in biliary copper excretion in a human hepatoma cell line and normal rat hepatocytes.

Harada M ，Sakisaka S ，Terada K ，Kimura R ，Kawaguchi T ，Koga H ，Taniguchi E ，Sasatomi K ，Miura N ，Suganuma T ，Fujita H ，Furuta K ，Tanikawa K ，Sugiyama T ，Sata M ... -  《GASTROENTEROLOGY》

The Wilson disease protein ATP7B resides in the late endosomes with Rab7 and the Niemann-Pick C1 protein.

Wilson disease is a genetic disorder characterized by the accumulation of copper in the body due to a defect of biliary copper excretion. Although the Wilson disease gene has been cloned, the cellular localization of the gene product (ATP7B) has not been fully clarified. Therefore, the precise physiological action of ATP7B is still unknown. We examined the distribution of ATP7B using an anti-ATP7B antibody, green fluorescent protein (GFP)-ATP7B (GFP-ATP7B) and ATP7B-DsRed in various cultured cells. Intracellular organelles were visualized by fluorescence microscopy. The distribution of ATP7B was compared with that of Rab7 and Niemann-Pick C1 (NPC1), proteins that localize in the late endosomes. U18666A, which induces the NPC phenotype, was used to modulate the intracellular vesicle traffic. GFP-ATP7B colocalized with various late endosome markers including Rab7 and NPC1 but not with Golgi or lysosome markers. U18666A induced the formation of late endosome-lysosome hybrid organelles, with GFP-ATP7B localized with NPC1 in these structures. We have confirmed that ATP7B is a late endosome-associated membrane protein. ATP7B appears to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via lysosomes. Thus, defective copper ATPase activity of ATP7B in the late endosomes appears to be the main defect of Wilson disease.

Harada M ，Kawaguchi T ，Kumemura H ，Terada K ，Ninomiya H ，Taniguchi E ，Hanada S ，Baba S ，Maeyama M ，Koga H ，Ueno T ，Furuta K ，Suganuma T ，Sugiyama T ，Sata M ... -  《-》

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 M ，Kumemura H ，Sakisaka S ，Shishido S ，Taniguchi E ，Kawaguchi T ，Hanada S ，Koga H ，Kumashiro R ，Ueno T ，Suganuma T ，Furuta K ，Namba M ，Sugiyama T ，Sata M ... -  《INTERNATIONAL JOURNAL OF MOLECULAR MEDICINE》

Niemann-Pick C1 protein transports copper to the secretory compartment from late endosomes where ATP7B resides.

Yanagimoto C ，Harada M ，Kumemura H ，Koga H ，Kawaguchi T ，Terada K ，Hanada S ，Taniguchi E ，Koizumi Y ，Koyota S ，Ninomiya H ，Ueno T ，Sugiyama T ，Sata M ... -  《-》