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, t he mechanism of biliary copper excretion has not been fully clarified, We e xamined the effect of copper on the intracellular localization of the Wilso n disease gene product (ATP7B) and green fluorescent protein (GFP)-tagged A TP7B in a human hepatoma cell line (Huh7), The intracellular organelles wer e visualized by fluorescence microscopy, GFP-ATP7B colocalized with late en dosome markers, but not with endoplasmic reticulum, Golgi, or lysosome mark ers 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 copp er-loaded states. ATP7B seems to translocate copper from the cytosol to the late endosomal lumen, thus participating in biliary copper excretion via l ysosomes. (C) 2000 Academic Press.